Room: 315B
Session Chairperson: TBA
1:30 pm
THE USE OF ION BEAM SURFACE MODIFICATION TECHNIQUES FOR CORROSION PROTECTION: P.M. Natishan, E. McCafferty, G.K. Hubler, B.D. Sartwell, Naval Research Laboratory, Washington, DC 20375
Ion beam alloying techniques overcome many of the problems associated with conventional alloying and provide a means to produce new and unique corrosion resistant alloys. These techniques can be used to tailor metal surfaces to enhance the corrosion resistance of the surface without affecting the bulk properties of the metal. In addition, novel metastable phases unattainable by conventional alloying can be produced, and scarce or critical materials can be conserved since only the surface of the metal is alloyed. This paper will discuss advances in and issues related to various ion beam alloying techniques including ion implantation, ion beam mixing and ion beam assisted deposition as related to their application to corrosion protection.
2:05 pm
CORROSION RESISTANT ALLOYS AND COATINGS PRODUCED BY PHYSICAL VAPOR DEPOSITION: Barbara Shaw, Elzbieta Sikora, Tim Miller, Department of Engineering Science and Mechanics, Penn State University, University Park, PA 16802
Evaporation techniques, such as PVD and CVD are increasing in popularity as methods for tailoring surface properties for specific engineering applications. One of the attributes of PVD is the ease with which graded, layered and nonequilibrium coatings and alloys can be produced. Not surprisingly, defects, coating morphology and deposit composition strongly influence deposit properties such as strength and corrosion resistance. As an example of how passivity enhancing species influence corrosion resistance, the addition of 8 at% Mo to Al (via electron beam PVD) was found to increase the pitting potential 600mV over that of pure Al. Similar enhancements have been observed with Al-Ta alloys. In addition to the constant composition deposits, graded and layered coatings can also be used to improve corrosion resistance and mechanical properties. In this presentation, the results of an ongoing investigation of nonequilibrium Al and Mg deposits ( both constant and graded composition deposits) produced via electron beam PVD will be presented and discussed.
2:40 pm
THE ELECTROCHEMICAL BEHAVIOR OF METAL SURFACES SUBJECTED TO PULSED ION BEAM SURFACE TREATMENT: N.R. Sorensen1, R.G. Buchheit1, K.S. Grabowski2, T.R. Renk1, M.O.Thompson3 ; 1Sandia National Laboratories, P.O. Box 5800 Albuquerque, NM 87185; 2Naval Research laboratory, Code 6670, Washington, DC 20375; 3Department of Materials Sciences, Cornell University, Ithaca, NY 14853
Pulsed high energy ion beams have been used to thermally treat metal surfaces to alter their electrochemical response. Two general processing regimens have been explored: 1) rapid melt and resolidification (RMR) and 2) ion beam mixing (IBM). RMR uses the pulsed ion beam to melt and in some cases ablate the top most several microns of the surface. Subsequent solidification is sufficiently fast (>106K/s) for nonequilibrium structures and compositions to be attained. IBM uses the ion beam to mix a previously applied metallic layer into the substrate to produce a compositionally and structurally distinct surface alloy. The surface that results from these treatments often displays interesting characteristics. For example, a Grade-2 Ti sample, which pits at a potential of 1.7V, is immune to pitting up to 2V following ion beam treatment. This talk will discuss the changes in electrochemical behavior of several alloys following ion beam treatment.
3:00 pm
CORROSION INHIBITION MECHANISMS IN EPOXY COATED ALUMINUM: R.D. Granata, R.C. MacQueen, R.R. Miron, M.M. Madani Zettlemoyer, Center for Surface Studies, Lehigh University, 7 Asa Drive, Bethlehem, PA 18015
Corrosion inhibition mechanisms in model systems were evaluated for use in barrier-type protective polymeric coatings systems. Emphasis was on complaint, low VOC coatings applications technologies such as powder coatings, UV-cured and electrocoating systems on aluminum substrates. Candidate inhibitor systems wee studied using low VOC epoxy polymer and porous polymer films on conversion coated, aluminum alloy 2024. Inhibition in these systems was observed in short exposure times. The model defect systems were studied using electrochemical impedance and positron annihilation lifetime spectroscopies. The positron lifetime measurements determined free volume cavity sizes and concentrations through which corrosion-active species diffuse. Electrochemically active and inactive (positron accessible) regions within the polymer matrix were monitored versus water saturation. Corrosion inhibitors modified the polymer matrix barrier properties in regions adjacent to the filler particles. Inhibition processes will be discussed relative to known mechanisms.
3:20 pm BREAK
3:40 pm
CYCLIC OXIDATION BEHAVIOR OF AN ALUMINIDE COATING FORMED ON DESULFURIZED Ni-BASED SUPERALLOYS BY CHEMICAL VAPOR DEPOSITION: Y. Zhang1, W.Y. Lee2, K.M. Cooley2, I.G. Wright2, P.K. Liaw1; 1Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996; 2Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
The cyclic oxidation behavior of Ni-based superalloys can be significantly improved by lowering the level of sulfur impurities in the alloys to below ~1 ppm. This presentation addresses the feasibility of preparing a low-sulfur bond coat, which would be compatible with desulfurized single-crystal superalloys and therefore could be attractive for possible use in advanced thermal barrier coating applications. Rene N5 substrates containing ~3 ppm and ~0.4 ppm sulfur were aluminized using a chemical vapor deposition technique. The level of sulfur incorporated into the aluminide coating was measured as a function of coating thickness by glow discharge mass spectroscopy. The effects of the sulfur content on the cyclic oxidation behavior of the aluminized substrates and the morphological stability at the scale-coating interface were studied and compared.
4:00 pm
AN XPS STUDY OF THE ROLE OF NITROGEN IN OXYANION FORMATION DURING AQUEOUS CORROSION OF MOLYBDENUM AND CHROMIUM NITRIDE COATINGS: G. Halada, C. Clayton, Department of Materials Science and Engineering, State University of New York at Stony Brook, NY 11794-2275; J. Beatty, J. D. Demaree, U.S. Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5069
A dual electrode electrochemical approach, in combination with variable angle X-ray Photoelectron Spectroscopy, was used to determine the role of nitrogen in the generation of oxyanionic species, MoO42- and CrO42-, from MoN and CrN coatings. During simultaneous anodic polarization of a coupling of Fe and either pure Mo and Cr or their respective nitrides in deaerated 0.1M HCl, the presence of nitrogen was found to enhance the formation of molybdate and chromate oxyanions. These oxyanions deposited back onto the nitride surfaces as insoluble salts formed with cations released from the iron electrode. The increased formation of oxyanions is postulated to be the result of deprotonation of electrolyte in contact with the nitride coating and a subsequent shift in pH to higher values. In addition to acting as a kinetic barrier, the oxyanionic species act as an electrostatic barrier to the ingress of the Cl- anions which cause pitting.
4:20 pm
A STUDY OF THE PASSIVATION MECHANISM IN HIGHLY CORROSION RESISTANT "STAINLESS STEEL" ALLOY COATINGS FORMED USING THE JVDTM PROCESS: Clive R. Clayton, M.E. Monserrat, G.P. Halada, Dept. of Materials Science and Engineering, SUNY at Stony Brook, NY 11794; Jamie Di, Takashi Tamagawa, Arun R. Srivatsa, Bret L. Halpern, Jet Process Corporation, 24 Science Park, New Haven, CT 06511
Recently we reported the formation of highly corrosion resistant "stainless steel" based alloy coatings formed using the JVD process. In this paper, a detailed study aimed at obtaining a fundamental understanding of the passivation mechanisms operating in these alloy coatings is reported. Passivation behavior of the coatings was determined by electrochemical polarization in 4.0M and 0.1M solutions respectively. The surface chemistry of the coatings was studied using XPS and correlated to the observed passivation behavior.
Room: 340B
Session Chairpersons: Dr. S. Krishnamurthy, UES, Inc., 4401 Dayton-Xenia Rd., Dayton, OH 45432; Prof. Carlos G. Levi, Materials Department, University of California, Santa Barbara, CA 93106
2:00 pm INVITED
SYNTHESIS AND PROCESSING OF CERAMICS, INTERMETALLICS, AND COMPOSITES BY FIELD-ACTIVATED COMBUSTION SYNTHESIS: Zuhair A. Munir, Division of Materials Science & Engineering, Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616-5294
Abstract not available.
2:30 pm
SYNTHESIS OF IN-SITU TiAl-BASED COMPOSITES FROM ELEMENTAL POWDERS: D.E. Alman, J.A. Hawk, U.S. Department of Energy, Albany Research Center, Albany, Oregon 97321
Alloys and composites based on the intermetallic compound TiAl are emerging as an important class of light-weight, high-temperature structural materials. Recently, it has been recognized that these alloys have applications in industries, such as the automotive industry, where cost is frequently a major concern in materials selection. However, for these alloys to be used in this type of application, new low cost methods for high volume component fabrication are required. One potential fabrication approach is reactive synthesis (also termed combustion synthesis). This technique involves initiating an self-propagating, high-temperature synthesis (SHS) reaction within an intimate mixture of elemental powders. This process has been used to fabricate intermetallics, ceramics and in-situ composites in the form of powders and dense monoliths. SHS reactions tend to initiate at low homologous temperatures of the forming compound (for aluminides near or at the melting point of Al, 660°C), and tend to go to completion in a short period of time (i.e., a few seconds). For some compounds, particularly aluminides, the reaction is ac companied by the formation of transient liquid phases. These factors can reduce the required processing parameters (time, temperature and pressure) needed to produce dense products by reactive synthesis techniques compared to conventional powder metallurgical approaches. This paper characterizes the reactions that occur and resultant microstructures of TiAl based composites fabricated from ternary mixtures of elemental Ti, Al and B or Si powders. Mixtures of the elemental powders were prepared corresponding to TiAl reinforced with 0, 10 25, 60 and 100 vol. pct. Ti5Si3 or TiB2. The powders were consolidated by reactive hot-pressing (at 1000°C and 20 MPa for 1 hr). It was found that the composites produced from Ti, Al and Si powders were dense, and the elemental powders transformed to the target phases of TiAl and Ti5Si3. Whereas, composites produced from the Ti, Al and B powders were porous and inhomogeneous, that is several aluminide (TiAl, Ti3Al and TiAl3) and boride phases (TiB2, AlB12, TiB) formed during hot-pressing. The different behavior observed by the two ternary systems can be attributed to both reaction sequence and phase diagram considerations. First, Differential Thermal Analysis (DTA) revealed that an endothermic reaction associated with the formation of Al-Si eutectic occurs prior to the initiation of an SHS reaction within the mixtures of Ti, Al and Si powders. No such pre-reaction melting occurred within the mixtures of Ti, Al, and B powders. Thus, the "extra" transient liquid phase that formed during the reaction between Ti, Al and Si systems enhances diffusion (hence homogenization) and densification within this system during reaction processing. Also, an examination of phase diagrams reveals that there exists no Al-Si compounds to compete with the formation of titanium-aluminide and titanium-silicides during reactions between Ti, Al and Si powders. However, there are several aluminum-boride phases that can compete with the formation of titanium-aluminide and titanium-boride during reactions between Ti, Al and B powders. The implications of this study is that TiAl-based composites can be designed for densification during reactive processing.
2:55 pm
REACTIVE SYNTHESIS OF NiAl-Nb COMPOSITE FROM ELEMENTAL POWDERS: L. Farber, A. Lawley, I. Gotman, Department of Materials Engineering, Drexel University, Philadelphia, PA 19104; I. Gotman, E. Y. Gutmanas, Department of Materials Engineering, Technion, Haifa 32000, Israel
A NiAl matrix composite reinforced with Nb particles was synthesized in the solid state from blends of ultrafine elemental Ni, Al and Nb powders. The fabrication method involved consolidation of elemental powder blends to full density followed by heat treatment. The maximum processing temperature did not exceed 800°C. Kinetics and the sequence of phases formation during synthesis were investigated. For Ni-Al-Nb blends, consumption of Al with the formation of Ni-Al intermetallic phases only was detected in the temperature range 425°C-550°C. Subsequent heat treatment at 800°C resulted in rapid completion of the synthesis reaction with the formation of the NiAl matrix. No reaction occurred between Nb particles and the matrix during synthesis. The phase stability of the composite in the 800°C-1100°C temperature range was investigated. Mechanical properties of the synthesized material are discussed in the context of resulting microstructure.
3:20 pm
FeAl-TiC AND FeAl-WC COMPOSITES - MICROSTRUCTURE AND MECHANICAL PROPERTIES: R. Subramanian,, J.H. Schneibel, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115
For applications of TiC- and WC-based cermets in corrosive environments, a potential binder material is an intermetallic, iron aluminide. In this investigation, it is shown that iron aluminide (Fe-40 at %Al) bonded TiC and WC composites can be processed to almost full density (> 99%) with carbide volume fractions ranging from 0.3 to 0.85 by conventional liquid phase sintering and pressureless melt infiltration techniques. The melt infiltration process was successful in the fabrication of composites with carbide volume fractions greater than 0.7 and important aspects of this technique will be discussed. Mechanical property data such as bend strength, hardness and fracture toughness will be presented and interpreted in terms of the composite microstructures. For FeAl-WC composites containing 60 vol.% WC, room temperature three-point bend strengths and fracture toughness values reached 1680 MPa and 20 MPa.m1/2, respectively. Consistent with the high fracture toughnesses, the fracture surfaces showed evidence of ductile deformation of the FeAl binder. Research sponsored by the Laboratory Directed Research and Development Program of the Oak Ridge National Laboratory, and by the Division of Materials Sciences, U.S. Department of Energy, under Contract No. DE-AC05-960R22464 with Lockheed Martin Energy Research Corporation, Inc. This research was also supported in part by an appointment to the ORNL Post-Doctoral Research Associates Program administered jointly by the ORISE and ORNL.
3:45 pm BREAK
3:55 pm
DEOXYGEN IN SILICIDE FORMATION: Chi-Fung Lo, Darryl Draper, Materials Research Corporation, Orangeburg, NY 10962
A preliminary study on the deoxygen behavior of tungsten-, molybdenum- and tantalum-silicide formations using powder technique was performed. During the synthesis under vacuum, the transformation of amorphous to crystalline silicon and the formation of silicides were monitored by X-ray diffraction. The oxygen content in the materials at various phase-transformation stages was measured. The results indicated that, independent of the synthesized metals, no significant change in the oxygen content was found until the formation of metal-disilicides. Via the formation of disilicides, the oxygen decreased from 1000-3000 ppm to less than 500 ppm. In this study, the exothermic behavior of silicon phase transformation and the silicide formations was also investigated.
4:20 pm
TITANIUM/TITANIUM CARBIDE COMPOSITE FORMATION BY GAS-SOLID IN-SITU REACTION: Yong Jin Kim, Hyungsik Chung, Department of Materials Processing, Korea Institute of Machinery and Materials, 66 Sangnam Dong, Changwon, Kyungnam 641-010, S-Korea; Suk-Joong L. Kang, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusong-Dong, Yusong-Gu, Taejon 305-701, S-Korea
Sponge titanium powder was die compacted and reacted with carbonaceous (CH4) gas at the temperature range of 700-1,000°C. Layered TiC film was formed uniformly on the surface of the powders in the green compact. The thickness of the TiC layer varied with the reaction temperature and time. The reacted compacts were sintered in a vacuum up to 1450°C. During the sintering, the TiC layer in the power surface was broken into small fragments and the fragment changed gradually into round shaped particles with increasing the sintering temperature. The relative sintered density over 94% was obtained at the sintering temperature of 1350°C for 2hrs. Ti/TiC composite containing up to 50 v/o of TiC was successfully made by the in-situ reaction and sintering. The volume of TiC in the sintered body mainly depends on the reaction temperature, time and Ti powder size. But the gas flow rate during the reaction affected little to TiC volume in the sintered composite.
4:45 pm
PROCESS-STRUCTURE RELATIONSHIPS FOR TAPE CASTING OF CONTINUOUS FIBER-REINFORCED MMC'S: Shin Yu and Dana M. Elzey, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903
The tape casting process offers a potentially cost-effective manufacturing route for continuos fiber-reinforced metal matrix composites. However, the ultimate performance is limited by the presence of microstructural defects, which evolve to an extent which depends sensitively on the constituent materials and processing conditions used. Results of an experimental study are reported in which the evolution of several important microstructural defects have been investigated for various processing conditions. These observations have been used as a basis for the development of predictive process-structure models for the tape casting of MMC's. The models may be used to explore processibility and cost issues for hypothetical matrix/fiber composite systems and processing conditions.
5:10 pm
FIBER FRAGMENTATION DURING PROCESSING OF METALLIC MATRIX COMPOSITES: Nicole M. Gorey, Donald A. Koss, John R. Hellmann, Department of Materials Science and Engineering, Penn State University, University Park, PA 16802
Fiber fragmentation can be a serious problem during the processing of metallic matrix composites. This research focuses on the fracture of continuous sapphire fibers during composite consolidation. During the latter stages of consolidation, matrix flow along the fibers may cause fiber fracture even in the absence of fiber bending. Fiber fragmentation by this mechanism has been examined using a theoretical analysis which predicts the extent of composite flow as a function of processing parameters and the resulting fiber fragmentation lengths. In order to validate the analysis, a model composite system, which consisted of a tin matrix and degraded sapphire fibers, has been "hot pressed" at room temperature to simulate elevated temperature consolidation of sapphire-reinforced Ni-base composites. A comparison of observed and predicted fiber fragmentation lengths indicate good agreement. The analysis can readily be applied to predicting conditions that should be used to prevent extension-induced fiber fracture during high temperature consolidation of structural composites. The research was supported by NASA.
Room: 230D
Session Chairman: J.L. Anjier, Kaiser Aluminum and Chemical Corp., Box 337, Gramercy, LA 70052
2:00 pm
FCB RETROFITTING OF ALUMINA ROTARY KILN: WHEN DRASTIC FUEL SAVING MEETS INCREASED CAPACITY: Vincent Giroud, Andre' Pinoncely, FCB- subsidiary of the Fives Lille Group, Mineral Processing and Carbon Plant Division, 32, rue fleury Neuvesel, BP 24-69702 Givors Cedex.
Alumina calcination using rotary kilns is an expensive operation. In 1972 an innovative concept of kiln retrofitting was introduced which greatly enhanced the overall thermal efficiency while preserving most of the existing capital equipment. As a result, nine kilns have been retrofitted over the last eighteen years, gradually highlighting the wide range of possible arrangements and the relevant strong process and mechanical reliability. This paper draws up the main features of these retrofits, namely the substantial energy saving and the correlative increased capacity. Long-term observations also demonstrated that alumina quality remains as consistent as previously with no significant impact on the calcined alumina size distribution. The latest retrofitting pattern including new cyclones and ducting arrangements are presented yielding a fresh look for a still useful technology.
2:25 pm
ALUMINA CALCINATION WITH THE MULTI-PURPOSE CALCINER: Jorgen Ilkjaer, Lars Bastue and Benny E. Raahauge, FLS Minerals A/S, Alumina & Bauxite Technology, Vigerslev Allé 77, DK-2500 Valby Copenhagen, Denmark
The Gas Suspension Calciner (GSC) and the rotary kiln are both well proven technologies for calcination of alumina. The GSC is mainly used for production of smelter grade alumina and the rotary kiln for special grade alumina. A multi-purpose calciner which combines these two technologies has been designed, constructed and commissioned in the summer of 1996. By combining these two calcination technologies it is possible to produce a wide range of alumina qualities only by changing a few parameters in the operation using a Fuzzy II Logic Control System and a CemScanner.
2:50 pm
PREDICTING MOISTURE CONTENT ON ALUMINAS FROM MEASUREMENT OF WATER ISOTHERMS: A.R. Gillespie, Comalco Research Centre, Thomastown, Vic., Australia; M.M. Hyland, J.B. Metson, University of Auckland, Auckland, New Zealand
Water adsorption isotherms on alumina can play an important predictive role in aluminium smelting since the level of moisture on the alumina influences its handling, feeding and dissolution characteristics, along with the potential for generation of emissions. Measurements of adsorption isotherms of water on smelter aluminas indicate moisture pick-up and loss is rapid, with initial rates of change in adsorbed water in excess of 0.1 wt% per minute, meaning the ex-situ measurements are not likely to be accurate. Adsorption and desorption curves, to water pressures in excess of 20 Torr, indicate near complete reversibility. The discrepancy is attributed to the irreversible formation of Al(OH)3. Analysis of the shape of the curves suggest several distinct mechanistic regimes within the adsorption curve.
3:15 pm BREAK
3:35 pm
ALUMINA QUALITY TESTING PROCEDURE: R.G. Haverkamp, B.J. Welch, Department of Chemical and Materials Engineering, University of Auckland, Auckland, New Zealand; S. Bouvet, Pechinay Centre de Recherches de Voreppe, Voreppe, France; P. Homsi, Aluminium Pechiney, St. Jean de Maurienne, France
A laboratory method for comparing characteristics of alumina dissolution in molten cryolite is described. The method uses fast modified linear sweep voltammetry combined with thermal analysis to determine the dissolution rate of alumina in a molten cryolite electrolyte. Practical aspects of the method are discussed. Emphasis is on consistent alumina feeding and stirring and a careful monitoring of the alumina moisture content.
