Room: 315B
Session Chairperson: TBA
8:00 am
TRIBOLOGICAL MEASUREMENT METHODS FOR COATINGS: Stephen M. Hsu, National Institute of Standards and Technology, Gaithersburg, MD 20899
Coatings are increasingly being used as a means to protect materials from harsh environments. As the coating technology becomes more sophisticated, the requirement for new and better measurement techniques to understand wear mechanisms and coating effectiveness soars. For functionally gradient coatings, the issue of measuring local properties vs global properties in determining the extent of compositional change necessary to achieve a particular performance level is critical. For very thin hard coatings on relatively soft substrates, the deformation and yielding of the substrate affect the coating effectiveness. This paper presents some new and novel techniques that can be used to measure the coating properties under rubbing conditions.
8:35 am
PLASMA-ASSISTED DEPOSITION OF TRIBOLOGICAL COATINGS: K. Sridharan, R.A. Breun, A. Chen, J.R. Conrad, R.P. Fetherston, J. Firmiss, J.P. Hockers, J.S. Kim, R.J. Matyi, M.M. Shamim, C. Tan, E.A. Treptow. University of Wisconsin, Madison, WI 53706
A variety of alloy and compound coatings can be synthesized using plasma-based techniques. At high target bias voltages, implantation of ions into the target can be achieved to dose levels sufficient to bring about beneficial surface modification. The range of compositions achievable, low processing temperatures and environmental cleanliness makes this technique potentially attractive for a number of applications. The paper will focus on the design and development of wear resistant coatings using the plasma source ion implantation method operated in the ion-assisted deposition mode. Results of microstructural characterization and tribological evaluation of these coatings will be presented. The work is supported by the US Army Grant No. DAAII04-94-G-0283 and NSF Grant No. DMI-9528746.
9:10 am
A COMPARATIVE ANALYSIS OF MECHANICAL PROPERTIES IN COATED SYSTEMS BY INSTRUMENTED INDENTATION: Larry Seitzman, Code 6170 Naval Research Laboratory, Washington, DC 20375
Vickers indentation was performed on a variety of coating-substrate combinations. Force-displacement curves were obtained by continuously monitoring the loading and unloading of the indentor. Different methodologies for analyzing the data (i.e. shape effect vs contact depth as well as regression vs polynomial fitting) were compared. Mechanical property profiles of the coated system were obtained from both the loading and the unloading curves, and the properties determined from both curves were compared. Analysis of the unloading curve readily yields hardness and elastic modulus data, while analysis of the loading curve yields additional information. The potential for using instrumented indentation as a quality control tool for coated systems will be discussed.
9:30 am
DAMAGE MECHANISM IN SOLID PARTICLE EROSION OF FeAl-Al203 THERMAL SPRAY COATINGS: Brian Schorr, Arnold Marder, Lehigh University, Bethlehem, PA 18015; Daniel Sordelet, Iowa State University, Ames Laboratory, Ames, IA 50011
The effect of microstructure and splat cohesion on the erosion damage mechanism of FeAl-Al203 plasma and high velocity oxy-fuel (HVOF) coatings was studied. The Al203 content in the cermet pre-sprayed powders was varied from 0-80%. Microstructural evaluation revealed a good correlation between the Al203 in the pre-sprayed powders and the final as deposited plasma coatings. In addition, increased porosity was measured as the Al203 content of the coatings increased. It was found that plasma sprayed coatings tend to fail via splat delamination due to poor cohesion and high porosity, providing accelerated weight loss compared to HVOF and wrought alloys. The addition of Al203 to the plasma sprayed FeAl increased the erosion rate of the tested coatings. Examination of the eroded surfaces revealed cracking of the Al203 which led to undercutting of the FeAl matrix. In contrast, partial removal of splats by gouging as well as cracking occurred in the HVOF coatings.
9:50 am
PLASMA NITRIDING OF TOOL STEELS: Sun K. Kim, Department of Metallurgical Engineering, University of Ulsan, Ulsan, Kyung Nam, Korea 680-749
In order to produce composite surface layers by combining nitriding and coating of titanium compounds, nitriding of tool steels to obtain only diffusion layer on surface is desirable. In this paper, results on experiments to obtain a diffusion layer with zero or minimum amount of compound layer were presented. With SKD11, SKD61 and SKH9 tool steels, experimental process parameters such as hydrogen and nitrogen gas ratios, temperature, pressure and time were changed to obtain an optimum condition.
10:30 am
MICROSTRUCTURE, WEAR RESISTANCE, AND HIGH TEMPERATURE OXIDATION RESISTANCE OF BORONIZED GAMMA-TiAl: Soosik Kim, Youngsic Yoon, Hansam Kim1, Kyeongsoon Park2,Met. Eng. Dept., Inha Univ., Inchon, Korea, 1Metall. Eng. Dept., Inha Tech. College, Inchon, Korea, 2Materials Eng. Dept., Chung-ju National Univ., Chungju, Korea
Ti-45.0 at% Al-1.6% Mn intermetallic compounds, which were fabricated by reactive sintering, were boronized in the temperature range 1150 to 1250°C under a flow of Ar gas in a graphite pack with boron carbide (B4C) powders. Energy dispersive x-ray spectroscopy (EDXS) and x-ray diffraction (XRD) were used to investigate the phase present in the coating layer. The coating layer was composed of Ti2B, TiB, and Al2Ti4C2 phases. The formation mechanism of the above compounds in the coating layer was investigated. Some vacancies were found below the coating layer. The thickness of the coating layer increased with increasing boronizing temperature and time. The activation energy of formation of the coating layer was calculated to be 320 Kj/mole. The microhardness of the coating layer was extremely high (700-800 Hv), compared to that (300-400Hv) of the substrate, improving the resistance to wear and high-temperature oxidation.
10:10 am BREAK
10:50 am
THE WEAR-RESISTANCE OF TiNi INTERMETALLICS WITH TiN COATING: H.C. Lin, H.M. Liao, J.L. He, K.M. Lin, K.C. Chen, Department of Materials Science, Feng Chia University. Taichung, Taiwan 407, China
The wear resistance of TiNi intermetallics with TiN coating was studied by wear test, hardness measurement, XRD and microstructure observation. Both TiN and Ti2Ni layers are found to form on the surface of ion-nitrided TiNi intermetallics. These layers can improve the wear-resistance of these TiNi intermetallics. The effects of nitriding temperatures, TiN/Ti2Ni thickness and applied wear-load on the wear behavior of TiNi intermetallics are investigated in this paper. Meanwhile, the major wear mechanisms in these ion-nitrided TiNi intermetallics are also discussed.
Room: 340B
Session Chairpersons: Dr. Edward S. Chen, U.S. Army Research Office, 4300 S. Miami Boulevard, Research Triangle Park, NC 27709; Dr. Douglas B. Gundel, Systran Co., Inc., 4126 Linden Ave., Dayton, OH 45432
8:30 am INVITED
INTERMETALLIC MATRIX COMPOSITES PREPARED BY MECHANICAL ATTRITION: A REVIEW: Carl C. Koch, Department of Materials Science & Engineering, North Carolina State University, Raleigh, NC 27695
The interest in intermetallic matrix composites has grown in recent years due to the realization that monolithic intermetallics would not likely satisfy the balance of properties needed for advanced aerospace systems. Processing of intermetallic matrix composites is a critical issue and a number of methods have been explored to fabricate such composites with either continuous or discontinuous reinforcements. While the latter category in general provides less improvement in mechanical behavior, this is the type of composite where mechanical alloying may provide an inexpensive processing route. Intermetallic systems to be discussed include Ni3Al, NiAl, Ti3Al, TiAl, and MoSi2. Early work on oxide dispersions in intermetallics by mechanical alloying, dispersions introduced by cryomilling, and nanocrystalline intermetallic composites will be covered by this review. The possibility of superplastic forming of nanocrystalline intermetallic matrix composites will also be considered.
9:00 am
MECHANICAL ALLOYING OF INERT GAS ATOMIZED Al-Li-Cu-Mg-Zr ALLOY/SiC SHORT FIBERS REINFORCED MMC POWDERS: S. Özbilen, Gazi University, Faculty of Technical Education, Department of Metals Education, Teknikokullar, Arkara, Turkey
MMC powders of Al-Li-Cu-Mg-Zr alloy base with variable amount SiC short filamentary reinforcement were produced in a pilot plant down-draught atomizer with a Mannessman type nozzle under Ar. Powder based alloy matrix composite powders were ground in a mechanical alloying attritor not only for introducing deformation but also to investigate the influence of this new and unique processing route on the microstructure and properties of the material system under investigation.
9:25 am
SYNTHESIS OF NANOSTRUCTURED SiC/Si3N4 COMPOSITE POWDERS THROUGH REACTION MILLING: Z.-G. Yang, L. Shaw, Department of Metallurgy and Materials Engineering, University of Connecticut, Storrs, CT 06269
In this study, synthesis of SiC/Si3N4 nanocomposite powders through reaction milling was investigated. Graphite and silicon powders were used as the source of carbon and silicon respectively, while the source of nitrogen was from either nitrogen or ammonia gases. Various compositions of the starting powder mixtures for forming nanopowders spanning from pure SiC to pure Si3N4 were investigated. It was found that nanocrystalline SiC powders could be synthesized at ambient temperature by milling silicon and graphite powders in argon atmosphere. However, the formation of SiC was retarded when milling was conducted in nitrogen or ammonia atmosphere. Crystalline Si3N4 formed only after post annealing the milled powder mixtures and the annealing temperature had a strong effect on the formation of the composite powders. Based on the results from XRD, TEM, DTA and TGA, the formation mechanisms of the composite powders will be discussed.
9:50 am INVITED
SYNTHESIS OF METAL MATRIX COMPOSITES BY MECHANICAL ALLOYING: F.H. Froes, C. M. Ward-Close, E.G. Baburaj, A. Vassel, College of Mines & Earth Research, University of Idaho, Moscow, ID 83844
Abstract not available.
10:20 am BREAK
10:30 am
AN INVESTIGATION OF THE VACUUM HOT PRESSING BEHAVIOR OF SILICON CARBIDE FIBERS COATED WITH NANOCRYSTALLINE Ti-6Al-4V: Joseph M. Kunze, Triton Systems, Inc., 114 Turnpike Road, Chelmsford, MA 01824; Haydn N. G. Wadley, Intelligent Processing of Materials Laboratory, Department of Materials Science & Engineering, University of Virginia, Charlottesville, VA 22903
The vacuum hot pressing of silicon carbide monofilaments coated with nanocrystalline Ti-6A1-4V has been studied and modeled. In the experiments, surprisingly high identification rates were observed, even at processing temperatures and pressures well below those used for processing conventional Ti-6A1-4V. From the cross sections of partially consolidated specimen, the evolution of coated fiber-fiber contacts and pore shapes were determined. The pores were found to be cusp-shaped throughout the consolidation process. Columns of coated fibers were observed to form which resulted in regions of locally high fiber volume fraction. In the model, the initial densification was based upon a micromechanical contact analysis for a metal coated fiber. Final stage densification was analyzed by modifying the Qian et al strain rate potential for a power law creeping body containing isolated cusp-shaped pores. Simulations of the VHP experiments were performed using this model which incorporated time and temperature dependent microstructure relations. Overall, the simulations compared well with the experimental density data, although the load supported by the regions of locally high fiber volume fraction resulted in the model slightly overestimating the observed densification time response.
10:55 am
MODEL-BASED SIMULATION OF THE CONSOLIDATION PROCESSING OF METAL COATED FIBERS: D.M. Elzey, R. Vancheeswaran, H.N G. Wadley, Intelligent Processing of Materials Laboratory, Department of Materials Science & Engineering, University of Virginia, Charlottesville, VA 22903
The metallization of structural ceramic fibers by physical vapor deposition, sputtering, etc., followed by consolidation (e.g. hot isostatic pressing) offers an attractive route for the manufacture of continuous fiber-reinforced metal matrix composites (MMC's). Recent models for describing the evolution of key microstructural features (such as porosity, interfacial reaction zone thickness and fiber microbending/fracture) during consolidation are described, and are combined to simulate changes in the composite's microstructural "state" during arbitrary consolidation process schedules. Results are presented for PVD Ti-6Al-4V -coated SiC monofilament fibers consolidated by vacuum hot pressing which illustrate the presence of optimal solutions to the process path planning problem. An optimization scheme is briefly described which allows identification of the consolidation process cycle providing maximum relative density with minimum fiber and interfacial damage. In addition to the process schedule, optimal quality is shown to depend strongly on the fiber/matrix combination, the initial coated fiber packing geometry and the (evolving) matrix microstructural state.
11:20 am
MODEL-BASED SIMULATION OF THE CONSOLIDATION PROCESSING: R.Vancheeswaran, H. N. G. Wadley, Intelligent Processing of Materials Laboratory, Department of Materials Science & Engineering, University of Virginia, Charlottesville, VA 22903
The performance of fiber reinforced titanium matrix composites (TMC) made by consolidation of spray deposited monotapes is strongly influenced by the processing conditions used. This high temperature consolidation step must simultaneously minimize fiber microbending/fracture, the interfacial reaction product layers at the fiber-matrix interface and at the same time eliminate matrix voids (i.e. increase the relative density). These three microstructural variables have conflicting dependencies upon the consolidation process variables (temperature, pressure and time), and it has been difficult to identify process pathways by trial and error that lead to composites of acceptable quality (where the fiber damage and reaction layer thickness are kept below some bounds, while matrix porosity is eliminated). Models for predicting the microstructure's dependence upon process conditions (i.e. the time varying temperature and pressure) are combined with consolidation equipment dynamics to simulate the microstructure evolution and to assess the relative "processability" of several silicon carbide fiber/titanium alloy matrix systems during their consolidation. We introduce the idea of process failure surfaces and show how this simulation tool in conjunction with a model predictive control (algorithm), is able to design "locally" optimal process cycles that minimize fiber damage, reaction product layer thickness and porosity. The approach is then used to path plan process schedules that will steer away from these damage surfaces for a variety of TMC systems.
11:45 am
STUDIES ON SINTERED ZIRCON-REINFORCED ALUMINUM ALLOY MATRIX COMPOSITES: J. U. Ejiofor, Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487; B.A. Okorie, Department of Metallurgical and Materials Engineering, Enugu State University of Technology, P.M.B. 01660, Enugu, Nigeria; and R. G. Reddy, Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487
Zircon, ZrSiO4, is a thermally stable mineral. Owing to its abundance, high hardness, excellent abrasion/wear resistance and low coefficient of thermal expansion, researchers are investigating its use for medium strength, tribological applications. In the present study, the conventional low-cost, double compaction powder metallurgy route in the synthesis of Al-13.5Si-2.5 Mg alloy(wt%) reinforced with ZrSiO4, was investigated. The mechanical, physical and tribological properties were determined following the development of optimum conditions of compaction and sintering. At 0.15Vf, the UTS, 0.2%Y.S. and hardness improved by 4%, 12.8% and 88% respectively while the adhesive wear rate and the coefficient of friction reduced by 99.55 and 35.5% respectively. At a critical volume fraction of zircon, between 0.03 and 0.05, a significant improvement in wear resistance was observed. The use of optical microscopy, EPMA, SEM and x-ray analysis revealed the phases and possible reactions at the matrix-reinforcement interface, fracture mode and compositions of fractured surfaces which are related to measured mechanical properties and, the influence of the reinforcement phase on wear rate. Further structural analysis showed that the improvement in mechanical properties is attributed largely to the load-bearing ability and intrinsic hardness of zircon than to particulate dispersion effects. An attempt was made to model the strength of the composites.
Room: 230D
Session Chairman: David Riner, Reynolds Metals Co., PO Box 9911, Corpus Christi, TX 78469
8:30 am
OPTIMIZATION OF ALUMINA PLANT OPERATION WITH RESPECT TO MARKET CONDITION: P. Das, National Aluminium Company Ltd., Damanjodi, Dist. Koraput, Orissa 763008, India
In international markets, wide fluctuations of alumina prices have been found to be a common phenomenon over the years. It has been observed that almost all the buoyant cycles have essentially been followed by recessionary market conditions. Hence, during the periods when alumina prices are relatively low, for survival it becomes obligatory on the part of the management to strike an operational philosophy suitable for achieving minimum cost of production. However, during buoyant market conditions it is wise to make attempts for maximization of production by suitable optimization of process parameters even if there is a marginal increase in unit cost of production. Since such attempts are directly related to the profitability of the organization, a careful study should be made taking into consideration all interrelated factors. This paper highlights the areas of an alumina plant where changes in process parameters, permissible on technoeconomic consideration, could be made for optimization of production and profitability.
8:55 am
DEVELOPMENT OF SOFTWARE FOR BAYER PROCESS ALUMINA PLANTS: C. Misra, V. Soi, Alumina Technology Associates, 714 Pine Valley Drive, Pittsburgh, PA 15239
PC based software packages have been developed to assist in the operation and management of Bayer process alumina plants. Software packages for digestion, residue washing and precipitation areas have been designed for use by plant operators to formulate operating policy and are integrated with existing or new process control systems. As example, important features and structure of software developed for the precipitation system are discussed in more detail.
9:20 am
DYNAMIC MODELING OF YIELD AND PARTICLE SIZE DISTRIBUTION IN CONTINUOUS BAYER PRECIPITATION: Jerry L. Stephenson, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069; Chris Kapraun, Alcoa Alumina & Chemicals, L.L.C., Point Comfort Operations, State Highway 35, Point Comfort, TX 77978
Process engineers at Alcoa's Point Comfort refinery are using a dynamic model of the Bayer precipitation area to evaluate options in operating strategies. The dynamic simulator, a joint development effort between Point Comfort and Alcoa Technical Center, predicts process yield, particle size distributions, and occluded soda for a given flowsheet of the precipitation and classification circuit. In addition to rigorous material and particle population balances, the model includes mechanistic kinetic expressions for particle growth, agglomeration, nucleation, and attrition. The kinetic parameters have been tuned to Point Comfort's data with excellent matches between the model results and plant data. The model is written for the ACSL package with specially developed input/output graphical user interfaces which provide a user-friendly tool. Features such as a seed charge controller enhance the model's usefulness for evaluating operating conditions and process control approaches.
9:55 am
INCREASING THE ACTIVITY OF SEED USED FOR PRECIPITATION OF THE SODIUM-ALUMINATE LIQUOR: Bi Shiwen, Yang Yihong, Fu Gaofeng, Wen Jie, Ju Aihua, Department of Nonferrous Metallurgy, Northeastern University, Shenyang, 110006, China
The activity of seed is one of the most important factors in the precipitation of the sodium-aluminate liquor. The industrial aluminumoxide-hydrate is treated with sulfuric acid to increase its activity, and then it is used as the seed of precipitation. It is demonstrated that the seed has the ability to increase the rate of precipitation. The reason of this phenomenon is analyzed.
10:10 am BREAK
10:30 am
SECONDARY NUCLEATION OF ALUMINUM TRIHYDROXIDE IN BAYER SODIUM ALUMINATE SOLUTION: Xue Hong, Bi Shiwen, Shuai Shiwu, Yan Yihong, Li Dianfeng, Department of Nonferrous Metallurgy, Northeastern University, China; Chen Wankun, The Great Wall Aluminum Company of China
In this paper, secondary nucleation of aluminum trihydroxide in Bayer sodium aluminate solution was discussed by picture analysis and scanning electron micrograph. The effects of temperature, seed size and aluminate concentration on secondary nucleation are determined with growth time. As this study has shown, the nucleation rate depends upon the experimental conditions of supersaturation, temperature and seed size or surface area. The nucleation can promote the formation of relatively large particles under an opportune condition.
10:55 am
BAYERITE - ALUMINIUM TRIHYDROXIDE: Maurycy M. Pyzalski, Technical University of Mining and Metallurgy, Faculty of Ceramics and Material Engineering, Ave. Micklewicz 30, A-3, 30 - 059 Cracow, Poland
The physico-chemical properties of Bayerite, which was obtained in semi-commercial scale using new technology, were investigated in detail. The properties of another polymorphic form of aluminum trihydroxide, i.e., hydrargillite (Gibbsite) obtained by means of Bayer's and Grzymek's methods were also evaluated in a similar way. The results thus obtained allow characterization of the properties of hydroxides. They also put a new light on their formation and polymorphism.
Room: 230A
Session Chairperson: Jeff Keniry, Comalco Research, 15 Edgars Road, Thomastown, VIC 3074, Australia
8:30 am
UNDERSTANDING BOUNDARY-LAYERS: Warren Haupin, 2820 Seventh Street Road, Lower Burrell, PA 15068
Understanding the physics and chemistry of boundary-layers, the thin stagnant zones that form at each bath interface, clarifies many cell phenomena. A non-wetting boundary at the anode causes the anode effect. The effect of bath velocity on the boundary-layer thickness and its effect on the heat transfer coefficient coupled with bath temperature and bath composition explains the formation and loss of frozen ledge and its relationship to heat losses from the cell walls. Similarly, the boundary-layer at the bath-aluminum interface ex plains cathodic overvoltage, the sodium content of the aluminum, current efficiency and the relationship of each to metal pad stability (magneto-hydrodynamic stability).
8:55 am
ON THE COMPOSITION OF SOLID DEPOSITS FROZEN OUT FROM CRYOLITIC MELTS: Asbjørn Solheim, Lisbet I. R. Støen, SINTEF Materials Technology, N-7034 Trondheim, Norway
Thermodynamically, the primary crystallization product formed by cooling a melt containing cryolite, AlF3, Al2O3 and CaF2 is expected to be cryolite with minor amounts of CaF2 and AlF3 in solid solution. In practice, however, any deposit frozen out from such melts may contain considerable amounts of bath constituents other than cryolite. The factors governing the composition of the freeze are studied theoretically and by experiment. Besides solid solution, the composition depends on two factors, 1) diffusion of bath constituents from the surface of the deposit towards the bulk of the melt, and 2) dendritic crystal growth with subsequent trapping of bath between the crystals. The condition which gives dendrite formation is formulated. Based on this criterion, a deposit frozen out from melts containing excess AlF3 and alumina would contain more AlF3 than a deposit frozen out from a melt containing excess AlF3 alone. This was confirmed by experiment.
9:20 am
THE GAS UNDER ANODES IN SMELTING CELLS. Part I: MEASURING AND MODELLING BUBBLE RESISTANCE UNDER HORIZONTAL DE-ORIENTED ELECTRODES: T. M. Hyde, B. J. Welch, Department of Chemical Engineering, University of Auckland, New Zealand
With a continuing drive to reduce energy and the tighter operating tolerances of modern aluminium smelting cells, there is an ever increasing need for a precise cell voltage equation. Precise correlation exists for the electrical conductivity in smelting cells, the reverse is not the case for the added resistance effect of gas bubbles. Where it has been allowed for, the models used have been based on those proposed for vertically oriented electrodes. Furthermore the measurements on which the model is based can be influenced by other electrochemical changes while the shape and dispersion and gas bubble differ from those expected in aluminium smelting cells based on model studies. An apparatus and high speed switching data acquisition technique have been developed to allow the ohmic resistance of a molten salt electrolyte to be isolated from all other contributors. Ceramic objects of known geometry, size and volume, rest in the electrolyte immediately under the upper electrode (anode) thus simulating gas bubbles. The technique developed enables the measurement of the direct increase in resistance due to the introduced volume of non-conducting simulated gas. The bubble parameters examined included volume, electrode coverage, depth and shape. The resulting data have been tested against existing models.
9:45 am
THE GAS UNDER ANODES IN SMELTING CELLS. Part II: GAS VOLUME AND BUBBLE LAYER CHARACTERISTICS: R. Aaberg, V. Ranum, The Norwegian University of Science and Technology, 7034 Trondheim, Norway; K. Williamson, B. J. Welch, Department of Chemical & Materials Engineering, The University of Auckland, New Zealand
Recent physical models have suggested that the gas bubbles formed under anodes in smelting cells tend to coalesce and release as large bubbles predominantly. Whilst it is well established that the gas bubbles increase the cell resistance, and correlations proposed include the gas volume or bubble layer depth and surface coverage. However, the volume and degree of coverage of the electrodes have been subject to speculation rather than accurate measurements. In this investigation, using a larger than normal laboratory cell, it has been confirmed that the gas released is consistent with the physical models with most of the gas being evolved in discreet large bubbles. The release frequency is similar to the dominant frequency found in operating cells. The average gas volume under an anode prior to release is between 0.4 and 0.5 cm3 per cm2 of electrode. From combined resistance studies it has been calculated that approximately two thirds of the anode is covered with gas at release with an average bubble thickness of 5 mm.
10:10 am BREAK
10:30 am
MICROPYRETICALLY SYNTHESIZED POROUS NON-CONSUMABLE ANODES IN THE Ni-Fe-Cu-Al SYSTEM: J. A. Sekhar, H. Deng, J. Liu, International Center for Micropyretics, Department of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH 45221-0012; V. de Nora, MOLTECH S.A., 9, Route de Troinex, 1227 Carouge, Geneva, Switzerland
A micropyretically synthesised porous Ni-Fe-Cu-Al intermetallic composite electrode has been developed for use as a non-consumable anode in the Hall Héroult cell. The oxidation behavior in air and under electrolysis conditions have been studied. The electrode is noted to be resistant to the corrosive conditions encountered during electrolysis for up to 300 hour tests in 10 Amp and 100 Amp cells. The synthesis procedures for the manufacture of the electrodes and the beneficial influence of the pores are discussed. Preliminary results on the metal contamination during electrolysis are also presented.
10:55 am
APPLICATION OF NONEQUILIBRIUM THERMODYNAMICS TO THE LEDGE SURFACE OF ALUMINIUM ELECTROLYSIS CELLS: Ellen Marie Hansen, Signe Kjelstrup, Department of Physical Chemistry, The Norwegian University of Science and Technology, N-7034 Trondheim, Norway
Nonequilibrium thermodynamics for surfaces has been applied to the interface ledge-electrolyte in aluminium electrolysis cells. The method describes the interface as a layer of finite thickness 
, having a bath-like part and a ledge-like part, with properties differing from the bulk properties. The method can explain the heat transfer coefficient for the interface in a new way, namely as a combination of the thermal conductivities in the two parts of the interface. Examples are given to show how the temperature "jump" between the two bulk phases may either be located in the ledge-like part of the interface, in the bath-like part, or in both. In analysis of ledge growth, the possibility of different surface temperatures should be taken into account, because this temperature may, together with the temperatures close to the interface on both sides, determine the rate of freezing or melting. It is also shown how the simple steady state model can be expanded into a dynamic one.
11:20 am
PHYSICO-CHEMICAL PROPERTIES OF Na3AlF6-AlF3-LiF-CaF2 SYSTEM UNDER THE SAME SOLVABILITY OF Al2O3: Li Dexiang, Chen Jianshe, Li Guohua, Department of Nonferrous Metallurgy, Northeastern University, Shenyang, 110006, China; Ma Xiufang, Beijing Nonferrous Metal Research Institute, Beijing, China
The concept of properties of electrolyte melts under the same solvability of alumina at nonequal temperature, that is, the properties of melts under equal solvability of alumina dissolving in the electrolyte at the temperature which is 20°C above the liquidus, were put forward. Based on this theory, the physico-chemical properties, such as the initial crystallization temperature, solvability of alumina, conductivity, density of (2.23-3.0) NaF·AlF3 - (0-5%) LiF - (0-15 %) CaF2 system were studied. The results will provide more scientific basis for choosing the optimum electrolyte composition in aluminium electrolysis.
11:45 am
MEASUREMENTS OF HF IN STACKS AND POT ROOMS USING A REMOTE SENSING EYE-SAFE LASER INSTRUMENT: H.I. Schiff, Unisearch Associates, Inc., 222 Suidercroft Rd., Concord, Ontario, Canada L4K 1B5
A remote sensing system for continuous measurement of HF and other gases has been developed based on eye-safe turnable gases. The laser, its controls and data acquisition system are contained in a small instrument which can be located anywhere in the plant, such as the control room. The optical beam is transported to one or more stacks or ducts by fibre optics which may be kilometres in length. It is then directed across the stack and returned by a retroreflector to the same optical fibre and retroreflector combination for pot-room or roof-top monitoring. The use of optical multiplexing permits a single instrument to make simultaneous measurements at a number of locations providing a very cost effective system which can operate in any environment. Systems have been installed in four Canadian smelters and one in the UK. Examples of some of the measurements made with these systems will be presented.
Room: 232A
Session Chairs: J.M. Toguri, Dept of Metallurgy and Materials Science, Univ. of Toronto, 184 College Street, Toronto, Ontario, Canada, M5S 1A4; U. Pal, Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Room 4-134, Cambridge, MA 02139
8:30 am
MEASUREMENT OF GAS COMPOSITIONS USING SOLID ELECTROLYTES: R.V. Kumar, D.J. Fray, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, United Kingdom
Sensors are required to measure gaseous species such as SOX, NOX, HCl, and water vapour at elevated temperatures. There are very few solid electrolytes which respond to these gases, and furthermore, the species are usually present with other gases to which the electrolyte may respond. In addition, for long periods of operation, a stable reference is required. In order to meet these challenges, sensors consisting of two electrolytes in intimate contact have been developed. To measure HCl, a proton-conducting electrolyte is interfaced with strontium chloride. The reaction for the cell: (-) Pt, Air + HCl(g))/SrCl2//SrCeO3 + 10 mole % Nd2O3// Air + HCl(g), Pt(+). At the various interfaces, the reactions are: anode: 2Cl- + SrHCl = SrCl2 + HCl(g) + 2e-interface: 2H+ + 2Cl- = 2HCl(interface) cathode: HCl(interface) + SrCl2 + 2e- = SrHCl + 2Cl- overall cell reaction: HCl(interface) = HCl(g). The net result is that the potential is independent of the oxygen potential of the gas and the reference is given by the interaction of the two electrolytes. There is no need for an external reference which overcomes the problems of forming gas thigh seals at elevated temperatures. Other examples of this approach for the measurement of SOX, NOX, CO2, and H2O will be given.
8:55 am
DEVELOPMENT AND APPLICATION OF OXYGEN SENSORS IN COPPER METALLURGY: S. Seetharaman, Du Sichen, A. Jakobsson, Division of Theoretical Metallurgy, Royal Institute of Technology, S-100 44 Stockholm, Sweden
Oxygen concentration cells with stabilized zirconia electrolytes are widely used today to measure the activity of oxygen in liquid metals. In the case of liquid copper, the activity of oxygen in the molten metal as well as the effect of a third element on the same have been extensively studied using galvanic cells of the type (-) Pt, W or cermet / Cu-O-M // ZrO2 (stabilized) // AO, A / Pt (+, where M is the third element in molten copper and AO / A represents a suitable oxide/metal reference electrode. The effect of a number of "third elements" like Mn, Zn, As, Se, and Te on the oxygen activity in liquid copper have been studied by this method. The Mn and Zn interact very strongly with oxygen in Cu ( ), while, in the case of arsenic, the interaction parameter is nearly zero. The behavior of Se and Te in liquid copper with respect to the effect on the activity of oxygen is unique. At oxygen levels of the order of 10-4, these elements lower the activity coefficient of oxygen in the melt, while, at lower oxygen levels, the interaction parameter values are positive. These results are discussed in the light of some of the theoretical models for solute interactions in liquid metals. The application of these sensors in flash smelting, converter, and casting sections of copper production are discussed along with their implications on process optimization.
9:20 am
APPLICATION OF RAMAN SPECTROSCOPY TO HIGHTEMPERATURE ANALYTICAL MEASUREMENTS. J.P. Young, S, Dai, Y. Lee, H. Xiao, Chemical and Analytical Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 378316142
There are numerous analytical applications of scatteremission and absorption spectroscopy to liquids and solids in the temperature range of 0° to 350°C; process control is made impossible by using fiberoptic probes and Raman spectroscopy, for example, in these measurements. We have developed a unique allsilica fiberoptic probe which can have analytical applications in the temperature range where silica is a solid, 0° to 1600°C, and in chemical situations where it is inert. We have also developed techniques to use the ratio of the Stokes/antiStokes Raman emission of diamond to measure temperature in the range of 400 to 1000°C. We will discuss our results of such measurements in molten chloride and fluoride salts, other liquids, and solids. We will also describe our plans for temperature measurements by Raman spectroscopy through optical fibers in the range of 1000 to 2500°C, a range that can include molten metals such as steel.
