Room: 315B
Session Chairperson: TBA
1:30 pm
OXIDE AND NITRIDE SUPERLATTICE COATINGS: William D. Sproul, BIRL, Northwestern University, 1801 Maple Avenue, Evanston, IL 60201
Over the past 10 years, three major advances in reactive sputtering technology have made it possible to deposit both conductive and non-conductive fully-dense films at high rates. These three advances are unbalanced magnetron (UBM) sputtering, partial pressure control of the reactive gas, and pulsed DC power. Multicathode UBM sputtering systems provide a dense secondary plasma that produces well-adhered, fully dense films. With both pulsed-dc power and partial pressure control, films such as aluminum oxide can now be deposited reactively at rates up to 78% of the pure metal rate. The reactive UBM sputtering process is used to deposit polycrystalline nitride superlattice films such as TiN/NbN or TiN/VN with hardnesses exceeding 50 GPa, more than double the hardness of either component in the film. The nitride superlattice work is being extended to oxide films. Clear, amorphous, nano-layered Al2O3/ZrO2 films have been deposited at high rates with a hardness of 10 GPa. Work is underway to deposit these films in a crystalline form, which should enhance their hardness.
2:05 pm
CONTROL OF INTERFACE STRENGTH IN NIOBIUM-ALUMINUM OXIDE MULTILAYERS BY ION BEAM ASSISTED DEPOSITION: G S. Was, H. Ji, J.W. Jones, Cooley Bldg., University of Michigan, Ann Arbor, MI 48109; N. Moody, Sandia National Laboratory, Div. 8712, MS 9403, Livermore, CA 94551
The toughness of a niobium-aluminum oxide multilayer depends on the interface strength, which can be controlled by both the orientation relationship of the constituents and the composition at the interface. As a first approximation to multilayers, niobium films were deposited onto {0001} sapphire substrates by ion beam assisted deposition (IBAD) under various conditions. In addition to the {110} fiber texture, strong in-plane texture was introduced by simultaneous ion bombardment. Stronger in-plane texture was developed with higher ion energy and ion to atom arrival rate ratio (R ratio). Different orientation relationships at the niobium-sapphire interface were achieved by varying the orientation of the sapphire substrates with respect to the ion beam incident direction. The hardness and modulus of the niobium layer were also modified by the ion bombardment. A dopant (Ag) was introduced at the interface at levels from a fraction of a monolayer to one monolayer during niobium layer deposition.
2:40 pm
CONTROLLING THE EVOLUTION OF TEXTURE IN SPUTTER DEPOSITED Mo FILMS: S.M. Yalisov, J.C. Bilello, University of Michigan, Department of Materials Science and Engineering, Ann Arbor MI 48119
Evolution of crystallographic ordering in sputter deposited polycrystalline refractory metal films has been observed in several laboratories. While the ordering in the growth direction, out-of-plane texture, is well known, the ordering in the plain of growth, in-plane texture, has only been reported by the ion enhanced growth community. The work presented here, will describe the conditions required for this behavior in the presence of energetic ions. Mo films were sputter deposited on amorphous substrates and grown to a large variety of thickness. The homologous temperature does not exceed 0.2 in any of the experiments performed. These films were characterized by a large battery of synchrotron x-ray, electron microscopy, and surface analysis. The data have led to an atomistic model to explain and predict the in-plane texturing based on shadowing and anisotropic growth rates which force a competitive grain growth mechanism during the growth. Detailed comparison to experiment will demonstrate the role that limited diffusion and mass transport play in the final microstructure of the film. Examples of how this model can be exploited to design a particular microstructure will be presented.
3:15 pm
CERAMIC-METALLIC COATINGS BY ELECTRON BEAM PHYSICAL VAPOR DEPOSITION PROCESS: Douglas Wolfe, M. Movchan, Jogender Singh, Applied Research Laboratory, Pennsylvania State University, University Park, PA 16804
Electron beam physical-vapor deposition (EB-PVD) process is considered to be a cost-effective and robust coating technology that has overcome some of the difficulties or problems associated with the metals spray, CVD and PVD processes. The EB-PVD process offers many desirable characteristics such as relatively high deposition rates (up to 100-500 mm/minute with an evaporation rate ~10-15 Kg/hour), dense coatings, precise composition control, columnar and poly-crystalline microstructure, low contamination, and high thermal efficiency. Various metallic and ceramic coatings (oxides, carbides, nitrides) have been deposited at relatively low temperatures. EB-PVD has the capability of producing multilayered nanolaminated metallic/ceramic coatings on large components by changing the processing conditions such as ingot composition, part manipulation, and electron beam energy. Attachment of an ion beam source to the EB-PVD process offers additional benefits such as dense coatings with improved adhesion.
3:50 pm BREAK
4:05 pm
COMMERCIAL APPLICATIONS OF PLASMA SOURCE ION IMPLANTATION: J.T. Scheuer, K.C. Walter, Los Alamos National Laboratory, Los Alamos, NM; W.G. Horne, Empire Hard Chrome, Chicago, IL; R.A. Adler, North Star Research Corporation, Albuquerque, NM 87109
Commercial plasma source ion implantation (PSII) equipment built by North Star Research Corporation has recently been installed at Empire Hard Chrome, Chicago, IL. Los Alamos National Laboratory has assisted in this commercialization effort via two Cooperative Research and Development Agreements to develop the plasma source for the equipment and to identify low-risk commercial PSII applications. The PSII system consists of a 1m x 1m cylindrical vacuum chamber with a pulsed, inductively coupled rf plasma source. The pulse modulator is capable of delivering pulses with peak currents of 100 kV and peak currents of 300 A at maximum repetition rate of 400Hz. The pulse modulator uses a thyratron to switch a pulse forming network which is tailored to match the dynamic PSII load. This presentation will focus on early commercial applications to production tooling and manufactured components and characterization of implanted coupons.
4:40 pm
SPUTTERED CHROME NITRIDE AS AN ALTERNATIVE TO ELECTROPLATED CHROME: Michael Graham, Keith Legg, Paul Rudnik, Peter Chang, BIRL, Northwestern University, Evanston IL 60201
BIRL has been involved in hardcoating development for engineering applications for several years. A major effort over the past four years has focused on the replacement of electroplated chrome in applications where the steel substrates have moderate hardnesses (Rc38-42) and therefore only modest support for hard PVD coatings. Much of the development work has been supported by the government through DARPA as part of an environmental thrust to eliminate pollution sources and health hazards from their OEM's as well as their repair facilities. BIRL has developed the use of duplex processing (plasma nitriding + sputter-coating) and thick PVD coating (15-20um) with CrN and demonstrated wear performance characteristics superior to commercial chrome plating. This paper reviews some of the process developments involved in these programs and the wear test results. Production cost estimates have also been conducted for certain components, and it has been demonstrated that PVD coating is competitive with electroplating when the total manufacturing process is taken into account.
5:00 pm
CHARACTERISTIC OF TiN FILM DEPOSITED ON STELLITE USING REACTIVE MAGNETRON SPUTTER ION PLATING: Whungwhoe Kim, Joungsoo Kim, Surface Treatment Group, KAERI, Taejon, Korea, Mingu Lee, Heesoo Kang, Wonjong Lee, Dept. of Materials Science, KAIST Taejon, Korea
TiN films were deposited onto stellite 6B alloy (Co base) by the reactive magnetron sputter ion plating. As the substrate bias increases, TiN film changes from columnar structure to dense structure due to densification and resputtering by ion bombardment. Oxygen, the major impurity, is decreased greatly when the substrate bias is applied. The preferred orientation of the TiN films changes from (200) to (111) with decreasing N2/Ar ratio. The change of the preferred orientation is discussed in terms of surface energy and strain energy which are related with the impurity contents and the ion bombardment damage. The hardness of the TiN film increases with increasing compressive stress generated in the film by virtue of ion bombardment.
Room: 340B
Session Chairperson: M.E. Fine, Northwestern University, Evanston, IL 60208
2:00 pm INVITED
TRANSITION METAL CARBIDES AND NITRIDES FOR ELECTRONIC DEVICES: Wendell S. Williams, Department of Physics, University of Illinois, Urbana, IL 61801
The need for thermally stable, diffusion-resistant but electronically conducting materials for interconnects in ultra large scale integrated circuits has led to the successful application of transition metal carbides and nitrides, particularly TiN. Another application is the use of superconducting NbN to make Josephson junctions NbN/Si/Nb and Nb/MgO/NbN. And high-temperature resistors with nearly zero temperature coefficients have been made from TaN. This family of materials, sometimes called "metallic ceramics," can be deposited as thin films by several processes, including reactive sputtering, metal-organic chemical vapor deposition and plasma-assisted chemical vapor deposition. An interesting but potentially troublesome characteristic of these NaCl-structured materials is their wide range of deviation from stoichiometry, involving many percent random atomic vacancies, scattering centers for conduction electrons. Hence film preparation requires that the non-metal/metal ratio be close to unity. It is not widely recognized that these defect-ridden crystal structures are non-equilibrium phases: when cooled slowly from high temperatures, some develop ordered phases with lower resistivities.
2:30 pm INVITED
ELECTROMIGRATION IN SUBMICRON Al-0.5%Cu INTERCONNECTS FOR SILICON ULSI: J.A. Prybyla, S.P. Riege, A.W. Hunt, Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974
Systematic studies of the influence of local microstructure on electromigration (EM) dynamics in submicron Al(0.5 wt % Cu) interconnects were performed using in-situ transmission electron microscopy (TEM) techniques. This approach has allowed us to observe in real-time voids forming, growing, migrating, pinning, failing a runner, and healing, all with respect to the detailed local microstructure of the runners. Here we will report and describe how grain boundaries dramatically influence almost all aspects of EM-induced void and failure dynamics in submicron runners. We also find a striking change in EM-mechanism as a function of temperature in the range 200-300°C. Studies as a function of linewidth and passivation state were also performed. Our findings have important implications for both electromigration modeling and conventional reliability testing.
3:00 pm INVITED
DOPANT ACTIVATION OF HEAVILY-DOPED Si BY HIGH CURRENT DENSITY: J.S. Huang K. N. Tu, Department of Materials Science & Engineering, UCLA, Los Angeles, CA 90095-1595
Novel dopant activation in the heavily boron-doped p+-Si was created by applying an electrical current of high current density. The heavily boron-doped p+-Si was obtained by ion implantation and annealed at 900°C for 30 min to achieve a partial boron activation. For additional activation, we gradually applied current until a current density of 2.5X10E7 A/cm2 was reached. The resistance of the p+-Si responded by a gradual increase, then it decreased with a precipitous drop. The resistance was reduced by a factor of 5 to 18. Mechanisms of the novel dopant activation will be proposed. Dopant activation in the heavily arsenic-doped n+-Si will also be discussed.
3:30 pm BREAK
3:50 pm INVITED
DEVELOPMENT OF LOW THERMAL-EXPANSION, HIGH-CONDUCTIVITY ALLOYS BASED ON THE Cu-Fe-Ni TERNARY SYSTEM: R.D. Cottle, R.K. Jain, C.C. Hays, Z. Eliezer, L. Rabenberg, Center for Materials Science and Engineering, The University of Texas at Austin, Austin, TX 78712; M.E. Fine, Northwestern University, Evanston, IL 60208
The FCC phase in Cu-Fe-Ni ternary system contains a miscibility gap within which tie-lines extend from nearly pure Cu toward the Invar composition, Fe - 36% Ni. This suggests that it should be possible to prepare alloys containing isotropic distributions of Invar within high conductivity, Cu-rich, matrices, and that the Invar fraction can be controlled by selecting starting compositions at various points along the tie line. The resulting combinations of low thermal expansion with high electrical and thermal conductivity will be of interest in the electronic circuit packaging industry. Technical difficulties in developing such alloys arise from incomplete solid solubility at high temperatures at the Cu-rich end of the series and from the slow approach to complete chemical phase separation at low temperatures. Quaternary element additions and mechanical deformation processes are being explored as approaches to creating more nearly homogeneous starting alloys. Microstructural developments and electrical and thermal properties will be reported and discussed.
4:20 pm
PROCESS OPTIMIZATION OF HIGH-STRENGTH, HIGH-CONDUCTIVITY Cu-Cr IN-SITU COMPOSITE: H. G. Suzuki, K. Adachi, S. Tsubokawa, T. Takeuchi, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305, Japan
High-strength, high-conductivity Cu-Cr in-situ composites were developed through the optimization of various process variables. Ingots were obtained by vacuum induction melting. Dendritic Cr was in-situ precipitated during solidification. After hot forging and solution treatment at 1000C, repeated cold working was performed to get fine lamellar spacing of single crystalline Cr second phase. The analysis of microstructure by TEM showed dynamic recrystallization of Cu matrix and fine distribution of Cr precipitates. These structures give the strength level of 900 MPa and relative conductivity, IACS, of 78%. The mechanism of high strength and high conductivity will be discussed.
4:40 pm
THE CHARACTERISTICS OF ELECTRICAL CONDUCTIVITY AND PRECIPITATION OF Cr BY AGING IN Cu-Cr IN-SITU COMPOSITE: J. Yan, H.G. Suzuki, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305, Japan
Aging treatment is one of the most important materials processing techniques for obtaining high electrical conductivity in Cu in-situ composite. In this work, we systematically investigated the effect of Cr precipitation on electrical conductivity of a Cu-15 wt % Cr in-situ composite, by means of aging treatment, electrical conductivity measurement, scanning electron microscopy, analytical electron microscopy, high resolution electron microscopy and X-ray lattice parameter measurement. The optimum aging condition for obtaining peak electrical conductivity has been determined. In addition, it is found that an appropriate amount of cold working can further enhance the electrical conductivity of the composite. The related mechanism has also been studied.
Room: 230A
Session Chairpersons: Alton T. Tabereaux, Reynolds Metals Company, Manufacturing Technology Laboratory, 3326 East 2nd Street, Muscle Shoals, AL; Peter Polyakov, Light Metals Department, Non-ferrous Metals Academy, Krasnoyarsk sabochiy St. 95, 660025, Krasnoyarsk, Russia
2:00 pm
IMPLEMENTATION OF POINT FEEDING IN THE SØDERBERG LINES AT HYDRO ALUMINUM KARMØY: Knut Arne Paulsen, Willy K. Rolland, Asbjørn Larsen, Hydro Aluminum a.s, Karmøy Plants, N-4265 Håvik, Norway; Marvin Bugge, Norsk Hydro a.s, Research Centre, N-3901 Porsgrunn, Norway
A concept for point feeding of alumina to Søderberg cells has been developed at Hydro Aluminum Karmøy. During 1996 and early 1997 the bar breaker equipment on all 340 cells will be replaced by point feeders. Alumina is fed by means of a fluidized feeder and mechanically forced into the bath. The lifetime of the equipment is comparable to that of the cathode life. The concept has proved to stabilize the operation of the cell. Furthermore, the stability improves the current efficiency and also allows the amperage to be increased. Implementation of point feeding includes revised operational procedures and new target values for the operational parameters and also affects the organization. The anode effect frequency has been reduced in several steps during the development period. Today, the anode effect frequency is about one tenth of the corresponding value for the previous bar breaker cells resulting in reduction of perfluorocarbon emissions.
2:25 pm
A UNIQUE, ECONOMIC SØDERBERG TO PREBAKE CONVERSION FOR THE RUSSIAN ALUMINIUM INDUSTRY: S. Tsymbolov, G. Necheav, Nadvoitsky Aluminium Smelter, Zavodskaya Street, 1, Nadvoitsy, 186430, Karelia, Russia; Lee E. Swartling, Kaiser Aluminum Technical Services, Inc. 6177 Sunol Boulevard, Pleasanton, CA 94566; G. Volfson, All-Russian Aluminium & Magnesium Institute, 86 Sredny Prospect, St. Petersburg, 199026, Russia
The majority of Russian aluminum smelting technology is Søderberg, historically associated with non-competitive performance and ecological problems. After conversion to conventional prebake cell technology was found economically unjustifiable, the Nadvoitsky Aluminium Smelter, Karelia, Russia commissioned the All-Russia Aluminium and Magnesium Institute and Kaiser Aluminum Technical Services Inc. to design a unique prebake technology cell with world class performance which could be economically retrofitted into the existing facility. This multi-national team utilizing state of the art modeling and process control technology, successfully designed and implemented a twelve pot test section at Nadvoitsy. Cell performance measured over twelve months has consistently exceeded minimum design indices and paces world class cell performance. Measurements of magnetic field, heat flow, and voltage distribution compare closely with predicted values. Design features, including a novel six anode superstructure, design methodology, test protocol, construction and operation practices, and cell performance data are presented in this paper.
2:50 pm
BATH TEMPERATURE MEASUREMENTS WITH THERMOCOUPLES: Paul Verstreken, Heraeus Electro-Nite Int. N.V., Grote Baan 27a, 3530-Houthalen, Belgium
After a brief introduction into the physical principles of thermoelectricity an overview of commonly used thermocouples is given. The construction of thermocouple sensors and assemblies is discussed. An overview of calibration procedures is given. Errors can arise from the materials (thermocouple wires and sheathing) used, and the way the actual measurement is performed. Reasons for drifting are discussed. There is a relation between the thermal properties (thermal mass and heat conductivity) of the sheathing material, the measuring procedure and the obtained accuracy of the temperature measurement. From this, recommendations on how to improve the quality of bath temperature readings, are made.
3:15 pm BREAK
3:35 pm
A NEW INSTRUMENT FOR FAST TEMPERATURE MEASUREMENT IN ALUMINIUM REDUCTION CELLS: Fucang Xu, Jie Li, Huazhang Wang, Yexiang Liu, Department of Metallurgy, Central South University of Technology, Changsha, Hunan 410083, China
A new instrument, with a single-chip microcomputer as its core and based on a new method named Dynamic Temperature Measurement, has been developed for fast temperature measurement in aluminium reduction cells. When a cold thermocouple is inserted into hot electrolyte, the instrument measures the thermocouple output curve and meantime identifies the parameters of a time series-analysis model which is used to describe the temperature-time curve. Until the convergence of the identification is verified, the instrument predicts the temperature of the electrolyte from the obtained information. In the way, the temperature can be indicated before the thermocouple output reaches its balance point, with the measurement process lasting only some 50 seconds and measurement accuracy reaching ±2°C, a range acceptable for industrial measurement.
4:00 pm
A DEVICE FOR CONTINUOUS ALUMINA FEED INTO AN ALUMINIUM ELECTRIC CELL: A.I. Begunov, E.V. Kudryavtseva, State Technical University, Lermontov Str. 83, Irkutsk, Russia
A new device is suggested here to cover the cell and feed alumina into it. The covering is designed having such thermal resistance that no crust develops on the electrolyte surface. Alumina is fed from the intermediate hopper, which is one piece with the covering plate, into the electrolyte through the narrow slot, the width of which ranges from 0.8 to 1.2 mm. The alumina feed rate is determined by its bulk properties ("sandy", "mealy", "moist"), the width and length of the slot and the intermediate hopper wall flare angle. The cold model of the device yielded the dependencies of alumina slot spead on the parameters mentioned above. The device has no crust-breaking appliances or volumetric dosers. Dosage is effected only to gravity feed of raw materials through a slot of predetermined cross-section. Because of that, low operation costs and high reliability of the suggested device are expected.
4:25 pm
VISUALISATION OF TAPPING OPERATIONS: Marcus Walker, Comalco Research Centre, P.O. Box 316, Thomastown, Australia 3074
The removal of molten aluminium from Hall- Heroult cells is known a "tapping". This operation causes process disturbances including entrainment of electrolyte and sludge in the tapped metal as well as producing localised wear of the cathode. This paper describes the use of a full scale physical model for determining the optimal tapping conditions to reduce both bath entrainment and cathode erosion for various cell operating strategies. Flow visualisation and numerical modelling has shown that the flow towards the tapping pipe is predominantly radial, however under and inside the pipe, the flow swirls intensely. Under certain conditions the swirling flow induces a vortex at the bath metal interface through which bath can be entrained in the flow. The swirling action was also seen to produce a region of locally high velocities on the cathode surface which enhances erosion of the cathode through a number of possible mechanisms.
4:50 pm
A NEW CONCEPT OF RESOLVING LADLE CLEANING AT SLOVALCO BY TECHMO: F. Zannini, F. Marchetti, R. Balasso, J. Ifju, Techmo Car SpA, Via R. Colpi 15/17, 35010 Limena (PD), Italy
Techmo has elaborated a new concept of resolving the problem of ladle cleaning based on standard features of the new aluminium smelter implemented by Hydro Aluminium's technology at SLOVALCO a.s. A thorough design work has resulted in a piece of equipment with new arrangement and orientation in good agreement with the tapping system and work organization of the plant. Some optimization was fulfilled in order to meet the requirements of the new plant in possible best manner.
Room: 232A
Session Chairs: B.G. Thomas, Dept of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801; B.Q. Li, Dept of Mechanical Engineering, Louisiana State University, Baton Rouge, LA 70803
2:00 pm
NUMERICAL ANALYSIS OF FLOATING ZONE REFINING PROCESSES: S.P. Song, B.Q. Li, Department of Mechanical Engineering, Louisiana State University, Baton Rouge, LA 70803
A numerical model is developed to represent complex electromagnetic, thermal and free surface deformation phenomena in floating zone refining and single crystal growth processes. The model is developed using a coupled boundary element and finite element method, with finite element meshes used for the melting zone region and boundary elements for the exterior region or free space. The free surface deformation model is developed using the weighted residual method. With the model, the complex transport and free surface phenomena in a floating, zone system are studied as a function of various operating conditions including applied current, frequency, inductor position and shape, surface tension, floating zone diameter and height. Model development and numerical results are presented.
2:25 pm
MODELING OF SOLIDIFICATION AND VELOCITY OF ATOMIZED MOLTEN DROPLET DURING ATOMIZATION AND SPRAY FORMING: Y.H. Su, C.-Y. A. Tsao, Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan, China
A mathematical model to describe the solidification behaviors of atomized droplets during flight, in terms of nucleation temperature, recalescence temperature, nucleation position, solid fraction at nucleation temperature, and droplet temperature and velocity, is formulated. The concept of transient nucleation is applied to model such short nucleation event. A maximum droplet velocity exists, beyond which droplet velocity shows an inflection phenomenon during the flight. For shorter flight distance, smaller droplet is faster to reach a given flight distance; however, for longer flight distance, the situation is reversed. Variations of the gas flow patterns have more effects on smaller droplet, and the effects are more significant at longer flight distance. A minimum surface heat transfer coefficient exists as the droplet flies. Prior to nucleation or recalescence, smaller droplet has lower temperature at a given flight distance, and has lower nucleation temperature. Medium size droplet flies over the shortest flight distance before the nucleation starts. Smaller droplet has larger solid fraction at the end of recalescence. Atomization gas has more effects on droplet momentum than on the heat content of the droplet.
2:50 pm
THE EFFECT OF FORCED COOLING A PERMANENT COMPOSITE MOLD ON AIR GAP FORMATION: D.R. Gunasegaram1, D. Celentano2, T.T. Nguyen1, 1CRC for Alloy and Solidification Technology (CAST) and CSIRO Division of Manufacturing Technology, Locked Bag 9, Preston 3072, Australia; 2International Center for Numerical Methods in Engineering, Edificio C-1 Campus Norte-UPC, Gran Capitan, s/n. 08034 Barcelona, Spain
It is well known that the air gap that forms between casting and mold during the solidification process of an aluminum alloy substantially alters the rate of heat transfer at this interface. This paper reports studies on the effect of force cooling a composite permanent mold on the initiation and growth of the air gap. Interesting comparisons are made with the case where no forced cooling is employed. The two experiments are simulated using a fully coupled thermo-mechanical model called VULCAN, a finite element code, and its temperature and displacement predictions are validated. The air gaps are measured using LVDTs. The alloy used is A356, and the mold comprises H13 steel and beryllium-copper. Air jets are used to force cool the mold component surrounding an isolated thick section of the casting. The inverse heat conduction problem is solved in order to obtain boundary conditions for VULCAN.
3:15 pm BREAK
3:25 pm
EFFECT OF TRANSVERSE DEPRESSIONS AND OSCILLATION MARKS ON HEAT TRANSFER IN THE CONTINUOUS CASTING MOLD: B.G. Thomas, D. Lui, B. Ho, G. Li, Y. Shang, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801
Results from mathematical models and plant experiments are combined to quantify the effect of transverse depressions and oscillation marks on heat transfer in the continuous casting mold. A heat transfer model has been developed to calculate transient heat conduction within the solidifying steel, coupled with the steady-state heat conduction with the continuous casting mold wall. The model features a detailed treatment of the interfacial gap between the shell and mold, including mass and momentum balances on the solid and liquid powder layers. The model predicts the solidified shell thickness down the mold, temperature in the mold and shell, thickness of the resolidified and liquid powder layers, heat flux distribution down the mold, mold water temperature rise, ideal taper of the mold walls, and other related phenomena. The important effect of non-uniform distribution of superheat is incorporated using the results from previous 3-D turbulent fluid flow calculations within the liquid cavity. Results from plant experiments confirm that transverse surface depressions and oscillation marks form at the meniscus and move down the mold. Measurements of mold thermocouple temperatures and breakout shell thickness were used to calibrate the models. The predicted local surface temperature fluctuations were consistent with transient mold temperature measurements. The results indicate that the surface depressions and oscillation marks are filled with mold flux, but still have a significant effect on decreasing heat transfer, especially locally. Insights are gained into the formation of associated surface cracks and breakouts.
3:50 pm
CHANGE OF PATTERN OF SOLIDIFICATION IN INGOTS CAST FROM THE BOTTOM, REPRESENTED BY A MATHEMATICAL MODEL AND ITS EFFECT ON THE APPARITION OF DEFECTS IN THE SEAMLESS TUBES OF C.V.G SIDOR: J. Rodriguez, A. Valles, C.V.G SIDOR, Puerto Ordaz, Venezuela, M. Rao, Universidad Nacional Experimental de Guayana, Puerto Ordaz, Venezuela
This paper shows a mathematical model based on finite elements, applied to bottom cast ingots of C.V.G Sidor Plant. The model was used as a strategy to determine the thermal effects that are produced when the solidification conditions are modified, without interfering with the production process. The modification consisted of placing a thermal insulant on top of mould. The results obtained by the model indicated that the solidification time increases with insulant on top of the mould. With these results a significant number of casts were run with and without insulant. Later by means of a metallurgical analysis it was determined that the ingots cast with insulant reduce the level of nonmetallic inclusions and the presence of internal blistering in seamless pipes.
4:15 pm
MATHEMATICAL MODELING AND EXPERIMENTAL MEASUREMENTS OF EXOTHERMIC PHENOMENA IN NON FERROUS SYSTEMS: S.A. Ferenczy, S.A. Argyropoulos, Dept of Metallurgy and Materials Science, University of Toronto, 184 College Street, Toronto, Ontario, Canada M5S 3E4
Microexothermic and macroexothermic phenomena have been indentified various non-ferrous systems, which from recent experimental and mathematical studies have been shown to enhance heat and mass transfer. This paper will present experimental results and computer simulations describing the transient exothermic dissolution of nickel cylinders into liquid aluminum. Axisymmetric heat, mass and momentum equations the SIMPLER algorithm was modified to incorporate phase change and the microexothermic macroexothermic events. Dissolution experiments were performed and the results compared to the mathematical simulation. The development of coupled temperature, concentration and momentum boundary layers are examined.
Room: 231A
Session Chairperson: Dr. E. Ozberk, Sherritt International, Bag 1000, Fort Saskatchewan, AB, T8L 2P2
2:00 pm
DEVELOPMENT OF AUTOMATIC MATERIAL HANDLING AND MONITORING SYSTEMS IN AN EXISTING ELECTROLYTIC ZINC PLAN: T. Yamada, R. Togashi, T. Aichi, Akita Zinc Co., Ltd., Iijima Refinery, Akita, Japan
Mainly due to the strong yen and the relatively low metal price, the zinc refineries in Japan are being forced to reduce man power. At IIjima, a new automatic material - handling system for cathode transportation was developed and the first system went to service in August 1994. The work was started in 1993 and all installation will be finished in the summer 1997. The critical part of this work was to achieve the designed cycle time because of the fairly complex cell-layout. As the cathodes are placed opposite direction in every other unit, cranks must be able to move toward two directions (X and Y) at the same time and to stop precisely at the tolerance level of a few millimeter. The central monitoring system for machine operation run by an original application software with MICROSOFT EXCEL© on WINDOWS 95©, was started in June 1996. There had been one person only for operating a manual crane before. Now an operator of a stripping machine can control the automatic crane for the same row at the same time. As a result, only one person can operate both a crank and a stripping machine for one row. And more labour saving is expected in the future.
2:25 pm
INDUSTRIAL SIZE "PLACID ELECTROWINNING CELL": C.Frías, M.A. García, G. Díaz, Tecnicas Reunidas, S.A., R & D Centre, Madrid, Spain
Under the auspicious of the Commission of the European Union, a consortium composed of six European organizations has developed the PLACID process, into the Brite Euram II Programme. The project began on January 1993 and was finished on April 1996. The PLACID process is based on a novel technology able to deal with different lead bearing materials, mainly lead oxide secondaries: Lead-acid batter pastes, lead fumes, furnace slags, oxide residues, etc., producing "four nines" pure lead in an efficient manner with a benign influence on the environment. In the PLACID process, lead is leached in warm, slightly acidic, brine to form soluble lead chloride. This solution is purified by cementation with lead powder. Pure lead is then won from the lead chloride electrolyte on the cathode of the electrowinning cell and is collected. This electrolytic cell is the heart of the process and it was especially developed to give optimum performance. Hydrochloric acid is reformed in the cell and returned to the leaching bath; reagent net consumption in the process is irrelevant. This paper is concerning the development of the PLACID electrowinning cell up to industrial size electrodes. The performed work has covered three levels of development: laboratory study, bench scale experimentation and pilot plant prototype testing (16 Kg/h electrolytic lead production). After 1,000 hours operating time, the achieved results of the pilot plant electrowinning cell have been very satisfactory, demonstrating the ability of the Placid electrowinning cell to produce top quality electrolytic lead (above 99.99% Pb) with high current efficiency and low energy consumption.
2:50 pm
CHARACTERIZATION OF ANTIMONY-GELATIN ADDITIVES IN ZINC SULPHATE ELECTROLYTES USING IMPEDANCE ANALYSIS: X. Tang, Southwire Copper Division, 372 Central High Rd., Carrollton, GA 30117; P. Yu, T.J. O'Keefe, University of Missouri-Rolla, Department of Metallurgical Engineering and Graduate Center for Materials Research, Rolla, MO 65409-1170; G. Houlachi, Noranda Technology Centre, Pointe-Claire, Quebec, H9R 1G5, Canada
Impedance measurements were used to investigate the electrochemical characteristics of acidic zinc sulphate electrolytes containing Sb3+, gelatin and their mixtures. The data were correlated with cyclic voltammetry curves made using synthetic as well as industrial electrolytes. The cyclic voltammetry results were similar to those obtained in previous studies in that antimony caused a depolarizing effect while gelatin gave an increase in the potential for zinc nucleation on an aluminum substrate. The electrochemical impedance spectroscope (EIS) evaluations were conducted on electrodeposited zinc at three overpotential values. The potentials were chosen to represent various current density regions in the zinc polarization curves. The antimony and gelatin gave characteristic impedance plots which correlated with expected behaviour, particularly current efficiency. Both antimony and glue appear to modify the intermediate zinc reaction sequence, but in different ways. The data strongly suggest that film formation and stability are major factor in the zinc ion reduction mechanism.
3:15 pm
EFFECTS OF ANTIMONY AND CONTINUOUS GELATIN ADDITION ON CURRENT EFFICIENCY IN THE HUDSON BAY ZINC ELECTROWINNING TANKHOUSE: P. Merrin, Hudson Bay Mining & Smelting Co., Limited, Flin Flon, Manitoba, R8A 1N9, Canada
This study was conducted at Hudson Bay Mining and Smelting's zinc electrowinning tankhouse to determine the effects of varying levels of antimony and continuous gelatin addition on current efficiency. The levels of antimony and gelatin were varied between 0.010-0.030 mg/l and 0-10 mg/l respectively, using the fresh electrolyte as reference. The test was designed to determine the optimum operating point for current efficiency, and to investigate any interaction that occurs between the two components. An non-linear mathematical model relating these three variables was produced, giving an optimum operating point of 6.5 mg/l of gelatin and increasing current efficiency with decreasing antimony levels. Individually, the antimony concentration was approximately linear with current efficiency, while gelatin concentration was parabolic. An interaction term is present but is not significant enough to improve the ability of the tankhouse to handle purification upsets in antimony.