4:00 pm
SINTERING AND HEAT CONDUCTIVITY OF ALUMINA: Terje Østvold, Øyvind T. Gustavsen, Heidi Mediaas, Institute of Inorganic Chemistry, Norwegian University of Science and Technology, N-7034 Trondheim, Norway; Torstein Haarberg, Hydro Aluminium, Technology Centre Årdal, N-5870 Øvre Årdal, Norway
Heat conductivities are measured in alumina powders treated with 0-7 wt% NaAlF4 at varying temperatures up to 900°C. The 
transition of alumina, triggered by addition of NaAlF4, was found to be essential for the observed increase in heat conductivity. A maximum heat conductivity was measured at 3.5 wt% NaAlF4 for aluminas heated to 700°C and at ~2 wt% NaAlF4 for heat treatments at 800 and 900°C. The heat conductivity was also measured versus temperature after the samples had been sintered. A decrease in heat conductivity with increasing sample temperature was observed. A mathematical model for the thermal conductivity of porous materials was applied and tested against the measured data, confirming the importance of sintering with respect to thermal conductivity. The relevance of the present findings concerning heat balance of industrial smelting cells is discussed.
4:25 pm
RECOVERING ALUMINA, SILICA AND BYPRODUCTS FROM COAL ASH THROUGH THE USE OF PROCESS FOR SILICON PRE-EXTRACTION: Victor L. Rayzman, 933 Regal Road, Encinitas, CA 92024; Solomon A. Shcherban, 110 Bennet Avenue, #3H, New York, N.Y. 10033
The large volume of coal combustion wastes cause a problem of great concern in environmental protection. Only about a quarter of these wastes are being used today, generally for construction materials production. At the same time, many million tons of aluminum and silicon contained in coal ash are lost in landfills annually. Of all the large number of processes for recovering alumina and byproducts from aluminum and silicon-bearing wastes only one, the lime-soda sintering process, has been commercially used on nepheline residue and red mud. To approach ash composition similar to these above-mentioned wastes, a process for silicon pre-extraction has been developed and pilot plant tested. The method reduces the material stream trough the sintering kiln in half and produces high pure silica alongside the alumina and calcium silicate. The heat consumption for the new process is estimated significantly lower than that for the sintering method and approaches the Bayer technology indices.
4:50 pm
FEATURES OF ALUMINA PRODUCTION TECHNOLOGY FROM ALUMINOSILICATE RAW MATERIAL WITH POTASSIUM'S HIGH CONTAIN: V.A. Lipin, N. N. Tikhonov Russian National Aluminium-Magnesium Institute (VAMI), 88, Sredny pr., St. Petersburg, 199026, Russia
Aluminosilicate raw materials have large differences in chemical and mineralogical structure, particularly in the relationship between sodium and potassium. Large deposits of raw materials with high portions of potassium alkalis are known and have been studied for the purpose of the industrial processing by the sintering and hydrometallurgical methods. Technological features of the processing of the high-potassium aluminosilicate raw materials utilize for the most part the processes of sintering, leaching and desilication. The optimum molecular ratios of the main components before sintering were found in each case. Distribution of alkaline metals between liquid and solid phases during leaching and desilicating was determined. Utilizing experimental data, equations have been developed predicting the dependence of desilicating indexes from chemical composition of processing ores. These relationships aid in choosing the most effective conditions for research of promising raw materials.
Room: 230A
Session Chairperson: Elmar Sturm, Hamburger Aluminiumwerk GmbH, P.O. Box 950165, D-21129 Hamburg, Germany
2:00 pm
ON THE BATH FLOW, ALUMINA DISTRIBUTION AND ANODE GAS RELEASE IN ALUMINIUM CELLS: Ove Kobbeltvedt, Department of Electrochemistry, Norwegian University of Science and Technology, N-7034 Trondheim, Norway; Bjørn P. Moxnes, Hydro Aluminium, Technology Centre Årdal, N-5870 Øvre Årdal, Norway
The bath flow was studied in prebake cells. The measurements were performed by recording the drop in bath temperature subsequent to alumina feeding as well as by measuring the wear of quartz rods immersed in the bath. The horizontal flow rate varied between 3 and 20 cm/s. It was found that the horizontal bath flow and consequently the alumina distribution pattern are determined mainly by a combined effect of the magnetic fields and the width of the channels above the working surface of the anodes. The quantity of anode gas which was drained into the centre channel was measured at different locations in a cell. The result showed that the distribution of the anode gas in the bath is strongly associated with the magnetic fields.
2:25 pm
ALUMINA DISTRIBUTION IN POINT-FED HALL-HEROULT CELLS: K. Tørklep, K. Kalgraf, T. Nordbø, Elkem a/s Research, P.O. Box 8040 Vaagsbygd, N-4602 Kristiansand, Norway
We describe the alumina concentration distribution in point-fed Hall cells in terms of finite physical elements. The need arose in the development of the New Søderberg technology at Elkem Aluminium ANS, but the technique is applied to prebake pots as well. The concentration at any point in the bath is computed from the dynamical equilibrium between consumption and transport of alumina (directly or indirectly dissolved) and presented as contour plots. Necessary inputs are the velocity field in the bath and the turbulent diffusivity, either measured or calculated. We prefer to measure both by injecting a small amount of a molten radioactive tracer and follow the distribution of this tracer in situ. Measured velocity fields have been found to vary significantly between presumed identical pots and over time. This is mainly ascribed to convective coupling with the metal, where the boundary conditions and hence the driving forces may well differ between pots and change with time. Contrary to extant models, our approach permits experimental verification through comparison of predicted and measured oxide concentrations at various locations in the pot under investigation.
2:50 pm
METAL PAD WAVE ANALYSIS USING FAST ANODE LOWERING METHOD: H. Q. Tang and N. Urata, Kaiser Aluminum & Chemical Corporation, Center for Technology, P.O. Box 877, Pleasanton, CA 94566
In order to study the metal pad wave in aluminum reduction cells, the two step fast anode lowering method was developed and applied to the operating cells. The metal pad waves after anode lowering were measured and analyzed. The period and shapes of the metal pad waves were determined by performing Fourier transform analysis of the measured data. The MHD wave equations were solved for cells of different magnetic fields to simulate the metal pad waves caused by this fast anode lowering. The period and shapes of the predicted steady state waves were in good agreement with the measured waves, although the measured wave had more transient nature. The cell stability was evaluated based on the metal pad wave analysis.
3:15 pm BREAK
3:35 pm
IMPURITY TRANSPORT MECHANISMS IN ALUMINIUM REDUCTION CELLS: M. Webster, Xiaoling Liu, Comalco Research Centre, Thomastown, Victoria, Australia; J. Metson, Department of Chemistry, University of Auckland, New Zealand
The purity of aluminum from pre-bake reduction cells is affected by the quantity of impurities introduced with the raw materials and the fraction of these reporting to the metal. The transport of Ti, V, Ga, Si, Fe and Ni from the reduction cell to the duct emissions stream has been studied for point feeder and bar break cells. Samples of material from bath, cell cover and duct emissions have been examined and analysed for a range of impurities. For elements with volatile, bath generated fluoride compounds, the impurity content of the cover and duct samples is proportional to the carbon content. Carbon grains with thick (>10 micron) impurity rich surface coatings are observed in both the loose cover samples and particles from bath skimmings. Thus a possible mechanism for the transport of these impurities may be postulated.
4:00 pm
PSEUDO RESISTANCE CURVES FOR ALUMINIUM CELL CONTROL--ALUMINA DISSOLUTION AND CELL DYNAMICS: Halvor Kvande, Hydro Aluminium a.s, P.O. Box 80, N-1321 Stabekk, Norway; Bjørn P. Moxnes, Jørn Skaar, Per A. Solli, Hydro AIuminium a.s, Technology Centre Årdal, P.O. Box 303, N-5870 Øvre Årdal, Norway
The pseudo resistance was measured as a function of the alumina concentration in the bath in five different types of cells. The pseudo resistance showed a minimum value of 5.0 to 5.5 mass% Al2O3, when the bath samples were analyzed by the LECO method. To the left of the minimum point on the curve the slope increased gradually until the anode effect occurred at 1.6 to 2.2 mass% Al2O3, while a nearly linear curve was found in some of the measurements. The difference in pseudo resistance determined just prior to the anode effect and at the minimum point, corresponded to a voltage difference between 100 and 300 mV. Immediately after the alumina feeding rate was reduced from overfeeding to underfeeding, a so-called "hysteresis effect" could be observed. This was characterized by a sudden decrease in cell voltage of about 100 mV in less than 30 minutes, in spite of practically constant bath composition and temperature in this time period. This effect may be caused by dissolution of alumina sludge in the bath phase above the metal pad, accumulated during the long overfeeding period of several hours, needed to reach concentrations to the right of the minimum point on the curve.
4:25 pm
THE INFLUENCE OF SODIUM ON THE ALUMINIUM REDUCTION CELLS: Mohamed O. Ibrahiem, Mohamed M. Ali, R&D Department, Aluminium Company of Egypt, Naga Hamadi, Egypt
Sodium always present in Hall-Heroult cells, has a decisive influence on cell performance and pot failure. In this paper, sodium was studied from three points of view. The first is the sodium mass balance. Alumina and cryolite are the major sources of sodium inputs to the electrolytic process, where 56.8% and 40.7% of sodium come from them, respectively. The second point is the sodium content in aluminium metal. Measured sodium content in aluminium of 203 kA prebaked cells is lower than that of 155 kA Søderberg due to lower bath ratio, higher excess aluminium fluoride, and higher magnetic fields. The third point is the study of sodium concentrations in failed carbon cathodes at different ages. This concentration at 3194 days is 8.5%, 7%, and 1% higher than that at 40, 60, and 1369 days, respectively.
4:50 pm
STUDY ON CATHODIC PROCESS OF Na+ IN THREE-LAYER ELECTROLYTIC REFINING OF ALUMINIUM: Li Guohua, Li Dianfeng, Zhao Xiangguo, Wang Qingna, Department of Nonferrous Metallurgy, Northeastern University, Shenyang, 110006, China
The Current-Voltage Method is adopted to study the cathodic process of Na+ in three-layer electrolytic refining of aluminium. The electrolyte studied is NaF-AlF3-BaCl2-NaCl molten system, whose composition is: NaF/AlF3 mole-ratio is 1.5-3.0, adding amount of NaCl is 0-8%, BaCl2 content is 60%. It is demonstrated that Na+ is not able to deposit on the aluminium cathode at the temperature range of 740-800°C while the cathodic current density is 0.4-0.8 A/cm2. This conclusion provides an important basis for modifying the electrolyte in three-layer electrolytic refining of aluminium.
Room: 232A
Session Chairs: L.L. Shaw, Dept. of Metallurgy & Materials Science, Univ. of Connecticut, Storrs, CT 06269-3136; R. Abbaschian, P.O. Box 116400, 132 Rhines Hall, Univ. of Florida, Gainesville, FL 32611-6400
2:00 pm
SPECTROSCOPIC METHODS FOR CONTROL OF THIN FILM GROWTH: A.G. Jackson, S.J.P. Laube, J. Jones, TMC, Inc., Materials Directorate, Wright Laboratory, WPAFB, OH 45433
Control of thin films during the growth process is dependent on several difficult-to-monitor parameters, including flux of film material, pressure, substrate temperature, composition, and thickness. One means for easing this difficulty is to take advantage of emission spectra associated with the process and the film. For pulsed laser deposition (PLD) the ion cloud generated by the laser has characteristic emission spectra that can be used to control the deposition. Raman spectroscopy affords the possibility of real-time control by sensing characteristic peaks associated with film composition and thickness. These spectroscopic methods offer a real-time alternative to process control that is very attractive because of the ability to accurately control films to achieve the engineered structures and properties sought. Examples are presented to illustrate the capabilities of these methods for this film preparation.
2:25 pm
RAMAN SPECTROSCOPY FOR DETERMINING YBCO THIN FILM PARAMETERS IN SITU: David P. Lubbers, Univ. of Cincinnati, Cincinnati, OH; John D. Busbee, A.G. Jackson, TMC, Inc., Materials Directorate, Wright Laboratory, WPAFB, OH 45433; Rand R. Biggers, David C. Liptak, SOCHE, Dayton, OH
This paper describes the application of Raman spectroscopy for characterizing superconducting YBCO thin film parameters. Attenuation of the substrate Raman spectrum as a function of material deposited is established. Also, a correlation between film quality and Raman spectrum is explored. The identification and discrimination of superconducting and nonsuperconducting phases of YBCO is presented. The critical temperature (Tc) of a film as a function of its oxygen content is also established using Raman peak ratios. These results provide significant implications toward the use of Raman spectroscopy for in situ monitoring and control of the PLD process. Film quality can be controlled via optimization of film oxygen content and reduction of improper YBCO phases. Film thickness can be controlled by monitoring the response of the substrate material. Also, the PLD process can be studied and modeled using this powerful observation tool.
2:50 pm
INTELLIGENT PROCESSING OF MATERIALS: AN APPLICATION TO POLYMER COMPOSITES: J.F. Maguire, M.A. Miller, Materials Development Dept., Southwest Research Institute, San Antonio, TX
The process control of polymeric components is a difficult problem in modern process control. These materials consist of a chemically reactive resin which impregnates a reinforcing fiber. The resin is subject to aging phenomena and is found that frequent adjustments of the process are needed in order to assure quality of the product. In order to increase quality and reduce manufacturing delays the manufacturing process was analyzed from a physico-chemical standpoint and intelligent control system was developed and implemented. It was determined that integration of a novel advanced sensor technology based on in situ Raman and Rayleigh light scattering with a state-of-the-art chemical kinetic and polymer transport model of the polymerization process would provide real (sensor) and virtual (model) information on which material process control decisions could be based. The sensor information provides chemical and physical analytic data in real-time. This data is analyzed and compared with the predictions of the model and adaptive control decisions are implemented. The control system was interfaced with customized processing hardware via a programmable logic controller (PLC) employing conventional ladder logic. The system has been tested extensively and has been able to process adaptively advanced composite components fabricated from quartz reinforced polyimides. Finally, the process logic control algorithms, which rely on the physical and chemical state of the material based on sensor information, are generic to any chemically reactive resin with minor modifications to initial parameter values.
3:15 pm BREAK
3:25 pm
ALUMINUM SENSOR FOR STEEL GALVANIZING BATHS: R.Sridhar, J.M. Toguri, Dept. of Metallurgy and Materials Science, University of Toronto, Toronto, Ontario M4S 3E4, Canada
The aluminum content of zinc galvanizing baths is an important parameter for producing good quality steel sheets for automotive applications. The present method of bath sampling and chemical analysis measures the total aluminum content of the bath which includes dissolved aluminum and aluminum in entrained dross. Also, this method does not provide quick analysis for process control purposes. It has been reported that the measurement of dissolved aluminum is essential to obtain a good zinc coating on steel. Laboratory experiments have shown that an electrochemical cell consisting of an aluminum electrode, an ionic fused salt and an electrode like Mo (inert to Zn) dipping in the zinc bath has good potential for quick dissolved aluminum measurements. Such a sensor can be ready adopted for process control. These results will be discussed.
3:50 pm
SOLID-STATE ALUMINUM SENSOR FOR USE IN MOLTEN ZINC: J.W. Fergus, S. Hui, Materials Research and Education Center, 201 Ross Hall, Auburn University, AL 36849
Aluminum is an important alloying addition to the zinc used in the hot-dip galvanization of sheet steel to control the properties and appearance of the resulting coating. Optimization of the galvanization process requires control of the alloy concentration, which can be improved through the use of chemical sensors. Aluminum sensors, based on molten electrolytes, are commercially available but are not widely used because of their high cost. One approach to reducing the cost is to use a solid electrolyte, which can simplify the sensor design and, thus, reduce the cost of fabrication. In this paper, the development of an aluminum sensor based on a solid fluoride electrolyte, specifically magnesium fluoride, will be described.
4:15 pm
APPLICATIONS OF Al SENSORS IN CONTINUOUS GALVANIZING: N. Qiang, N.-Y. Tang, G.R. Adams, Cominco Ltd., Product Technology Centre, Sheridan Science and Technology Park, Mississauga, Ontario L5K 1B4 Canada
Aluminum is the most important alloy addition to Zn baths for controlling the reaction kinetics between the steel substrate and molten Zn in continuous galvanizing operations. The control of effective bath Al content is particularly critical for galvannealing where a high bath Al content may lead to incomplete alloying during postannealing, and a low bath Al content may result in other problems, such as an excessive bottom dross accumulation and difficulties in coating thickness control. The amount of Al in a galvanized coating has a strong influence on coating properties and the overall product quality. Yet, due to the complexity of the Zn-Fe-Al ternary system, the measurement and accurate of Al sensors has made the real-time measurements of bath Al contents possible. To facilitate their application, a computer interface and a palm-size data logger have been developed. Plant applications indicated that the sensor possessed sufficient accuracy for process monitoring and control. Potential benefits of Al sensor applications include improvements in process control and product quality, reductions in product transition periods for dual product lines, and a reduction in the overall production cost.
Session Chairperson: George Demopoulos, Dept. of Mining and Metallurgical Engineering, McGill University, Montreal, Quebec, Canada H3A 2A7
2:00 pm
A PYRIDINE-BASED TRIDENTATE CHELATING SOLVENT EXTRACTION SYSTEM FOR SELECTIVE EXTRACTION OF NICKEL AND COBALT: Batric Pesic1, and Taili Zhou2, 1University of Idaho, College of Mines-McClure Hall, Moscow, ID 83843; 2The Shepherd Chemical Co., 4900 Beech St., Cincinnati, OH 45212
A novel pyridine-based tridentate chelating extractant, 2,6bis-[5-n-nonylpyrazo-3-yl] pyridine (BNPP), has been developed and characterized. The solvent extraction of Ni and Co by a mixed system of BNPP and dinonyl naphthalene sulfonic acid (DNNSA) was studied as a function of pH, diluent, temperature, and DNNSA concentration. Stripping of Ni and Co was examined as a function of HCl and H2SO4 concentration. The novel system can extract Ni and/or Co selectively against Fe, Mn, Ca, Mg, and Al from acidic sulfate solutions at a pH as low as 0.5. Separation of Ni and Co can be achieved either during loading, or during stripping stages of solvent extraction. The extractant system is stable and can be regenerated with acid. The novel solvent extraction system was also tested on the real solutions produced by leaching of cobalt bearing concentrates, (1) cobaltite concentrate from Blackbird Mine, Idaho, and (2) siegenite concentrate from Lead-Belt, Missouri. A flowsheet for recovery of cobalt and nickel has been proposed based on these studies. The review of the current status of solvent extractants for cobalt and nickel will be given by comparative presentation with our novel extractantion system.
2:20 pm
DIELECTRIC STUDIES ON PbS-KEX-K2Cr207 SYSTEM UNDER FLOTATION CONDITIONS: Antonio Huerta, Juan Genesca, Armando Solis, Dept. de Ingenieria Metalurgica, Fac.de Qulmica, Universidad Nacional Autonoma de Mexico. Cd. Universitaria, CP.04510, Mexico
The effects of potassium ethyl xanthate used as collector and dichromate potassium a depressor on a PbS mineral were studied by the recently accepted technique in Mexico, high frequency impedance (transformed to dielectric values). Results of dielectric values at 100 MHz suggested that is possible to obtain from isotherm adsorption the adequate industrial collector concentration being this in the range of 1E-3 to 5E-3M of KEX. The e' values (320-420) in the PbS-KEX system was increased as the KEX concentration was lowered). In the other hand the PbSK2Cr207 system showed higher values of e' (420-510) as the K2Cr207 concentration was increased. The PbS-KEX-K2Cr207 system was evaluated, obtaining the KEX concentration dominion on K2Cr207.
2:40 pm
GYPSUM CRYSTALLIZATION IN ACIDIC WASTEWATER TREATMENT: A REVIEW OF CURRENT PRACTICE AND A VIEW ON PROCESS IMPROVEMENT: S. Omelon, G.P. Demopoulos, McGill Department of Mining and Metallurgical Engineering, 3450 University St., Montreal, Canada H3A 2A7
Acidic sulphate-containing wastewater streams are currently neutralized with lime before discharge to the environment. The most common neutralization process design involves a one-step neutralization followed by a settling tank that separates an ultra-fine, low solids density gypsum by-product. The final gypsum quality is undesirable as it is voluminous and has a high surface area that sorbs metal ions. The paper will critically review the current practice of gypsum precipitation. It will also report the progress of a project which uses crystallization principles and supersaturation control to develop a new process. The new process design utilizes a model that was constructed to predict gypsum solubilities in H2SO4-ZnSO4-FeSO4-MnSO4-MgSO4 solutions from 25-60°C. By maintaining a low gypsum supersaturation with a series of CSTR's and providing gypsum seed with a solids recycle, the generation of high solids density gypsum is favoured. Early results will be presented, as well as results on Zn2+ adsorption.