9:45 am
SOLID STATE CURRENT-POTENTIAL SWEEP SENSOR FOR THE IN-SITU MONITORING OF COMPOSITION AND TRANSPORT PROPERTIES IN HIGH TEMPERATURE METALLURGICAL SLAGS: S.C. Britten, V. Stancovski, U. Pal, Dept of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 4-134, Cambridge, MA 02139
An in-situ solid-state electrochemical technique for measuring the concentrations of easily dissociable oxides in slags at temperatures between 1200 to 1600°C is being developed. The technique consists of using a stabilized zirconia solid electrolyte, which conducts oxygen ions, to separate a reference gas compartment from the slag of interest. Using a potentiostat, a direct current potential sweep is applied between the inner and outer compartments of the electrolyte, driving oxygen ions from the slag into a reference gas. With the use of open circuit reference electrodes, the resulting magnitude of the current potential profile reveals the concentration of dissociable oxides such as those of iron, manganese, and chromium. The open circuit potential recovery indicates the type of oxide present and its thermodynamic activity within the slag. The technique should therefore determine multiple properties of several different oxides with only one measurement. The limits imposed by the electronic short-circuit property of the zirconia electrolyte on the sensitivity of the technique are also under investigation.
10:10 am BREAK
10:20 am
APPLICATIONS OF SENSORS IN MOLTEN SALT TECHNOLOGY FOR METAL PROCESSING: P.T. Velu, R.G. Reddy, Dept of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487
The use of emf measurements to derive classical thermochemical data has been in use for many years. The reaction associated with electrochemical process is harnessed in a galvanic cell and energy involved measured in terms of electromotive force. The property requirements of sensor electrodes used differ for various aqueous, molten salt, and solid electrolyte systems. The electrodes for molten salt electrolytes need special care for construction. This paper describes the studies carried using an Ag/AgCl reference electrode. This electrode was used to measure the solubility of compounds in molten salt electrolytes. The results obtained using this electrode are in excellent agreement with the values from chemical analysis method.
10:45 am
NOVEL SOLID STATE SENSOR FOR MEASURING ARSENIC IN MOLTEN METALS: G.M. Kale, Dept of Mining and Mineral Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom; D.J. Fray, Dept. of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3 QZ, United Kingdom
A novel solid state sensor for measuring arsenic dissolved in molten metals has been developed based on a novel solid electrolyte conducting K+ ions. The solid state sensor can be schematically represented as: (-)Mo, Zn-As/ /K-323 SE/ /K-
Fe2O3+Fe2O3+02, Fe-Cr(+). The open circuit emf of the above sensor was measured in molten zinc containing less than 0.1 wt % As at a temperature of 823K. The emf of the sensor was found to vary linearly as a function of 1nXAs, where XAs is the mole fraction of As in An(1). The ionic conductivity of the novel solid electrolyte (K-323) was measured over a range of temperature (370<T<770K) using a vector impedance analyzer. The K+ ion conductivity of K-323 at 823K was found to be 1 X 10-3
-1cm-1. The performance of these arsenic sensors is currently being evaluated in plants in the United Kingdom and Germany.
11:10 am
MEASUREMENT OF NITROGEN AND SULPHUR IN MOLTEN METALS USING SOLID ELECTROLYTES: Y.C. Avniel, T.E. Warner, D.J. Fray, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, United Kingdom
One of the major problems of the iron and steel industry is the presence of phosphorus, sulphur, nitrogen, and silicon. Careful control and removal of these elements is required, and an on-line measurement of the concentration during removal would greatly improve the efficiency of the process. The oxygen content of molten metals is usually measured by using a sensor based upon stabilized zirconia, in which the oxygen ion is mobile. However, for nitrogen and sulphur, stable ionically conducting solid electrolytes for nitrogen and sulphur do not exist. The approach adopted in this work is to use electrolytes which conduct alkali and alkaline earth elements. For example, when a sodium ion conducting electrolyte is placed in a situation where sodium is not present, the sodium comes to equilibrium with the species which forms the most stable compound with sodium. Examples are given where sodium, strontium, and calcium beta alumina respond to sulphur and oxygen. Regions of response to a given species depend upon the concentration of other species in the melt and the standard free energy of formation of the various compounds. In the case of nitrogen measurement, it proved necessary to develop a new electrolyte, based upon rare earth oxides, in which nitrogen is soluble in the anion lattice. Results are presented for the measurement of sulphur and nitrogen partial pressures and for these species in molten iron and steel.
Room: 231A
Session Chairperson: D.B. Dreisinger, University of British Columbia, Department of Metals and Materials Engineering, 309-6350 Stores Road, Vancouver, B.C., Canada
8:30 am
INDUSTRIAL IN-PULP Co-Ni ALLOY ELECTRO-WINNING AT THE GECAMINES-SHITURU PLANT: K. Twite, J.-M. Dereydt, K. Mujinga, Gecamines Shituru Plant/Likasi, Bd. du Souverain 30, 32, B1170 Brussels, Belgium; P. Louis, Union Miniere, Allée de la Frènaie, B 1300 Wavre, Belgium
GECAMINES is a large mining concern and the world's leading cobalt producer having some of the richest cobalt deposits in the world. Cobalt is associated in the ore with copper as sulphides and oxides and in some locations with nickel too. Specific hydrometallurgical processes have been developed by GECAMINES which had done an important contribution to the development of the cobalt hydrometallurgy. In the Shituru plant, cobalt is obtained from an unique in-pulp electrolysis process, while in Luilu, cobalt is electrolyzed in a clear acidic solution giving a purer deposit. In the beginning of 1996 Shituru started the treatment of mixed Cu-Co-Ni Shinkolobwe hydrates obtained as by-product of an uranium solvent extraction plant. A typical analysis of this feedstock is: Cu: 2%, Co: 8%, Ni: 4%. The nickel sulfide depolarized cementation process developed previously by GECAMINES was inefficient to treat such a high level of Nickel contamination and it was decided to produce alloyed Cobalt-Nickel cathodes in the Shituru tankhouse. As anticipated from laboratory tests as previous studies and publications, a lower Ni/Co in the deposit was obtained compared to the Ni/Co ratio solution, despite the nickel reversible electrochemical potential is somewhat higher than the one of cobalt (-0.25 V vs -0.28 V). In this paper, the process flow-sheet and production data are given. Cobalt alloy with 5 - 20 % Ni was obtained at a production level of 300 t per month. The process developed is a first industrial realization in this way, bringing a new contribution to cobalt hydrometallurgy.
8:55 am
ELECTROLYTIC PROCESSING OF MANGANIFEROUS SILVER ORES IN ACIDIC NITRATE MEDIUM: O. Rutten, S. Van Sandwijk, G. Van Weert, Department of Raw Materials Technology, Delft University of Technology, Mijnbouwstraat 120, 2628 RX Delft, The Netherlands
Cathodic and anodic reactions in the acidic nitrate medium were studied in reference to the electrolytic production of manganese dioxide from pyrolusite (Mn02) ores by reductive leaching. Two USA ores were investigated. The reductant for Mn02 is produced cathodically and can either be nitrous acid or nitrogen oxide gas. In this work emphasis was placed on the nitrous acid leach. Manganese and silver are solubilized, iron is not. Cathodic regneration of nitrous acid was investigated in the range of 0.5 to 3.0 M nitric acid, 0.0 to 0.1 nitrous acid on graphite, platinum and platinized titanium cathodes at 20 to 80°C. It was established that the formation of the nitrosyl ion (N0+) is a prerequisite for the cathodic reduction of nitric acid. At cathode potentials < +700 mV (SHE), cathodic reduction of nitrous acid to nitric oxide takes place. Anodic deposition of manganese is as flaky -Mn02, similar to that produced in sulphate electrolytes. A conceptual flowsheet is presented and discussed.
9:20 am
A NOVEL ELECTROMETALLURGICAL PROCESS FOR THE TREATMENT OF REFRACTORY GOLD CONCENTRATES: N. de Jager, M.J. Nicol, University of the Witwatersrand, School of Process and Materials Engineering, Johannesburg, South Africa
In order to liberate gold from refractory gold ores and concentrates it is necessary to oxidize the surrounding sulphide minerals, typically pyrite and arsenopyrite. Traditional methods of oxidation include pressure leaching, roasting and bacterial oxidation. In recent years, bacterial oxidation has found increasing favour, although it is by no means completely satisfactory and is subject to large residence times. It is also extremely sensitive to operating conditions. Similarly, pressure leaching and roasting have their own particular disadvantages. A novel process has been developed as an alternative to the traditional methods whereby electro-generated ferrate [iron (VI)] ions in alkaline solution are used to oxidize a pyrite concentrate. This process has been observed to proceed fairly rapidly and could prove to be a more economically viable process, as well as being more environmentally acceptable. As an added benefit, operating in an alkaline environment is advantageous for downstream cyanidation processes. Iron (VI) is a relatively unknown species, due mainly to its instability in acidic solutions. However in alkaline solution it has been observed to be sufficiently stable for use as an oxidant when kept under the correct conditions. Iron (VI) is most conveniently manufactured electrolytically via the dissolution of high-carbon iron anodes in strongly alkaline solutions. Some literature has been published on the electrolytic generation of iron (VI) and relatively high efficiencies have been observed by both the authors and other researchers. This study utilizes both electrochemical techniques and leaching experiments to examine the kinetics and mechanism of the oxidation of pyrite by iron (VI). Cyclic voltammetry, rotating disk voltammetry and potential step experiments have been used to investigate the mechanism and kinetics of the oxidation process. Other potentiodynamic and poteniostatic techniques have also been employed. Leaching experiments have been used to provide a more detailed investigation into the kinetics of the process.
9:45 am
ELECTROLYTIC RECOVERY OF MERCURY FROM LOW CONCENTRATION BRINE SOLUTIONS: M. Rockandel, Universal Dynamics Ltd., Vancouver, Canada
Universal Dynamics Ltd. of Vancouver, Canada has developed, patented and commercialized the "REMERC" process for the treatment of mercury contaminated sludges and soils. Mercury is extracted into an acidified and oxidizing, sodium chloride brine solution. REMERC was initially developed to treat mercury contaminated EPA listed wastes (K106) generated by the chlor-alkali industry. More recent work has expanded the capability of REMERC to include remediation of mercury contaminated sites, equipment and building materials. In the process mercury is currently recovered from solution by cementation on iron powder in an agitated reactor. The process recovers high purity elemental mercury (99.9% purity). Cementation typically recovers about 90-95% of the mercury in 30 minutes. Higher recovery is not necessary because of the recirculation of the leach solution. When treating highly contaminated chloralkali wastes (5-13% mercury content), REMERC will reduce the mercury laden solutions from 400-1,000 mg/l mercury to 50-100 mg/l. In the treatment of less concentrated wastes (<1,000 mg/kg mercury) such as those encountered in site remediation, the treated solutions will generally contain 10-20 mg/l mercury. Cementation while being simple and able to achieve the required recovery has the undesirable properties of; requiring a solid-liquid separation and adding iron to solution which must be precipitated, ultimately increasing the weight of residue to landfill. The potential advantages of electrolysis were recognized early in the development of REMERC. Mercury electrolysis is well known in gold and chloralkali processing. Initial testwork utilized a liquid mercury cathode and a coated titanium anode both common to chloralkali producers. The mercury cathode appeared susceptible to polarization and solution impurities significantly affected performance. Agitation of the mercury pool improved performance but it was still not possible to achieve the reduction objectives. Current efficiencies were low, near 10%, and it was apparent that a relatively large cathode pool would be required to limit the current density. A number of electrode combinations with and without a membrane were then tested in a vertical electrode configuration but the desired performance was not obtained. In 1995 Universal Dynamics working with Dremco Ltd. of Arizona, USA began the development of a plate and frame style electrolytic cell. The objective of the electrolytic process was to achieve similar removals to those obtained by cementation, while producing high purity elemental mercury (>99.9% purity) and chlorine at the anode. Although current efficiency is a relatively minor concern the design objective was to achieve at least 50% CE. The current efficiency goal would require operation of the cell at current densities approaching the limiting current flow. The final cell current densities would therefore be in the range of 0.1 - 1.0 A/m2. Operation of a laboratory scale cell has demonstrated that the operating objectives can be achieved with a cell consisting of closely spaced shiny titanium cathodes and ruthenium oxide coated titanium anodes. Numerous variables were observed to be important including; inter electrode velocity, current density, pH and chlorine stripping. The cell has been tested on solutions generated by two REMERC operations, solution produced during site remediation pilot testing and on more highly concentrated solutions generated by oxidation of calomel generated at Cominco Metals, Norzink facility in Trail, B.C.
10:10 am BREAK
10:30 am
RECOVERY OF Cu2+ AND Cd2+ FROM DILUTE AQUEOUS SOLUTIONS BY ION FLOTATION AND ELECTROLYSIS: F.M. Doyle, University of California at Berkeley, Department of Materials Science and Mineral Engineering, Berkeley, CA 94720-1760; K. Sreenivasarao, Argonne National Laboratory, Energy Systems Division, Argonne, IL 60439
Copper and cadmium metal has been recovered from dilute (3 X 10-4 mol/dm3) chloride solutions by ion flotation with dodecysulfate, followed by electrolysis. This approach should facilitate treatment of effluents too dilute for effective direct electrolysis. The adsorption density of metal dodecylsulfate complexes on bubble surfaces was estimated from surface tension data, and compared well with experimentally-observed metal removal kinetics, and ultimate recoveries. Copper and cadmium were recovered by electrolyzing the foamate, using steel wool cathodes and a graphite anode. The stability constants of the copper and cadmium dodecysulfate complexes are estimated, and used to analyze the thermodynamics of electrolysis. Dodecysulfate was unaffected by the electrolysis process, and hence could be recycled to ion flotation. A conceptual flowsheet for an overall effluent-treatment process is presented.
10:55 am
NITROX METALS CORPORATION'S PROCESS FOR DIRECT LEACHING OF COPPER CONCENTRATES: R.N. O'Brien, E. Peters, Vancouver, B.C., V6N 2G1
It has been discovered that copper concentrates can be leached in strong (40-60%) sulfuric acid with air as the primary oxidant, if nitric acid is present as a catalyst. Chalcopyrite is rapidly decomposed at temperatures well below the boiling temperature of the lixiviant (150C.) and the resulting copper and ferric salts are precipitated as CuSO4 H2O or CuSO43 H2O and FeH(SO4)24H2O. Other metal sulfides such as zinc, lead, nickel, etc. are also converted to sulfates that are nearly insoluble. Sulfur is partially converted to elemental and partially to sulfuric acid. Reduction products of nitric acid can be recovered from the distillate with good recovery. Conversion of as-received copper concentrates is largely complete in about 1 hour. A number of process flow sheets are possible, and one that utilizes existing solvent extraction and electrowinning technology is considered economically feasible. This flow sheet involves (a) separation of metal sulfates and unleachable residues from excess acid by centrifuge, (b) water leaching of salts with partial neutralization (with limestone) of excess acid, to a tenor of 10 g/l Cu2+, (c) solvent extraction of copper using one of the LIX reagents, and (d) precipitating most of the ferric iron from raffinate with more limestone, so that it can be used as recycled water in step (a). Gold and silver are retained in a water insoluble small volume residue also containing any elemental sulfur formed, while minor elements like arsenic, antimony, etc. are retained by the strong sulfuric acid that is centrifuged from solids in step (a). These can be removed from this solution using methods previously developed for the purification of copper electrorefining electrolytes.
11:20 am
ACID RECOVERY AND PURIFICATION USING ABSORPTION RESIN TECHNOLOGY: M. Sheedy, Prosep Technologies Inc., Pickering, Ontario, Canada
Strong mineral acids, principally sulphuric, are widely used as electrolytes for the electrorefining and electrowinning of metals. Impurities in these electrolytes are controlled by continuously bleeding solution form the tank house. In addition to the contaminant these bleed streams contain high levels of sulphuric acid and the metal being recovered. Subsequent treatment of these bleed streams often requires neutralization which generates large volumes of solid waste. Absorption resin technology employing a novel ion exchange technique known as Recoflo allows the separation of the mineral acid from dissolved metal salts. The recovered acid is suitable for recycle back to the electrolyte circuit. The metal salt and other contaminants leave the process free of sulphuric acid. In this process, known commercially as the APU, ion exchange resin is used to sorb sulphuric acid while excluding the metal salts. The purified acid is then removed by washing the resin with water. The process has been extensively used for the recovery of waste pickling acids in the steel industry and anodizing solutions in the aluminum industry. In the mining industry the process has been successfully evaluated for the separation of excess sulphuric acid from copper electrolytes, the removal of magnesium and manganese contaminants from zinc electrolytes, and antimony, bismuth and nickel from copper electrolytes.
11:45 am
ELECTRODEPOSITION OF THIN MULTILAYER MAGNETIC MATERIALS: Z. Liu, K.C. Liddell, Washington State University, Department of Chemical Engineering, Pullman, WA 99164-2710
High-quality multilayers exhibiting giant magnetoresistance have been made by electrodeposition. The thickness of the individual layers was varied by changing the duration of the deposition pulses. Smooth and adherent layers as thin as 1A were made and characterized.
Room: 340A
Session Chairperson: Dr. Subodh K. Das, ARCO Aluminum, Inc., P.O. Box 32860, Louisville, KY 40232
8:30 am
PREDICTING THE FORMABILITY OF ALUMINUM AUTOBODY SHEET ALLOYS: J. Daniel Bryant, Tatsuhito Koya, Armand J. Beaudoin, Reynolds, Metals Corporate Research and Development, Fourth and Canal Streets, P.O. Box, 27003, Richmond, VA 23261
While aluminum alloys based on the Al-Si-Mg-Cu system are currently being used in the production of a number of automotive body panels, the continuing demands for improved formability in these alloys have led alloy developers to the study of novel compositions and processing practices. Predicting stamping performance for a wide range of alloy variants, however, remains a difficult problem. Uniaxial tension tests, while providing reproducible assessments of mechanical behavior, are performed in a strain state that is quite different from that encountered in most stamping operations. As such, more elaborate, and often and less reproducible, methods of assessment are often employed, such as limiting dome height measurements and the construction of forming limit curves. In the present work, we have analyzed the tensile behavior of a series candidate alloys and used these data to predict the forming limit curve over a range of strain states. Using a modified form of the Voce work-hardening model, a Marciniak-Kuczinski simulation has been constructed and used to predict the forming limit curve minimum (FLC0). These predictions are then related to experimentally determined forming limit curve data for the candidate alloys. The comparison of predicted and measured forming limit curve data indicates that the model can be successfully used to predict mechanical behavior under a state of plane strain using uniaxial tensile data. The results of the model indicate that the slope of the work-hardening curve, particularly at high strain values, is intimately related to the forming limit curve minimum. These correlations provide alloy developers with an inexpensive method of comparing the formability new alloy variants by more thoroughly exploiting the data concealed within the full uniaxial tensile curve.
9:00 am
TOOL WEAR DURING MACHINING OF AA356 ALUMINUM ALLOYS: Zhongnan Dai, J.G. Morris, Light Metals Research Labs, Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506
As a casting material, AA356 Aluminum alloy is widely used in the automotive industry. During machining, the tool wear mechanism for this alloy is significantly different from that for steel. For different as-cast metallurgical microstructures, materials with harder dispersed particles and stronger matrices show higher resistance to seizure because of an increase in the pressure requirement above which seizure occurs. This results in better machinability. On the other hand, hard particles act as small cutting edges on the tool materials, thereby causing tool wear due to the particle's abrasive characteristics. The wear characteristics of cutting tools were investigated in this study. Scanning electron microscopy, optical microscopy, EDX analysis were used to identify wear mechanisms. The results obtained show that there are a number of different wear mechanisms that contribute to tool damage, and hence, to tool-life. The role of the as cast microstructure on tool wear was also studied in order to determine under what structural states tool wear would be reduced.
9:30 am
THE EFFECTS OF PREAGING TREATMENTS ON FORMABILITY AND PAINT BAKE RESPONSE IN ALUMINUM AUTOBODY SHEET ALLOYS: J. Daniel Bryany, Reynolds Metals Company, Corporate Research and Development, Fourth and Canal Streets, P. O. Box 27003, Richmond, VA 23261
The use of heat treatable aluminum alloys for automotive body panels is presently increasing, due to aluminum's attractive combination of low density and compatibility with current production methods. In these applications, the automotive paint bake cycle is used to impart a modest artificial aging response, referred to as the paint bake response (PBR), in the alloys following stamping. Unfortunately, the short duration of the paint bake cycle (as dictated by production demands) is generally insufficient to exploit more than a small fraction of the age hardening potential of the alloys. Reynolds Metals Company has developed a thermal treatment which has been shown to be effective in increasing the paint bake response by up to a factor of four, while at the same time improving the formability of alloys and reducing the natural aging rate. Through the use of atomic resolution microscopy and differential thermal calorimetry, the mechanism of pre-aging can be shown to be the result of changes in the precipitation sequence of metastable variants of Mg2Si, resulting in an increase in the precipitation kinetics during the paint bake cycle and a finer distribution of strengthening precipitates in the painted component. Through the use of pre-aging, our research has shown that 6XXX autobody sheet alloys may be produced which have both superior stamping performance as well as higher strengths in the stamped and painted components, resulting in automotive body panels with up to 50% higher dent resistance.
10:00 am
THE EFFECT OF THE DISPLACEMENT CONTROL ROUTINE ON THE ELONGATION TO FAILURE AND FAILURE MORPHOLOGIES IN SUPER PLASTIC AA 5083: A.L. Lund, S.G. Pitman, M.A. Khaleel, M.T. Smith, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352
It has been noted in the literature that superplastically formed Al alloys fail by cavitation. The morphology of the final cavitated fracture region may be important in determining optimum forming conditions, by determining whether failure occurs parallel or perpendicular to the principal stresses. In addition, the displacement control routine may have a large effect on the total elongation that can be expected during forming operations. Tests were performed to evaluate failure in a AA5083 base alloy, by the following methods: 1) uniaxial tension tests at a constant true strain rate were interrupted at 80%, 60,G, 40%, and 5% of the maximum load, and microstructurally evaluated to identify the failure path and 2) tests were performed with various displacement control routines, and the elongation to failure was measured. The following displacement routines were used: smooth test, two-step strain test, multi-bump strain rate tests with various sizes of bumps scheduled at various intervals, and variable load oscillation tests.
10:30 am BREAK
11:00 am
EVOLUTION OF ALUMINUM MICROSTRUCTURES IN THE ALUMINUM EXTRUSION PROCESS: Woiciech Z. Misiolek, Aluminum Processing Program, Rensselaer Polytechnic Institute Troy, New York 121803590
The final microstructure and its uniformity is responsible for the physical properties and surface quality of the extruded profiles. Extrusion is time dependent process and its deformation variables such as, deformation zone and dead zone geometry as well as extrusion speed and temperature, change in time. The final microstructure depends on the above mentioned extrusion parameters as well as billet microstructure and post processing treatment. Metal flow conditions are influenced by the process parameters. Both physical and numerical process modeling techniques have been applied to predict metal flow behavior during extrusion through dies with different geometries. Additional information, allowing understanding of microstructure evolution, can be obtained from the crystallographic characterization of the typical deformation zone regions such as dead metal zone, main deformation zone and recrystallized zone on the billet-container interface using the electron backscattering diffraction (EBSD) technique. This technique has been utilized to follow in detail the orientation aspects of the deformed grains in extruded aluminum. This analysis provides information which can be used in the die and process design to improve metal flow uniformity and therefore the microstructure of the final product. It also allows prevention of the typical extrusion defects like surface tearing.
11:30 am
METALLURGICAL SAMPLE PREPARATION AND IMAGE ANALYSIS TECHNIQUES USED FOR THE EVALUATION OF AUTOMOTIVE MATERIALS: Matthias Hoffman, George A. Blann, Buehler Ltd., 41 Waukegan Rd., P.O. Box One, Lake Bluff, IL 60044; William R. Creech, BMW Manufacturing Corp., Greer, SC
This paper focuses on the commercial application of aluminum alloys and composite materials used in the automotive market. Today's automotive materials require a high degree of reliability. Therefore, efficient and accurate material testing and characterization methods are essential. Automotive alloys and composite materials often times are evaluated for microstructural properties. This work focuses on the developments in the metallurgical Q & A and research lab by highlighting the latest advancements using automated and semi-automated sample preparation techniques. The interpretation and quantitative analysis of these microstructures Ts accomplished by utilizing automated image analysis techniques. Image Analysis allows for an efficient as well as accurate analysis of dimension measurements, constituent analysis, porosity measurements, etc.
Room: 230C
Session Chairperson: Boris M. Triko, Aluminum Company of America, 1000 Riverview Tower, 900 South Gay Street, Knoxville, TN 37902-1848
8:30 am
GREEN PASTE POROSITY AS AN INDICATOR OF MIXING EFFICIENCY: Per Stokka, Norsk Hydro Research Centre, N-3901 Porsgrunn, Norway
Variations in green paste porosity were studied as a function of pitch content and mixing parameters. Porosity in paste from paste plants operating with different mixing systems, was measured and used to indicate the efficiency of the mixing. Changes in paste porosity during remixing in the laboratory were also studied.
8:55 am
POTENTIALITIES IN THE PASTE PLANT: S. Wilkening, VAW Aluminium-Technologie GmbH, P.O. Box 2468, 53114 Bonn, Germany
Over the last decade much progress in paste plant technology originated from computerized process control, improved process philosophy and P & ID's as well as full level 2 operation. This paper will focus on materials aspects to get out more from the intrinsic properties of coke and pitch. Proposals will be made how to utilize in a better way the structural properties of petroleum coke and the fluid and carbonization properties of binder pitch. Potential changes in equipment and lay-out will also be discussed.
9:20 am
VERTICAL ANODE CRACKING - THE VALCO EXPERIENCE: Norbert A. Ambenne, Volta Alumium Company Ltd (VALCO), P.O. Box 625, Tema, Ghana, West Africa
During the period 1990 - 1995 the VALCO aluminum smelter experienced a serious anode cracking problem. Approximately 12 % of the anodes split mainly along a particular set of anode stubs. About half of these splits resulted in carbon pieces falling into the reduction cell with attendant operating difficulties. This cracking phenomenon started when the plant was converted from 41.5 to 48 inches longer anodes with the extra length added to one end of the anode. Results of the investigations revealed that several operating variables contributed to anode cracking in varying degrees. These factors include mix profile in anode former mold, anode stub-to-gap ratio, anode setting practices, pot condition, anode symmetry, and moisture content in anode aggregate. This paper discusses these factors and how they affected anode cracking at Valco.
9:45 am
AN APPROACH FOR A COMPLETE EVALUATION OF RESISTANCE OF A MATERIAL TO THERMAL SHOCK (PART 1): APPLYING TO THE CASES OF ANODES AND CATHODES: Christian Dreyer, Bernard Samanos, Aluminium Pechiney, LRF BP 114, 73303 Saint Jean de Maurienne, Cedex, France
The aim of this article is to describe a new method for characterizing a material in terms of resistance to thermal shock. Such characterization takes into account the criteria of thermal shock resistance to initiation (Kingery criterion) and propagation (Hasselman criteria). It can be applied equally well to hard or soft thermal shock. This new approach has the following main advantages : 1) characterization of the material in terms of thermal shock is complete, 2) thermal shock tests or empirical formulae, the validity of which are often hard to establish, become unnecessary. Examples of the use of this new approach are presented for anodes and cathodes.
10:10 am BREAK
10:30 am
AN APPROACH FOR A COMPLETE EVALUATION OF RESISTANCE OF A MATERIAL TO THERMAL SHOCK (PART 2): APPLYING TO AN INDUSTRIAL PROBLEM AT ALBA: Bernard Samanos, Christian Dreyer, Aluminium Pechiney, LRF BP 114, 73303 Saint Jean de Maurienne Cedex, France; A. Hameed, G. Abbas, Jaffar G. Ameeri, Aluminium Bahrain, 570 Manama, Bahrain
This article presents in detail the steps taken to successfully resolve the problem of anode breakage due to thermal shock et ALBA. These steps can be essentially characterized as follows: 1) establishment of a method of accounting for anode breakages, 2) parametric studies on benchscale anodes, 3) effects on the process. Characterizing anodes in terms of resistance to thermal shock, following the method described in Part 1, allowed us to appreciate the importance of each of the adjustable parameters of the process. The applied solution draws on a new grain size distribution formulation.
10:55 am
ANODE PROPERTY DEVELOPMENT DURING HEAT TREATMENT: Mona Jacobsen, Department of Thermal Energy and Hydro Power, the Norwegian Institute of Science and Technology, N-7034 Trondheim, Norway; Oyvind Gundersen, Department of Engineering Cybernetics, The Norwegian Institute of Science and Technology, N-7034 Trondheim, Norway
Change of weight, density, permeability and porosity of anode specimens were measured after being baked to temperatures between 300 and 1250°C. Test specimens were cut from a green anode and analysed prior to the baking to study green property variations. Density variations in the green anode were significant and influenced the permeability measured in the green specimens. In mathematical modeling of the baking process, anode property models for description of heat and mass transport phenomena in the anodes are required. As basis for the derivation of the property models, the anode was considered to be a composite medium consisting of pitch coke, filler coke and pores. The filler coke was divided into a coarse and fine size fraction. The fine fraction mix with the binder pitch to constitute the binder matrix. It was assumed that the binder matrix was uniformly distributed on the surface of the remaining coarse filler particles. The models were compared and verified against the data.
11:20 am
ANODE IMPREGNATION SYSTEM FOR ALUMINIUM REDUCTION CELLS: Georges Berclaz, Avenue St-François, 3968 Veyras/Sierre, Switzerland; Vittorio de Nora, Jean-Jacques Duruz, Gaynor Johnston, MOLTECH, 9 Route de Troinex, CH 1227 Carouge-Geneva, Switzerland
The minimization of anode carbon consumption in aluminium reduction cells has an important technical, environmental and economical impact. The basic anode elements, such as coke and pitch, do not always have the desired properties and there is an increasing need to protect the anodes against oxidation by air and CO2. A solution based on boric acid impregnation of the upper part of the anode has been tested at the industrial scale. Anodes have been impregnated using specially designed equipment to place the protection in the appropriate part of the anode and to avoid metal contamination. Results are shown for different levels of impregnation. Comparison to metal spraying protection is also analyzed.
Room: 230B
Session Chairperson: Seymour G.Epstein, The Aluminum Association Inc., 900 19th St., N.W., Washington, DC 20006
8:30 am
UPDATE ON MOLTEN METAL INCIDENT REPORTING: S.G. Epstein, The Aluminum Association Inc., 900 19th St., N.W., Washington, DC 20006
Millions of pounds of molten aluminum are handled every day, safely and without incident, in nearly every segment of the aluminum industry. However, there are inherent hazards in handling any molten material and explosions involving molten aluminum and water or other oxidizing contaminants continue to occur in plants throughout the world. While these are infrequent events that often result in little or no damage to equipment or injury to personnel, an awareness of the possible consequences of an explosion is critical to maintaining a safe casthouse. The aluminum industry has made an extensive effort to gain an understanding of molten metal explosions, the factors that promote them, and how they might be prevented. The effort has included laboratory studies, conducted over the past 45 years, and thorough investigations of plant incidents. As part of this effort, the Aluminum Association established in 1985 a world-wide molten metal incident reporting program to obtain and share information on plant incidents. Presently, there are more than 230 participants in the program representing about 300 plants located in about 20 countries. Findings from the nearly 1200 reports submitted to date are reviewed in this paper.