3:40 pm
THE EFFECTS OF SOME FOAMING REAGENTS ON ACID MIST CONTROL AND ZINC ELECTROWINNING FROM KIDD CREEK ZINC ELECTROLYTE: A.M. Alfantazi, D.B. Dreisinger, University of British Columbia, Department of Metals and Materials Engineering, Vancouver, B.C., V6T 1Z4, Canada; J. Synnott, M. Boissoneault, Falconbridge Ltd., Kidd Creek Division, P.O. Bag 2002, Timmins, Ontario, P4N 7K1, Canada
The effects of five commercially available foaming reagents (range of 0 to 25 ppm) namely Dowfroth 250 Saponin, Yucca, Licorice and Meta-Para Cresol on acid mist control, current efficiency, polarization behaviour, and deposit morphology and orientation were investigated using a bench scale electrolysis apparatus (cell volume 3L). The deposition was carried out at 500 Am-2 and 38°C for 3 hours from Kidd Creek zinc electrolyte. The acid mist control capability of the various reagents was studied and compared by characterizing the foam layer generated during actual electrowinning conditions and by direct quantitative measurements of acid mist levels on top of the electrowinning cells. Within the range considered, the addition of these reagents reduced the current efficiency, refined the grain size of the deposit, and changed to preferred orientation of most of the deposits. Among the reagents tested, acid mist measurements indicated that Licorice and Dowfroth 250 were the best acid mist suppressant at emissions of 0.30 mg/m3 and 0.31 mg/m3 respectively while Yucca and MPC produced the most mist at 3.0 mg/m3 and 3.3 mg/m3 emission rates respectively.
4:00 pm
ELECTROPURIFICATION OF ZINC LEACHING SOLUTION: S. Yamashita, K. Hata, S. Goto, Department of Metallurgy, Chiba Institute of Technology, Chiba, Japan
The average consumption of zinc dust for purification of zinc leaching solution is more than 25 kg per ton of electrolytic zinc. Authors proposed to remove impurities in zinc leaching solution by electrolysis instead of cementation by zinc dust. The effects of copper and arsenic on electrodeposition of cobalt in zinc sulfate solution were examined fundamentally by using potentiostat. The mesh cathodes of stainless steel and lead anodes are used in the electrolytic cell for removal of cobalt and an electrolyte is circulating rate of electrolyte, concentration of copper and arsenious ions on removal of cobalt are studied. Removal of Ni, and Cd are also examined.
4:25 pm
Cl ANION ELIMINATION FROM Zn SULPHATE SOLUTION BY PERIODICAL REVERSE ELECTROLYTIC SYSTEM: T. Yoshida, M. Kahata, M. Dobashi, M. Suzuki, Mitsui Mining and Smelting Co. Ltd., Sairama, Japan
In Japan, almost 30% of steel is produced by electric arc furnace (EAF) melting of iron scrap. And the dust from EAF includes approximately 20-30 wt % of Zn and 3.5 wt % of C1. They are treated as industrial waste to recover Zn as Zn oxide mainly by pyro metallurgical process. On the other hand, high purity zinc recovery by direct hydro-metallurgical processing is one of the most effective method. In this case, Cl in the EAF dust is dissolved in liquid phase by leaching, but the Cl anion in electrolyte attacks anode which is made of a lead base alloy. Several processes have been proposed to remove Cl anion from acidic sulfate solution. In this study, an electrolytic process is established to eliminate Cl anion from Zn sulfate electrolyte. It is known that Cl anion can be removed by anode oxidation. From our study it can be said that the elimination rate of Cl anion depend on the anode material, i.e. the elimination rate is Pb - Ag alloy > Pb DSE. Furthermore in industrial electro-winning process, electrolyte includes Mn dioxide. Therefore, the effect of Mn in electrolyte should also be considered for Cl elimination. It seems that Mn dioxide deposition on anode decreases the efficiency of Cl anion removal. The periodical reverse system was induced to prevent from efficiency decrease. By using periodical reverse system, deposited Mn dioxide is removed very rapidly when the current was reversed for short time. More than 95% of Cl anion can be removed in extremely short period than conventional method. At the symposium the detailed data will be presented about Cl anion elimination by periodical reverse system.
4:50 pm
THE ROLE OF COPPER AND ANTIMONY ADDITIVES IN THE REMOVAL OF COBALT FROM ZINC SULPHATE SOLUTIONS: V. Van der Pas, D. Dreisinger, University of British Columbia, Department of Metals and Materials Engineering, Vancouver, British Columbia, V6T 1Z4 Canada
Zinc sulphate electrolyte used for zinc electrowinning must be purified for cobalt ions. The cobalt is removed in a cementation stage by the addition of zinc dust. Copper and antimony are frequently used additives which enhance the cementation of cobalt. This paper aims at a better understanding of how copper and antimony promote the removal of cobalt. Initial experiments were done in a batch cementation reactor. Copper and antimony precipitated in the early stages of cementation indicating that a preferential substrate was formed. The individual role of copper and antimony was further investigated in an electrochemical cell. On a microscale, the growth process, morphology and the composition of the precipitates under various conditions were examined with SEM and XRD. It was found that cobalt could not be deposited in its pure form but as a cobalt-zinc alloy with zinc as the prime constituent. The effect of copper addition is of increasing the cathodic surface area of zinc dust by precipitating as numerous dendrites. Antimony acts as a cathodic surface onto which a cobalt-zinc alloy with an increased cobalt content is deposited.
Room: 230B
Session Chairperson: Kurt Ehrke, Aluminium Essen GmbH, Sulterkamp 71, D-45356 Essen, Germany
2:00 pm
REFRACTORY SOLUTIONS DESIGNED TO OVERCOME CORUNDUM GROWTH IN ALUMINIUM FURNACES: Duncan Jones, Morganite Thermal Ceramics Ltd., Liverpool Road, Neston, South Wirral, L64 3RE, England
Corundum is an extremely hard, high temperature form of aluminium oxide. Its formation in aluminium melting furnaces and metal treatment units can lead to a reduction in operating efficiency and premature failure of the furnace lining. The formation of corundum is known to be dependent on several factors, including furnace atmosphere, operating temperature, alloy composition and refractory type. The paper describes solutions to this phenomenon identifying its cause and effect whilst highlighting refractory design criteria. Results from an extensive testing programme, classifying resistance to corundum growth against various qualities of refractory product are discussed.
2:20 pm
USE OF SMALL DIAMETER IMMERSION HEATERS IN MOLTEN ALUMINUM: Mark Palmer, Pyrotek Inc., E. 9503 Montgomery Avenue, Spokane, WA; Andre Teytu, Atherm, Rue de Moirind 13, 38420 Domene, France
Small diameter electric immersion heaters offer unique benefits when used in molten aluminum heating applications. The 1" diameter heaters allow greater flexibility in vessel design than traditional immersion heating systems. The electric heating elements are inside a Sialon sheath, which is non-wedded by molten aluminum and offers long life. Since the development of these heaters, they are being used in many different types of molten aluminium holding vessels. Pechiney Aluminium Engineering utilizes these small heaters in Alpur degassing vessels and the Pechiney Deep Bed Filter Heaters are also used in die casting holding furnaces for both primary and supplemental heating applications. The net result of using the small immersion heaters is high metal heat-up rates, compact vessel designs, energy savings, uniform metal temperatures, and user friendly equipment designs. The paper describes the capabilities of the heaters, the design flexibility they allow, and performance results obtained from initial installations.
2:40 pm
IMPACT OF GOOD METAL CIRCULATION AND FURNACE OPERATION FOR INCREASED PERFORMANCES FOR SIDEWELL FURNACES: G. Riverin, W. Stevens, Arvida Research and Development Centre, Alcan International Limited, 1955 Mellon Blvd., Jonquière, Québec, Canada G7S 4K8; D. Bristol, Alcan Rolled Products Company, P.O.Box 837, Greensboro, 30642; Y. Kocaefe, Université du Québec à Chicoutimi 555, Boul. de l´Université E, Chicoutimi, Quebec, Canada G7H 2B1
Sidewell furnaces have long been operated for scrap melting, including UBC. The paper discusses important criteria for the optimum energy and melt rate performances for these types of furnaces. Intensive work has been done in several Alcan recycling installations in order to increase these furnace performances. Several operating parameters are outlined combined with the importance of melt stirring in the main hearth and in the sidewell. Mathematical and physical modeling provided key elements responsible for better furnace operation. The impact and advantages of the improved melt stirring and furnace operation are explained and discussed in detail.
3:00 pm
CAST HOUSE WATER TREATMENT WITH AEC TECHNOLOGY: Ed Grodecki, Betz Water Management Group, 4150 Washington Road, Bldg.2, Suite 206, McMurray, PA 15317
REPLACEMENT PAPER
Presented by: George Binczewski
3:20 pm
MOLTEN ALUMINUM PLUS WATER--A DIFFERENT POINT OF VIEW: George J. Binczewski, S C Systems, PO Box 6154, Moraga, CA 94570
For forty years, the Aluminum Industry has conducted and sponsored investigations directed at establishing a better understanding of the safety aspects associated with the sometimes explosive occurrence which may happen when there is a physical contact between molten aluminim and water. Industry concern has resulted in a poling of resources among companies, associations, and technical organizations. There has been a substantial funding of investigative projects conducted by capable research organizations employing sophisticated techniques. While useful information has been gained and translated into operational procedures, the basic cause remains elusive. A completely different, and additional, investigative approach is suggested based on cumulative experience and observation of daily occurrences. This can provide the informational basis to alleviate the safety and liability concerns associated with direct contact between molten aluminum and water.
3:40 pm BREAK
3:50 pm
THIN GAUGE TWIN-ROLL CASTING, PROCESS CAPABILITIES AND PRODUCT QUALITY: O. Daaland, M.L.Nedreberg, A.B.Espedaal, Enge Alwestad, Hydro Aluminium a.s, R&D Materials Technology, N-4265 Håvik, Norway
Traditionally industrial twin roll casters have been operated at gauges 6-7 mm, depending on the type of caster and the final product requirements. Over the past few years it has become apparent that a significant increase in productivity can be achieved when the casting gauge is reduced. Hydro Aluminium embarked on an extensive R & D thin gauge casting program in the beginning of the 1990's, and this paper presents results of a five year lasting project (joint program between Hydro Aluminium and Lauener Engineering). Based on over 400 casting trials the major benefits and limitations of casting at reduced gauge and increased speed are outlined. Important aspects for product quality are discussed including: cooling rates and dendrite structure, microstructural characteristics (as-cast grain structure and texture), segregation behaviour, surface quality and mechanical properties after thermomechanical processing. Results for casting of several alloys (including the 5xxx and 8xxx-system) are given. Additionally, numerical modelling results of the strip casting process are included.
4:10 pm
PECHINEY JUMBO 3CMTM--START-UP OF THE NEUF-BRISACH THIN STRIP CASTER: Pierre-Yves Menet, Pechiney Rhenalu Neuf-Brisach, Z.I.Biesheim, BP 49, F-68600 Neuf-Brisach, France; Robert Cayol, Pechiney Aluminium Engineering, Centr'Alp-725 rue Aristide Bergès, F-38340 Voreppe, France; Jacques Moriceau, Pechiney Rhenalu Melting and Casting Direction of Technology, Centr'Alp-725 rue Aristide Bergès, F-38340 Voreppe, France
Following extensive research and development work at the Pechiney Research Center in Voreppe, a new Jumbo 3CMTM thin strip caster has been installed at the Pechiney Rhenalu Neuf-Brisach plant. First of its generation, it is capable of casting a 2m wide strip under a maximum load of 2900 tons. This paper reviews the various features of the equipment which make possible the casting of thin strip of aluminum alloys covering a wide range of applications, from foil stock to can stock. Initially scheduled for start-up in June '96, the equipment was started on time. Performances concerning the installation itself and the casting of several alloys are given. A video of the installation and an actual casting will be shown during the Cast-Shop session.
4:30 pm
AN UPDATE ON DOWN-GAUGING THE FATA-HUNTER SPEEDCASTERTM AT NORANDAL, HUNTINGTON (TN): R. Beals, B. Taraglio, C. Romanowski, FATA Hunter Inc., 6147 River Crest Drive, Riverside, CA 92507
The first of a new generation of Thin-Gauge/High-Speed FATA Hunter machines is now in operation at Norandal's Huntington (TN) facility. Following the late February 1996 start-up of the machine, a down-gauging program was commenced which combined normal 5 mm gauge production with a series of pilot production trials at progressively lighter gauges. This paper overviews this start-up program and compares the production rates and metallurgical characteristics of the thin-gauge cast material with conventional-gauge, twin-roll cast strip. In addition, a brief video tape of the FATA Hunter 86" wide SpeedCasterTM in operation will be presented.
4:50 pm
MAGNETIC EDGE DAMS IN A TWIN ROLL ALUMINIUM CASTER: Craig Anderson, Peter Davidson, Engineering Department, Cambridge University, Cambridge CB2 1P2, United Kingdom
In the twin roll casting process, molten aluminium is fed between two cooled rotating rollers where it cools, solidifies and is carried by roller rotation to the nip, where it is compressed to a single sheet and expelled. To prevent aluminium escaping laterally, from the roller edges, dams are required. Physical edge dams are subject to erosion from the rollers and molten metal and require maintenance and replacement. Hence there is a strong economic case for using magnetic edge dams, where the interaction of a magnetic field and a current provide sufficient repulsive force to contain the molten aluminium, which do not physically touch either the rollers or molten metal and require little or no maintenance. This paper discusses the theory behind high frequency magnetic edge dams and describes the design and construction of a practical system. Laboratory testing of the magnetic edge dam system is shown to give good agreement with theory and the installation and operation of the system on an experimental twin roll caster is described.
5:10 pm
DECOATING TECHNOLOGY FOR THE ALUMINIUM INDUSTRY: O.H. Perry, Stein Atkinson Stordy Ltd., Midland House, Ounsdale Road, Wombourne, Wolverhampton WV5 8BY, England
The technology for recycling aluminium scrap has evolved over a number of years through five major changes as follows: direct charging, side bay melter with puddlers, rotary furnaces, shredding and flat belt delacquering machines, shredding and rotary kilns, today it is now possible to fully decoat any aluminium material which can be shredded. With the invention of IDEX® rotary kiln systems all materials from UBC, extrusions, coated foils, through to 6 micron aseptic foils can be successfully reclaimed and either remelted or processed with minimal metal loss. During 1996 three systems have been commissioned in the Americas for decoating materials which contain 3 to 80% VOC by weight and ranging from 4 to 7 tonnes per hour. This paper discusses the changing technology and the current "state of the art" in rotary kiln technology.
Room: 330C
Session Chairperson: John Morral, Univ. of Connecticut, Dept. of Metallurgy, Storrs, CT 06269
2:00 pm INVITED
ALUMINIUM-BASED NANOPHASE COMPOSITES BY DEVITRIFICATION: A.L. Greer, University of Cambridge, Department of Materials Science & Metallurgy, Pembroke Street, Cambridge CB2 3QZ, UK
Al-TM-Ln alloys (TM... transition metal; Ln...lanthanide) can be rapidly quenched into a fully amorphous state and then partially devitrified to give a nm-scale microstructure of aluminium crystallites uniformly dispersed in an amorphous matrix. This is a highly unusual microstructure for an aluminium alloy, indicating a high density of independent nucleation events in the glass. This study focuses on the development and stability of microstructure in a series of Al-Ni-Y alloys. The effects of various single- and two-stage heat treatments are explored. The emphasis is on the particular features associated with the unusual nm-scale among these is the overlap between coarsening and further transformation arising from capillarity effects on the crystallites.
2:30 pm INVITED
KINETICS OF NANOPHASE CRYSTALLIZATION IN Al-Fe-Gd ALLOYS: A.A. Csontos, G.J. Shiflet, Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903
This presentation will provide results an the formation and subsequent growth of nanocrystalline aluminum phases in an amorphous matrix. A prototype for this family of metallic glass alloys that can be transformed into nanocrystalline material is the Al90Fe5Gd5 system. Detailed measurements of nanocrystalline isothermal growth from an amorphous Al90Fe5Gd5 matrix were made from 150 to 500°C. Coupled with growth of the nanocrystals, measurements of Gd and Fe segregation between the nanocrystal and the matrix were secured in a TEM with a field emission gun. Both Fe and Gd are preferentially rejected into the remaining matrix as the aluminum-rich nanocrystal grows. After reaching a specific size, which varies with temperature, growth slows down and funkier changes are slight until subsequent nucleation and growth of compound phases. such as Al4Gd occur. The relative stability of the formation of nanocrystals from an amorphous matrix will be addressed. Research supported by the University of Virginia Academic Enhancement Program.
3:00 pm INVITED
DIFFUSION FIELD IMPINGEMENT DURING PRIMARY CRYSTALLIZATION OF ALUMINUM NANOCRYSTALS: D.R. Allen, J.C. Foley, J.H. Perepezko, Materials Science and Engineering, University of Wisconsin - Madison, 1509 University Avenue, Madison, WI 53706
Aluminum-rich glasses containing about 85 at% Al and a combination of transition and rare earth element additions have yielded microstructures of Al nanocrystals in an amorphous matrix with nanocrystal volume fractions approaching 20% and excellent mechanical properties. A high density of nanocrystals (>1020 m-3) develops during the primary crystallization reaction but growth is limited. A new kinetics analysis shows that diffusion field the nanocrystals. The kinetics model has been applied to DSC exotherms that correspond to primary fcc nanocrystal formation. A thermodynamic model of the fcc-liquid phase support heat evolution rate calculations used in the model. The results indicate that modification of the nucleant density should be the primary focus in limiting nanocrystal growth due to reduced length scales.
3:20 pm
MICROSTRUCTURAL AND THERMAL ANALYSES OF CRYSTALLIZATION IN ULTRAFINE AMORPHOUS TITANIA PARTICLES: J.-S. Yin, L. He, G.L. Griffin*, E. Ma, Mechanical Engineering, *Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803
Ultrafine amorphous titania particle aggregates, with a mean particle size of 145 nm, were prepared using a hydrolysis technique in an aerosol reactor. Their crystallization bahavior has been studied using transmission electron microscopy, differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. The amorphous powder crystallized into anatase with a crystallization enthalpy of 27 kJ/mol and an apparent activation energy of 2.0 eV. The anatase phase nucleated preferentially in contact regions between neighbouring particles. This crystallization mode is interpreted as a consequence of the presence of appreciable local pressure (stress) which was predicted by model calculations and observed under TEM. An analysis suggests that the pressure effect reduces the relative stability of the amorphous phase by enhancing the thermodynamic driving force for nucleation and possibly also the crystallization kinetics. The nucleation and growth behavior observed has important implications when these amorphous particles are used as precusors to form nanocrystalline titania. The results are also discussed in comparison with the crystallization behavior reported previously for other ultrafine-structured oxides.
3:40 pm BREAK
3:55 pm INVITED
PRESSURE INDUCED CRYSTAL-TO-AMORPHOUS TRANSFORMATIONS: R.B. Schwarz, P.J. Yvon*, Center for Materials Science, Los Alamos National Laboratory, Los Alamos, NM 87545, *Present address: SRMA, Centre d'Etudes Saclay 91191 Gif/Yvette, France
Pressure-induced crystal-to-glass transformations have been observed in tetrahedrally coordinated elements (e.g. Ge, Si), ionic and molecular crystals (alpha-SiO2, FeSiO4, AlPO4, Fe PO4, SnBr4), and hydroxides (ice, Ca(OH)2, Co(OH)2). In these materials, the crystal transforms polymorphically to a higher density glassy phase. Crystal-to-glass transformation have also been observed to occur through pressure-induced reactions between mixtures of elements such as germanium and aluminum. This paper reviews the formation of amorphous phases in alloys and elemental mixtures and discusses the possibility of obtaining bulk amounts of amorphous phases.
4:25 pm
STABLE VS. METASTABLE PHASE EQUILIBRIA IN FACETED/NON-FACETED METALLIC GLASS SYSTEMS: T.M. Adams, M.J. Kaufman, Materials Science and Engineering, University of Florida, Gainesville, FL 32611
Since metallic glasses can be used as precursors for nanocrystalline structures, it is important to understand the relationship between the transformation characteristics of the stable faceting phases and the metastable ordered phases (MOP's) in faceted/non-faceted systems. Such an understanding of the competitive nucleation and growth kinetics should allow better control of the transformation structures. Following some past work on Al-Ge alloys, it has been proposed that, in general, for faceted/non-faceted systems, no equilibria exist between the MOP's and the stable faceted phases. In order to support this assertion of generality, the Hf-Be and Al-Ge systems are being investigated. Crystallization of amorphous melt spun ribbons and co-evaporated thin films is effected by standard furnace anneals and in-situ electron beam heating. Once annealed, the resulting microstructures are characterized using XRD and TEM. In addition, in-situ hot-stage TEM is used to examine the relationship between the MOP and the stable faceting phase while the transformations are occurring. All of this work is being done in the vicinity of the stoichiometric composition of the most stable MOP (Hf-50Be and Al-50Ge). Basic modelling efforts of the metastable phase equilibria are also under way using THERMOCALC with estimated heats of formation for the MOP's determined through DSC/DTA and empirical formulations.
4:45 pm
STRUCTURAL TRANSITIONS IN TI/AL NANOLAYERED THIN FILMS: R. Banerjee, X.D. Zhang and H. L. Fraser, Materials Science and Engineering, Ohio State University, Columbus, OH 43210; M. Asta, A.A. Quong, Computational Materials Science, Sandia National Laboratories, Livermore, CA, R. Ahuja, Multi Arc Scientific Coatings, Troy, MI
Nanolayered materials often exhibit unusual structural features which are significantly different from those of their bulk counterparts. Such structural transitions could lead to novel properties of the material motivating research directed towards engineering the structure at the nanoscale. Laminated thin films based on Ti, Al and Ti-aluminides have potential application as coatings for components used in high temperature aerospace applications. A series of structural transitions were observed in Ti/Al multilayered thin films on reducing the layer thickness of the Ti and Al layers1. An hcp-fcc transition was found to occur in the Ti layers on reduction of the layer thickness to 5 nm. Al too exhibited an fcc-hcp transition on reducing the layer thickness to 2.5 nm. Interestingly, a 2.5 nm Ti layer had an hcp structure. An atempt was made to explain these transformations in the stacking sequence of the Ti and Al layers using a model initially proposed by Redfield and Zangwill. Subsequently, first principles electronic structure calculations are in progress to determine the effect of bulk, interfacial and thin film strain energies on the structural stability of the multilayers. Initial results suggest that strain energy may be playing a pivotal role in determining the structure.
5:05 pm
NANOSTRUCTURES AND PROPERTIES IN RAPIDLY SOLIDIFIED Ti(50)Ni(50-X)Cu(X) ALLOYS: V.G. Pushin, S.B. Volkova, N.M. Matveeva*, A.S. Chistjakov, Institute of Metal Physics, Ural Division of Russian Academy of Sciences, S. Kovalevskoi 18, 620219 Ekaterinburg, Russia; *Baikov Institute of Metallurgy, Russian Academy of Sciences,Leninskij prospect 49, 117911 Moscow, Russia
Rapidly solidified Ti-Ni-Cu alloys prepared by melt spinning were studied. It is found that under super rapid cooling rates alloys with 25-40 at% Cu are formed in initial amorphous state, with 15-25 at% Cu in amorphous-crystalline state, with 15 at% Cu don't become amorphous under spinning. Crystallization heat treatment of amorphous alloys leads to the formation of nano-scale TiNi-based solid solution, which undergo martensitic B2->B19 martensitic transition in cooling. Temperatures of martensitic transformations for RS-alloys have been established to be lower, than for same alloys prepared under traditional cooling rates, because of nano-scale grain size of B2-phase crystalizing from amorphous structure. The martensite in a nano- and micro grains may have different morphology and orientations. Nanophase (B2-TiNiCu) and nanocomposite (B2+B11(TiCu)) structures formed under crystallization by means of laser treatment, heating effect of electrical current and high temperature treatment were investigated. The ribbons with such structures in optimum state have good elastic and shape memory properties.
Room: 332
Session Chairpersons: Sungho Jin, Lucent Technologies, Bell Laboratories, Room 7G-326, 700 Mountain Avenue, NJ 07974; Iver E. Anderson, Ames Laboratory, Iowa State University, 122 Metals Development Bldg., Ames, IA 50011
2:00 pm INVITED
THE INFLUENCE OF MICROSTRUCTURE ON THE FAILURE OF EUTECTIC SOLDERS: John W. Morris, Jr., H. Reynolds, Department of Materials Science and Mineral Engineering, University of California, Berkeley, and Center for Advanced Materials, Lawrence Berkeley Laboratory, CA 94720
There are three key mechanisms of failure during the life of microelectronic solder joints: overload failure during handling, thermal fatigue failure during service, and, particularly in the case of joints for optoelectronic devices, dimensional changes during service. Each of these failure modes is strongly influenced by microstructure of the solder, which is, in turn, affected by the composition of the solder, the chemical nature of the substrate, and the manufacturing process that is used to create the joint. The present talk will discuss the varieties of microstructure that are found in common solder joints, their influence on lifetime and failure mode, and the metallurgical techniques that can be used to control microstructure and modify the nature and kinetics of joint failure.
2:25 pm INVITED
DIFFUSION PROCESSES IN LEAD BASED SOLDERS USED IN MICROELECTRONIC APPLICATIONS--AN OVERVIEW: Devendra Gupta1, J. M. Oberschmidt2, K. Vieregge3, 1IBM T. J. Watson Research Center, P.O. Box 218, Yorktown Heights, NY 10598; 2IBM Semiconductor Research and Development Center, Rt. 52-AP1, Hopewell Junction, NY 12533; 3Hoogovens Aluminium GmbH, 5400 Koblenz, Germany
Lead based solders are main stay of the microelectronic industry. Besides their use in printed boards, they are employed in interconnections of Si chip-to-substrates such as the multi-chip-modules, the thermal-conduction-module, the tape-automated bonding etc. During their service, the solder interconnections, commonly known as C-4 joints, are subjected to temperatures of the order of 100°C which translate to homologous temperatures of T/Tm 0.5 where Tm is the melting temperature in Kelvin. At these temperatures, a host of diffusion and related phenomena become operative notably the diffusion in the lattice and grain boundaries, creep and fatigue which eventually determine reliability of the device packaging. We have carried out extensive diffusion studies on the Pb-In and Pb-Sn solders over a range of composition using radioactive tracer techniques. We will discuss therein the various diffusion process, their modifications through ternary solute additions such Au and Cu and the role of unstable microstructure particularly in the eutectic solders.
2:50 pm INVITED
DEFORMATION, FATIGUE CRACKING AND COARSENING IN A LEAD-TIN EUTECTIC: T. Plookphol1, Donald S. Stone1 and S.-M. Lee2, 1Materials Science and Engineering Dept., University of Wisconsin, Madison, WI; 2Samsung Electronics Co., Suwon, Korea
Over the last several years, we have experimented with lead-tin eutectic carefully controlled microstructure in order to learn about creep, microstructural evolution, and fatigue cracking in this alloy. The purpose of those experiments has been to formulate a mechanistic basis for modeling the creep-fatigue interaction. In this paper we review the work. Creep tests, tensile tests, and load relaxation tests combined with microstructural characterization and theoretical modeling have helped to provide insight into the roles of dislocations and colony boundary sliding during creep. Colony boundary sliding impacts upon cracking and coarsening during fatigue. Work hardening and dynamic recovery during creep affect subsequent coarsening. Fatigue experiments examining the effects of frequency and strain range on fatigue crack growth have revealed transitions in mode of crack growth accompanying the onset of colony boundary sliding at low strain rates. Experimental studies of the effect of prior deformation on subsequent coarsening reveal that the factor by which coarsening accelerates depends on the rate of deformation. *Supported by the Wisconsin Alumni Research Foundation.
3:15 pm BREAK
3:25 pm
A NEW METHODOLOGY TO MEASURE DAMAGING STRAINS IN LEAD/TIN SOLDERS: Abbas I. Attarwala1 and Juan M. Sanchez2, 1Hewlett-Packard Company, IC Business Development Division, Palo Alto, CA 94304; 2Center for Materials Science, The University of Texas at Austin, TX 78712
A new methodology was developed to isolate and measure the damaging strains in lead/tin solders. The new methodology is based on load controlling cycling as opposed to strain controlled cycling. Under load controlled cycling conditions it is easy to separate out the effects of the different strain components. It was determined that the damaging strains were primarily creep strains, even at a cyclic rate of 0.5 Hz at a temperature of -40°C. Fractographic analysis of the fractured specimens confirmed that failure even at -40°C occurs by creep processes. The envelope strain curve generated from load controlled cycling data is a direct measure of the damaging strains stored in the material. A new parameter, 
D was identified. D is the damaging strain stored per cycle. The damaging strains per cycle measured for various solder compositions tested at varying frequencies, temperatures and microstructures could all be correlated by simple linear relationships. It was observed that the damaging strain stored during the secondary creep region of the envelope strain curve ranges from 2% strain to 18% strain depending on the test conditions.
3:45 pm
CREEP CRACK PROPAGATION OF 63Sn/37Pb WITH EMPHASIS ON COLONY BOUNDARY DEFORMATION AND RUPTURE: Scott A. Schroeder1 and M. R. Mitchell1 and A. G. Evans2, 1Rockwell Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360; 2Division of Applied Sciences, Harvard University, Pierce Hall, 29 Oxford Street, MA 02138
Experiments on deformation and rupture of eutectic Sn/Pb solder will be discussed. These involve in-situ field emission SEM observations made during tensile and thin-walled torsional shear testing at room and elevated temperatures. Deformation concentrates on colony boundaries, leading to cavitation, cracking, and tertiary creep. Cavity formation also induces a large anelastic (time-dependent recoverable strain) effect. Progressive colony boundary damage has been mapped from sequential in-situ images. Subsequent strain field mapping and animations, highlight and quantify the relative deformations. High magnification image sequences characterize cavity growth and coalescence mechanisms. Upon combining with calculations of stress distribution, creep induced cavitation and crack propagation have been quantified.
4:05 pm
MECHANICAL PROPERTIES OF Pb/Sn SOLDERS AT THE TEMPERATURE RANGE OF -200°C TO 150°C: W. Kinzy Jones, Yanqing Liu, Marc A. Zamino, Gerardo L. Gonzales, Department of Mechanical Engineering, Florida International University, Miami, FL 33199
The mechanical properties (E, 
0.2, UTS and 
%) of five Pb-Sn solder alloys (63Sn/37Pb, 62Sn/36Pb/2Ag, 96Sn/4Ag, 95Pb/5Sn, 90Pb/10Sn) commonly used in electronic packaging have been determined over the temperature range of -200°C to 150°C using uniaxial tensile test, dynamic mechanical analysis, and acoustic pulse method. The following results have been found: (1) the elastic moduli decreases linearly with increasing temperature until 70°C, then rapidly drop for the temperature 100°C and above; the strength (0.2, UTS) decreases with increasing temperature with the exception that for the solid solution solder (95Pb/5Sn, 90Sn/10Sn) which remain approximately constant; (3) the ductility change is complex: for lead matrix solid solution solders; the total elongation (r) increasing slowly with increasing temperature, the uniform elongation (u) is relatively high (>20%), and decreases slowly with increasing temperature, and the neck elongation (n) increases sharply with increasing temperature; whereas, for the eutectic solders (63Sn/37Pb, 62Pb/36Ag/2Ag, 96Sn/4Ag), the super-plasticity occurs at high temperature (>100°C), while at low temperature (-150°C) the brittle fracture occurs, the higher uniform elongation occurs at about -100°C.