3:00 pm
ANALYSIS OF THE HEMATITE PRECIPITATION PROCESS FROM A CRYSTALLIZATION POINT OF VIEW: T.C.-M. Cheng, G.P. Demopoulos, McGill Department of Mining and Metallurgical Engineering, 3450 University St., Montreal, Canada H3A 2A7
Iron removal and disposal in zinc and nonferrous hydrometallurgical plants at large constitutes one of the major environmental challenges to the industry. So far three technologies have been used by the zinc industry to effect iron rejection, namely the Jarosite, the Goethite, and the Hematite Processes. Among them, it is the Jarosite Process that has dominated the scene. However jarosite residues tend to be voluminous (only 25% Fe content) and highly toxic due to incorporation of Zn, Cd, Pb, and other heavy metals, not to mention the relatively high Zn losses. The industry addresses the heavy metal release problem by further stabilizing jarosite prior to disposal as is done, for example, in the Jarofix Process. On the other hand, hematite residues produced by the Hematite Process have a very high iron content and low zinc losses but come with a relatively high operating cost. At present, commercial produced hematite residues are still considered a waste because of the impurities contained in them whereas the two major troublesome impurities are sulfur and zinc. Hematite technology may become more attractive if the produced hematite is clean enough to be used as a feed material for iron-steel making. In this paper, the practice of industrial hematite precipitation and the relevant technical literature are reviewed with the objective to identify the critical processing parameters which are responsible for the contamination of hematite with sulfur and zinc. The analysis is done from a crystallization theory standpoint. The role of supersaturation control or lack of it is emphasized in the analysis. Finally, the main elements of a research program focus ing on crystallization of hematite that is currently underway at McGill University will be outlined.
3:20 pm BREAK
3:30 pm
INFLUENCE OF HYDROLYSIS--PRECIPITATION MEDIUM ON THE NATURE OF ALUMINIUM HYDROXIDE GELS AND Al203 POWDER CHARACTERISTICS: M. Thiruchitrambalam, V.R. Palkar*, V. Gopinathan, P. Ramakrishnan, M.S. Multani*. Dept. of Metallurgical Engineering and Materials Science, I.I.T, Bombay - 76; *Tata Institute of Fundamental Research, Bombay -5, India
Aluminium hydroxide gels have been widely used in applications like sorbents and catalyst supports. Thermal treatment of aluminium hydroxide gels i.e., calcination and/or sintering, first leads to dehydration and then a series of phase changes. Once dehydration is complete several transition aluminium oxides namely , 
and 
appear, and finally Al2O3 is formed at about 1200°C. In the current investigation boehmite (AIOOH) a bayerite (Al(OH)3) have been prepared in the presence of water-glycerol solutions. The results indicate that the precipitation media have considerable influence on the nature of aluminium hydroxide precipitate. Aluminium hydroxide gels thus prepared were characterised by TEM and XRD. Calcined powders were examined by XRD for phase content, by SEM for morphology and BET method for specific surface area. Calcination of aluminium hydroxide gels prepared by Hot water hydrolysis-Controlled precipitation technique yielded agglomerate free, spherical a Al2O3 powder. Al2O3 was also prepared by calcining the aluminium hydroxide gels at 600°C and characterised by XRD, TEM and BET method.
3:50 pm
CONTINUOUS BACTERIAL LEACHING OF A LOW-GRADE MANGANESE DIOXIDE ORE: S. Agatzini Leonardou, J.G. Zafiratos, Laboratory of Metallurgy, Department of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, Greece
The leaching of a Greek low-grade manganese dioxide ore, not amenable to conventional mineral processing operations, was studied using a mixed culture of Thiobacillus sp. bacteria. The experiments were carried out in specially designed continuously aerated and stirred tank reactors arranged in two-tank series. The first tank of each series was loaded with an elemental sulfur culture suspension while the second was loaded with a manganese ore high density slurry. The bacterial culture had been previously adapted to grow on elemental sulphur and also in the presence of manganese ore and dissolved manganous ion. A two level full factorial design, was constructed in order to study the effects of the ferric ion concentration in the leach solution, the "elemental sulphur weight to ore weight" ratio, the ore pulp density and the composition of the dispersed gas. The responses which were investigated included percentage manganese recovery, co-dissolution of iron and manganese dissolution rate. Parameters with constant values throughout the experiment were the leach solution pH, the nutrient medium composition, the dilution rate and the ore and sulphur grain sizes. It was found that the ferric ion concentration was the most significant factor and had a positive effect on the final percentage extraction of manganese from the ore and also on the rate of manganese solubilisation from the ore. The effects of the other factors studied are discussed in detail.
4:10 pm
Ni, Co & Cr RECOVERY FROM NICKEL LATERITE LEACH LIQUORS BY BIOSORPTION USING IMMOBILISED ALGAL BIO-MASS: S. Agatzini-Leonardou, J.G. Zafiratos, Laboratory of Metallurgy, Department of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, Greece
The objective of this work was to prove repeated loading capacities of physically stabilized algal biomass from Spirulina platensis and Chlorella sp. for the removal and recovery of cobalt, nickel and chromium from laterite heap leach liquors. The testwork was carried out on a bench scale in small columns and proved that it is possible to immobilize the biomass on the highly porous surface of pumice stone. Nickel and cobalt could be removed from pure aqueous solutions of each metal by cyanobacterial biomass of the species Spirulina platensis and Chlorella sp. immobilized on the mineral. Nickel and also cobalt biosorption was sensitive to the initial solution pH. The maximum amount of cobalt was retained on the biomass at pH 6.0, while nickel was removed most effectively at pH 5.5. Repeated loading capacities of physically stabilized algal biomass from Spirulina platensis and Chlorella sp. were proven effective for the removal and recovery of cobalt and nickel from solutions resembling diluted laterite heap leach liquors. A lifetime of at least 5 loading cycles of the immobilized biosorbent material was obtained. The loading capacity of the immobilized biomass for nickel was comparatively lower than the capacity of the same biomass for cobalt. Cobalt recoveries up to 80% were achieved after 5 loading cycles under unoptimized conditions whereas nickel was removed completely (100%) under the same conditions. The described process might be applicable to recover cobalt from diluted laterite heap leach solutions.
Room: 340A
Session Chairperson: Dr. George J. Kipouros, Technical University of Nova Scotia, Department of Mining, and Metallurgical Engineering, P.O. Box 1000, Halifax, Nova Scotia, Canada B3J2X4
2:00 pm
FILLER METAL-ASSISTED RESISTANCE SPOT WELDING TECHNIQUE: Hua Xin Li, Mark T. Smith, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352
A new technique is developed to overcome or minimize the inherent problems associated with aluminum RSW. Test results on 1 mm thick 6061 aluminum alloy sheets have shown that the new method can dramatically improve almost all of the problems encountered using conventional RSW. By using the new method, the following improvements have been achieved: 1) reducing/eliminating electrode contamination; 2) eliminating/minimizing surface indentation and deformation; 3) increased weld nugget size by 200% with same welding parameters; 4) maintaining consistent weld nugget size; and 5) no cleaning is needed, particularly at faying surfaces. Peeling strength is high and failure in peeling testing occurs in base metal around weld nugget. Metallographic investigation shows favorable oval nugget shape on cross section, which can improve weld nugget high peeling strength. The ratio of major axis to minor axis is 7 with major axis being 6.5 mm long. Weld nugget mechanical properties such as tension-shear strength is being evaluated and will be presented.
2:30 pm
INFLUENCE OF MICROSTRUCTURE AND THERMAL HISTORY ON THE CORROSION SUSCEPTIBILITY OF AA5083: J.S. Vetrano, R.E. Williford, S.M. Buremmer, R.H. Jones, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352
The utilization of aluminum alloys for lightweight automotive structures can be increased by improved formability and a reduction of stress corrosion cracking (SCC) problems associated with magnesium additions greater than about 3%. We have utilized a series of thermomechanical treatments on several 5xxx alloys (5052, 5082, 5083, 5454 and 5754) to alter the dispersoid density and size, as well as the distribution of eutectic constituents. The aim has been to optimize grain size for specific forming operations and post-formed properties. In addition, the role of the grain size and particle distribution, as well as the magnesium content and microstructure, on the SCC resistance has been investigated. It was found that the grain size could be controlled by the distribution of the dispersoid particles, with a minimum grain diameter of 8 µm achieved in the 5083. The effect of grain size on SCC susceptibility was also evaluated.
3:00 pm
APPLICATION OF THE METAL COMPRESSION FORMING PROCESS FOR THE PRODUCTION OF AN ALUMINUM ALLOY COMPONENT: R.M. Purgert, Precision Metal Forming Co., P.O. Box 25441, Garfield Heights, OH 44125; S. Viswanathan, Metals and Ceramics Division, Oak Ridge National Lab, Oak Ridge, TN 37831-6083
Metal Compression Forming (MCF) is a variant of the squeeze casting process, in which molten metal is allowed to solidify under pressure in order to close porosity and form a sound part. However, the MCF process applies pressure porosity and form a sound part. However, the MCF process applies pressure on the entire mold face, thereby directing pressure on all regions of the casting and producing a uniformly sound part. The process also enhances the solidification rate of the metal promoting a very fine grain structure which results in improved properties. Consequently, the process is capable of producing parts with properties close to that of forgings, while retaining the near net shape, complexity in geometry, and relatively low cost of the casting process. The paper will describe the casting process development involved in the production of a 356 alloy engine mounting bracket, including the use of a filling and solidification model to design the gating and determine process parameters. Tensile and fatigue properties of the component will also be presented and correlated with those of forged components. *Research sponsored by the U.S. Department of Energy under contract DE-AC05-96ORT22464 with Lockheed Martin Energy Research Corporation.
3:30 pm BREAK
4:00 pm
MICROSTRUCTURAL AND TRIBOLOGICAL PROPERTIES EVALUATION OF CHAR-REINFORCED Al-Si ALLOY COMPOSITES: J.U. Ejiofor, R.G. Reddy, Department of Metallurgical and Materials Engineering, The University of Alabama, P.O. Box 870202, Tuscaloosa, AL 35487
The application of carbon-reinforced aluminum composites in electromechanics has continued to attract new research investigations. The factors of interest range from low cost and availability of materials to low-temperature processing methods. This study has investigated the conventional double-compaction, powder metallurgy processing of Al-13.5Si-2.5Mg alloy (wt.%) reinforced with coconut shell chars. The mechanical, physical and relevant tribological properties were determined after achieving the optimum compaction and sintering conditions. Use of optical microscopy, EPMA, SEM and energy dispersive analysis were made in characterising the matrix-reinforcement interfaces, the fracture surfaces and the nature of the adhesive dry wear. At 0.02Vf of the char, the alloy exhibited properties suitable for antifriction applications. Increased additions of the chars resulted in largely reduced strength, hardness and sintered density. This is attributed to poor bonding of the char particles with the matrix alloy. Parallel investigations with palm-kernel shell char as the filler phase yielded identical results. Initial formation of A14C3 in the composites was detected at a sintering temperature of 600°C. Reinforcement of the alloy with chars activated in CO2 to various bum-off percentages were found to yield marginal results.
4:30 pm
ADVANTAGES OF CERAMIC COMPONENTS IN THE LOW PRESSURE CASTING PROCESS FOR ALUMINUM WHEELS: J. Pennemann
Room: 230C
Session Chairperson: Prof. Yasar Kocaefe, Université du Quebec à Chicoutimi, Chicoutimi, Quebec, Canada G7H2B1
2:00 pm
BUTTS CLEANING AT SLOVALCO IMPLEMENTED BY TECHMO: J. Ifju, F. Zannini, F. Marchetti, M. Fontolan, Techmo Car S.P.A., Via R. Colpi, 15/17 35010 Limena (PD) Italy
The best use of anode carbon and bath materials withdrawn from the smelting process by anode changing involves their recycling. In order to provide optimal composition of recycled carbon and bath, a butt cleaning technology is required with the aim to avoid their contamination by each other. A technology and equipment has been elaborated for implementing above objective. Some optimization was fulfilled in order to meet the requirements of the new aluminium smelter implemented by Hydro Aluminium technology, taking into account very tough requirements to the material quality, as well as fitting a piece of equipment into the technology flowsheet planned.
2:25 pm
DUST CONTROL TECHNOLOGY FOR ANODE BUTT RECYCLING: Nathalie Perreault, Betz Water Management Group, Casier Postal 232, Baie Comeau, Québec, Canada G4Z 2G9; Eric Grondin, Engineering Environment and Water Treatment, Reynolds Metals, 100 route Maritine, Baie Comeau, Québec, Canada G4Z 2H7
There are several dust control problems in the Aluminium industry, amongst them is the process of recycling anode butts. In general, prior to being recycled, the butts are cleaned, taken off the hexapod rods and stored and/or shipped to be processed as new anodes. A particular area of concern for fugitive dust during the anode preparation process is anode butt stripping inside the anode rodding room. This process generates a lot of carbon dust. It has been both a health and safety issue, as well as cleaning burden for operating personnel. This paper presents different alternatives, both mechanical and chemical, for controlling fugitive dust, and a decision process for using chemical treatment. In addition, the theory behind the chemical application and a case history will also be presented.
2:50 pm
EFFICIENT ANODE-COLLAR CAST IRON MICROSTRUCTURE: Michael Barstow, 1152 Southvale Road, Pittsburgh, PA 15237
Cast iron is used to secure the steel stub of an anode rod to a carbon block for aluminum reduction cells. The quality is measured by the millivoltage drop across the stub-carbon interface. The electrical resistivity of cast iron varies with it's microstructure, which changes with temperature. Cast iron cannot be simply specified by analysis since it is section sensitive, and the microstructure is affected by minor elements, time, and rate of cooling. If the metallurgical control is limited, collars will develop variable electrical efficiencies. Recycling cast iron callors also causes a change inthe minor element analysis (S,P) which will change the microstructure / electrical resistivity. A cast iron designed for optimum fluidity with low level minor elements will provide lower electrical resistance than one with buildup of Mn, S. Other melting efficiencies are predicted.
3:15 pm BREAK
3:35 pm
AUTOMATIC STUB STRAIGHTENING SYSTEM: Jòn Hjaltalin Magnusson, ALTECH Ltd., Borgartun 18, 105 Reykjavik, Iceland; William Cannon, Portland Aluminium Ltd., Portland, Victoria 3305, Australia
For improving the economy and environment aluminium smelters have increased the automation of diverse tasks. An automatic system has been developed for the task of straightening anode rod stubs instead of cutting them off the rod yoke and welding new onto the yoke. The stub toe-in problem cannot be eliminated, but significant degree of control can be implemented to eliminate its adverse effects and increase the useful life of the stubs and reduce the considerable cost of reparation and stub material. This paper describes the cause of the stub bending in the electrolitic cells together with the details of the new automatic stub straightening system based on preheating the stubs with induction heating coils prior to straightening in a hydraulic cylinder press. Implementation of this straightening system at Portland Aluminium in Australia is also described, where the system was installed in February 1996. The system is installed "in-line" in the P&F overhead monorail and the bending of the stubs is measured automatically for deciding if the straightening is required or not. It will be shown how this system improves the useful life of the stubs leading to significant operational savings for the smelter.
Session Chairperson: Dan J. Thoma, Los Alamos National Laboratory, Materials Science Technology Division, MS G770, Los Alamos, NM 87545
2:00 pm
OPTIMIZATION OF THE ANGULAR WIDENING OF A CAST PLATE: J. Stetina, F. Kavicka, Technical University of Brno, Mechanical Engineering Dept., Technicka 2, 616 69 Brno, CZECH REPUBLIC; J.M. Khodadadi, Mechanical Engineering Dept., Auburn University, Auburn, AL 36849-5341
A 2-D numerical model was used to analyze the temperature field of a vertically cast 1700x600x40mm plate with different angles of widening in its cross section (0 to 4.4°). From the side of the widening, the plate was either isolated (using Plastizol) or non-isolated. A non-isolated plate has an optimum angular widening of 3° and the widening of 2° lies on the boundary of the origins of internal defects (e.g. shrinkages). The isolated plate has an optimum angle of widening of 2°. Using the calculations it is possible to predict that the plate itself will have the same internal quality with a widening of 3° after crystallization without isolation as with 2° of widening with the isolation. The knowledge gained in this study can lead to the reducing of the volume of liquid metal needed and to the lowering of costs for working the surface. (Authors are grateful to the US-Czech Science and Tech. Program for support of this research.)
2:20 pm
TEXTURE EVOLUTION IN 
-TiAl SHEETS PRODUCED VIA THE MELT OVERFLOW RAPID SOLIDIFICATION PROCESS: M.L. Weaver, Center for Nonlinear and Nonequilibrium Aeroscience, Florida A&M University, 1800 E. Paul Dirac Rd., Rm. A337, Tallahassee, FL 32306-4005; H. Garmestani, Dept. of Mechanical Engineering, FAMU-FSU, College of Engineering, Florida A&M University, Tallahassee, FL 32306; G. Das, United Technologies, Pratt & Whitney, P.O. Box 109600, West Palm Beach, FL 33410-9600
The production of -TiAl foils by conventional ingot metallurgy involves casting ingots, hot forging ingots into billets, followed by several hot rolling, heat treatment, and surface grinding sequences. These methods, however, can result in production losses in excess of 50%. Recently, researchers at NASA-Langley and Ribtec have developed the Plasma Melt Overflow Process which combines plasma arc skull melting in a water cooled copper crucible with Melt Overflow Rapid Solidification Technology (MORST) allowing near-net-shape processing of strips that can be hot pack rolled to foil gauge with minimal production losses. Preliminary results indicate that foils produced via this method exhibit finer more uniform microstructures, higher strength, and higher ductility than comparable ingot metallurgy foils. In this investigation texture evolution has been evaluated in -TiAl alloys sheets produced via this technique. The results are compared with recent studies of texture in conventionally processed -TiAl.
2:40 pm
LIQUID METAL-SOLID METAL REACTIONS WITH INTERMEDIATE INTERMETALLIC COMPOUND FORMATION: Robert J. Hanrahan Jr., Dan J. Thoma, Loren A. Jacobson, Los Alamos National Laboratory, Materials Science Technology Division-MST-6, TA 3, MS G770, Los Alamos, NM 87545
The study of liquid metal reactions have in most cases involved systems where the solid is dissolved by the liquid. The case where an intermetallic compound forms between the two metals has not been thoroughly investigated. As an example of this class of system we have chosen to study the reaction of Beryllium (solid)--with Rare Earths (liquid). Although most of the Be-RE phase diagrams are poorly defined in terms of solubility and the location of the eutectics, all have been characterized to the extent of having a single intermetallic compound with a melting point in excess of 1500°C and two simple eutectics with minimal solubility range in the solid phases. The intermetallic in each case is the same structure, Mbe13. The reaction kinetics, measured using the thickness of the intermetallic layer at various times, can be described by a parabolic model suggesting that the reaction is controlled by diffusion through the intermetallic. Variations in kinetics are observed between the various systems which are analyzed considering factors such as melting point of the liquid (eutectic temperature), Be solubility in the liquid, and compositional range of the intermetallic.
3:00 pm
POTENTIAL OF SQUEEZE CASTING ALUMINUM (Al) AND ALUMINUM-REINFORCED METAL MATRIX COMPOSITES (Al-MMC) FOR BOTH THE AUTOMOTIVE AND ARMY GROUND VEHICLE APPLICATIONS: Paul J. Huang, Army Research Laboratory, AMSRL-MA-B, APG, MD 21005; Robert Purgert, Precision Metal Forming Co., P.O. Box 25441, 9545 Midwest Ave., Garfield, OH 44125
The main driving forces for lightweight materials for the automotive industry and military applications are cost effectiveness, high-strength, and wear resistance. Precision Metal Forming Company (PMF) has developed a new and innovative squeeze casting process called metal compression forming (MCF). MCF integrates the deceptively simple concept of solidification of metal under direct pressure with closed die forging and low-pressure permanent-mold fill technologies. This hybrid process therefore combines the advantages of traditional direct squeeze casting and low-pressure permanent-mold casting. This study discusses property advantages attained with this process over traditional aluminum casting processes.
3:20 pm BREAK
3:30 pm
KINETIC COMPETITION DURING DUPLEX PARTITIONLESS SOLIDIFICATION: Donald R. Allen, John H. Perepezko, Dept. of Mat. Science and Eng., University of Wisconsin - Madison, Madison, WI 53706
A structure composed of both partitionless face-centered cubic (fcc) and bodycentered cubic (bcc) phases has been observed following high undercooling solidification of nickel-vanadium (Ni-V) alloys for the composition range 4751.7 at.% V. Transmission electron microscopy analysis has identified regions in which fcc and bcc grains on the order of 100 nm in size coexist in a duplex structure. Splat-quenched foils were analyzed both in plan view and cross section. This structure has revealed a unique set of kinetic conditions that can allow for duplex solidification, since similar nucleation and growth rates are required for a range of compositions. A nucleation and growth kinetics analysis has been developed to describe the conditions under which this structure may form. The duplex partitionless structure previews an entirely new class of microstructures achievable during high undercooling solidification processing. The support of NASA (NAG8-1278) is gratefully acknowledged.
3:50 pm
MICROSTRUCTURAL EVOLUTION IN Al-Cu-Si ALLOY MELT SPUN RIBBONS: K.-P. Cooper, J D. Ayers, H.N. Jones, R. Vardiman, Naval Research Laboratory, Code 6321, Washington, DC 20375-5343
Several Al-Cu-Si alloys were melt spun to produce stable, fine grain microstructures that would be amenable to superplastic deformation and consolidation. Scanning electron microscopy of the ribbon cross-sections showed two distinct alternating microstructural morphologies suggesting transitions in solidification behavior. One consisted of intimately interlocked Al and A12Cu () phases with dispersed Si. The other consisted of equiaxed dendritic Al with inter-dendritic and Si. The latter was found usually in the middle portion of the ribbon cross-section. The solidification mechanism for the interlocked structure is not understood, but its formation may have involved multiple nucleation of the phase or a degeneration of a more regular, but unknown, initial structure as the ribbon cooled to ambient temperature. The equiaxed dendritic structure probably arose as a result of independent nucleation events in the supercooled liquid ahead of the solid-liquid interface. Transmission electron microscopy revealed Al grain sizes varying from 1µm near the wheelside to 8µm with subgrains near the free surface and different shapes and sizes for and Si in the interlocked and dendritic regions.