8:55 am
INVESTIGATION OF COATINGS WHICH PREVENT MOLTEN ALUMINUM/WATER EXPLOSIONS - PROGRESS REPORT: R.T. Richter, D.D. León, T.L. Levendusky, Aluminum Company of America, Alcoa Technical Center, Alcoa Center, PA 15069
The aluminum industry has used Porter International 7001 (Tarset Std.) successfully as a protective coating in casting pits for over 20 years to prevent molten aluminum and water explosions until it was withdrawn from the market in 1994. The Aluminum Association contracted with Alcoa in 1995 to identify and test alternate coating materials which would be an acceptable replacement for Tarset Std. This paper will report the status of the program which was initiated in September 1995 and will be concluding in late 1996. Included in this paper are the screening and selection processes of the candidate coatings, results of initial molten aluminum/water explosion tests and the selection of the best performers for final explosion tests.
9:20 am
PROMOTING AWARENESS OF POTENTIAL HAZARDS IN ALUMINUM SCRAP: D.C. Pierce, C.H. Kenney, Reynolds Metals Company, 6601 West Broad Street, Richmond, VA 23261
There are a variety of potential safety hazards in any industrial activity and this includes the melting of aluminum scrap. The source of most hazards in scrap aluminum is the moisture or contamination that the scrap contains. Melting internal or purchased scrap remains the prevailing cause of molten metal incidents today. Everyone who handles scrap aluminum, from the first collection through to the melting, needs to be aware of the potential hazards. Facilities need to use a variety of approaches to increase safety awareness in all the operations. Scrap collectors, suppliers and brokers must be mindful of what the scrap hazards are, and the receiving plants must take steps to keep the hazards out of their casthouses. One of the new tools that plants have available is a fax-notification system operated by the Aluminum Association for information on scrap that has been rejected by another facility for safety or health reasons. This system is felt to offer an important safety enhancement, because scrap dealers have been known to resell unsafe scrap after it has been rejected. Although the Scrap Rejection Notification System is currently operational, its success will be measured by how infrequently it is needed.
9:45 am BREAK
9:55 am
NEW GUIDELINES FOR SOW CASTING AND MELTING: G.N. Chaffin, Quality Challenges, Midlothian, VA 23112; J.E. Jacoby, Consultant, 3398 North Hills Road, Murrysville, PA 15668
The aluminum industry has experienced many incidents of explosions as a result of wet or contaminated sows being charged into molten metal. The presence of moisture in the cavity of a sow is often impossible to detect and therefore the sow is assumed to be safe. However, this undetected moisture can cause a serious explosion if it is submerged into molten aluminum. The Aluminum Association has prepared guidelines for sow casting, inspection and melting to help facilities protect themselves from the potential hazards associated with melting sows. The guidelines and this paper consider mold designs, casting, transportation & storage, inspection and melting operations. Recommendations are offered which can be used in conjunction with each plant´s practices. The recommendations can help both the casting facility and the melting plant work toward a decrease in the possibility of an incident involving the melting of sows.
10:20 am
THE SEARCH FOR PROTECTIVE CLOTHING FOR WORKERS EXPOSED TO THE HAZARDS OF MOLTEN ALUMINUM AND MOLTEN BATH: Ronald R. McHaney, Kaiser Aluminum and Chemical Corporation
Burns are one of the leading causes of work injuries within the aluminum industry. Some physical and chemical properties of molten aluminum - low emissivity and viscosity - contribute to the potential for injury-producing incidents. Other properties, including high heat of fusion and shrinkage characteristics during cooling, add complexity to the task of identifying suitable protective clothing for workers exposed to the hazards of molten aluminum and bath. This presentation will address the initiative to identify protective clothing for workers exposed to those hazards and the progress that has been made including the development and application of the American Society for Testing Materials (ASTM) designation: F955, "Standard Test Method for Evaluating Heat Transfer Through Materials for Protective Clothing Upon Contact with Molten Substances". In addition, I will discuss the need to consider worker comfort and the potential for heat stress in the selection process.
10:45 am
PANEL DISCUSSION: All Speakers
Room: 240A
Session Chairperson: John Grandfield, Comalco Research Centre, P.O.Box 316, Thomastown, Victoria 3074, Australia
8:30 am
MODELLING OF SOLIDIFICATION IN Al-ALLOYS: Nigel Saunders, Thermotech Ltd., The Surrey Research Park, Guildford GU2 5YG, and IRC in Materials for High Performance Applications, University of Birmingham, Birmingham B15 2TT, United Kingdom
Solidification in Al-alloys is a complex process usually occuring under non-equilibrium conditions with the possible formation of metastable low melting point eutectics and non-equilibrium phases. However, it has recently been shown that it is possible to use thermodynamic phase diagram calculations to simulate the non-equilibrium solidification of complex Al-alloys under so-called 'Scheil' conditions. Excellent results can be obtained for features such as fraction solid transformed as a function of temperature, phase formation, latent enthalpy and Cp of solidification etc. All of these features are important input into modelling of solidification processing particularly for software packages which simulate heat flow during casting. The paper will present the results of 'Scheil' simulations for a wide range of commercial Al-alloys showing comparison with experimental results for fraction solid transformed and phase formation. The use of subsequently derived Cp and heat evolution parameters in casting simulation packages will be discussed and examples of its application shown.
8:50 am
THE APPLICATION OF EFFICIENT PARALLEL PROCESSING TO FINITE ELEMENT MODELING OF FILLING, SOLIDIFICATION, AND DEFECT PREDICTION FOR ULTRA-LARGE SHAPE CASTINGS: David Snyder, Aluminum Company of America, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069; David Waite, Consultant, Coralville, IA; Alpesh Amin, HP/Convex Corporation, Atlanta, GA
Finite element modeling has become widely to used simulate the filling, solidification, and defect formation in casting processes. For extremely large, complex parts, typical of automotive structural applications, the high cost of tooling makes process modeling an extremely useful tool. However, as the size and complexity of casting part geometry increase, the computational requirements for modeling become formidable. To address the challenge for modeling ultra-large shape castings, a finite element code was developed to efficiently take advantage of shared-memory parallel computing systems. This paper gives a brief description of the mathematical models which describe the casting processes. The implementation of the models and the numerical issues regarding memory architecture, parsing of computations, cpu synchronization, and overhead minimization for parallel processing are discussed. Examples are presented for filling and solidification analyses of permanent mold, tilt-pour, and die casting models run on an 8-CPU HP/Convex SPP-1000 computer.
9:10 am
IN-SITU TEMPERATURE MEASUREMENTS IN LOW PRESSURE PERMANENT MOLD CASTING: Florence Paray, Joe Gruzleski, Department of Mining and Metallurgical Engineering, McGill University, 3450 University Street, Montreal, Quebec, Canada H3A 2A7; Joe Clements, Grenville Castings Ltd., Merrickville, ONT, Canada K0G 1N0; Bahadir Kulunk, Timminco Metals, Research and Development Center, Haley, ONT, Canada K0J 1Y0
The low pressure casting process has an increasing popularity as it allows a rapid production of components close to the final "near net shape" with a very good casting yield. Depending on the property requirements of the final product, it is often necessary to control casting soundness. Internal porosity can cause a loss of pressure tightness, a critical factor in parts such as engine blocks and manifolds which are required to keep various gases and fluids. The development of criteria functions should allow the prediction of the thermal conditions required to maintain porosity below some critical predetermined level. In order to determine criteria functions, it is necessary to acquire thermal data during casting solidification. A low pressure casting machine and die were instrumented to obtain "in situ" thermal analysis curves during the solidification of flat plates of thickness varying from 1/8" to 3/4" in Sr modified and unmodified 6290, 356 and 319 alloys. The paper describes that effort and some of the results obtained.
9:30 am
A TECHNIQUE FOR THE ESTIMATION OF INSTANTANEOUS HEAT TRANSFER AT THE MOLD/METAL INTERFACE DURING CASTING: Michael Trovant, Stavros Argyropoulos, Department of Metallurgy & Materials Science, University of Toronto, 184 College Street, Toronto, Ontario, Canada M5S 3E4
Many current advancements responsible for improving the accuracy of solidification algorithms have resulted from the incorporation of additional complex casting related phenomena into the numerical calculation scheme. More recently, however, the proper specification of boundary conditions has been found to play a critical role in limiting model inaccuracy. Of particular interest to casting are the temperature boundary conditions, which when adopted by many models appear to be the most troublesome. Temperature boundary conditions can vary significantly with time and position along the face of the casting and accurate heat transfer coefficients are notoriously difficult to obtain experimentally for all points on the mold/metal interface, especially when the influence of thermal contraction is acknowledged. A novel technique which minimizes the error associated with selecting boundary conditions without experimentation is proposed. Advanced knowledge of the air gap formation and its correlation to the heat transfer coefficient at the mold/metal interface is used to formulate a coupled mathematical model which determines the increase of the air gap and predicts the instantaneous cooling conditions at a given mold wall. The objective is to allow the modeler to estimate effect of thermal contraction on the heat loss at mold/metal interfaces without resorting to experimentation.
9:50 am
MECHANISM OF DENDRITE FRAGMENTATION IN CASTINGS: Shan Liu, Shu-Zu Lu, A .Hellawell, Michigan Technological University, Dept. of Metallurgical and Materials Engineering, Houghton, MI 49931
A temperature gradient stage was designed with a controlled deceleration mechanism to simulate the columnar growth in castings/ingots where the growth velocities and temperature gradients at a dendritic front undergo a continuous decrease during solidification. Transparent materials of SCN-H2O and NH4Cl-H2O systems were used so that the solidification process with various decelerations could be directly observed and video recorded. It is observed that fragmentation of secondary arms is directly related to the deceleration and this provides an intrinsic resource for the formation of equiaxed grains in castings where convection may be available for transportation of the fragments to the open liquid. The responses of a dendritic array to the deceleration, including primary spacing adjustment and tip radius adjustment etc., are also observed and discussed.
10:10 am BREAK
10:20 am
THE VISUALIZATION OF THE PARTICLE CONTENT OF LIQUID ALUMINUM ALLOYS: N.D.G. Mountford, A. Simionescu, I.D. Sommerville, Department of Metallurgy & Materials Science, University of Toronto, Toronto, Ontario, Canada M5S 3E4
Aluminum alloys can contain heterogenous impurities which will affect the strength of the final product and result in either failure during manufacture or in service. Pulsed ultrasound, conveyed down metal guide-rods from energized piezo-electric crystals, is passed into the liquid metal and reflections from any impurities can be recorded by special counting devices. Small particles of the order of 10 to 15 µm can be resolved and their behaviour such as in settling recorded. Sequential tests using particles of identified size and distribution such as SiC and TiAl3 demonstrated the systems reproducibility. Such changes in composition resulting from imposed turbulent transfer with the associated pick up of very small oxide particles could also be shown. The effect of "sludge" formation such as that found in die-casting applications due to intermetallic phase precipitation could also be measured. This could be of value in process control of die casting systems. The developed system is adaptable to on line quality measurement and the recording of molten aluminum cleanliness in crucibles, ladles, furnace wells, launders and other transfer systems.
10:40 am
FRACTAL ANALYSIS: POROSITY IN ALUMINUM CAST ALLOY: Bo-Tao Lee, Shu-Zu Lu, A. Hellawell, Michigan Technological University, Dept. of Metallurgical and Materials Engineering, Houghton, MI 49931
Porosity is a very common defect in Al-Si cast alloy. To examine the porosity, a fractal analysis was conducted to characterize the pores using two numbers, Fractal Dimension, D, and Shape Factor, 
. This analysis was based on the measurement of perimeters/areas of all individual pores using an image analyzer with changing magnifications. The result indicates that two types of pores, i.e., rough/shrinkage pores and smooth/hydrogen pores, can be distinguished by these fractal numbers. The shrinkage pores show a larger value of fractal dimensions whereas the hydrogen pores have a fractal dimension close to one. Combined with analysis for silicon particles, it is suggested numerically that shrinkage pores are more likely associated with the silicon phase that is not well modified, showing a rather coarse flake structure, and the hydrogen pores are in the regions where modification was well done with fine silicon particles.
11:00 am
NUMERICAL SIMULATION OF DIE FILLING IN SEMISOLID METAL PROCESSING: Andreas N. Alexandrou, François Bardinet, Mechanical Engineering Department, Worcester Polytechnic Institute, Worcester, MA 01609; Willem Loué, Pechiney CRV, Centre de Recherche de Voreppe BP27, 38340 Voreppe, France
Semisolid Metal Processing is gaining interest very rapidly. This manufacturing approach offers distinct advantages over other near-net-shape technologies, like a more homogenous microstructure and less porosity and thus excellent mechanical properties. A perfect control of the die filling during processing is however necessary, especially in the case of semisolid forming of aluminum, where a non-controlled die filling can lead to oxide inclusions. Numerical simulation would be a powerful tool, as it would allow to predict die filling and the optimization of die design. However, the constitutive behaviour of such semisolid metals is rather complex. Their non-Newtonian behaviour does not depend only on the volume fraction of liquid, but also on the metal´s history prior to processing and the processing conditions. In this paper, a Bingham power-law relation is presented, capable of describing correctly the rheological behaviour of the semisolid metal. This constitutive equation is then introduced in a modified version of the casting simulation package SIMULOR. Simulation results on the filling of a 2-D cavity under various conditions are shown. Issues related to die design of dies, using numerical simulation will also be addressed.
11:20 am
SOLIDIFICATION PROCESSING OF ALUMINUM CASTING ALLOY REINFORCED WITH CERAMIC MICROSPHERES FOR THIXOFORMING: P.D.D. Rodrigo, K. Xia, N. Setargew, Materials Group, Department of Mechanical and Manufacturing Engineering, University of Melbourne, Parkville, Victoria, Australia 3052; P. Fitzgerald, G. Withers, Cyco International, 1297 Nepean Highway, Cheltenham, Victoria, Australia 3192
A cast aluminum matrix composite based on an Al-Si-Mg alloy has been developed. The reinforcement was in the form of hollow microspheres, a ceramic by-product from coal power stations. The particles were incorporated into the aluminum alloy melt by mechanical stirring either in the semisolid state or full liquid state. The composite melt was cast from full liquid temperature to produce slugs for thixoforming. A variety of compositions, reinforcement volume fractions and processing parameters were used. The as-cast microstructure consisted of fine, equiaxed dendritic primary grains in a matrix of secondary grains and eutectic phases. The primary dendritic grains evolved to become non-dendritic after reheating the slugs to semisolid temperature. The slugs were subsequently thixoformed at a temperature corresponding to a primary solid fraction of about 50% into thin plates and alternator pulleys. Special wear tests on the pulleys showed that they were comparable to steel pulleys. The material is potentially suitable for those applications demanding good wear resistance, light weight and low cost.
Room: 330C
Session Chairperson: Walter W. Milligan, Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931
9:00 am INVITED
SYNTHESIS AND MECHANICAL PROPERTIES OF NANOCRYSTALLINE INTERMETALLICS AND MULTIPHASE MATERIALS: J.A. Eastman*, M. Choudry*,**, M.N. Rittner***, C.J. Youngdahl*,***, M. Dollar**, J.R. Weertman***, R.J. DiMelfi****, and L.J. Thompson*, *Materials Science Division, Argonne National Laboratory, 9700 S. Cass Ave., Bldg. 212, Argonne, IL 60439, **Mechanical, Materials, and Aerospace Engineering, Illinois Institute of Technology, Chicago, IL 60616, ***Materials Science and Engineering Department, Northwestern University, Evanston, IL 60208, ****Reactor Engineering Division, Argonne National Laboratory, Argonne, IL 60439
The mechanical behavior of nanocrystalline intermetallic and multiphase materials has been investigated using disk bend, tensile, and compression techniques. Materials such as NiAl, TiAl, Al-Al3Zr, and Cu-SiOx were synthesized by the gas-condensation technique using electron beam heating. Disk bend tests of nanocrystalline NiAl and TiAl showed evidence of improve ductility at room temperature in these normally extremely brittle materials. In contrast, tensile tests of multiphase nanocrystalline Al-Al3Zr samples showed significant increases in strength, but substantial reductions in ductility with decreasing grain size. Results from compression tests of nanocrystalline Cu and Cu-SiOx will also be described. Implications for the operable deformation mechanisms in these materials will be discussed. *This work was supported by the U.S. Department of Energy, BES-Materials Science, under Contract W-31-109-Eng-38, the Alcoa Corporation, and by AFOSR Grant # FY9620-92-J.
9:30 am
INFLUENCE OF PROCESSING ON INTERNAL STRUCTURE OF NANOCRYSTALLINE Ni: B.R. Elliott, and J.R. Weertman, Northwestern University, Evanston, IL , Metallurgy Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-0001
Different processing routes can vary the internal structure of nanocrystalline compacts. As a result a single grain size measurement is insufficient to interpret mechanical property results. Blind comparison between samples with different processing histories may be hazardous since their internal structures (grain size distribution, grain boundary character, pore size distribution, adsorbed or chemically bonded impurities) are shown to vary. In particular, annealing samples to grow the grain size for producing Hall-Petch plots is shown to drastically change the pore size distribution and density in powder compacted samples that are not outgasssed prior to compaction. Improvements in processing, particularly compaction procedure, are illustrated by microscopy, XRD, SANS, PGAA, FNAA, archimedes density, and indentation tests. It is shown that with care and knowledge of the process inert gas condensed and compacted samples can be produced with few extrinsic defects.
9:50 am
MECHANICAL PROPERTIES OF NANOCRYSTALLINE Ni: B.R. Elliott, J.R. Weertman, Northwestern University, Evanston, IL
The influence of improved processing on the internal structure of n-Ni has lead to improved mechanical properties. Correlation between the internal structure (including grain size, pore size distribution, and impurities) and results of a variety of mechanical properties measurements will be presented including hardness, tensile and compression tests. Some comparison will also be made between samples produced by traditional inert gas condensation (IGC) and the newer jet blown arc IGC. (JBA-IGC). Possible deformation mechanisms will be discussed in light of the structure and property measurements.
10:10 am
A CRITICAL ASSESSMENT OF THE WILLIAMSON-HALL METHOD FOR THE DETERMINATION OF RESIDUAL STRESS IN NANOCRYSTALLINE STRUCTURES: F.S. Miller, D.C. Van Aken, Metallurgical Engineering, E.W. Bohannan, J.A. Switzer, Chemistry, The University of Missouri-Rolla, Rolla, MO 65409
An important aspect of the processing<>microstructure<>property relationships is the characterization of nanocrystalline structures by x-ray diffraction. The Williamson-Hall analysis is often used to deconvolute the line broadening effects of grain size and residual stress. In this study, Cu/Cu2O nanocrystalline films were produced by electro deposition. This technique produces a composite structure consisting of pure Cu and Cu2O grains each with diameters in the range of 10 to 20 nm. Electro deposited films were characterized by x-ray diffraction to determine both grain size and residual stress. The Williamson-Hall analysis was tested by direct measurement of the grain size by TEM and by using thermal treatments to vary the state of residual stress in the films.
10:30 am BREAK
10:45 am
MECHANICAL PROPERTIES OF Cu/Ag MULTI-LAYER COMPOSITES: Qing Zhai, Augusto Morrone, Fereshted Ebrahimi, Materials Science & Engineering, University of Florida, Gainesville, FL 32611
When materials microstructure reaches nanometer scale, their properties often appear to be unusual, which cast much consideration these days. Specifically, the extraordinarily high strength has been the subject of many recent investigations. The nanomaterials discussed in this paper is a Cu/Ag multi-layered composite, which is produced by electrodeposition in a single-bath cyanide solution. In this paper the effects of copper layer thickness and heat treatment on interfacial structure and mechanical properties of Cu/Ag multi-layered composites are presented. Tensile testing was used to investigate the mechanical properties of the samples. SEM, X-ray diffraction and TEM were used to analyze the relation between the mechanical properties and microstructure of these composites.
11:05 am
STABILITY OF NANOCRYSTALLINE ALLOYED AND MULTILAYER PVD NITRIDE FILMS: R. A. Andrievski, Institute for New Chemical Problems, Russian Academy of Sciences, Chernogolovka, Moscow Region, 14232 Russia
The alloyed and multilayer films of TiN, ZrN, NbN, and CrN with nanocrystalline structure prepared by arc deposition were investigated by XRD, electron microscopy and microhardness measurements. A general tendency of the microhardness to increase with decreasing layer thickness was found in TiN-NbN(ZrN) systems. The unmonotonous change has been revealed in TiN-CrN one. The influence of spinodal decomposition, recrystallization, and heterodiffusion on the films' properties is also demonstrated and discussed in detail. R.A.Andrievski, 1 A.Anisimova, V.P.Anisimov et al, Thin Solid Films 261(1995) 83.
Session Chairperson: M.A. Self, Mechanical Engineering Dept., Tuskegee University, Tuskegee, AL 36088
8:30 am
DOUBLE CANTILEVER BEAM TEST APPLIED TO MODE I COMPOSITE DELAMINATON: A COMPARISON OF ANALYSIS METHODS FOR FIBER BRIDGING MATERIALS: W. Richards Thissell, Anna K. Zurek, Los Alamos National Laboratory (LANL), MST-5, G755, Los Alamos, NM 87545; Frank Addessio, Todd O. Williams, T-3, B-216, Los Alamos, NM 87545
The double cantilever beam (DCB) test is widely used to characterize the mode I delamination and bridging behavior of laminated continuous fiber composite materials. Many composite systems exhibit significant large scale fiber bridging that is not included in the derivation of the analysis methods. The bridging contribution to fracture energy is statistical in nature. A comparison is made of several analysis methods for applicability to systems exhibiting significant fiber bridging. A general DCB analysis method is described that takes into account loading pin effects, material orthotropy, crack root inelasticity, and large scale deformation behind the crack faces. Some material system specific characteristics that lead to enhanced fiber bridging are described.
8:50 am
HYGRO-MECHANICAL BEHAVIOR OF A CLASS OF SWELLING-TYPE THREE-DIMENSIONALLY BRAIDED COMPOSITES: Surya R. Kalidindi, Abdel Abusaifeh, Materials Engineering Department Drexel University, Philadelphia, PA 19104
A new class of swelling-type composite materials using three-dimensionally braided graphite or Kevlar fibers have been designed and processed for potential applications in bone implants. These composites derive their swelling from the hydrophillic nature of the matrix material used in their production. A combined experimental and modeling study was undertaken to study the hygro-mechanical behavior of this class of materials. The properties of interest included the swelling strains, elastic properties, yield strengths, and impact strengths. Note that these properties for the braided composites are highly anisotropic. Furthermore, the mechanical properties are strongly affected by the amount of absorbed water. Cylindrical samples of braided composites were produced with varying fiber volume fractions, braid angles, fiber type (graphite and Kevlar), matrix cross-linking (to control the degree of swelling in the composite), and fiber architecture (uniaxial, rectangular braided, and circular braided). Swelling strains at saturation were measured in these samples. Simple compression tests were performed on these samples in at least two principal material directions in both dry and saturated conditions. Elastic moduli and yield strengths were extracted from these tests. Cylindrical samples of the matrix material (without fibers) were also produced and utilized to fully characterize the hygro-mechanical behavior of the matrix material. Constitutive models have been proposed to predict the various hygro-mechanical properties of the 3-D braided composites in both dry and saturated states as a function of the fiber and matrix properties, fiber volume fraction, and fiber orientations. A weighted average of the currently employed isostrain and isostress models in literature for this class of materials was found to consistently yield better predictions for the anisotropic elastic moduli, when compared to the predictions of either of these models. The weighting factor was found to be dependent primarily on the fiber and matrix materials (i.e. independent of the type of loading, fiber volume fraction, and fiber orientation) and has been interpreted as an interaction parameter between the various fiber and matrix systems. These models were then extended to predict the swelling behavior and yield strengths of the 3-D braided composites. The accuracies of the proposed models were evaluated by comparisons against experimental measurements described above as well as the predictions from a finite element simulation of the response of a representative unit-cell of the braided composite. These comparisons revealed that the proposed models are reasonably accurate in their predictions.
9:10 am
RF MAGNETRON SPUTTERING OF MoSi2 + X SiC COMPOSITE TO FIIMS: S. Gonodaryan1, J.J. Moore1, T.R. Ohno2, 1Advanced Coatings and Surface Engineering Laboratory, Dept. of Met. and Materials Eng., Colorado School of Mines; 2 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.).
FATIGUE OF MONOLITHIC NIOBIUM AND BNIOBIUM-BASED "IN-SITU" COMPOSITES: William A. Zinsser, Jr. and John J. Lewandowski, Department of Materials Science and Engineering, Case Western University, Cleveland, OH 44106
9:30 am
EFFECT OF COMBINED LOADING ON CRACK-TIP DEFORMATION IN GRAPHITE/EPOXY COMPOSITES: M.A. Seif, C.M. Hargrove, Mechanical Engineering Dept., Tuskegee University, Tuskegee, AL 36088
An experimental investigation of the crack displacement and failure modes of graphite/epoxy plates [0/±45/90]2s under tensile loading with central cracks at various angles (15°, 30°, 60°, 75°, and 90°) was carried out. A mixed mode state of stresses developed at the center of the crack as a result of the crack orientation. Laser Speckle technique, a high sensitive noncontact technique, was employed to measure Crack Opening Displacement (COD) and Crack Shearing Displacement (CSD) of the crack emanating from the normal and tangential stresses at the crack center. Damage zones of the material at different crack orientation were examined and evaluated. The critical stress intensity factors for mode I and mode II were obtained from COD and CSD at failure. Detail studies were performed to investigate the behavior of the material during loading application and the effect of the angles on the stress distribution. The data obtained were compared with the Linear Elastic Fracture Mechanics (LEFM) solutions. The comparisons suggested a correlation within ±8 percent deviation. It was concluded from this investigation that the theoretical analysis could be applied to obtain the fracture properties of graphite/epoxy composites.
9:50 am
INCREASING THE OFF-AXIS AND MONOLITHIC STRENGTHS IN CONTINUOUS FIBER REINFORCED ALUMINUM MATRIX COMPOSITES: Colin McCullough, Paul R. Nisson*, Steven R. Pittman Bill E. Birkholz, MMC Program, 3M Company, St. Paul, MN 55144-1000; *3M/MMC Production Plant, Middleway, WV 25430
Tremendous progress has been made in the properties of aluminum alloys reinforced with 60-70 vol. % of continuous alumina fibers, with tensile strengths routinely averaging 250 ksi (1.7 GPa) in the longitudinal direction. The choice of matrix and its resulting microstructure is critical in obtaining such strengths and the matrices used at 3M to date are a pure Al and an Al-2%Cu alloy. This leads to design considerations in composite performance (transverse and shear strengths) and in any unreinforced areas. To date, the pure Al and Al-2%Cu matrix composites have transverse strengths of 25 ksi (170 MPa) and 40 ksi (275 MPa) respectively. While these values have applications, higher strengths may be desirable. Also unreinforced areas could benefit greatly from higher yield strengths. Use of traditional higher strength alloys is seriously restricted due to both the reactivity with the fiber and their segregation behavior which dramatically reduces longitudinal strength. How ever a new aluminum alloy matrix composition promises to combine all the desired features of the matrix. Data will be presented showing retention of high longitudinal strengths while also achieving much higher transverse and monolithic strengths. The specifics of this system will be discussed as well as directions for optimization.
10:10 am BREAK
10:20 am
STRUCTURE AND PROPERTIES OF ALUMINUM BASED PARTICULATE COMPOSITES SYNTHESIZED BY MECHANICAL ALLOYING: J.M. Molnar, T.H. Courtney, Department of Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931
Aluminum-based particulate composites have potential application in services requiring high strength combined with low density. We have used mechanical alloying followed by hot isostatic pressing (HIPing) to fabricate a series of Al-Si-C particulate composites. Pure Al or Al-Si eutectic powder was mixed with graphite and SPEX milled for varying times. Consolidation of the mechanically alloyed powders was done by HIPing at 180MPa (26 ksi) which resulted in a fully dense composite. Aluminum carbide (Al4C3) is formed during consolidation. Formation of SiC is a possibility as well. Maximum hardnesses following HIPing correspond to an approximate yield strength of 990 MPa (144 ksi). Properties as they depend upon processing conditions and the resulting microstructure are discussed. This work was supported by the Army Research Office.
10:40 am
THERMOMECHANICAL PROCESSING OF SUPERPLASTIC SICP/6061 ALUMINUM ALLOY COMPOSITE MADE BY A VORTEX METHOD: Tsunemichi Imai1 and Takeo Hikosaka2, 1National Industrial Research Institute of Nagoya, 1 Hirate-cho, Kita-ku, Nagoya 462, Japan; 2Industrial Research Institute, Aichi Prefectural Government, Nishishinwari Hitotsugi, Kariya City, Aichi 448, Japan
Thermomechanical processing to produce the HSRS for the SiC/6061 Al alloy composite fabricated by a vortex method before squeeze casting and extrusion was investigated. The SiC/6061 A1 composites hot-rolled in rolling strain per passes of 0.05~0.3 and at 573K indicate the m value of 0.4~0.6 and the total elongation of 200~300% in the strain rate of 0.08~1.3 s-1 and at 853K. The total elongations of the composite hot-rolled at 523 and 623K decrease to less than 150%. The flow stress of the composite heat treated by T6 after rolling increased and the total elongation decreased as compared with those of the composite without T6 due to reaction between SiC and matrix. The fracture surface of the composite has a partially liquid phase and filaments and it is thought that an interfacial sliding at the liquid phase contributes to the HSRS in addition to grain boundary sliding in the SiC/6061 Al composite fabricated by a vortex method.
11:00 am
COMPATIBILITY OF SEVERAL REINFORCEMENTS WITH Ti-Al AND DEVELOPMENT OF THE COMPOSITES: Chikura Fujiwara, Nagoya Aerospace Systems Works, Mitsubishi Heavy Industries, Ltd., 10, Oye-Cho, Minato-Ku, Nagoya, 455 Japan
Titanium aluminide matrix composites have received considerable attention due to their potential to have high specific strength and stiffness at high temperature. And SiC fibers are considered to be promising candidates for reinforcement of the composites. SiC/TiAl composites, however, are difficult to be fabricated in good state because of severe reactions at the interface being taken place during fabrication process. One of the most effective means to suppress the excessive reaction is to apply the diffusion barrier coating on the surface of SiC fiber. Another solution to fabricate a TiAl matrix composite is to apply the reinforcement which has good compatibility with matrix, TiAl. Several candidates for diffusion barrier coating between SiC fiber and TiAl were evaluated, then W and HfC showed excellent effects on suppress excessive interfacial reaction, while other candidates such as Al2O3, Zr, B2, Ce2O3 were not effective. Based on these results, a desirable interface model of organic polymer derived SiC reinforced TiAl composite is proposed. Other fibers were evaluated as reinforcements of TiAl matrix composites. Then it was found that W, W-Re, Re were good in compatibility with TiAl and consolidated with TiAl in good state. As a result, W-3%Re/TiAl showed 680 Mpa at 1373K.
11:00 am
THE EFFECT OF MATRIX MICROSTRUCTURE ON THE MECHANICAL PROPERTIES OF Ti3Al/TiB PARTICULATE COMPOSITES: Satoshi Emura, Masuo Hagiwara and Yoshikuni Kawabe*, National Research Institute for Metals, 1-2-1 Sengen Tsukuba Ibaraki 305 Japan; *Chiba Institute of Technology, 2-17-1 Tsudanuma Narashmo Chiba 275 Japan
Ceramic particulates reinforced composite is considered to be an effective way for improving the mechanical properties of Ti alloys and Ti-A1 intermetallics. In the present study, Ti-24Al-llNb(at%)/l0wt%TiB in-situ composites were prepared by the blended elemental powder metallurgy method. The tensile and high cycle fatigue properties of the composites were found to be much superior to those of the unreinforced matrix. Modification of the matrix microstructure was performed by annealing the composite at 1573K and air cooling, which resulted in a very fine 2+ microstructure. The mechanical properties, particularly the fatigue property, were further improved by this microstructural modification technique.