4:25 pm
A MODEL OF REACTIVE WETTING FOR THIN DROPS: James A. Warren1, W. J. Boettinger1, A. R. Roosen2, 1Metallurgy Division, 2Ceramic Division, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899
When a liquid alloy spreads on a substrate, interdiffusion may result in melting of the substrate of the substrate and/or formation of intermetallic phases. We investigate the former case and describe the evolution of the non-planar interface on the lower surface of the drop. An approximate diffusion analysis is performed for a drop whose height is much smaller than its width. The coupling between the melting process and the rate of advance of the triple junction is explored for a variety of contact angle conditions. Numerical solution of the governing equation are performed and compared to experimental results for Bi-Sn alloys spreading of a droplet on a grain boundary.
4:45 pm
EFFECT OF COMPOSITE STRENGTHENING STRATEGIES ON THE MICROSTRUCTURAL EVOLUTION IN A TIN-SILVER SOLDER: A.W. Gibson, S.L. Choi, J.L. McDougall, T.R. Bieler, K.N. Subramanian, Department of Materials Science and Mechanics, Michigan State University, East Lansing, MI 48824
Pending Federal regulations provide the impetus for using Pb-free solders. Automotive electronics and solders are exposed to thermal cycles in the range of -40°C to 150°C under cyclic and quasi-static conditions, and they experience low and high frequency mechanical fatigue vibrations. Since coarsening of microstructural features is known to affect fatigue resistance, the effects of aging behavior is investigated using eutectic Sn-Ag solder as a model system, with and without intentionally added intermetallic strengthening phases. Small single shear lap specimens with a size similar to joints in microelectronic applications are used to obtain microstructures that are obtained in real solder joints. Eutectic Sn-Ag solder joint microstructures coarsen when aged between 40 and 150°C for as little as a week. The microstructural evolution and its effect on mechanical properties is monitored with ageing temperature and time, and the kinetics of ageing is determined. The effects of adding composite intermetallic phases on the solder interface and ageing behavior are compared to the model Sn-Ag system.
5:05 pm
FORCED DIFFUSION THERMOGRAPHY FOR NONDESTRUCTIVE EVALUATION OF MICROSTRUCTURES: David A. Jahnke, Bela I. Sandor, Nuclear Engineering and Engineering Physics Dept., University of Wisconsin, 153 Engineering Research Building, Madison, WI 53704
Forced Diffusion Thermography (FDT), differential temperature detection across a material flaw while providing a controlled AC heat flux input, has been developed recently for structural integrity assessment in large structures. This paper presents FDT to identify microscopic flaws by both finite element analysis and experimentation. The technical difficulties are the production of a microscopic width heat flux line pattern and the spatial and temperature resolution of the infrared camera. A finite element model one millimeter square and one-third millimeter deep of tin solder material with various surface crack sizes specimens with known microscopic flaws were performed using an infrared camera with a temperature resolution of one mK. A seven mW helium-neon laser provided an AC heat input area of 250 micron wide by five millimeters long to the specimen's surface. The results show that this method can be applied to detect flaws in small specimens of solder and similar materials.
5:25 pm
TiN-BASED, ACTIVE METAL CONTAINING SOLDERS FOR JOINING OF ALUMINA: Tim Schwilm, O.T. Inal and Frederick G. Yost, Materials and Metallurgical Engineering Department, New Mexico Tech, Soccoro, NM 87801; Sandia National Laboratories, Albuquerque, NM 87815
Room: 340C
Session Chairs: E.H. Chason, Sandia National Laboratories, Albuquerque, NM 87185-1415; R.C. Cammarata, Surface and Interface Science Branch, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375
SURFACE AND INTERFACE STRESS EFFECTS ON THIN FILM GROWTH: R.C. Cammarata, Surface and Interface Science Branch, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375
Associated with any solid surface is a surface stress. It is an intrinsic thermodynamic quantity that represents the reversible work per unit area needed to elastically stretch the surface. In materials where there is a large surface area to volume ratio, such as thin films, surface stresses can have a major influence on the growth and structure. In the case of a solid-solid interface, there are two interface stresses that represent the work needed to stretch the two phases on either side of the interface. Simple models for surface and interface stresses will be presented. These will then be used to analyze thin film epitaxial growth as well as intrinsic stress generation in nonepitaxial films. It will be shown that surface and interface stresses play a central role in determining the critical thickness for epitaxy, and can lead to significant intrinsic stresses in nonepitaxial films, especially during the early stages of growth.
2:40 pm INVITED
STRESS MONITORING DURING THIN FILM GROWTH: Jerrold A. Floro, Eric Chason, Sandia National Labs, P.O. Box 5800, Albuquerque, NM 87185-1415
Thin films are typically deposited under severe kinetic constraints, resulting in highly non-equilibrium microstructures. These films often exhibit stress levels far in excess of the bulk yield strength. The origin and evolution of the film stress during deposition is, in most cases, poorly understood. We have developed a technique for real-time measurement of film stress during deposition--the Multi-beam Optical Stress Sensor (MOSS). MOSS is a technique for determination of stress through measurement of the substrate curvature. It has the virtues of low sensitivity to ambient vibration, simplicity of setup, and ease of use. We will describe the technique, and demonstrate its use for the particular case of SiGe heteroepitaxial growth on Si. We first discuss the elastic/plastic behavior of SiGe, and then focus on the surface segregation of Ge during SiGe growth. The latter topic, while somewhat specialized, is well-suited to demonstrate the interpretation of MOSS data, and to highlight both the strengths and limitations of the technique.
3:20 pm
ELASTIC MODULUS MEASUREMENT OF THIN FILM USING A DYNAMIC METHOD: Y. Kim, Department of Metallurgical Engineering, Chonnam National University, Kwangju, 500-757, Korea
The effect of external medium (air in this study) and specimen damping was estimated for the elastic modulus measurement using the sonic resonance method. A two-layer composite model was developed and applied for measuring the elastic modulus of thin film that is generally difficult to measure. The Ti coated Si wafer composites were produced using magnetron sputtering and used to test the developed model.
3:40 pm BREAK
4:00 pm INVITED
EPITAXY AND STRESS IN METAL THIN FILM COMPOUNDS AND MULTILAYERS: B.M. Clemens, T.C. Hufnagel, V. Ramaswamy, M.C. Kautzky, C.T. Wang, Department of Materials Science and Engineering, Stanford University, Stanford, CA 93405-2205
Epitaxial growth can be used to control and help understand thin film properties. We use sputter deposition to grow a variety of epitaxial thin film structures, including compounds and multilayers. The large stresses observed in these materials can have a large effect on properties. Using in-situ stress measurements and x-ray diffraction we study the stress evolution during growth and relate this behavior to thin film structure and properties. For Fe on Cu (001), we find that Fe is fcc up to a thickness of 10-12 monolayers, whereupon bcc Fe is observed in first the Pitsch and then the Bain orientations. The fcc Fe shows some relaxation of the misfit from the Cu, as do the Pitsch orientation bcc, which is in tension, and the Bain orientation bcc, which is in compression. In the giant magnetostrictive compound TbFe2, we have used epitaxy and differential thermal contraction to control the stress and hence the orientation of magnetization. This understanding and and control can lead to improved device performance.
4:40 pm
THE MECHANICAL BEHAVIOR OF PZT THIN FILMS DEPOSITED BY A SOL-GEL TECHNIQUE: D.F. Bahr, J.S. Wright, L.F. Francis, N.R. Moody*, W.W. Gerberich; Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, *Sandia National Laboratories, Livermore, CA 94550
Lead-zirconate-titanate (PZT) thin films are used in microelectromechanical systems (MEMS) as piezoelectric components. Both the mechanical and electrical properties of the PZT layer must be known in order to understand the piezoelectic response of the PZT for use as either a sensor or actuator. These properties are controlled by the composition and structure of the PZT film and its interface. Variations in PZT film structure and morphology are caused by changing solution processing conditions. PZT films have been deposited to thicknesses between 400 and 600 nm onto a multilayered electrode structure of platinum, titanium, titanium dioxide and silicon oxide. Nanoindentation has been used to characterize the effects of grain size and structure on the mechanical properties of the PZT films. The effects of the substrate and the multilayered electrode are accounted for to determine the modulus and hardness of the PZT films.
5:00 pm
ADHESION OF CVD TiN ON 316L SURGICAL STAINLESS STEEL OBTAINED IN A MASS TRANSFER REGIME: M.H. Staia, School of Metallurgy and Materials Science, Universidad Central de Venezuela, Apartado 49141, Caracas 1042-A, Venezuela; C. Julia Schmutz, Swiss Centre for Electronics and Microtechnology Incorporated, P.O. Box 41, Neuchatel, Switzerland
An investigation has been undertaken to study the adhesion of TiN coatings deposited by using CVD process at 900°C on surgical stainless steel. The microscratch test method (CSEM) was employed to evaluate the coating adhesion. Three scratches were performed at progressive load under the test conditions. Observation of the surface damages by means of an optical microscope permitted to determine the critical load. No acoustic emission detections or frictional force fluctuations could be correlated with the optical observations. In this investigation, the critical load corresponds to the regular occurrence of delamination. Scanning electron microscopy provided the essential and detailed information about the mode of failure of the coatings along the scratch channel. It was found that the coatings presented high plastic deformation and cohesive fracture at values lower than the critical load, Lc.
Room: 330E
Session Chairpersons: Hamish L. Fraser, Dept. of Materials Science and Engineering, Ohio State University, Columbus, OH 43210; Hubert I. Aaronson, Dept. of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
2:00 pm INVITED
PHASE TRANSFORMATION BEHAVIOR OF GAMMA TITANIUM ALUMINIDE ALLOYS DURING SUPERTRANSUS HEAT TREATMENT: S.L. Semiatin*, V. Seetharamann, D.M. Dimiduk*, Y-W. Kim, K.H.G. Ashbee* *Wright Laboratory Materials Directorate, WL/MLLM, Wright-Patterson AFB OH 45433; UES, Inc., 4401 Dayton-Xenia Rd., Dayton OH 45432
Recent work has suggested that near-fully lamellar or fully-lamellar microstructures may provide attractive combinations of room and elevated temperature properties in near-gamma titanium aluminide alloys. The development of such microstructures via thermal processing high in the two-phase (alpha+gamma) field or in the single-phase (alpha) field is described. In particular, the interaction of the dissolution of gamma grains and the growth of alpha grains during isothermal and transient heat treatment processes will be summarized. Models for the kinetics of gamma grain dissolution and alpha grain growth will be presented. The broad application of such models for the design of heat treatments to obtain fully lamellar microstructures will be illustrated for several forged gamma components.
2:30 pm
THE ROLE OF THE 
2 PHASE IN ULTRAFINE LAMELLAR MICROSTRUCTURES DEVELOPED IN TWO-PHASE 
-TiAl ALLOYS: P.J. Maziasz, C.T. Liu, Metals & Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831- 6115
-TiAl alloys (i.e., Ti-47Al-2Cr-2Nb(at.%)) have ultrafine fully-lamellar structures after processing or heat-treatment above the 
-transus temperature; such structures produce outstanding high-temperature strength. The lamellar colonies consist of fine laths of 2 and phases, with 100-200 nm average lamellar spacings and 200-500 nm 2-2 spacings. Generally these structures are dominated by /2 interfaces rather than / interfaces, and they are relatively free of various structural defects often found in fully-lamellar structures. Aging studies of different alloys at 800-1000°C indicates that dissolution of the fine 2 lamellae is one of the critical first steps that triggers instability and continuous coarsening of the overall lamellar structure during aging or creep. This paper focuses on detailed TEM/AEM characterization of the 2 component of the microstructure and how that information feeds into designing better TiAl alloys. Research supported by the U. S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Industrial Technologies, Advanced Industrial Materials (AIM) Program, and Assistant Secretary for Defense Programs, Technology Management Group, Technology Transfer Initiative, under contract DE-AC05-96OR22464 with Lockheed-Martin Energy Research Corp.
2:50 pm
MICROSTRUCTURE EVOLUTION THROUGH THE 
PHASE TRANSFORMATION IN A TI-48 AT.% AL ALLOY: T. Kumagai, E. Abe, M. Nakamura, National Research Institute for Metals, Tsukuba-shi, Ibaraki 305, Japan
The (disordered h.c.p.) 
(TiAl; ordered L10 structure) massive transformation is partially suppressed even in a Ti-48 at.%Al alloy, when the alloy is quenched rapidly from the high temperature a phase filed. The untransformed (meaning 'not massively transformed') regions show an extremely fine 2 (Ti3Al; ordered DO19 structure) / lamellar structure rather than an 2 single phase structure, which is commonly observed in the quenched alloys with Al concentration of less than 47 at.%Al. By the subsequent aging treatment this fine 2/ lamellar structure changes easily to the fine grain structure, which is quite similar to the massively transformed grain structure. The microstructural development of the extremely fine 2/ lamellae during the isothermal aging treatments is presented and the phase transformation through the 2/ lamellar structure will be discussed.
3:10 pm
THE GAMMA TO ALPHA TRANSFORMATION IN A TI-48AL ALLOY: K. Muraleedharan, T.M. Pollock, Dept. of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213; P. Wang, V.K. Vasudevan, Dept. of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH 45221
The transformation from to in a Ti-48Al alloy during aging in the + phase field between 1275-1350°C is reported using microhardness, optical, scanning and transmission electron microscopy. The results indicate that on heating a primary structure to temperatures in the two-phase + phase field, packets of a nucleate within the grains in four orientations parallel to the four {111}g planes. The a platelets generally nucleate at grain boundaries and stacking faults on {111} planes bounded by 1/6<112] Shockley partial dislocations appear to serve as nuclei for them. The a precipitation kinetics, volume fraction and packet thickness depend strongly on the aging temperature, generally increasing with increase in temperature. These changes are also accompanied by significant hardening with time at temperature, from the initial value to a maximum, followed by a decrease at longer times. The morphology of the resulting microstructures, nucleation mechanisms, orientation relationship between the phases, sub-structure development and kinetics of precipitation during the transition will be discussed.
3:30 pm BREAK
3:50 pm
THE ORDERING TIE LINES AND TIE TRIANGLES IN TITANIUM ALUMINIDES: D.-H. Hou, H.L. Fraser, Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210
The site occupancies of alloying elements in TiAl and the ordering states in orthorhombic titanium aluminides are investigated using the newly developed Ordering Tie Line (OTL) analysis. The OTL, which can represent the atom configuration in an ordered alloy in a graphical and intuitive way, is a parameter that is unique to ordered alloys. There are two properties of an OTL, one being its slope, indicating the trend for sublattice occupancy, and the other the compositional endpoints, corresponding to the compositions of the individual sublattices. The slope can be determined conveniently by Atom Location by Channeling Enhanced Microanalysis (Alchemi) experiments, whereas the compositional endpoints may be determined either from additional information concerning the ordering scheme or determined by other experiments/simulations. In the present study, compositional endpoints are determined by simulation using the dynamical theory of electron diffraction. The OTL analysis which was originally developed for ternary compounds has been further extended to quaternary systems such as TiAl with two alloying elements and ternary system with three sublattice sites such as the orthorhombic alloys based on Ti2AlNb. For the TiAl alloys, the effect of alloying elements of Nb, Cr, Mo and Mn on the OTL are determined and discussed. For the orthorhombic alloy, it will be shown how the ordering state can be described by the Ordering Tie Triangle (OTT), and how to measure the OTT by the Alchemi experiments. Since the OTL can provide a direct measure of the ordering state, it will be an important parameter for alloy design. This work has been supported by the US ONR, Dr. George Yoder as Program Manager.
4:10 pm
DECOMPOSITION OF -TiAl/2-Ti3Al LAMELLAR STRUCTURE: J. Zhang, Z.H. Zhang, D.X. Zou, Z. Y. Zhong, Central Iron and Steel Research Institute, Beijing 100081, China
It's found in the cast Ti-46.5Al-2.5V-1.0Cr (at%) ingot, that the discontinuous coarsening (DC) dominates the decomposition of the lamellar structure when annealing at temperatures lower than 1273K while the continuous coarsening (CC) does at the temperature between 1373K and 1473K. In the case of CC, the lamellae coarsened segmentally and then the FL microstructure decomposed to a finer equiaxed near gamma (NG) microstructure as annealing time went on. The TEM observation showed that the prior lamellae are quite neat and perfect and the annealed lamellae have inner terminations. Thus, the Rayleigh's perturbation and breakdown of lamellae was believed to have occurred along with the CC. Furthermore, a cycle heat treatment of 1173K-1423K has been designed to increase the density of the inner terminations of lamellae. After that, the FL microstructure has been decomposed to a more homogeneous and even finer equiaxed NG microstructure.
4:30 pm
MICROSTRUCTURE EVOLUTION DURING POSTWELD HEAT TREATMENT OF GAS TUNGSTEN-ARC AND ELECTRON BEAM WELDS IN CAST Ti-48Al-2Cr-2Nb ALLOY: W.A. Baeslack III, C.M. Jensen, H. Zheng, Department of Industrial, Welding and Systems Engineering, Ohio State University , Columbus, OH 43210; T.J. Kelly, GE Aircraft Engines, 1 Neumann Way, Evendale, OH 45215
The microstructures of multi-pass gas tungsten-arc (GTA) welds produced in cast Ti-48Al-2Cr-2Nb (at.%) have been evaluated in the as-welded condition and following postweld heat treatment over a range of temperatures from 1000 to 1300°C. Although postweld heat treatment did not significantly affect the cast, HIP'ed and heat-treated base metal microstructure, it did promote transformation of a predominantly lamellar 2+ microstructure in the as-welded fusion zone, to microstructures comprised principally of equiaxed grains. An increase in the heat treatment temperature resulted in an increased proportion of 2 located principally at grain boundaries and grain boundary triple points. These microstructural changes were associated with softening and toughening of the fusion zone, both of which increased with an increase in postweld heat treatment temperature. Featureless, hard bands (>400 DPH as-welded) observed to parallel the fusion boundaries, which exhibited an extremely fine lamellar microstructure, were also softened by postweld heat treatment, although they remained harder than the surrounding weld metal microstructure. This work was supported by a grant to the Carnegie Mellon University from the Air Force Office of Scientific Research.
4:50 pm
INTERACTION BETWEEN TIAL AND ALN AT HIGH TEMPERATURES: Y. Paransky, E.Y. Gutmanas, Department of Materials Engineering, Technion, Haifa 32000, Israel
In this work, interfacial reactions between TiAl intermetallic and aluminum nitride have been studied in the 800-1200°C temperature range. Titanium aluminides are developing as a new group of materials for high temperature applications. Their load bearing capacity can be considerably improved by introducing high strength ceramic fibers, such as SiC or boron. Due to the high reactivity of Ti-containing materials, chemical interaction between fibers and TiAl matrix takes place at the processing and/or service temperatures resulting in deterioration of mechanical properties. Fibers can be protected by a thin coating layer which dissolves slowly enough to prevent the matrix from attacking the fiber during the composite lifetime. AlN is a possible choice for such a coating in Ti-containing matrices. Interfacial reactions between AlN and TiAl matrix have been studied using the diffusion couple approach. Phases growing at the interface between TiAl and AlN have been identified by XRD, SEM/EDS, AES and TEM; the kinetics of reaction layer growth has also been investigated. It has been found that AlN is more stable in TiAl than in pure Ti. In the latter case, the dissolution of AlN is faster due to the higher activity of Ti and high diffusivity or nitrogen in Ti.
Room: 230C
Session Chairpersons: James C. Daley, Daley & Associates, 1020 W. Cactus Wren Drive, Phoenix, AZ 85021; John M. Rapkoch, Davy International, 2440 Camino Ramon, San Ramon, CA 94583
RECYCLING OF MAGNESIUM ALLOY SCRAP, A NECESSITY: Christine Brassard, Lisabeth Riopelle, Oddmund Wallevik, Hydro Magnesium Market Development Center, 21644 Melrose Avenue, Southfield, MT 48075-9705
The use of magnesium alloys is growing rapidly, particularly in die cast parts for the automotive industry. Supporting this growth in the future means that Mg has to be an economically and ecologically attractive material, and recycling of alloy scrap becomes a necessity. What kinds of magnesium scrap will be on the market? What are the opportunities and challenges for this emerging recycling industry? Different recycling processes have been developed, and operation facilities are today recycling large volumes of class 1 diecast returns based on a flux refining technology. Characterization of the recovered metal demonstrates that the performance of appropriately recycled magnesium alloy is comparable to an alloy made from primary electrolytic metal. The sludge generated from this process can also be recycled through the existing primary Mg operations in order to close the environmental loop.
1:55 pm
INMETCO CADMIUM RECOVERY FACILITY: George Cingle III, INMETCO, 245 Portersville Road, Ellwood City, PA 16117; Gerald LaRosa, Davy International, One Oliver Plaza, Pittsburgh, PA 15222
The INMETCO Cadmium Recovery Facility currently processes commercial and industrial nickel/cadmium batteries at their Ellwood City, PA plant. The facility receives recycled nickel/cadmium batteries to recover cadmium shot product and nickel/iron scrap. The technology employed for the dismantling of industrial cells and the distillation of cadmium is under license from SAFT-NIFE in Sweden. In addition, INMETCO has installed a thermal pretreatment pilot unit for processing commercial and consumer cells which has recently demonstrated encouraging results. The INMETCO facility began detailed design in February 1995. The first cadmium distillation furnace was brought on-line December 1995, and the complete facility was operational April 1996. The facility can process 2450 short tons per year of industrial cells and 630 short tons per year of consumer cells. The facility design incorporated provisions for future expansion to allow INMETCO the ability to keep up with the forecasted growth of recycling nickel/cadmium batteries through the year 2000.
2:20 pm
COPPER RECYCLING FROM INDUSTRIAL WASTE BY MATTE SMELTING: Kazuhiro Asai, Yasuhito Kawasaki and Junzo Hino, Nippon Mining & Metals Co. Ltd., Toranomon 2-10-1, Minato-ku, Tokyo 105, Japan
Hitachi Refinery of Nippon Mining & Metals Co., Ltd. installed a reverberatory type recycling furnace in 1978 in order to treat the industrial wastes which contain metal elements such as copper, gold and silver. Waste materials and pyrite such as galvanizing sludge, hydroxide slime and dust, are smelted together, and sulfidized copper, iron and precious metals are transformed into matte and other metallic elements are oxidized into slag. This copper matte is transported to Saganoseki smelter, and copper and precious metals are recovered. Recently it became difficult to get pyrite economically because of the decrease of pyrite production. Therefore, new treating process of the liquid waste has been investigated at Hitachi. In this process, the sulfide or sulfate from the liquid waste are smelted as the sulfur source instead of pyrite.
2:45 pm BREAK
3:00 pm
THE SUBMERGED ARC FURNACE AND ITS APPLICATION IN THE NON-FERROUS RECYCLING INDUSTRY: Gero Rath, Mannesmann Demag, Huttentechnik MDH
Residues from the non-ferrous industry contain highly valuable metallic substances which make their recovery by thermal treatment desirable from the economic and environmental point of view. The electric slag resistance furnace, a variant of the submerged arc furnace is one which is used more frequently for these recycling purposes. In the last decade Mannesmann Demag has built and commissioned most of these furnaces. The paper will give an overview of the operational applications and characteristics based on the experience gained so far in lead and copper recycling.
3:25 pm
AUTOMATIC SORTING OF ALUMINUM PACKAGINGS FROM DOMESTIC REFUSE: G.J. Nijhof ea., Hoogovens R&D, P.O. Box 10.000, 19709 CA IJmuiden, The Netherlands
This work is part of a major European research project on the re-use of packaging materials in their post consumer state. The first stage of the recovering of aluminum from a waste stream is to free the non-ferrous metals with an Eddy Current machine. Previous research has given excellent results on the separation of aluminum from pre-separated packaging material. At this moment there were two reasons for a new test series: In the Netherlands all cities are obliged to collect the organic waste separately from the other waste, thus leading to a rest fraction with a high potential on aluminum. The newest generation Eddy Currents work with a higher separation efficiency. This report will discuss the results of these test series. The recovered aluminum is used for remelting trials in another sub-project of this research programme.
3:50 pm
PILOT SCALE INVESTIGATION OF FLEXIBLE ALUMINUM PACKAGING BY THERMAL PRETREATMENT: H. Rossel, R. Pietruck, VAW aluminum AG, Research & Development, Georg-von-Bosselager-Strabe 25, 53117 Bonn, Germany; Y. Bertaud, Y. Caratini, Pechiney CRV, Vorreppe, France
Laminates with aluminum are typically combined with other materials like plastics, paper, etc. The aluminum content is considerably below 50%. Therefore the separation of the laminate partner by a thermal procedure before the melting process is a successful solution. The paper reports the practical experiences with a pilot equipment in the 100kg-scale. Additionally the numerical approach to simulate the thermal process is presented. This work is part of a major European research project (PACK-EE) on the re-use of packaging materials in their post consumer state. Preliminary information on this project can be found in Light Metals, 1996.
4:15 pm
REMELTING AND PURIFICATION OF ALUMINUM PACKAGING WASTE: G.H. Nijhof ea., Hoogovens R&D, P.O. Box 10.000, 1970 CA IJmuiden, The Netherlands
This work is part of a major European research project on the re-use of packaging materials in their post consumer state. Recovering aluminum from household refuse leads to a mix-up with other metals, e.g. copper and steel. The aluminum industry aims to make packaging materials from waste packagings. Therefore, a purification step is required during the remelting operation. This research is focused on the removal of excess iron from the melt. The technique used is the formation of intermetallic compounds of FeMn by adding Mn, followed by separating these intermetallics from the molten metal. Theoretical studies of the ternairy and quarternairy phase diagrams, using computer modeling, have predicted the possible limits of purification. After laboratory trials some large scale remelting experiments have been performed to study the applicability of this technique.
Room: 231C
Session Chairpersons: Richard D. Hagni, Chairman, Geol./Geophysics Dept., Univ. Missouri, Rolla, MO; Kenneth A. Brunk, Mineral Consultant, Former Vice President, Newmont Gold Co. Denver, CO
THE ROLE OF PROCESS TECHNOLOGY AS A KEY BUSINESS UNIT: Kenneth A. Brunk, Minerals Consultant, and Former Vice President, Newmont Gold Company, Aurora, CO 80016
This address discusses how "Mineral Processing Technology" can play a major role in the life and profitability of a mining company. Examples of past and present technological breakthroughs and their impacts will be examined. Also, the future of processing technology will be emphasized.
2:35 pm
OPERATION OF NEWMONT'S BIOOXIDATION DEMONSTRATION PLANT AND PRODUCTION OF GOLD FROM LOWER GRADE REFRACTORY ORES: R.M. Perry, F.-P. Sawyer, A.J. Schindler, M.I. Shutey, Newmont Gold Company, Carlin, NV 89822; H.B. White, Newmont Metallurgical Services, Salt Lake City, UT 841O8
Test work on biooxidation pretreatment of low grade refractory gold has been ongoing at Newmont Gold Company since 1988, including laboratory testing and pilot biooxidation heaps (400 to 25,000 st). Metallurgical results of an oxidation process utilizing Thiobacillus ferroxidans have culminated in the design, construction and operation of a 780,000 ton bioxidation demonstration facility. The facility has processed 780,000 tons of refractory ore, using a batched process with separate pads for bioxidation and ammonium thiosulfate gold extraction. Siliceous sulfide refractory (SSR) and carbonaceous (CSR) ores are treated separately during biooxidation pretreatment unit operation. Procedures and results of grinding, agglomeration and pad biooxidation cycle (180 days) are followed by lime neutralization, and dumped on oxide leach pads, or stacked on the ammonium thiosulfate leach pad. Gold is leached with either cyanide for SSR ores or ammonium thiosulfate for preg-robbing CSR ores.
3:00 pm
BIOLEACHING AND PROCESSING OF A REFRACTORY GOLD ORE: N.S. Lynn, Lyntek, Inc., 775 Mariposa Street, Denver, CO 80204
A new process has been developed to bioleach refractory gold ores to expose the precious metal values using Thiobacillus ferrooxidans bacteria. The ore is hosted in a limestone rock with secondary replacement of carbonaceous and pyritic minerals. Crushing, stacking, bioleaching, rinsing and neutralization have been completed in a 45-day total time cycle. The use of sulfuric acid operation, and concentrated Thiobacillus ferroxidans population allows the short bioleaching cycle. The ore is then processed using conventional carbon-in-leach cyanide recovery techniques.
3:25 pm BREAK
3:35 pm
OXYGEN DIFFUSION INTO WET ORE HEAPS IMPEDED BY WATER VAPOR UPFLOW: R.W. Bartlett, K.A. Prisbrey, Univ. of Idaho, College of Mines and Earth Resources, Moscow, ID 83844-3025
Natural bioxidation of shallow, refractory ore heaps, relying on gaseous oxygen diffusion from the heap surface is attractive because of its simplicity and potential low cost, especially without using a lined pad, which is possible if percolation of leachate through the heap is avoided. In this case, the excess oxidation enthalpy must be removed by water evaporation from within the wet ore heap, and the rising water vapor flux within it will impede the downward oxygen flux. An analysis of this process shows that for typical values of pyrite grades and limited temperature increases. In the ore heap, the oxidation rate and penetration into the heap is reduced to values between about 30 percent and 50 percent of those obtained when leachate percolation occurs and water evaporation is not significant mechanism of heat removal.
4:00 pm
ECONOMIC CRITERIA FOR CHOOSING BIOHEAP PRETREATMENT OF MIXED OXIDE/REFRACTORY GOLD ORE: Robert W. Bartlett, Univ. of Idaho, College of Mines & Earth Resources, Moscow, ID 83844-3O25
Bioheap pretreatment of sulfidic refractory gold ore prior to cyanide leaching is a promising new technology, especially for low-grade ores that cannot be oxidized by pressure leaching or roasting. Ores containing both refractory and amenable gold require economic decisions whether, or not, to pretreat before cyanide leaching. This choice is more complex than familiar ore/waste cut-off grade decisions. Pretreatment may increase recovery but delays receiving revenue. An equation has been developed that computes a "critical cyanide leachable gold grade" for determining whether pretreatment will be profitable. If the ore's actual cyanide leachable grade, without pretreatment, is above critical grade, pretreatment will not pay. The parameters in this equation are: waste/ore cut-off grade, pretreatment yield, total gold grade, pretreatment operating cost and project's financial discount rate. Calculations are provided for use in mine development planning when bioheap pretreatment is an available option.
Room: 315A
Session Chairpersons: V. Selvamanickam, Intermagnetics General Corporation, Latham, NY; M.J. Kramer, Ames Laboratory, Ames, IA
CRITICAL CURRENT IN SMALL ANGLE GRAIN BOUNDARIES: C. S. Pande, R.A. Masumura, Naval Research Laboratory, Washington, DC 20375-5343
It is now well known that even small angle grain boundaries (misorientation angle 
¾ 10) show drastic reduction in inter-grain critical current. Drawing upon on our previous work, we show that this reduction must be ascribed to the stress field in proximity of the dislocations forming the small angle boundary. The alternate view that the reduction is due to the presence of dislocation cores is investigated by calculating their size as a function of misorientation. We show that the concept though probably valid for large misorientation ( 
10) leads to serious disagreement with experiments for small values ( ¾ 10).
2:20 pm INVITED
DIRECT OBSERVATION OF CURRENT DISTRIBUTIONS IN THIN SUPERCONDUCTORS USING MAGNETO-OPTIC IMAGING: T.H. Johansen, M. Baziljevich, H. Bratsberg, Department of Physics, University of Oslo, Box 1048 Blindern, 0316 Oslo, Norway; Y. Shen, P. Vase, NKT Research Center, Sognvej 11, 2605 Brøndby, Denmark
A thin film of YBa2Cu3O7- prepared by laser ablation and shaped by etching as a long strip was studied by magneto-optic imaging. The penetration of a perpendicular magnetic field was investigated in detail, and a model-independent method of determining the space-resolved current distribution was developed. The inverse magnetic problem, i.e., that of using a field map to derive the underlying current distribution, is formulated and solved analytically for the strip geometry. The observed current profile across the strip gives direct evidence for the assumptions made in the Bean model. Also other geometries were investigated, demonstrating the new application of magneto-optics as a tool to determine current flow patterns.