4:10 pm
HEAT TRANSFER AND SOLIDIFICATION IN UPCASTING OF COPPER: K. Harkki, L. Holappa, Helsinki University of Technology, Laboratory of Metallurgy, Vuorimiehentie 2, FIN-02150 Espoo Finland
An extensive study has been conducted to find out heat transfer and solidification behaviour in the copper upcasting mold. The casting direction in the upcasting process is vertically upwards and it has applications for copper and copper based alloys. The study combined industrial scale measurements, mathematical modeling and me/allographic examination of the cast rod samples. The industrial scale measurements involved temperature measurements with 14 thermocouples inserted in the copper jacket of the mold. Also temperature measurements of the cooling water were carried out. Axial heat flux profiles were determined quantitatively from the temperature measurements and they were used as boundary condition for the mathematical model calculations. The heat flux was observed to have a maximum value near the meniscus and to decrease rapidly with increasing distance up to the mold. Temperature profiles in the cast rod were simulated using a model based on finite element method. The results of the simulations were utilized for further understanding of the heat transfer and solidification process in the mold. Copper rod samples were examined to evaluate crystal growth of the cast copper rod. The results of the investigation work can be utilized to optimize the copper upcasting process.
4:30 pm
RISERING EFFECT ON THE MICROSTRUCTURE OF ASTM F-75 INVESTMENT CASTINGS: M. Castro, L.F. Ramirez, M. Herrera, H. Maucha, M. Mendez, J. Mendez, Centro de Investigacion y Estudios Avanzados del IPN-Unidad Saltillo, Carr. Saltillo-Monterrey Km. 13, 25000 Saltillo, Coahuila, Mexico
4:50 pm
THE CONTROL OF DENDRITE TIP GROWTH RATE AS A WAY TO PROMOTE GOOD MICROSTRUCTURES IN DENRITIC ALLOYS: H. Mancha, F. Cepeda, M. Herrera, J. Mendez, M. Castro, M. Mendez, Centro de Investigacion y de Estudios Avanzados del IPN-Unidad Saltillo, Carr. Saltillo-Monterrey Km. 13-Apdo. Postal 663, 25000 Saltillo, Coahuila, Mexico
5:10 pm
MODELLING QUENCHED IN SHORT-RANGE ORDER IN METALLIC ALLOYS: A. Varschavsky, E. Donoso, Universidad de Chile, Facultad de Ciencias Flsicas y Matematicas IDIEM, Casilla 1420, Santiago, Chile
Using a rate vacancy loss equation and an overall rate constant for order establishment, a model for describing the roles of quench temperature, quench rate and vacancy sink density is proposed. This model allows computation of the retained value of the first short-range order parameter of quenched binary alloys and the prediction that the most highly disordered state obtainable occurs with quenches from intermediate temperatures. Numerical results were tested against experimental data based on energetic analysis of differential scanning calorimetric traces pertaining to a reordering process towards the equilibrium state. Kinetic evaluations of these traces yield experimental estimates of quenched-in vacancy concentrations. Good agreement between modelled and experimental assessments was obtained in Cu at.% Zn alloy.
Room: 230B
Session Chairperson: Gregory J. Hildeman, Aluminum Company of America, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069
2:00 pm
MORPHOLOGICAL ASPECTS OF INCLUSIONS IN AA3104 D&I CAN STOCK ALLOY: Xiangwen Wang, Manufacturing Technology Laboratory, Corporate Research & Development, Reynolds Metals Company, 3326 E. 2nd St., Muscle Shoals, AL 335661
Metallic and non-metallic inclusions have long been recognized as one of the most important quality issues for aluminum can body alloys. Existence of the inclusions is often the cause of pinholes and high tear-off rate in the canmaking process. They also impose severe complications for alloy down-gauging. This paper presents the morphological aspects of the major inclusions commonly seen in AA3104 can stock alloy. The potential sources which may introduce inclusions in the alloy are also described. Some case studies are conducted to isolate the inclusions for characterization. The results can be utilized for understanding the mechanism of the inclusion formation and selection of proper materials in dealing with the molten alloy prior to ingot casting in order to minimize or eliminate the potential inclusion sources.
2:20 pm
USE OF MULTIPLE MOLTEN METAL QUALITY INDICATORS TO ASSESS IMPACT OF FILTRATION AND FLUXING MODIFICATIONS ON INTERNAL QUALITY OF PLATE PRODUCTS: Michael M. Niedzinski, Reynolds Metals Company, McCook Sheet & Plate Plant, 1st Avenue & 47th Street, McCook, IL 60525-3294
Feasibility of modifying the molten metal filtration system used on aircraft plate alloys was examined using LiMCA, LAIS, AlSCAN and Ramsley tests with attempts to correlate to final ultrasonic quality of the final product. Simultaneously, impact of alternate fluxing system on an ultrasonic quality was examined using aforementioned tests. Sensitivity of the tests vis-à-vis practice changes is discussed.
2:40 pm
EVALUATION OF THE EFFICIENCY OF CERAMIC FOAM AND PARTICLE BONDED CARTRIDGE FILTRATION SYSTEMS: N.J. Keegan, Foseco International Ltd., 285 Long Acre, Nechells, Birmingham B7 5JR, United Kingdom; W. Schneider, H.-P. Krug, VAW aluminium AG, Georg-von-Boeselager-Str.25, D-53117 Bonn, Germany; V. Dopp, Foseco GmbH, Postfach 1220, D-4280 Borken, Germany
A joint programme was set up between Foseco and VAW aluminium AG in order to establish data on the relevant positions of fine foam ceramic filters and more specifically, to investigate the performance characteristics of bonded particle tube cartridge filter systems. The object of this work was to generate fundamental data on the filtration efficiency of a number of in-line treatment units used singly and in combination. The impact of these treatments on metal quality was determined by LiMCA, PoDFA and LAIS for carefully controlled plant conditions. This paper expands on the result of the first phase of the programme which was presented to TMS in 1996. It goes on to present results of inclusion size distribution removal data for medium and fine pore CFF´s and for the cartridge tube filter. Results of metallographic examination of spent tubes and ceramic foam reported along with PoDFA data of typical metal. After summarizing the relative efficiencies of each of these systems it also includes results of the impact of a degassing unit run alone and in combination with a ceramic foam filter.
3:00 pm
CHARACTERISTICS OF PARTICULATE CAPTURED BY A RIGID TUBE FILTER: Glenn Mabry, W.C. Setzer, KB Alloys Inc., Corporate Technology, 3293 McDonald Road, Robards, KY 42452; John Kaems, Aluminum Company of America, Alcoa South Plant, 300 North Hall Road, Alcoa, TN 37701; Douglas Granger, Aluminum Company of America, Alcoa Technical Center, Alcoa Center, PA 15069
Spent rigid tube filter sections were examined following a number of alloy 3004 casts. Examination revealed the presence of the phases normally found in 3004 which formed during solidification, as well as the capture of salt, oxide and grain refiner particulate. Chemical and SEM analysis revealed that, for the most part, two mechanisms of filter blockage appear to be operative. In addition to filter cake buildup, on a portion of the tube, some of the 1-2 micron grain refiner particulate have reacted within the filter body forming coarser complexes. The blockage mechanisms and their impact on filter life and filter design and usage are discussed.
3:20 pm
INFLUENCE OF Al-Ti GRAIN REFINER ON THE FILTER LIFE: T. Yoshida, K. Kakimoto, Mitsui Mining & Smelting Co. Ltd., TKR Division, 2-26-6 Higashinihonbashi, Chuo-ku Tokyo 103, Japan; A. Hane, T. Nishizaka, K .Hoshino, Mitsui Mining & Smelting Co. Ltd., Corporate R&D Center, 1333-2 Haraichi, Ageo-shi Saitama 362, Japan
It has been known that grain refiner such as Al-Ti and Al-Ti-B would influence on the filter life in molten aluminum filtration. A new experimental technique was conducted to make clear the influence of Al-Ti master alloy on a filter life of Rigid Media Filter (RMF). It is shown that the concentration of titanium in the grain refiner and holding time after adding the grain refiner affect the filter life.
3:40 pm BREAK
3:50 pm
DEPOSITION OF PARTICLES TO A BUBBLE: Elin Haugland, Thorvald A. Engh, Norwegian University of Science and Technology, Department of Metallurgy, Alfred Getz Vei 2b, N-7034 Trondheim, Norway
Experiments have been performed to study turbulent deposition of particles to a bubble. Water, containing particles, flowed down through a column. Bubbles were let into the column through a glass capillary tube in the lower part of the column, and then held at the capillary tube. The experiments were carried out with quartz particles in both clean distilled water and in water which amine was added. The bubble was allowed to rise into a collector tube. To determine the amount of particles collected by the bubble, the water/particle dispersion was filtered and the remaining mass was weighted. Velocities and turbulence were measured by laser doppler velocimetry. Particle-bubble collisions were studied with a high-speed videocamera. The results indicate that particle collection on the bubbles reaches saturation. The particles seem to have a certain residence time at the bubble surface, before they leave the bubble.
4:10 pm
ENHANCED FLOTATION OF INCLUSIONS TO BUBBLES DUE TO TURBULENCE: Rune Gammelsæter, Stein Tore Johansen, SINTEF Materials Technology, N-7034 Trondheim, Norway; Knut Bech, The Norwegian University of Science and Technology, N-7034 Trondheim, Norway
Experimental results indicate that turbulence may enhance the flotation rate of non-metallic inclusions to bubbles significantly. In this paper possible flow phenomena responsible for such effects are investigated. We recognize that the turbulent flow consists of a spectrum of eddy sizes. The eddies larger than the bubble diameter can only displace the bubble. Only the smaller eddies contribute to an enhanced turbulent deposition of inclusions. The turbulent flow over single bubbles are computed and the turbulent trajectories of inclusions approaching the bubbles are calculated. The resulting collection efficiencies are discussed and compared to available experimental results.
4:30 pm
KINETICS OF INCLUSION REMOVAL FROM MOLTEN ALUMINUM UNDER AN APPLIED ALTERNATING MAGNETIC FIELD: Ashish D.Patel, Nagy El-Kaddah, Department of Metallurgical & Materials Engineering, The University of Alabama, P.O. Box 870202, Tuscaloosa, AL 35487-0202
Electromagnetic filtration is an emerging technology for purification of molten metals. This particle separation method relies on the huge difference in the electrical conductivity of the metal and non-metallic inclusions to drive the motion of the under an applied force field. The principle of electromagnetic separation will be briefly reviewed together with methods of generating a force field in molten metals. Also described is an induced current separator for the removal of non-metallic inclusions from molten aluminum. The key feature of this system is that the force field has no stirring component, which is necessary to prevent particle entrapment within flow eddies. The system was used to investigate the kinetics of inclusion removal from molten aluminum using 100 and 200µ size particles at low applied magnetic field of 0.015 T. The results show complete removal of these inclusion particles under these conditions and particle migration in the melt occurs in a direction opposite to the force field, as predicted by the theory. Analytical expression was developed to predict the rate of inclusion removal in induced current systems. The experimentally determined rate was found to be in good agreement with theoretical predictions. The scale-up of the system for industrial applications will be discussed.
4:50 pm
CONSISTENCY OF INCLUSIONS IN PURE MAGNESIUM: Per Bakke, Dag Ove Karlsen, Norsk Hydro a.s., P.O. Box 2560, N-3901 Porsgrunn, Norway; Jean-Alain Laurin, André Provost, Norsk Hydro Canada Inc., 7000 boul. Raoul-Duchesne, Bécancour, Québec, Canada G0X 1B0
In order to examine the consistency of metal quality with respect to oxide inclusions, salts and intermetallic particles, filter samples were taken randomly from the casting chamber during normal production of pure magnesium at Norsk Hydro Canada in 1995. The contents of oxide particles, oxide films, salts and intermetallic particles were measured by optical microscopy and image analysis of the sliced and polished filter samples. The results indicate that the contents of oxide particles, oxide films, salts and intermetallic particles are low and consistent; normally well below 1 mm3/kg for all types of inclusions. Oxide inclusions and intermetallic particles are usually smaller than 50 µm and 20 µm, respectively. The filter sampling method and analysis technique used in the quantitative microscopy are discussed in some detail, emphasising advantages and drawbacks. The impact of the most common inclusions in pure magnesium on aluminium alloy quality is discussed from a thermodynamic point of view.
5:10 pm
THE EFFECTS OF MAGNESIUM, ATMOSPHERE COMPOSITION, AGITATION AND TEMPERATURE ON THE SURFACE OXIDE FILM FORMATION AND MELT INCLUSION CONTENT IN Al-Mg ALLOYS: Daryoush Emadi, Mihriban Pekguleryuz, Alcan-UQAC Chair in Solidification and Metallurgy of Aluminum, University of Quebec at Chicoutimi, Local 4-333 Chicoutimi, Quebec, Canada G7H 2B1
To obtain high quality ingots, the generation of inclusions must be prevented during the various stages of liquid metal manipulation. In an attempt to understand the nature of oxide film generation, the oxidation behaviour of Al-Mg melts with different Mg contents of 1 wt%, 3 wt% and 5 wt% were studied in air, argon and carbon dioxide. Moreover, the effects of agitation and temperature on the nature of melt surface oxide films were investigated. For each condition, the growth process and the morphology of the surface oxide films behaved differently. In addition, this study used the Liquid Metal Cleanliness Analyzer (LiMCA) and Porous Disk Filtration Apparatus (PoDFA) to investigate the effect of melt agitation and Mg content on the melt inclusion content. The results indicate that agitation and magnesium increase both the melt inclusion content and the average inclusion size. In addition, the oxide film removal from the surface of the melt affects the melt oxidation behaviour significantly.
Room: 330C
Session Chairperson: Philip Nash, Illinois Institute of Technology, METM Dept., Chicago, IL 60616
2:00 pm INVITED
MECHANICAL BEHAVIOR OF BULK NANOSTRUCTURED Fe/Cu ALLOYS: Walter W. Milligan, John E. Carsley, Stephen A. Hackney, Metallurgical and Materials Engineering, Elias C. Aifantis, Mechanical Engineering and Engineering Mechanics, Michigan Technological University, Houghton, MI 49931
The mechanical behavior of bulk iron alloys containing 10% copper was investigated. Grain sizes were varied by processing, and ranged from 45 nm to 900 nm. Deformation in all cases occurred by intense localized shear banding as the first and only mechanism of plastic deformation, from the yield point until fracture or buckling. Mechanical response was elastic-perfectly plastic. Shear band angles and an asymmetry of the yield strength in tension and compression both indicated the possibility of a pressure-sensitive yield criterion. Continuum models based on this approach proved promising. Shear band widths increased with microstructural coarseness, and were correlated successfully with a gradient plasticity approach. A number of similarities between the behavior of these alloys and amorphous materials such as metallic glasses and amorphous polymers will be discussed.
2:30 pm INVITED
DEFORMATION MECHANISMS IN METALLIC NANOLAMINATES: Tim Foecke, Metallurgy Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-0001
It has been seen that the introduction of a nanolayered microstructure can increase the yield strength and hardness of a material to many times that of a conventional microstructure. The deformation mechanisms that operate (or fail to operate) at such a small length scale is not understood and is only beginning to be investigated. An in situ TEM deformation experiment has revealed a dislocation generation mechanism that operates in Cu/Ni single crystal nanolaminates. Dislocation loops nucleated at several locations within a Ni layer at the Cu/Ni interface, and were seen to expand until they intersected the next interface. Two Orowan bows were then seen to expand in opposite directions along the layer. Discussion will include possible nucleation sites and thin film artifacts, as well as presentation of other TEM observations of fracture and deformation in metallic nanolaminates.
3:00 pm INVITED
DEFORMATION AND FRACTURE BEHAVIOR OF HIGH-STRENGTH Al94(V2,Ti)4Fe2 ALLOYS CONSISTING OF NANOGRANULAR AMORPHOUS AND Al PHASES: Akihisa Inoue, Hisamichi Kimura and Kenichiro Sasamori, Institute for Materials Research, Tohoku University, Sendai 980-77, Japan
A new mixed structure consisting of nanogranular amorphous and fcc-Al phases was formed in melt-spun Al94V4Fe2 and Al94V2Ti2Fe2 alloys and the complete replacement of V by Ti causes the change into a mixed structure of nanogranular Al phase surrounded by an amorphous phase. The structural change appears to result from the difference in solidification processes, i.e., the formation of the amorphous phase as a primary phase, followed by the Al phase for the V-containing alloys and the primary formation of the Al phases and then the amorphous phase for the V-free alloy. The former type is a unique process which is observed in the limited alloys containing V with icosahedral-forming ability and low diffusivity. The coexistence of the nanogranular amorphous phase is expected to affect significantly the mechanical strength, deformation behavior and fracture mode. These mixed phase alloys have good bending ductility and exhibit high tensile strength of 1390 MPa for Al94V4Fe2, 1370 MPa for Al94V2Ti2Fe2 and 1320 MPa for Al94Ti4Fe2 at room temperature. The fracture mode is analogous to that for amorphous alloys. At the meeting, we will report the detailed results on the temperature dependence of mechanical strength, deformation behavior and fracture mode for the nanogranular amorphous alloys.
3:30 pm BREAK
3:45 pm
FATIGUE BEHAVIOR OF NANOCRYSTALLINE AND ULTRAFINE-GRAINED Cu: S.R. Agnew1, R.Z. Valiev2, J.R. Weertman1, 1Northwestern University, Evanston, Illinois, 2Institute for Metals Superplasticity Problems, Russian Academy of Sciences, Ufa, Russia
One of the tests that can give insight into the deformation mechanisms of nanocrystalline and ultrafine-grained metals is fatigue. In the past, we investigated the microstructural stability of nanocrystalline (~20nm) Cu under cyclic loading. We observed good stability of the microstructure using XRD. An SEM study revealed extrusions on the surface, similar to those of persistent slip bands, oriented in the direction of maximum shear. The presence of extrusions suggests deformation by a shearing process. To augment our understanding of this phenomenon, we have begun studying the fatigue behavior of UFG Cu with a grain size of about 200nm. There we have observed similar extrusions as in the previous study. We are investigating the microstructural stability of this metal using the TEM. We will discuss our experimental results and their contribution to our understanding of the deformation mechanisms operative in pure FCC metals with ultra-fine microstructures.
4:05 pm
COHERENT SOLUBILITY LIMITS OF '-TYPE PHASES IN FOUR BINARY Ni-BASE ALLOYS: F. Li and A.J. Ardell, Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095-1595
The equilibrium solubilities of coherent phases can be affected by the initial solute concentration of the alloy, Xo. This differs completely from incoherent equilibrium, wherein the solubility limits are independent of Xo. To investigate the relationship between coherent equilibrium solubility and Xo, Ni-Al, Ni-Ga, Ni-Ge and Ni-Ti alloys, each with several different values of Xo, were prepared by arc melting, rolling into sheet, solution, treating, and aging for times up to 1632h at 500°C. The variation of solute concentration in the Ni-rich matrix, X, with aging time, t, was followed using measurements of the ferromagnetic Curie temperature. The equilibrium solubilities, Xeq, were estimated by plotting the data as X vs. t-1/3 and extrapolating to t-1/3=0 (t=
), thus presupposing that coarsening of the expected '-type phases in all four alloys is responsible for the variation of X. Xeq is unequivocally dependent on Xo, but whereas Xeq in the Ni-Al, Ni-Ga and Ni-Ti alloys increases with increasing Xo as predicted theoretically by Ardell and Maheshwari, Xeq in the Ni-Ge alloy system decreases. TEM is currently in progress to confirm the identity and state of coherency of the precipitate phases present. This work is supported by the National Science Foundation
4:25 pm INVITED
SYNTHESIS, STRUCTURE AND PROPERTIES OF Cu/Nb NANOLAYERED COMPOSITES: H. Kung, A.J. Griffin, Jr., Y.C. Lu, M.F. Hundley, T.-E.Mitchell, M. Nastasi, Los Alamos National Laboratory, MS K765 Los Alamos, NM
The effect of composition wavelength (
) on the structure, electrical resistivities and mechanical properties of Cu/Nb nanolayered composites were evaluated. The as- sputtered multilayers, with varying between 25Å and 1000Å, exhibit a strong Kurjudmov-Sachs orientation relationship between the close packed planes and directions of the fcc Cu and bcc Nb: <110>{111}Cu//<111>{l10}Nb. As ~decreases to 11Å, the entire multilayer shows bcc structure. The Cu grows pseudomorphically on the bcc Nb which acts as a template for the normally fcc Cu. The layers are heavily strained and there is a high density of dislocations present. As increases from 11Å to 25Å, it is suspected that there is enough loss of coherency to transform bcc Cu martensitically to fcc Cu. The mechanical and electrical properties of nanolayered Cu/Nb composites with Cu in either fcc or bcc structure will be reported.