11:20 am
A STRUCTURE DESIGN OF CARBON FIBER REINFORCED ALUMINUM MATRIX COMPOSITE: Jiwen Wang ,Geyang Li, Tao Hong, Pengxing Li, Anjing Yang, Dept. of Mat. Sci., Shanghai Jiao Tong University, Shanghai, 200030, China
A process which combines fiber coating and particles hybridizing together has been utilized for the structural optimization of carbon fiber reinforced aluminum matrix composite. SiC coating was derived by Sol-gel method and SiC particle hybridizing was processed in Sol-gel solution simultaneously. Squeeze-cast process was used to get bulk composite materials. SEM analysis of the material showed a well fiber distribution in Al matrix by particles hybridizing. Mechanical properties of the composite were improved especially for the axial strength. HRTEM research indicated the coating to be an effective barrier of the interface reaction. C/Al interfacial reaction was also studied meantime which revealed that pan-based carbon fiber reacted heavily with aluminum matrix. The nucleation and growth of the reactants were discussed.
Room: 332
Session Chairperson: Sung K. Kang, IBM Corp., T.J. Watson Research Center, Room 37-250, P.O. Box 218, Yorktown Heights, NY 10598; Professor Jorma Kivilahti, Helsinki University of Technology, Materials and Manufacturing in Electronics, Vuorimiehentie 2A, Fin-02150 Espoo, Finland
8:30 pm INVITED
FLIP CHIP SOLDER INTERCONNECTIONS--A RELIABILITY PERSPECTIVE: Karl Puttlitz, IBM Microelectronics, B/330-1AX44-173, GFKA, Rt. 52, Hopewell Junction, NY 12533
The solder ball flip chip or so-called C-4 connection was introduced by IBM nearly three decades ago as an alternative to manual wire bonding whose productivity and reliability were not acceptable at the time. A very large data base indicates that flip chips are the most reliable interconnection scheme in the industry since its inception. Moreover, the combination of C-4 mounted die and alumina multilayer ceramic (MLC) substrates provided the highest overall package reliability. This paper will discuss several key technical attributes such the joint controlled collapse feature, self-centering and throughput which is independent of die I/O count. Joint design, process, compositional and metallurgical factors will be discussed in the context of the very significant effect they have on reliability as well. Flip chip technology is flexible, having been successfully utilized with several generations of chip carriers. Important also is the ability to predict the thermal-mechanical (fatigue) behavior of C-4 joints. When attached to ceramic carriers, the failure rate of flip chip joints obey a distance-from-neutral point (DNP) dependence defined by the Coffin-Manson (C-M) relationship. Modifications to the C-M relationship necessary for this application will also be discussed. It will be shown that the technology is sufficiently extendible to satisfy the trends of smaller, lighter, faster, denser, etc. which are expected to continue in the future. New developments such as chip underfill and future trends including DCA and their reliability implications will also be discussed.
8:55 am INVITED
A NEW RELIABILITY ASPECT OF HIGH DENSITY INTERCONNECTIONS: Jorma Kivilahti, Helsinki University of Technology, Materials and Manufacturing in Electronics, Vuorimiehentie 2A, Fin-02150 Espoo, Finland
Increasing importance of portability in telecommunication and consumer electronics is activating the research and development work on reliable, cost-effective fine-pitch interconnections and substrate technology alternatives. However, high density interconnections may produce increasing difficulties, e.g. in paste printing, component alignment and acceptable residual levels. Moreover, increasing microjoint densities are related to decreasing solder joint volumes, and therefore, it is even more likely that the whole solder volume will take part in the reactions, for example, between a solder, Flip Chip (FC) bump and substrate metallisation. Similar consequences of the miniaturization are encountered in the bump-limiting metallurgy; the total volumes (or thicknesses) of the diffusion barriers and adhesion layers and the original filler, alike, can transform into the matrix of intermetallics, which due to their inherent brittleness make the microjoints mechanically too weak to withstand thermal stresses. Accordingly, for confirming adequate reliability of microjoints it is essential to have better understanding and control on metallurgical compatability of dissimilar materials being in contact with each other. In this communication results of metallurgical studies on various FC bump-solder-substrate metallization reactions are presented. As specific examples, the bump-solder-substrate interactions have been studied experimentally with Au- as well as with Ni-bumped test chips, which were reflow-soldered with the eutectic SnPbAg filler at 235°C for various times onto Au/Ni- and Cu-conductors on the FR-4 substrates. The electrical properties, structural integrity and evolution of microstructures (i.e., intermetallics, Pb-rich solution or eutectic structure) of reflow-soldered Flip Chip joints were examined in detail with the conventional tests and materials characterization methods. For studying the metallurgical compatibility and controlling the reaction kinetics between Au, Ni and eutectic SnPb and SnPbAg, the wedge-shaped diffusion couple experiments which more clearly illustrate the effect of solder layer thickness on the volume fraction of the intermetallics in the microjoints, were conducted using the RMA flux as well as a vacuum furnace. The thermodynamics of the AuSnPb, NiSnPb and CuSnPb systems were critically modeled and used for rationalizing the observed bump-solder-substrate reactions in the Flip Chip joints as well as in the diffusion couples. On the basis of metallurgical considerations a new Pb-free solution to this "small-volume-problem" is also addressed.
9:20 am INVITED
EFFECT OF FLUX TYPE AND SURFACE COATING ON THE WETTING FORCE BETWEEN COPPER AND EUTECTIC Pb-Sn SOLDER: Guna Sevaduray, Wayne Lee and Selgon Yee, Department of Materials Engineering, San Jose State University, San Jose, CA
9:45 am INVITED
A STUDY ON THE SOLDER JOINT RELIABILITY OF THE OPTOELECTRONIC PACKAGING WITH FLIP-CHIP BONDING: Jong Tae Moon, G.J. Joo, M K. Song, K.E. Pyun, H.M. Park, Semiconductor Research Division, Electronics and Telecommunications Research Institute, 161 Kajonj-Dong, Yusong-Gu, Taejeon, 305-350, Korea
The optical transmitter and receiver modules were fabricated by applying flip chip bonding process. It was possible that the degree of alignment accuracy controlled below 1 µm by the force of solder self-alignment. To minimize parasitic capacitance and inductance induced from the solder joint, the reflowed solder ball on Si substrate was varied from 100 µm to 5 µm. The Pb-In, Pb-Sn, In-Sn and In-Ag alloys as the bonding materials were deposited above UBM on the Si substrate by using thermal evaporation method. During the reflowing process, the behavior of solder ball formation, and the intermetallic compounds between the UBM and solder composition were inspected with various heating rates and the use of flux. During the flip chip bonding process, the solder joint shape and the gap between Si substrate and optical devices were controlled by means of a various temperature profiles and bonding force. The solder joints reliability of the flip chip bonded optical submodules were evaluated by shear, thermal shock, and thermal cycling test. In the case of the thermal shock test, the range of temperature was from 25°C to the liquid N2. Thermal cycling numbers were 1000 cycles from -40°C to 120°C. These samples were analyzed by optical microscopy, SEM/EDS and TEM.
10:10 am INVITED
RELIABILITY CHALLENGES AND MODELING OF MINIATURIZED SOLDERED ASSEMBLIES: Jean-Paul Clech, EPSI Inc., P.O. Box 1522, Montclair, NJ 07042
Miniaturized electronic packages have emerged that bring about new reliability challenges and, in some cases, have revived the concerns of Leadless Chip Carriers (LCCCs) on organic substrates: 1) most of these packages are leadless; 2) their Coefficient of Thermal Expansion (CTE) is low because of the high silicon contents of shrinking or disappearing packages; 3) the assembled packages may have a low stand-off height (for miniaturization purposes); 4) typical assemblies are very fine-pitch with micro-solder joints having smaller load bearing or crack propagation areas than conventional surface mount assemblies. The above attributes may be detrimental to long term solder joint integrity and suggest that reliability be looked at carefully, more so than with conventional surface mount assemblies. This talk will present thermal stress and reliability models that can help tackle those problems and ensure that assembly reliability is built-in during the early stages of product design. Two examples of engineering models of miniaturized assemblies will be discussed that enable rapid assessment of the impact of package geometry and materials on assembly reliability. The first example is a model of flip-chip assemblies with underfill. The model quantifies the solder joint relief provided by the underfill layer and its effect on assembly stiffness. The mechanics of flip-chip with underfill are unique since they involve an increase in assembly stiffness to provide for solder joint strain relief. The analysis is that of a multilayer structure (board/underfill/die) that deforms under thermal loads and 'external' forces and moments exerted by the solder joints. Predicted shear strains in the underfill layer are in good agreement with moiré measurements. In the limiting case where the shear modulus of the encapsulant is very low, the model converges to Hall's axisymmetric model for conventional LCCC assemblies. The analysis also gives interfacial stress distributions, a useful feature to assess whether the encapsulant/die and substrate interfaces are overstressed. Various parametric studies are conducted showing that the encapsulant modulus must be high enough to provide adequate strain relief in the solder joints, in agreement with experimental results and advanced finite element studies. Increasing the encapsulant modulus stiffens the assembly, because of mechanical coupling between the die and substrate, but the increased stiffness is overshadowed by much larger reductions in the solder joint strains. The second example is that of a micro-BGA construction where a compliant elastomer layer provides for decoupling between the die and substrate. The package is modeled as a multilayer structure (dielectric film/elastomer/die) where the low modulus elastomer layer behaves like an adhesive bond in shear. The analysis enables tailoring the compliant layer (modulus and thickness) to achieve targeted assembly reliability goals. Both mechanical models capture the reliability impact of the design parameters and materials in a quantitative manner. They can be easily implemented as PC-based design-for-reliability tools to conduct parametric studies on chip, board and assembly parameters.
10:35 am BREAK
10:45 am INVITED
QUALIFICATION TEST FOR SOLDER ATTACHMENT OF CHIP-SCALE BGA PACKAGING: Vern Solberg, Tessera Inc., 3099 Orchard Drive, San Jose, CA 95134
Chip-scale package family for silicon products can be combined to help the engineer and designer meet the most demanding goals for electronic miniaturization,. The significant advantage to employing the miniature Chip-Scale Packaging (CSP) technology is three-fold: higher component density, more efficient assembly automation and enhanced product performance. Bare or unpacked die may be considered for miniaturization, however, a significant advantage a packaged device has over bare die is the ability to test and screen the product before surface mount technology, chip-scale BGA devices have proved efficient, rugged and easily adapted to existing high volume SMT manufacturing processes. Of primary concern to anyone utilizing a new technology is finished product reliability. In this paper, the author will describe several chip-scale device structures, the operational environments they are expected to withstand and the results of, long-term thermal stress testing of the 46 I/O µBGA Flash Memory packages that have been reflow solder attached to conventional laminated circuit structures. Topics covered include: Standards for CSP Technology, Assembly Process Methods, Defining Product Use Environment, Planning the Assembly Test Strategy. Although many of the products being introduced in the miniature chip scale package are compatible with existing surface mount assembly processes, the contact size and pitch are relatively small. And although high assembly yields have been achieved, developing a reliable product using chip-scale devices requires uniform solder paste printing and continued assembly process monitoring.
11:10 am INVITED
RELIABILITY OF ENCAPSULATED SYSTEMS FOR FLIP-CHIP ASSEMBLIES: Cindy M. Melton, Daniel R. Gamota, Motorola, Interconnect & Assembly Technology Research Group, Corporate Manufacturing Research Center, Room 1014, 1301 East Algonquin Road, Schaumburg, IL 60196
Encapsulant materials for flip chip on board assemblies were developed to address the issues of thermal mismatch between the various materials used in this assembly methodology. Several experimental encapsulant materials with enhanced flow properties, shorter cure schedules, and lower stresses have been studied for their effect on manufacturability and their behavior as a compliant structure surrounding the solder joints. Materials characterization studies were performed on the various encapsulants to determine the glass transition temperatures (Tg), tensile elastic and loss modulii (E' and E''), flow profiles, coefficients of thermal expansion (CTE), radii of curvature, stress relaxation as functions of temperature and moisture, and apparent strengths of adhesion. In addition, reliability tests were conducted using FR4 substrates populated with die and underfilled with the various encapsulants to determine the relationship between materials properties and, package and solder joint reliability responses.
11:35 am INVITED
DESIGN OF FLIP-CHIP MCM/BGA PACKAGING FOR OPTIMUM SOLDER JOINT RELIABLITY: T. Dixon Dudderar, Yinon Degani, B. J. Han, V. Reddy Raju, Lucent Technologies, 700 Mountain Avenue, Room 1A-105, Murray Hill, NJ 07974
It is well recognized that the thermal strains associated with material incompatibilities have been the root cause of many failures in both single chip microelectronic packages and in their soldered connections to circuit boards, etc. In so far as solder joints are concerned, flip chip interconnections and the joints under unleaded packages such as BGAs are in many ways "worst case" examples. This paper will describe in detail the unique choices of materials properties and encapsulation structure designed to provide a flip-chip soldered Multichip Module in a BGA package qualified for commercial telephone applications which was both highly reliable and cost effective.
12:00 pm
NANOSTRUCTURAL ANALYSIS OF PADS-TREATED SOLDER SURFACE: James L. Marshall and Brett Piekarski, Department of Chemistry, University of North Texas, Denton, TX 76203-5068; Army Research Laboratory, AMSRL-EP-RC, 2800 Powder Mill Road, Adelphi, MD 20783
Room: 340C
Session Chairs: A. Zangwill, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332; S.A. Barnett, Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208
9:00 am INVITED
LOW-ENERGY ION AND HYPERTHERMAL NEUTRAL BEAMS FOR FILM GROWTH: EFFECTS ON NUCLEATION, MICROSTRUCTURE EVOLUTION, EPITAXIAL THICKNESS, ROUGHENING, AND STRAIN RELAXATION: Joe Greene, Materials Science Dept., Univ. of Illinois, Urbana, IL 61801
Low-energy (10-100 eV) ion and hyperthermal neutral irradiation during filmgrowth from the vapor phase are used to provide new chemical reaction pathways, modify film growth kinetics, and, hence, controllably alter film properties. During low-temperature epitaxial growth from hyperthermal Si beams, critical epitaxial thicknesses were increased by up to an order of magnitude over those obtained with MBE due to enhanced interlayer mass transport and more effective filling of interisland trenches. For heteroepitaxial Si1-xGex growth on Si(001), AFM and XTEM studies show that strain-induced roughening, which occurs at elevated growth temperatures, is strongly suppressed at Ts between 300 and 400°C, with no indication of low-temperature kinetic roughening. The use of low-energy primary- ion beam sources in which ion energy and ion/neutral flux ratios can be varied independently during the growth of Al, Cu, and TiN polycrystalline layers on SiO2 will be shown to provide dramatic differences in nucleation rates, mosaicity, preferred orientation, strain, and microstructure evolution.
9:40 am INVITED
GLANCING-ANGLE ION BOMBARDMENT FOR MODIFICATION AND MONITORING OF SEMICONDUCTOR SURFACES: J.G.C. Labanda, S.A. Barnett, Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208; Lars Hultman, IFM, Linköping University, S-581 83 Linköping, Sweden
Using glancing-angle ion bombardment for surface modification rather than conventional near-normal incidence ions has the advantages of reducing damage and implantation projected ranges, reducing channeling, reducing sputtering, and preferentially removing surface asperities leading to flat surfaces. The effect of bombardment conditions on the surface morphology and perfection of GaAs(001), InP(001) and Si(001) surfaces are reported. Air-exposed surfaces were cleaned and smoothened to near atomic flatness without damage for optimal conditions: for example, with GaAs this was observed for 1000 eV Ar ions incident at 15° from the surface plane at a dose of 2x1016 ions/cm2. For a given set of bombardment conditions, ion damage (observed as small dislocation loops in a 20-30 nm thick surface layer) decreased with decreasing ion incidence angle, and was eliminated below a critical angle. Sputtering yield, measured using film thicknesses and changes in reflection high-energy electron diffraction oscillations, decreased with decreasing incidence angle. The low sputtering yield and minimal damage make a glancing-angle geometry ideal for real-time characterization by ion scattering spectroscopy. Surface composition measurements on single monolayers of InAs on GaAs showed that the glancing-angle Ar beam did not did not measureably change the In coverage over relatively long times.
10:20 am
INFLUENCE OF PROCESSING PARAMETERS ON THE STABILITY OF MAGNETRON SPUTTERED DEPOSITED GROUP VI THIN FILMS: M.J. O'Keefe, Avionics Directorate, Wright Laboratory, WPAFB, OH 45433
Sputter deposition of metallic thin films is commonly used to fabricate electrically conducting contacts and interconnects on semiconductor devices. For military applications, the stability of the patterned metal under adverse environmental conditions, such as prolonged exposure to elevated temperatures, can significantly influence the reliability of the device. In this investigation the influence of magnetron sputter deposition processing parameters on the stress, adhesion, resistivity and crystal structure Group VI (i.e.. Cr, Mo, W) thin films was studied. The influence of elevated temperature on the stability of the films was evaluated, in part, using a Tencor Flexus-2900 thin film stress measurement system. Results from the study indicate that minor changes in processing conditions can significantly affect the as-deposited and elevated temperature properties of the films.
10:40 am BREAK
11:00 am INVITED
KINETIC ROUTES TO COHERENT ISLANDS: Andrew Zangwill, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332; Harvey T. Dobbs & Dimitri D. Vvedensky, Blackett Laboratory, Imperial College, London SW7 2BZ, UK
The Stranski-Krastanov growth morphology of heteroepitaxy consists of three dimensional islands that nucleate on top of a few strained layers of film material that wet the substrate. It is well understood on the basis of energetic considerations that such islands can be entirely free of misfit dislocations, i.e., coherent, until they grow rather large. But the kinetic processes that govern their formation are far less clear. Motivated by recent scanning tunnelling microscopy studies of this phenomenon for Ge/Si(111), InAs/GaAs(001), and InSb/GaAs(001), we present a combination of atomistic Monte Carlo simulations and mean-field rate theory designed to reveal the kinetic pathways to coherent islands. Particular emphasis is placed on the role of interface alloying and the dynamics of the wetting layers.
11:40 am
MORPHOLOGICAL INSTABILITIES AND EVOLUTION OF THIN FILMS: H. Wong, P.W. Voorhees, M.J. Miksis, S.H. Davis, Northwestern University, Evanston, IL 60208
The driving force for morphological evolution of thin films increases as the size of the films decreases. Thus, to further miniaturize microelectronic and optoelectronic devices, the morphological instability and evolution of thin films need to be understood. We study the linear instability of two film shapes commonly encountered in experiment: a strip on a substrate, and a hole in a uniform film on a substrate. We assume that the instability is driven by capillarity and the film evolves via surface diffusion. The contact angle is fixed at a value between 0 and 180 degree. We find that both film shapes are unstable to certain disturbances. We also simulate numerically the evolution of the film shapes triggered by an unstable disturbance to reveal new stable steady states. The implications of these results on the long term stability of solid-film devices will be discussed. *Supported by NSF and DOE.
Room: 330E
Session Chairpersons: Robert O. Ritchie, Dept. of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720; Kwai S. Chan, Southwest Research Institute, San Antonio, TX 78228-0510
8:25 am OPENING REMARKS
8:30 pm INVITED
FATIGUE AND FRACTURE OF TiAl PST CRYSTALS: Y. Umakoshi, Department of Materials Science and Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565 Japan
Orientation and temperature dependences of cyclic hardening, fatigue life and fracture mode of TiAl PST crystals were investigated. Deformation twins and vein-like structure containing high density of ordered dislocations were formed below 500°C depending on the type of ordered domain in the 
phase. The vein-like structure was responsible for strong cyclic hardening, while deformation twins were formed at the initial stage of fatigue and did not contribute the hardening. Formation of twins and vein-like structure was suppressed at 700°C and fatigue life rapidly decreased showing cyclic softening. Deformation twins produced extrusions on the specimen surface and played an important role for crack initiation and fatigue failure. Effect of additional third elements such as V and Nb on the cyclic hardening and fatigue life will also be presented.
9:00 am
FUNDAMENTAL ASPECTS OF FATIGUE FRACTURE IN TiAl ALLOYS: Kwai S. Chan, Southwest Research Institute, San Antonio, TX 78238; D.S. Shih, McDonnel Douglas Aerospace, St. Louis, MO 63166
The fatigue mechanisms in a TiAl alloy heat-treated to the lamellar and equiaxed microstructures were studied to determine the effects of microstructure on the initiation of microcracks and their subsequent growth into large cracks. The results indicated microcracks initiated at grain/colony boundaries and at slip bands. Most microcracks were arrested after nucleation, but a few grew at K below the large crack thresholds. The populations of non-propagating and propagating cracks varied with life fractions. Ligaments in the wake of a fatigue crack were prone to fatigue failure. The destruction of the crack-wake ligaments resulted in lower fracture resistance in materials under cyclic loading than those under monotonic loading. *Supported by the AFWL Materials Directorate through Contract No. F33615-92-C-5951.
9:20 am
MICROMECHANICS OF FATIGUE AND FRACTURE IN LAMELLAR TiAl: Bimal K. Kad, Robert J. Asaro, Department of Applied Mechanics & Engineering Science, University of California-San Diego, La Jolla, CA 92093
Finite element based numerical procedures, incorporating physically based crystal plasticity models, are employed to study the evolution of non-uniform deformation, under monotonic and fully reversed (R=-1) cyclic loadings, in lamellar TiAl microstructures. The impetus for such efforts is to gather fundamental insight into microstructure sensitive deformation mechanisms, and to extract additional information, not obtainable from traditional mechanical property measurements. Such an effort is particularly desirable to help track various aspects of plastic anisotropy of specific layers, and microconstituents as implicit in polycrystalline aggregates. Computational efforts are directed to address constant strain, as well as constant stress amplitude loading schemes in the low cycle fatigue regime. Irreversible deformation twinning effects are fully accounted for in the fatigue maximum of 100 cycles. We will present several examples of experimentally observed, and numerically computed results, to identify hot spots for strain localization in monotonic and fully reversed loadings, and prescribe microstructural remedies to alleviate such effects.
9:40 am
MICROCRACK NUCLEATION AND PROPAGATION IN TiAl: Zhe Jin, George T. Gray III, Los Alamos National Laboratory, Los Alamos, NM 87545
Microcrack nucleation and propagation in a PST-TiAl crystal and a duplex -TiAl alloy at high and quasi-static strain rates and temperatures from 196°C to 1200°C was investigated under compression loading. In PST crystals, two microcracking habit planes, the {110} planes for translamellar cracking and the (111) interface plane for interlamellar cracking, were observed when the <110> directions in the lamellar interfaces were perpendicular to the loading direction. However, three microcracking habit planes were observed when the <321> directions in the lamellar interfaces were perpendicular to the loading direction. Most microcracks were found to nucleate at/near the lamellar interfaces and propagate into the laths along their habit planes to form translamellar cracks. In the fine-grained duplex microstructure, both grain interior microcracks and grain boundary microcracks were observed. The grain interior microcracks occurred primarily within the equiaxed grains and appeared to be formed by shear displacements along the maximum shear planes. An attempt to correlate the microcrack formation with the crystal deformation modes and crystal orientations is made and the microcrack nucleation and propagation mechanisms in TiAl are analyzed.
10:00 am BREAK
10:10 am INVITED
DAMAGE MODELING OF GAMMA TITANIUM ALUMINIDES: M.J. Pfuff, B.U. Wittkowsky, GKSS-Forschungszentrum Geesthacht GmbH and SFB 371, Institut für Werkstofforschung, Max-Planck-Str., D-211502 Geesthacht, Germany
A common feature of Gamma Titanium Aluminides is the heterogeneous character of their microstructure. This heterogeneity causes failure processes to be progressive, with a continuous transition between a diffused and a localized mode of damage, the relative contribution of both modes to failure being determined by the degree of randomness of microstructural heterogeneity. At room temperature the failure is preceded by the formation of microcracks which control the strain to failure either by microcrack coalescing or by the nucleation of a critical-size crack. The size and local distributions of microcracks reflect the heterogeneity of microstructure, and depend on stress state, size and geometry of the specimens. The results of model calculations are presented, which are based on mesoscale lattice of beams models used in statistical physics in order to treat the relationships between microcracking and failure. A comparison of the numerical results to the experimental findings emphasizes the significant role microstructural heterogeneity plays during the failure process of Titanium Aluminides.
10:40 am
LARGE-SCALE MOLECULAR DYNAMICS SIMULATIONS OF THREE-DIMENSIONAL FRACTURE IN A 
-TiAl ALLOY: S.J. Zhou, D.M. Beazley, P.S. Lomdahl, B.L. Holian, Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545
We have carried out new large-scale molecular-dynamics (MD) simulations of fracture in a titanium-aluminum alloy, using the methods we developed in previous MD simulations, where we studied dislocation emission from a crack in a three-dimensional thin film of embedded- atom-method copper, comprising 35 million atoms. In that first study, we observed a variety of dislocation emission modes in a sample that was sufficiently thick that we could be sure that the results did not depend on the thickness. The sequence of dislocation emission in the crack blunting process strongly depends on the crystallographic orientation of the crack front and differs strikingly from anything previously conjectured. This finding is essential to establish a precise dislocation emission criterion (i.e. intrinsic ductility criterion). We will report on similar calculations for the TiAl system, with emphasis on the crack-tip plasticity and interaction between a crack and lamellar interfaces.
11:00 am
ATOMISTIC SIMULATIONS OF FRACTURE IN TiAl: Julia Panova, Diana Farkas, Department of Materials Science and Engineering, Virginia Polytechnic Institute, Blacksburg, VA 24061
Atomistic simulations of fracture in L1o TiAl were carried out using EAM interatomic potentials and molecular statics. We studied the behaviour of semi-infinite cracks under mode I loading in different crack-tip orientations. From the [1-10](111) crack tips we observed extensive dislocation emission, involving the formation of several planar faults, such as APB, CSF and SISF. We found that the edge dislocations with 1/2[110] Burgers vector that were emitted from [001](110) cracks were very compact and mobile. No planar fault formation was involved in the dislocation emission from this crack geometry. Cracks with [001](100) orientation were observed to cleave near the Griffith value of loading in a purely brittle manner.
11:20 pm
ON THE CORRELATION BETWEEN MECHANISMS OF PLASTICITY AND FRACTURE IN Ti-48 AT.% Al ALLOYS: J.M.K. Wiezorek, P.M. DeLuca, M.J. Mills, H.L. Fraser, Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210
The technologically most relevant two-phase (-2) TiAl compounds contain a significant volume fraction of morphologically lamellar grains. Interestingly, a change in the predominant fracture mode has been observed from transgranular at room temperature to intergranular at elevated temperature for both equiaxed and duplex microstructures. It has previously been suggested that the segregation of alloying additions and/or impurities to grain boundaries during exposure at elevated temperature could be responsible for this change in fracture characteristics. However, the origin for the observed fracture mode change has not been ascertained to date. In this study binary Ti48at.%Al alloys of equiaxed, duplex and fully lamellar microstructure have been deformed in tension to various degrees of strain up to fracture, at both room and elevated temperature. The active fracture modes have been identified by SEM fractography. Moreover, the deformation modes active in these two phase TiAl compounds during tensile loading have been determined by TEM. Thin foils for the TEM characterization have been obtained from cuts perpendicular and parallel to the load axis at various locations in the gage sections as close as 10 µm from the actual fracture surface. The results of these investigations are discussed specifically with respect to the origin of the reported fracture mode changes, and the mechanisms fundamentally underlying the plasticity and fracture of these (-2) TiAl compounds. This work has been supported by a grant from the National Science Foundation with Dr. Bruce MacDonald as program manager.
11:40 am
FINITE ELEMENT ANALYSIS OF GRAIN BOUNDARY CAVITATION IN FULLY LAMELLAR TITANIUM ALUMINIDE INTERMETALLIC ALLOY: Anirban Chakrabort, James C. Earthman, Materials Science and Engineering, University of California, Irvine CA 92697
Creep constrained grain boundary cavitation in fully lamellar form of titanium aluminide intermetallic alloy has been studied using finite element techniques. Two different forms of fully lamellar models are considered. Cavitation is modeled in the presence of grain boundary sliding for the case of straight former grain boundaries and cavitation without grain boundary sliding is considered for fully lamellar microstructure with serrated former grain boundaries. Effect of interaction of cavitating facets on rupture life has been studied. A comparison between the fully lamellar forms and a dual phase equiaxed microstructure having the same phase ratio (2/) is also made to examine the relative susceptibility of these microstructures to high temperature damage.
Room: 231C
Session Chairpersons: Jan D. Miller, Professor, Univ. of Utah Met. Engineering Dept., Salt Lake City, UT; and Philip Thompson, President, Dawson Metallurgical Laboratories, Inc., Salt Lake City, UT
8:30 am Keynote
PROJECTING LABORATORY AND PILOT TEST DATA INTO OPERATING REALITY: Robert R. Beebe, Consultant, Former Vice President, Newmont Mining Corporation, P.O. Box 32048, Tucson, AZ 85751-2048
Laboratory and pilot-scale tests are almost invariably required before metallurgical development can proceed. Difficulties with sampling, as well as with classical chemical and physical scale-ups are normally anticipated and relatively well-understood, but more subjective factors also come into play, including misunderstandings of the operating scheme chosen, wrong "lessons" learned from similar operations, failures to handle data appropriately, and even arbitrary intervention by management. The paper examines some of these subjective factors and suggests ways to guard against them. Several anecdotal case studies are used as examples, including when and where to heap leach or to mill specific types of gold ore.
9:05 am
PREDICTING PRODUCTION HEAP LEACH CYCLE TIMES FROM LABORATORY COLUMN TEST DATA: Philip Thompson, President, Dawson Metallurgical Laboratories, Inc., Murray UT 84157-0685
Carefully planned Laboratory test programs provide valuable data regarding the amenability of low grade gold ores to heap leaching. Several problems are encountered in laboratory column simulation of gold heap leaching. A problem most commonly associated with column testwork is the limit on test column height. Most laboratories use a 3 to 5 meters (or 9 to 15 feet) high column as a standard test due to building ceilings and sample size limitations, etc. The problem with this column height is that most commercial heaps are at least 10 to 15 meters (25-35 feet) high, with some heaps reaching 100-200 meters (225-450 feet). This paper presents a data interpretation method whereby the data from test columns of virtually any height can be used to predict a first approximation leach cycle time for commercial heaps. Other important factors, e.i. sample preparation protocol, preliminary bottle roll testing, column diameter requirements, and leach solution analysis, are also discussed.
9:25 am
AGGLOMERATION PRACTICE AT KENNECOTT BARNEYS CANYON MINING COMPANY, BARNEY CANYON, UT: Philip L. LeHoux, Chief Metallurgist, Kennecott Barneys Canyon, Magna, UT 84O44
Kennecott Barneys Canyon Mining Company has been a gold heap leaching facility in operation since 1989. In 1994, a flotation plant was commissioned to remove sulfide minerals from refractory sulfide ore. Tailings from the plant are mixed with oxide heap leach material in order to produce a geotechnically stable agglomerate from which the gold is leached and recovered in a conventional heap leach cyanidation process. The experience to arrive at an effective blending methodology is discussed.
9:50 am BREAK
10:00 am
ZARAFSHAN NEWMONT J.V. MURUNTAU HEAP LEACH OPERATION, UZBEKISTAN: Sevket Acar, Senior Metallurgist, Newmont Metallurgical Services, Salt Lake City, UT 841O8; Tim Acton, Newmont Gold Company, One Norwest Center, 17OO Lincoln St., Denver CO 8O2O3
Zarafshan/Newmont is a 50/25/25 joint venture between Newmont Gold and two entities of the Republic of Uzbekistan, the State Committee for Geology and Mineral Resources, and Navoi Mining and Metallurgical Combinat. Zarafshan/Newmont joint venture consists of a heap leaching operation, which will process 220 million metric tons of existing stockpiles of low-grade oxide ore averaging 0.036 oz Au/T from the Muruntau mine. Net recovery over the 17-year life of the project is expected to be 4.8 million ounces of gold. The plant started in October 1993, and the operations commenced on May 25, 1995. The crushing plant consists of four stages of crushing and screening to produce 95% -3.35 mm product followed by heap leaching and gold recovery by Merrill-Crowe process. The Dore metal is refined at the Muruntau refinery. All gold produced by the joint venture is sold on the world market.