2:40 pm INVITED
FABRICATION OF BIAXIALLY-TEXTURED THICK FILM Y-Ba-Cu-O SUPERCONDUCTOR: V. Selvamanickam, M.S. Walker, P. Haldar, R.S. Sokolowski, Intermagnetics General Corporation, Latham, NY 12110; A. Ivanova, A.E. Kaloyeros, State University of New York at Albany, Albany, NY 12222; D.E. Fenner, Fenner Engineering Associates, Simsbury, CT 06070
High current densities have been recently demonstrated at 77 K in thick film YBCO superconductor deposited on biaxially-textured metallic substrates. The effort at Intermagnetics has been directed towards the development of an industrially scaleable process based on biaxially-textured substrate technology. Biaxially-textured metallic substrates have been fabricated in long lengths with an average in-plane orientation better than 10° and an average out-of-plane orientation better than 7°. Buffer layers that are structurally and chemically compatible with YBCO have been deposited on the metallic substrates with a biaxial texture similar to that of the substrate. Metal-Organic Chemical Vapor Deposition (MOCVD) has been used for deposition of YBCO since this technique enables a high rate of deposition that is not limited by line-of-sight. Stoichiometric, dense, and biaxially-textured films of YBCO superconductor have been successfully deposited by MOCVD on the biaxially textured substrates. This research was partially supported by the Department of Energy.
3:00 pm INVITED
HIGH CRITICAL CURRENT DENSITY TAPES BY EPITAXIAL DEPOSITION OF SUPERCONDUCTING THICK FILMS ON BIAXIALLY TEXTURED METAL SUBSTRATES: A. Goyal, D.P. Norton, M. Paranthaman, E.D. Specht, J.D. Budaj, D.M. Kroeger, D.K. Christen, Q. He, B. Saffian, F.A. List, D.F. Lee, S. Shoup, P.M. Martin, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6116
A method to obtain long lengths of flexible, biaxially oriented substrates with smooth, chemically compatible surfaces for epitaxial growth of high temperature superconductors is reported. The technique uses well established, industrially scaleable, thermomechanical processes to impart a strong biaxial texture to a base metal like Ni. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield chemically compatible surfaces for HTS film deposition. Substrates prepared using this method are referred to as Rolling Assisted Biaxially Textured Substrates (RABITS). Epitaxial YBCO films grown using laser ablation on RABITS have critical current densities exceeding 7 x 105 A/cm2 at 77 K in zero-field and have field dependences similar to epitaxial films on single crystal ceramic substrates. The texture of the base metal has been achieved in lengths over 1 m and scaleable techniques are being pursued to deposit epitaxial multilayers. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high Jc wire capable of carrying high currents in high magnetic fields and at elevated temperatures. Research sponsored by U.S. DOE under contract DE-AC05 960R22464.
3:20 pm INVITED
TRANSPORT BEHAVIOR OF GRAIN BOUNDARIES IN YBa2Cu3O7
: A COMPARISON BETWEEN THIN FILM AND BULK Bi-CRYSTALS: D.J. Miller, V.R. Todt, M. St. Louis-Weber,* D.G. Steel, X.F. Zhang, K.E. Gray, U. Balachandran*, Materials Science Division and *Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439
The structure and transport properties of grain boundaries in thin film and bulk bi-crystals of YBa2Cu3O7
have been studied in detail. The thin film bi-crystals were prepared by sputter deposition onto SrTiO3 bi-crystal substrates while the bulk bi-crystals were prepared by a dual-seeded melt textured growth process. The structures of these two types of grain boundaries can be very different: thin film boundaries typically exhibit meandering and impurity phases that extend through the thickness of the film while the bulk boundaries tend to be very straight and relatively free of impurity phases. A comparison of the transport behavior between these two types of boundaries will be presented and the implications of the similarities and differences will be discussed. This work was partially supported by the U.S. Department of Energy, Basic Energy Sciences-Materials Sciences, under Contract No. W-31-109-ENG-38 and by the National Science Foundation through the Science and Technology Center for Superconductivity under Contract No. DMR 91-20000.
3:40 pm BREAK
3:50 pm INVITED
PROCESS OPTIMIZATION FOR YBCO THICK FILMS: J.S. Abell, T.C. Shields, J. Langhorn, S.C. Watcham, School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UK
Superconducting thick films are finding technological exploitation in various applications; for example as inductive components in power engineering designs such as fault current limiters, and as microwave devices like filters in cellular communications applications. For efficient performance in these different fields superconducting properties require optimisation with respect to different parameters such as critical current density (Jc) and surface resistance (Rs). The microstructural control to deliver these properties demands careful processing. Flux pinning additions, composition control, doping, and novel processings techniques have been employed to improve the characteristics of the films. Barrier layer technology to enable the exploitation of low dielectric loss and economically attractive alumina substrates has been studied. The relationship between processing, microstructure and superconducting behavior will be discussed.
4:10 pm
MULTI-WAFER MANUFACTURING OF LARGE-AREA YBCO THIN FILMS FOR R.F. DEVICE APPLICATIONS: C.N. Soble, V.C. Matijasevic, Z. Lu, T. Kaplan, K. von Dessonneck, Conductus, Inc., Sunnyvale, CA 95123
Scaling up PVD and CVD techniques to reasonable manufacturing levels has been a scientific and engineering challenge for companies developing HTS materials for commercial applications. In this paper, we discuss the process development and optimization work associated with ramping up a multi-wafer reactive co-evaporation deposition system capable of depositing high quality YBCO on 2" to 8" wafers (R-pl sapphire or LaAlO3). YBCO thin films deposited using this technique exhibit good electrical properties with transition temperatures 85-87 K and Jc >2 x 106 A/cm2 at 77K. Microwave surface resistance, R, is <1 m
at 10 GHz and 77 K. HTS films on R-pl and LaAlO3 have been fabricated into r.f. devices for applications in NMR spectroscopy, Magnetic Resonance Imaging, and wireless communications.
4:30 pm INVITED
PHASE DIAGRAM AND CATION DISORDER STUDIES IN RE1+xBa2xCu3O7+
, RE= Pr, Nd, Sm, Eu, and Gd: M. J. Kramer, H. Wu, K.W. Dennis, R.W. McCallum, Ames Laboratory, Iowa State University, Ames, IA 50011
For the light rare earth elements, the orthorhombic REBa2Cu3O7- structure forms not as a line compound but with varying degrees of RE+3 substitution on the Ba+2 sites and additional oxygen incorporated in the basal plane to balance charge. It has been demonstrated that for RE = Nd, Pr, (Nd + Pr), and (Nd + Gd), the occupation of RE on Ba sites is a function of the oxygen partial pressure (pO2) and temperature. Not only is the minimum value of x effected but for a fixed value of x, large changes in the superconducting transition are observed. By manipulating the pO2 and T profile, phase assemblage can be modified. Under proper processing conditions, these second phases can form pinning sites in these materials, resulting in enhanced high field critical currents. Supported by U.S. Department of Energy, under Contract No. W-7405-Eng-82.
4:50 pm INVITED
THE EFFECT OF PROCESSING PARAMETERS ON Hg-1223 TAPE FABRICATION: R. Meng, Y.Wang, B. Hickey, K. Ross, Y. Xue, C.W. Chu, Texas Center for Superconductivity, University of Houston, Houston, TX 77204-5932
We have developed a process to fabricate Hg-1223 tape on a metal substrate with a transition temperature of 130 K and a self-field critical current density of 2 x 104 A/cm2 at 77 K. However, the reproducibility of the tape is poor and weak links exist in the tape so prepared. We have therefore investigated the chemical stabilities, processing parameters, and Ni doping effect on the Hg-1223 phase formation and grain growth. We found that doping can suppress the volatility of Hg in Hg-1223 and speed up the growth of Hg-1223. While Ni was found to be better than the other metal substrates tested it failed to retain its integrity for prolonged exposure to the processing conditions. Only a slight amount of Ni can be incorporated into the Hg-1223 grain, and it usually enters the Cu sites leadiing to a slight suppression of Tc. Proper processing conditions to eliminate the diffusion of Ni to Hg-1223, while favoring the growth and alignment of the Hg-1223 tape, will be discussed.
5:10 pm
PREPARATION OF HIGH-TEMPERATURE SUPERCONDUCTING SILVER-SHEATHED HgBa2CuO4+ TAPES: G.B. Peacock,1 M. Khaliq,2 G. Yang,2 T.C. Shields,2 I. Gameson,1 J.S. Abell,2 and P.P. Edwards,11School of Chemistry, 2School of Metallurgy and Materials, The University of Birmingham, Edgbaston, Birmingham, B152TT,UK
We have produced silver-sheathed HgBa2CuO4+ superconducting wires and tapes exhibiting a transition temperature of 96 K. Progress in the synthesis of these tapes was achieved by packing the stoichiometric mixtures of oxides into the silver tubes, air-quenching the samples and the novel use of thermal cycling. Superconducting properties were assessed by SQUID and a.c. susceptibility measurements. Various routes have been adopted to optimize superconductivity in HgBa2Ca2Cu3O8+ tapes: these include packing superconducting Hg-1223 powders in tubes, mixing pre-formed materials with mixtures of oxides in different ratios, using precursors, etc. Phase purity, texture and morphology of samples has been investigated using XRD and SEM.
Room: 231B
Session Chairperson: P.J. Bania, Timet, P.O. Box 2128, Henderson, NV 89015
PHASE EQUILBRIA IN Ti-Al-Nb ALLOYS: K. Muraleedharan, Dept. of Materials Science & Eng., Carnegie Mellon University, Pittsburgh, PA 15213; D. Banerjee, Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500058, India
The phase equilibria in the technologically important Ti-Al-Nb ternary system are presented. Special emphasis is made in the composition regime where the Orthorhombic (O, Ti2AlNb, Cmcm) phase has considerable presence in the microstructures. Isothermal sections at temperatures at and above 700°C are presented along with three vertical section at 22.5, 25 and 27.5 atomic % Al levels. The difficulties experienced in determining the phase diagrams, arising out of low diffusivities and the nature of the alpha2+B2O peritectoid transformation, are highlighted. The presence of a large solubility range for the single phase O phase field close to an Al content 27.5% is discussed in the light of the experimental results. Finally a clear definition of the areas wherein there exists a lack in our current understanding of the Ti-Al-Nb system are highlighted.
2:30 pm
PROCESS/MICROSTRUCTURE/PROPERTY RELATIONSHIPS IN AN ORTHORHOMBIC TITANIUM ALUMINIDE ALLOY: A.P. Woodfield, GE Aircraft Engines, 1 Neumann Way, Cincinnati OH 45215; S.K. Srivatsa, V.K. Vasudevan, University of Cincinnati, Cincinnati, OH 45215
An orthorhombic titanium aluminide alloy ingot with a nominal composition of Ti-22Al-26Nb (atom percent) has been produced and converted to 6" diameter billet. A continuous cooling transformation diagram was generated using compression samples, and TEM performed to understand phase evolution during cooling. A series of melts were cut from the 6" billet and either forged into pancakes or rolled into rings using a variety of process routes. The effects of process variables and final heat treatment on the microstructure and mechanical properties of the pancakes and rings have been evaluated. Mechanical properties included tensile (room temperature to 1300°F), creep (1000° - 1200°F), fracture toughness (room temperature) and fatigue (room temperature to 1200°F).
2:50 pm
THE ORDERING BEHAVIOR OF THE ORTHORHOMBIC PHASE IN Ti-Al-Nb ALLOYS: K. Muraleedharan, D. Banerjee, Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderbad 500058, India
The ordering behavior of the orthorhombic (O, Ti2AlNb, Cmcm) phase are presented. The presence of the O phase in two distinct forms with different site occupations is discussed. They are (1) the O1 phase Nb atoms occupying the Ti sublattice randomly and (2) the O2 phase with a specific sublattice for the Nb atoms. Both O1 and O2 exhibit the same space group and lattice periodicity and this makes their identification from one another a difficult task. We present in this paper, the various diffraction effects which arise due to the different ordering behavior of the O phase, for both X-ray and electron diffraction. Specific reflections are singled out. A definition of the order parameter and its experimental determination are presented. Possible transitions between the two forms are presented in the spirit of the Landau-Lifshitz theory for order-disorder transformations.
2:10 pm
EFFECT OF EXPOSURE ON FATIGUE OF COATED AND UNCOATED ORTHORHOMBIC Ti- ALUMINIDES: J.R. Dobbs, M.F.X. Gigliotti, GE CR&D, P.O. Box 8, K-1, MB105, Schenectady, NY 12301; M.J. Kaufman, Dept. Materials Science and Engineering, Univ. of Florida, 201 Rhines Hall, Gainesville FL 32611
Both uncoated and coated fatigue samples of the alloy Ti-22Al-26Nb were subjected to elevated temperature exposures in air. Oxygen ingress and interdiffusion (and reaction) of elements between coating and substrate cause changes in both microstructure and properties (i.e., embrittlement). After exposure, the microstructures of the substrate, the reaction zone and the oxidation products were examined, and fatigue tests were conducted. The suitability of selected coatings for protection of orthorhombic alloys against property degradation from exposure at elevated temperatures will be discussed.
3:30 pm BREAK
3:50 pm INVITED
ORTHORHOMBIC TITANIUM ALUMINIDE ALLOY DEVELOPMENT: C.G. Rhodes, Rockwell Science Center, Thousand Oaks, CA; J.C. Chesnutt, General Electric Aircraft Engines, Evendale, OH; J.A. Hall, Allied Signal Inc., Phoenix, AZ; J.R. Porter, Rockwell Science Center, D.A. Miracle, M.L. Gambone, Materials Directorate, USAF, Wright-Patterson AFB, OH
The development of a Ti-based metal matrix composite (MMC) material, capable of sustained and repeated exposure to service temperatures in the range of 650-760°C (1200-1400°F), has been undertaken in a U.S. Air Force sponsored program. Several performance characteristics qualify as "critical" for specific turbine engine component applications and service environments. To define these component-critical MMC characteristics, we selected a turbine engine compressor rotor, in which transverse tensile and creep strengths were found to be critical issues. Improvements in MMC transverse tensile and creep strengths can be made by increasing the matrix properties through alloy chemistry modifications, as well as through microstructural manipulation. This program, and others, have examined, in a systematic way, the effects of elemental additions, such as Mo, Ta, Si, V, and O, on mechanical properties, environmental resistance, and processability of Ti-Al-Nb alloys. These efforts have led to the state-of-the-art MMC matrix orthorhombic titanium aluminide alloy. This work was supported by Contract F33615-91-C-5647.
4:10 pm
THE EFFECT OF HEAT TREATMENTS ON THE MECHANICAL BEHAVIOR OF AN ORTHORHOMBIC Ti-ALLOY: S. Lutjering, D. Eylon, University of Dayton, Dayton, OH 45469-0240; P.R. Smith, Materials Directorate, Wright Laboratory, Wright-Patterson AFB, OH 5433-7817
Titanium aluminide alloys containing the ordered orthorhombic phase, based on Ti2AlNb, are considered as potential materials for the compressor section of aerospace engines both in their monolithic form and as matrices in metal matrix composites. The microstructure (volume fraction of the ordered alpha-2, B2 and orthorhombic phases, grain size, lath size and spacing) has a significant effect on the mechanical properties of these materials. In this study two heat treatments of the orthorhombic alloy Ti-22A1-23Nb resulting in a fully transformed and a duplex microstructure were investigated. Room temperature and elevated temperature tensile and cyclic behavior including fatigue life, fatigue crack initiation and propagation will be discussed with respect to these microstructural conditions.
4:20 pm
EFFECT OF MICROSTRUCTURE ON THE CREEP AND RT TENSILE BEHAVIOR OF O+B2 ALLOYS: C.J. Boehlert, B.S. Majumdar, V. Seetharaman, UES, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432-1894
The phase evolution, room temperature tensile, and elevated temperature creep behaviors of Ti-25Al-25Nb and Ti-23Al-27Nb have been examined. A variety of microstructures, consisting of different volume fractions of B2 and O were achieved through deformation processing and heat treatments. Supertransus heat treated microstructures suffered from intergranular attack and exhibited low ductility. Subtransus heat treated microstructures exhibited a balance of RT tensile and elevated temperature creep performance. Creep samples showed evidence of microstructural instability, involving cellular/widmanstatten precipitation of O phase within the B2 grains. The kinetics of O phase precipitation at the creep temperature, 650°C, and the effect of this instability on creep are presented. In addition, overall effects of microstructural features on tensile, creep, and damage accumulation are discussed.
4:40 pm
PRODUCTION OF HIGH TEMPERATURE TITANIUM ALUMINIDE FOILS VIA PLASMA SPRAY PROCESSING: R.S. Thakur, Mohit Sisodia*, M.K. Bhargava, Materials Procurement Division, Hindhustan Motors Company, Indore, India; *Dept. of Metallurgical Engineering, Malaviya Regional Engineering College, Jaipur 302 017, India
Plasma Spray Forming is a upscaled version of droplet deposition method from the melt, which combines the steps of melting, rapid solidification, and consolidation into a single operation. The present paper critically reviews the versatility of this process which is successfully applied to the synthesis of Ti alloys and Ti- aluminide preforms for subsequent cold rolling into thin foils. These Plasma Sprayed preforms are transformed into dense wrought Ti-aluminide foils by a roll consolidation process. It has been observed that production of this dense foils are as continuous coil, which would improve process efficiency and yield high quality at low cost. Actually these high strength Ti alloys and Ti-aluminide foils are required for fabricating composite structures for advanced aerospace technology and space shuttles. In addition to it, various parameters are discussed which primarily includes designing of optimum interface, growth kinetics etc., and became necessary in enhancing service life of these foils at elevated temperatures.
Room: 330B
Session Chairman: Y. A. Chang, Department of Materials Science & Engineering, University of Wisconsin, Madison, WI 53706-1595
OPENING REMARK: Y.A. Chang, Department of Materials Science & Engineering, University of Wisconsin, Madison, WI 53706-1595
2:05 pm KEYNOTE
CONSTITUTION AND THERMODYNAMICS OF MONOTECTIC ALLOYS: Prof. Dr. B. Predel, Max-Planck-Institut für Metallforschung, Inst. für Werkstoffwissenschaft, Seestrabe 92, D-70174 Stuttgart, Germany
Many binary systems exhibit miscibility gaps in the liquid state. It is well known that melts which are passing a miscibility gap on cooling, solidify to a regular consisting of two layers. Such metallic solid bodies are not interesting for technical applications and have also scarcely been investigated scientifically. Genuine interest in demixing systems only arised as it seemed possible to prevent layer formation under zero gravity. However, experiments in space have shown that even under migro-g conditions, phase separation is occurring, yet in another way as on earth and also not finely dispersed. Afterwards, there resulted an intensive disclosure of the thermodynamics and the kinetics of the separation of liquid immiscible phases. After the discussion of the results obtained it is indicated how layer formation can be prevented and a finely dispersed structure can be realized in order to enable technical use.
2:50 pm INVITED
ENTHALPY OF FORMATION OF LIQUID [TRANSITION METAL-sp METAL] BINARY ALLOYS: M. Gaune-Escard, J.P. Bros, IUSTI-UMR 129, Université de Provence, Centre de St-Jérôme, 13397 Marseille, France
With a fully automated high temperature calorimeter (Tmax = 1800K) and using the direct drop method, the molar integral of formation of the binary liquid alloys (Ga and In with Fe, Co, Ni, Rh, Pd, Ir, and Pt) have been measured with an accuracy of about 6%. From these results the molar partial enthalpies have been calculated and the transfer of electrons from the sp-metal to the transition metal has been deduced. Moreover some liquidus points of the equilibrium phase diagram of these systems have been obtained.
3:25 pm BREAK
3:40 pm INVITED
HIGH-TEMPERATURE THERMOCHEMISTRY OF INTERMETALLIC COMPOUNDS OF TRANSITION METALS AND RARE EARTH METALS WITH TiN: S.V. Meschel, O.J. Kleppa, James Franck Institute, University of Chicago, Chicago, IL 60637
A wide range of intermetallic compounds of transition metals and rare earth metals with tin have been studied by direct synthesis calorimetry at 1473 ± 2K. The results provide a picture of the systematic dependence of the standard enthalpy of formation of the compounds on the number of 3d-, 4d- and 5d-electrons in the considered transition metals, and on the number of f-electrons in the lanthanide metals. The results will be compared with earlier experimental data, where available, and with predictions from the semi-empirical model of Miedema and co-workers.
4:20 pm INVITED
APPLICATIONS OF EMF MEASUREMENTS IN THERMODYNAMIC STUDIES: A. Mikula, Institut für Anorganische Chemie, Universität Wien, Vienna, Austria
The use of emf measurements for the determination of thermodynamic properties of materials is reviewed. The development of a new galvanic cell techniques will be presented and their advantages and disadvantages in their application for certain problems will be discussed. There is a wide field for new applications of this technique like fuel cells, production of hydrogen, developments of new batteries, control of production processes and developments of new sensors. Scientific applications include kinetic measurements and studies of thermodynamic properties. This work will concentrate on the use of emf measurements of the thermodynamics of phase and reaction equilibria.
4:55 pm INVITED
HEAT CAPACITY OF LIQUID ALLOYS: F. Sommer, Max-Planck-Institut für Metallforschung, Institut für Werkstoffwissenschaft, Seestr. 75, D-70174 Stuttgart, Germany
Some specific features of the temperature and concentration dependence of the heat capacity Cp of ordering or segregating liquid alloys will be discussed. Some recent experimental Cp-data (e.g. Al-La-Ni, Bi-Ga, Al-In) obtained using a new adiabatic calorimeter are presented. The ability of some models to describe the different characteristics of the Cp(T,x)-course of liquid alloys is demonstrated. A direct connection between the thermodynamic properties of liquid alloys and the atomic transport properties like diffusion and viscosity will be described.
Room: Salon 6
Location: Clarion Plaza Hotel
Session Chairs: Hani Henein, Advanced Matls. and Proc. Lab, University of Alberta, 606 Chem-Min Eng. Bldg, Edmonton, AL T6G 2G6; Thomas Battle, DuPont White Pigments and Mineral Products, Edge Moor Plant, Edge Moor, DE 19809
BENEFITS OF MEMBRANE SURFACE FILTRATION IN THE NON-FERROUS INDUSTRY: Christine E. Kafka, W L. Gore and Associates, Inc., 101 Lewisville Road, P.O. Box 1100, Elkton, MD 21922-1100
Stricter particulate emission regulations and the competitive requirements to produce metal as economically as possible are driving the non-ferrous processing industry to focus on cleaner and more efficient technologies. One area of interest is the air cleaning systems. Presently, there are many different air filtration technologies employed by the industry. Fabric filtration systems with expanded polytetrafluoroethylene (ePTFE) membrane filters are increasingly being chosen to provide optimum performance over conventional depth filtration. The selection of filtration technology greatly affects the performance of the baghouse and process. The ePTFE membrane surface filtration provides consistently higher airflow and longer filter life, while also providing the additional benefit of the lowest particulate emission of any fabric filtration media. Membrane filtration provides these benefits in concentrate drying, primary and secondary smelter and converter baghouses, with case histories around the world.
2:25 pm
PHYSICAL EXAMINATION AND HANDLING OF WET AND DRY C60: K. Lozano1, X. Sheng1, A. Gaspar-Rosas2, F. Chibante3, E. V. Barrera1, 1Rice University, Dept. Mechanical Engineering and Materials Science, P. O. Box 1892, Houston, TX 77251; 2Paar Physica USA, Houston, TX 77388-8909; 3Nanotechnologies of Texas, Houston, TX 77081
The structure-property relationships of C60 dissolved in decahydronaphtalene (decalin) and a petroleum solvent viscous standard (PSVS) were studied. This work was motivated mainly by the interest to improve fullerene dispersion in powder processing by wet methods. Measurements of solubility, density, viscosity and elasticity were conducted varying the concentration level of C60. A Decalin solution was mixed with Cu powder and the C60 dispersion and Cu grain-size growth were evaluated. Decalin can dissolve 1.9 mg/ml of C60 while the PSVS dissolves 0.15 mg/ml. The viscosity behavior shown by both solutions was Newtonian, with a small increase in viscosity as a function of fullerene concentration. The elastic portion of the solvents did not change with fullerene concentration. The samples prepared by wet methods showed less C60 agglomerates. This presentation will also emphasize the aspects of handling the fullerene powder in wet and dry methods. This work was supported by National Science Foundation DMR-9357505.
2:50 pm
ON THE IMPROVED FLOWABILITY OF COHESIVE POWDERS BY COATING WITH FINE PARTICLES: R. Mei1, J.F. Klausner2, H. Shang1, and E. Kallman2, 1Department of Aerospace Engineering, Mechanics, and Engineering Science 2Department of Mechanical Engineering, University of Florida, Gainesville, FL 32611
Poor flowability of cohesive powders is the source of frequent concern in powder handling in many industrial processes. Coating of fine particles on the surface of primary powder particles can be applied to improve powder flowability. In this paper, we examine quantitatively the effect of coating fine particles on the cohesion force between primary powder particles by extending the JKR theory to include the effect of coating particles on the force-displacement relationship. It is shown that the cohesion force between two primary powder particles in the presence of a fine coating particle is directly proportional to the size ratio of the coating particle to the primary powder particle resulting in a drastic reduction in the cohesion force. Through discrete element simulation of powder flows the improved flowability is demonstrated. The effect of coating on improving the flowability is also quantified by comparing the measured angles of repose at a static condition and the flow rates of the gravity driven flow through a funnel for powders with and without particle coating.
3:15 pm
POROSITY CALCULATION OF PARTICLE MIXTURES: Z.P. Zou1, A. B. Yu1, P. Zulli2 , School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia; 2BHP Research - Newcastle Laboratories, P. O. Box 188, NSW 2287, Australia
A packing of particles is an assemblage of particles and is widely encountered in many industries. Porosity or packing density is known to be the simplest and most accessible parameter in characterising particle packing. It is very useful to develop a method for predicting the porosity and related packing properties of particulate mixtures for property and/or process control. Particle characteristics affect porosity mainly via three factors: (dimensionless) particle size distribution, particle shape and absolute particle size, giving various packing systems from the simple (coarse) spherical particle packing to the complicated system involving fine and non-spherical powders. Consequently, the modelling of the relationship between porosity and particle characteristics may be carried out by considering these three factors. This paper presents a mathematical model developed on the basis of some simple and physically sound concepts in this direction, with examples provided to confirm its applicability.
3:40 pm
A STUDY OF THE MECHANISMS OF POWDER ENTRAPMENT IN PACKED PARTICLES: D. Pinson1, A.B. Yu1, P. Zulli2, M. J. McCarthy2. 1School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia; 2BHP Research - Newcastle Laboratories, P.O. Box 188, NSW 2287, Australia
Gas-powder-liquid multiphase-phase flow in packed beds can be found in many industrial applications. One typical example is the flow in the lower part of a modern ironmaking blast furnace with high pulverised coal injection, which includes an upward flow of gas and (unburnt) coal and downward flow of liquid iron and slag in a coke bed. Understanding the mechanisms governing the powder entrapment in packed particles is an important step toward the modelling of such a flow system. This paper presents a study of the mechanisms through a model experiment in which the form and volume of deposits, i.e. the entrapped powder, can be visualised. It is found that the contact point between particles plays an important role in capture of powder, and the presence of a liquid may significantly increase the powder entrapment and lead to a dramatic increase in gas pressure drop. The effects of variables relevant to the blast furnace process, such as liquid properties, gas, powder and liquid flowrates, and the size ratio between (flowing) powder and (packed) particle have been studied, and correlations have been formulated for modelling purposes.
4:05 pm
RECENT DEVELOPMENTS IN THE TECHNIQUE FOR CHARACTERIZING THE SHAPE, SIZE, AND TEXTURE OF METAL POWDER GRAINS: B.H. Kaye1 , L.C. Paquette2, 1Professor of Physics, 2Research Associate, Department of Physics, Laurentian University, Sudbury, Ontario, P3E 2C6
Computer image analysis continues to develop rapidly and the falling costs and increasing power of personal computers make it possible to characterize the shape, angularities and, for rough texture powder grains, the fractal dimensions. New data on the characterization of various types of metal grains will be presented. Assessment of the size distribution of powders using diffractometers and time of flight spectrometers is making it possible to characterize the shape and size of metal powder grains in real time. Again, new data demonstrating the utility of this type of information for the powder metallurgist will be presented. Some of the newer size characterization equipment uses small quantities of powder samples and new procedures for taking representative samples from free fall tumbler mixers will be reviewed and sampling data presented.
4:30 pm
CHARACTERIZING THE FLOW OF METAL POWDERS USING THE CONCEPTS OF FRACTAL GEOMETRY AND CHAOS THEORY TO INTERPRET THE AVALANCHING BEHAVIOR OF A POWDER DEPENDENT ON POWDER GRAIN CHARACTERISTICS:B. H. Kaye1, L.C. Paquette2, 1Professor of Physics, 2Research Associate, Department of Physics, Laurentian University, Sudbury, Ontario, P3E 2C6
The avalanching behavior of a portion of powder in a slowly rotating disc can be related to the flow behavior of powder in processing equipment. To interpret the observed avalanching behavior a new data processing procedure has been developed which permits instant visual recognition of shifts in the flow behavior. This can be caused by changes in powder grain structure; additives (such as glidants) and changes in ambient properties (such as humidity). Data on these four metal powders of different size, shape and texture will be presented.
Room: 232C
Session Chairpersons: I.D. Troshkina, D. Mendeleyev, University of Chemical Technology of Russia, Miusskaya Sq. 9, Moscow 125047, Russia; Tom A. Millensifer, Powmet, Inc., 2625 Sewell St., P.O. Box 5086, Rockford, IL 61125
EXTRACTION OF RHENIUM FROM MOLYBDENITE CONCENTRATES: Mahesh C. Jha, William A. May, Entech Molybdenum Inc., 5950 McIntyre Street, Golden, CO 80403-7499
By-product molybdenite concentrates from copper mines are the most important source of rhenium. The rhenium content is low, generally in the few hundred ppm range. Almost all of these concentrates are roasted to technical grade molybdic oxide, the most common molybdenum product sold commercially. Rhenium oxide is volatilized at high roasting temperatures and condensed downstream at lower temperatures, eventually reporting to the scrubber liquor as a dilute solution. This paper reviews several hydrometallurgical approaches that have been used commercially and for researched and recommended to recover the rhenium from such dilute solutions. The methods include ion exchange, solvent extraction, selective leaching/precipitation, and crystallization for concentration and purification steps. Ammonium perrhenate is typically the end product.
2:20 pm
A DATABASE APPROACH TO THE RECYCLING OF RHENIUM: Laird G.L. Ward, Noble and PGM Recycling Representation, 23 Longview Road, E. Fallowfield, Coatesville, PA 19320-4311; David P. Dillard, Research Librarian, Paley Library, Temple University, Philadelphia, PA
Since its discovery by the German investigators W. Noddack, Ida Tacke and 0. Berg in 1925 and, at about the same time, by the Czechs J. Heyrovsky and V. Dolejsek, and the British investigators J.G.F. Druce and F.H. Loring, rhenium, element of atomic number 75 has gradually established a niche for itself in the industrial world. With the technology of rhenium now well established, its further technical progress may be impeded for the lack of a ready means to recover it from scrapped sources. This conference, being the next to follow the Rhenium Conference in l963, affords an opportunity to review the approaches published for the recovery of the element rhenium from some of the diverse products in which it has played a unique and very special ro1e.
2:40 pm
PROCESSING OF SPENT PLATINUM-RHENIUM CATALYST FOR RHENIUM RECOVERY: Mahmoud I. ElGuindy, Gemini Industries Inc., 2311 South Pullman Street, Santa Ana, CA 92705
Annually, over 5 million lbs of spent Reformer Catalysts are treated for the recovery of contained Platinum and Rhenium. In this publication a summary of available technology and methods employed for the processing of spent Pt-Re Catalyst will be discussed. Special emphasis will be on Rhenium recovery, purification and production of Catalytic Grade Ammonium Perrhenate. Furthermore, the factors influencing the chemical processing, the residence time and the purity of products in addition to metal accountability will be discussed. Recommended actions to be taken by petroleum processors to assist and facilitate recovery operations will also be presented.