Room: 332
Session Chairpersons: Puligandla Viswanatham, Texas Instruments Inc., Circuit Card Assemblies, 2501 South Highway 121, Mail Stop 3450, Lewisville, TX 75067; Walter L. Winterbottom, Reliability Consultant, 30106 Pipers Lane Court, Farmington Hill, MI 48331
2:00 pm INVITED
ISSUES AFFECTING RELIABILITY OF SURFACE MOUNT SOLDER JOINTS: Sung K. Kang, IBM Corp., T.J. Watson Research Center, Room 37-250, P.O. Box 218, Yorktown Heights, NY 10598
Surface mount technology (SMT) has been practiced as the principal soldering method for the assembly of printed circuit boards (PCB) last ten years. SMT packages connected by solder joints occupy more than two thirds of a PCB real estate. SMT packages consist of both conventional formats such as small outline package (SOP), small outline 'J' leads (SOJ), plastic leaded chip carriers (PLCC), or quad flatpack (QFP), and fairly new packages such as thin small outline package (TSOP), tape carrier package (TCP), chip-on-board (COB), ball grid array (BGA), and many more. In this talk, recent developments of SMT soldering technologies are briefly reviewed, followed by discussion of several technical issues affecting the reliability of SMT solder joints. The subject matters to be discussed include solder joint defects, microstructure, interfacial reactions, thermal fatigue, and Pb-free solders.
2:25 pm INVITED
RELIABILITY CONSIDERATIONS WHEN CHOOSING WATER SOLUBLE FLUX FOR ELECTRONIC ASSEMBLY: Laura Turbini, Georgia Institute of Technology, School of Materials Science and Engineering, 778 Atlantic Drive, Atlanta, GA 30332
There is a need for a fundamental understanding of the interaction of processing chemicals such as fusing fluids, soldering fluxes and cleaning agents with printed wiring board substrates. This need is driven by two factors: (1) the increased density of today's electronic products creates voltage gradients which are high enough to enhance degradation modes which are not important for less dense circuitry, and (2) the elimination of chlorofluocarbons (CFCs) and other ozone depleting cleaning agents due to their destructive effect on the stratospheric ozone layer has lead to a proliferation of new soldering fluxes and cleaning agents whose interactions with the printed wiring board (PWB) are not well characterized. Water soluble fluxes have been effectively used in high volume electronic manufacturing operations for a number of years. Their use has increased dramatically as they provided an opportunity to eliminate CFCs in the cleaning process. They provide excellent soldering with low defect levels and with a proper cleaning process can produce highly reliable electronic circuits. However, some water flux and fusing fluid formulations contain ingredients which can have deleterious effects on the reliability of a product under certain operating and use conditions. There is a failure mechanism known as conductive anodic filament formation (CAF) which has been observed in PWBs boards treated with certain water soluble fluxes. This failure mode involves a debonding of the epoxy-glass interface and the formation of a conductive filament which grows along this interface from anode to cathode. This paper will report on those chemicals which tend to enhance this failure mode and will make recommendations on assuring the reliability of electronic assemblies.
2:50 pm INVITED
INFLUENCE OF COMPONENT SOLDERABILITY ON RELIABILITY OF SOLDER JOINTS: Colin Lea, National Physical Laboratory, Teddington, Middlesex TW11 0LW, UK
The commonest mode of service failure of solder joints on circuit board electronics assemblies is low-cycle fatigue cracking from differential expansion during power-up and power-down of the equipment. The resistance of a solder joint interconnection to fatigue cracking is governed by both its microstructure and its geometry. In turn, these are both governed by the soldering process and the manner in which the molten solder wets and flows on the component metallisation; the component's solderability. Data will be presented, for surface mount assemblies, that relate component/circuit board solderability to solder fillet shape, and in turn to solder joint reliability. The best fillet geometry varies markedly between the many different styles and compositions of metallisation found on surface mounting components. Furthermore, the pass/fail criteria of solderability measurements are not necessarily related to the required solder fillet geometry for best reliability. Both infra-red reflow and wave soldering have been used, since the use of solderability on solder fillet shape may be quite different for the different manufacturing routes.
3:20 pm INVITED
SOLDERABILITY AND SURFACE MOUNT SOLDER JOINT SHAPE PREDICTION: D.J. Lewis1, M.R. Notis1, G.C. Munie2, D.M. Noctor3, 1Materials Science and Engineering Department, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015; 2Lucent Technologies, Naperville, IL 60563; 3Lucent Technologies, Bell Laboratories, Room 22W-208eo, 555 Union Boulevard, Allentown, PA 18103
As a part of a program supported at AT&T Network Systems for continuous improvement in solderability, solderability modeling, and solderability specifications, an assembly trial was performed to determine the correlation of assembly yield to different combinations of solder volume, component coplanarity, component aging, and solder alloy. Through the use of wetting balance data and assembly yield statistics, soldering process charts correlating assembly yield to solder volume and coplanarity show that severe lead surface finish degradation would require (unmanufacturable) component coplanarities of less than 1 mil to maintain 100% assembly yield. The 132 I/O, 25 mil pitch, BQFPs were pre-conditioned using high temperature and humidity to degrade lead surface finish. Standard tin-lead solder and three commercially available lead-free solders were used to vary the solder wetting characteristics. To determine a process window for solderability, solder volume was varied by using two different stencil thicknesses, and coplanarity was measured to determine the effect of mechanical tolerance. Electrical continuity and visual inspection showed that assembly yield decreased with decreasing solder volume, poorer mechanical tolerance, and increased component aging time. Wetting balance data showed trends for aging conditions, but a correlation to coplanarity was not found. Contact angle results indicate that tin-lead had best wetting properties however this conflicts with assembly trial results where tin-lead had the higher failure level than the lead-free alloys. The goals of this project were: to further define a process window for solderability with tolerances for volume and coplanarity distributions; (2) to refine solderability specifications; and (3) to verify a computer model used to assess solder joint geometry and joint quality based on solder alloy and component lead properties. Assembly yield was examined based on different combinations of solder volume, component coplanarity, component aging, and solder alloy.
3:45 pm BREAK
3:55 pm INVITED
A SIMPLE DESIGN TOOL FOR EVALUATING LOW CYCLE SOLDER FATIGUE OF PACKAGE TO BOARD INTERCONNECTIONS: Ted Carper, Robert Von Mayr and Puligandla Viswanatham, Texas Instruments Inc., Circuit Card Assemblies, 2501 South Highway 121, Mail Stop 3450, Lewisville, TX 75067
Low cycle solder joint fatigue analysis is an important aspect of assessing the package to board solder interconnection performance of circuit card assemblies. A simple analysis tool that takes into account the significant environmental conditions for storage, operation, transportation, etc., and calculates the number of cycles to failure for a given set of input parameters is described. These parameters include coefficient of thermal expansion (CTE) of individual elements of the assembly structures, temperature, duration, number and frequency of cycles. Both leadless and leaded component configurations are included in the design of this tool. Lead stiffness for leaded components are calculated using equations published in the literature.
4:20 pm INVITED
QUALIFICATION OF BALL GRID ARRAY ASSEMBLIES FOR SPACE FLIGHT APPLICATIONS: Sharon Walton, Kirk Bonner, Electronic Packaging and Fabrication Section, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109
JPL, in a partnership with an industrial consortium, is engaged in the investigation of reliability and quality issues of Ball Grid Array Packages as they may be applied to space flight electronics. Performing tests to determine the solder joint reliability of assemblies using BGAs under temperature cycling is proving to be a real challenge for test engineers. It was recognized early in the program that a large number of the BGA solder joints would be under test simultaneously and that some sort of computer based assistance would be required to accurately track the failures and the time at which they occurred. JPL has been using the National Instrument LabVIEW software and SCXI hardware to set up our system. The data acquisition program, DAQ.VI, was written around LabVIEW, a graphics based operating system. The program controls the temperature chambers, gathers data from the interface cards, logs data, and provides operator interface. This system can monitor over 1500 channels for electrical continuity and 32 channels for temperature. This software/hardware system greatly simplifies the task of monitoring and tracking failures and the conditions when the failures occurred of a large number of solder joint channels through the automatic gathering and recording of the test results onto a personal computer data base.
4:45 pm
SOLDER JOINT INTEGRITY IN TESSERA'S µBGA PACKAGE: Rao K. Mahidhara1 Vern Solberg, Tom DiStefano1 and Steve Greathouse2, 1Tessera Inc., 3099 Orchard Drive, San Jose, CA 95134; 2Intel Corp., CH6-315, 5000 W. Chandler Blvd., Chandler, AZ 85226
Chip-scale packages (CSP) are miniaturized IC packages that are being developed for applications ranging from memory chips to advanced high-performance processors. Adaptable to volume manufacturing, this type of package offers the performance and size advantages of a bare die, while conforming to the established infrastructure for electronic assembly. Tessera's µBGA belongs to this new family of CSP, wherein the need to underfill the device has been eliminated. The reliability of solder joints in Tessera's µBGA package is presented. Modeling studies on solder joint integrity have been conducted via finite element analysis (FEA) to predict stress and strain distributions at the solder ball-joint interfaces and potential failure points. The modeling work is complimented by studies involving ball shear testing and, intermetallic growth via optical/SEM/EDAX techniques following long time static annealing and temperature cycling. These reliability studies are suggestive that Tessera's µBGAs are robust packages.
5:05 pm
MECHANICAL AND CREEP CHARACTERISTICS OF Sn-3.5Ag FOR SOLDER-JOINT RELIABILITY: Hong Yang*+, P. Deane*, P. Magill* and K.L. Murty+*, *Microelectronics Center of North Carolina, Research Triangle Park, NC 27709; +North Carolina State University, P.O. Box 7909, Raleigh, NC 27695
Constant-load creep and stress relaxation tests of Sn-3.5Ag solder alloy were performed at high homologous temperatures from 25°C to 180°C. Single lap shear tests were conducted on joined flip chip packages with 33X33 area array of Sn-3.5Ag solder bumps. Tensile creep tests were performed on bulk solder specimens. The steady-state strain-rates span 7 orders of magnitude ranging from 10-9 to 10-12 (1/s). The apparent activation energy of creep was found to be 0.57 ev. The stress exponent (n) in the power-law creep equation is found to be about 10 which is unusually high compared to that for many other metals. A constitutive equation relating stress, temperature and strain-rate for Sn-3.5Ag solder alloy was established. Low-temperature dislocation-climb deformation mechanism (with dislocation-pipe diffusion) is believed to be dominant in the medium-to-high stress region with power-law breakdown at very high stresses. Numerical simulations of a flip chip package were performed to characterize the failure modes. The effects of different design parameters were studied with regard to strain accumulation and stress distribution in the package under thermal cycles. Recommendations are made for design optimization. This work has been supported by the Microelectronic Center of North Carolina.
5:25 pm
LEAD FINISH COMPARISON OF THREE LEAD FREE SOLDERS versus EUTECTIC SOLDER: Mark A. Kwoka, Dawn M. Foster, Harris Corporation, Semiconductor Sector, P.O. Box 883, Melbourne, FL 32902
The use of lead in electronics manufacture will probably be disallowed in the not too distant future. While data is currently being taken regarding the material properties of lead free solders, very little has been published regarding how the new lead free solders will respond to existing methods of solderability assessment. This study will provide an I.C. component lead finish comparision of three selected lead free solders with standard 63/37 Sn/Pb solder using wetting balance and "Dip and Look" solderability test techniques. In addition, an association between board level soldering performance, wetting balance and "Dip and Look" solderability test parameters of the lead free solders will be established.
5:45 pm
INTERFACIAL REACTION BETWEEN PALLADIUM AND LEAD-TIN SOLDERS: G. Ghosh, Dept. of Materials Science and Engineering, Northwestern University, Evanston, IL 60208-3108
Room: 340C
Session Chair: E.P. Kvam, School of Materials Engineering, Purdue University, West Lafayette, IN 47907-1289
2:00 pm INVITED
NEW INSIGHTS INTO THE STRESS DRIVEN 2D TO 3D TRANSITION: D.E. Jesson, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6030
An understanding of the stress driven 2D to 3D transition is central to many key issues in materials science including the growth of planar but strained semiconductor layers and the fabrication of quantum dots. We will overview our current understanding of the transition and identify the conditions under which stress driven instabilities occur during film growth. Nucleation mechanisms of roughening compete with instabilities and this will be illustrated by annealing experiments which demonstrate the formation of rippled surface morphologies by cooperative nucleation events.
2:40 pm INVITED
SPONTANEOUS COMPOSITION MODULATION IN SEMICONDUCTOR ALLOYS: Joanna Mirecki Millunchick, Sandia National Laboratory, Albuquerque, NM 87195-0601
Lateral composition modulation (CM) has been observed to occur spontaneously in III-V semiconductors, producing quantum wires. CM is presumed to originate from surface undulations arising from compositional inhomogeneity, as well as lattice mismatch between the epilayer and the substrate. We observe CM in homogeneous alloys or in short period superlattices. Samples were characterized using cross-sectional transmission electron microscopy (XTEM), polarized photoluminescence spectroscopy (PPL), reflection difference spectroscopy (RDS), and magneto-luminescence (ML). For example, XTEM micrographs of InAs/GaAs superlattices show contrast due to CM only in the projection, with a period 150Å. PL measurements show that emission is red-shifted and polarized with a ratio of up to 4. InAlAs buffer layers, on the other hand, have much higher polarization ratios (up to 10), indicating that these films may also be compositionally modulated. XTEM images of nominally lattice-matched InxGa1-xAs / InxAl1-xAs superlattice structures grown on InP (001) show that only the InAlAs layers exhibit contrast due to CM along the direction, in agreement with polarized PL results. The modulation period for such a structure deposited at Ts=475°C, for example, is 50Å. Preliminary temperature-dependent PL and ML results for InAlAs epilayers show that the emission is independent of T and B, suggesting carrier confinement due CM. These phenomena are under investigation in an effort to determine the dependence of the material system on CM. Finally, a model of the effect of CM on the band structure will be discussed. Supported by U.S. Department of Energy, OER/BES Division of Materials Science Grant No. DE-AC02-83-CH10093.
3:20 pm
STRUCTURAL STABILITY OF LOW TEMPERATURE GROWN InGaAs/GaAs HETEROSTRUCTURES: Chanro Park, C.G. Park, Dept. of Materials Science and Engr., Pohang University of Science and Technology, Pohang 790-784, Korea; C.D. Lee, S.K. Noh, Materials Evaluation Center, Korea Research Institute of Standards and Science, Taejon, 305-340, Korea
Microstructural evolution of the InGaAs/GaAs heterostructures grown by MBE at low temperatures (200-250°C) has been studied using double crystal x-ray diffraction and transmission electron microscopy. Dislocation formation was suppressed at low growth temperatures, and the layers sustained metastable structures which would undergo microstructural change at high temperatures. Misfit dislocations formed at InGaAs/GaAs interfacial region during annealing relieved accumulated strain caused by lattice mismatch between the InGaAs and GaAs. Arsenic precipitates formed during the annealing process also played an important role for strain relaxation by forming misfit dislocations along matrix/As interface. Structural stability of the low temperature grown layers in discussed in terms of the microstructural evolution observed at various growth and annealing temperatures.
Room: 340D
Session Chairperson: J.E. Hoffman, Jan H. Reimers and Associates USA, Inc., P.O. Box 420545, Houston, TX 77242-0545
This session will present five papers describing the major unit processes of copper extractive metallurgy. The five unit processes are: smelting, converting, fire refining and casting, electrolytic copper refining, and copper solvent and electrowinning. As set forth in the title of this seminar, the companies participating were chosen as exemplars of the finest practice in their particular area of copper extractive metallurgy. The goal of this session is to provide an accurate description and clear understanding of these unit processes. This session will provide a overall knowledge of the extractive metallurgy of copper, particularly useful to those outside the copper industry.
2:00 pm
EXEMPLARY PRACTICE IN THE FLASH SMELTING OF COPPER SMELTER CONCENTRATES: Gerald Roose, Phelps Dodge Mining Company, Hidalgo Smelter, P.O. Box 67 Playas, NM 88009
2:25 pm
EXEMPLARY PRACTICE IN THE PIERCE SMITH CONVERTING OF COPPER MATTE: Andreas Specht, NORDDEUTSCHE AFFINERIE Aktiengesellschaft Hamburg, Germany
2:50 pm
EXEMPLARY PRACTICE IN THE FIRE REFINING AND ANODE CASTING OF COPPER: Allen Levert, Robert Matthews, INCO Ltd., Copper Cliff Copper Refinery, Copper Cliff, Ontario, Canada POM IND
3:15 pm BREAK
3:30 pm
EXEMPLARY PRACTICE IN THE ELECTROLYTIC REFINING OF COPPER: Harry Tallert, ASARCO Amarillo Copper Refinery, Amarillo, Texas; Michael King, V. Ramachandran, ASARCO, Technical Services Center, Salt Lake City, UT
3:55 pm
EXEMPLARY PRACTICE IN THE SOLVENT EXTRACTIOIN AND ELECTROWINNING OF COPPER: Name to be supplied, Magma/BHP Copper Company, 200 Redington Rd., San Manuel, AZ 85631
REPLACEMENT PAPER:
THE HUELVA EXPANSION PROJECT: Miguel Palacios, Atlantic Copper, S.A., Av Francisco Montenego SA, Huelva 21001, Spain
Room: 330E
Session Chairpersons: Patrick L. Martin, Rockwell International Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360; Kevin J. Hemker, Dept. of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218-2686
1:55 pm OPENING REMARKS
2:00 pm INVITED
REDUCTION OF PRIMARY CREEP IN TiAl ALLOYS BY PRESTRAINING: Jian N. Wang, L.M. Hsiung, T.G. Nieh, Lawrence Livermore National Laboratory, L-370, P.O. Box 808, Livermore, CA 94551-9900
In some engineering applications, TiAl components are limited to undergo less than 0.3-0.5% creep distortion. However, existing fully lamellar TiAl alloys deform to this strain within a short period of time during primary creep. Thus, the reduction of primary creep has become a key issue. Present experiments show that this creep can be significantly reduced by prestraining. A sample prestrained at a high stress could undergo no forward deformation at a subsequent low stress even after a long period of time. Microstructural examination indicates that the motion of misfit dislocations along interfacial and thermal twin boundaries is the dominant mode of deformation at low stress. The mobility of these dislocations after prestraining and the physical origin of this effect will be discussed.
2:30 pm
CHANGES IN MICROSTRUCTURE DURING PRIMARY CREEP IN A Ti-47Al-2Nb-1Mn-0.5W-0.5Mo-0.2Si ALLOY: D.Y. Seo, T.R. Bieler, Department of Materials Science and Mechanics, Michigan State University, East Lansing, MI 48824-1226; D.E. Larsen, Howmet Corporation, Whitehall, MI 49461
Cast gamma titanium aluminides are gaining acceptance as potential replacements for superalloy and steel components in many applications. One particular alloy with W, Mo and Si additions has shown exceptional primary creep resistance. Quantitative microscopic comparisons were made between microstructures in the grip sections and the deformed gage section in creep specimens deformed to 0.5% strain, using optical, SEM and TEM techniques. The lamellar spacing in lamellar grains systematically decreased after creep deformation. Precipitates containing refractory elements nucleated and grew at a faster rate in the deformed part of the specimen, as compared to the deformed region, and the precipitates were generally smaller and more homogeneously nucleated. Precipitates have been identified to be silicides or beta phase. These observations indicate that strain assisted nucleation of precipitates accounts for much of the excellent creep resistance.
2:50 pm
EVOLUTION OF MICROSTRUCTURE DURING THE ELEVATED TEMPERATURE CREEP OF SINGLE-PHASE GAMMA Ti47Al51Mn2 ALLOY: Min Lu, Kevin J. Hemker, Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD 21218
Mechanical experiments have shown that single-phase gamma TiAl does not exhibit steady-state creep. Instead, the microstructure evolves along the creep curves. To investigate microstructure/property relations, constant stress creep tests on single-phase polycrystalline gamma Ti47Al51Mn2 were conducted at temperatures below and above the peak temperature (600°C). Primary creep, minimum strain rate regions and tertiary creep were investigated. Creep tests conducted at 550°C, 550°C and 700°C were stopped at different stages and specimens were prepared for TEM observations. No evidence of the subgrain formation has been found in any of the creep tests. Faulted dipoles and superdislocations, as well as a few ordinary dislocations, were present in the microstructure of the early stage of the creep tests. At longer creep times, faulted dipoles were annihilated and superdislocations were found to form "roof" like barriers. TEM observations of faulted dipoles and superdislocations were correlated, where appropriate, with computer simulations. The density and the degree of bowing of the "cusps" on ordinary dislocations increased dramatically with increasing creep strain. The configuration of the "cusps" formed on the ordinary dislocations were studied with weak-beam TEM and were compared to those found in the yielding and the prestraining studies of the same alloy.
3:10 pm
MICROSTRUCTURE EVOLUTION AND CREEP DEFORMATION OF A MO-CONTAINING NEAR-GAMMA ALLOY: Eric Ott, Tresa Pollack, Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
The addition of Mo in near-gamma alloys promotes the formation of the beta phase. The presence of the beta phase stabilized by Mo as well as other alloy additions including Nb and Cr has been shown to result in good hot working characteristics. Microstructural evolution of a Ti-46.4Al-2Nb-2Cr-0.8Mo fine grained wrought alloy during annealing and subsequent heat treatment will be reported with a specific emphasis on the effects of the beta/B2 phases on the development of gamma and lamellar microstructures. Results of creep testing and subsequent microscopy of near-gamma and duplex microstructures will also be discussed and compared to that of a similar Ti-48Al-2Nb-2Cr type alloy containing no Mo.