10:25 am
PROCESS MINERALOGY OF HEAP LEACHABLE ORE DEPOSITS: J.G. Davidson, N.A. McKay, Lakefield Research Ltd., Lakefield, Ontario KOL 2HO
Heap leachable ore deposits from many countries have been submitted for process mineralogical evaluation and laboratory testwork. Numerous factors must be addressed and integrated by the mineralogist, geologist, metallurgist and engineer. Projects encompass grass roots exploration, preliminary petrographic analysis, predictive and process mineralogy, dye penetration analysis of rocks and thin sections, metallurgical beneficiation testwork and plant optimization studies. The significance of mineralogical factors, such as geological controls, degree of oxidation, dye amenability, liberation, deleterious minerals, refractoriness, and the impact of mineralogy on gold recovery and process considerations, will be presented.
10:50 pm
COLD WEATHER HEAP LEACHING OPERATIONAL METHODS: Kenneth E. Smith, Lyntek, Inc. 775 Mariposa St., Denver, CO 80204
Cold weather heap leaching can be grouped into two basic regions; Arctic and near-Arctic, with various operational techniques or combinations of operating techniques dictated by latitude and site topography. The basic cold weather regions are Arctic areas, (between 50( and 60( North latitude). As techniques and operational philosophy have advanced, heap leaching operations have moved into progressively colder regions.
11:15 am
HEAP LEACHING IN EXTREME NOTHERN CLIMATES, AN OVERVIEW OF THE BREWERY CREEK MINE, YUKON, CANADA: Thomas Haper, Sitka Corporation; Rod Samuels, RM Samuels Consulting; Rupert Allen, Consulting Geologist, Viceroy Resources Corporation, Vancouver, B.C., Canada
Viceroy Resource Corporation of Vancouver, B.C., has recently developed and brought into production the Brewery Creek Mine, an open-pit heap leach gold mine, located 55km east of Dawson City in Yukon, Canada. Mineable reserves are 15.2 million tonnes of ore grading 1.45 grams/tonne, containing 22 tonnes (707, 315 oz) of gold. Ore processing employs the heap leach technology using run-of-mine ore. Highlights of 1996 activity included construction of a 158,000m2 of leach pad, placing 1.9 million tonnes of ore at a grade of 1.46 gpt to the leach pad, construction and successful commissioning of the ADR plant, and pouring of the first gold bar on November 15th. Permitting of this mine has drawn significant attention because of the innovated heap leach technology; although this technology has been proven in other jurisdictions, it has not been used at such northern sites where winter temperatures routinely reach -45(C for extended periods. Acknowledgments are extended to the staff of the Viceroy Resources Corporation for their participation in developing the successful heap leaching technology under extreme frigid climatic conditions.
Room: 315A
Session Chairpersons: L.R. Motowidlo, IGC Advanced Superconductors, Waterbury, CT; J. Schwartz, National High Magnetic Field Laboratory, Tallahassee, FL
8:30 am INVITED
Bi-2212/Ag HTSC MAGNETS FOR HIGH FIELD GENERATION: H. Kitaguchi, H. Kumakura, K. Togano, T. Kiyoshi, K. Inoue, National Research Institute for Metals, 1-2-1 Sengen Tsukuba 305, Japan; M. Okada, K. Tanaka, Hitachi Ltd., 7-1-1 Ohmika, Hitachi 319-12, Japan; J. Sato, Hitachi Cable Ltd., 3550 Kidamari, Tsuchiura 300, Japan
Two kinds of compact superconducting magnet have been fabricated with Bi-2212/Ag multifilamentary tapes. These magnets are stacked double pancake type and made by a wind and react process. One of them has the dimensions of 55 mm in height, 49 mm in outer diameter, and 12.5 mm in clear bore. The magnet was inserted in a 21-T-class superconducting magnet system and tested in various field at 4.2 K. In zero bias field, the magnet carries 400 A (criterion: 10-13 Wm) and generates 2.5 T. In the bias field of 21.1 T, the magnet successfully generates 1.76 T with the current of 281 A, i.e., the total field reaches 22.8 T which is the highest field ever achieved with a superconducting magnet. Transport current properties in bias fields for the other magnet with the outer diameter over 90 mm are also reported.
8:50 am INVITED
EFFECTS OF MECHANCIAL STRAIN ON Bi2Sr2CaCu2Ox/AgX COMPOSITE CONDUCTORS: J. Schwartz, B.C. Amm, H. Garmestani, Y. Hascicek, D.K. Hilton, National High Magnetic Field Laboratory, Tallahassee, FL 32310
The development of powder-in-tube Bi2Sr2Can-1)CunOx technology has progressed such that high critical current density (Jc) conductors are produced by many researchers. An important issue that remains, however, is the effects of mechanical strain. While it is evident that large strains induce irreversible damage, applications may be limited by fatigue at low strain values due to crack propagation. Here we report upon the effects of cyclic fatigue on Jc of Ag and Ag-alloy clad Bi2Sr2CaCu2Ox as measured by electrical transport and magnetic hysteresis. Measurements of the constituent and composite mechanical properties and bulk Bi2Sr2CaCu2Ox fracture toughness are also reported. As Jc may be limited by microcracks before straining, studies of crack propagation and mechanical strain effects may also provide insight into the fundamental limits to transport Jc. Results are interpreted within this framework as well.
9:10 am INVITED
PROPERTIES AND PROCESSING OF MULTIFILAMENTARY PIT FORMED USING THE CTFF PROCESS: M.D. Sumption*, S.X. Dou**, N.V. Vo**, and E.W. Collings*; *MSE, The Ohio State University, Columbus, OH, USA; **CSEM, The University of Wollongong, NSW, Australia
Multifilamentary Bi2212 strands with up to 37 filaments have been formed using Continuous-Tube-Forming-Filling (CTFF). The CTFF process is used for the initial monocore, which is then restacked via a conventional PIT process, and these strands are then rolled into tapes. A sterling Ag outer shell is used, but the matrix region used pure Ag. Self field Jc at 4.2 K is 9.16 kA/cm2. The resulting filaments are aspected, with dimensions 7.5 x 370 mm. A vibrating sample magnetometer has been used to measure M-H loops (losses). Losses were measured, and it was possible to separate out; (i) critical state losses, (ii) eddy current losses, (iii) logarithmic type creep influences on the losses, and (iv) exponential type creep influences on the losses.
9:30 am INVITED
Bi2Sr2Ca1Cu2Ox MULTIFILAMENT WIRES AND TAPES FOR MAGNET APPLICATIONS UP TO 20 K: L.R. Motowidlo, G. Galinski, G.M. Ozeryansky, F. Krahula, R.S. Sokolowski, IGC Advanced Superconductors, Waterbury, CT 06704
Long lengths of Ag-alloy sheathed Bi2Sr2Ca1Cu2Ox (2212) multifilament wires and tapes have been fabricated and heat treated. Sample lengths of one to two meters are cut after melt processing and wound into standard holders used to test NbTi for MRI. The performance characteristics of the 2212 conductors, that is the critical current density, the overall critical current density, and the n-values of a number of samples as a function of the applied magnetic field (0-9 Tesla) at 4.2 K will be reported. Work supported by IGC Advanced Superconductors.
9:50 am
IMPROVEMENTS IN Bi2Sr2CaCu2Ox CONDUCTOR VIA DOPANTS: J. Schwartz*, A. Bhargava**, B. Boutemy*, and W. Wei*; *National High Magnetic Field Laboratory, 1800 E. Dirac Dr., Tallahassee, FL 32310; **University of Queensland, Brisbane, Qld 3072, Australia
An important characteristic of high temperature superconducting materials is the ability to carry large Jc at high magnetic field. As a result, the NHMFL anticipates using HTS conductor for the highest field region of the 1 GHz NMR magnet system. Two obstacles to high field Jc over long lengths are poor flux pinning and carbon-induced bubbling and tunneling. Here we report progress on these two challenges via fine-scale additives to the starting powder. To address the flux pinning issue, we are investigating nano-scale MgO additions. By growing the 2212 grains around the MgO particles, pinning centers are directly incorporated in the superconducting grains. To prevent bubbling and tunneling from CO2 gas that forms during melt processing we are investigating Ba-O additions. By trapping the carbon in BaCO3, CO2 formation is prevented. We report magnetic and electrical measurements of Jc, extensive microscopy, and x-ray diffraction of tapes formed with these approaches.
10:10 am INVITED
CRITICAL CURRENT DENSITY, HYSTERESIS LOSSES AND STRUCTURE ALONG HTSC WIRES: P.V. Bratukhin, I.A. Rudnev, Moscow State Engineering Physics Institute (Technical University), Kashirskoe sh. 31, 115409, Moscow, Russia
Critical current density hysteresis and losses were measured along Bi-HTSC/Ag wire. X-ray diffraciton analysis of the same samples allowed to observe structure features connected with critical current distribution along wire length.
Room: 232B
Session Chairperson: Sara Dillich, U.S. Department of Energy, 1000 Independence Ave. S.W., Mail Stop 6A-116, EE-20, Washington, DC 20585
8:30 am
ALUMINUM INDUSTRY/GOVERNMENT PARTNERSHIP FOR COLLABORATIVE R&D: Hank Kenchington, U.S. Department of Energy, 1000 Independence Avenue S.W., Washington, DC 20585
In 1996, the U.S. Department of Energy signed a contract with the aluminum industry to establish a research partnership for collaborative research and development. The partnership will identify appropriate areas for joint R&D that can improve the quality of life in the United States and promote the manufacture of competitively priced and ecologically sustainable aluminum products. To implement the partnership, DOE will work with the aluminum industry to develop a technology roadmap that delineates and prioritizes the technological needs for global competitiveness into the 21st century.
9:00 am
TECHNOLOGY ADVANCEMENTS IN RESISTANCE WELDING OF ALUMINUM FOR AUTOMOTIVE APPLICATIONS: Chon L. Tsai, Ohio State University, 1960 Kenny Road, Columbus, OH 43210-1063
A strategic plan for advancing the resistance welding technology for aluminum based materials will be presented. The purpose of this work is to identify the critical issues associated with the current technology and to develop innovative approaches to advancing the technology for automotive applications.
9:20 am
JOINING ALUMINUM MATERIALS USING ULTRASONIC IMPACTORS: Glenn Freitas, Aztex, Inc., 303 Bear Hill Road, Waltham, MA 02154-1196
The joining approach being presented here uses ultrasonic impactors to insert steel pins directly to join aluminum to aluminum or aluminum to composite materials. The concept does not require any machining or preparation of the aluminum components to be joined. Using this process, inexpensive mill products, sheet, extrusions, etc. can be used directly without additional machining to create complex structures. More importantly, this process will produce very high performance structures similar to the weight efficiency of co-cured carbon composites at a fraction of the cost.
9:40 am
THERMAL SPRAYING OF ALUMINUM AS AN ADHESIVE BOND PRETREATMENT: Guy Davis, DACCO SCI, Inc., 10260 Old Columbia Road, Columbia, MD 21046
DACCO SCI, Inc., (DSI) evaluates two-wire arc thermal spray coatings as an adherent pretreatment. This work will build on previous experience of DSI with plasma spray coatings as treatments for aluminum adherents. These treatments exhibit performance equivalent to the best chemical treatments but are environmentally benign. Thermal spray processes generate no gaseous or liquid wastes and minimal solid wastes. Additionally, they are robust processes that are capable of being preformed on localized areas in the field or depot during repair/refurbishment operations. Alternatively, parts may be sprayed in advance and stored indefinitely prior to use. The two-wire arc process is considerably cheaper and less complicated then the plasma spray process.
10:00 am BREAK
10:20 am
UTILIZATION OF RECYCLED AND UNRECOVERABLE ALUMINUM SCRAPS IN MANUFACTURING CELLULAR CONCRETE: Jiann-Yang (Jim) Hwang, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295
In manufacturing cellular concrete, finely divided metallic aluminum powder is used to react with hydroxides, forming minute bubbles of hydrogen gas throughout the concrete mixture. Traditionally, high cost pure aluminum powder is used in manufacturing cellular concrete which greatly increases the cost of the products. To use traditionally unrecoverable aluminum wastes, a pretreatment process will be employed to separate magnetic metal and dirt from the stream and to grind the main stream waste into aluminum powder. The effect of moisture content in the waste on grinding quality will be examined and evaluated. The effects of the amount of recycled aluminum and the alkalies concentration in the mixture will be studied. Finally, the mechanical and physical properties of the cellular concrete will be examined and evaluated.
10:40 am
SOLID-STATE SPRAY FORMING OF ALUMINUM NEAR-NET SHAPES: Ralph Tapphorn, Howard Gabel, Innovative Technology, Inc., P.O. Box 8392, Las Cruces, NM 88006
Solid-state spray forming (SSF) is a promising new technology for saving energy in the production of aluminum near-net shapes. Because SSF does not require melting of the feedstock, ITI anticipates producing aluminum parts at significantly lower energy input than conventional alternatives require. The light weight, high strength, and recyclable features of these parts will propagate this energy savings through the life of the parts. SSF is potentially applicable to the production of aluminum metal matrix composites, also in near-net shapes; and provides the compelling possibility of producing MMCs with non-traditional strengthening phases, including nonophase particles.
11:00 am
THE ALUMINUM INDUSTRY OF THE FUTURE: John Green, The Aluminum Association, 900 19th Street, N.W., Washington, DC 20006
On behalf of the U.S. aluminum industry, Dr. Green will describe the industry's vision of the future as published in The Aluminum Association's report titled "ALUMINUM INDUSTRY: INDUSTRY/GOVERNMENT PARTNERSHIPS FOR THE FUTURE." The report describes how the aluminum industry will maintain and build its competitive position in worldwide markets through research and development. Dr. Green will also solicit comments on the newly developed technology roadmap for the aluminum industry.
Room: 232C
Session Chairpersons: Prof. Gerhard E.Welsch, Materials Science and Engineering, Case Western Reserve University, 514 White Bldg., Cleveland, OH 44106-7204; Michael Kangilaski, Advanced Methods and Materials, 1798 Technology Drive, #251, San Jose, CA 95110
8:30 am
STRESS/RUPTURE STRENGTH OF RHENIUM AT EXTREMELY HIGH TEMPERATURES: B. Fischer, D. Freud, Jena Polytechnic, Tatzendpromenade 1 b, D-07745 Jena, Germany; D. Lupton, W.C. Heraeus, GmbH, Heraeusstrasse 12-14, D-63450 Hanau, Germany
For the safe high-temperature use of rhenium we have the task of measuring the stress/rupture strength at extremely high temperatures. For stress/rupture tests on high melting metals we designed and built a test system that allows measurements to be made at temperatures up to 3,000°C under an inert atmosphere. Using this test unit we determined stress/rupture diagrams of rhenium in several material conditions in the range of 2,100°C to 3,000°C. The discussion of the measured values is based on me/allographic test results, scanning electron microscopy (SEM) images of rhenium samples after the stress/rupture tests, the determination of trace impurities using secondary ion mass spectrometry (SIMS) and the results of the residual gas analysis of rhenium.
8:50 am
INFLUENCE OF COLD ROLLING ON PLASTIC RESPONSE OF PM AND CVD RHENIUM: G. Subhash, B.J. Koeppel, Mechanical Engineering-Engineering Mechanics Department, Michigan Technological University, Houghton, MI 49931
Plastic response of rhenium (Re) produced by powder metallurgy (PM) and chemical vapor deposition (CVD) was investigated under uniaxial compression. The PM Re was also cold rolled by 50% and 80% reduction (denoted as PM50 and PM80, respectively) in thickness. Both cold rolled and CVD Re have been found to have a strong basal texture. Cylindrical specimens from the above four types of Re (i.e., PM, PM50, PM80 and CVD) were subjected to uniaxial compressive loads in the range of strain rates from 1x10-3 s-1 to 9.5 x 103 s-l. Low strain rate experiments were performed in an Instron machine and high strain rate experiments were performed in a split Hopkinson pressure bar. The deformed specimens were metallographically prepared and etched to study microstructural changes and identify the micromechanisms of deformation. Rhenium exhibited a two stage hardening in its plastic response. It revealed a high strain hardening rate and a strong strain rate sensitivity of flow stress. Increased cold work in the PM Re resulted in an increase in the initial yield stress with a concurrent reduction in the hardening rate and failure strain. CVD Re exhibited a distinctly higher hardening rate and ultimate flow stress than the above cold rolled PM Re. After accumulating a certain amount of plastic strain, the deformation in the specimens localized leading to formation of shear bands at an angle to the loading axis. Fracture immediately followed the shear bands. Twinning was found to be a dominant deformation mode in both PM and CVD Re. Extensive twinning was observed in larger grains of CVD Re. Twins in fine "rained PM specimens were less common and occurred primarily in the regions close to the shearband. Based on the experimental results and microscopic investigations, the micromechanisms of deformation responsible for the observed behavior of Re will be discussed.
9:10 am
STEADY STATE CREEP RATES OF W-4Re-0.32HfC: John J. Park, MS E506, Los Alamos Laboratory, Los Alamos, NM 87545; Dean L. Jacobson, Dept. of Chem, Bio. and Materials Engineering, Arizona State University, Tempe, AZ 85287-6006
Second phase particle-strengthened tungsten alloy, tungsten-4w/o rhenium-0.32w/o hafnium carbide (W-4Re-0.32HfC), was creep-tested at temperature ranges of 2200 to 2400K and stress ranges of 40 to 70 Mpa in a vacuum of better than 1.3 x 10-6 Pa (1 x 10-8 torr). The resulting steady state creep rates were applied to three particle-strengthened creep models and compared. The three creep models were Ansell-Weertman, Lagneborg, and Roesler-Arzt. None of the three models precisely predicted the steady state creep rates of W-4Re-0.32HfC. However, the recovery creep model of Lagneborg qualitatively fit the creep rates.
9:30 am
TEMPERATURE AND LOAD DEPENDENCE ON THE HARDNESS OF ROLLED RHENIUM SHEETS BEFORE AND AFTER ANNEALING: K. Peter, D. Lagerlöf, Seog-Young Yoon, Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106; Boris D. Bryskin, Jan-C. Carlén, Rhenium Alloys, Inc., Elyria, P.O. Box 245, OH 44036
The microhardness of rolled rhenium sheets was determined as a function of indentation load and temperature. Sheets of rhenium were produced from rhenium metal powder by pressing, presintering and sintering, followed by cold rolling. After a production anneal to define the structure of the starting material, sheet samples were deformed using cold rolling to about 30% strain in 5% deformation increments without intermediate annealings. One of the deformed samples was annealed at 1600°C for 20 minutes. The temperature dependence of the microhardness between room temperatures and 900°C (using 50° increments) was studied using a Nikon Model QM hot hardness tester equipped with a Vickers indentor. The load dependence of the microhardness was investigated using both a Vickers anda Knopp indentor, and the indentation size effect (ISE) was best explained using the normalized Meyer's law. The hardness of the annealed rhenium sheet approached that of the as-rolled sheets at large indentation loads because of workhardening under the indentor during indentation. The hardness at "zero load" (obtained from extrapolation of the load dependence of the hardness) suggests that the hardness is controlled by two different mechanism having different thermal activation. The activation energy of the mechanism controlling the hardness at low temperatures is approximately 0.02 eV whereas that at high temperatures is approximately 0.5 eV. The transition temperature between the two controlling mechanisms occurs at about 250C.
9:50 am BREAK
10:10 am
A REVIEW OF THE INTERACTION OF COLD WORK AND ANNEALING IN THE PROCESSING OF RHENIUM: O.S. Es-Said, Mechanical Engineering Department, Loyola Marymount University, Los Angeles,CA 90045; R.H. Titran, NASA Lewis Research Center, 21000 Brookpark Road, Mail Stop 49-1, Cleveland, OH 44135
Twinning is a dominant deformation mode in both PM and CVD rhenium. Although severe work hardening occurs during cold rolling, extensive twinning enables rhenium to retain moderate ductility. It is believed that as the deformation process progresses, twinning becomes the predominate mode contributing to the plastic deformation of rhenium. At all deformations, the hardness and strength of rhenium decreases at annealing temperatures corresponding to the temperature of the onset of recrystallization. It is known that the recrystallization temperature of rhenium decreases with increasing amounts of cold work, from 1750°C for 5% deformation to 1200°C for 40-60% deformation. This strong dependence exist because the nucleation of recrystallization occurs at the intersection of twin crystals and growth proceeds on the bases of the twins. When a polycrystalline material is deformed, the individual grains tend to orient themselves so that the active slip systems become more favorably oriented with respect to the direction of the principal strain. This leads to crystallographic anisotropy or preferred orientation. In a recent study, the effect of rolling mode on PM rhenium was evaluated. Samples rolled at a 45° direction showed a higher work hardening rate than samples rolled along the width and length of rolled sintered bars. This paper will review the interactions of cold work and annealing on the work hardening, recrystallization, and texture of rhenium.
10:30 am
SOLID SOLUTION MOLYBDENUM-RHENIUM ALLOYS: Lynn B. Lundberg, Materials Consultant, 2832 W. 33rd N., Idaho Falls, ID 83402; Boris D. Bryskin, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036
It has been known for many years that the brittleness commonly seen in commercial-pure molybdenum around room temperature can be greatly reduced or eliminated by alloying with rhenium within the solubility range fro rhenium in molybdenum. Molybdenum-based solid solution alloys with rhenium represent a technically important class of refractory metal alloys whose behavior is reviewed in this paper. Mechanical and physical properties are reviewed as well as the fabrication characteristics of the alloys. Data from the vast amount of research performed on molybdenum-rhenium alloys in the former Soviet Union and more recently in Russia are referenced, summarized and reviewed. For the area of advanced materials' applications such analysis is appropriate to make intelligent decisions on how to proceed.
10:50 am
AN OVERVIEW OF W-Re ALLOYS FOR TEMPERATURE MEASUREMENT APPLICATIONS: D.A Toenshoff, R.D. Lanam, Engelhard-CLAL, 700 Blair Road, Carteret, NJ 07008
Two Tungsten-Rhenium alloy pairs are the predominant combinations used in the measurement of temperatures up to 2400°C and higher under protective inert or vacuum conditions. These alloy pairs are W-3Re vs. W-25Re and W-SRe vs. W-26Re. Other combinations are used in regional areas or for special applications. These include W vs. W-25Re and W-5Re vs. W-20Re. A historical review of the materials and the evolution of their use will be given. A discussion of alternate materials e.g. Ir vs. Ir-40Rh to measure high temperatures will be included. The effect of composition and environment on the EMF characteristics will be summarized. The future use of W-Re alloys for temperature measurement applications will be projected.
11:10 am
THE MECHANICAL PROPERTIES OF W-Re MADE BY PM METHOD: N. Danilenko, V. Panichkina, Yu. Podrezov, O. Radchenko, Frantsevich Institute for Problems of Materials Science, 3 Krjijanovskogo Str. 252680 Kiev, Ukraine
The tungsten sheets made by using the powder metallurgy method displayed low plasticity and were apt to delamination in the rolling plane. In order to improve plasticity of the sheets and suppress delamination the additions of the W-Re and HfO powders were employed. On the basis of such compositions the tungsten sheets were obtained which were plastically deformed at 223K. That sheets manifested the fracture toughness in the rolling plane by factor of five higher as compared with the initial sheets.
11:30 am
TECHNETIUM, A MANMADE SISTER ELEMENT AND BACKUP ALLOYING AGENT FOR RHENIUM: Edwin D. Sayre, 218 Brooke Acres Drive, Los Gatos, CA 95032
Room: 330A
Session Chairperson: Soo Woo Nam, Dept. of Materials Science & Eng., Korea Adv. Inst. of Science and Technology, Taejon 305-701 Korea
8:30 am
AN EVALUATION OF THE DAMAGE TOLERANCE CHARACTERISTICS OF Ti6Al2Sn2Zr2Mo2Cr SHEET: T.D. Bayha, Lockheed Martin Aeronautical Systems, Marietta, GA 30063; D.L. Yaney, Lockheed Martin Missiles and Space Palo Alto, CA 94304
Ti-6Al-2Sn-2Zr-2Mo-2Cr (Ti-6-2-2-2-2) is an alpha-beta titanium alloy typically utilized in thick section, damage tolerance-driven aerospace applications. This alloy was developed for deep hardenability, with high strength, and moderate fracture toughness. Ti-62222, research efforts to date have been primarily focused on rolled plate and forged products; however, there is interest in developing thin sheet material for wing skin applications. A rolling practice to produce Ti-6-2-2-2-2 sheet materials for conventional and superplastically formed structure has been developed. The work described here characterizes the properties, microstructure, and fracture behavior or Ti-62-2-2-2 solution treated and aged sheet samples subjected to tensile and cyclic loadings. Tensile and fatigue crack growth tests were performed over a wide temperature range (-65°F to 500°F) to assess the suitability of the sheet in various applications. Crack growth testing was performed utilizing two Rratios at each temperature of interest. Test data indicates that the crack growth behavior of Ti-6-2222 is superior to Ti-6Al-4V sheet in the Paris regime under comparable test conditions. A complete metallurgical analysis utilizing both scanning electron and transmission microscopy was conducted to develop property/microstructure relationships, and selected test specimens were examined to provide insight regarding fracture mechanisms with respect to typical cyclic loading conditions.
8:50 am
EFFECT OF 
/
VOLUME FRACTION ON THE SUPERPLASTIC DEFORMATION BEHAVIOR OF Ti6Al4V ALLOY: J.S. Kim, D.M. Li, C.S. Lee, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790784, Korea
Present investigation has been made to study the superplastic deformation behavior of Ti-6AI4V alloy with respect to the variation of / volume fraction. Load relaxation tests were employed at 600 and 800°C, to obtain stressstrain rate curves for the microstructures of 3 and 16µm grain sizes. Superplastic deformation test was also carried out to confirm the results of load relaxation test. The experimental results were analyzed by the theory of inelastic deformation which consists of two mechanisms, i.e., one is the grain matrix deformation and the other is the phase/grain boundary sliding. Grain matrix deformation is dominant at 600°C and well described by the state equation when permeability parameter, p, is 0.15. Phase boundary sliding is dominant at 800°C and also consistent with the viscous flow equation with Mg=2.
9:10 am
CHARACTERIZATION OF INTERMETALLIC PRECIPITATES IN A / TITANIUM ALLOY: X.D. Zhang*, J.M.K. Wiezorek*, D.J. Evans**, L. Fraser*; *The Ohio State University, Department of Materials Science and Engineering, 2041 College Rd, Columbus, OH 43210; **Materials Directorate, Wright Laboratory, WL/MLIM, Wright Patterson AFB, Dayton, OH 45433
A two phase - titanium alloy, Ti6Al2Mo2Cr2Sn2Zr0.2Si (Ti-6-22-22S), has recently been reconsidered as a structural material for aircraft applications. This alloy exhibits specific strength and fracture toughness superior to that of Ti6A14V. However, similar to other alpha-beta titanium alloys, microstructural stability is one of the major concerns regarding industrial application of Ti62222S. For instance, precipitation of additional phases during long term high temperature exposure is predicted to affect significantly the performance of components in service. Three different precipitates have been observed in Ti-6-2222S alloys, namely silicides, 
and 2 phases. The presence of intermetallic precipitates, such as 2, in the parent a matrix has been reported to result in brittle behaviour of the / alloys due to the formation of intense planar slip on {101U} prismatic planes. The present paper presents results of the characterization of intermetallic 2 precipitates in the phase of Ti62222S by methods of scanning ant transmission electron microscopy (SISM and TEM respectively). The precipitation of 2 precipitates has been studied as a function of heat treatment conditions in order to examine the microstructural stability and growth behaviour. The observed dispersion of small, brittle intermetalllic precipitates is expected to have a detrimental effect on the fracture performance of Ti-6-22-22S. Hence, it is important to ascertain the origin of this precipitation phenomenon. The 2 precipitates have been characterized chemically and structurally by high spatial resolution microanalysis and high resolution electron microscopy.
9:30 am
CRACK PROPAGATION IN GRADIENT MICROSTRUCTURES IN TITANIUM ALLOYS: A. Berg, J. Kiese, L. Wagner, Technical University of Brandenburg at Cottbus, 03013 Cottbus, Germany
Fatigue crack nucleation, microcrack growth and long crack growth are often oppositely affected by microstructural changes. For example, refining the microstructural unit size, e.g., grain size, improves the material's resistance to crack nucleation and microcrack growth, while long crack characteristics often deteriorate. To obtain optimum resistance of a component to various stages of fatigue life, microstructural gradients were developed in the near- titanium alloy TIMETAL 1100 and the metastable alloy Ti3Al8V6Cr4Mo4Zr (Beta C) by thermomechanical treatments. In TIMETAL 1100, the prior grain size of fully lamellar microstructures was varied from about 100 µm at the surface of the component to about 500 µm in the bulk, while for Beta C, the degree of age-hardening was varied over the cross section resulting in hardness values ranging from 700 HV 0.1 at the surface to 300 HV 0.1 in the bulk. Fatigue tests were performed in 3point bending using a servohydraulic testing machine. Optical microscopy was used to study fatigue crack nucleation and crack growth. The results are compared with nongradient references.
9:50 am
MECHANICAL AND THERMOMECHANICAL SURFACE TREATMENTS TO ENHANCE BCF STRENGTEI IN HIGHSTRENGTH- TITANIUM ALLOYS: J. Kiese, W. Walz, L. Wagner, Technical University of Brandenburg at Cottbus, 03013 Cottbus, Germany
Shot peening and deep rolling with and without subsequent heat treatments were performed on various microstructures of the highstrength metastable titanium alloys Ti3Al8V6Cr4Mo4Zr and TilOV2Fe3Al to improve the fatigue behavior. To evaluate optimum process parameters, a wide range of Almen intensities, rolling forces and annealing temperatures was chosen. The change in surface layer properties was evaluated by TEM, X-ray diffraction, optical microscopy and microhardness measurements. Smooth and notched (K+ = 3.0) specimens were tested in rotating beam loading and the fatigue behavior was compared to the electrolytically polished reference. The results are explained in terms of the resistance to fatigue crack nucleation and microcrack growth as affected by the changes in near surface dislocation structure, residual compressive stresses and extensive precipitation hardening.
10:10 am
INVESTIGATION OF THE CREEP DEFORMATION MECHANISM OF THE LAMELLAR TiAl ALLOY MADE BY HOT EXTRUSION OF A BLENDED ELEMENTAL POWDER MIXTURE: Soo Woo Nam, Han Seo Cho, SunKeun Hwang*, and Nack I. Kim**, Dept. of Mat. Sc. & Eng., Korea Advanced Institute of Sci. & Tech. Taejon 305-701, *Inha University, and **Pohang Univ. of Sci. & Tech., Korea
Creep properties of the lamellar structured Ti46.6AI1.4Mn2Mo (at.°/O) alloy, which is made by hot extrusion of a blended elemental powder mixture, are investigated in air environment over the temperature range from 750°C to 900°C at constant stress levels ranging from 100MPa to 250MPa. Average grain size of 150µm is measured and the grain boundary phase is distributed inhomogeneously before the creep tests. The dislocation climb controlled creep deformation is suggested on the basis of the measured average activation energy for creep of 388kJ/mol and normalized stress exponent of 4.3 within the temperature range from 775°C to 900°C at stress level ranging from 150MPa to 250MPa. However, activation energy of 90kJ/mol within the temperature range of 750°C to 775°C and stress exponent of I.3 at 800°C within the stress range of 100150MPa are measured. Microstructural studies conducted on the creep fractured specimens showed the secondary cracks along the lamellar grain boundaries and these secondary cracks are assumed to be formed by pore nucleation, growth and coalescence during the tertiary stage.