3:00 pm
RHENIUM RECOVERY FROM NON-TRADITIONAL RESOURCE: A.M. Chekmarev, I.D. Troshkina, D. Mendeleyev, University of Chemical Technology of Russia, Miusskaya Sq. 9, Moscow 125047, Russia
About 50% world resource of rhenium is found in non-traditional carbon-based resource. The search of rhenium occurrence and the study of rhenium distribution in high-viscous oil, native bitumen and oil shale processing are performed by the radiotracer and kinetic methods of analysis. The products-concentrate of rhenium are determined. Methods of rhenium recovery from the processing products including hydrometallurgical techniques are developed. Sorption methods are worked out for rhenium recovery from additional resource; waste water, intermediate products in processing of various types of source etc.
3:20 pm BREAK
3:40 pm
RHENIUM AND OSMIUM RECOVERY FROM SULFURIC ACID SCRUB SOLUTIONS: I.D. Troshkina, A.M. Chekmarev, A.B. Mayboroda, D. Mendeleyev University of Chemical Technology of Russia, Miusskaya Sq. 9, Moscow 125047, Russia
The presence of radiogenic osmium-187 formed by by-fussion of rhenium-187 is the specific characteristic of some rhenium -containing source. The technology for the recovery of rhenium and osmium from sulfuric acid scrub solutions formed by wet gas purifying in pyrometallurgical processing of sulfide polymetallic ores was developed. The technology is based on extraction and sorption techniques following preliminary conversion of the metals into the optimal chemical species. The technology ensures quantitative recovery, concentration and separation of rhenium and osmium, production of commercially viable concentration of the elements.
4:00 pm
RECYCLING OF RHENIUM: D.V. Drobot, V.I. Bukin, Moscow State Academy of Fine Chemical Technologies, Pr. Vernadskogo 86, 117571 Moscow, Russia
The aim of the investigation is the generalization of the published results according of rhenium extraction from secondary materials. Such materials can be classified as binary W-Re and Mo-Re alloys; several composition Ni-Re alloys; Al-Pt-Re catalysts and other Re-containing secondary products. The range of technological processes is very mice and depends on forms and Re concentration in secondary materials. For Re extraction from binary alloys can be used processes including interaction with KNO3 or oxidation. In the last case it may be obtained volatile Re207. Purification can be done by rectification Re2O7. The full extent of Re extraction from such materials is 92-94%. Combination of the chlorination process with solvent extraction allows to obtain Re metal with extent of extraction ~92%. Re can be obtained from Mo-Re, W-Re alloys by means of electrochemical process (alkali solutions) or H:SO. solutions (Ni-Re alloys). For the production of the pure Re products it's necessery to use combination with solvent extraction or sorbtion. Complex Re and Pt extraction metals from A1-Pt-Re containing catalyst is the most important problem. There are known two methods, which differ at the first step: annealing with Na2CO3 or annealing in oxidation atmosphere are possible. Extents of Re and Pt extraction are 90 and 92%.
4:20 pm
BEHAVIOR & RECOVERY OF RHENIUM DURING THE CONVERSION OF MOLYBDENUM CONCENTRATES AND MISCELANEOUS TYPES OF THE SECONDARY RAW MATERIALS: N.N. Rakova, L.V. Miakisheva, K.N. Yegorychev, V.S. Strizhko, The Moscow State Institute of Steel & Alloys, Moscow, Russia
The definite works to create scientific foundations and the technology for the recovery of rhenium from the primary and secondary raw materials were initiated in the 60's at the Chairs of the rare-earth metals & powder metallurgy led by the Distinguished Metallurgist of Russia, professor A. N. Zelikman. 1. The molybdenum concentrates- one of the prime sources to recover rhenium along with the sulfide copper and copper/moly raw materials. The researches have been tested to investigate a behavior of rhenium during roasting process of the molybdenum concentrates and during the attack by the nitrogen acid. 2. The researchers have been tested with form and mechanism of extraction of molybdenum and rhenium from sulfur acid and nitrogen/sulfur acid solutions of different compositions. During the elaborations of the extraction methods of distribution and the recovery it has been taken into account the differences in the forms of molybdenum and rhenium presence in the acid atmospheres and it has been suggested to utilize the neutral, anion- and cation exchange extragents. 3. The processes of the deep cleaning of the rhenium combination through trihydroxychloride, having the below melting and flashing temperature have been developed. The purity of the recovered ammonium perrhenate and metallic rhenium is exceeding their purity during the production and refinery by the other methods. 4. Some methods have been tested to regenerate rhenium, tungsten, molybdenum from the wastes of W-Re & Mo-Re alloys with further treatment of the mixtures of chlorides of tungsten and rhenium by the water with the presence of oxidant and oxidation of alloys by means of oxygene and sublimation of rhenium oxide.
4:40 pm
RHENIUM RECOVERY FROM SECONDARY RAW MATERIALS OF VARIOUS TYPES: A.V. Elutin, M.V. Istrashkina, Z.A. Peredereeva, State Research Centre-State Institute of Rare Metals-GIREDMET, 5 B. Tolmachevsky Per., Moscow 109017, Russia
This report submits data of high-efficiency methods for rhenium recovery from secondary raw materials of various types, such as exhausted platinum-rhenium catalysts and scrap of rhenium-containing molybdenum, tungsten and nickel based alloys. Developed methods are used on a commercial level at industrial enterprises of Russia and CIS. A process for selectively recovering rhenium from exhausted Pt-Re catalysts includes next steps: roasting, acid- or alkali-assisted leaching, ion-exchange recovery or rhenium from the solution and preparing high-purity ammonium perrhenate (99.99%). Results of developing commercially applicable methods are useful for rhenium recovery from scrap of rhenium-containing alloys.
5:00 pm
DETERMINATION OF RHENIUM BY RADIOTRACER METHODS OF ANALYSIS: I.D. Troshkina, A.M. Chekmarev, V.I. Shamaev, D. Mendeleyev, University of Chemical Technology of Russia, Miusskaya Sq. 9, Moscow 125047, Russia
Radiometric correction and interpolation methods have been worked out for rhenium determination with extraction of the tetraphenylphosphonium complex into dichlorethane. Radiotracer 188Re (16,9 h) is obtained in 188Re-generator which is a glass column filled with aluminium oxide with a parent isotope 188W (69, 4 d) adsorbed firmly. The isotope 188Re formed is eluted from the generator by 0,9% solution of sodium chloride. Liquid scintillation counting was used. The method allows to determine from 1 to 100 mg of rhenium (VII) in analyzed probe. The relative standard deviation is 0.05-0,09 over the whole concentration range.
5:20 pm
AN OUTLINE OF THE PROCESS OF ACCESSORY RHENIUM EXTRACTION FROM MOLYBDENITE CONCENTRATES IN FLUID-BED ROASTERS: R.A. Apriamov, E.D. Doronkin, and F.V. Baroev, OAO "TVERDOSPLAV", 56 Warshavkoye Shosse, Moscow, Russia
Room: 330A
Location: Orlando Convention Center
Session Chairperson: W.E. Frazier, Code 4342, Naval Air Warfare Center, Patuxent River, MD 20670
THE DEVELOPMENT OF TEXTURE IN AlLi 2195 ALLOY DURING RING ROLL FORGING: Lan Zhang, Peter N. Kalu, Department of Mechanical Engineering, FAMUFSU College of Engineering, Tallahassee, FL 32310
This study presents results of texture and microstructural development in AlLi 2195 alloy processed by near-net-shape roll forging method. The manufacturing technique is a multistage process that combines conventional ingot conversion, back extrusion, and ring rolling to produce a heavy walled cylindrical forging preform. The preform is then rolled to nearfinal diameter using contoured rolling mandrels. A combination of optical microscopy, Orientation Distribution Function (ODF) and Orientation Imaging Microscopy (O1M) was used in this investigation. At the early stage of processing, (110) fiber texture was predominant. Following the second stage of processing, the texture was similar to characteristic fcc rolling texture. At the conclusion of processing, {001}<110> and {112}<110> shear components were developed at the expense of Brass ! component. The possible mechanisms responsible for the texture changes are discussed in relation with the microstructural evolution.
2:25 pm
ALLOY COMPOSITION EFFECT ON THE GLASS FORMING ABILITY AND THERMAL STABILITY OF THE Al86Mm4Ni10-xFex AMORPHOUS ALLOYS: H.W. Jin, Y.J. Kim, C.G. Park, Center for Advanced Aerospace Materials, Pohang Univ. of Sci. & Tech., Pohang 790784, Korea; M.C. Kim, Research Inst. of Industrial Science and Tech., Pohang 790600, Korea
Amorphous aluminum alloys show an attractive combination of high tensile strength and low density. The commercial applications of these alloys, however, have been restricted due to relatively poor thermal stability and glass forming ability (GFA). The GFA and the thermal stability of Al86Mn4Ni10-xFex alloys have been investigated with various alloy composition. Amorphous ribbons with the thickness from 20pm to 30µm were prepared by single roll melt-spinner. The microstructural evolution upon heating was observed by using X-ray diffraction and transmission electron microscopy (TEM). The GFA of the present alloys decreased with the increase of Fe content. However, the first (lowest) crystallization temperature, Txl, increased with increasing Fe content. The effects of alloy composition on the GFA and the thermal stability will be discussed in terms of the atomic bonding and electronic structure of the amorphous alloy.
2:50 pm
EFFECT OF STRETCHING PRIOR TO AGING ON MECHANICAL PROPERTIES AlCuLi (2195) ALLOY: Z.X. Li1, R A. Mirshams1, E.A. Kenik2, P.J. Hartley3 ;1Department of Mechanical Engineering, Southern University, Baton Rouge, LA 70813; 2Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831; 3Lockheed Martin Manned Space Systems, New Orleans, LA 70189
The Al-Cu-Li (2195) alloy was stretched uniaxially from 0% to 15% of plastic deformation prior to aging. The tensile properties of naturally and artificially aged specimens in 0, 45, and 90 degrees with respect to the pre-stretching direction were evaluated and their microstructures were characterized via TEM. The results indicated that the naturally aged specimen exhibited mainly ' (Al3Li) precipitates whose size appeared to be insensitive to pre-stretching. The moderate increase in yield strength by prestretching was attributed to work hardening effect. On the other hand, it was found that the precipitates of the artificially aged (at 180°C) specimen were primarily T1 (Al2CuLi) phase. The size of the T1 precipitates decreased with increasing amount of pre-stretching. A pronounced increase in yield strength by pre-stretching was observed with the presence of fine T1 precipitates. The relationship between mechanical properties and microstructures will be discussed. This work was sponsored partially by the Louisiana Board of Reagent and DOE-SHaRE program at Oak Ridge National Laboratory.
3:15 pm
CONTROL OF PROPERTIES BY RE (RARE EARTH METALS) ADDITION IN HIGH Mg CONTAINING Al ALLOYS: S.D. Park, J.H. Jung, H.K. Cho, Departments of Metallurgical Engineering, Kyungpook National University, Taegu 702-701, Korea
Recently, there is a great deal of interests in Al-Mg alloys due to their good combinations of strength and formability. To further improve their properties, high Mg containing Al alloys have been studied although serious problems associated with the precipitation of 
(Mg5Al8), such as low thermal stability and poor corrosion resistance, are generated with higher Mg concentration. In the present study, changes in precipitation behavior and mechanical properties by RE addition in high Mg containing Al alloys have been investigated. It has been shown that the precipitation of phase is restrained and mechanical properties are improved by RE addition.
3:40 pm
EFFECT OF COMPOSITION AND TEMPERATURE ON THE STRENGTH AND FRACTURE TOUGHNESS OF AL-CU-LI-AG ALLOYS: Cynthia L. Lach, NASA Langley Research Center, Mail Stop 188A, Hampton, VA 23681; Richard P. Gangloff, Department of Materials Science and Engineering, Thornton Hall, University of Virginia, Charlotttesville, VA 22903
The use of Al-Cu-Li-Ag-Mg-Zr alloys for fabricating aerospace vehicle components can potentially reduce system weight. For damage tolerant analysis, it is important to characterize and understand alloy strength and fracture toughness, particularly as affected by minor changes in composition and test temperature. The uniaxial tensile deformation, plane strain fracture toughness, and plane stress tearing resistance of two precipitation hardened alloys, AA2095 and AA2195, were examined as a function of Cu and Li levels and temperature from -185°C to 135°C. As temperatures decreased, the crack initiation toughness of AA2095 declined mildly while the toughness of AA2195 increased mildly. Alloy AA2195 demonstrated superior toughness in all cases. For each alloy the elastic modulus, yield strength and work hardening coefficient increased with decreasing temperature, while ductility declined from 135°C to -185°C. A plastic strain-critical distance-based micromechanical model utilized these properties to predict that KICI increased mildly with declining temperature for each alloy. The slope of this trend was in good agreement with measurements for AA2195, but less so far AA2095. In all cases fracture occurred without delamination and by microvoid nucleation, growth and coalescence involving second phase particles which were particularly large in the higher Cu/Li variant (AA2095). This difference, along with separate relationships between nearest-neighbor particle spacing and the critical microstructural distance from the model explain the higher toughness of AA2195.
4:05 pm
EFFECT OF Be ADDITION ON THE PRECIPITATION AND MECHANICAL PROPERTIES OF Al-Cu-Li-Mg-(Ag)-Zr ALLOYS: D.S. Chung, S.H. Cho*, H.K. Cho*, Dept. of Metallurgy, Changwon Industrial Master's College, Changwon 641772, KOREA ; * Dept. of Metallurgical Engineering, Kyungpook National University, Taegu, 702701
The effect of Be addition on the precipitation and mechanical properties of Al-Cu-Li-Mg-(Ag)-Zr alloys has been investigated by detailed transmission electron microscopy and hardness and tensile tests. It has been shown that the Be addition accelerates the aging response and improves the ductility while maintaining the strength of Al-Cu-Li-Mg-(Ag)-Zr alloys. Such improvements in mechanical properties are due to changes in precipitation behavior of Al-Cu-Li-Mg-(Ag)-Zr alloys by Be addition.
4:30 pm
MICROSTRUCTURAL EVOLUTION AND GRAIN DISTRIBUTION IN SUPERPLASTICALLY FORMED AlLi 8090 ALLOY: Peter N. Kalu, H. Garmestani, Department of Mechanical Engineering, FAMUFSU College of Engineering, 2525 Pottsdamer St., Tallahassee, FL 32310
With the advent of new analytical tools to study microstructures and microtexture, it is now necessary to re-characterize materials with complex structures. Using Orientation Imaging Microscopy (OIM), several microstructural parameters were obtained for superplastic Al-Li 8090 alloy deformed in tension. Grain orientation and distribution as well as the effective grain size based on standard definition of large angle grain boundaries were determined as a function of strain. The data was correlated with various models for superplasticity. The implications of the results on the deformation mechanisms operating during superplastic deformation is discussed.
4:55 pm
DISLOCATION STRUCTURES PRODUCED DURING HIGH TEMPERATURE DEFORMATION OF ALLI AA8090 ALLOY: W. Fan, M.C. Chaturvedi, Department of Mechanical and Industrial Engineering, University of Manitoba Winnipeg, Manitoba, Canada, R3T 2N2; N.C. Goel, N.L. Richards, Bristol Aerospace Ltd, Winnipeg, Manitoba, Canada, R3C 2S4
Deformation microstructures of an aluminum-lithium AA8090 SPF grade sheet have been studied by TEM. The alloy was deformed in tension at the superplastic deformation temperature of 530°C and at a strain rate of 1x10-3/sec. The tensile testing machine was fitted with a specially designed in-situ water quenching apparatus to preserve the deformation microstructure produced at the temperature of testing. The TEM thin foils were made from samples deformed and in-situ quenched from different strain levels. Most of the thin foils were prepared with the surface parallel to the through thickness cross-section of the sheet, rather than parallel to the rolling plane. Dislocation pairs and dislocation networks were observed in the deformed samples even when deformation was as large as 475%. The observed characteristics of dislocation configuration suggest that dislocation interactions take place during superplastic deformation, in which grain boundary sliding is considered to play a dominant role and the role of dislocations is mainly to accommodate grain boundary sliding. In this paper, the possible implications of dislocation interactions and the mechanism of superplastic deformation in aluminum-lithium alloy AA8090 are discussed.
Room: Salon 3
Location: Clarion Plaza Hotel
Session Chairman: Dr. K. G. Kubarych, Solar Turbines, 2200 Pacific Highway, P.O. Box 85376, San Diego, CA 92186
MODELING ENGINE COMPONENT CREEP DEGENERATION: A.K. Koul, X.J. Wu, Structures and Materials Propulsion Laboratory, Institute of Aerospace Research, National Research Council of Canada, Ottawa, Ontario, Canada K1A0R6
The paper presents a mechanistic approach to modeling creep degeneration of superalloy components with a view to developing residual life prediction algorithms. In accordance with the deformation decomposition rule: E = Eg + Egbs, we classify degeneration mechanisms into two categories: 1) grain boundary deformation controlled degeneration mechanisms, including grain boundary sliding (GBS), cavitation and GBS assisted oxidation; and 2) intragranular deformation controlled degeneration mechanisms. The evolutionary creep equation for each strain component is thus mechanism-based. Generally, GBS is responsible for the transient, while intragranular deformation mechanisms, particularly dislocation glide-plus-climb and dislocation multiplication, contribute to tertiary creep deformation during short term tests. When coupled with cavitation and oxidation, GBS also contributes to tertiary creep. The total creep strain is a result of the summation of all above contributions, and the entire creep, as a continuous process, is thus described. Superimposed on these mechanisms are various fracture criteria to predict the eventual event of creep rupture.
2:30 pm
THE EFFECT OF DEFECTS ON THE LCF BEHAVIOR OF AN ADVANCED SINGLE CRYSTAL SUPERALLOY: K.A. Dannemann, H. Jang, W.T. King, GE Power Generation, Schenectady, NY 12345
The defect propensity in single crystal castings is enhanced with increased casting size. As the industrial gas turbine community moves towards the application of large single crystal castings, there is increasing concern regarding the effects of grain and casting defects on part life. Although aircraft engine experience provides a basis for single crystal grain limits, the cycle and life requirements of large industrial gas turbines differ considerably. The effect of several types of defects on the low cycle fatigue behavior of an advanced single crystal alloy will be discussed. Tests were run on cast-to-size LCF bars with intentional defects (freckles, inclusions, low angle boundaries, recrystallized grains, slivers, mis-oriented grains) in the gage section. A correlation between defect size and LCF life was observed. Work to date indicates LCF life is more dependent on defect size than type.
2:50 pm
HOT FORMING CHARACTERISTICS OF NI-BASE SINGLE CRYSTAL SUPERALLOY CMSX-6: D. Zhao, H. Dong, M. Zelin, A. Dalley, Concurrent Technologies Corporation, 1450 Scalp Ave., Johnstown, PA 15904
High temperature deformation processing of Ni base single crystal superalloy CMSX-6 has been shown to be a feasible process. However, it is essential that the single crystal material be deformed at a low strain rate and within an appropriate temperature range to prevent recrystallization and fracture. In order to establish these limits, the hot forming behavior of Ni base single crystal superalloy CMSX-6 was investigated by performing high temperature compression, bending, and rolling tests. Stepwise deformation and annealing tests were also conducted to simulate multi-pass rolling practice. The flow stress and recrystallization behavior were characterized over a range of temperatures, strain rates, and strains. Metallurgical phenomena, such as changes in size and morphology of 1 particles, orientation change of the single crystal specimens, subgrain boundary formation, recovery, and recrystallization, occurred during the high temperature deformation processes. These phenomena were analyzed to understand their influence on forming of single crystals. Deformation at too high temperatures resulted growth of 1 particles and deteriorated the service properties of single crystals. Highly mis-oriented subgrain formation around 1 particles lead to recrystallization. Deformation mechanisms were investigated by analyzing the results of compression and indentation tests. The primary slip systems activated were of (111)<110> type. This work was conducted by the National Center for Excellence in Metalworking Technology, operated by Concurrent Technologies Corporation under contract No. N00140-92-C-BC49 to the U.S. Navy as part of the U.S. Navy Manufacturing Technology Program.
3:10 pm
EFFECT OF TEMPERATURE ON THE DEFORMATION CHARACTERISTICS OF A NI-MO-CR ALLOY: W.C. Johnson, D.L. Klarstrom, Haynes International, 1020 W. Park Avenue, P.O. Box 9013, Kokomo, IN 46904; M. Dollar, Haynes International, Engineering 1 Bldg., 10 W. 32nd Street, Chicago, IL 60616
The high temperature, age hardenable, Ni-Mo-Cr alloy HAYNES 242 shows a change in deformation characteristics dependent upon the testing temperature. Aged material shows microtwinning to be a dominant deformation mechanism at all testing temperatures. However, this does not preclude the occurrence of slip at room temperature and elevated temperature. Grain boundaries also seem to play a role in the fracture propagation mechanism at work in tested samples. Samples in the aged condition fracture with a combined mode of dimple rupture and cleavage as opposed to annealed samples which fracture through a dimple rupture mode alone. The fracture surface shows microvoid coalescence but the fracture takes place in a shear-type mode as opposed to the traditional cup and cone ductile fracture.
3:30 pm BREAK
3:50 pm
SOLID PARTICLE EROSION RESISTANCE OF IRON, NICKEL AND COBALT-BASED ALLOYS: B.F. Levin, J.N. DuPont, A.R. Marder, Lehigh University, Energy Research Center, Bethlehem, PA 18015
The erosion behavior of commercially available iron, nickel and cobalt-based alloys was evaluated and a relative ranking of their erosion resistance was developed. Microhardness tests were conducted in the vicinity of the eroded surface to measure the size of the plastic zone beneath the eroded surface. It was found that all alloys deformed plastically and a new toughness parameter has been proposed which shows good correlation with erosion resistance. To find a relationship between mechanical properties and erosion resistance, elevated temperature mechanical test were conducted for all alloys. The erosion resistance of tested materials exhibited good correlation with their tensile toughness. Relationships between the ability of materials to deform plastically, mechanical properties (i.e., hardness and tensile properties) and erosion resistance are discussed.
4:10 pm
THERMAL AND MECHANICAL PROPERTIES OF THERMAL BARRIER COATING ON CU-SUBSTRATE PREPARED BY DETONATION-GUN THERMAL SPRAY METHOD: Y.M. Rhyim, H.W. Jin, C.G. Park, Center for Advanced Aerospace Materials, Pohang University of Science & Technology, Pohang 790-784, Korea; S.B. Kim, M.C. Kim, Research Institute of Industrial Science & Technology, Pohang 790-600, Korea
Thermal barrier coating (TBC) consisting of Y2O3-stabilized ZrO2 top coat on a MCrAlY bond coat has been developed for thermal protection of hot components used in steel plant, especially the tuyeres in blast furnace. Since the tuyere is used under extremely harsh chemical environment and high temperature (up to 2300°C) within the blast furnace, it is essential to develop a strong and tough protective coating, that is fully compatible to the tuyere's pure copper substrate, by applying the detonation-gun thermal spray method. As fuel gas amount increased, the porosity of MCrAlY coat layer generally decreased to less than 1%, but microcracks can be formed with extreme fuel gas amount. The metallic bond coat with the thickness greater than 100 µm is required to sustain the ceramic top coat. In obtaining the best top coat, the spraying condition with maximum detonation temperature was found as an optimum condition from the computer simulation. A partially stabilized zirconia top coat layer deposited by this condition exhibited the low porosity with high hardness (~640 DPH) which is better than the coating made by plasma spraying. The thermal fatigue resistance of the present TBC was revealed to depend on both the thickness of ceramic top coat and the composition of the stabilizer. The result on the thermal conductivity is also discussed.
4:30 pm
ELECTROCHEMICAL PROCESSING OF THERMAL BARRIER COATINGS: S.W. Banovic, K. Barmak, A.R. Marder, C.M. Petronis, D.G. Puerta, D.F. Susan, Lehigh University, Department of Material Science and Engineering, 5 E. Packer Ave., Bethlehem, PA 18015
Multilayer, graded thermal barrier coatings have been fabricated using electrochemical methods. The inner two layers of the coatings are electro-deposited from aqueous baths and consist of 18 vol. % Al and 20 vol. % Al + 7 vol. % alumina, respectively, in a Ni matrix. The outer two layers are electrophoretically deposited form non-aqueous baths and contain an oxidation-resistant alumina 1 zirconia layer and a thermal-resistant yttria-stabilized zirconia outer layer, respectively. The alumina + zirconia layer was formed by reaction bonding of an aluminum-alumina-zirconia precursor powder. In addition to the details of the fabrication, the results of thermal cycling and mechanical testing of these four-layer coatings will be presented.
4:50 pm
ELECTRON BEAM PHYSICAL VAPOR DEPOSITION OF NICKEL-BASE ALLOYS USING REFRACTORY ADDITIONS: D.A. Madey, A.M. Ritter, S. Tin, M.R. Jackson, S. Rutkowski, R.A. Nardi, GE Corporate Research & Development, P.O. Box 8, Schenectady, NY 12301
Many potential applications of electron beam evaporation demand tight compositional control in the deposits and high deposition rates. Adding tungsten to nickel-based evaporation pools can increase evaporation rates and improve compositional control in deposits. Effects of tungsten addition on several alloys, NiCoAl, NiCoCr, and NiCrAl were investigated. Magnitudes of compositional gradients in the deposits, measured using electron microprobe techniques, were used to evaluate the sensitivity of vapor cloud chemistry to fluctuations in processing parameters. Compositional and microstructural gradients in quenched evaporation pools, studied using microprobe and SEM, yielded information about the evolution of steady state in the pools. Tungsten distributions in the pools, which may significantly affect temperature distribution, fluid flow, and heat transfer, were mapped using back scattered electron microscopy and energy dispersive X-ray analysis. Currently, pool surface temperatures are being mapped using an infrared imaging radiometer and effects of refractory additives other than tungsten are being evaluated.
5:10 pm
RF MAGNETRON SPUTTERING OF MOSI2+X SIC COMPOSITE THIN FILMS: S. Govindarajan, J.J. Moore, Advanced Coatings and Surface Engineering Laboratory, Dept. of Met. & Materials Eng., T.R. Ohno, Dept. of Physics, Colorado School of Mines, Golden, CO 80401-1887
A critical component of a prototype coating system being developed to protect molybdenum against high temperature oxidation (i.e. at 1600°C for 500 hours) is a functionally graded layer based on MoSi2+x SiC (where x is the variable mole fraction of SiC in the film). Different approaches for synthesizing composite films include sputtering from elemental or compound targets, reactive sputtering, and direct sputtering of composite targets. This paper will explore the feasibility of synthesizing composite films by RF magnetron sputtering of a composite target. Results of compositional depth profiling using Auger Electron Spectroscopy, microstructural evaluation and X-Ray diffraction analyses of the films will be presented. In particular, the diffusion of silicon and carbon in to the substrate will be characterized using a "ball-cratering" technique followed by auger electron spectroscopy (AES). This technique will help to overcome the disadvantages associated with ion-beam sputtering during depth profiling (e.g. different sputter yields for the constituent elements, interface broadening effects, etc.).
Room: Salon 4
Location: Clarion Plaza Hotel
Session Chairperson: M.S. Wechsler, North Carolina State University, 106 Hunter Hill Place, Chapel Hill, NC 27514-9128
CALCULATIONS OF RADIATION EFFECTS ON 316 STAINLESS STEEL CONTAINER MATERIALS FOR THE NSNS: M.S. Wechsler1, M.H. Barnett1, L.K. Mansur2, J.M. Barnes2, L.A. Charlton2, J.O. Johnson2; 1North Carolina State University, Dept. of Nuclear Engineering, Raleigh, NC 27695-7909; 2Oak Ridge National Laboratory, Computational Physics and Engineering Division Oak Ridge, TN 37831-6376
A current pre-conceptual design for the National Spallation Neutron Source (NSNS) considers the target to be flowing liquid mercury contained within a double-walled 316 stainless steel vessel. Calculations are underway to determine the neutron flux and to estimate the rates at which displacements, helium, and hydrogen are produced. The primary computational tools are MCNP, SPECTER, HETC, and LAHET. The displacement and helium production rates range up to about 10-7 DPA/s and 10-6 appm He/s due to the spectrum of neutrons produced by a 1700 MeV proton beam. The variation of calculated damage rates throughout the target region of NSNS is described and discussed.
2:30 pm
HELIUM PRODUCTION RATES ARISING FROM SPALLATION NEUTRONS IN THE LANSCE RADIATION EFFECTS FACILITY: F.A. Garner1, W. F. Sommer2, P. D. Ferguson2, M. S. Wechsler3, M.H. Barnett3, B.M. Oliver4; 1Pacific Northwest Laboratory, Richland, WA 99352; 2Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545; 3North Carolina State University, Raleigh, NC 27695-7909; 4Rockwell International Corporation, Canoga Park, CA 91303-2790
Foils of pure Cu, Co, Fe and Ni were irradiated in the second inboard tube of the rabbit system adjacent to the beam stop of the LANSCE facility. After irradiation, the foils were cut in half to determine neutron fluence and spectra via measurement of gamma activation, and to measure helium generation via isotopic dilution mass spectroscopy. The measured helium concentrations were 0.110, 0.152, 0.122 and 0.097 appm for Fe, Ni, Cu, and Co, respectively. The dpa level calculated for copper was 0.011 dpa, yielding a value of 11.1 appm/dpa. Comparisons with improved calculations of neutron flux/spectra and helium and displacement production rates are in progress to characterize the neutron environment of the rabbit system and to assess its radiation damage effects.
3:00 pm
THE EFFECT OF THE NEW NUCLEON-NUCLEUS ELASTIC SCATTERING MODEL IN LAHET VERSION 2.8 ON DAMAGE CROSS SECTION CALCULATIONS: E.J. Pitcher1, P.D. Ferguson1, G.J. Russell1, J.D. Court1, L.L. Daemen1, M.S. Wechsler2, R.E. Prael1, D.G. Madland1; 1Los Alamos National Laboratory, Los Alamos, NM 87545; 2North Carolina State University, Raleigh, NC 27695-7909
The latest release of the medium-energy Monte Carlo transport code LAHET includes a new nucleon-nucleus elastic scattering treatment based on an interim global medium-energy phenomenological optical-model potential. Implementation of the model in LAHET allows nuclear elastic scattering for neutrons with energies greater than 15 MeV and for protons with energies greater than 50 MeV. Previous investigations on the impact of the new elastic scattering model revealed that the addition of the proton elastic scattering channel can lead to a significant increase in the calculated damage energy. We report here results of further investigations on the impact of the new elastic scattering model on calculated damage cross sections and recoil spectra for materials and particle energies prototypic of spallation target environments. With the new elastic scattering treatment, the damage cross section for 20-MeV neutrons on light nuclei (A < 30) as calculated by LAHET is in much better agreement with SPECTER calculations, where significant discrepancies have previously been observed.
3:30 pm BREAK
3:50 pm
THE INFLUENCE OF SUBCASCADE FORMATION ON DISPLACEMENT DAMAGE AT HIGH PKA ENERGIES: R.E. Stoller, Oak Ridge National Laboratory, Metals and Ceramics Division, Oak Ridge, TN 37831-6376
Molecular dynamics (MD) simulations of displacement cascades have been extended to energies as high as 40 keV. These simulations are the highest energy cascades completed to date and they provide valuable insight on the formation of primary damage in irradiated materials. An MD simulation at 40 keV is equivalent to a PKA energy of 61 keV, which is the average PKA energy from a neutron with an energy of 1.8 MeV. Although peak neutron energies in a spallation neutron source will be much higher than 1.8 MeV, the degree of subcascade formation observed at MD energies above 20 keV suggests that little change in the primary damage state will be observed for higher energies. This implies that fission reactor data should provide a good simulation of the displacement damage observed in a spallation neutron source. Thus, the effect of transmutation products is likely to be the most important difference between the two irradiation environments.
4:20 pm
INVESTIGATION OF HIGH-ENERGY-PROTON EFFECTS IN ALUMINUM: C.J. Czajkowski, C.L. Snead, M. Todosow, Brookhaven National Laboratory, Upton, NY 11973-5000
Specimens of 1100 aluminum were exposed to several fluences of 23.5-GeV protons at the Brookhaven Alternating Gradient Synchrotron. Although this energy is above those currently being proposed for spallation neutron applications, the results can be viewed as indicative of trends and other microstructural evolution with fluence that take place with high-energy proton exposures such as those associated with an increasing ratio of gas generation to dpa. TEM investigation showed significantly larger bubble size and lower density of bubbles compared with lower-energy proton results. Estimates of H and He gas generation made using Monte Carlo are also used in this comparison. Additional testing showed that the tensile strength increased with fluence as expected, but the microhardness decreased, a result for which an interpretation is still under investigation.