3:30 pm BREAK
3:50 pm
CREEP DEFORMATION OF NEAR/FULLY LAMELLAR Ti-48Al-BASED ALLOYS: G.B. Viswanathan, V.K. Vasudevan, Dept. of Mat. Sci. &Eng., Univ. of Cincinnati, Cincinnati, OH 45221
In this study, the creep properties of the binary Ti-48Al and quarternary Ti-48Al-2Cr-2Nb alloys are investigated for the near and fully lamellar microstrutures in the temperature range of 700-815°C and stress of 103-240 MPa. The creep behavior of all the tested microstructures is best described by the power law creep. Activation energy (Q) between 350-370 KJ/mole and stress exponent (n) in the range of 5.0-8.0 was obtained for the binary Ti-48Al alloy. The corresponding values for the Ti-48Al-2Cr-2Nb alloy were ~315 KJ/mole and ~5.0. The effect of grain size and the lamellar spacing on the creep behavior is discussed. Defect analysis through weak beam dark field imaging was carried out to elucidate the dislocation mechanisms in the crept samples. Observations of the crept samples with the fully lamellar structure in the binary alloy indicate that both 1/2<110] and 1/2<112] dislocations are active, that the deformation is highly anisotropic and that the lamellar interfaces obstruct slip (depending on the orientation). The combination of low creep rates with a high stress exponent for the fully lamellar structures is thought to be caused by the combined effect of anisotropic deformation and lamellar boundaries obstructing slip; the dislocations that are piled up at the interfaces overcome these obstacles by local climb, which is reflected in the Q values near that of self-diffusion of Ti in TiAl. The formation of substructures within the laths and the lamellar interface structures before and after creep will be discussed.
4:10 pm
DEVELOPMENT AND EVALUATION OF AN OXIDATION-RESISTANT COATING ALLOY FOR GAMMA TITANIUM ALUMINIDES: M.P. Brady, W.J. Brindley, J.L. Smialek, MS 106-1, NASA Lewis, Cleveland, OH 44135
A two-phase (TiAl) + Laves (Ti[Cr,Al]2) oxidation-resistant coating alloy, Ti-51.25Al-12.25Cr at.%, has been developed for the + 2 class of titanium aluminides. The composition of the coating alloy was selected so that the microstructure consists of the g phase, and a minor volume fraction of the oxidation-resistant Laves phase. By basing the microstructure on the g phase, the mechanical properties and substrate compatibility are optimized. The volume fraction of the Laves phase is kept to a minimum because it is extremely brittle. The Ti-51.25Al-12.25Cr coating alloy was applied to the + 2 alloy, Ti- 48Al-2Cr-2Nb, by low pressure plasma spray (LPPS). Oxidation tests at 800°C and 1000°C in air indicated that the coating successfully protected the substrate from oxidation. The oxidation behavior and mechanical properties of the coating alloy will be discussed.
4:30 pm
VERY LONG TERM OXIDATION OF Ti-48Al-2Cr-2Nb AT 704°C IN AIR: I.E. Locci, M.P. Brady, R.A. MacKay, J.W. Smith; MS106-5, NASA Lewis, Cleveland, OH 44135
The alloy Ti-48Al-2Cr-2Nb was exposed from 500h to 9000h at 704°C in air. A complex, mixed alumina/titania scale, rather than a protective alumina scale, was formed. After 9000h, this scale was approximately 15 microns thick. A continuous Ti-rich nitride layer was formed at the alloy/scale interface. The alloy ahead of this nitride layer was depleted in Ti and enriched in Al. Comparisons with the oxidation behavior of binary TiAl alloys, and implications of the scale microstructure for mechanical properties will be discussed.
4:50 pm
RECENT DEVELOPMENTS ON THE OXIDATION OF TiAl: R. Wheeler, R. Banerjee, H.L. Fraser, Department of Mater. Sci. and Eng., Ohio State University, Columbus, OH 43210
The high level of Al in TiAl based alloys does not always relate to slow oxidation kinetics. While protective alumina scales are formed during high temperature exposures in an oxygen environment, mixed Al2O3/TiO2 scales are formed when similar tests are conducted in air. In this latter case, the surface corrosion products form a complex layered structure which governs oxidation rates. In a Ti-48Al-2Cr (at.%) alloy oxidized in air at 800°C for 1 hour, two distinct layered microstructures are observed. One is composed of an Al depleted underlayer and a mixed Al2O3/TiO2 outerlayer. The other is composed of the same depleted layer with a multicomponent, multilayered outerscale. This second microstructure is characteristic of a nitrogen effect found to be associated with increased oxidation kinetics. Detailed TEM analyses has been conducted to identify the reaction products present in the scale. The deduced reaction paths suggest a rate behavior based on both interfacial reactions and the inward and outward anion and cation diffusion.
5:10 pm
CLOSING REMARKS: Kwai S. Chan, Southwest Research Institute, San Antonio, TX 78228-0510
Session Chairperson: J.J. Stephens, Sandia National Laboratories, Albuquerque, NM 87185
2:00 pm
EFFECTS OF TEMPERATURE AND OXYGEN PRESSURE ON OXIDATION KINETICS OF V-4wt.% Cr-4wt% Ti AND V-5wt.% Ti ALLOYS: M. Uz, Chemical Engineering Department, Lafayette College, Easton, PA 18042; K. Natesan, Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439; N. Barbosa III, Chemical Engineering Department, Lafayette College, Easton, PA 18042
We conducted comparative investigation to determine the effects of temperature and oxygen pressure on the oxidation behavior and microstructure of V-4wt.% Cr-4wt.% Ti and V-5wt.% Cr-5wt.% Ti Alloys. The samples were cut from 1-mm-thick cold-rolled sheet stock and annealed at 1050°C for 1 h before their use in oxidation studies. The oxidation experiments were performed at oxygen pressures of 760, 0.1, 5x10-4, and 5x10-6 torr and at temperatures of 
350 to 700°C. Oxidation models, oxide type and thickness, partitioning of oxygen between oxide and substrate alloy, and alloy grain size were determined as a function of temperature and oxygen pressure. The results for the two alloys are discussed and compared with one another and with those from similar studies on unalloyed V reported in the literature. Work supported by the U.S. Department of Energy, Office of Fusion Energy Research, under contract W-31-109-Eng-38.
2:20 pm
OXIDATION BEHAVIOR OF Al3Ti INTERMETALLICS: R.G. Reddy, X. Wen, Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487
The oxidation kinetics of Al3Ti intermetallics have been studied at the temperature range of 1123K to 1273K in pure dry oxygen. The oxygen diffusion rates were investigated using TGA method. Parabolic rate constants were calculated and compared with other research results. The oxidation scales were analyzed using SEM, EDS and X-ray diffraction. A continuous Al203 scales with a little Ti02 (rutile) were formed on the intermetallic surface. The Al3Ti intermetallic exhibited excellent oxidation resistance among the Ti-Al base intermetallics.
2:40 pm
SUPERHEATING BEHAVIOR OF NiAl: N. Kullcarni, Dept. of Materials Science & Eng., University of Florida, 245 Rhines Hall, Gainesville, Fl-32611; K.T. Hong, Division of Metals, Korea Inst. of Science & Tech (KIST), 39-1 Hawolkog-dong, Sungbook-Gu, Seoul, Korea 136-791
The intermetallic compound NiAl, when processed in a microgravity environment under electromagnetic levitation, exhibited a unique superheating effect up to 65 degrees over the melting point. This superheating behavior appeared to be related to the high supercoolings (200-250 degrees) experienced by molten NiA1 samples that rapidly solidified in the rnicrogravity levitation environment. The superheating observed appeared to be permanent and reduced asymmetrically for compositions that deviated from stoichiometry. On reaching the maximum or critical superheating temperature, an anomalous transformation occurred that caused the temperature of the sample to drop to its melting point, after which melting commenced. It appears that this transformation is an order-disorder type, that is explicitly associated with the superheating behavior in NiAl.
3:00 pm
A STUDY OF POTENIAL EUTECTIC BRAZE ALLOYS IN THE Au-Ag-Ge TERNARY SYSTEM: P.T. Vianco, J.J. Stephens, C.A. Walker, Sandia National Laboratories, Albuquerque, NM 87185-0367
Despite the need for low vapor pressure alloys with brazing temperatures in the 400-600°C range, there are in fact very few commercially available alloys to use in this range. This study was motivated by the need to develop a brazing process with a maximum allowable brazing temperature of 500°C. A survey of ternary phase diagrams, combined with previous experience with the binary 88wt.% Au-12 Ge alloy, led us to select the Au-Ag-Ge ternary system for further study. We have found that the 77.32 wt.% Au-12.62 Ag-10.06 Ge composition is a eutectic alloy with a eutectic temperature of ~447°C. Hermetic seals to metallized alumina tensile buttons (ASTM F19 design) have been obtained with this system. This talk will present results braze joints strength results, along with a discussion of the as-solidified microstructure of this alloy. This work conducted at Sandia National Laboratories, supported by U.S. Dept. of Energy under contract number DE-AC04-94AL85000.
3:20 pm BREAK
3:30 pm
THERMAL AND PROCESS MODELING OF MICROFIBROUS MANUFACTURING IN A SINTERING FURNACE: J.M. Shire, J.M. Khodadadi, Mechanical Engineering Department, B.J. Tatarchuck, Chemical Engineering Dept., Auburn University, Auburn, AL 36849
Mathematical modeling and numerical simulation of the thermal field for the operation of a continuous belt hydrogen furnace used for sintering applications of microfibrous materials are presented. Particular emphasis is placed on metallic fibers being sintered into a web-like matrix. Utilizing thermal energy balance and simplified heat transfer equations, the mathematical model is capable of predicting the instantaneous temperature of products as they pass through the furnace. The manufacturing process is optimized with respect to the belt speed, furnace zone temperature setting and sintering material configuration.
3:50 pm
DIFFUSION IN SILICIDES OF Mo AND W: P.C. Tortorici, M.A. Dayananda, Purdue University, School of Materials Engineering, 1289 MSEE Building, West Lafayette, IN 47907-1289
Diffusion studies were carried out with Si in contact with Mo and W at selected temperatures between 900°C and 1350°C for the formation and growth of silicides of Mo and W. Interdiffusion between MoSi2 and Mo and between MoSi2 and W was also studied for the development of silicide layers, such as MO5Si3, MO3Si, (Mo,W)5Si3, W5Si3 and nonplanar interface morphologies. Integrated interdiffusion coefficients calculated for the various silicide layers from concentration profiles are presented. The relative diffusion behavior of Si, Mo and W in selected silicide layers will be discussed in the light of diffusion structures and marker motion.
4:10 pm
FOCUSED ION BEAM MILLING AND MICROMANIPULATION FOR CROSS-SECTION TEM SPECIMEN PREPARATION: L.A. Giannuzzi, Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, 4000 Central Florida Blvd., Orlando, FL 32816-2450; S.R. Brown, Kirk Resources, 9333 S. John Young Parkway, Orlando, FL 32819; R.B. Irwin, F.A. Stevie, Lucent Technologies, 9333 S. John Young Parkway, Orlando, FL 32819
A technique for cross-section transmission electron microscopy (TEM) sample preparation of mutt-layered and difficult materials as described. A focused ion beam (FIB) device is used to slice an electron transparent specimen from an area of interest. Micromanipulation procedures are then used to transport the electron transparent specimen from the bulk sample to a formvar/carbon coated copper grid for subsequent TEM analysis. The versatility of this technique is demonstrated by presenting cross-sectioned TEM specimens from a wide range of materials. TEM specimens that have been produced with the FIB method include a multi-layered thin film electronic device, a metallic diffusion couple, and a ceramic fiber.
4:30 pm
IMPROVEMENT OF COATING ADHERENCE OF HOT-DIP GALVANIZED SHEET STEELS CONTAINING SILICON: Jong-Sang Kim, Jin-Hwan Chung, Kwangyang Research Labs., Pohang Iron and Steel Company, P.O. Box 22 Suncheon, Korea
The effects of silicon in steels on the coating adherence of hot-dip galvanized steel sheets have been investigated to reduce the weight of automobile body. The presence of a stable silicon oxide formed on the steel surface has shown to be very detrimental to proper wetting by liquid zinc. A critical silicon concentration depended on the operating conditions such as mechanical pretreatments, furnace conditions and alloying composition of zinc bath.
4:50 pm
OXIDATION AND DECARBURISATIOIN KINETICS OF AN EUTECTOID STEEL DURING STATIC SPHEROIDISATION: Sedat Ozbilen, Gazi Univ. Fac. Tech. Educ. Metal Dept., Teknikokullar, Ankara, Turkey
Eutoid steel with a composition of 0.59%C-0.69%Mn-1.19%Si-0.022%P and 0.061%S (in wt%) was austenitised at 805°C after casting. Samples were furnace and air cooled to obtain fine (0.26µm) and coarse (0.57µm) mean interlamellar spacing of pearlite. Samples of 1x10.4cm was annealed at 600°C and 700°C for varying times up to 2200 hr. x-ray diffraction, SEM investigation, wet chemical analysis and theoretical erf calculations were carried out to observe and measure the response of the eutectoid steel to oxidation and decarburisation.
5:10 pm
EFFECT OF SEM TILTING ON MEAN INTERLAMELLAR SPACING CALCULATIONS OF PEARLITE IN EUTECTOID STEEL: Sedat Ozbilen, Gazi Univ. Fac. Tech. Educ. Metal Dept., Teknikokullar, Ankara, Turkey
Eutectoid steel with a composition of 0.59%C-0.69%Mn-1.19%Si-0.022%P and 0.061%S (in wt%) was cast before austenitisation at 850°C. Samples were furnace cooled to obtain coarse pearlitic mean interlamellar spacing of 0.57µm measured from SEM micrographs of samples. To observe the effect of SEM tilting on "mis" of pearlite samples of 1x1x0.4cm were annealed at 700°C for 115 hr. SEM micrographs with and without 30° tilt on samples were taken. Results of metallographic investigation will be presented.
Room: 232B
Session Chairperson: Larry Boxall, Fluor Daniel/C107I, 100 Fluor Daniel Drive, Greenville, SC 29607-2762
2:00 pm
DEGASSING LIQUID ALUMINUM ALLOYS BY ARGON IN CLOSED CIRCUIT: Robert A. Rapp, L.S. Fan, Ohio State University, Department of Material Science and Engineering, 116 W. 19th Ave., Columbus, OH 43210
The large reduction in the solubility of dissolved hydrogen in aluminum as it is solidified to form ingots, strip, sheet or cast products necessitates that the liquid metal is degassed prior to casting. Pure argon is frequently injected into the liquid alloy through a submerged lance or bubbler, so that dissolved hydrogen enters the argon bubble prior to discharge into the environment. This work introduces a proprietary concept to achieve the same argon degassing of liquid aluminum alloys, with recirculation of the argon in a closed loop such that the cost of the argon is saved. In practice, the hydrogen entrained by the argon from the liquid alloy would be oxidized to form H2O() by reaction with a fixed bed of copper oxide pellets and the H2O() product would be extracted by a desiccator bed. When the reactant bed of copper oxide is mostly reduced to copper and the desiccator approaches saturation, a relay is activated, causing a redirection of the gas flow which replaces the spent reactants with newly regenerated ones.
2:30 pm
CLOSED-LOOP NITROGEN-CHLORINE DEGASSING/FLUXING OF LIQUID ALUMINUM ALLOYS: L.S. Fan, Robert A. Rapp, Ohio State University, Department of Material Science and Engineering, 116 W. 19th Ave., Columbus, OH 43210
The need to degas liquid aluminum alloys to reduce dissolved hydrogen prior to solidification to form any product is indigenous to all aluminum processing plants. Likewise, to produce aluminum sheet and some other products, dissolved sodium and calcium must be fluxed by reaction with chlorine. Today, the combined degassing and fluxing is often achieved by the bubbling of a nitrogen-chlorine gas mixture into the melt, with release of the product HCl and unreacted Cl2 into the environment. This work introduces a proprietary concept to accomplish the degassing/fluxing of aluminum melts by the usual nitrogen-chlorine gas mixture, but with recirculation of the chlorine within a closed-loop system so that it is not released to the environment. Reaction of HCl and Cl2 from the degassing product gases with copper oxide pellets in a fixed bed lead to their conversion to copper chlorides, and the H2O() product is safely vented to the environment. Ambient air is used to regenerate the reactant copper oxide from the product copper chloride.
2:50 pm
ENERGY AND OTHER COST SAVINGS THROUGH NOVEL, STATIC DEGASSING IN RECYCLED ALUMINUM PRODUCTION: David A. Larsen, Blasch Precision Ceramics, Inc., 580 Broadway, Albany, NY 12204
A novel method of producing ceramic degassing components through freeze-casting and injection molding is employed to manufacture components used in the production of recycled aluminum metal, where contaminant levels are higher than normal, resulting in lower than normal grade metals. Recycled aluminum degassing operations based on today's standard practice are inadequate for the task, requiring either costly rotary components which require high maintenance, and operating costs, or large pore ceramic porous plugs which fail to deliver the necessary fine gas bubble pattern reliably and continually.
3:10 pm BREAK
3:30 pm
EVALUATION OF A NEW MATERIAL FOR HALL-HEROULT CELL CATHODES: Thomas J. Mroz, Advanced Refractory Technologies, Inc., 699 Hertel Avenue, Buffalo, NY 14207
A new, non-oxide material has recently been identified which exhibits electrical resistance 2 orders of magnitude less than graphite, and which can be formed by reaction hot pressing or sintering at relatively low temperatures. Additionally, this material is easily machined, and exhibits good oxidation resistance and excellent thermal shock resistance. It appears to be a good candidate for Hall cell cathode applications. Additionally, there appears to be an opportunity to inexpensively surface treat this material to obtain TiB2 integral coatings. We will evaluate the corrosion resistance of this material with and without the TiB2 coating and further evaluate the parameters required to produce the TiB2 coating.
3:50 pm
DISPOSAL OF HALL-HEROULT CELL POT-LINING: J.R. Divine, ChemMet, Ltd., P.O. Box 4068, West Richland, WA 99353-2309
The proposed disposal process provides an energy efficient mechanism for recovering salts from the pot-lining and disposing of the carbonaceous liner itself. The proposed method is to grind the spent pot-liner into small particles and then oxidize them. The method which appears most likely to be successful is to grind to about 1 mm diameter, heat to about 1300 K in an "inert" atmosphere of CO2, and then react with steam. The resulting mixture of CO and H2 can be used as fuel in a boiler to generate steam, preheat the spent pot-liner, or provide co-generation for feeding electrical power back into the grid or into the aluminum process.
4:10 pm
AN ALUMINA CONCENTRATION SENSOR: James Oxley, Oxley Research Inc., 25 Science Park, New Haven, CT 06511
This work concerns development of a novel electroanalytical sensor to monitor the depletion in alumina concentration which occurs during electrowinning of aluminum from molten cryolite-alumina baths. The concept relies on the use of an inert indicator electrode which responds directly to variations in dissolved alumina concentration. The electrical signal thus produced can be used in a control algorithm to enable the automatic feeding of alumina to the bath, thereby avoiding the occurrence of "anode effect".
Room: 240D
Session Chairpersons: Jan-C. Carlén, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036; Dr. R.H. Tuffias, Ultramet, 12173 Montague St., Pacoima, CA 91331
2:00 pm
EVALUATION OF A RHENIUM COATING ON A MOLYBDENUM SUBSTRATE: Amber M. Dalley, C. Bagnall, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA 15904; R.W. Buckman, Jr., Refractory Metals Technology, Pittsburgh, PA 15236
2:00 pm
RHENIUM AND IRIDIUM: Evan K. Ohriner, Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6083
Rhenium is used together with the metal iridium in a number of applications. Iridium has been used as coating for rhenium rocket thrusters and as an oxidation-resistant coating in a number of other applications. The high strength of rhenium at elevated temperature is combined with the oxidation resistance and high melting point of iridium. The use of the two metals together is advantageous due to the absence of any stable intermediate compounds. Coating life and properties are effected by solubility and diffusion rates. Rhenium and iridium alloying additions both improve the ductility of tungsten. The high solubility of rhenium in iridium is also being taken advantage of to produce iridium-based materials with a reduced electron work function. The uses of rhenium in conjunction with iridium are discussed. Managed by Lockheed Martin Energy Research under contract DE-AC05-96OR22464 with the U.S. Department of Energy.
2:20 pm
DEVELOPMENT OF THE PARAMETERS OF THE PROCESS OF MANUFACTURING COMPLEX SHAPE PARTS FROM RHENIUM POWDER: Eugene P. Kratt, Victor N. Samarov, Laboratory of New Technologies, PO Box 31, 103001 Moscow, Russia,; Boris D. Bryskin, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036
The research was aimed at developing the parameters of the process of manufacturing hollow parts from rhenium and rhenium alloy powders. With this purpose, the hot isostatic pressing technique was proposed. Tool design and choice of material for the tool were the main problems of the research. On the basis of the fulfilled experiments a rational scheme of manufacturing hollow complex shape parts with minimal allowances was developed. the parameters of this scheme are made the basis of the technology of manufacturing rocket engine nozzle type parts.
2:40 pm
PREPARATION OF TEFLON PIPES WITH METALLIZED LAYER: E.G. Rakov, D. Mendeleyev University of Chemical Technology of Russia, Miusskaya Sq. 9, Moscow 125047, Russia
The method of deposition of thin rhenium layers on inner wall of teflon pipes (tubes) by means of filling the pipes by volatile rhenium compound and subsequent chemical reduction of this compound inside teflon pores was developed. The method allows to diminish permeability of teflon for gases or liquids and to change its electric properties: the inner layer becomes electroconductive. Such teflon pipes and details are necessary for neutralization of static electric charges in some devices. The depth of metallized layer, as it was shown by microscopic examination of pipe cross sections, did not exceed some tenth of millimeter. The method allows to deposit -metallized layers of definite configuration.