10:30 am
MECHANICAL BEHAVIOR OF BINARY AND TERNARYALLOYED Al2Ti: J.C. Ma, J.E. Benci, Department of Materials Science and Engineering, Wayne State University, Detroit, MI 48202
Polycrystalline binary Al2Ti was produced via casting or powder metallurgy and then further processed yielding material in six conditions. The yield strength as a function of test temperature and the room temperature fracture toughness were measured for these six material conditions. The fracture toughness values were determined from the critical load necessary to initiate cracks with a Vickers indenter. Both properties show a strong dependence on processing condition. Off-stoichiometric al2±Ti1± and ternary-alloyed Al2Ti + X were also produced, and samples in the as-cast and cast & annealed conditions were prepared. The composition of the off-stoichiometric alloys was varied between 63 and 71 at% aluminum in 2% increments. Ternary-alloyed Al2Ti contains approximately 2 at% of either Si, V, Cr, Mn, Fe, Ni, Cu, Nb, Mo or W. The room temperature hardness and fracture toughness and the room and elevated temperature yield strength were measured for each composition in both the as-cast and cast & annealed material conditions. The effect of thermal mechanical processing, such as hot forging, on the room temperature properties was also investigated.
10:50 am
MICROSTRUCTURAL EVOLUTION DURING HIGH TEMPERATURE DEFORMATION OF -TiAI INTERMETALLIC COMPOUNDS: Hee Y. Kim, Woong H. Sohn, Soon H. Hong, Dept. of Mat. Sci. & Eng., Korea Advanced Institute of Science and Technology, Taejon, 305701, Korea
The microstructural changes during high temperature deformation behavior of Ti-(46,48)Al2W and Ti47Al2Cr4Nb intermetallic compounds have been investigated by isothermal compression tests at temperatures ranged from 1000°C to 1200°C with strain rates ranged 10-3/10-1/s-1. The stressstrain curve exhibited a peak stress then the flow stress decreased gradually into a steady state with increasing strain. The stressstrain curves showed a flow softening which is attributed to the dynamic recrystallization. The dependences of flow stress on temperature and strain rate were formulated using Zener-Hollomon parameter. The activation energies were measured as 437kJ/mol, 374kJ/mol and 300kJ/mol and the stress exponents were measured as 5.8, 5.3 and 4.9 for Ti46AI2W, Ti48AI2W and Ti47AI2Cr4Nb, respectively. The dynamically recrystallized microstructures were investigated and the relationships between recrystallized grain size and temperature compensated strain rate was discussed. The texture evolution during high temperature deformation was analyzed using the orientation distribution function (ODF). The controlling mechanisms during high temperature deformation of TiAl intermetallic compounds with varying temperature, strain and strain rate were discussed.
11:10 am
COMPARISON OF FATIGUE CRACK GROWTH RESISTANCE OF GAMMA ALUMINIDES AND Ti-BASED ALLOYS: S. Lesterlin, C. Mabru, C. Sarrazin, G. Henaff, J. Petit, Laboratoire de Mechanique et de Physique des Materlaux, URA CRNS 863 ENSMA, BP 109, 86960 Futuroscope, France
Gamma aluminides present attractive properties for high temperature structural applications and could be adopted against traditional titanium alloys. The resistance to fatigue crack growth is critical against traditional titanium alloys. The resistance to fatigue crack growth is critical for aeronautical applications. In this paper, the fatigue behavior of long cracks in Titanium Aluminides (lamellar and fully ) is compared, based on microstructure, temperature and environment criteria, with five conventional Titanium alloys in different thermomechanical conditions. At room temperature, higher threshold (related to enhanced near-threshold contribution of crack closure) and lower KIC contributes to much more steep propagation curves on TiAl. At high temperature in air, the crack growth regime identifies on Ti alloys as a corrosion-fatigue mechanism assisted by water vapor is shown to be also oporative for TiAl alloys. In all the cases, the propagation of fatigue cracks in both types of materials seems to be governed by the same mechanisms and the TiAl alloys appears to be more sensitive to moisture than Ti based alloys.
11:30 am
ENVIRONMENTALLY ASSISTED FATIGUE CRACK PROPAGATION IN Ti 6246 at 500°C: J. Petit, C. Sarrazin-Baudoux, S. Lesterlin, Y. Chabanne, Laboratoire de Mechanique et de Physique des Materlaux, UFA CNRS 863, ENSMA, BP 109, 86960 Fuuturoscope, France
The fatigue and crack propagation behavior of Ti 6246 alloys elaborated with a fine Windmanstatten microstructure, has been investigated at 500°C. Tests were performed in air, high vacuum (10-4 Pa), low vacuum (1Pa) and humidified Argon (100 Pa and atmospheric pressure). Partial pressures of water vapour and oxygen were controlled by mean of hygro-metals and mass spectrometer. Crack closure was detected using a capacitive gauge mounted at the mouth of the notch of CT specimens. The enhancement of the crack growth rates in the mean-threshold area and the mid-rate range observed in the different environments in comparison to high vacuum, is clearly related to the presence of water vapor even at very low partial pressure. Critical conditions (partial pressure, frequency, closure, load ratio) for the occurrence of water vapor assisted corrosion-fatigue, creep-fatigue and stress-corrosion are explored, and the specific role of oxygen and water vapor is discussed on the basis of microfractographic observations, fracture surface analysis (R.B.S. technique) and closure measurements.
Room: 314B
Session Chairpersons: J.R. Childress, University of Florida, PO Box 116400, Gainesville, FL 32611
8:30 am INVITED
LASER PROCESSING OF ADVANCED MATERIALS: J. Narayan, North Carolina State University, Burlington Labs, Raleigh, NC 27695-7916
9:05 am INVITED
ROLE OF ENERGETIC SPECIES DURING LASER ABLATION THIN FILM GROWTH: David P. Norton, Oak Ridge National Laboratory, Oak Ridge, TN 37831
9:40 am INVITED
ROLE OF THE CO2 LASER IN DUAL-LASER ABLATION: Sarath Witanachchi, University of South Florida, Tampa, FL 33620
10:00 am
PHOTOSTIMULATED DESORPITON OF Co FROM GEOLOGICAL CALCITE FOLLOWING 193 NM IRRADIATION: Kenneth M. Beck, David P. Taylor, Wayne P. Hess, Pacific Northwest National laboratory, Richland, WA 99352
10:15 am BREAK
Session Chairperson: J. Narayan, North Carolina State University, Burlington Labs, Raleigh, NC 27695-7916
10:30 am INVITED
TBA: Clinton B. Lee, NC & AT University
11:00 am INVITED
GROWTH AND CHARACTERIZATION OF SELF-DOPED COLOSSAL MAGNETORESISTIVE MANGANITE THIN FILMS: D. Kumar, Rajiv K. Singh, University of Florida, PO Box 116400, Gainesville, FL 32611
11:30 am
EFFECT OF ELECTRODES ON THE FERROELECTRIC CAPACITOR FOR DEVICE APPLICATIONS: M.R. Alam, A. Kumar, A. Mangiaracina, I. Ahmed, and G. Wattuhewa; University of South Alabama
11:45 am
TBA: A.J. Paul, NIST
Room: Salon 4
Location: Clarion Plaza Hotel
Session Chairperson: C.L. Snead, Brookhaven National Laboratory, Upton, NY 11973-5000
8:30 am
PRE-CONCEPTUAL DESIGN AND PRELIMINARY NEUTRONIC ANALYSIS OF THE PROPOSED NATIONAL SPALLATION NEUTRON SOURCE: J.O. Johnson, J.M. Barnes, L.A. Charlton, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6363
The Department of Energy has initiated a pre-conceptual design study for the National Spallation Neutron Source (NSNS) and given preliminary approval for the proposed facility to be built at Oak Ridge National Laboratory. The pre-conceptual design of the NSNS consists of an accelerator system capable of delivering a 1-2 GeV proton beam, with 1 MW of beam power, in an approximate 0.5 microsecond pulse, at a 60 Hz frequency onto a single target station. The NSNS will be upgraded in stages to a 5 MW facility with two target stations (a 60 Hz station and a 10 Hz station). There are many possible layouts and designs for the NSNS target stations. This paper gives a brief overview of the proposed NSNS with respect to the target station, as well as the general philosophy adopted for the neutronic design of the NSNS target stations. A reference design, based upon experience at existing sources and on designs for proposed new, high power, sources is presented, and some of the preliminary design neutronic results for the NSNS are briefly discussed.
9:00 am
CALCULATED NEUTRONIC PERFORMANCE AND RADIATION DAMAGE PARAMETERS FOR THE UPGRADED MANUEL LUHAN, JR., NEUTRON SCATTERING CENTER TARGET SYSTEM: P.D. Ferguson, G.J. Russell, E.J. Pitcher, J.D. Court, Los Alamos National Laboratory, Los Alamos, NM 87545
The upgraded MLNSC target system is designed to be a split target with two tiers of moderators. The original suite of moderators serving 12 flight paths has been optimized and an additional pair of moderators, one water and one LH2, have been added in a new upper moderator tier serving 4 additional flight paths. The upper moderators are coupled and viewed in backscattering geometry, as opposed to the decoupled moderators in the existing MLNSC target system which are viewed in transmission. Fabrication of this new target system is currently in progress and installation is expected in 1998. The neutronic performance of the target system s presented in the form of time and energy spectra for each of the planned moderators with comparisons to the existing MLNSC moderators. Results of several studies, including moderator thickness, upper target length, and reflector material, are presented. For the upper and lower targets, target canister material, and moderator structural material, we present neutron and proton energy spectra, helium production, and DPA calculations. Existing accelerator materials damage data are referenced, where applicable, to draw general conclusions on component lifetime.
9:30 am
CALCULATED NEUTRONIC PERFORMANCE OF A LONG-PULSE SPALLATION SOURCE: G.J. Russell, E.J. Pitcher, P.D. Ferguson, J.D. Court, D.J. Weinacht, Los Alamos National Laboratory, Los Alamos, NM 87545
Neutronic performance studies of a Long-Pulse Spallation Source (LPSS) at the Los Alamos National Laboratory show that a 1-MS LPSS has world-class neutronic performance with low technical risk. An LPSS uses coupled moderators (moderators that communicate neutronically at all energies with an adjacent reflector). There are potential gains of about a factor of 6 in time-averaged neutron brightness for a coupled moderator compared to a decoupled one; however, this gain comes at the expense of putting "tails" on the neutron pulses. The particulars of a neutron pulse from a moderator (e.g., rise time, peak intensity, pulse width as measured by the standard deviation or full-width at half maximum of the pulse, and decay constant(s) of the tails) are crucial parameters for instrument design/performance at an LPSS. Moderator neutronic performance can be altered in a variety of ways: a)target material and geometry; (b) moderator material and geometry; c) target-moderator geometry; d) reflector material; e) presence of decouplers and flight path liners; and f) the proton pulse width. We will discuss the neutronic performance of an LPSS and describe the variety of neutronic optimization studies that have been done to improve the neutronic performance of such a neutron source.
10:00 am BREAK
10:20 am
NEUTRONIC DESIGN OF THE APT MATERIALS IRRADIATION AT THE LOS ALAMOS SPALLATION RADIATION EFFECTS FACILITY: P.D. Ferguson1, W.F. Sommer1, M. S. Wechsler2, G.J. Russell1, E.J. Pitcher1, R.B. Kidman1; 1Los Alamos National Laboratory, Los Alamos, NM 87545; 2North Carolina State University, Raleigh, NC 27695-7909
The APT project is in the process of qualifying materials for use in the target/blanket assembly. As part of the process, an eight month irradiation of prospective target, blanket, beam entry window, and structural materials is taking place at LASREF in the 800-MeV, 1 mA proton beam. The irradiation is configured to produce samples at prototypic APT radiation environments, as well as samples at reduced damage rates to provide information as to how the materials age in an APT environment. In addition, three prototype lead blanket modules are being irradiated along with several aluminum tubes filled with 3He to experimentally determine the extent of tritium implantation in the APT system and to explore possible mitigation techniques. In this paper, we detail the methodology of the neutronic design of the irradiation. Neutron and proton spectra are presented for several irradiation locations and materials, as well as calculated gas production and dpa estimates.
10:50 am
PROGRESS REPORT ON THE ACCELERATOR PRODUCTION OF TRITIUM MATERIALS PROGRAM: S.A. Maloy, W.F. Sommer, Los Alamos National Laboratory, Los Alamos, NM 87545
Progress will be reported on the status of an irradiation by 800 MeV protons and spallation neutrons to determine the change in mechanical properties of materials to be used in the APT project. Materials will be irradiated for 8-9 months at the Los Alamos Radiation Effects Facility (LASREF). The irradiation matrix, developed by members of several laboratories nationwide, consists of specimens of candidate materials, scaled components and a closed-loop water system to measure rates of corrosion in irradiated water. The objectives are to determine the performance (particularly, mechanical and corrosion properties) of materials in APT-prototypic proton and neutron radiation and temperatures, to test manufacturing processes for producing components, and to develop a surveillance program to monitor the properties of materials during the life of the APT target/blanket.
Room: 231B
Session Chairpersons: KNona Liddle, Washington State University; V. Ramachandran, ASARCO, Inc., 3422 S. 700 W., Salt Lake City, UT 84119-4191
8:30 am
THERMAL PLASMA ENHANCED CHEMICAL VAPOR INFILTRATION: Patrick R. Taylor, Banqiu Wu, Edgar E. Vidal, University of Idaho, Department of Metallurgical & Mining Engineering, Moscow, ID 83844-3024
A novel method for chemical vapor infiltration, using thermal plasma technology, has been developed. The use of a thermal plasma source may allow much greater infiltration rates than conventional CVI. Precursors that are fed into the flame region of the plasma are vaporized and forced to flow through a porous preform, at a controlled temperature, where condensation or chemical reactions occur. Exploratory experiments, using silica and methane as precursors and graphite felt for the preform, have been performed. The change in the pressure drop across the preform, as infiltration occurred, is compensated by the use of a vacuum pump on the discharge of the reactor. The product was characterized using SEM and x-ray diffraction. A uniform infiltration rate of SiC was observed along the width of the preform.
8:55 am
SOME KINETIC ASPECTS OF THE GASEOUS CHLORINATION OF TITANIUM-BEARING RAW MATERIALS: C.A. Silva, D.H. Gameiro, V.A. Leao, I.A. Silva, C.S. Paulo, Escola de Minas da UFOP, Departamento de Metalurgia, Praca Tiradentes 20, 35400-000, Ouro Preto, MG, Brazil
The kinetics of chlorination of titanium-bearing raw materials has been investigated. For comparison purposes pellets of controlled macro-porosity, made of analytical grade TiO2 and anatase concentrate (Brazil), have been exposed to different combinations of gas composition - co, CO2, Cl2 , gas flowrate and temperature. A thermogravimetric technique and an adapted grain model have been used in order to assess the influence of the several experimental parameters upon the chlorination behavior.
9:20 am
KINETICS OF OXYCHLORINATION OF CHROMIUM (III) OXIDE: I. Gaballah, N. Kanari, Mineral Processing and Environmental Engineering, Lem, CNRS URA 235, Ensg, Inpl, BP 40, 54501 Vandeuvre, France
The oxychlorination kinetics of pure Cr2O3 with C12+O2 is studied by ThermoGravimetric Analysis (TGA) in non and isothermal conditions up to 1000C. The final reaction product is CrO2Cl2. The reaction Of Cr2O3 with Cl2+O2 chlorination gas mixtures starts at about 500C. The apparent activation energy of the oxychlorination reaction of Cr2O3, as well as the apparent reaction orders with respect to the reactive gases are determined. The reaction rate is maximum for a Cl2/ O2 molar ratio equal to 4.
9:45 am
CHLORINATION: A POTENTIAL APPROACH FOR THE BENEFICATION OF CHROMITE: N. Kanari, I. Gaballah, Mineral Processing and Environmental Engineering, lem, cnrs ura 235, ensg, inpl, bp 40, 54501 Vandeuvre, France
One of the criteria to define the market value of chromite concentrate is its chromium to iron ratio. Changing this ratio for a definite chromite is impossible by physical processing. This study investigates the possibility of increasing this ratio through the carbochlorination of chromite concentrate by Cl2+CO between 500 to 900C. The evolution of the reaction products' characteristics is determined by SEM, XRD and chemical analysis. The carbochlorination of a chromite concentrate at 600C leads to the selective partial elimination of iron allowing a higher Cr/Fe ratio of the treated concentrate. A flow-sheet for the benefication of chromite is suggested.
10:20 am BREAK
10:20 am
ARSENIC VOLATILIZATION FROM ENARGITE CONCENTRATE: R. Padilla, Y. Fan, M. Sanchez, and I Wilkomirsky, Department of Metallurgical Engineering, University of Concepcion, Casilla 53-C, Concepcion, Chile
A thermogravimetric study has been conducted to follow the decomposition and volatilization of arsenic from enargite concentrate in nitrogen and slightly oxidizing atmospheres, Temperature has a large effect on the rate of volatilization of arsenic. Fractional volatilization of arsenic as high as 95% were reached in less than 30 min. at 650°C in nitrogen atmosphere, while in slightly oxidizing atmosphere the same volatilization could be achieved in less than 20 min. It was found that As volatilizes as sulfide in nitrogen atmosphere and as a mixture of sulfide and oxide in atmospheres containing 1% oxygen.
10:45 am
OXIDATION OF COPPER MATTE PARTICLES IN SIMULATED FLASH CONVERTING CONDITIONS: Kirsi M. Rijhilahti, Ari Jokilaakso, Department of Materials Science and Rock Engineering, Helsinki University of Technology, FIN-02150 Espoo, Finland; Hong Yong Sohn, Manuel Perez-Tello, Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112
The oxidation characteristics of solid copper matte particles under simulated Kennecott-Outokumpu Flash Converting conditions are presented. This project is concerned with the determination of the effects of operating variables on the reaction of the particles. Experiments were carried out in a large laboratory-scale flash furnace with 72 wt% Cu matte by varying initial particle size, temperature, oxygen partial pressure, oxygen to matte mass-ratio and residence time. Chemical analysis and optical and scanning electron microscopy were used to study the oxidation, morphology and mineralogy. Fractional conversion and sulfur removal, in general, slightly decreased with initial particle size while higher oxygen to matte mass-ratio mainly resulted in higher fractional conversion and more efficient sulfur removal. The fractional conversion values represented the overall extent of oxidation more closely than degree of sulfur removal.
11:10 am
MICROSCOPICAL STUDY OF ROASTED NICKEL CONCENTRATES PRODUCED IN SIMULATED FLASH SMELTING CONDITIONS: Satu Stromberg, Ari Jokilaakso, Satu Jyrkonen, Department of Materials Science and Rock Engineering, Helsinki University of Technology, Espoo, Finland and Tilna Jokinen, Outokumpu Research Oy, Pori, Finland
Four different nickel concentrates were oxidized in a laboratory scale Laminar flow furnace in simulated flash smelting conditions. The major nickel- and iron-bearing minerals in the concentrates were pentlandite, violarite, gersdorffite, and pyrite and pyrrhotite, respectively. Thermal decomposition, ignition and oxidation behavior of nickel and iron sulfides were examined by using optical and scanning electron microscopy. General reactivity of the concentrates was monitored with sulfur removal which was most effective in violarite-based concentrate. Penlandite-concentrates needed higher experimental temperatures for complete desulfurisation and gersdorffite-based concentrate contained 5 - 10 % of the original sulfur even at the most oxidizing conditions studied (11000C, 50 vol-% O2). The reactivity of the iron minerals were found to depend on the other minerals present in the concentrate. In this paper, observed reaction products and mineralogical changes are presented and preliminary conclusions of possible reaction mechanisms of nickel-bearing minerals are discussed.
11:10 am
THERMODYNAMIC MODELING OF Co-Cu-Fe-Ni-S MATTES AND APPLICATIONS IN THE SIMULATION OF SMELTING PROCESSES: F. Kongoli, A.D. Pelton, Centre de Recherche en Calcul Thermochimique, Ecole Polytechnique de Montreal, P.O. Box 6079, Station Downtown, Montreal (Quebec) H3C 3A7
The modified quasichemical model has been applied to Co-Cu-Fe-Ni-S mattes. A small set of model parameters was obtained from optimization of experimental data for the binary Co-S, Cu-S, Fe-S and Ni-S systems. The thermodynamic properties of the ternary, quaternary and quinary systems are then predicted a priori by the model with no additional adjustable parameters. Agreement with all available data for ternary and quaternary mattes is within experimental error limits. The parameters are stored as a database of the F*A*C*T thermodynamic computer system and can be used along with other F*A*C*T databases for alloy, slag, speiss and gas phases, and with Gibbs energy minimization software, to simulate equilibria during smelting processes.
11:35 am
THERMODYNAMIC MODELING OF Co-Cu-Fe-Ni-S MATTES AND APPLICATIONS IN THE SIMULATION OF SMELTING PROCESSES: F. Kongoli, A.D. Pelton, Centre de Recherche en Calcul Thermochimique, Ecole Polytechnique de Montreal, P.O. Box 6079, Station Downtown, Montreal (Quebec) H3C 3A7
Session Chairperson: S.K. Varma, Dept. of Metallurgical and Materials Engineering, University of Texas at El Paso, El Paso, TX 79968
8:30 am
IDENTIFICATION OF CONSTITUENT PARTICLES IN 2024-T3 AND 7075-T6 ALUMINUM ALLOYS: Ming Gao, Robert P. Wei, Dept. of Mechanical Engineering and Mechanics, Lehigh University, 7 Asa Dr., Bethlehem, PA 18015; Jerry Feng, Metallurgy Division, Naval Research Laboratory, Washington, DC 20375
Constituent particles in 2024-T3 and 7075-T6 aluminum alloys were identified by analytical electron microscopy (AEM) to aid the understanding of particle-induced pitting corrosion. Convergent beam electron diffraction (CBED) was used, in conjunction with energy dispersive x-ray spectroscopy (EDS), for determining their structure and composition. Typical phases in these alloys (CuA12, CuMgAl2 and Fe4CuA123) were identified. In addition, a complex rhombohedral phase, with composition close to (Fe, Cu, Mn, Si)Al, was also identified. Detailed aspects of these particles are described, and their role in pitting corrosion are discussed. *Research supported by the Air Force Office of Scientific Research, Grant F49620-93-1-0426, and the Federal Aviation Administration, Grant 92-G-0006.
8:50 am
TEM STUDIES OF PARTICLE-INDUCED CORROSION IN 2024-T3 AND 7075-T6 ALUMINUM ALLOYS: Robert P. Wei, Ming Gao, , Dept. of Mechanical Engineering and Mechanics, Chi-Min Liao, Dept. of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015
To better understand particle-induced pitting corrosion in aluminum alloys, thin- foil specimens of 2024-T3 and 7075-T6 aluminum alloys, with identified constituent particles, were immersed in aerated 0.5 M NaCl solution and then examined by transmission electron microscopy (TEM). The results clearly showed matrix dissolution around the iron and manganese containing particles (such as, Fe4CuAl23). Matrix dissolution was also observed around CuAl2 particles, while CuMgAl2 particles tended to dissolve relative to the matrix. These results are consistent with previous SEM observations of pitting corrosion, and are discussed in terms of the electrochemical characteristics of the particles and the matrix. Research supported by the Air Force Office of Scientific Research, Grant F49620-93-1-0426, and the Federal Aviation Administration, Grant 92-G-0006.
9:10 am
RELATIONSHIP BETWEEN THE SOLUTIONIZED MICROSTRUCTURES AND THE TRANSIENT CURRENT RESPONSE FROM SCRATCH TEST EXPERIMENTS IN 6061 ALUMINUM ALLOY AND A COMPOSITE CONTAINING ALUMINA PARTICLES: Shane Andrews, S.K. Varma, Department of Metallurgical and Materials Engineering, The University of Texas at El Paso, El Paso, TX 79968-0520
The sensitivity of the scratch technique towards understanding the corrosion behavior of 6061 aluminum alloy reinforced with 0.1 volume fraction of alumina particles and in the monolithic form has been explored. Identical solutionizing treatment in the two materials shows different transient current responses. The depassivation and repassivation kinetics appear to differ considerably during the impact and continuous scratches since a balance between the two results in stabilized value of peak current during continuous scratching experiments only. The total charge density increases linearly with solutionizing time for both materials while grain growth law (square of the grain diameter is directly proportional to the solutionizing time) is valid for up to 25 hours of solutionizing time. Near surface microstructures have been examined with the help of TEM as well as SEM. This research has been supported by the National Science Foundation through the grant number HRD9353547.
9:30 am
SCC BEHAVIOR OF SENSITIZED ALLOY 600 LASER-SURFACE ALLOYED WITH Cr-NJ POWDER: Joung Soo Kim, Jin Kuk Shin, Sun Ki Woo, Jeong Hun Suh, Yun Soo Lim, I1 Hyun Kuk, Korea Atomic Energy Research Institute P. O. Box 105, Yusung, Taejun, Korea
In order to prevent and/or mitigate intergranular stress corrosion cracking(IGSCC) occurring in sensitized Alloy 600, the surface of the material was alloyed with Cr or Cr-Ni powder using a CO2 laser beam. The thickness of the alloyed region was measured to be around 200 250 µm. The Microstructure and the compositional variations of the alloyed layers were analysed with a transmission electron microscope (TEM) and analyzed using EDX attached to the TEM. The alloyed molten metal was observed to solidify epitaxially from the boundary between the melted and unmeted(matrix) regions, like the microstructure of sensitized Alloy 600 surface-melted by a CO2 beam. The compositional change in the alloyed layer was very small, i.e. very homogeneus. The surface-alloyed specimens were tested in a sodium tetrathionate (Na2S406) solution at room temperature using a CERT technique. IGSCC was completely prevented by the surface-alloying using a CO2 laser beam, i.e. the specimen was ruptured and the fracture surface was observed to consist of dimples, which is a typical morphology of specimen fractured by ductile failure(rupture). The relationship between the microstructure and the susceptibility to IGSCC will be discussed.
9:50 am
CORROSION-FATIGUE AND STRESS-CORROSION CRACK GROWTH IN PRECIPITATION-HARDENABLE STAINLESS STEELS: P.S. Pao, C.R. Feng, R.A. Bayles, Naval Research Laboratory, Washington, D.C. 20375; G.R. Yoder, Office of Naval Research, Arlington, VA 22217
The effect of load ratio on the corrosion-fatigue crack growth kinetics and the stress-corrosion cracking of the precipitation-hardenable stainless steels PH13-8Mo, 15-SPH, and 17-4PH in a 3.5% NaC1 solution were investigated. All three PH-class stainless steels exhibit good stress-corrosion cracking resistance with stress-corrosion cracking thresholds in excess of 70 MPa
. These steels also demonstrate good corrosion-fatigue cracking resistance in a 3.5% NaC1 solution as the crack growth rates in a 3.5% NaC1 solution are less than twice the rates in ambient air. The corrosion-fatigue cracking thresholds progressively decrease as the load ratio (R) increases from 0.10 to 0.90. PH138Mo exhibits anomalous corrosion-fatigue crack growth kinetics and a concomitant change in fracture mode at R=0.90. The observed crack growth behavior, the deformation microstructure, and the significance of high load ratio corrosion fatigue will be discussed.
10:10 am BREAK
10:30 am
THE MICROSTRUCTURE AND PROPERTIES OF NITROGEN GAS ATOMIZED ALLOY 690: G.E. Fuchs, Lockheed Martin Company, P.O. Box 1072, Schenectady, NY 12301-1072
Alloy 690 exhibits excellent resistance to stress corrosion cracking (SCC) and is frequently used in steam generator applications. In order to achieve the desired microstructure for SCC resistance in A690, high temperature solution annealing heat treatments are required. These heat treatments, though, can result in extensive grain growth and relatively low strength. Powder metallurgy processing and the addition of nitrogen during atomization results in an alloy with significantly improved microstructural control and properties. This study examines the microstructure and properties of a nitrogen gas atomized A690 heat consolidated by HIP and extrusion. The effects of consolidation temperature and subsequent hot working is also discussed.
10:50 am
THE BRITTLE-TO-DUCTILE TRANSITION IN NiA1 SINGLE CRYSTALS: S. Shrivastava, F. Ebrahimi, Materials Science & Engineering Department, University of Florida, Gainesville, FL 32611
Intermetallic compound NiAl has the potential to be used as a turbine blade material for aerospace applications due to its low density, high thermal conductivity, and good oxidation resistance. However, it suffers from insufficient toughness at low temperatures. The purpose of the present study was to investigate the effects of displacement rate on the brittle-to-ductile transition (BDT) in NiAl single crystals. Double-notched-tensile specimens with [110] tensile axis were used for fracture toughness testing. The results of this study show a strong strain rate dependence of BDT temperature, however, the low temperature toughness level was insensitive to the applied displacement rate. Fracture paths of the specimens fractured at different temperatures and strain rates were analyzed and the crack initiation and propagation mechanisms were investigated. In this paper, the process of BDT in NiAl single crystal will be discussed in terms of thermally activated deformation processes and their effects on crack initiation and propagation.
11:10 am
PRECIPITATION BEHAVIOR OF GAMMA PRIME AND SIGMA PHASE OF HIGH STRENGTH STAINLESS STEEL FOR SEA WATER APPLICATIONS: Minoru Suwa, Hideto Kimura, Materials and Processing Research Center, NKK Corporation, 1 Kokancho, Fukuyama, 721, Japan
The effect of y'-Ni,(Ti, Al) and a phase precipitation on the mechanical properties and the corrosion resistance to sea water was investigated in Fe-(2025)%Cr-35%Ni-(4.5-6)%Mo-2%Ti-0.3%Alalloys. Though the hardness of the alloy increases after ' and a phase precipitation, pitting-corrosion resistance is deteriorated by a phase, while deterioration by ' phase precipitation is little. The precipitation of ' is found to occur almost simultaneously with a phase in 25%Cr-4. 5%Mo alloy. However, in 20%Cr-6%Mo alloy, the aging condition for ' phase to precede 
phase is found, which achieves both Vickers hardness of 320, and critical pitting temperature(CPT) of 323K.
11:30 am
MICROSTRUCTURE CHANGE IN SILICON NITRIDE DURING SUPERPLASTIC DEFORMATION: Naoki Kondo1, Eiichi Sato2, Fumihiro Wakai1, 1National Industrial Research Institute of Nagoya, Hirate-cho, Kita-ku, Nagoya, Aich 462, Japan; 2The Institute of Space and Astronautical Science, Yoshino-dai, Sagamihara, Kanagawa 229, Japan
Three dimensional (3-D) microstructures of 
=1.34 (280 % deformed) silicon nitride nitride specimen were calculated using the stereological analysis. The grain radius slightly increased during deformation. The aspect ratio remained almost constant up to = 0.88, and then, largely increased. The orientation angle decreased monotonously. A dominant deformation modes are considered to be grain sliding (= 0.88-1.34). Grain rotation and alignment also act as sub-dominant deformation mode all through the deformation.
Session Chairperson: David H. Carter, Los Alamos National Laboratory, MS G770, Los Alamos, NM 87545
8:30 am
A TEM STUDY ON THE MICROSTRUCTURALEFFECTS ON PLASTIC DEFORMATION IN ALUMINUM ALLOY2219: Carlos D. Rincon, Roy Arrowood , Department of Metallurgical and Materials Engineering and Materials Research Institute, The University of Texas at E1 Paso, E1 Paso, TX 79968-0520
A fundamental transmission electron microscopy (TEM) investigation is being conducted on the effects of microstructure on the plastic deformation of 2219-T87 aluminum. A previous study showed inhomogeneous and locally extreme work hardening in the heataffected-zone (HAZ)- regions in Variable Polarity Plasma Arc (VPPA) 2219-T87 butt welds, which strongly suggests that the HAZ microstructure plays a major role in the deformation and fracture process. Due to the small size of these butt welds, it can be quite difficult to accurately quantify the stress-strain behavior of the HAZ. Therefore, precipitate structures similar to ones found in the HAZ are being produced by heat treatment of tensile specimens machined from 2219-T87 plate. Heat treatments involve varying the aging time and temperature to obtain GP zones followed by the precipitation of transition phases. Uniaxial tensiIe tests will be performed on the heat treated specimens at low strain rates (0.01 mine-1 and 5.0 min-1') at room temperature in order to quantify the effect of precipitate structure on the stress-strain behavior. This work was supported by the General Electric Faculty of the Future Program.