4:50 pm
RESPONSE OF STRUCTURAL MATERIALS TO RADIATION ENVIRONMENTS: C.J. Czajkowski, Brookhaven National Laboratory, Upton, NY 11973-5000
An evaluation of proton and neutron damage to various materials has been performed. The proton studies were conducted at energies of 0.2, 0.8, and 23.5 GeV and consisted of evaluation of proton-irradiated window/target materials from accelerators. The materials evaluated for the proton irradiations included high-purity (6 9's), 1100, and 5052 aluminum, 304 stainless steel, and inconel 718. The neutron damage research centered on 6061 T-6 aluminum from a control rod follower from the BNL HFBR, which received thermal fluence up to ~4 x 1023 n/cm2. The effects of thermal-to-fast neutron flux ratios are discussed. The increases in tensile strength in the proton-irradiated materials are shown to be due to atomic displacements, resulting in radiation hardening. Production of helium in the grain boundaries of proton-irradiated 6 9's aluminum is also discussed. The major factor contributing to the mechanical-property changes in the neutron-irradiated 6061 aluminum is transmutation products formed by interactions with thermal neutrons.
Room: 314B
Session Chairperson: TBA
FILLET-LIFTING IN PLATED-THROUGH-HOLE EOMETRICS: Carol Handwerker, Ursula Kattner, Bill Boettinger, NIST, 223/A153, Gaithersburg, MD 20899; Chris Bailey, University of Greenwich, Wellington Street, Woolwich, London SE18 6PF
Separation of the solder fillet from the circuit board pad along the solder-intermetallic interface has been observed for a wide range of lead-free solder alloys. The tendency for such separation depends on a number of factors, including solder composition, the freezing range (also known as the pasty range), the mechanical properties of the solder, and the interfacial toughness. The processes leading to fillet-lifting will be described and the potential for eliminating this problem in lead-free alloys will be discussed.
2:30 pm INVITED
CONCLUSIONS OF THE NCMS LEAD-FREE SOLDER DEVELOPMENT PROJECT: Duane Napp, NCMS, 3025 Boardwalk, Ann Arbor, MI 48108-3266
A summary of the completed 4 year study of lead free solder alloys will be presented. In addition to toxicological considerations it was critical to define and agree on the factors and the methodology used in the down selection of 79 alloys to 7 promising alloys. It was necessary to conduct a manufacturing evaluation of compatible surface finishes and generate manufacturing process parameters necessary to assemble test hardware. The results of the extensive reliability evaluations and the modeling of the final down selected alloys will be presented. Follow-on NCMS material interconnect projects will be discussed.
3:00 pm INVITED
HIGH TEMPERATURE FATIGUE RESISTANT SOLDER - A NCMS PROJECT: Duane Napp, NCMS, 3025 Boardwalk, Ann Arbor, MI 48108-3266
To address the critical issue of placing electronic assemblies in extreme temperature environments that exceed the operating temperatures of commonly used eutectic Sn-Pb solder or high-Pb content alloys, National Center for Manufacturing Sciences (NCMS) initiated a national consortium in 1996 titled "High Temperature Fatigue Resistant Solder Project". The project objective is to demonstrate and deploy the technology to substantially improve the performance of solder joints at elevated temperatures under thermal cycling conditions. Two types of solder are to be developed: one with a performance objective of up to 160C, "Alloy 160", for organic substrate; and a second alloy with a performance objective of 205C, "Alloy 205", for ceramic substrate, copper die bonding substrates, and hybrid technology. The goal is to demonstrate a thermal fatigue resistance that, in the respective temperature ranges, is equal to or better than that of conventional solders. The need for these new alloys is being driven by the automotive, telecommunications, avionics, and military industries. The project is organized into four task groups with five phases of work, and extends over a period of 33 months. The participants include automotive and military companies, solder suppliers, academic institutions, and national laboratories.
3:30 pm BREAK
3:50 pm INVITED
MICROSTRUCTURE AND PHASE EQUILIBRIA IN THE Ag-Cu-Sn TERNARY SYSTEM: M.R. Notis, Department of Materials Science and Engineering, Lehigh, University, 5 East Packer Ave., Bethlehem, PA 18015
The Ag-Cu-Sn system is of interest for use in Pb-free solder alloys, brazing alloys, and in alloys for dental applications. The nature of the invariant reactions in the Sn-rich corner remain in question, and little is known about the effect of Cu addition on the width of the Ag3Sn phase field and its adjoining two- and three-phase fields at lower temperatures. A series of alloys were prepared and studied by metallography and by thermal analysis in order to elucidate these aspects of the Ag-Cu-Sn system.
4:20 pm INVITED
TAPE AUTOMATED BONDING (TAB) TECHNOLOGY FOR CHIP INTERCONNECTIONS: Sung K. Kang, IBM T.J.Watson Research Center, P.O.Box 218, Rm 37-250, Yorktown Heights, NY 10598
Tape automated bonding (TAB) technology has been widely used in low-cost consumer products as well as in high-performance multichip modules. TAB technology facilitates the chip-on-board (COB) assembly scheme in most applications. In this talk, two key issues of TAB technology, wafer bumping and inner lead bonding, are reviewed in conjunction with COB applications. Bumping refers to the process of adding raised metal contacts to bond pads in order to provide both the necessary bonding metallurgy for chip-to-lead bonding and a physical standoff to prevent lead-chip shorting. This is done on a wafer or on a TAB tape. Various bumping processes in use are discussed in terms of bump materials/processing, structure, geometry, bump properties and behavior during bonding.
4:50 pm
MONTE CARLO SIMULATION OF STEP COVERAGE OF COPPER: Y.G.Wang, X.W.Zhou, R.A.Johnson, H.N.G.Wadley, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903
A new Monte Carlo procedure for atomistically simulating physical vapor deposition processes is developed and used to model the two-dimensional physical vapor deposition of the step coverage of copper. The method consists of an implant approximation for the initial adatom adsorption on a surface and a multipath diffusion analysis to simulate subsequent surface morphology and interior atomic structure evolution. An embedded atom method is used to determine the activation energies for each of the many available diffusion paths. The method has been used to predict the morphology/structure evolution of copper films over the length and time scales encountered in practical deposition processes. The modeling approach has enabled determination of the effect of vapor processing variables such as flux orientation, deposition rate, substrate temperature, kinetic energy and aspect ratio on deposit morphology/microstructure and step coverage behavior.
5:10 pm
PEEL STRENGTH IN A Cu/Cr POLYIMIDE SYSTEM: I. S. Park, Jun Yu, Department of Materials Science and Engineering, KAIST, P.O. Box 201, Cheongryang, Seoul, 130-650, Korea
The adhesion strength of a metal film on a substrate is usually measured by the Peel Test. This test is not a direct measure of the interfacial energy because of the severe plastic deformation of the metal film accompanying the test. In the present analysis, using the Cu/Cr/polyimide system, the surface energy was deduced from the peel strength measurements and corresponding elasto-plastic analysis of the peel test. The metal/polyimide interface energy was varied by changing the pretreatment condition of the polyimide surface in Ar(+) RF plasma, and the adhered film thickness and yield stress were varied by changing the electroplating conditions. After the peel test, the chemistry of the Cr/polyimide interfaces were studied by AES and XPS.X-ray measurements of the residual strain in the peeled films were very useful in estimating the plastic work expenditure accompanying peeling. Results indicate that the deduced interfacial fracture energy is usually much smaller than the peel strength and is influenced by the RF pretreatment, but the interfacial energy is independent of the mechanical properties of the metal film, as expected.
Room: 232B
Session Chairperson: J.K. Shang, Department of Materials Science and Engineering, University of Illinois, Urbana, IL 61801
DAMAGE TOLERANCE IN BRITTLE MATERIALS: R.O. Ritchie, Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720
A critical factor in the design of advanced materials for structural application is the development of sufficient damage tolerance, i.e., resistance to fracture and subcritical crack growth in the presence of pre-existing flaws. In practical terms, this implies designing microstructures with adequate fracture toughness based on toughening mechanisms that are resilient to cyclic loading, and where appropriate elevated temperatures and adverse environments. In this presentation, such considerations will be reviewed for a number of "low ductility" advanced materials, including ceramics (Si3N4, SiC) and intermetallics (g-TiAl, MoSi2, Nb3Al) in the form of monolithic, composite and layered materials.
2:30 pm
PROCESSING, MECHANICAL BEHAVIOR, AND MICROSTRUCTURAL CHARACTERIZATION OF LIQUID PHASE SINTERED INTERMETALLIC-BONDED CERAMIC COMPOSITES: C.B. Thomas, P.K. Liaw, Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996-2200; T.N. Tiegs, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115
Intermetallic-bonded ceramic (IBC) composites with various amounts of a WC or TiC carbide phase mixed with a Ni3Al or FeAl binder phase were successfully fabricated by liquid phase sintering and hot isostatic compaction methods. The influence of carbide type, binder type, and binder content on the flexural strength, hardness, fracture toughness, and corrosion resistance of IBC composites was investigated. Experimental techniques used to characterize the mechanical behavior included Vickers hardness, four-point flexure at 25 and 800°C, indentation fracture, indentation strength, and mass loss corrosion testing. In addition, the microstructure was characterized using optical and scanning electron microscopy to examine the polished and etched microstructures, the cracks located at the corners of the hardness indents, and the fracture surfaces produced by flexure testing. Correlations were made between the mechanical properties of flexural strength and hardness and the microstructural parameter of contiguity. Experimental results indicate that the strength of IBC composites with Ni3Al at 800°C compares favorably to the room-temperature strength. At 25°C, plastic deformation of the Ni3Al and FeAl binders occurs, but the strength of the composite with FeAl is higher due to strong bonding along the carbide-binder interfaces. WC-based composites yielded higher flexural strength and fracture toughness values, while TiC-based composites produced higher hardness values. Increased binder amounts produced higher values of flexural strength and fracture toughness due to a reduction in the number of carbide-carbide interfaces and an increase in plastic deformation in the crack-tip region, respectively.
3:00 pm
INTERFACIAL SLIDING ALONG SOLDER/INTERMETALLIC INTERFACES: C. Zhang, D. Yao, J.K. Shang, Department of Materials Science and Engineering, University of Illinois, Urbana, IL 61801
Intermetallic cells formed during reactive wetting of metal substrates often lead to a microcellular interface morphology. Evidence is given of interfacial sliding as the crack grows, along these interface, subcritically at very low strain energy release rates under cyclic loading. Physical model was constructed to capture the salient aspects of the interfacial sliding mechanism. The model predicted that the crack shielding should arise from interfacial sliding and the magnitude of the crack shielding depended on loading-mode, roughness of the interface, and sliding resistance of the interface. Experiments designed to test the validity of the model will be described and comparisons will be made between model predictions and experimental results.
3:30 pm BREAK
4:00 pm INVITED
MICROMECHANISMS OF CRACK-TIP DEFORMATION AND TOUGHENING TITANIUM ALUMINIDES IN INTERMETALLICS: W.O. Soboyejo, C. Mercer, Department of Materials Science and Engineering, The Ohio State University, 2041 College Road, Columbus, OH 43210-1179; P.B. Aswath, Materials Science Program, Department of Mechanical Engineering, The University of Texas at Arlington, P.O. Box 19301, Arlington, TX 76019
The micromechanics of crack-tip deformation and toughening are elucidated for a range of 2- and -based titanium aluminides. Crack-tip deformation is shown (via crack-tip transmission electron microscopy) to occur by a combination of microcracking and slip under cyclic loading. Toughening mechanisms in 2-based alloys (crack-tip blunting, bridging, deflection and microcrack shielding/anti-shielding) are also modeled using micromechanics. Similarly, the crack tip deformation and toughening mechanisms in gamma-based titanium aluminides (deformation-induced twinning and slip) are elucidated for a range of experimental and near commercial alloys. Micromechanical models are also presented for the prediction of toughening in gamma alloys. The paper shows clearly that crack-tip shielding mechanisms do not necessarily result in slower fatigue crack growth rates.
4:30 pm
SHEAR LIGAMENT TOUGHENING AND MICROMECHANICAL MODELLING IN IRON ALUMINIDE INTERMETALLICS: Scott X. Mao, Department of Mechanical Engineering, University of Calgary, Calgary, Canada T2N 1N4
The fracture behavior of an iron aluminide intermetallica in air environment was studied. At room temperature, round tensile specimens were tested at different strain rates. By carefully examining the lateral surface of the tensile specimens, ligament-like structures that connected between microcracks were found. SEM pictures show that these structures, which can be called shear ligments, undergo ductile fracture by shearing. This type of fracture dissipates more energy and was believed to enhance the fracture toughness of the material. By use of a micromechanical model of shear ligment toughening, fracture toughness of the material, K, was estimated at different strain rate. The values of critical parameters, which are ligment length, area fraction and work to fracture by shear were obtained from SEM observations on different tensile specimens. K was found to be decreased towards lower strain rates. This strain rate effect was similar to that obtained experimentally. This outcome verified the importance of shear ligments in determining the materials fracture toughness.
5:00 pm
MICROMECHANISMS OF CRACK-TIP DEFORMATION IN ZIRCONIA TOUGHENED INTERMETALLICS: F. Ye, G-Y. Lu, P. Ramasundaram and W.O. Soboyejo, Department of Materials Science and Engineering, The Ohio State University, 2041 College Road, Columbus, Ohio 43210-1179
The micromechanisms of crack-tip deformation will be elucidated for zirconia toughened nickel aluminide and molybdenum disilicide intermetallic composites reinforced with partially stabilized zirconia particles with different particle sizes. The transformation toughening components associated with different stabilizers (ceria, magnisia and yttria) are also quantified using micromechanics models and experimental results obtained from laser Raman spectroscopy and optical interference analyses. Shielding contributions from other applicable toughening mechanisms are also discussed. Stable fatigue crack growth in zirconia toughened intermetallics is attributed to the effects of kinematic irreversibility due to stress-induced martensitic transformations under cyclic loading. The relative contributions from microcracking and slip phenomena (to kinematic irreversibility) are also discussed.
Room: 230D
Session Chairperson: David G.C. Robertson, Center for Pyrometallurgy, Univ. of Missorui-Rolla, Rolla, MO 65401
A TWO-LIQUID SLAG MIXING EXPERIMENTAL TECHNIQUE FOR STUDYING THE OXIDATIVE PRE-FUMING TREATMENT OF LEAD BLAST FURNACE SLAG: Adrian Deneys, David Robertson, and Nick Schupp Center for Pyrometallurgy, University of Missouri-Rolla Rolla, MO 65401
An experimental technique has been devised for studying the reaction kinetics of the homogeneous, liquid phase reaction: ZnO+FeO = Zn(g)+Fe203, by which zinc evolution can occur from a molten Al203-CaO-FeO-Fe203-SiO2-ZnO bath in the absence of a carbonaceous reductant. When studying the reaction kinetics by heating from room temperature, solid state reactions and poorly defined melting points may obscure the starting point of the reaction. In order to eliminate this problem, an experimental technique was devised whereby two molten slags could be melted independently, and then mixed, to provide a well defined starting point from which to begin taking measurements. Two crucibles were mounted in a vertical reaction cylinder. The upper, mild steel, crucible had a bottom pouring plug which was sealed by a steel stopper rod. A fayalite mixture was contained in this crucible. The lower crucible contained an Al203-CaO-SiO2-ZnO mixture. Once the two slags had been melted, the steel stopper rod was removed from the upper crucible. The upper, reduced slag (fayalite in equilibrium with the upper steel crucible), drained into the lower crucible where the two slags were mixed by submerged argon stirring. Dip samples were taken to measure the zinc content of the final mixture as a function of time. The experimental procedure will be described, as well as results of experiments which were conducted on synthetic slags. The system investigated was similar to the lead blast furnace slag which is produced by the primary lead smelters of Missouri, USA.
2:20 pm
QUENCH DROSSING OF LEAD BULLION:: Funsho K. Ojebuoboh, Asarco Inc., Technical Services Center, 3422 South 700 West, Salt Lake City, UT 84119
New technology has been developed for drossing lead bullion. The technique was developed to replace conventional copper drossing, so-called rough crossing, performed in kettles. With quench drossing, water granulation of bullion exiting the smelting furnace, usually above 900°C (1700°F), is used to arrest equilibrium formation of the dross species. The process is based on granulating lead bullion from the furnace, thereby quenching the bullion, and subsequently sweating lead off the granules in a rotary kiln furnace. The major benefit of the new technology is expected to be reduced air-borne lead which is normally associated with conventional drossing. The process also has the potential of making lead crossing metallurgy more susceptible to better process control. The process and its development are described.
2:40 pm
RECYCLING OF MAGNESIUM ALLOY SCRAP, A NECESSITY: Christine Brassard, Lisabeth Riopelle, Oddmund Wallevik, Hydro Magnesium Market Development Center, 21644, Melrose Avenue, Southfield, MI 48075-9705
The use of magnesium alloys is growing rapidly, particularly in die cast parts for the automotive industry. Supporting this growth in the future means that Mg has to be an economically and ecologically attractive material, and recycling of alloy scrap becomes a necessity. What kinds of magnesium scrap will be on the market? What are the opportunities and challenges for this emerging recycling industry? Different recycling processes have been developed, and operation facilities are today recycling large volumes of class 1 diecast returns based on a flux refining technology. Characterization of the recovered metal demonstrates that the performance of appropriately recycled magnesium alloy is comparable to an alloy made from primary electrolytic metal. The sludge generated from this process can also be recycled through the existing primary Mg operations in order to close the environmental loop.
3:00 pm
THE REACTION MECHANISM OF OXIDIZED CHALCOPYRITE CONCENTRATE PARTICLES AND COPPER MATTE WITH IRON SILICATE SLAG: K. Fagerlund1, P. Nurrni1, H. Jalkanen1, P. Taskinen2, 'Helsinki University of Technology, Laboratory of Metallurgy, Vuorimiehentie 2, FIN-02150 Espoo Finland; 2Outokampu Research Oy, P.O.BOX 60, SF-28101 Pori, Finland
The reaction mechanism and settling behaviour of oxidized chalcopyrite particles and coppper matte droplets introduced into synthetically prepared fayalite type slag under nitrogen and argon atmosphere have been investigated in this work. As a part of the investigation into flashsmelting reaction phenomena in a settler region, a laboratory experiments were conducted by means of a X-ray image system and a vertical tube furnace. The reaction phenomena of oxidized chalcopyrite in iron silicate slag was studied in a tube furnace, temperature being 1300°C, and inert gas flow (N2). The partly oxidized samples of chalcopyrite were blown into synthetic fayalitic slag. Reaction products were studied and analysed using light optical microscope (LOM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and chemical methods. Industrial copper matte and oxidized chalcopyrite were introduced into iron silicate slag. The melting and settling behaviour, the variation of the copper matte droplet shape and the movement of melting interface were continuously monitored by X-ray image system.
3:30 pm BREAK
3:40 pm
MELTING OF HIGH PURITY CHROMIUM: Raymond K.F. Lam, Giuseppe Colella, Materials Research Corporation, 542 Route 303, Orangeburg, NY 10962
Unacceptable levels of impurity were noted from high purity chromium melting operation. Analysis of past chromium melting determined that total oxygen content was the critical parameter. Thermodynamic analysis of oxides and liquid chromium was presented. Acceptable operating conditions were identified. A new process of melting high purity chromium with oxide addition for controlling the activity of Cr2O3 was recommended. Experimental results of the new melting process were presented.
4:00 pm
ADVANCED NON-FERROUS SCRAP MELTER: J.S. Becker, J.F. Heffron, R.J. Hewertson, E. Keith Riley, Air Products and Chemicals, Inc., 7201 Hamilton Boulevard, Allentown, PA 18195-1501
Technology developed and first implemented in the United Kingdom enables very low grade non ferrous scraps containing sils, organics, plastics and ferrous metals to be directly charged, without pretreatment, into a unique melting furnace. Two furnaces have been in full scale production for over four and two years, respectively. A third furnace was only recently commissioned. The oxy-fuel-based furnace design incorporates internal afterburning in the furnace's hot zone, producing excellent thermal efficiency and very low emissions. Advanced process control insures complete combustion of all volatiles in an environment that is not oxidizing to the melt. Thus metal yields have been excellent. The furnace is very low in Nox. This paper will provide both theoretical background and extensive operating results for this new melting concept. Applications describing both purpose built new furnaces and retrofits of existing reverberatory furnaces will be presented. Extensive operating emissions data will be presented.
4:20 pm
OXYGEN ENHANCEMENT OF BURNERS FOR IMPROVED PRODUCTIVITY: D.J. Krichten, W.J. Baxter, C.E. Baukal, Air Products and Chemicals, Inc., 7201 Hamilton Blvd., Allentown, PA 18195
A method of retrofitting air-fuel burners with oxy-fuel capability overcomes the potential problems associated with oxygen combustion in aluminum melting furnaces. Several years of operation in rotary furnaces reclaiming dross and UBC scrap and since 1993 in revereratory furnaces prove the usefulness of the retrofit approach. The retrofit burner uses the existing combustion air connection, burner housing, and burner tile and replaces the gas tube with an oxy-gas burner. Maintaining a portion of the air flow to the burner reduces the potential for localized overheating. This technique optimizes the mix of air and oxygen to the burner for the given furnace geometry and meltrate desired. Proper design of the burner reduces Nox emissions by moderating the flame temperature with furnace gas recirculation. Economic analysis of using merchant oxygen shows the benefits are increased productivity and reduced overall unit cost of melting. In practice, the melt rate in rotary furnaces increases by up to 50% and by up to 35% in reverberatory furnaces. Oxygen enhancement reduces melting cost by 1/23/4 cents per pound of aluminum melted.
4:40 pm
THE REDUCTION BEHAVIOR OF HEMATITE COMPACTS BY H2 and H2-CO GAS MIXTURES: I.J. Moon, C.H. Rhee, Materials Science & Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea
The reduction behavior of hamatite by H2 and H2-CO gas mixtures was investigated to elucidate the reduction mechanism at 1073~1223K. The hetatite compacts were made by Cold Isostatic Pressing to produce compacts of uniform shape and size. The compacts were sintered at 1273K for 30 min., and showed a contraction of 29%. Mercury pressure porosimeter and BET technique were used for measuring the total porosity, pore size distribution and pore surface area of the compacts. Reduction was followed up by means of weight-loss technique using Cahn Balance (Model: TG-171, capacity 10g, accuracy ± 10 µg.) Microscopic examination (SEM, EPMA), X-ray, and carbon analysis were used to correlate the structure of reduced compacts with the mechanisms of reduction and carbon deposition. The values of apparent activation energy for H2 reduction were between 11.21 kcal/mol and 14.38 kcal/mol. Structural changes, kinetics, and mechanisms of reduction and carbon deposition with H2 and H2-CO gas mixtures is discussed.
5:00 pm
MECHANISM OF NB TRANSFER TO HOT METAL FROM SLAG: Fan Peng, Yang Tianjun, Zhou Yusheng, Dong Yicheng, Wei Shoukun, Sichuan Union University, P.O. Box 373, Chengdu, Sichuan, 610065, China
Nb-bearing iron ores are today the most significant source of niobium in China. Ferroalloy of Nb, as the main product of Nb recovered from Nb-bearing iron ores, is recently produced by the following route. Nb-bearing iron concentrate is reduced in a blast furnace to generate Nb-bearing hot metal, which is then smelted in a converter to yield Nb-enriched slag. Finally Nb- enriched slag is reduced in an electric furnace to get ferroalloy of Nb. In order to improve the recovery ratio of Nb, it is important to acquire a deep understanding on how Nb is transferred to hot metal from slag. In the present work, raw material containing niobium oxide were carbothermally reduced under the conditions of calm metal-slag interface or stirred metal-slag interface, respectively. Under the former condition, the quenched samples were found through SEM observations that NbC layer occurred at the metal-slag interface. In this case, Nb transfer to hot metal from slag slows down and the rate controlling step is Nb diffusion in NbC layer. Under the later conditions, it was found that no NbC layer occurred at the metal-slag interface, indicating that NbC formed at the interface sunk into hot metal due to the higher density of NbC than that of hot metal. In this case, the rate controlling step is Nb diffusion in slag.
Room: Salon 8
Location: Clarion Plaza Hotel
Session Chairperson: Charles O. Bounds, Rhone-Poulenc Rare Earths and Gallium, Cranbury, NJ 08512; Danesh Chandra, Dept. of Chemical and Metallurgical Engineering, University of Nevada, Reno, NV 89557
SURFACE FILMS ON MmNi.5.5Co0.8Al0.7 ELECTRODES IN 30% KOH THEIR IMPACT ON HYDROGEN STORAGE CAPACITY AND REACTION RATES: M.E. Fiorino, Bell Laboratories, Lucent Technologies, Whippany, NJ 07981; R.L. Opila, Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974; K. Konstadinidas, Bell Laboratories, Lucent Technologies, Norcross, GA 30071, W.C. Fang, Utmost Industrial Corp., Taipei, Taiwan, China
Misch metal based intermetallics are currently employed as reversible hydride-forming electrodes in Ni - Metal Hydride batteries with 30% KOH electrolyte. In spite of the thermodynamic instability of rare earths in this medium, these electrodes retain storage hydrogen ability and support rapid electron transfer for hundreds of hydriding-dehydriding cycles. Results of electrochemical and XPS studies of one such intermetallic MmNi3.5Co0.8Al0.7, have led to the development of a model to explain these properties.
2:00 pm
THERMAL AGING OF LaNi5-xMnx HYDRIDES: S. Bagchi, D. Chandra, W.N. Cathey, University of Nevada, Reno, NV 89557-0136 USA, R.C. Bowman Jr., Aerojet Electronic Systems, P.O. Box 296, Azusa, CA 91702; F. E. Lynch, Hydrogen Consultant Inc., 12420 N. Dumont Way, Littleton, CO 80125
The Joule-Thomson expansion of hydrogen gas offers a method to produce temperatures below 30K for use in cryocollers in space surveillance satellites. Metal hydrides are a critical components of these devices, providing a non-mechanical method to compress the hydrogen gas. The LaNi5-xMnx-hydrides have potential applications in cryocooling devices: Luo and coworkers1 presented detailed studies on their hydriding behavior. In this study, thermal aging behavior of two LaNi-5-xMnx-hydrides (x=0.4, and 1.5) was investigated to evaluate its long term stability. The hydriding behavior of La1.02Ni4.6Mn0.4 did not change significantly after thermal aging at 453K for 260 hours.
2:30 pm
EFFECT OF RARE EARTH SUBSTITUTIONS FOR La ON THE HYDROGEN ABSORPTION OF La-BASED AB5 ALLOYS: C.O. Bounds, B.M. Ma, J. Patel, Rhône-Poulenc, Rare Earths and Gallium, CN 7500, Cranbury, NJ
The performance of Ab5-type alloys for hydrogen absorption including the electrochemical absorption as an electrode for rechargeable batteries has been demonstrated to be a complex function of the composition, microstructure and surface condition. The compositional studies have focused primarily on substitutions for Ni on the B-site (e.g. Co, Al, Mn, etc.). This current study examines the effect of rare earth substitutions for La on the A-site and considers both other "light" rare earths (Ce, Nd, Pr) and "heavy" rare earths (Dy, Sm, etc.).
3:00 pm BREAK
3:30 pm
GAS-PHASE HYDROGENATION PROPERTIES AND ELECTRODE PERFORMANCE OF La(Ni,Al,Co,V)5 ALLOYS: L.-C. Lei, S.-U. Liu T.-P. Perng, Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, 30043
A series of LaNi5-based alloys, with partial substitution of Ni by Al, Co, or V, were prepared. The gas-phase hydrogen absorption kinetics and pressure-Composition-temperature curves were measured. The activation became easier and the plateau pressure was reduced as Ni was partially substituted by Al. Substitution with Co reduced the hysteresis as well as the hydrogenation capacity. Less degradation of hydrogenation capacity after long cycles of hydriding- dehydriding was observed when substituted with both Al and Co. Vanadium is often considered as a hydride former, but when it was added to LaNi5 it was found that V occupied the B site. A small amount of substitution of Ni with V led to a higher hydrogenation capacity and faster activation rate.
4:00 pm
ATOMIZATION PROCESSING EFFECTS ON HYDRIDING BEHAVIOR OF AB5 ALLOYS FOR BATTERY APPLICATIONS: R.C. Bowman, Jr., C. Witham, B. Fultz, California Institute of Technology, Pasadena, CA 91125; B.V. Ratnakumar, Jet Propulsion Laboratory, Pasadena, CA 91109; T.W. Ellis, Kulicke and Soffa Industries, Inc., Willow Grove, PA 19090; I.E. Anderson, Ames Laboratory, Ames, IA 51122
Hydriding characteristics of some AB5 alloys produced by high pressure gas atomization (HPGA) were examined during reactions with hydrogen gas, and In electrochemical cells. Hydrogen storage capacities and equilibrium pressures for HPGA LaNi5, LaNi4.75Sn0.25, and MmNi3.5Co0.8Al0.4Mn0.3 were nearly identical to cast alloys after extensive annealing. The large discontinuous volume change across the alpha-beta plateau region for HPGA LaNi5Hx produced extensive fracturing in all but the smallest alloy spheres.
4:30 pm
NEW ANISOTROPIC RARE EARTH LASER FLUORIDES BaR2F8(R=Y,Dy-LU): GROWTH AND CHARACTERIZATION: Alexander A. Kaminskii, Andrei V. Butashin, Institute of Crystallography, Russian Academy of Sciences, Leninskii prosp. 59, 117333, Moscow, Russia
Anisotropic fluoride crystals doped with Ln3+ ions have attracted a great interest of investigators as effective active materials for designing multi-wave crystalline lasers, which emit stimulated emission (SE) in the unique number of the 4fN4fN and 4fN-15d14fN manifold-to-manifold transitions in UV, visible, and IR spectral ranges. Among them BaR2F8 crystals are distinguished by their Congruent melting at 
950°C, good capacity to dissolve activator Ln3+ ions, wide transparency ranging from VUV to far IR, birefringence and short phonon spectra.
Room: 314A
Session Chairpersons: Professor James A. Joyce, Department of Mechanical Engineering, U.S. Naval Academy, 590 Holloway Road, Annapolis, MD 21402; Professor Ronald W. Armstrong, Department of Mechanical Engineering, University of Maryland, College Park, MD 20742
DETERMINING THE J-CRACK GROWTH RESISTANCE BEHAVIOUR OF A DUCTILE MATERIAL: Edward Smith, Manchester Materials Science Center, Manchester University and UMIST, Grosnover Street, Manchester M1 7HS, UK
Ductile fracture has been the major theme of Frank McClintock's research career. This paper is concerned with the determination of a ductile material's crack growth resistance behaviour when it is expressed in terms of the deformation J-integral JD. Attention is focussed on the determination of the crack growth resistance curve from load, load-point displacement and crack extension measurements using single loaboratory test specimen. A commonly used procedure is based on the separation of JD into an elastic component JE and a plastic component JDP, and the ability to express JDP for a non-growing crack in terms of the plastic energy integrals via eta factors that are independent of the applied loadings. The paper highlights the conditions which must be satisfied for JDP to be expressed in this way, and the limitations of some currently used practices based on this JDP formulation are indicated. Against this background, the author reviews his "two extremes" procedure, whereby the appropriate eta factors are obtained by ensuring that JDP assumes the correct form at the two extreme levels of deformation: small-scale yielding and extensive deformation at limit load conditions. Determination of the eta factors requires only a knowledge of the stress intensity factor and the limit load solutions, and not the material flow properties. The "two extremes" procedure is validated by comparing its predictions with well documented results for specific geometrical configurations. However, the procedure can be applied to any geometrical configuration, and the paper provides some examples.