3:00 pm IRIDIUM-COATED RHENIUM RADIATION-COOLED ROCKETS: Brian Reed, James Biaglow, and Steven Schneider, NASA Lewis Research Center, 21000 Brookpark Road, Cleveland, OH 44135
Room: 240D
Session Chairperson: Dr. Urs O. Hafeli, Project Scientist, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195
3:40 pm
DEVELOPMENT OF A METALLIC RADIOACTIVE RHENIUM SOURCE FOR THE TREATMENT OF RESTENOSIS AFTER ANGIOPLASTY: Urs Hafeli, Eric Lee, Jay Ciezki, Roger Macklis, The Cleveland Clinic Foundation, Desk T28, 9500 Euclid Ave., Cleveland, OH 44195
Radioactive Rhenium sources can be prepared in a nuclear reactor by bombarding the non-radioactive metal with neutrons. In a n, -reaction, the two 
-emitters 186Re and 188Re are produced with high yield. One application of thus prepared radioactive Rhenium wires is the prevention and treatment of restenosis after balloon angioplasty. For this brachytherapeutic application, the source must be very stable, enclosed and safe to handle. The necessary encapsulation of the radioactive source was done by plasma coating with a 240 nm layer of titanium, as confirmed by scanning electron microscopy. This resulted in a highly radiochemically stable source. The response of endothelium and smooth muscle cells to a radioactive Rhenium-wire and its dosimetry was determined in an in vitro cell model. Our results confirmed that radioactive sources made from 186Re and, even more so, 188Re, are excellent candidates for restenosis inhibition because of their narrow treatment range, sharp dose gradient, inexpensive preparation, excellent stability, easy shielding and conveniently short treatment times.
4:00 pm
PRODUCTION OF RHENIUM-186 AND RHENIUM-188 AT ORNL HFIR: Saed Mirzadeh, A.L. Beets, F.F. (Russ) Knapp, Nuclear Medicine Group, Health Science Research Division, Oak Ridge National Laboratory (ORNL), Oak Ridge, TN 37831-6229
4:00 pm
PRODUCTION OF RHENIUM-POWDER WITH A JET MILL AND ITS INCORPORATION IN RADIOACTIVE MICROSPHERES FOR THE TREATMENT OF LIVER TUMORS: Urs Hafeli, Gayle Pauer, Roger Macklis, The Cleveland Clinic Foundation, Desk T28, 9500 Euclid Ave., Cleveland, OH 44195; Randall German, Penn State University, 118 Research Building West, University Park, PA 16802-6809
Metallic rhenium powder of 325 mesh is readily available. Well characterized powder of micrometer size, however, is less easy to obtain. In this presentation, we describe how we prepared rhenium powder with an average particle size of 1-2 µm, starting from 325 mesh material and using a jet mill. The particle size distribution was confirmed by light and scanning electron microscopy, and laser diffraction. The change in density and surface characteristics (porosity) was also analyzed. Biodegradable poly(lactic acid) microspheres were prepared, by a solvent evaporation method, from the resulting rhenium particles and were neutron activated in a nuclear reactor to directly yield 186/188Re-microspheres, useful for the treatment of liver tumors. Biodistribution data in rats as well as first treatment results of Novikoff tumors are presented.
4:20 pm
RADIOIMMUNOTHERAPY WITH RHENIUM-186 AND RHENIUM-188: Alan R. Fritzberg, Fu-Min Su, NeoRx Corporation, 410 W. Harrison, Seattle, WA 98119
The radioisotopes of rhenium, Re-186 and Re-188, have physical properties that make them attractive for radiotherapy via antibody mediated targeting. Rhenium186 has a half life of 3.78 days, maximum beta energy of 1.07 MeV and imageable gamma rays. Rhenium-188 has a half life of 17 hours, maximum beta energy of 2.12 MeV and imageable gamma rays. Rhenium-186~with its longer half life is appropriately matched with the larger antibody forms, IgG of 150 kD molecular weight and its F(ab')2 fragment of 100 kD size. Rhenium-188 with its shorter half life may be preferred in instances of rapid tumor uptake and shorter tumor retention. N,S amide thiolate chelating agents such as mercaptoacetylglycylglycyl--aminobutyrate have been developed for the attachment of the rhenium radioisotopes to antibodies. With this agent, over 150 patients with solid tumors have been treated with up to 550 mCi of Re-186. Several have had partial responses (> 50% decrease in tumor size).
Room: 232C
Session Chairpersons: Dr. Evan K. Ohriner, Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6083; Forrest Hall, Hoskins,10776 Hall Road, P.O. Box 218, Hamburg, MI 48139-0218
2:00 pm
METALLOGRAPHIC TECHNIQUE FOR INCREASED GRAIN BOUNDARY DELINEATION OF RHENIUM ALLOYS: Mitchell A. Jacobs, Jozef Fedko, Metallurgical Services Inc., Maywood, IL 60153
Current metallographic preparation techniques for rhenium alloys have been based on the etch and back polish technique due to the soft nature of the rhenium alloys. To date the etch and back polish technique has adequately removed the flowed rhenium material to reveal the microstructure. Recent technology has allowed new polishing media to provide better removal of the flowed material. The resulting microstructure exhibits two dimensional relief in a slightly overetched condition. The significantly increased grain boundary delineation permits better review of the grain size.
2:20 pm
ION-IMPLANTATION DOPED RHENIUM AND REFRACTORY METALS: G. Welsch, P.T. Szozdowski, R.M. Collins, Materials Science and Engineering, Case Western Reserve University, 514 White Bldg., Cleveland, OH 44106-7204; K.T. Kim, Research Institute of Industrial Science and Technology, P.O. Box 135, Pohang, 790-600, Korea
Rhenium and other refractory metals in various product forms can be doped with potassium to stabilize an overlapping recrystallized grain structure for high temperature creep strength. Doping has been performed by ion-implantation into the surface layers of flat sheets. During fabrication of pressure-bonded or roll-bonded multi-layer composites the dopant was incorporated along strategically located internal planes. The dopant is arranged in planar arrays of fine bubbles which play the role of fenceposts as they anchor grain boundaries during recrystallization and grain growth. Doped layer composites can be heated to over 2000°C and maintain an overlapping "brick layer" grain structure whereas undoped layer composites develop grains and grain boundaries that transverse the entire width of the composite. Acknowledgment: The research was funded by The National Science Foundation.
2:40 pm
THE INFLUENCE OF ROLLING DIRECTION AND ANNEALING ON THE TEXTURE OF RHENIUM SHEETS: Boris D. Bryskin , Jan-C. Carlén, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036; K. Peter D. Lagerlöf, Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106; Neil Goldfine, JENTEK Sensors, Inc., Boston, MA 02135
2:40 pm
SYNTHESIS AND APPLICATION OF ARTIFICIAL GRAIN STRUCTURES IN POTASSIUM-IMPLANTED RHENIUM: R.M. Collins, G. Welsch, Materials Science and Engineering , Case Western Reserve University, 514 White Bldg., Cleveland, OH 44106-7204
Layer composites of rhenium (re) were made by the chemical vapor deposition (CVD) process. The Re layers range from 0.05 to 0.10 mm in thickness. Between Re layer depositions, potassium atoms were injected into the metal matrix by ion implantation to a depth of 600 angstroms and a peak concentration of 1 at%. At high temperatures, the implanted atoms cluster and form bubbles that remain stable and act as barriers that pin grain boundaries thus producing a means for creating artificial grain architectures. The grain structure of the implanted CVD layer composites is compared to that of the un-implanted CVD composite. Room temperature tensile tests show that the artificial grain architecture increases the overall tensile strength of the CVD rhenium composite.
3:00 pm BREAK
3:20 pm
TENSILE AND CREEP PROPERTIES OF RHENIUM AND RHENIUM ALLOYS: Michael Kangilaski, Advanced Methods and Materials, 1798 Technology Drive, #251, San Jose, CA 95110; M.M. Paxton, Westinghouse Hanford Company, Richland, WA
Tensile properties of rhenium sheet, produced by powder technology techniques, were established from room temperature to 2000°C. The strength of rhenium decreased gradually with increasing temperature while the elongation decreased drastically (from 20% to 5%) as the temperature increased from 1100 to 1200°C. The elongation remained below 5% at temperatures up to 2000°C. Tensile tests were also performed on rhenium -1% tungsten and rhenium-2% iridium. Both alloys were stronger than pure rhenium with the rhenium-1% tungsten alloy being the strongest. Limited creep and creep rupture tests were performed in the 1025 to 1225°C range. The creep tests, with relatively low stresses, indicated a very low stress exponent of 1.3.
3:40 pm
MICROSTRUCTURE CHARACTERISTICS OF Mo-Re ALLOYS SINTERED AT MEDIUM TEMPERATURES: Rodolfo L. Mannheim, Jorge L. Garin, Department of Metallurgical Engineering, Universidad de Santiago de Chile, Casilla 10233, Santiago, Chile
Mixtures of molybdenum and rhenium powders with particle size distribution bearing 2µm average, were prepared in a planetary mill to yield the Mo-25%Re and Mo50%Re compositions. Tablets were then obtained by compaction at various pressures in the range of 300 to 800 MPa. The pieces were subject to sintering at temperatures of 1400 to 1700°C, under protecting atmosphere of Ar-10%H2 to avoid oxidation of the component metals. The solution of rhenium in the molybdenum matrix was followed by means of X-ray diffraction: it was found that at all sintering temperatures rhenium was totally dissolved in the Mo-25%Re, while small amounts of an intermediate phase were detected in the case of the Mo-50%Re alloy, in good agreement with the phase diagram. The densification of the sintered parts increased with temperature and compaction pressure up to values around 90%. The microstructure of the specimens was observed by means of scanning electron microscopy, while the homogeneity of the sintered alloys was corroborated by EDX line-scan analysis. The microstructure showed well defined equi-axed grains with some microporosity distributed across the surface. A few initial tests on cold rolling of the resulting specimens were conducted with very promising results; in fact, owing to the fine particle size of the powders, the sintering temperature can be lower than those normally utilized in the refractory metals industry.
4:00 pm
EFFECT OF IRRADIATION ON THE TENSILE PROPERTIES OF RHENIUM: James A. Horak, Lockheed Martin Energy Systems, Inc., K-25 Technical Support Organization, P.O. Box 2003, MS7353, Oak Ridge, TN 37831; Michael Kangilaski, Advanced Methods and Materials, 1798 Technology Drive, #251, San Jose, CA 95110
Because of their capability for producing high power densities without interruption for long time periods (years) small, fast neutron energy spectrum nuclear reactors are candidates for applications such as orbiting satellites, lunar and Mars terrestrial power stations and manned trips to Mars. To provide high efficiency in the conversion of thermal energy to electrical energy, these reactors must operate at high temperatures (e.g. >1000°C) and they are cooled with liquid metals such as lithium. Because of its high temperature strength and excellent chemical compatibility with lithium, rhenium (Re) has been considered for use in nuclear reactors for space power. In a space reactor the Re would be subjected to fast neutron irradiation to fluences of more than 1x1022n/cm2 (Ea > 0.1MeV) during several years of operation. The current work was performed to provide information on the tensile properties of Re as a function of test temperature and the effects of neutron irradiation at high temperatures on these properties. Ductility of Re is high (~40%) at low temperatures but decreased abruptly to less than 5% at temperatures about ~900°C. The work hardening coefficient is very high at room temperature and decreases slowly with increased test temperature. Fast neutron iradiation at approximately 1000, 1100, and 1300°C to fluences of 8x1021 and 4x1022n/cm2 resulted in increases in strength and decreases in ductility for tests at room temperature, at the irradiation temperature, and at fifty degrees above the irradiation temperature. These effects decreased with increased irradiation temperature and increased with increased fluence. Also, irradiation lowered by more than 200°C the temperature of the abrupt increase in ductility.
4:20 pm
MECHANICAL PROPERTIES OF Cr-Re ALLOYS AT HIGH TEMPERATURE: N. Brodnikovsky, V. Pisarenko, A. Rakitsky, A. Sameljuk, Frantsevich Institute for Problems of Materials Science, 3 Krjijanovskogo Str. 252680 Kiev, Ukraine
The microstructure and mechanical characteristics of cast alloys Cr-35 Re and Cr-18 Re have been investigated within the wide temperature interval (20-1300°C). It was found that under uniaxial tension within 20-600°C the plasticity of the alloys run into 10-20, whereas it decreased when the temperature rose above 700°C. The appearance of the plastic intercrystalline fracture at the temperatures above 900°C resulted in the sharp decrease of strength and plasticity of the alloys. It was established that small quantities of impurities CN, C, O) contained in source materials effected the fracture mechanisms substantially. The additives of Fe to the alloys under investigation did not altered plastic characteristics at high test temperatures. The other perfomed research permitted to consider that the Cr-Re alloys can be obtained with high mechanical properties and within the temperature interval 700-1300°C.
Room: 330A
Session Chairperson: K. Jata, WL/MLLM, Wright Patterson Air Force Base, OH 45433
2:00 pm
EFFECT OF PROCESSING VARIABLES ON MECHANICAL PROPERTIES OF RHEOCAST AZ9ID Mg ALLOYS: C.D. Yim, K.S. Shin, School of Materials Science and Engineering and Center for Advanced Aerospace Materials, Seoul National University, Shinrim-dong, Seoul, Korea
Rheocast ingots of an AZ9 ID magnesium alloy were produced with different processing conditions. Processing variables included stirring rate (Vs) and stirring temperature (Ts). The microstructures of the rheocast AZ9lD magnesium alloys were similar to those of composite materials consisted of soft primary particles distributed in the hard matrix. A detailed examination was made on the relation between processing variables and mechanical properties. With increasing Vs and Ts, the size and the solid volume fraction of the soft primary particles decreased and the hardness and the UTS of the rheocast alloys increased. The mechanical properties of the rheocast alloys were analyzed quantitatively as a function of microstructural parameters such as the size and the solid volume fraction of the primary particles.
2:25 pm
DEFORMATION MECHANISMS AND MECHANICAL BEHAVIOR OF A NOVEL IN-SITU Be-Al COMPOSITE: X.D. Zhang1, J.M.K. Wiezorek1, G. Meyrick1, F.C. Grensing2, H.L. Fraser1, 1Department of Materials Science and Engineering, The Ohio State University, 2041 College Rd., Columbus, OH 43210; 2Brush Wellman, 14710 West Portage River South Rd., Elmore, OH 43416
There has been considerable interest in the production of light weight composite materials for aerospace applications. One of the promising candidates is an in-situ composite consisted of Be and Al. This material combines a high elastic modulus, low density with a relatively high melting point. Unlike the brittle Be, which does not undergo extensive plastic deformation prior to failure, the Be-Al alloys examined in the present study exhibit a remarkable formability. Both extruded and rolled products have been prepared successfully. However, the mechanisms responsible for these attractive characteristics of the Be-Al alloys have not yet been identified. Thus, it is timely and important to ascertain the active deformation modes governing the deformation charac teristics of Be when present in a continuous matrix of aluminum. Furthermore, it is necessary to examine the effect of the aluminum on the inhibition of initiation of cleave in the Be-Al alloys. In the present paper, we will present the results on the microstructural characterization of mechanically tested samples using SEM and TEM. The deformation behavior has been studied by SEM based fractography and TEM based on defects analyses. The observed fracture mechanisms will be discussed in terms of dislocation mobilities in the Al and the BE phase respectively.
2:50 pm
EFFECT OF ALLOYING ELEMENTS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF SQUEEZE CAST MgAl ZnX ALLOYS: Jae Joong Kim, Do Hyang Kim*, Sang Hyuk Kim, Nack J. Kim, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790784, Korea, *Dept. of Metallurgical Eng., Yonsei Univ., Shinchondong, Seodaemunku, Seoul, Korea
Mg alloys offer the potential for significant weight savings in aerospace components because of their low density. Nevertheless, there is a strong need for Mg alloys with much improved mechanical properties. The main objective of the present research is to improve the mechanical properties of Mg alloys by squeeze casting and by alloy modification. The addition of Si results in the formation of Mg2Si in two morphologies; polygon and chinese script. While the polygonal Mg2Si improves the mechanical properties of Mg alloys, the chinese script Mg2Si promotes the brittle fracture along the Mg2Si/matrix interface, resulting in poor ductility. Microalloying elements have been added to modify the morphology of chinese script Mg2Si. It has been shown that the additions of Ca or P eliminate the chinese script Mg2Si so that all of the Mg2Si particles are present in polygonal form, resulting in the improvement of mechanical properties.
3:15 pm
PHENOMENOLOGICAL MODELING OF SUPERPLASTICITY: F. Booeshaghi, H. Garmestani, P. N. Kalu, Department of Mechanical Engineering, FAMUFSU College of Engineering, Tallahassee, FL
There has been an increased interest in the mechanics and materials field to improve the constitutive relations for the superplastic deformation of advanced materials. This interest has been stimulated partly due to the discovery of high strain rate superplasticity, and partly due to the availability of powerful computers. In this paper, an attempt was made to develop new type of constitutive relations to elucidate superplasticity. Although the model was derived from Hart's model, it incorporates detailed microstructural parameters and can be extended to multiaxial deformation. An attempt was made to use the model to explain the deformation mechanisms in superplastic AlLi 7475 and Al-Li 8090 alloys. Load relaxation and jump strain rate tests were employed in this investigation. Microstructural characterization was carried out by optical nicroscopy and orientation Imaging Microscopy.
3:40 pm
WATERJET ABRASIVE APPLICATIONS FOR LIGHT WEIGHT ALLOYS: Lin Zhong Lee, Laser Applications, Inc., Westminster, MD 21157
As the aerospace applications of light weight alloys expand, waterjet abrasive process is a viable approach to manufacturing. This technology utilizes high pressurized water and an abrasive passing through a nozzle that is capable of cutting most materials up to 9" thick. It provides precision cutting of any contour, shape, and size which will allow engineers and designers the freedom to create more complex designs. The main components of a waterjet system consist of an ultrahigh pressure intensifier, a cutting head, and a CNC controller. The jet parameters consist of the water pressure, orifice size, nozzle size, abrasive type, abrasive flow rate and cutting head feedrate. The kinetic energy is created from the mass of the water and abrasive exiting the nozzle at twice the speed of sound. At this high velocity, the jet stream acts like a solid medium that erodes the material. The efficiency of the waterjet is dependent on the initial energy leaving the nozzle and the energy required to remove the material. Therefore, it is easier to cut a soft and thin material than a hard and thick material. Through this process, superior edge quality is achieved with no heat affect zone (HAZ), no metal contamination, no distortion, no slag, and no delamination.
4:05 pm
MICROMECHANICAL ANALYSIS OF ADHESION STRENGTH FOR A BRITTLE FILM COATED SUBSTRATE: Jeunghyun Jeong, HaeSeok Park, JeongHoon Ahn and Dongil Kwon, School of Materials Science and Engineering, Seoul National University, Seoul 151742, Korea
In this work, we attempted to estimate the interface adhesion strength through the stress analysis in a brittle film coated substrate by two methods: scratch method and film cracking method. Firstly, in a scratch test, the critical load used as a qualitative estimate of adhesion is converted into work of adhesion by analyzing the stress field beneath the indenter, which results from three contributions, i.e., the static indentation added by the blister stress field, the friction between the indenter and film, and the residual stress. Secondly, in uniaxial loading of a brittle film coated soft substrate, the adhesion dependency of the development behavior of the transverse film cracks is analyzed specifying the film tensile stress and the interface shear stress which induce film cracking and interface failure, respectively. Then, the interface adhesion is quantified as interface shear strength because the stoppage of film cracking with further straining means the interface failure by the excessive interface shear stress, and the saturated value of crack spacing and strain can be used for the qualitative comparison of adhesion.
4:30 pm
ELECTROMAGNETIC PULSED CALIBRATION OF THIN ALUMINUM ALLOYS SHELLS: Sergey F. Golovashchenko, Moscow State Technical University, visiting at Ford Motor Company Scientific Lab Material Science Department, 20000 Rotunda Dr., P.O.Box 2053,MD3182, SRL, Dearborn, MI 481212053
Pulsed electromagnetic field have been used to size thinwalled shells inside calibration dies. This works even when the shell have been formed by bending sheet metal and closed by a welding seam. Deformation is accomplished by a highvoltage discharge of capacitors through a coil inside the shell. Experimental results for AlCuFeM high strength alloy rings are presented. They show a significant improvement of the accuracy of shell dimensions with increasing pressure amplitude. Results of the numerical simulation of the shell-die contact interaction are obtained assuming that shell is elastoplastic and the die is elastic. Solid mechanics equation of motion and elastoplastic flow rule have been used to simulate this process. This simulation takes account of multiple impacts, spring back, stress waves in shell and die and has been experimentally validated.
4:55 pm
THERMAL ANALYSIS OF AGED BINARY Al-Li ALLOYS: Sedat Ozbilen, Gazi University, Faculty of Technical Education, Metal Educational Department, Teknikokullar, Ankara, Turkey
Al-Li binary alloys with nominal Li contents of 0.1, 1.0, 2.8 (in wt%) were aged naturally (for 3 months) and artificially (not only for 2 months both at 65% and 100°C but also for 2 days at 190°C) after water quenching to 25°C following solutionizing at 530°C for 20 minutes. Aging behaviour of these binary alloys were studied by Vicker's Hardness measurements and DSC/DTA thermal analysis. The results of this investigation will be presented.