8:50 am
COMPREHENSIVE FLOW STRESS DETERMINATION IN EXTRUDED ALUMINUM PRODUCTS: Michael S. Paulson, Roger N. Wright, Materials Science and Engineering Department, Rensselaer Polytechnic Institute, Troy NY 12180
Physical modeling of the aluminum extrusion process e reductions is difficult due to the large reductions and the complex extrudate shapes. Conventional machines flow stress specimens are not likely to be representative of the metal as it is extruded. A method of directly testing the total cross section is needed to properly represent extrudate flow stresses for process modeling purposes. Such a method is presented, as applied to rapidly heated commercial aluminum extrudates at temperatures and strain rates pertinent to die exit conditions. Resulting constitutive equations are compared to those developed for starting billet stock from the same lot of metal. Sponsored by the Rensselaer Aluminum Processing Program.
9:10 am
EFFECT OF REDISTRIBUTING RESIDUAL STRESS ON THE FATIGUE BEHAVIOR OF SS330 WELDMENT: Yong-Bok Lee, Chin-Sung Chung, Dept. of Mechanical Eng., Hong-Ik University of Seoul; Nam-Ik Cho, Dept. of Mech. Eng. Chon-Ju Tech. College; and Ho-Kyung Kim, Dept. of Automotive Eng., Seoul National Polytechnic University, 172 Kongnung-dong, Nowon-ku, Seoul, Korea
Effect of residual stress and its redistribution in weldment on the fatigue crack propagation was investigated. Fatigue tests were conducted using center notched specimens machines from welded plats. The residual stress and its redistribution were measured by a magnetizing stress indicator and hole drilling method. The residual stresses were found to be redistributed during crack propagation. Crack growth rates were predicted and compared with the experimental results. It has been found that the predicted crack growth rates have a better agreement with the experimental results when the redistributing residual stress, rather than residual stress, was considered. Also when the concept of partial crack closure was adopted in the analysis of crack growth rates, fatigue crack growth rates were a good agreement with, in spite of variation of stress ratio.
9:30 am
COMPRESSIVE STRENGTH AND FATIGUE PROPERTIES OF BE-A1 ALLOYS: R. Schneeberger, B. Bavarian, School of Engineering and Computer Science, California State University at Northridge, Northndge, CA 91330; R. Hayes, Metals Technology, Inc., 19080 Nordhoff St., Northridge, CA 91330
Both 40 and 62 wt.% beryllium compositions were evaluated for ambient and elevated temperature compressive strength at low and high strain rates. Data indicated a strong influence of beryllium percentage along with an increase of yield point for fast strain rates of 0.5-1 inch/minute. Fatigue properties of a ternary BeAl-Ag cast and extruded material were determined for full reversal and standard tension fatigue conditions. Typical S-N curve behavior including endurance limit was observed.
9:50 am
CREEP BEHAVIOR OF TWO BERYLLIUM-ALUMINUM ALLOYS: R. Schneeberger, B. Bavarian, School of Engineering and Computer Science, California State University, Northridge; 18111 Nordhoff St., Northridge, CA 91330; R. Hayes, Metals Technology, Inc., 19080 Nordhoff St., Northridge, CA 91330
Creep testing performed on 40 and 62 wt.% beryllium compositions of a powder metallurgy composite alloy at several elevated temperatures indicated a dependence of steady state creep rates and times to rupture on beryllium content, test direction, stress, and test temperature. A stress exponent of 8.5 for 40% beryllium and 10 for 62% beryllium was obtained from tests at 550 degrees F. A lower stress exponent of 6.7 was found for 62% beryllium at 630 degrees F. Activation energies for creep were somewhat higher than for self-diffusion in either pure metal, and exhibited significant anisotropy.
10:10 am BREAK
10:20 am
NEUTRON DIFFRACTION STUDY OF THE CO-DEFORMATION BEHAVIOR OF BERYLLIUM-ALUMINUM: David H. Carter, Los Alamos National Laboratory, MS G770, Los Alamos NM 87545
Neutron diffraction measurements of internal elastic strains during mechanical deformation are performed on Be-50%Al. The material is produced from hot isostatically pressed powder which is rapidly solidified using a gas atomization process. Under rapid solidification, Be-A1 undergoes liquid phase separation, and upon complete solidification two intimately interpenetrating phases exist. The resulting microstructure can be described as a three-dimensional interpenetrating composite, where each phase is continuous. Strain measurements are taken at the Los Alamos Neutron Scattering Center (LANSCE) using a pulsed neutron source, which provides time-of-flight diffraction data. The elastic strains in the individual phases are measured as a function of applied stress. This data is used to quantify the deformation behavior of each phase. The A1 phase is highly constrained by the Be phase due to the morphology of the composite as well as the high stiffness and low Poisson's ratio of Be. The results provide more insight into the overall deformation behavior of Be-Al.
10:40 am
DEFORMATION OF Al70Pd21Mn9 ICOSAHEDRAL QUASICRYSTAL WITH DECAGONAL PHASE LAMELLAE: Hisatoshi Hirai, Mater. Eng. Dept., Kyushu National Indust. Res. Inst., 807-1 Shuku, Tosu, Saga 841, Japan; Fuyuki Yoshida, Hideharu Nakashima, Dept. Mater. Sci. & Tech., Grad. Sch. Eng. Sci., Kyushu Univ., Kasuga, Fukuoka 816, Japan
In our previous work, we prepared Al70Pd21Mn9 icosahedral quasicrystal by zone melting technique. The obtained sample contained fine lamellae of decagonal phase Al69Pd13Mn18. The Vickers indentation test revealed that the existence of fine lamellae and annealing improved the fracture toughness of the sample to be about 2.1 Mpam1/2 which is about 1.5 times as large as those without lamellae. In this paper, we will report the results of high temperature creep test of the sample with fine lamellae. We will also discuss the effects of decagonal lamellae on the high temperature plastic deformation of icosahedral phase, if possible. Detailed results will be presented at the meeting.
11:00 am
THE PROCESSING AND PROPERTIES OF P/M FE-MN-AL ALLOYS: Chun Sien Lin, Materials Research Laboratory, ITRI, Hsinchu, Taiwan ; Shih-Chin Chang, Dept. Materials Science and Eng., Tsing Hua University Hsinchu, Taiwan
Powder metallurgy processing of Fe-Mn-Al alloys was studied. FeMn-Al alloy powder was produced by mechanical alloying of commercially available pure Fe, Mn, Al and C powder. The effect of ball milling, composition, pressure and sintering conditions on the microstructure and mechanical properties of resulted specimens were studied. For standard Fe-30Mn-lOAl-lC composition, 12 hour ball-milling is enough for producing the fcc structure of Fe-Mn-Al alloy after compaction and sintering at a temperature of 1240°C or higher. It is found that the hardness, strength and ductility of the sintered specimens increase with sintering density. The specimen compacted with 800 MPa and sintered at 13260°C for one hour in Ar have a sintered density of 6.18 g/cm3 (94.3% of theoretical density), hardness of HRC 32, and 0.2% offset yield strength of 1026 MPa. These mechanical properties are comparable to that of conventional casted material and are much better than that of the P/M carbon or stainless steels.
11:20 am
LOAD RELAXATION AND SUPERPLASTIC DEFORMATION BEHAVIOR OF A PB-SN ALLOY: Tae Kwon Ha, Young Won Chang, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784, Korea
The deformation characteristics of Pb-Sn eutectic alloy, a typical microduplex superplastic material, has been investigated. For this purpose, a series of load relaxation tests has been conducted to obtain the flow curves under the condition of a constant structure and the results have consequently been analyzed based on the recently proposed internal variable theory of structural superplasticity. The effects of grain size and volume fraction of constituent phases on superplastic deformation behavior of this eutectic alloy has also been examined. The boundary sliding in this two phase alloy was characterized as a viscous flow process with the power index value of Mg=0.5. This value is much less than the previously reported value of Mg=1.0 for GBS obtained in several single phase alloys. The optimum strain rate is found to shift into a faster region as the grain size decreases.
Room: Salon 8
Location: Clarion Plaza Hotel
Session Chairpersons: Barry T. Kilbourn, Molycorp, Inc., Executive 46 Office Center, 710 Route 46, East Fairfield, NY 07004; Charles O. Bounds, Rhone-Poulenc, Rare Earths and Galliu, CN 7500, Cranbury, NJ
8:30 am
MAGNETIC REFRIGERATION: Karl A. Gschneidner, Jr. and Vitalij K. Pecharsky, Ames Laboratory and Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011-3020
Magnetic refrigeration is based on the magnetocaloric effect (MCE), i.e. the temperature change (usually an increase) of a magnetic material near its mag netic ordering temperature due to the application of an external magnetic field. For many lanthanide materials the temperature increase is sufficiently large that one can utilize these materials as magnetic refrigerants. The best materials are those which order ferromagnetically and contain a heavy lanthanide metal Gd, Tb, Dy, Ho, or Er, and possibly Nd, since the available magnetic entropy, and therefore, the cooling power is proportional to the total quantum number, J. Generally antiferromagnetic, ferromagnetic and spin glass behaviors are not nearly as effective as ferromagnetic ordering. Studies to date have indicated that the MCE can be used as a method for the ligquefaction of cryogenic gasses, freezers for food processing plants, supermarket chillers and large scale building air conditioning.
9:00 am
RARE EARTH RAW MATERIALS AND APPLICATION MARKETS: A BALANCING ACT: J.M. Tourre, Rhône-Poulenc Rare Earth and Gallium 25 Quai Paul Dourmer, 92408 Courbevoie Cedex, France
1995 has seen a continuation of a positive trend in the Rare Earth industry. The availability of greater diversity of raw materials has brought additional flexibility to the producers permitting better economics. China remains the major raw material source; Chinese concentrate producers have increased capacity in 1995 (Baotou, Sichuan, etc..). China's role in the Rare Earth industry will continue to evolve; the acquisition of a majority equity position in Magnequench by San Huan will have significant impact on both the Rare Earth and Magnet markets. Chinese producers are increasing the quality of their products and realize their true values. The Chinese market, itself, is also changing as the internal needs for the separated rare earths grow.
9:30 am
THE COMMERCIAL SIGNIFICANCE OF MIXED-LANTHANIDE DERIVATIVES: Barry T. Kilbourn, Molycorp, Inc., Fairfield, N.J
It is not widely appreciated that, currently, the largest consumption byfar of lanthanides is in mixed-lanthanide forms. Such forms are based on either "natural-ratio" or "modified natural-ratio" materials, where the "natural-ratio"
is the inherent blend of the Ln elements in the dominant ore bodies. The reason for the choice of mixed-lanthanides is simplesuch forms are the most economical. The same economics will obviously apply to new technologies under development such as, for example, solid oxide fuel systems based on lanthanide-containing ceramics and nickel-lanthanide hydride battery systems. Their commercialization depends on the availability and the economic accessibility of suitable raw materials, and, in many cases, that will mean using mixed-lanthanide derivativesnot pure lanthanide compounds. The production process from ore to mixed-lanthanide derivatives will be traced.
10:00 am BREAK
10:30 am
Re-BASED METAL HYDRIDES AND NiMH RECHARGEABLE BATTERIES: L.Y. Zhang, Ph.D., Energizer Power Systems, Gainesville, FL 32614
The current status of metal hydride alloys for NiMH batteries was systematically reviewed. Extensive application-oriented R&D has successfully made the NiMH batteries an important part, with growing potential, among rechargeable batteries. The rare earth-based metal hydrides (AB5) have been considered the best alloy material for use in the negative electrode in NiMH batteries. However, being in demand for high performance by electronic markets, the still young NiMH industry is facing serious technical challenges in developing better products. Among other efforts to respond to the challenges, advanced AB5 alloys are in great demand: the capacity enhancement race requires new or improved alloys processing higher volumetric capacity; high corrosion resistance when subjected to electrochemical cycling. Finally, price competition mandates MH materials with ow cost.
11:00 am
HIGH PERFORMING Sm(Co,Fe,Cu,Zr)z POWDERS FOR THE BONDED MAGNET APPLICATION: W. Gong, B.M. Ma, and C.O. Bounds, Rhône-Poulenc, Rare Earths and Gallium, CN 7500 Cranbury, NJ 08512
The outstanding thermal stability and high energy product make Sm (Co,Fe,Cu,Zr)z type alloys attractive for advanced applications. The near net-shape production of Sm(Co,Fe,Cu,Zr)z bonded magnets make them potentially superior to any magnets made by sintering. Although pioneering work done by Shimoda et al. And other investigators provide insights on the nominal compositional selection and process control of this alloy system, additional work is still necessary to improve our understanding of alloy behavior at various processing stages and to increase the production yield during powder processing. In this paper we report on the development of anisotropic Sm(Co,Fe,Cu,Zr)z alloy powders for the bonded bonded magnet application.
Room: 314A
Session Chairpersons: Professor Viggo Tvergaard, Department of Solid Mechanics, Technical University of Denmark, DK-2800 Lyngby, Denmark; Professor Peter K. Liaw, Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996
8:30 am INVITED
DAMAGE ACCUMULATION AND DUCTILE FRACTURE--GLOBAL AND LOCAL PERSPECTIVES: F. Zok*, D. Lahaie**, and John D. Embury**; *Department of Materials Science, University of California, Santa Barbara, Santa Barbara, CA 93106; **Department of Materials Science and Engineering, McMaster University, 1280 main Street, Hamilton, Ontario, L8S 4L7, Canada
This presentation will consider the quantification of damage accumulation in metals and composites. Consideration will be given to the influence of hydrostatic pressure and strain path on nucleation and damage accumulation process. Models of fracture based on the influence of damage accumulation on both the stability of plastic flow and the attainment of critical damage levels will be discussed. In the final portion of the presentation, the use of damage accumulation in relation to the design of hydrostatic extrusion processes will be discussed.
8:55 am INVITED
PREDICTION OF DUCTILE BEHAVIOUR IN WELDED STRUCTURES (DUCTILE TO BRITTLE TRANSITION BEHAVIOUR, SHEAR LIP, NOTCH ACQUITY, AND SPECIMEN SIZE): James R. Matthews, Dockyard Laboratory, Department of National Defence, Defence Research Establishment, Atlantic, Dartmouth, Nova Scotia B2Y 3Z7, Canada
Design of ships against fracture requires, at the simplest level, that the minimum service temperature of the ship coincide with the upper shelf of the structural ductile to brittle transition curve for the steel and weldments. Material specifications in shipping standards often have no requirement for notch toughness and when they do specify toughness the specimen is of insufficient size and notch acquity to reflect the structural transition behaviour and to guarantee that the structure will be ductile at the lowest service temperatures. Consequently minimum standards should be adopted and specimen size and notch acquity requirements should be sufficient to predict ductile behaviour. In this paper, it will be shown that the transition behaviour for Charpy six specimens can be 50 to 100°C below that for larger DT specimens. It will he shown that replacing the standard notch with an EDM notch in Charpy speci mens moves the transition curve towards the DT curve but as little as 20 degrees for some materials. This leaves the DT specimen as the simplest existing specimen whose transition behaviour would approximate that of a structure. Data will be presented for 350WT and A517 steels. Refinement of the DT specimen to include an EDM notch as opposed to a machined and pressed notch may marginally reduce cost of testing. Relying on a shear lip width transition curve as opposed to an energy based transition curve can reduce the cost considerably. Data will be presented to show that shear lip width is related to the fracture energy of specimens over a wide range of temperatures, compositions and weldment locations. Finally data will also be presented to show that the relationship between shear lip and energy is independent of specimen thickness between l6 mm and 25 mm thickness.
9:20 am INVITED
A COMPUTER SIMULATION OF THE EFFECTS OF LOADING PATH ON THE MECHANICAL PROPERTIES OF POROUS COPPER: Anthony Kee, Peter Matic, Jennifer Morris and Andrew Geltmacher, Mechanics of Materials Branch, Code 6382, Naval Research Laboratory, 4555 Overlook Drive SW, Washington D.C. 20375
The present research examines the local stress and strain rates generated during loading in porous copper specimens produced by the GASAR gas-eutectic process, developed by Shapovalov and Timshenko. Two-dimensional explicit finite element simulations are performed on a representative microstructure taken from a 21.5 percent pore volume fraction bulk sample which contains high aspect ratio pores. The fraction bulk sample which contains high aspect ratio pores. The models investigate the role of multiple pore interactions and their effect on the mechanical properties of the porous materials. Previous research has shown the dependence of bulk strength and ductility on factors such as pore density, spacing, constraint and axial offset for uniaxial tensile loading. The present study extends the effort by applying biaxial and shear boundary conditions to the specimen, which simulates the effects of strain path on the deformation and fracture behavior of the porous materials. From these finite element models, the shape of the yield surface has been determined for the porous materials.
9:45 am
HIGH SPEED TEMPERATURE AND OPTICAL MEASUREMENTS OF DUCTILE FAILURE EVENTS IN METALS: Ares J. Rosakis, G. Ravichandran, Raman P. Singh, Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena, CA 91125
An experimental investigation has been conducted to study dynamic crack initiation in precracked highly ductile steel specimens. The specimens are fabricated out of 4340 mild steel and 304 stainless steel and subjected to dynamic three point bend loading by impacting them in a drop weight tower at various loading rates. This dynamic impact of the pre-cracked steel specimens results in deformation followed by fracture initiation at different loading rates. During the dynamic deformation and failure process the time history of the transient temperature and deformation fields around the crack tip are recorded experimentally. The transient temperatures are recorded using high speed infrared detectors, while the deformation fields are obtained using the optical method of Coherent Gradient Sensing (CGS) in conjunction with high speed photography. The experimental information is used to extract fracture parameters of interest, such as the time history of the dynamic J-integral (Jd(t)) and its critical value at initiation (JdInitiation) This is the first time that a noncontact temperature measurement is used to evaluate Jd(t). The applicability and accuracy of this technique is validated through comparison with the simultaneously performed CGS optical measurements. Finally, the data provided by the two techniques is used to identify various ductile failure mechanisms and quantify the fracture initiation toughness in terms of JdInitiation at different loading rates.
10:05 am
ANALYSIS OF FAILURE MODES IN IMPULSIVELY LOADED PRE-NOTCHED STEEL PLATES: Ramesh C. Batra, N.V. Nechitailo, Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0219
We analyze transient plane-strain thermomechanical deformations of a pre-notched 4340 steel plate impacted by a 4340 steel projectile in the direction of two parallel notches, and study the influence of the impact speed and notch tip radius on the localization of the deformation. The plate configuration is identical to that in Kalthoff's experiments (1987, 1988). There is no failure or fracture criterion included in our work. However, the computed evolution of stress and plastic strain fields strongly suggest that with an increase of impact speed and decrease in notch tip radius, there is a failure mode transition from a tensile crack opening at approximately 70° to the notch ligament to an adiabatic shear band propagating at (-5°) - (-15°) to the notch ligament. This is in qualitative agreement with Kalthoff's findings.
10:25 am BREAK
10:35 am
EFFECT OF STRAIN RATE ON THE FRACTURE TOUGHNESS REFERENCE TEMPERATURE To FOR FERRITIC STEELS: Kim Wallin, Materials and Structural Integrity Department, VTT Manufacturing Technology, P.O. Box 1704, FIN-02044 VTT, Finland
The new master curve concept for describing materials fracture toughness in the transition region, with the help of a reference temperature To, is a candidate for structural integrity assessment codificaton. Normally, To is determined for (quasi) static strain rates, while often dynamic values are required. The master curve concept can of course be applied also to dynamic tests, but this would require a double amount of testing. Therefore, if the effect of strain rate on To can be quantified with sufficient accuracy, the applicability of the master curve concept for structural integrity assessment codification would be strongly enhanced. For this purpose, fracture toughness data found in the literature was analyzed with the master curve concept, and, using the Zeller-Hollomon strain rate parameter, a simple semiemperical expression for the strain rate dependence of To was developed. The error of the expression is only of the order ±20% covering yield strength levels from 200 to 1400 MPa.
10:55 am
DYNAMIC PLASTICITY OF DUCTILE MATERIALS AT THE MESOSCOPICAL SCALE LEVEL: Yuri I. Mescheryakov, Institute of the Mechanical Engineering Problems, Russian Academy of Sciences, Saint-Petersburg, V. O. Bolshoi 61, 199178, Russia
Dynamic tests of ductile materials (copper, aluminum, ductile steels) were carried out under uniaxial strain conditions to determine the criterion of transition between translational (shear banding) and rotational modes of deformation. All the basic processes defining the mode of plastic deformation were found to occur at the mesoscopical scale level (0.1 - 10 µm) and depend on the particle velocity distribution at that level. The later has been recorded with a velocity interferometer modified for measuring both average mesoparticle velocity and particle velocity dispersion simultaneously. The kind of kinematical mechanism (translational or rotational) is determined by difference between longitudinal and transverse components of the mesoparticle velocity dispersion. This conclusion results from theoretical analysis of rotational motion of medium by using the mesomechanics approach.
11:15 am
FLOW AND FAILURE OF HIGH DENSITY MATERIALS IN BALLISTIC IMPACTS: Lee S. Magness1, Jr., Deepak Kapoor2 and Moon Chung2, 1U. S. Army Research Laboratory, Aberdeen, MD 21005; 2U. S. Army Armament Research, Development and Engineering, Picatinny Arsenal, Dover, NJ 07806
High-density alloys and composites are employed as the penetrator core materials in modern armor-piercing projectiles. During ballistic impact with an armored target, the length of the penetrator core is eroded or back-extruded as a cavity is opened in the armor. The core material is deformed to very large strains at strain-rates exceeding 104 per second. The hydrostatic component of the stresses on the penetrator can exceed 5 GPa (1 Msi), suppressing void nucleation and growth as a fracture mechanism. However, plastic localization and failures (shear bands) are promoted by the high rate, adiabatic deformation. The ballistic performances of a number of high-density alloys and composites are compared. Deformation and failure behaviors are categorized via optical metallographic examinations of penetrators recovered from ballistic impacts.
11:35 am
ANALYTICAL MODELING OF THE SHEAR MODE AND OPENING MODE OF DUCTILE FRACTURE: G. Rousselier and G. Barbier, Electricité de France, Research Division, Les Renardières, F-77250 Moret-sur-Loing, France
Strain localization in the vicinity of a surface is a precursor to ductile fracture of materials. It can be analyzed by considering the stability of a linear perturbation. For a broad class of materials: plastic, rate-dependent, with void-growth damage and loading conditions: three-dimensional, thermomechanical and dynamic, a closed-form solution is obtained for the stability condition. From this condition, a mode of ductile fracture can be predicted: shear or opening. In a plastically incompressible material, the shear mode of fracture only is obtained; it results from a competition between strain hardening and thermal softening. In a void-growth damaging material, the opening mode is promoted by stress triaxiality. The analytical results are in agreement with experimental observations and numerical results from the literature.
11:55 pm
LOADING RATE INFLUENCE OF FRACTURE TOUGHNESS IN INSTRUMENTED PRECRACKED CHARPY-TYPE TESTING: Thomas Varga and Friedrich Loibnegger, Technische Versuchs- und Forschungsanstalt, Technische Universität Wien, A-1040 Wien, Karlspaltz 13, Austria
12:15 pm
EFFECTS OF INCLUSIONS ON DUCTILE FRACTURE OF AN Fe-42PCT Ni ALLOY IN TENSION AND SHEAR: N. Yuki*, R. Foley** and G. Krauss***, *Nippon Mining and Metals Company Ltd, 3 Kurami, Samukawa, Koza, Kanagawa 253-01, Japan; **Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, IL 60616; ***Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO 80401
Effects of inclusions on ductile fracture have been examined with laboratory produced Fe-42 pct Ni alloy. The inclusion volume fraction was varied between approximately 0.01 and 3.00 pct. Axisymmetric tensile bars and cylindrical, double shear test samples were tested in the recrystallized condition. In the tensile test, increasing inclusion volume fraction significantly reduced post-uniform elongation and strain to fracture . In the shear test, fracture displacement obtained from load-displacement data and strain to fracture calculated from shear test samples decreased with increasing inclusion volume fraction. The fracture behavior in tension and in shear is related to inclusion distribution. Applicability of different models is considered.
12:35 pm
DUCTILE FRACTURE TOUGHNESS EVALUATION AT HIGH STRAIN RATES USING STRETCH ZONE: M. Nari Bassim* James R. Matthews**; *Department of Mechanical and Industrial Engineering University of Manitoba, Winnipeg, Manitoba, Canada R3T SV6; **Department of National Defence, Defence Research Establishment Atlantic, Dartmouth, Nova Scotia, Canada B2Y 3Z7.
Fracture studies of high strength low alloy steels, at very high loading (strain rates) of up to equal to 107 were conducted using specially designed Split Hopkinson Bar equipped with a swing arm mechanism capable of fracturing CT specimens with a thickness of 12.7 mm. While it was possible to reproduce the load-displacement curves for the specimens, evaluation of the fracture toughness was mostly obtained from post-test examination of the stretch zone ahead of the crack using scanning electron microscopy. Several factors affecting the stretch zone were identified including the effect of fatigue precracking as well as the method of measurement of the stretch zone (nine point vs. three point approach). Significant differences in the stretch zone were observed which are attributed to the extent of the constraint factor ahead of the crack due to fatigue precracking which demonstrates the occurrence of some nonlinearity in the initial part of the J-Stretch Zone Width relationship.
12:55 pm
NEUTRON IRRADIATION EFFECTS ON THE DUCTILE-BRITTLE TRANSITION OF FERRITIC/MARTENSITIC STEELS: Ronald L. Klueh and D.J. Alexander, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
Below ~450°C, neutron irradiation hardens the Cr-Mo ferritic/martensitic steels considered for future fusion power plants. Hardening reduces ductility, but the major effect is an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy (USE), as measured by a charpy impact test. After irradiation, DBTT values can increase to well above room temperature, thus increasing the chances of brittle rather than ductile fracture. Such a shift in DBTT could eliminate certain steels for nuclear applications. Steels are being developed for fusion applications that have a low DBTT prior to irradiation and then show only a small shift after irradiation. Low-chromium (3% Cr) and high-chromium (9% Cr) Cr-W steels are being investigated. A martensitic 9Cr-2WVTa (nominally Fe-9Cr-2W-0.25V-0.07Ta-0.1C) steel had a much lower DBTT than the conventional 9Cr-1MoVNb (Fe-9Cr-1Mo-0.25V-0.06Nb-0.1C) and 12Cr-1MoVW (Fe-12Cr-1Mo-0.25V-0.5W-0.5Ni-0.2C) steels prior to neutron irradiation and showed a much smaller increase after irradiation. The tantalum in 9Cr-2WVTa was concluded to affect the fracture stress. For the 3Cr steels, the type of bainitic microstructure formed during heat treatment affected the impact behavior. Granular bainite had inferior properties compared to an acicular bainite. Alloying was used to promote the acicular bainite. Improved toughness makes the steels candidates for both nuclear and non-nuclear applications.
Room: 330B
Session Chairperson: Prof. Enrique J. Lavernia, Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92717; Dr. Prabir K. Chaudhury, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA, 15904
8:30 am KEYNOTE
THERMO-FLUID ISSUES IN SPRAY FORMING: Michael M. Chen, University of Michigan, Ann Arbor, MI, 48109-2125; Dawn White Ford Scientific Laboratories, Dearborn, MI, Chuan Li, University of Michigan, Ann Arbor, MI, 48109-2125
A critical review on the heat transfer and fluid mechanical issues of spray forming will be presented. The paper will focus on those thermo-fluid issues which have important influence on the spray and solidification processes as well as the properties of the product, combining the perspectives of materials and manufacturing scientists and specialists in heat transfer and fluid mechanics. Among the topics to be considered are atomization, dynamics of sprays, including oversprays, droplet solidification, splat formation due to impact of liquid droplets and partially solidified particles with the substrate, heat transfer and solidification in the formed part, and residual stress formation. Emphases will be placed on current levels of understanding of the physics from a first principles point of view, semi-quantitative estimates of the length and time scales of interest, and current capabilities for accurate modeling and prediction. Recommendations for future research and development will also be made, based on results of the survey.
9:00 am INVITED
NUMERICAL INVESTIGATION OF MULTI-PHASE FLOW INDUCED POROSITY FORMATION IN SPRAY DEPOSITED MATERIALS: J.-P. Delplanque, E.J. Lavernia, R.H. Rangel, Department of Chemical Engineering and Materials Science, University of California, Irvine, Irvine, CA 92697-2575
Several mechanisms have been recently identified as responsible for porosity formation in spray deposited materials. These mechanisms may be categorized according to their underlying fundamental nature; chemical (e.g., porosity generated by a foaming agent), physical (e.g, solidification shrinkage porosity), or dynamical (e.g., liquid-jet overflow). This investigation focuses on the latter category: pore formation mechanisms related to liquid metal flow and interactions between the flowing liquid metal and the irregular solid formed by the previously deposited droplets. These mechanisms are investigated using a combination of analytical models and detailed numerical simulations. The numerical model is based on a Navier-Stokes solver combined with the Volume Of Fluid method to track free surfaces. A multi directional algorithm is used to simulate the solidification process. The model case considered is that of liquid metal flooding of a random dense particle packing made of solidified droplets. Particular attention is devoted to cases where there is insufficient liquid to fill all the interstices and to capillary effects.
9:20 am
CALCULATION OF POWDER SIZE IN CENTRIFUGAL ATOMISATION AND SPRAY FORMING: Huiping Li, P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, England, UK
A model of the flow of melts on rotating disks has been combined with models based on wave theory to predict the size of powder particles in centrifugal atomisation/spray forming. The analysis considers the role of process parameters and materials properties on powder size. The dependence of powder particle size on disk diameter and rotating speed as well as type of melt are calculated and compared to experimental results.
9:40 am
NUMERICAL SIMULATION OF GAS ATOMIZATION IN SPRAY FORMING PROCESS: Huimin Liu, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA 15904
The spray forming process is emerging as a cost-effective manufacturing route for net and near-net shape preforms in a wide range of materials. In the past, numerical simulations have been made to model the melt delivery, the spray deposition, and the consolidation stages in the spray forming process. However, the atomization stage, particularly gas flow in the nozzle-close region and melt break-up kinetics, have not been adequately simulated. Atomization is a key stage in the spray forming process because it determines the size, size distribution, and initial conditions of the particles, hence, influences particle velocity, temperature, cooling rate, microstructure, and thus the mechanical properties of the spray-formed preforms. This work uses numerical tools to model atomization mechanisms. The full compressible Navier-Stokes equations are solved to simulate the gas flow in the nozzle-close region. The melt flow and heat transfer are modeled on the basis of the boundary layer theory and the modified van Driest and Cebeci mixing-length turbulence model. The information on the flow and temperature fields obtained from the numerical simulation is then used to investigate melt break-up and droplet formation during atomization.
10:00 am BREAK
10:20 am
MODELING OF OSPREY SPRAY METAL FORMING PROCESS: T.R. Govindan, The Pennsylvania State University, Applied Research Laboratory, P.O. Box 30, North Atherton Street, State College, PA 16804-0030
A detailed computational model of the spray metal forming process is being developed. The model provides process figures of merit, identify process control parameters, and help process design in support of the process development activity. The core of the model is an Eulerian-Lagrangian flow solver in which the gas phase is treated in an Eulerian framework involving the Reynolds Averaged Navier-Stokes equations and the droplets are treated as a discrete phase involving single particle dynamics. Statistics are generated from the discrete phase by computing a large sample of particle "trajectories" in the force field due to the gas phase. In turn, particle statistics generate forces in the gas phase equations. Models are used in the discrete phase for particle drag, heat transfer, and solidification. The computer code is capable of handling complex three-dimensional geometries. Results will be presented showing details of the two-phase flow in a typical Osprey spray chamber; gas flow velocity and temperature distributions, gas flow and droplet interactions, droplet cooling curves and deposition profiles. Computed results will be compared with available experimental data.