2:25 pm INVITED
PREDICTING THE DUCTILE-TO-BRITTLE TRANSITION IN NUCLEAR PRESSURE VESSEL STEELS FROM CHARPY SURVEILLANCE SPECIMENS: James A. Joyce, Department of Mechanical Engineering, U.S. Naval Academy, 590 Holloway Road, Annapolis, MD 21402
One important application of elastic-plastic fracture mechanics has been to assure the structural integrity of nuclear reactor pressure vessels. Present toughness requirements are based on the postulation of a large defect size, the use of dynamic test data to give lower bound toughness values, and the use of safety factors on the allowable stresses. As vessels have aged the material toughness has degraded and the ductile-to-brittle transition has shifted toward the vessel operating temperature. Extrapolating this process means that many existing vessels will not meet the present toughness requirements well before the end of their design lives. The need to superimpose multiple safety factors, as is presently done has thus been questioned, and much recent research has been directed toward lessening the toughness requirements while maintaining a high level of structural integrity. The situation remains difficult, however, at least in part because only Charpy specimens are available as surveillance specimens for many commercial reactor vessels, and these specimens are too small to obtain any type of "valid" fracture toughness information using standard ASTM methods. Presently a lower bound KIR toughness curve is shifted relative to reference temperature RTNDT and used to define the ductile-to brittle transition. The RTNDT is thus a very critical value, and difficulties have arisen because of the wide variability that can result in its estimation. Recent work by ASTM Committee E08 has proposed a method to obtain a new reference temperature and a method to define using a probabilistic approach, a median ductile-to-brittle transition curve from a set of six properly tested small samples which would in many cases be precracked Charpy specimens. This method seems to be very robust, predicting a reference temperature with small variability. From the results of these specimens a "master curve" can be developed defining the median ductile-to-brittle transition curve as well as statistical confidence bounds. This curve is plant specific and could be used to assure that the pressure vessel had adequate toughness for continued operation. This paper presents a large data set on two pressure vessel steels, A515 and A533B, obtained to investigate the newly proposed ASTM test method. Data is available on a large number of precracked Charpy specimens, as well as data on standard IT C(T) and SE (B) specimens. Additional data is also available on large specimens, specimens with shallow cracks (a/W = 0.1), and surface cracked geometries tested in tension, bending, and combined tension and bending. Most specimens demonstrated cleavage failure - in some instances after significant amounts of ductile crack extension. Since the data sets are not presently complete, how well the new procedure fares cannot be determined. The applicability of constraint quantification and correction techniques that are presently being developed separately by this project will be included in the final analysis. The comparison of the large and small specimens, the surface cracked and through cracked specimens, and the predominantly bend and tensile loadings should allow a clear determination of the value of the new proposed ASTM "master curve" approach.
2:50 pm INVITED
A COMMON FORMAT APPROACH FOR APPLYING DUCTILE FRACTURE MECHANICS: John D. Landes+ and J. R. B. Cruz*, +Department of Mechanical and Aerospace Engineering, University of Tennessee, Knoxville, TN 37996; IPEN, *São Paulo, Brazil (on leave to the University of Tennessee)
Applications of ductile fracture mechanics methods to prediction of structural behavior can be done using numerical or analytical methods. Numerical methods can be more accurate but are often beyond the capability of ordinary engineering organizations. Also the result may have relevance only to the specific structure being analyzed. Analytical methods have often used a failure diagram approach in which the failure load of a structure can be estimated. A ductile fracture methodology proposed by Landes, et. al. took the load versus displacement for a laboratory specimen and through a series of analytical steps predicted the load versus displacement behavior for a structural component. The prediction could be made for any geometry where the information on limit load, and the calibration of fracture parameters was available. This prediction gave a more complete information in that both the maximum load could be determined as well as the stability of the structure after maximum load. The prediction of the loading behavior during ductile fracture depends on the deformation behavior of the structure and the cracking behavior, usually the former is the more important. The ductile fracture methodology uses a principal of load separation proposed by Ernst in which the loading of a cracked body can be specified by separate but multiplicative functions, one of geometry, that is cracking behavior, and one of deformation. The load versus displacement for the specimen is separated into two functional behaviors, a transfer is made for these functions from the specimen geometry to the structural component geometry and two functions are combined to predict load versus displacement of the structural component. The entire procedure could be completed with a hand calculator. Since the first proposal of this ductile fracture methodology, additional work has been done on the determination of the deformation behavior for the structural component. Donoso, et. al. showed that deformation behavior of any structural component, including test specimens geometries, can be derived from the basic stress-strain behavior of the material. With this the deformation behavior of the component can be determined from that of the specimen using common functional expressions with similar constants, ones that be determined from the stress-strain behavior and transferred to any common geometry with a set calibration factors that pertain to that geometry. This approach was labeled, the "common format" approach. Using this "common format" approach the ductile fracture methodology was revisited to see if the procedure could be simplified using the calibration factors to transfer from one geometry to another, namely from test specimen to structural component. This paper describes the result of that study. What was found was that the 'common format' calibration factors can be used to transfer the load factors based on material stress. However, a difficulty rose with the transfer of strain factors. The relation of the structural displacement to strain behavior is sensitive to the type of displacement being measured, that is placement of the gage, and gage length. In order to complete an easy transfer of specimen deformation characteristics to the structural component, strain calibration factors need to be determined. With the development of these, the procedure in the ductile fracture methodology can be made easier and application of ductile fracture mechanics greatly facilitated.
3:15 pm BREAK
3:25 pm
A NEW MODEL TO CALCULATE THE CRACK EXTENSION: Inhoy Gu, Department of Mechanical Engineering, Chung-Ang University, Seoul 156-756, South Korea
A fracture analysis method is proposed on the criterion that the resistance to crack extension can be characterized in the critical CTOA, an instantaneous ratio of CTOD increment to stepwise crack extension. The CTOD of finite element analysis is written in a function of crack length and applied stress for the load range up to near the limit load. The normalized CTOD function for the compact specimen is independent of crack length ratio with some conditions, under which the function can be used in the crack-extension analysis. After crack initiation, the CTOD increments due to a load increment and a crack increment are successively calculated to determine another crack extension, with their integrations during the stable crack growth. The calculations are made to fit to the tests of effective crack lengths by appropriate fracture constants. The cleavage fracture mode is characterized in the crack growth without crack opening. The total CTOD for the cleavage fracture of Al 7075-T651 increases a little as the specimen size increases greatly. Thus the cleavage fracture may occur with a rising load in big specimens and with a falling load in small specimens. The critical CTOA for the ductile fracture of Al 2024-T351 decreases with an increasing specimen size. The size-corrected fracture constants are applied to calculate the failure loads on other compact and center-cracked specimens, in good agreement with the available test loads. The fracture-predicting capability of the proposed method seems promising from cleavage to ductile fracture modes regardless of crack extension, probably, except the limit-load fracture. Therefore, the fracture constants may account for specimen property as well as material property, and they are transferred between specimens.
3:50 pm INVITED
DUCTILE FRACTURE OF HIGH TOUGHNESS STEELS UNDER MULTIAXIAL TENSION: D. M. Goto, J.P. Bandstra, D. A. Koss, Department of Materials Science and Engineering, Penn State University, University Park, PA 16802; Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA 15904
The influence of stress state on ductile fracture is examined on the basis of both experiments and computational modeling. Using HY-100 steel as a model material, we examine the failure of notched tensile specimens in terms of the void initiation, growth, and linking process. Particular attention is given to the issue of void linking as a result of either global coalescence, which occurs at high stress triaxilities, or a localized void-sheet process, as is observed at high stress triaxilities. The void-sheet mode of linking is modeled on the basis of microstructural conditions present in the HY-100 steel with the result that the predicted influence of stress state agrees well with experimental observations. The transition to global void coalescence, and a much greater sensitivity of failure stress to stress state, is also addressed. This research was supported by the Office of Naval Research, the Naval Surface Warfare Center, and Concurrent Technologies Corporation.
4:15 pm INVITED
MIXED-MODE NON-LINEAR FRACTURE ALONG INTERFACES: John L. Bassani, N.J.-J. Fang, Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104
Recently, problems in interfacial fracture have led to a general interest in planar crack growth under mixed-mode loading. Of particular interest is the relationship between the applied stress intensity/mode-mix and the corresponding quantities near the crack tip. We have developed mixed-mode solutions of the HRR type and of the Hui-Riedel type for stationary and propagating interface cracks. In contrast, asymptotic and small-scale yielding solutions for the crack growth in a time-independent elastic-plastic material predict that the mode mix (tension versus shear) in the vicinity of the crack tip can only take on discrete values rather than varying continuously with the mode mix of the remotely applied elastic fields. In the case of a stationary interface crack or a growing creep crack in either homogeneous materials or along interfaces we have found crack-tip solutions which admit a continuous variation of mode mix within certain limits. Slip line solutions for stationary interface cracks have also been developed. These asymptotic solutions are in good agreement with small-scale-yielding finite element calculations that include the transient growth period.
4:40 pm
RECENT ADVANCES IN THE APPLICATION OF THE GURSON MODEL TO THE EVALUATION OF DUCTILE FRACTURE TOUGHNESS: Winfried Schmitt, D. -Z. Sun, J. G. Blauel, Fraunhofer Institut Werkstoffmechanik, Fraunhofer IWM Wöhlerstraße 11, D-79108 Freiburg, Germany
For many metallic materials the Gurson model modified by Needleman and Tvergaard describes the ductile rupture process characterized by nucleation, growth and coalescence of voids. Since these local processes are similar in smooth specimens and in cracked specimens, a material dependent critical volume fraction of voids, fc, may be determined from numerical analyses of tensile tests. However, because of the strong gradient in the stress-strain field at the crack tip an additional length parameter, lc, is required to model the coalescence process in cracked specimens. Since the effects of triaxiality are adequately taken into account in the model, fc and lc may be transferred to specimens with different shapes and sizes. Hence, it is possible to evaluate ductile fracture resistance curves for different geometries and loading conditions with the same set of micromechanical parameters. The authors have applied this local approach to ductile fracture for a series of ferritic and austenitic steels including weld materials even after neutron embrittlement. Besides notched and smooth tensile specimens of standard sizes also miniature specimens with diameter down to 2 mm have been used for the determination of fc. Dynamic effects have been taken into account based on dynamic tensile tests and visco-plastic formulation to model the strain-rate sensitivity of the stress-strain curves. The characteristic length is usually determined for small SENB-specimens. As examples, instrumented impact tests with SENB and Charpy specimens have been simulated using three-dimensional models.
5:00 pm
SUPERIMPOSED EFFECTS OF DSA AND NEUTRON-IRRADIATION ON MECHANICAL AND FRACTURE BEHAVIOR OF FERRITIC STEELS IN THE UPPER SHELF REGION: Rao K. Mahidhara1 and K. Linga Murty2, 1Tessera Inc., 3099 Orchard Drive, San Jose, CA 95134; 2North Carolina State University, P. O. Box 7909, Raleigh, NC 27695
It is now well established that radiation embrittlement of ferritic steels such as used for pressure boundary applications is sensitive not only to the alloying elements (Cu, Ni, P etc.) and interstitial impurities (IIAs) such as C and N, but also radiation flux and irradiation temperature. The increased strength and decreased ductility in the DSA region leads to reduced energy to fracture and this region usually lies in the upper shelf regime. This is also clearly evident in the elastic-plastic fracture toughness (JIC). While dips in the fracture energy are noted in steels, pure (Armco) showed peaks in this region apparently due to the increased rates of work-hardening. Exposure to neutron irradiation suppressed the effects of DSA leading to apparent increased energy values at temperatures where dips are noted in the unirradiated materials. Such tests on pure iron are in progress and results to-date will be reported here. Radiation effects on Hall-Petch relation are investigated in pure iron, and radiation exposure resulted in increased friction hardening and decreased source hardening which lead to interesting effects of thermal neutrons on radiation hardening of these materials.
5:20 pm
USE OF X-RAY TOMOGRAPHIC MICROSCOPY TO STUDY DUCTILE FRACTURE: Wayne E. King, G.H. Campbell, D.L. Haupt, J.H. Kinney, R.A. Riddle, W.L. Wien, Chemistry and Materials Science Directorate, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-9900
X-Ray tomographic microscopy (XTM) is a promising technique to investigate ductile fracture because voids formed under conditions of high triaxiality can be directly observed nondestructively. In this experiment, ultra high vacuum diffusion bonding has been used to make model specimens in the Al/sapphire system. Samples were prepared in the 4-point bend geometry with notch. XTM images acquired after several loadings of the sample revealed the morphology of the growing voids. The primary finds are that (i) damage ahead of the notch initiates by interface debonding at a location coinciding with maxima in triaxiality and tensile traction at the interface, (ii) debonding occurs at the most early stages in the observation of plasticity, (iii) the debond expands for a limited distance, likely arresting due to crack tip blunting, (iv) this lenticular debond then becomes spherical with further strain, and (v) intergrowth of the spherical voids leads to the typical ductile rupture fracture surfaces observed in the system. This work performed under the auspices of U. S. Department of Energy and the Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
5:40 pm
MICROPLASTICITY AND DUCTILE FRACTURE IN METALS: Wally O. Soboyejo, B. Rabeeh, J. Dipasquale, R. Pryor, Department of Materials Science and Engineering, The Ohio State University, 2041 College Road, Columbus OH 43210-1179
Recent evidence of microplasticity in ductile metals is presented for a range of ductile metals with cubic and hexagonal closed packed structures deformed to failure under monotonic loading. Microplasticity is shown to occur at very low stress levels (~5 - 10%) of the bulk stress. Microscopic of microplasticity evidence is shown to include: slip band localization via shear localization; grain boundary sliding; subgrain formation; deformation-induced precipitation; and localized flow mechanisms. Ductile fracture is shown to initiate by coalescence of voids that are nucleated around stress-induced precipitates. Deformation in the so-called elastic regime is shown to be associated with the spread of localized plasticity phenomena across the gauge. Linear plasticity concepts are used to explain the initial deformation characteristics. The implications of microplasticity are also assessed for fatigue damage initiation and ductile fracture initiation.
Monday-Thursday Room: 314A
Session Chairperson: Dr. R. K. Mahidhara, Tessera Inc., 3099 Orchard Drive, San Jose, CA 95134
A working out of nonlinear fracture mechanics criteria and application of calculation methods requires the availability of solutions to elastic-plastic crack problems. Such solutions depend on details of deformation behaviour of materials. For most cases the solutions must be computed numerically and that could be connected with some difficulties. Therefore, a working out of approximate analytical solutions is an actual problem. New analytical solutions relate J-integral to applied stress, notch (crack) geometry and strain hardening. The method is based on stress concentration analysis near a notch-crack tip in strain hardening solid. Approximate analytical J-solutions are calculated in accordance with the theoretical stress concentration factor formulas of Neuber for several crack configurations: elliptical notch in infinite plate, deep grooved shaft, deep double etch notch, shallow double notch in tension. The important role of J-integral is a measure of the intensity of the near-tip stress and strain that can be written in the form of the HRR-singularity. So, to assess J-dominance for fully plastic conditions the HRR-model and the method based on an equation of equilibrium was employed. It was assumed that (i) the characteristic size of the singularity is determined by the condition of the equality of the singularity stress and the applied stress, (ii) the force, that is not transmitted by the crack, is counterbalanced by the additional force of the singularity stress field depends strongly on the crack size and weakly on hardening. To predict the behaviour of a crack in ductile materials it is necessary to use non-linear fracture mechanics criteria. One such criterion can be associated with the failure assessment diagram (FAD) which merges the two extreme brittle fracture and plastic collapse. New FAD has been obtained from the energy balance taking into account crack tip blunting and difference between the energy of surface stresses and the surface energy. The present work assumes the relation between crack blunting and J-integral.
ESTIMATION OF DUCTILE FRACTURE TOUGHNESS FROM TENSILE TESTS FOR ENGINEERING APPLICATIONS: S.K. Ray, A.K. Bhaduri and P. Rodriguez, Fracture Mechanics Section, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India
An empirical method for characterizing the ductile fracture toughness using two parameter (viz., Gf and hf) that can be determined from tensile test data of smooth cylindrical specimens has been evolved for engineering applications by Ray, Bhaduri and Rodriguez (herein after referred to as the RBR method). This stipulates that the post-necking regime during tensile deformation is demonstrated by microvoid growth and coalescence processes, and therefore the energy absorbed in this regime can be used to estimate the resistance of the necked region to ductile fracture. The test procedure employed is simple, and does not require gauge-length extensometry. The test is carried out in a screw-driven machine at constant cross-head speed, with on-line deformation of the load train. The method of computing RBR parameters, Gf and hf from the tensile test data at ambient and elevated temperatures, is described.
With Wpn the energy absorbed by the specimen from necking to fracture and An the uniform cross-sectional area at the necking point, the parameters GfWpn/An estimates the average energy per unit cross-sectional area required to cause fracture. Also, with Af as the minimum cross-sectional area of the neck at fracture, ln(An/Af) measures the average longitudinal plastic strain perpendicular to the plane of the neck accumulated from the point of necking to fracture. Therefore, the parameter, ¥f=Gf/ln(An/Af) estimates the average incremental plastic energy per unit volume by the specimen per unit longitudinal plastic strain at the neck to sustain the fracture process. In the post-necking regime of tensile deformation with progressive development of the neck, the absorption of energy tends to get increasingly confined to the near-neck section, and therefore Gf and more so ¥f reflect the resistance of this region to microvoid growth. Hence, for an initially homogeneous ductile specimen, the RBR parameters estimate the toughness in a severely work-hardened condition and for a state of stress which is a combination of uniaxial tensile and hydrostatic stresses. For a specimen with gradient in toughness along its length, for example a transverse-weld specimen the neck is expected to initiate at the section least resistant to microvoid growth. For such a specimen, therefore the RBR method automatically determines the toughness of the weakest section, without a prior knowledge as to its location or the need for placing a notch or crack in the section. The advantage of the RBR method has been successfully exploited to characterize the effect of aging of three different dissimilar metal weld (DMW) joints viz. (i) an Alloy 800/2.25Cr-1Mo steel joint (at 300 K), (ii) an Alloy 800/9Cr-1Mo steel joint (at 300 K) and (iii) a type 316LN stainless steel/Alloy 800 joint (at 773 K), including determination of the optimum post-weld heat treatment (PWHT) temperature determined from the RBR toughness parameters is identical to that determined by the conventional method of correlating the microstructure with conventional tensile properties. For the Alloy 800/9Cr-1Mo steel DMW joint, the RBR toughness parameters led to unambiguous identification of the optimum PWHT temperature while the conventional structure-property method failed to do so. The efficacy and sensitivity of the two new ductile fracture toughness parameters have also been demonstrated.
SIMPLE STOCHASTIC MODELS OF FRACTURE WITH HEALING: M. Ausloos, R. D'Hulst, N. Vandewalle, SUPRAS, Institut de Physique B5, Université de Liège, B-4000 Liège, Belgium
There are several ways of approaching the problems of fracture. One of them is through algorithmic modelisation. We follow the ideas of a stochastic process, i.e. the most extreme situation, in order to find whether general behaviors of fracture phenomena can be quantified and if so through which ingredients. We use the numerical power of coarse grain cases allowing for easy access to asymptotic time regimes. Atoms on sites in a two dimensional plane are supposed to be ejected inside or outside an initial boundary. Several "percolation/fracture-like" path were found as a function of size. The concentration of the various crack thresholds, the distribution of clusters, the fractal dimension of the cracks were obtained. Power law features were indicative of essential processes. It will be shown that the rules give sometimes rise to "healing processes".
ATOMISTIC STUDIES OF CRACK PROPAGATION: Diana Farkas, Vijay Shastri, Department of Materials Science and Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0219
We will present the results of atomistic studies of fracture in ordered intermetallic alloys using the embedded atom method. The propagations of cracks is studied through atomistic computer simulation with particular emphasis on the competition between crack propagation and dislocation emission processes at the crack tip. The boundary conditions for these simulations are obtained from continuum elasticity theory and the region close to the crack is allowed to relax in order to achieve the minimum energy configuration. The atomistic simulations enable the study of the local atomic configuration at the crack tip in a realistic crystal structure and its importance for crack propagation. The studies include the simulation of crack structure and propagation in the presence of dislocations, in an effort to contribute to the modeling of ductile fracture processes.
COMPARISION OF LOCALIZED NECKING CRITERIA USED IN FINITE ELEMENT ANALYSIS OF SHEET METAL FORMING OPERATIONS: Sriram Sadagopan, Robert H. Wagoner, Department of Materials Science and Engineering, The Ohio State University, 2041 College Road, Columbus, OH 43210
Localized necking is one of the most common failure modes limiting formability in technological sheet metal forming operations. Prediction of localized necking for general three dimensional components using finite element simulations can be very useful in die/process design. Different failure criteria, based on macroscopic quantities, are used to predict localized necking. This presentation will compare the results from these different failure criteria for some standard geometries. The effect of applied boundary conditions on these results will also be discussed.
MICROPLASTICITY AND DUCTILE FRACTURE IN A METASTABLE BETA TITANIUM ALLOY: Wally O. Soboyejo+, B. Rabeeh* and S. Rokhlin*, +Department of Materials Science and Engineering, The Ohio State University, 2041 College Road, Columbus OH 43210-1179; *Department of Industrial, Welding and Systems Engineering, The Ohio State University, 190W. l9th Ave. Columbus OH 43210
Micromechanisms of tensile deformation and fracture in a metastable beta Ti-15V-3Cr-3Al-3Sn alloy are elucidated in this paper. Tensile deformation is shown to be associated with significant levels of microplasticity at stress levels above ~10% of the tensile yield strength. Microplasticity in the so-called elastic regime is shown to occur via shear localization and concomitant slip band formation; grain boundary sliding; subgrain formation; stress induced a phase precipitation; and atomic flow mechanisms that are not fully understood at present. Ductile fracture is also shown to initiate by decohesion around a precipitates produced largely via stress-induced precipitation. Catastrophic failure in the metastable beta Ti-15V-3Cr-3Al-3Sn alloy is shown to occur by the coalescence of microvoids produced via decohesion around a precipitates. Attempts are made to model the ductile fracture processes using classical ductile fracture theories. The implications of the microplasticity phenomena are also discussed within the context of elasticity and plasticity theories.
DAMAGE EVOLUTION IN HYPO- AND PSEUDO-EUTECTIC Al-Si ALLOYS: Tz. Kamenova, R. Doglione, J.L. Douziech, C. Berdin and Dominique François, École Centrale Paris, Laboratoire De Méchanique, Grande Voie des Vignes, F-92295 Châtenay-Malabry Cedex, France
The evolution of fracture processes in an hypoeutectic and in an eutectic Al-Si cast alloys has been studied by means of in situ tensile tests SEM observations. Chilled and cast alloys were investigated. It has been established that the damage initiates at low strains (of the order of 0.5%) by fracture of the largest Si particles, situated at the periphery of eutectic colonies. When the strain increases, finer and finer particles break within the colonies. In the hypereutectic alloys further straining induces a concentration of the damage along the fine interdentritic particles alignments. This leads to the formation of intensive slip bands in these regions followed by microcracks coalescence. The cracks thus created stop at the eutectic colonies, until final fracture by their propagation. The validity of the Weibull statistics to describe the number of cracked Si particles as a function of the applied load was proven. It was also observed that the volume increase of the microcracks was very small. These observations allowed to build a model of damage evolution based on micromechanics of inclusions at two different scales, that of eutectic colony and that of the whole specimen, yielding the fracture probability in the various zones.
EFFECTS OF INCLUSION DISTRIBUTION ON THE FRACTURE TOUGHNESS OF STRUCTURAL STEELS: Warren M. Garrison, Jr., Department of Materials Science and Engineering, Carnegie Mellon University, 3301 Wean Hall, Pittsburgh, PA 15213; Andrzej L. Wojcieszynski, Crucible Research Center, Campbells Run Road, Pittsburgh, PA 15205; Luena E. Iorio, Department of Materials Science and Engineering, Carnegie Mellon University, 3301 wean Hall, Pittsburgh, PA 15213
When fracture occurs by micro-void coalescence the fracture toughnesses of structural steels are controlled by both the inclusion distribution and the fine-scale microstructure. The characteristics of the inclusion distributions which influence toughness include volume fraction, spacing and void nucleation resistance. The effects of inclusion distributions on toughness are, however, not independent of the fine-scale microstructure and the extent to which varying characteristics of the inclusion distributions influences toughness can depend on the fine-scale microstructure. This talk will focus on three areas. First the effects of inclusion spacing and void nucleation resistance of inclusion particles will be discussed. Second, the degree to which such effects are influenced by fine-scale microstructure, in particular austenite grain size, will be considered. It has been found that the most effective way of minimizing the detrimental effect of inclusions on fracture toughness is to getter sulfide as titanium carbo-sulfide as particles of titanium carbo-sulfide are more resistant to void nucleation than particles of other sulfides such as MnS. Therefore, the third topic to be considered will be the effect of alloy composition on the formation of as titanium carbo-sulfide. This work was funded by the National Science Foundation, The Army Research Office, Teledyne Allvac and the Ben Franklin Program of Pennsylvania.
FRACTURE TOUGHNESS OF WC-Co CERAMIC-METAL COMPOSITES: James M. Densley, Carolyn E. Graves, John P. Hirth, Department of Materials and Mechanical Engineering, Washington State University, Pullman, WA 99164
The fracture toughness of a normal and nanoscale grain size WC-Co ceramic-metal composite with same compositions are compared. The fracture behavior is discussed as a mechanism of localized plastic deformation. Analysis of the cermets is done by both pure mode I and mixed-mode I/III fracture toughness methods.
EFFECT OF LOADING MODE ON FRACTURE PROPERTIES OF A VANADIUM ALLOY: H.-X (Huaxin) Li, R.J. Kurtz, R.H. Jones, Pacific Northwest National Laboratory, P. O. Box 999, Mail Stop IN P8-15, Richland, WA 99352
The effect of mode I and mixed-mode I/III loading on the fracture behavior of a vanadium alloy containing 4 wt% Cr and 4 wt% Ti (V4Cr4Ti) was investigated at room temperature. The V4Cr4Ti alloy was annealed at 1000°C for 1 hour in vacuum. Compact tension (CT) specimens were used to study mode I properties and modified compact tension (MCT) specimens were used for mixed-mode I/III. A MCT specimen is the same as a CT specimen except the principal axis of the crack plane is slanted at an angle of 25 and 45 degrees from the load line. When the crack angle is equal to zero, a MCT specimen becomes a CT specimen. With the MCT specimen, an applied load can be resolved to mode I load (Pi) and mode III load (Piii) at the crack tip. The mixities [Piii/Piii+Pi] used were 0, 0.32 and 0.5 for crack angles 0, 25 and 45 degrees, respectively. It was found that the introduction of Piii dramatically lowered fracture toughness of V4Cr4Ti alloy. The mechanism how mixed-mode I/III loading affects fracture behavior of the V4Cr4Ti alloy is discussed.
DYNAMICALLY GENERATED DISLOCATIONS SUB-STRUCTURE AHEAD OF A CRACK TIP: N. Zacharopoulos*, D.J. Srolovitz* and R. A. LeSar**, *Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109; **Center for Materials Science, Los Alamos National Laboratory, NM 87545
We investigate the propagation of a semi-infinite, mode III crack at constant KIII. At each time step, crack can grow and/or screw dislocations can be emitted from the crack tip. This model incorporates dislocation interactions with the crack, other dislocations, and all image dislocations. The emitted dislocations can significantly shield the crack. Dislocation-dislocation and dislocation-crack interactions are calculated using the fast multipole method applied within a stress-function framework. Dislocation-crack interactions are described using a conformal mapping procedure. Dislocation microstructures, generated from the crack tip, are shown over a wide range of loading rates. With increasing loading rate, a transition is observed from ductile-to-brittle behavior. However, even when the crack propagates in a brittle manner, significant dislocation emission occurs first. The dislocation microstructures observed are very complex and highly organized. As the load continues to increase, several distinct transitions in dislocation microstructure are observed. The effects of pre-existing dislocation network within the material are also examined. The dislocation network is strongly modified by the crack, decreases dislocation emission from the crack tip and, after evolution in the crack tip field, provides some crack tip blunting.
MECHANISMS OF DUCTILE FRACTURE IN PURE SILVER UNDER HIGH-TRIAXIAL STATES: Michael E. Kassner, Department of Mechanical Engineering and The Center for Advanced Materials Research, Oregon State University, Corvallis, OR 97331
Experimental and finite element method (FEM) analyses were used to study the mechanisms of ductile fracture of constrained, high purity, silver interlayers under high triaxial stress states. Interlayer bonds loaded in simple tension develop a principal stress state that is large and axisymmetric. Ductile, plastic-strain failure was observed in these bonds when the maximum mean stress to yield ratio () approached approximately four, in agreement with recent numerical analyses by other investigators, who postulated unstable growth of a cavity subjected to a far-field axisymmetric stress state at this ratio, without significant far-field plastic strain. Ambient temperature delayed-failure (creep) tests of constrained silver interlayers, at relatively low applied loads, also appear to be due to unstable cavity growth. The mechanism of ductile fracture was further studied by biaxially loading these interlayers through the application of various combinations of tension and torsion loads. Low macroscopic-strain ductile fractures are again observed, but the axisymmetric and non-axisymmetric failure-stress values and FEM analysis of the stress levels required for cavity instability do not directly support an unstable growth model, even when considerations for plastic incompatibilities across grain boundaries are considered. Other ductile fracture theories such as cavity nucleation and interlinkage warrant consideration.
THE EFFECTS OF STERILIZATION AND OXIDATION ON THE FRACTURE OF 'ARTIFICIAL CARTILAGE' (ULTRA-HIGH MOLECULAR WEIGHT POLYETHYLENE): Thomas J. Mackin and Jeff Windau, Department of Mechanical and Industrial Engineering, The University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801
Ultra-high molecular weight polyethylene (UHMWPE; 4x103 g/mole) is commonly used as artificial cartilage in orthopedic implants. Several processing methods are used to fabricate the stock material, followed by machining, and gamma-irradiation sterilization prior to final implantation. Over the 15 year anticipated lifetime, cyclic and tribological loading change the properties of the material. The need for improved implant lifetimes motivated a detailed investigation of the relationships between processing/sterilization and properties in UHMWPE. Gamma irradiation changes the mechanical properties by promoting enhanced crystallization, while lifetime aging results in the formation of carbon-oxygen groups that change the subsequent properties. Both effects improved the ductility of the materials and led to overall improvements in yield strength, tensile strengths elastic modulus. These results are in sharp contrast to previous studies where any increase in crystallinity decreased the ductility of the UHMWPE. A broad array of experimental techniques were utilized to verify the measured changes in microstructure and properties. We will report on these changes in mechanical properties coupled with a fractographic analysis of failed specimens to relate the mechanisms of ductile failure in UHMWPE to the microstructural changes brought about by production, fabrication, sterilization and aging of these implant materials.
A MIXED-MODE FRACTURE MECHANISM MAP: M. Manoharan, Division of Materials Engineering, School of Applied Science, Nanyang Technological University, Singapore-639798, Singapore
As fracture mechanics has developed as a discipline, many parameters have been developed to characterize the instability condition. However, a majority of this work has been confined to the investigation of mode I fracture. Thus, we have standardized methods for experimentally determining KIC, JIC and J-resistance curves for mode I crack propagation. However, cracks in real materials can be subjected not just to tensile stresses but to complex stress states so that the development of suitable parameters to characterize mixed-mode crack initiation and propagation is important in the evolution of suitable design criteria. Further, observations indicate that initially flat cracks in some tough materials tend to reorient themselves to oblique planes during growth. For these materials, crack propagation can be said to occur under combined mode conditions. A considerable amount of work on mixed mode I/III fracture toughness of materials is available. The superposition of mode III loading results in drastic reduction in fracture toughness in some materials whereas in other materials it has little effect or even results in an increase in the fracture toughness. Fracture mechanism maps delineating regions of susceptibility to tensile and shear loads have been proposed. In this paper, data on a wider range of materials, including steels, aluminum alloys, metal matrix composites, ceramics and polymers will be used to extend and reinforce the fracture mechanism map concept.
EFFECTS OF STRESS STATE ON DEFORMATION AND FRACTURE OF STRUCTURAL MATERIALS: John J. Lewandowski, Dept. of Materials Science and Eng., Case Western Reserve University, Cleveland, OH 44106
The deformation and fracture of structural materials is significantly affected by changes in the microstructure and imposed stress state. Such changes in stress state may affect the micro-mechanisms of failure whereby a material which normally fails in a ductile manner may undergo a ductile-to brittle transition. In other cases, the imposition of a more severe stress state may accelerate the stages of ductile fracture to such an extent that very low ductility is obtained. The imposed stress state may be easily changed via testing notched specimens or via testing with confining pressure in monolithic materials. The presentation will review previous and ongoing work investigating the effects of stress state on the fracture of a variety of metallic materials, including more recent work on metallic composites.