10:40 am
INVESTIGATION OF THE PROCESS PARAMETERS CONTROLLING THE MICROSTRUCTURAL CHARACTERISTICS AND THE POROSITY OF SPRAY DEPOSITED TANTALUM ALLOYS: J.-P. Delplanque, W.D. Cai, R.H. Rangel, E.J. Lavernia, Department of Chemical Engineering and Materials Science, University of California, Irvine, California 92697-2575
An induction skull melting (ISM) spray forming process was used to investigate the spray atomization and deposition of tantalum alloys. Several systems were considered in order to tackle the scientific issues inherent to the spray forming of refractory metals in a gradual manner. Optical microscopy, X-ray diffraction and scanning electron microscopy were used to characterize the spray formed materials and oversprayed powders. A theoretical and numerical analysis of the deposition and solidification of tantalum alloy droplets was conducted concurrently. This approach is based on a multi-directional solidification model combined with a Navier Stokes solver for flows with interfaces. Various droplet size and impact velocities consistent with the experiments were considered. The simulation results and the experimental data were compared and analyzed in order to identify the critical process parameters controlling the microstructure and porosity of as-deposited tantalum alloys.
11:00 am
DROPLET ENTHALPY MEASUREMENT BY CALORIMETRY FOR CONTROLLED SPRAY FORMING: C. Tuffile, A. DiVenuti, Department of Mechanical Engineering, Tufts University, Medford, MA 01255; T. Ando, Department of Mechanical, Industrial and Manufacturing Engineering, Northeastern University, Boston, MA 02115; J.H. Chun, Laboratory for Manufacturing and Productivity, Massachusetts Institute of Technology, Cambridge, MA 02139
A non-adiabatic calorimetric method was developed and used to determine the enthalpy of droplets in a spray as a function of flight distance with the purpose of providing critical information for the controlled spray forming using uniform-droplet sprays (UDS). A UDS consists of droplets that are uniform in size and thermal history and can be used to produce a variety of novel deposit microstructures in a controlled manner. Such controlled spray forming, however, requires thorough characterization of the thermal state of the uniform droplets. The calorimetric method developed accounts for the heat loss that occurs while collecting the droplets in the calorimeter, and uses a data acquisition system for in-situ determination of droplet enthalpy. Comparison of measured droplet enthalpy values and those predicted by model calculations shows a very good agreement.
11:20 am
SIMULATION OF THE SPRAY FORMING PROCESS USING A WIRE-FED LASER TECHNIQUE: T. Seefeld, E. Schubert, G. Sepold, Universitat Bremen, Verfahrenstechnik/FB4, Postfach 330440, D-28334 Bremen, Germany
The spray forming process offers advantages for both material properties and process technology. A deeper understanding of the spray forming process, with particular concern to the complex disintegration phase and the formation of the deposit. The present work introduces an experimental set-up to investigate the in-flight behavior of sprayed droplets. In a chamber with controlled atmosphere, a spray cone is wire. This process allows to skip the complete melting unit of a spraying facility and facilitates maintaining a spraying experiment for a desired period of time (a couple of minutes generally) and changing the set of parameters for the next experiment within minutes in order to save time diameter and feed rate, laser beam power and intensity, and atomizing gas flow. During spraying of mild steel with nitrogen, the nitrogen content of droplets sampled at various locations within the spray cone is investigated. The results of the in-flight interaction of the sprayed dropletes with the ambient atmosphere are discussed.
11:40 am
THE ROLE OF ALUMINA PARTICULATE IN MICROSTRUCTURAL AND FORGING PROPERTIES OF SPRAY ATOMIZED AND DEPOSITED Fe-Al ORDERED INTERMETALLIC COMPOUNDS: L. Martinoz, M. Amaya, O. Flores, Instituto de Fisica, UNAM, A.P. 48-3, 62251, Cuernavaca, Morelos, Mexico; D. Lawrynowics, R.J. Lavernia, Department of Chemical Engineering & Materials Science, University of California, Irvine, CA 92697-2575
Spray atomization and deposition, hot isostatic pressing, and forging at high temperatures were used for processing FeAl intermetallic compounds alloyed with Boron and fine alumina particulates. Extensive optical microscopy, SEM, and TEM studies, as well as mechanical properties characterization are described. The alumina particulate play a role in refining and stabilizing the material microstructure and improves forgeability. The advantages of spray atomization and deposition are discussed. Work supported by CONACYT grant 3878A.
12:00 pm
MODELLING DROPLET BEHAVIOUR DURING SPRAY FORMING USING FLUENT: P.S. Grant, R.P. Underhill, B. Cantor, Oxford Centre for Advanced Materials & Composites, Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH; D.J. Bryant, Rolls-Royce plc, Elton Road, P.O. Box 31, Derby DE24 8BJ, UK
A finite difference based fluid dynamics software program, FLUENT, has been used to model the 2-dimensional dynamic and thermal behaviour of Udimet 720 droplets during gas atomisation and spray forming. The effect of atomising gas pressure pressure, spray distance and melt mass flow rate (MFR) on the equilibrated droplet spray temperature has been examined and the predictions compared with measured maximum deposit temperatures from spray forming experiments performed under the same process conditions. The predicted spray temperatures at the substrate were always higher than the measured deposit temperatures under all conditions, and were found to increase with (I) decreasing gas pressure, (ii) decreasing spray distance, and (iii) increasing MFR. Mean droplet temperatures and velocities were found to be strongly dependent on droplet size with mean droplet temperature decreasing, and mean droplet axial velocities increasing, with decreasing droplet size.
Room: 330G
Session Chairperson: Diana Farkas, Dept. of Materials Science and Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0237
8:30 am INVITED
MAKING LINKS BETWEEN GRAIN BOUNDARY CHARACTER DISTRIBUTIONS AND POLYCRYSTALLINE PROPERTIES: Alexander H. King, Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794-2275
Automated orientation analysis makes it possible to perform an "epidemiological" kind of materials research in which the occurrence of certain types of grain boundary is associated with certain types of polycrystalline property. What is left out of many studies of this kind, however, is the causal link that relates a certain grain boundary character distribution to a particular polycrystalline behavior. In this presentation, I will caution that focusing upon the grain boundary character in terms of "small-angle," "coincidence-related" and "general" categories can be misleading. I will provide a number of examples to show that these are not always the important (or desirable) features of the grain boundary character distribution, drawing my illustrations from work on high-Tc superconductors and metallic polycrystalline thin films. Finally, if time permits, I will comment upon the characterization of triple-junctions and show, once again, that currently popular types of characterization are seriously misleading. Acknowledgment: This work is supported by the National Science Foundation, under grant number DMR-9530314.
9:10 am
THE STRUCTURE OF DEFORMATION INDUCED HIGH ANGLE BOUNDARIES: D.A. Hughes, Materials and Engineering Sciences Center, Sandia National Labs., Livermore, CA 94550
Internal interfaces develop during deformation at the places where grains subdivide. Some of these interfaces develop into high angle boundaries that subsequently have a large effect on the materials properties including local crystallographic textures, flow strength and annealing behavior. The structure of very high angle boundaries (>30=B0) formed during deformation by dislocations and texture processes was examined using transmission electron microscopy and convergent beam diffraction. The large misorientation angles that develop by these processes are similar to those angles encountered in ordinary grain boundaries. These boundaries are characterized according to their angle/axis pair, boundary plane, tilt/twist character, thickness, sigma value and their association with trapped glide dislocations. In general these boundaries have a complex character and are not low sigma boundaries. The structure of these deformation induced boundaries is then compared to that of equilibrium grain boundaries such as those that form during recrystallization. This work supported by U.S. DOE under contract No. DE-AC04-94AL8500.
9:30 am
ANALYSIS OF TWINS AND STACKING DEFECTS IN THE CUBIC LAVES PHASE OF THE Hf-V-Nb ALLOY SYSTEM: D.E. Luzzi, D.P. Pope, A. Goldberg, G. Rao*, Dept. of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104-6272; *Present Address: Applied Materials Corporation, Santa Clara, CA
The brittle nature at low temperatures of Laves phase intermetallic compounds remains a major obstacle to the use of these complex-structured materials for their excellent high temperature properties. Deformation by twinning is seen as a possible mechanism by which to obtain acceptable levels of ductility and toughness at low temperatures. In this paper, the microstructures of a cubic HfV2+Nb Laves phase is studied before and after compressive deformation using conventional and high-resolution electron microscopy. The Laves phase occurs as precipitates within a matrix of a V-Nb bcc solid solution. In the underformed material, narrow stacking defects with thicknesses of from one to three times the (111) interplanar spacing are seen lying on the (111) crystallographic planes. The distribution of these defects is anisotropic on the mesoscopic scale with spacings ranging from approximately 2 nm to over 200 nm. The deformed material shows extensive twinning of the Laves phase precipitates. The twins occur in clusters and twin bands as small as 2 nm in width are seen. Analysis of the structure of the stacking defects and twins and comparisons between the mesoscopic distributions of stacking defects in the undeformed materials and twins in the deformed materials will be presented.
9:50 am
DISSOCIATION MECHANISMS FOR EXTRINSIC GRAIN BOUNDARY DISLOCATIONS: S.G. Song, J.S. Vetrano, S.M. Bruemmer, Pacific Northwest National Laboratory, Richland, WA 99352
The plastic deformation of grain boundaries (GBs) is central to the understanding of a wide range of materials behavior including superplasticity and creep. In analogy to the bulk deformation carried out microscopically by lattice dislocations, GB deformation cannot occur without the involvement of grain boundary dislocations (GBDs). The present investigation examines the stability of extrinsic GBDs in Al alloys. It is found that the dissociation of extrinsic GBDs not only is a function of temperature but also of other variables such as solute content and GB structures. Given a boundary structure, the Burgers vectors of the secondary GBDs, resulting from the dissociation of extrinsic GBDs in general GBs, can be predicted based on the DSC-lattice. The visibility of the secondary dislocations varies with the magnitude of their Burgers vectors. The GBD stability of different boundary misorientations is compared so that common properties of grain boundary plastic behavior can be drawn. Work supported by the Materials Division, Office of Basic Energy Sciences, U.S. Department of Energy under Contract DE-AC06-76-RLO 1830.
10:10 am
EFFECT OF THE MAGNITUDE OF GRAIN BOUNDARY DISLOCATION BURGERS VECTORS O DISSOCIATION OF EXTRINSIC GRAIN BOUNDARY DISLOCATIONS: S.G. Song, J.S. Vetrano, S.M. Brummer, Structural Materials Interfaces, Pacific Northwest National Laboratory, Richland, WA 99352
The concept of Burgers vectors of secondary grain boundary dislocations (SGBDs), resulting from the dissociation of extrinsic grain boundary dislocations (EGBDs), in general grain boundaries can be extrapolated from those of GBDs in CSL boundaries. Increasing CSL boundary index results in the decrease in magnitude of the basis vectors of the corresponding DSC lattice on which the Burgers vectors of the SGBDs are determined. There exists a critical size of the elementary Burgers vectors of the dissociated grain boundary dislocations. Below this value, an EGBD disappears eventually after the SGBDs resulting from the dissociation spread to a sufficient distance that is dependent on temperature and instrument parameters. On the other hand, the resulting SGBDs are always visible if their Burgers vectors are above the critical size.
10:30 am BREAK
10:50 am INVITED
CONTROL OF METAL PRECIPITATE MORPHOLOGY BY SOLID STATE REACTIONS: Monika Backhaus-Ricoult, CECM-CNRS, 15 Rue G. Urbain, F 94 407 Vitry sur Seine
Internal reduction of transition metal doped mixed oxides yields formation of fine dispersion of metal particles within the oxide matrix. Selection of special reaction parameters like oxygen partial pressure gradient, reaction temperature, chemical composition of the mixed oxide and the type of matrix oxide and dopant allows to control the microstructure of the reduced scale, the morphology of the metal precipitates and the fine-structure of the metal-ceramic interfaces down to an atomic scale. Experimental results for different mixed oxides containing magnesia, alumina or zirconia will be reported. Growth and thermodynamical equilibrium shapes of the precipitates will be presented. Precipitate morphology, relative orientation relationship and interface fine structure will be interpreted in terms of the diffusion field (which allows the metal precipitation), the chemical reaction at the precipitate interface, the interface energy and its anisotropy and the mechanical response of the system to solid state reaction related stresses.
11:30 am
INTERFACIAL DEBONDING IN MULTI-LAYER THIN FILM SYSTEMS: X.H. Liu, C.F. Shih, Division of Engineering, Brown University, Providence, RI 02912
To improve the reliability of electronic devices, it is important to understand the interfacial debonding of multi-layer thin film systems. The interfacial fracture energy can be measured experimentally using a sandwich four-point bending specimen. This interfacial fracture energy includes both the intrinsic debonding energy of the metal/ceramic interface and the plastic dissipation in the metal layers. The plastic dissipation makes a substantial contribution to the interfacial fracture energy. In contrast to the plastic dissipation, which depends on the layer thickness, the intrinsic debonding energy is a material property of the interface and is important in the evaluation of interface adhesion and design of multi-layers. A micromechanical model is used to investigate interfacial debonding. From the model the intrinsic debonding energy can be obtained using the measured interfacial fracture energy. The effects of interfacial adhesion and metal layer properties on the interfacial fracture energy are discussed.
Room: 330F
Session Chairpersons: T.H. Sanders, Georgia Institute of Technology, Atlanta, GA 30332-0245; G. Das, Pratt and Whitney, P O Box 109600, West Palm Beach, FL-33410-9600
8:30 am
STABILITY OF NANOCRYSTALLINE MICROSTRUCTURES IN A Ti-47.5A1-3Cr ALLOY PRODUCED BY MECHANICAL ALLOYING AND HOT ISOSTATIC PRESSING: N. Srisukhumbowornchai, M.L. Ovecoglu*, O.N. Senkov, and F.H. Froes, Institute for Materials and Advanced Processes, University of Idaho, Moscow, ID 83844-3026, USA; *Department of Metallurgical Engineering, Faculty of Chemistry & Metallurgy, Istanbul Technical University, Maslak, Istanbul 80626, Turkey
Fully dense nanocrystalline Ti-47.5A1-3Cr intermetallic compacts were produced by mechanical alloying and hot isostatic pressing. Grain growth behaviour of these compacts was studied in the temperature range of 725 to 1100°C for annealing times of 0 to 500 hours, using analytical transmission electron microscopy techniques. The temperature and time dependencies of the grain sizes and the grain size distributions were determined, allowing the evaluation of the prevailing transport mechanism responsible for the growth of nano-sized grains to be defined.
8:50 am
PHASE FORMATION AND PROPERTIES OF MECHANICALLY ALLOYED Mg-BASED MULTICOMPONENT LIGHTWEIGHT ALLOYS: J. Eckert, N. Schlorke, C.A.R.T. Miranda1, and L. Schultz; Institute fur Festk"rper-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.
9:10 am
HIGH TEMPERATURE DEFORMATION BEHAVIOUR OF MECHANICALLY ALLOYED Al-10Ti-XSI ALLOY: C.J. Choi, W.W. Park, Department of Materials Processing, Korea Institute of Machinery and Materials, 66 Sangnam-Dong, Changwon, Kyungnam 641-010, S.Korea ; J.K. Park, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusong-Dong, Yusong-Gu, Taejon 305-701, S. Korea
The creep property of mechanically alloyed A1-10Ti-xSi (in wt%, x=0,2 4) alloy was investigated in a wide range of stress (60-310MPa) and temperature (300-450°C). Creep mechanisms were analyzed in some details and compared with each other. Two distinctive creep mechanisms have been observed depending on the testing stress and temperature, ie, Coble creep at low stresses and temperatures and dislocation creep at high stresses and temperatures. True creep activation energies in dislocation creep regime were calculated using modified semi-emperical creep equation. The calculated values were in good agreement with that for self lattice diffusion in pure aluminium. The diffusional (Coble) creep regime significantly enlarged to high stress and temperature region with an increase of Si content due to an increasing volume fraction of dispersiods.
9:30 am
MECHANICAL ALLOYING OF Ti-Ni BASED MATERIALS USING THE HORIZONTAL ATTRITOR: H. Zoz1, D. Ernst2, I.S. Ahn3, W.H. Kwon;1Zoz GmbH, D-57482 Wenden, Germany; 2University of Siegen, D-57068 Siegen, Germany; 3Gyeonsang National University, Chinju, Gyeongnam, 660-701 Korea
The production of large quantities of contamination free mechanically alloyed powders from titanium and nickle based materials has proven to be a major challenge. Feasibility of such a goal can be carried out, at laboratory level, by any milling device like the very common planetary ball mill. In this case however, the possibility of a subsequent scaling up for larger production is hindered by the intrinsic limits of a planetary ball mill design. On the contrary the horizontal Zoz attritor can be experimented at laboratory level using small volume chamber-units (0.25, 0.5, and 2.1) and, for industrial production, using the large volume units (up to 400 1) based on the same conceptual design. Therefore, experiments have been conducted on blended elemental Ti-Ni compositions in the proportions Ti-51.5Ni, Ti-50Ni, Ti-49.5Ni and Ti-48.5Ni (at %) using a Zoz attritor with a small unit-chamber (0.51). Due to the inherent ductility of the powder, the material has the tendency to adhere to the grinding unit and the grinding media. Further, in order to avoid high contamination and to make the process realistic from an economical point of view, the milling time has to be reduced to a minimum. The above points identify a Critical Milling Behaviour (CMB) of the system under investigation that must be kept under control to achieve the wanted goal. It will be shown by the present paper that by adopting a suitable milling and discharging procedure (Cycle Operation by Operation Cycle and Discharging Cycle) low contamination and good yield have been substantially achieved. This is investigated by chemical analysis, by scanning electron microscopy and X-ray diffraction.
9:50 am
MICROSTRUCTURAL EVOLUTION OF MECHANICALLY ALLOYED AND HOT ISOSTATICALLY PRESSED NANOCRYSTALLINE Ti-47.5A1-3Cr ALLOY DURING ANNEALING AT 120°C AND AIR COOLING: M.L.Övecoglu, O.N.Senkov, N.Srisukhumbowornchai, N. Hoo, C.M. Ward-Close, P. Goodwin, P.Tsakiropoulos, F.H. Froes, Institute for Materials and Advanced Processes University of Idaho, Moscow, ID 83844-3026; Department of Metallurgical Engineering, Istanbul Technical University, Maslak, Istanbul 80626, Turkey; DRA Farnborough, Hampshire, UK; University of Surrey, Guildford, Surrey, UK
Mechanical alloying and hot isostatic pressing techniques were employed to synthesise a fully dense Ti-47.5AJ-3Cr alloy containing equipped nanocrystalline TiA1 grains. Isothermal annealing was conducted at 1200°C (above the eutectoid transformation temperature) at holding times of 5, 10, 25 and 35 hours. Analytical transmission electron microscopy investigations revealed the presence of a dual structure comprising 2/ laths and equipped g grains some of which were twinned. The grains coarsened during annealing and the 2/ laths were formed during cooling as a result of the eutecroid transformation. At the maximum annealing time studied (35 hours), the average grain size of grains was about 2 mm and the width of the 2/ laths was -0.3mm.
10:10 am BREAK
10:30 am
CHARACTERISATION OF A Ti-48AJ-2Nb-2Cr ALLOY SYNTHESIZED FROM MIXED GAS ATOMIZED AND MECHANICALLY ALLOYED POWDERS: O.N. Senkov, N. Srisukhumbowarnchai, M.L Ovecoglu*, N. Hoo, C.C. Ward-Close**, P. Goodwin**, P. Tsakiropoulos*, F.H. Froes, Institute for Materials and Advanced Processes, University of Idaho, Moscow, ID 83844-3026; *Department of Metallurgical Engineering, Istanbul Technical University, Maslak, Istanbul 80626, Turkey; **DRA Farnborough, Hampshire, UK; University of Surrey, Guildford, Surrey, UK
Gamma TiA1 based compacts were synthesized by hot isostatic pressing (HIP'ing) a mixture of pre-alloyed Ti-48A1-2Nb-2Cr gas atomized and mechanically alloyed powders. Mechanical alloying of the initial powder was performed in a SPEX mill for 15 hours. HIP'ing was conducted at 850°C under 206 MPa pressure. Two different volume proportions of the gas atomized and mechanically alloyed powders were utilized in the HIP'ing process. This allowed production of microstructures in HIP'd compacts: a homogeneous nanocrystalline structures, when 100% mechanically alloyed powder was used, and a bimodal structure consisted of the mixture of micron-sized and nono-sized grains, when the compacts were HIP'd from a blend of the gas atomized and mechanically alloyed powders. Evolution of the microstructure during mechanical alloying and HIP'ing was studied by XRD, SEM and TEM techniques.
10:50 am
FLOW AND COOLING CHARACTERISTICS OF AL-SI DROPLETS/PARTICLES DURING GAS ATOMIZATION: Seong-Yeon Yoo, Sang-Yoon Lee; Rapidly Solidified Materials Research Center, Department of Mechanical Design Engineering, Chungnam National University, Taejon, 305-764, KOREA
There are two important parameters in gas atomization - particle size and cooling rate. These two parameters are mainly controlled by gas flow and heat transfer between gas and droplets/particles. The purpose of this research is to investigate flow structure, cooling rate and trajectory of Al-Si droplets/particles by numerical simulation. Gas flow is simulated using finite volume method, and particle trajectory is simulated using Eulerian method. Rosin-Rammler formula is used for the particle size distribution. Gas field influences particle trajectory, reversely particles alter the gas field. So momentum and heat exchange between gas and particles are calculated by iterative method. Particle trajectory is found to depend on particle size, the location of particle formation, and turbulent motion of gas. Cooling rate of particles is calculated by taking into account latent heat of melt and local heat transfer between particle and gas. Small particle cools down rapidly, while large diameter particles solidifies very slowly.
11:10 am
PREPARATION OF Ti POWDER BY A MECHANICAL MILLING INDUCED REDUCTION REACTION: E.G. Baburaj, Kevin T. Hubert, Carl Powell, C. Suryanarayana, and F.H. Froes, IMAP, University of Idaho, Moscow, ID 83844-3026
A displacement reaction between TiC14and Mg, induced by mechanical milling, has been employed for preparation of fine Ti powder. The present work shows the possibility of considerable reduction in milling time by the use of pre-milled Mg which enhances the reactivity due to an increase in surface area and surface activity. The milled product has been leached repeatedly to obtaining pure Ti. The reaction products before and after leaching have been examined by XRD, SEM, and TEM. The product after leaching, as determined by XRD is pure Ti. The particle size, as observed by TEM is in the range of 5-200nm. The EDX analysis of individual crystals or agglomerates using TEM, does not show the presence of chloride. Small amount of oxygen and nitrogen as impurities have been detected. Further work on the analysis of the powder is in progress.
11:30 am
MICROSTRUCTURE-PROPERTY STUDIES IN AL-8Fe-4Ni-2 5Zr ALLOYS: P. Keramidas, P. Tsakiropoulos; Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, England, UK
The microstructures of shill cast ingots, gas atomised powders and extruded bars of Al-8Fe-4Ni-2.5Zr (wt%) were studied. Phase selection in the wedge shaped ingots and in the gas atomised powder particles will be discussed. The microstructures of the as extruded and heat treated alloy will be presented and related to the hardness, tensile properties and texture of the alloy. The latter will be compared to the properties of Al-8Fe-4Ni and the effects of Zr addition on the properties of the alloy will be discussed.
11:50 am
STRUCTURE AND PROPERTIES OF RAPIDLY SOLIDIFIED Al-Li-Cu-Mg ALLOYS CONTAINING Zr AND Ag: V.G. Pushin, L.I. Kaigorodova, E.I. Selnikhina, Institute of Metal Physics, Ural Division of Russian Academy of Sciences, +1620219, +0+1 Ekaterinburg, Russia
Rapidly solidified Al-Li-Cu-Mg alloys prepared by argon atomization process were investigated. Using cold compaction and canning, the powder was hot extruded into a bar of diameter 17 mm. Compared with traditional ingot metallurgy alloys, the microstructure and properties of rapidly solidified powder metallurgy alloys has been significantly improved. The effects of adding minor Zr, Ag or rare earth (RE) Nd and La on the Al-Li-Cu-Mg alloys are different. Minor Zr and Ag can efficiently accelerate the ageing process and increase the strength and hardness of alloys. Minor RE raises the ductility. The microstructure of alloys forms due to precipitation process of metastable binary phase Al(3)Li, ternary Tl-phase Al(2)CuLi with hexagonal crystal structure, and also tetragonal metastable phases on base of Al(2)Cu. These three coexistent channels of phase transformations are responsible for strengthening of alloys during subsequent ageing. The particle size of atomized powder for alloys was in the range of 10-150nm, but after optimal thermo-mechanical treatments the microstructure of alloys has been significantly dispersed and more refined. The grains are more homogeneous and have a nano-scale size on the average. In this state particles of this phase has a globula form and preferably heterogenuons nucleation at consequent aging.
12:100 am
MODELLING AND CONSOLIDATION OF NANOCRYSTALLINE ALUMINIUM: J.S. Idasetima, R.B. Bhagat, M.F. Amateau, The Pennsylvania State University Applied Laboratory, Box 30, New ARL Building, State College, PA
Room: 340D
Session Chairpersons: N.L. Piret, Piret & Stolberg Partners, Im Licht 12, D-47279 Duisburg, Germany; Paul B. Queneau, Hazen Research, Inc. 4601 Indiana St., Golden, CO 80403
8:30 am INVITED
WASTE DISPOSAL BY RESIDUE RECYCLING AT KGHM POLSKA MIEDZ SA: Helena Byrdziak, Jerzy Dobrzanski, Jan Garbaczewski, Janusz Piatkowski, KGHM Polska Miedz SA, P-59300 Lubin, Ul. Sklodowskiej 48, Poland
KGHM Polska Miedz SA, existing since seventies, operates three underground mines and three smelters with local production of over 400,000 mtpy of electrolytic copper. Its impact on the environment, very serious in the past, has been gradually reduced, In general, recently emission into the air and water has been put under control. Nowadays tailings and residues disposal has turned to be the subject of first environmental importance. The total bulk of tailings is enormous as copper ore contains only about 2% of copper, so 98% of extracted material must be disposed gradually in each step of technology. The main Streams are tailings from the flotation, slags, captured dust from dedusting systems and gaseous compounds like SO2 and CO. Much effort has already been done and is still being done to utilize them for by-products production or to dispose them within the process by recycling. The most effective measures taken up so far and present activity towards waste disposal are presented.
9:00 am
RECYCLING OF PRINTED CIRCUIT BOARDS BY SMELTING WITH OXIDIZING/REDUCING TOP BLOWING PROCESS: Andrea Bernardes, Isrun Bohlinger, Diosnel Rodriguez, Wolfgang Wuth, Technical University Berlin, Institute of Metalllurgy, Strabe des 17. Juni 135, D-10623 Berlin, Germany
Printed circuit boards (PCBs) of varying compositions have been converted by incineration, followed by smelting to an environmentally stable slag and a copper-nickel-tin alloy, containing the precious metals. The environmentally compatibility of the slag was established according to the German Standard DIN 38414, Part 4. The concentration of toxic elements in the lixiviates was found to be lower than the threshold value for drinking water (CE-Standards). In each experiment the charge was 500 g scrap from PCBs and 100 g flux. The products were a king of mullite slag, poor in iron, which was recirculated, and an alloy containing up to 0.3% gold. With a burner the process gas was combusted without soot formation and the generated mixed zinc-lead oxide fume containing silver was separated as flue dust.
9:30 am INVITED
COPPER FROM COPPER BEARING SCRAP, A MOVING TARGET: Albert W. Spitz, Robert A. Spitz, Michael Saltzburg, 560 Bedford St., B-12, Abington, MA 02351
Profitably recovering copper and precious metals from copper bearing scrap is a demanding and frustrating combination of art, science and economics. With fluctuating markets, varying raw materials and increasingly stringent environmental regulations requiring process revisions, practically everything is changing. The volatile copper market constantly shifts the percentage of copper in the scrap that can be economically processed. Scrap that has value one day may incur a disposal cost the following day. Also with less copper in the scrap, more residuals, slag, fume, etc. are generated which frequently present disposal problems and infrequently generate income. The ever increasing amounts of electronic scrap add value to the copper produced by virtue of the precious metals present. Printed circuit board materials create more slag and organic off gases which must be treated. Finally, the emphasis on reducing emissions of organics and other metals, especially lead, is a continuing challenge. Stack gases, fugitive emissions and ambient air quality all demand constant surveillance.
10:00 am BREAK
10:30 am
CHANGES IN THE DUST HANDLING SYSTEM AT HUDSON BAY MINING & SMELTING CO., LTD: Keith McTaggart, Hudson Bay Mining & Smelting Co., Ltd, P.O. Box 1500, Flin Flon, Manitoba R&A 1N9, Canada
The waste gas cleaning system of the Hudson Bay Mining & Smelting copper smelter in Flin Flon, MB, consists of an electrostatic precipitator followed by a baghouse. These units collect the copper and zinc bearing dusts, respectively, from the gas streams of the reberberatory furnace and Pierce-Smith converting furnaces. A process change in 1993 led to the rapid destruction of the existing baghouse fibreglass filter bags, shortening their life-span from 15 to 3 months. A decision was made in September 1994 to replace this type of filter media with an expanded polytetrafluoroethylene (PTFE) membrane filter supplied by W.L. Gore Associates, Inc. Following the original installation a dramatic increase in dust capture was observed, however high pressure drops across the filter material lead to decreased flow through the off-gas handling system, limiting ventilation of the process. This increase in pressure drop across the PTFE bags was a function of the PTFE material and the inability of the baghouse shaker system to release the dust layer from the PTFE bags. Recently acoustic horns have been tested as a replacement to the shaker cleaning mechanism. Preliminary results indicate a dramatic reduction in pressure drop across the bags and a subsequent increase in process ventilation. This allows for fewer production interruptions caused by fugitive process emissions. The final acoustic horn results will be presented.
11:00 am INVITED
THE ECONOMIC AND ENVIRONMENTAL BENEFITS OF AUSMELT TECHNOLGY IN SECONDARY COPPER SMELTING AND CONVERTING: Edward N. Mounsey, Ausmelt Ltd., 12 Kitchen Rd., Dandenong 3175, Victoria, Australia; Norbert L. Piret, Piret & Stolberg Partners, Im Licht 12, D-47279 Duisburg, Germany
The requirements to smelt secondary copper more economically, to process a wide range of materials with large fluctuation in size and composition and to cope with the increasingly stringent environmental constraints have put considerable pressure on existing conventional secondary copper smelters. The Top Submerged Lance (TSL) process, developed and commercialized by Ausmelt Ltd over the past 20 years, offers a low cost technology, which is particularly suitable for the treatment of copper-bearing scrap and residues, because of its low investment, use of cheap fuel and reductant, high rate of recovery of metals and low slag losses, potential use of oxygen, high flexibility with regard to feed material, applicability to high and low throughputs, absence of dioxins in the process gas, simplicity of handling of feed, process gas and slags. This presentation outlines the application of Ausmelt technology in secondary copper smelting, producing converter grade copper ready for anode furnacing, both for a new installation and for a retrofit of the smelting or converting stage of an existing smelter. The economic and environmental benefits of its application are highlighted.
11:00 am INVITED
METALLURGICAL UTILISATION OF REUSABLE PRODUCTS FROM THE RECYCLING INDUSTRY IN A SECONDARY COPPER SMELTER: Andreas Nolte, Huttenwerke Kayser AG (HK) Postfach 15 60, D-44505, Lunen, Germany
This paper includes a comprehensive report about the metallurgical utilisation of reusable products from the electronic scrap recycling, car scrapping industry, used glasses and various waste products such as for example slimes and flue dusts in a secondary copper smelter. Dependent on the copper content, the existing copper compound and further aspects of the additional material content, the materials are treated in reducing and oxidizing furnace operations. HK's pyro- and hydrometallurgical processes, blast furnaces, converters, anode furnaces, tin lead alloy plant and tankhouse will be explained. The treated reusable products are structured according to the origin of the materials and then presented in quantity and quality balances. Processing methods, processable quantities and required qualities of the reusable products are described. The utilization degree of the most important metals (copper, tin lead and zinc) is described with graphics. The report is rounded by information on operating licence according to the emission protection regulations of the Federal Republic of Germany and informations concerning supply and contracts.
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