THE ROLE OF DISLOCATION NUCLEATION IN THE BRITTLE-TO DUCTILE TRANSITION IN SILICON SINGLE CRYSTALS: K. Jimmy Hsia, Department of Theoretical and Applied Mechanics, University of Illinois, 216 Talbot Laboratory, 104 South Wright Street, Urbana-Champaign, IL 61801
EFFECT OF HYDROGEN ON THE MECHANICAL PROPERTIES OF LOW CARBON STEEL: B. Sarkar, D. Mukerjee, R&D Centre for Iron and Steel, Steel Authority of India Limited, Ranchi-834002, India
The effect of hydrogen on the mechanical properties of a low carbon steel has been investigated. In-situ tensile and hardness tests have been carried out while charging hydrogen. It has been observed that there is a substantial reduction in ductility as a result of hydrogen charging while there is no change in hardness. The strain hardening exponent (n) value decreased from 0.26 to 0.22 ( a decrease of about 15%) whereas, the total elongation decreased from a value of 44.2% to 33.8% (a fall of about 24%) as a result of hydrogen charging. This is suggestive of the fact that hydrogen charging affects all the stages of ductile fracture. Hydrogen charging has been found to increase the number of dimple nucleating sites. Consequently there was a decrease in the average dimple size. It is believed that the effect of hydrogen on the reduction of ductility is more prominent in the post necking region. It has been concluded that hydrogen charging enhances the number of dimple nucleating sites which promotes the process of ductile fracture.
Room: Salon 7
Location: Clarion Plaza Hotel
Session Chair: Dr. Phillip Parrish, MATSYS Inc., Arlington, VA
3-D HIP MODELING: RESULTS ON NON-AXISYMMET4RIC PARTS: W.B. Eisen, Crucible Research Center, 6003 Campbell's Run Rd., Pittsburgh, PA 15205
Abstract not available.
2:30 pm
MODELING OF THE POWDER/MONOTAPE METHOD FOR TITANIUM MATRIX COMPOSITE CONSOLIDATION: C.C. Bampton, K.J. Newell, Rockwell Science Center, P.O. Box 1085, Thousand Oaks, CA 91358
A computer model, Discrete Element Consolidation Analyzer (DECA), is described which was developed with support from Wright Laboratory, to assist in the optimization and control of the so-called tape-cast powder monotape processing method for titanium matrix composite consolidation. DECA simulates the viscoplastic densification of a randomly packed spherical titanium alloy powder aggregate and continuous fiber array by hot pressing. Using state variable analysis together with automated remeshing, the model performs a continuous simulation of powder particle contact-contact interaction, free surface evolution and void closure. A unique capability of this model is the realistic simulation of the final random powder packing geometry, prior to consolidation, following the debulking, i.e., binder off-gassing, and powder settling and fiber rearrangement, of the initial tape-cast powder/fiber monotape.
3:00 pm
A DENSIFICATION CONSTITUTIVE MODEL FOR POWDER BASED ALUMINUM MATRIX COMPOSITES MATERIALS: Erik J. Jilinsk, John J. Lewandowski, Dept. of Material Science and Engineering, Case Western Reserve University, Cleveland, OH 44106; Paul T. Wang, The Aluminum Company of America, Alcoa Technical Center, Alcoa Center, PA 15169
Intelligent, cost effective processing of powder based materials requires an understanding of the key physical variables during processing and the ability to implement these variables into suitable analytical models that can describe the overall consolidation behavior of the powdered material during fabrication. In this presentation, a modified form of the Gurson continuum level densification model, derived through a micromechanical approach, is developed and applied to an aluminum metal matrix composite reinforced with SiC particulate. The results of this model, also applicable to short or chopped fiber reinforced powder based composite material, capture the influence that volume fraction of reinforcement has on the densification of the powder based aluminum alloy metal matrix composite and provides the first step of the analytical framework needed for designing a process model capable of describing the consolidation behavior of the composite material during a powder forging type fabrication process.
3:30 pm
MODELING THE HOT CONSOLIDATION OF METAL POWDERS AND METAL-MATRIX COMPOSITES: R.E. Dutton, S.L. Samiatin, Materials Directorate, Wright Laboratory, WL/MLLM, Wright-Patterson AFB, OH 45433
The modeling of the deformation and densification behavior of metal powders during hot consolidation processes was treated through the application of a continuum yield function and associated flow rule modified to incorporate microstructure effects such as grain growth, pore size, and pore geometry. It was shown that consolidation behavior can be described over the entire range of densities through two parameters, Poisson's ratio and the stress intensification factor, which are readily measured using uniaxial upset tests. The accuracy of the material modeling approach was validated by comparing the densification predicted from both a simple analytical model and an FEM with observed behavior during the die-pressing of monolithic gamma titanium aluminide powder and the hot-isostatic pressing of tapecast monotape composite layups comprising alpha-two titanium powder and continuous silicon carbide fibers. In addition, the effect of pore anisotropy on the yielding and flow behavior of partially consolidated powder compacts was addressed.
4:00 pm
PHYSICAL MODELING OF THE EARLY STAGES OF METAL POWDER CONSOLIDATION AND COMPARISON TO EXISTING ANALYTICAL MODELING APPROACHES: David P. DeLo, Henry R. Piehler, Dept. of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
The important mechanisms during the early stages of metal powder consolidation are not well understood nor are they properly included in consolidation models. The result is that models tend to underpredict strain-rates, particularly during the early stages of consolidation. In a series of interrupted HIP experiments, PREP Ti-6Al-4V powder was consolidated in thin-walled containers, and the resulting partially consolidated specimens examined metallographically. Stereo micrographs of fractured specimen surfaces were examined qualitatively and quantitatively to gain insights into early stage mechanisms and appropriate modeling approaches. Evidence of particle rearrangement was found throughout the early stages of consolidation. Contact areas between particles increase in size at a much slower rate than is predicted by popular mechanistic models. Particle size effects, including rigid body motion of larger particles facilitated by preferential deformation of small particles, contribute to rearrangement. The critical assumptions required for common mechanistic and continuum models are not consistent with the observed mechanisms and behaviors requiring new modeling approaches that are consistent with the observed behavior.
4:30 pm
CONSOLIDATION OF NANOSTRUCTURED METAL POWDERS BY RAPID FORGING: PROCESSING, MODELING, AND SUBSEQUENT MECHANICAL BEHAVIOR: G.R. Shaik, Walter W. Milligan, Dept. of Metallurgy and Materials Engineering, Michigan Technological University, Houghton, MI 49931
Nanostructured metals are a potentially-promising class of materials with ultrafine grain sizes. A limitation on commercial implementation of nanostructured materials has been grain coarsening during consolidation. In this research, attritor-milled powders with 20 nm grain sizes inside micrometer-sized powder particles were consolidated by induction heating and rapid forging of cold-pressed compacts. Grain growth was limited by minimizing the time at consolidation temperature. Fully-dense materials were obtained at relatively low temperatures around 500°C. The consolidation process was successfully modeled with the Arzt-Ashby-Easterling HIP model, modified slightly for geometrical constraints, stress state and the nature of the nanostructured metal. Modeling and mechanical testing indicated that creep dominated the consolidation process, apparently due to the ultrafine microstructures. Mechanical properties at ambient and elevated temperatures. We gratefully acknowledge the support of the Air Force Office of Scientific Research, under grant F49620-94-1-0255, which is monitored by Dr. Walter Jones, and the National Science Foundation, under grant DMR-92-57465, which is monitored by Dr. Bruce MacDonald.
Room: 340A
Session Chairperson: Dr. Ricardo B. Schwarz, Center for Materials Science (MS-K765), Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM 87545
STRUCTURE OF BULK AMORPHOUS ALLOYS DETERMINED BY SYNCHROTRON RADIATION: T. Egami, W. Dmowski, Department of Materials Science and Engineering (LRSM/K1), University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104-6272; Yi He, Ricardo B. Schwarz, Center for Materials Science (MS-K765), Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545
The atomic structure of Pd-Ni-P bulk amorphous alloys was studied by the anomalous (resonance) x-ray scattering technique using synchrotron radiation tuned near the Pd K-edge. Bulk samples of Pd40Ni40P20, Pd30Ni50P20, and Pd50Ni34P16 amorphous alloys were prepared by the flux method in the form of rods with the diameter of 10-14 mm. X-ray measurements were carried out at the X-7A beamline of the NSLS, Brookhaven National Laboratory. The results show that the structures are basically described by the dense random packed structure with small chemical short-range order. The implication of this result with respect to the stability of the glass will be discussed.
2:40 pm INVITED
CAN A BULK AMORPHOUS PHASE BE OBTAINED FROM LIQUID SILICON OR GERMANIUM?: Yan Shao, Frans Spaepen, Division of Engineering and Applied Sciences, Pierce Hall, Harvard University, 29 Oxford Street, Cambridge, MA 02138
A number of methods have been used to undercool liquid silicon and germanium: levitation melting, flux treatments, atomization, rapid cooling following laser melting of thin films, and quenching of droplet dispersions. An amorphous phase has been produced so far only in small volumes. The competition between the kinetics of nucleation and growth of the crystalline and the amorphous phases under these various conditions will be reviewed, and the possibility of obtaining bulk amounts of the amorphous phase will be assessed.
3:20 pm BREAK
3:40 pm INVITED
THERMODYNAMIC FRAMEWORK FOR SOLID-STATE AMORPHIZATION: D. Wolf, Materials Science Division (MSD-212), Argonne National Laboratory, Argonne, IL 60439
Atomistic computer simulations are used to expose important thermodynamic parallels between melting and solid-state amorphization and the important role of nanocrystalline microstructures. Molecular-dynamics simulations demonstrate that every crystal can, in principle, melt by two entirely different causes and underlying mechanisms; a comparison with experiments suggests that both can be operative in solid-state amorphization1. Also, simulations of a model nanocrystalline material exhibit the existence of low- and high-frequency lattice-vibrational modes not seen in the perfect crystal but also present in the amorphous phase2. The possibility of a reversible, free-energy based transition between these two metastable phases that is governed by a critical grain size is discussed together with possible mechanisms for the transition. Work supported by the US Department of Energy, BES-Materials Science under Contract No. W-31-109-Eng-38.
4:20 pm INVITED
THERMODYNAMIC AND KINETIC PROPERTIES OF AMORPHOUS AND LIQUID STATES: A.V. Granato, Physics Department, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL 61801-3080
The magnitude and temperature dependence of the liquid state shear modulus G, specific heat Cp, diffusivity D and viscosity 
are all closely related, according to the interstitialcy model. It has been proposed by Dyne, Olsen and Christensen that the viscosity is given by =h0exp(F/kT) where h0 is a reference viscosity and F is given by the work required to shove aside neighboring particles in a diffusion process, where F=GVc and Vc is a characteristic volume. In the interstitialcy model, the high frequency thermodynamic liquid state shear modulus is given by G(T)=G0exp[(-(T-T0)], where G0 is the shear modulus at a reference temperature T0 which can be taken as the glass temperature. The resulting non-Arrhenius behavior of the viscosity is compared with experimental data for the shear modulus.
Room: 330G
Session Chairperson: V. Vitek, Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104
GRAIN BOUNDARY MIGRATION EFFECT OF MISORIENTATION, IMPURITIES, PHASE TRANSITIONS AND TRIPLE JUNCTIONS: L.S. Shvindlerman1, G. Gottstein, U. Czubayko, D.A. Molodov, V.G. Sursaeva1, Institut für Metallkunde und Metallphysik, RWTH Aachen, D-52056 Aachen, Germany; 1Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow District, 142432 Russia
The mobility of high-angle grain boundaries and triple junctions is the key factor, which controls the recrystallizations and grain growth processes. The mobility of individual <111> tilt grain boundaries in Al was measured under the constant driving force, in-situ, over a wide range of temperatures, in the vicinity of special misorientation and away from it, in ultra-pure Al and in Al doped with small amount of soluble impurities. The steady state motion of grain boundary systems with triple junctions was investigated in-situ at different temperatures on tricrystals of Zn. A transition of the steady state motion of the grain boundary system with triple junction from junction kinetics to grain boundary kinetics was observed. For the first time it was shown that triple junctions are able to drag grain boundary motion. The grain structure evolution in polycrystals for different kinds of kinetics will be discussed.
2:10 pm
MECHANISMS AND CRYSTALLOGRAPHY OF GRAIN BOUNDARY MIGRATION: A TWO DIMENSIONAL COMPUTER SIMULATION STUDY: M. Upmanyu, R.W. Smith, D.J. Srolovitz, Dept. of Materials Science and Eng., University of Michigan, Ann Arbor, MI 48109
Two dimensional molecular dynamics simulations of grain boundary migration are performed using the half-loop bicrystal geometry employed in the experiments performed by Shvindlerman, et al. We examine the dependence of the steady state grain boundary velocity on grain boundary curvature by varying the half-loop width at constant temperature. The grain boundary velocity is proportional to the half-loop curvature and the grain boundary mobility follows an Arrhenius relationship. In the present study, we examine grain boundary migration for several different grain misorientations. We employ movies of these simulation in order to deduce the dominant mechanisms of grain boundary migration and how these mechanisms depend on grain boundary structure.
2:30 pm
INTERACTION OF SOLUTE SEGREGATION AND GRAIN BOUNDARY SLIDING PROCESSES: J.S. Vetrano, E.P. Simonen, S.M. Bruemmer, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352
The sliding of grain boundaries can be influenced by the presence of solute segregants. Additionally, the sliding mechanism itself also triggers vacancy fluxes that may result in the non-equilibrium redistribution of solute atoms at boundaries and triple points. The interaction of these two processes have been studied in Al Mg-Mn based systems with and without additions of Sn, an equilibrium segregant. Fine-grained structures have been produced and samples tested under conditions that induce grain boundary sliding (GBS). The presence of Sn on the boundaries before deformation allows easier GBS with lower cavitation. High-resolution grain boundary composition measurements on deformed samples revealed that the Sn remains on the boundary during GBS but the Mg is redistributed in a heterogeneous manner. The points to the possibility of engineering the grain boundary composition for optimized deformation characteristics and post-formed properties such as stress corrosion cracking resistance. Work supported by the Materials Division, Office of Basic Energy Sciences, U.S. Department of Energy under Contract DE-AC06-76RLO 1830.
2:50 pm
ATOMISTIC CHARACTERIZATION OF CERAMIC/METAL INTERFACES: SIMULATION AND EXPERIMENTS: D.A. Shashkov, R. Benedek, & D.N. Seidman, Northwestern University, Department of Materials Science and Engineering, Evanston, IL 60208-3108
Our research on ceramic/metal (C/M) interfaces that utilizes transmission electron, high-resolution electron, Z-contrast microscopy, and atom-probe microscopies, in collaboration with ab initio atomistic modeling, is presented. Heavy use is made of atom-probe microscopy to address questions concerning the chemistry of the terminating plane and segregation of solute species to the ceramic/metal interfacial region. Detailed results are presented for the {222} MgO/Cu, {222} CdO/Ag, {222} MgO/Cu(Ag), and {222} CdO/Ag(Au) interfaces. All the C/M interfaces were created via internal oxidation, at elevated temperatures, of high-purity binary or ternary metallic alloys, thereby producing atomically clean interfaces. Solute-atom segregation was induced at the {222} C/M interfaces by annealing specimens containing a ternary addition at 500°C for prolonged periods of time. The level of segregation, i.e., the Gibbsian interfacial excess, is determined directly by the atom-probe technique. Results concerning ab initio atomistic modeling of the {222} MgO/Cu coherent interface (zero-misfit approximation), using local density functional theory (LDFT) within the plane-wave pseudopotential framework, are presented for two polar {111} and two nonpolar {100} MgO/Cu and CdO/Ag interfaces and are discussed with respect to our experimental observations. This research is supported by the Department of Energy/Basic Energy Sciences.
3:10 pm BREAK
3:30 pm INVITED
COMPUTER SIMULATION STUDIES OF THE KINETICS OF INTERFACE DIFFUSION AND PHASE FORMATION: J.M. Rickman, Dept. of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18105-3195
Two kinetic processes associated with grain boundaries are discussed. In the first study, we examine quantitatively the impact of heterogeneous nucleation on the temporal evolution of a phase transformation with particular emphasis on the correlation of nucleation site distribution and product phase microstructure. This is accomplished by investigating spatial correlations in the transforming system via the calculation of nonequilibrium correlation functions and by characterizing product grain sizes and shapes. Computer simulations of transformations are employed in order to validate our theoretical description and to relate microstructural features of the evolving phase to relevant length and time scales in the problem. In the second study, we investigate the kinetics of grain boundary diffusion using a spatially inhomegeneous lattice gasmodel. It is found that atomic transport can be accurately described by a series of approximate rate equations and that one can ascribe a bias, in a certain sense, to tagged atoms.
4:10 pm INVITED
THERMODYNAMICS OF GRAIN BOUNDARY ANISOTROPY AND GRAIN BOUNDARY WETTING: W. Craig Carter, John W. Cahn, Materials Science Engineering Laboratory, NIST, Gaithersburg, MD 20899
Abstract not available.
4:30 pm
MICROCHEMISTRY OF INTERNAL INTERFACES DURING IRRADIATION: E.P. Simonen, S.M. Bruemmer, Pacific Northwest National Laboratory, P.O. Box 999, MS P8-15, Richland, WA 99352
Nonequilibrium microchemistries develop at irradiated interfaces in alloys. The driving force for the radiation-induced segregation is the flow of radiation produced defects to internal interfaces. A unique feature of these segregation profiles is the narrow nanometer dimension near grain boundaries. Theoretical predictions and analytical measurements indicate that nonequilibrium composition gradients normal to grain boundaries are in excess of 106 atom fraction/cm. Fast arrival rates of radiation-produced point defects create potential influences on grain boundary structure and dynamics. Conventional theories assume that dominant mutual recombination of grain boundary defects prevents their influence on boundaries. In the present paper, the dynamics of defect arrival and annihilation are examined in relation to extreme nonequilibrium conditions at internal interfaces. This work was supported by the Materials Sciences Branch, BES, U.S. Department of Energy, under Contract DE-AC06-76RLO 1830.
Room: 340D
Session Chairperson: Dr. Krishna Rajan, Rensselaer Polytechnic Institute, Materials Engineering Department, MRS-110, Troy, NY 12180-8554
TITLE TBA: Mr. Jeff Lawrence, Associate Administrator of Legislative Affairs, NASA Headquarters, Suite 9L33, Washington, DC 20546
2:30 pm
THE DEVELOPMENT OF NATIONAL RESEARCH AND DEVELOPMENT PRIORITIES: INDUSTRY-ACADEMIC GOVERNMENT COOPERATION: Mr. Ken Kay, Podesta Associates, 1001 G Street, NW, Suite 900E, Washington, DC 20001
Abstract not available.
3:00 pm BREAK
3:15 pm
BRIDGING THE UNIVERSITY AND INDUSTRY CULTURES: A CANADIAN PERSPECTIVE: Prof. J. Keith Brimacombe, O.C., Alcan Chair in Materials Process Engineering, The Centre for Met. Process Engineering, University of British Columbia, Room 112-2355 East Mail, Vancouver BC V8T 1Z4
Abstract not available.
3:45 pm
STATUS-UNIVERSITY-INDUSTRY COLLABORATIVE RESEARCH IN JAPAN: Professor Shuji Hanada, Institute of Materials Research, Tohoku University, Katahira 2-1-1, Sendai, Japan
There are two types of universities in Japan; national universities and private universities. Basically, the former are supported mainly by the government (The ministry of education, culture and science-the Monbusho), while the latter partly by the government. Among them, the national universities are active to collaborative research with industry. In this talk the various systems and their activities concerning the research collaboration between national universities and industry will be addressed. In addition some recent topics will be mentioned briefly. From the early 1980s, new systems of joint research with the private sector, endowed chairs and funded research departments and centers for cooperative research were introduced. Consequently, the exchange of researchers between universities and the private sector industries has become quite active, and the sources of research funds for national universities has become diversified. Currently over three thousand outside researchers participate in research activities at universities and the total amount of funding from industry has become almost as large as the Monbusho grants-in-aid budget.
In the system of the joint research with the private sector, national universities receive researchers and funding from private industry. Then university researchers and private industry researchers combine efforts to do joint research on common projects, to enhance the likelihood of achieving excellent results. Under the commissioned research system, scientific researchers in universities are commissioned by industrial firms, government research institutes, local governments or other outside organizations to carry out research by contract. No researchers from the industrial world join in carrying out the research at the universities. In the commissioned researchers system, national universities accept technicians and researchers currently employed in private industry and other outside agencies. They are given guidance in doing research at the graduate level, which helps them to improve their abilities. Endowed chairs can be established within a faculty or department of a national university. Funded research departments can be established in a research laboratory attached to the university or in an inter-university research institute. The wages of the visiting professors or associate/assistant professors, who are appointed by the universities, and the educational and research expenses of the chairs and departments are paid totally from the endowments from the private sectors. Many national universities have Centers for Cooperative Research. These centers employ professors as part-time directors as well as full-time associate professors and part-time visiting professors. They are equipped with all purpose research facilities and provide technical consultation and training of technicians and researchers, in addition to their functions of engaging in joint and commissioned research. National universities accept donations from both private organizations and individuals to support scientific research and educational activities. Quite recently, the ministry of international trade and industry (MITI-The tsusansho) has started supporting and funding basic research at universities whose results will bring new industries in future.
Room: 330F
Session Chairpersons: C.M. Ward-Close, Structural Materials Center, R50 Building, Defense Research Agency, Farnborough, Hampshire, GU14 6TD, United Kingdom; S. S. Cho, Vice President of Rapidly Solidified Materials Research Center, (RASOM), Chungnam National University, Taedok Science Town, Taejon 305-764 Korea
PRODUCING METHOD AND MECHANICAL PROPERTIES OF TiB2 PARTICLE REINFORCED HIGH MODULUS STEEL: Kouji Tanaka, Tadashi Oshima, Takashi Saito, Toyota Central Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi, 480-11, Japan
In our effort to develop high modulus steel, titanium diboride (TiB2) has proved to be the best reinforcement because of its high Young's modulus and excellent thermodynamic stability in iron-based alloys. In this paper, mechanical properties of the developed steel and the methods applied to practical parts fabrication are discussed. Conventional P/M techniques, including liquid phase sintering to achieve its full density and reaction sintering using low-cost ferroalloy powders, have been successfully utilised. Tensile strength, fatigue strength, and abrasive wear resistance of the developed steel were investigated in order to evaluate its potential application. These mechanical properties revealed a linear improvement with the increase in TiB2 volume fraction. The developed steel also provided hot workability required in die-forging process. Trial forged parts demonstrated a possibility of producing high performance automobile parts.
2:20 pm
A STUDY ON MANUFACTURING METHOD AND ABRASIVE CHARACTERISTICS OF SUBSIEVE SIZE SiCp REINFORCED A1 ALLOY COMPOSITE: S.W. Han, S.W. Kim, Department of Metallurgical Eng, Chonbuk National University, Chonju, 560-756, Korea
This study aims to manufacture A1 alloy composites reinforced by subside size (3 mm, 5mm, 10mm) SiCr with duplex process of squeeze-infiltration (1st process) and squeeze casting (2nd process) developed in this study, to investigate effects of alloying element and heat exposure on the microstructures and heat and wear resistance of A1-Si-X(Cu, Cr, Ni)-SiCr). In the last process, when the melt is infiltrated into SiCr bed. At the same time, melt is flowed to loser part along the gap between mould and SiCr bed. Then, the melt is filtrated into upper-direction conversely. At infiltrating depth of 30-40% into SiCr bed, the vertical lamellar infiltration is appeared heterogeneously due to lack of the melt and increase of viscosity. Although pre-composite fabricated by 1st process has excellent distribution of SiCp on matrix, the SiCp wt% is high as applying industrial articles. Being modelled, the pre-composite and A1 alloy are squeeze casted follow melted, agitated in the caster. Through these processes, SiCp wt% is freely controlled as well as the distribution is increased owing to active plain on SiCp during agitation of the 2nd process. A1-12Si-2Mg-3Cu-SiCp has the least wear loss amount among all the composites manufactured in this study. But, A1-12Si-2Mg-3Ni-SiCp has the lowest relative ratio of wear loss amount (wear loss amount after 350°C, 70hr exposure)-(wear loss amount before 350°C, 70hr exposure)/(wear loss amount before 350°C, 70hr exposure) at high sliding speed. Composites with 15wt%(10mm)SiCp increased the wear amount with the increase of sliding speed because of change abrasive wear to adhesive or melting wear. But composite with 35wt%(10mm SiCp) decreased wear amount with the increase of the sliding speed because abrasive wear with power debris occur in high sliding speed and wear debris with block type occur in low sliding speed.
2:40 pm
A STUDY ON THE DEVELOPMENT OF HIGH STRENGTH AND WEAR RESISTANCE INTERMETALLIC COMPOUNDS/ALUMINIUM ALLOY MATRIX COMPOSITES BY SQUEEZE CASTING METHOD: D.C. Choi, S.H. Park, C.W. Won, National University, Chungmann Nation University
Recently, particle reinforced A1 alloy matrix composites accomplished weight reduction by utilising A1 alloy matrix and improved wear resistance, heat resistance and mechanical properties. This technique is believed to have advantages compared to the conventional manufacturing process, in that the intermetallic compounds enforcers as well as density and shape of the perform are more easily controlled. In this study, perform composition of 25, 40, 50, 60 and 75at%A1 were manufactured. The perform swelled after the reactive sintering process in the case of 25at%A1 composition. On the other hand, the perform shrinkage in the case of 60at%A1 and 75at%A1 composition. Microstructures of the composite samples squeeze casted at the mould temperature of 500°C and the A1 alloy melt of 610°C were investigated using X-ray diffractometer, energy dispersive spectrometer, micro-vickers hardness and etching experiments. In the case of Fe-25at%A1 and 40at%A1 composites, mixture of the compound and the A1 alloy matrix were observed at the top part of the ingot, whereas small amount of A1 alloy matrix were dispersed within the compound islands at the bottom part. Composite structure were observed throughout the whole sample in the case of 50at%A1, which is the structure initially intended to obtain.
3:00 pm
FABRICATION AND MECHANICAL PROPERTIES OF SQUEEZE CAST Mg MATRIX COMPOSITES: Yoon-suck Choi, Kyung-mox Cho, Ik-min Park, Dept of Metal Eng Pusan Nat Univ. Pusan, Korea
In the present study, AZ91 Mg matrix composites were fabricated with a variation of the applied pressure using squeeze infiltration technique. Alumna short fibre (Saffil and Kaowool) and aluminium borate whisker were chosen as reinforcements. Performs of reinforcements from the slurries with different binder compositions were consolidated by vacuum suction method. Microstructural observation was performed to investigate the effects of reinforcements and squeeze casting condition including applied pressure and preheating temperature of performs etc on the solidification microstructure of the Mg matrix composites. Mechanical properties such as bending strength and fracture toughness were measured to evaluate properties of the squeeze cast Mg matrix composites. In-situ SEM fracture test was performed to observe the fracture process of the Mg matrix composites.
3:20 pm
SYNTHESIS OF MoSi-BASED COMPOSITES: S. Walloe, L. Christodoulou, Department of Materials, Imperial College, London SW7 2BP, UK. P. Goodwin, M. Ward-Close, Structural Materials Centre, Defence Research Agency, Farnborough GU14 6TD, UK
A study has been undertaken to investigate process parameters controlling the formation of moist composites using elemental powder-based reaction synthesis techniques. The size and shape of reinforcement have been correlated to the processing conditions and the starting powder characteristics.
4:00 pm
FABRICATION AND MECHANICAL PROPERTIES OF SQUEEZE CAST MG MATRIX COMPOSITES: Y.S. Choi, K.M. Cho, I.-M. Park, Dept of Metal Eng, Pusan Nat Univ. Pusan, South, Korea
In the present study, AZ91 Mg matrix composites were fabricated with a variation of the applied pressure using squeeze infiltration technique. Alumna short fibre (Saffil and Kaowool) and aluminium borate whisker were chosen as reinforcements. Performs of reinforcements from the slurries with different binder compositions were consolidated by vacuum suction method. Microstructural observation was performed to investigate the effects of reinforcements and squeeze casting condition including applied pressure and preheating temperature of performs etc on the solidification microstructure of the Mg matrix composites. Mechanical properties such as bending strength and fracture toughness were measured to evaluate properties of the squeeze cast Mg matrix composites. In-situ SEM fracture test was performed to observe the fracture process of the Mg matrix composites.
4:20 pm
PHASE FORMATION AND PROPERTIES OF MECHANICALLY ALLOYED Mg-BASED MULTICOMPONENT LIGHT-WEIGHT ALLOYS: J. Eckert, N. Schlorke, C.A.R.T. Miranda1, and L. Schultz, Institute fur Festkorper-und Werkstofforschung Dresden, Institute fur Metallische Werkstoffe, D-01171 Dresden, Germany; 1Permanent Address: LIJÓ-Barcelos, Portugal
Multicomponent Mg-Y-Cu lightweight alloys were prepared by mechanical alloying of elemental powder mixtures. The progress of alloying, the resulting phases and their thermal stability were characterised by x-ray diffraction, differential scanning calorimetry (DSC) and thermo-mechanical analysis (TMA). Coexistent amorphous and nanoscale crystalline phases are found for a variety of alloys with different composition. The thermal stability data of the materials as obtained by constant-rate heating DSC and TMA measurements and isothermal annealing experiments are discussed with respect to phase separation in the undercooled liquid state and nucleation and growth of nanocrystalline phases. Some characteristic properties of the glassy phase are presented and discussed with respect to the composition dependence of the glass transition and the crystalline temperature. The results are compared with data for melt-quenched samples. Finally, the influence of processing conditions and contamination effects during milling on the phase formation and the thermal stability of the mechanically attrited powders is critically assessed.
4:40 pm
IRON AND ALUMINIUM MICRO/NANOLAMINATES PROCESSED BY HIGH RATE DEPOSITION: C. Loader, D. Dunford, Z. Kulikowski, C.M. Ward-Close, Structural Materials Centre, Defence Research Agency, Farnborough GU14 6TD, UK
A model iron-aluminium system was employed to understand the toughness characteristics observed in multi-layered materials. The process for fabricating laminates by physical vapour deposition using either thermal or electron beam evaporation is described. Laminates are deposited onto a rotating collector and are typically around 2-4mm thick. In this work a range of laminates were fabricated with layer thickness varying from 10nm to 5mm. Microstructural evaluation of the laminates was performed using SEM, XRD, EPMA, and TEM; mechanical property data was generated using tensiles, four-point bend, notched bend, and microhardness. Results show strength and toughness increases are obtained in multi layered materials compared to monolithics primarily due to crack deflection and blunting. The effect of changing layer thickness on the strength and toughness is reported.
5:00 pm
MICROSTRUCTURE PROPERTY STUDIES IN Fe-Al LAMINATE MATERIALS: G. Shao, P. Tsakiropoulos, C. Loader, D. Dunford,* and C.M. Ward-Close,* Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, England, UK; *Structural Materials Centre, Defence Research Agency, Farnborough GU14 6TD, UK
Fe/Al laminates of different layer thicknesses were produced by PVD. TEM studies showed that as deposited microstructure depends on the ratio of the nominal thicknesses of the Fe and Al layers and on the actual layer thickness. For dfe:dal=0.4mm the microstructure consisted of nanocrystals of Fe/Al solid solution with A2 or B2 structure and Al2Fe. For dfe:dAl>>44nm or 2.1mm:0.7mm laminated structures were produced. The laminates consisted of layers of Fe(A2-bcc) and of solid solution of Fe in Al with B2 (ordered bcc) structure which was formed by interdiffusion between the Fe and Al layers. Thermodynamic modelling showed that interdiffusion and interface reaction in the as deposited materials are closely related to the overall heat of mixing. The mechanical properties of the laminates will be related to their microstructures.
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