Room: 314B
Session Chairpersons: S.J. Pearton, University of Florida, 343 NSC, PO Box 116400, Gainesville, FL 32611-6400
2:00 pm INVITED
EFFECT OF DRY ETCHING ON III-NITRIDES SURFACE: F. Ren, S.J. Pearton*, C.R. Abernathy*, J.R. Lothian, Bell Laboratories, 600 Mountain Ave., Rm. 7-B-207, Murray Hill, NJ 07974; *University of Florida, 343 NSC, PO Box 116400, Gainesville, FL 32611-6400
2:30 pm INVITED
GaAs SURFACE CHEMISTRY AND SURFACE DAMAGE IN A Cl2/Ar HIGH DENSITY PLASMA ETCHING PROCESS: Charles R. Eddy, Jr., O.J. Glembocki, D. Leonhardt, V.A. Shamamian, R.T. Holm, J.E. Butler, Naval Research Laboratory, S.W. Pang, University of Michigan, Ann Arbor, MI 48109-1120
3:00 pm
HIGH DENSITY ELECTRON CYCLOTRON RESONANCE ETCHING FOR METALS: K. Jung, J.W. Lee, Y. Park, J.R. Childress, S.J. Pearton, University of Florida, P.O. Box 116400, Gainesville, FL 32611
3:15 pm INVITED
DAMAGE EVOLUTION IN DRY-ETCHED GaAs: Comparison Between Reactive Ion Etching and Low Energy Electron Enhanced Etching: M.S. Goorsky, H.P. Gillis, A.M. Andrews, University of California, Los Angeles, CA
3:45 pm BREAK
Session Chairperson: F. Ren, Bell Laboratories, 600 Mountain Ave., Rm. 7-B-207, Murray Hill, NJ 07974
4:00 pm INVITED
SEMICONDUCTOR MATERIALS PROCESSING UTILIZING AN INDUCTIVELY COUPLED PLASMA BEAM SOURCE: C. Constantine, Plasma Therm, Inc.; R.J. Shul, Sandia National Laboratories; S.J. Pearton, University of Florida, Gainesville, FL 32611
4:30 pm INVITED
NANOMETER-SCALE STUDIES OF NITRIDE/ARSENIDE HETEROSTRUCTURES PRODUCED BY NITROGEN PLASMA EXPOSURE OF GaAs: Rachel S. Goldman1,2, B.G. Briner3, R.M. Feenstra2, M.L. O'Steen4, R.J. Hauenstein4, 1Present address; University of Michigan, Ann Arbor, MI; 2Carnegie Mellon University, Pittsburgh, PA; 3Fritz-Haber-Inst. Der Max-Plank-Gescllschaft, Germany; 4Oklahoma State University
5:00 pm
COMPARISON OF ECR PLASMA CHEMISTRIES FOR ETCHING OF InGaP AND AlGaP: J. Hong, J.W. Lee, C.R. Abernathy, S.J. Pearton, C. Constantine1, W.S. Hobson2, and F. Ren2, University of Florida, Gainesville, FL; 1Plasma Therm Inc.; 2Bell Laboratories
5:15 pm
COMPARISON OF DRY ETCHING OF II-V SEMICONDUCTORS IN Icl/Ar AND Ibr/Ar ELECTRON CYCLOTRON RESONANCE PLASMAS: J.W. Lee, J. Hong, E.S. Lambers, C.R. Abernathy, S.J. Pearton, University of Florida, PO Box 116400, Gainesville, FL 32611; W.S. Hobson, F. Ren, Bell Laboratories
Room: 231B
Session Chairpersons: P.R. Taylor, University of Idaho, Dept. of Metallurgical & Mining Engineering, Moscow, ID 83844-3024; J.R. Groza, Chemical Engineering and Materials Science Dept., University of California at Davis
2:00 pm
ZIRCONIUM CARBIDE SYNTHESIS IN A HIGH TEMPERATURE PLASMA REACTOR: Patrick R. Taylor, Banqiu Wu and Edgar E. Vidal, University of Idaho, Department of Metallurgical & Mining Engineering, Moscow, ID 83844-3024
Zirconium carbide powder has been synthesized from zircon concentrate and methane using a high temperature plasma reactor. A non-transferred DC plasma torch was used as heat source. A high temperature filter consisting of graphite felt was designed, built and operated to separate the zirconium carbide from silicon carbide during the process. Characterization of the collected powders was done by wet chemical analysis using Atomic Absorption (AA), Scanning and Transmission Electron Microscopy (SEM and TEM) and X-Ray Diffraction (XRD). It was found that the zirconium carbide purity was around 95% with silicon carbide being the primary impurity. The powders had particle sizes between 30 and 80 nm. Based on the XRD pattern a lattice parameter of 4.6932A was calculated for the zirconium carbide. The effect of several experimental variables is presented as well as a mathematical model that describes the temperature and velocity profiles in the reactor.
2:25 pm
PRECIPITATES ROLE IN SUPERPLASTICITY OF HIGH PERFORMANCE COPPER ALLOYS: Ken R. Anderson, Joanna R. Groza, Chemical Engineering and Materials Science Dept. University of California at Davis, A.T. Dumitrescu, Metallurgical Research Institute, Bucharest, Romania
High strength, high thermal conductivity copper alloys are in continuous demand for a variety of applications such as actively cooled structures, electric and electronic parts, molding tools or welding electrodes. The goal of the present work is to understand the interrelationship between processing and microstructure of these alloys to promote superplastic behavior. Chemistry and processing variations were applied to achieve precipitation of different dispersoids in the copper matrix. High temperature, high strain rate deformation was performed to characterize the superplastic behavior. Precipitate identification and microstructural studies were correlated to mechanical properties.
2:50 pm
MECHANICAL PROPERTIES AND MICROSTRUCTURAL CHARACTERIZATION OF THE COMMERCIAL ALUMINUM ALLOY 6063 UNDER DIFFERENT HOMOGENIZING THERMAL TREATMENTS: J.R. Rendon, C.V.G Venalum, Puerto Ordaz, Venezuela, B. Hidalgo, Universidad de Oriente, Cumana, Venezuela, Mokka N. Rao, Universidad Nacional Experimental de Guayana, Puerto Ordaz, Venezuela
Cylinders of commercial aluminum alloy 6063 were homogenized under different conditions. The experimental results indicate that the general mechanical behavior as related to curves of 0.2% yield strength, ultimate tensile strength, and ductility versus homogenizing process is the same in both cases. These mechanical properties as compared to those required by plant specifications, tend to be better with increasing values of %Mg2Si in the alloy, as expected. The electron microscopy investigations revealed that in both homogenizing processes the resulting microstructure consist of significant spheroidizing of the alpha phase (AlFeSi) and fine - needle type structures of the beta phase. The alpha phase was also present in a Chinese scripture type structure. Furthermore, the slow cooling within the furnace resulted in the nucleation and growth of Mg2Si precipitates generally along the grain boundaries.
3:15 pm
THE FIRST EXPERIENCE WITH FORMATION OF "NATURAL" METAL-MATRIX COMPOSITE BY THE APPROPRIATE THERMO-MECHANICAL TREATMENT OF POLYCRYSTALLINE METALS: A. Korbel, W. Bochniak, F. Ciura, H. Dybiec, K. Piela, The Department of Structure & Mechanics of Solids, Academy of Mining and Metallurgy, Mickiewicza 30, 30-059 Krakow, Poland
The progress in understanding of the nature of strain localization in metallic materials and in particular understanding of the role of external (deformation conditions) and internal (material substructure) factors in the development of the tendency toward concentration of plastic flow within transgranular shear bands has laid at the background of the pointed in the title idea. Following this idea, a practical possibility of replacement a homogeneous in a micro scale mode of deformation by transgrasnular shear bands gives a chance to change the arrangement of dislocation substructure in the material from that typical for homogeneous deformation into a long wavelength (transgranular), pseudo-periodic dislocation walls. The presence or formation of such a substructure in a thermodynamically unstable matrix may result in formation of the products of phase transformation along shear bands, giving rise to a composite like structure. The experimental verification of the idea is the main aim of the work. The spectrum of different materials undergoing (post or during shear banding) different phase transformations: precipitation from supersaturated solid solution in Al-base alloys, martensitic transformation in Fe-Ni alloy, austenite-ferrite and austenite perlite transformation in the plain carbon steel and - transformation in Cu-Zn brass has been studied by use of the optical and electron microscopy. The effect of this way induced structures on some mechanical properties (strength of materials, shape memory effect in Fe-Ni alloy) is also shown in the work.
3:40 pm BREAK
3:50 pm
STUDIES ON GROWTH MECHANISMS AND CHARACTERISTIC FACTORS FOR THE HYDROTHERMAL PREPARATION OF A-QUARTZ CRYSTAL POWDERS: Kee Jeung Lee, Kyung Won Seo, Young Mok, Department of Chemical Engineering, Ajou University, 5 Wonchon-Dong, Paldal Gu, Suwon 442-749 Korea; Hyo Shin Yu, Korea Institute of Geology, Mining & Materials, Resources Utilization & Materials Division, 30 Kajung-Dong, Yusung Gu, Taejon, 305-350, Korea
In this study the characteristic factors and formation mechanisms for the hydrothermal preparation of -quartz crystal powders were investigated to find the optimum synthetic conditions. The degree of -quartz crystal face development depended on the relative growth rate of a particular form that varies considerable with the degree of supersaturation, the reaction temperature, the concentration of mineralizers, and the presence of seed crystals in the feedstock. Alkali hydroxides and alkali halides were found to be effective in the reactions as mineralizers, which added in order to increase the solubility of the feedstock. The fine quartz crystal powders were obtained in the temperature range of 250-500°C and pressure range of 100-300 atm. As the concentration of mineralizers increased, the particle size of crystalline powders became smaller with lower reaction temperatures. The fractional size distribution of synthetic crystal powders was depended on the hydrothermal conditions. As the reaction time and the amount of seed crystals increased, the width of particle size distribution became narrower. The weight mean particle size was in the range of 1 to 10µm. The characterization of the products were carried out using XRD, SEM, PSA, FTIR, Raman Spectrometer.
4:15 pm
THE INTRAGRANULAR FERRITE PLATE AND ITS NUCLEATING INCLUSIONS IN HAZ OF X-60 PIPE STEEL: Jiang Guo Chang, Zhu Yu Ru, Guo Shu Qiang, Xu Jian Lun, Department of Materials, Shanghai University, 149 Yan Chang Road, Shanghai 200072, China; Wang Yue Qlang, Pan Li Ying, Yu Di Wei, Bao Shan Iron & Steel Corporation
To improve the HAZ toughness of X-60 pipe steel the intragranular ferrite plate (IFP) technology was used. The characteristics of IFP is claimed to be much fine ferrite plates appear inside the original austenite grains. By means of a suitable Re, Zr, Ti additions in a bath with a higher initial oxygen potential, and a good control over the peak temperature as well as the cooling rate during welding simulation, one get a%IFP in volume over 50%, and the toughness goes up from 55J to 160J. It was found that the inclusions most effective on nucleating IFP are some deformable complex silicates which either entrapping Re, Zr, Ti oxides or containing these elements. The more the evenly distributed and effectively nucleating inclusions, the more the % IFP in volume, and the finer the microstructure of the HAZ, so the better the relevant toughness. Generally, these silicates behave as fine spheres along a line. The present authors revealed that these fine spheres result from the remelting of the silicates due to temperature raising up in the process of welding simulation. These silicates used to get a higher sulfur capacity, so MnS deposits might be observed on the periphery of the silicates. IFP was proved to be directly rooted in the [Mn] depleting zone which locates beside MnS deposits.
4:40 pm
ZIRCONIUM PURIFICATION IN THE PROCESS OF METAL RAW MATERIALS IODINATION: Z.B. Moukhametshina, V.I. Adamovich, A.M. Chekmarev, Mendeleev University of Chemical Technology of Russia, Miusskaya sq., 9, Moscow 125047, Russia
The process of various zirconium alloys iodination by the iodine vapor was investigated. The nature of impurities, conditions of iodination, iodine flow rate, and zirconium tetraiodide condensation rate effect on the metal impurities transfer process was analyzed, both qualitative and quantitative correlations were established. Impurities were classified according to their transfer extent. Another classification of impurities transport dependence on iodination process temperature was also offered Obtained results were compared with impurities transport data in the process of iodide refining available in literature. Some impurities transport mechanisms and iodide-refined metals improvement possibility by means of iodination conditions control were discussed.
Room: 240A
Session Chairpersons: Prof. J.E. Morral, Univ. of Connecticut, 97 N. Eagleville Road, Storrs, CT 06269-3136; Dr. H. Merchant, Gould Electronics, Inc, 35129 Curtis Blvd., Eastlake, OH 44095-4001
2:00 pm INVITED
EXPERIMENTAL AND OPTIMIZED BINARY SYSTEMS OF POST-TRANSITIONAL ELEMENTS: B. Legendre, Y. Feutelais and E. Dichi, Laboratoire de Chimie-Physique Minérale et Bioinorganique, Faculté de Pharmacie, 5 rue J.B. Clément, 92296 Châtenay-Malabry, France
Post transitional elements present a lot of physical properties, especially in the fields of electronic and opto-electronic. Thus the knowledge of binary and ternary phase diagrams is of great importance both for the elaboration of alloys and for their application. One of the characteristics of the elements of post transition is a low melting point and for a large number of them a high vapor pressure. For this last reason it is of great interest to include the gas phase with the condensed phases and to calculate the pressure dependence of the phase diagram. In this lecture, we present experimental data and the result of the optimization for some systems such as: cd-Ge, Cd-Te, Zn-Te, Cd-Zn-Te, Ge-Te, Si-Te, Au-Te. All of these binary systems are included in a database (POSTRANS) compatible with Thermocalc.
2:30 pm
PHASE EQUILIBRIA AND THERMOCHEMISTRY OF THE In-Se SYSTEM: C. Mallika, C.H. Chang, A. Davydov, B.J. Stanbery, T.J. Anderson, Dept. of Chemical Eng., Univ. of Florida, Gainesville, FL 32611
The phase diagram and thermochemistry of the In-Se system have been studied by several investigators, however, the liquid mixture behavior is not well understood. The following galvanic cell: W|In(I),In2O3(s)||In2O3(s),[In]In-Se(s or 1)|C|W was used to determine the activity of In in In-Se liquid alloys in the compositional range 0.10<xse,0.60 and the temperature range 800 to 975 K. Slightly positive deviations from ideal solution behavior were observed in the liquid solution and the measured liquids temperatures were in good agreement with those reported in the literature. In addition, the Gibbs energy of formation for each intermediate compound was derived from the measured values of emf. These results were then combined with other experimental data available in the literature to reassess the thermochemistry and the In-Se phase diagram. Four intermediate solid phases (In4 Se3, InSe, In6Se7, and In2Se3) were considered to be line compounds in this assessment and the Redlich-Kister expression was used to model the liquid phase.
2:50 pm
ASSESSMENT OF THE PHASE DIAGRAM AND THERMODYNAMIC PROPERTIES OF THE As- Ga-Sb AND As-In-Sb SYSTEMS: A. Watson, Univ. of Sheffield, Mappin St., Sheffield S1 3JD, United Kingdom; A. Davydov, S. Misra, T.J. Anderson, Dept. of Chemical Engr., Univ. of Florida, Gainesville, FL 32611
Group III arsenides and antimonides are extremely important materials used in the manufacture of high speed and high frequency electronic devices. In the III-V semiconductor family As-Ga-In-Sb, there are four ternary subsystems. By selecting different compositions within these subsystems, electrical and optical properties of the material can be changed in order to satisfy different applications. In this work, experimental phase diagram information and thermochemical data available in the literature for the As-Ga-Sb and As-In-Sb systems have been critically assessed as a preliminary step towards the study of the As-Ga-In-Sb system. Thermodynamic descriptions of the phases that are consistent with selected experimental data have been produced using the ternary optimizing program TERGSS and thermodynamic descriptions of the binary and unary phases from previous assessments. Phase equilibria and thermodynamic properties are presented which have been calculated from the optimized coefficients using MTDATA. This information can be used for optimizing materials growth conditions and device manufacture.
3:10 pm
POTENTIOMETRIC DETERMINATION OF THE THERMODYNAMIC STABILITY OF SB2O3: R. Lowery, C. Mallika, and T.J. Anderson, Dept. of Chemical Engr., Univ. of Florida, Gainesville, FL 32611
Precise values of thermodynamic properties of Sb2O3 are required to synthesize and characterize the alloys of antimony for applications in thermoelectric devices and semiconductor technology. The Gibbs energy formation of Sb2O3 has been reliably reported in the literature using solid electrolyte emf measurements. This work is extended to determine the phase equilibrium temperatures in Sb/Sb2O3 system. The galvanic cell used in this study can be represented as W|C|Sb(s or 1), Sb2O3(s or 1)_YSZ_ Cu2O,Cu|W. The oxygen potential for the biphasic mixtures were derived from the cell potential data over the temperature range 790 to 983 K. Phase transition temperatures of 845.5 K (Sb2O3, orthorhombic to Sb2O3, cubic), 905.6 K (Sb,s to Sb,1) and 930.0K (Sb2O3,cubic to Sb2O3,1) were obtained from discernible breaks in the emf-T plots. These results agree well with calorimetric values. A value of -712.4 kJ/mol calculated by third-law treatment for DH°f,298 (Sb2O3, orthorhombic) reasonably agrees with literature data.
3:30 pm
PREDICTING OF THE THERMODYNAMIC PROPERTIES FOR THE TERNARY SYSTEM Ga-Sb-Bi: Dragana Zivkovic, Zivan Zivkovic, Univ. of Belgrade, Technical Faculty, 19210, Yugoslavia, Jaroslav Sestak, Czech Acad. of Sciences, Inst. of Physics, 18040 Praha, Czech Republic
Ternary system Ga-Sb-Bi belongs to the group of alloy systems containing semi-conducting compounds, which are important from both the scientific and practical point of view. While binary systems Ga-Sb, Bi-Sb and Ga-Bi are mostly thermodynamically determined, there are only a few data about the thermodynamics of the investigated ternary system Ga-Bi-Sb. Because of the experimental difficulties in thermodynamic determination of this system, connected with the oxidation and volatizing of the present components at investigation temperatures, thermodynamic predicting is applied, and results of the comparative determination of thermodynamic properties in ternary system Ga-Sb-Bi by using following methods: Toop, R-function and general solution model, are given in this paper. Activities, activity coefficients, partial and integral molar quantities for all components in five quasibinary sections of the ternary system Ga-Sb-Bi are determined at temperature 1073K.
3:50 pm
THERMODYNAMIC PROPERTIES AND VAPOR-LIQUID EQUILIBRIUM RELATIONS OF INDIUM-CONTAINING BINARIES: Dajian Wang, Kunming University of Science and Technology, Yunnan, 650093, China
To establish the vapor-liquid equilibrium composition relations of In-Sn, In-Pb, In-Zn, the Miedema's cellular model of heat of formation of binary liquid alloys are employed to correlate the activity coefficients of each component in the binary. Based on the dissimilar Wigner-Seitz atomic cells model, a quantitative analysis of heats of mixing and solution of binary alloys was Miedema. Tanaka deduced the relation between mixing enthalpy and excess entropy of liquid binary alloy. Through the correlation between the heat of formation and excess Gibbs free energy, the activity coefficients and their practical pressures can be analyzed. The obtained results have met the needs of activity coefficients of each component in above alloys in the applications of vacuum separation techniques, as well as in the development of lead-free solder of In-Sn binary or related multicomponent systems.
4:10 pm
APPLICATION OF KNUDSEN EFFUSION MASS SPECTROSCOPY FOR THE STUDY OF THERMODYNAMIC AND PHASE DIAGRAM PROPERTIES OF TRANSITION METAL-TELLURIUM SYSTEMS: M. Sai Baba, Dept. of Chemistry, Texas A&M Univ., College Station, TX 77843; R. Viswanathan, Materials Chemistry Div., Chemical Group, Indira Gandi Centre for Atomic Research, Kalpakkam - 603 102, Tamil Nadu, India
Knudsen effusion mass spectrometric technique has been employed to study the thermodynamic and phase diagram properties of transition metal-tellurium systems. Preferential evaporation of these metal tellurides has been made use of to generate the nonstoichiometric telluride phases in situ. From the variation of tellurium activity as a function of composition, homogeneity ranges of the nonstoichiometric metal tellurides have been arrived at. By applying Gibbs-Duhem integration the thermodynamic activity of the second component could be arrived at. From the activities, partial molar Gibbs free energies were derived. Some of the metal tellerium systems studied include Fe-Te, Cr-Te, Mo-Te and Mn-Te. In this paper we describe some of our results with emphasis on the usefulness of Knudsen effusion mass spectrometric method for deriving such information.
4:30 pm
THE INTERFACIAL REACTIONS IN THE As-Se/Zn COUPLES: Ming-Horng Lin, Sinn-wen Chen, Dept. of Chemical Engr., National Tsing-Hua University, Hsinchu, Taiwan 30043, China; Jinn-lung Wang, Chemical Systems Research Div., Chung-Shan Institute of Science and Technology, Lung-Tan, Taiwan, China
The As-Se-based chalcogenide glasses are IR transparent, and are considered an ideal braze to the ZnSe and ZnS substrates in the IR detector. The interfacial reactions between As-Se and Zn are investigated for fundamental understanding. Three different kinds of reaction couples were prepared, and they were As-50at%Se/Zn at 350°C. As-50at%Se/Zn at 370°C, and As-60at%Se/Zn at 350°C annealed for various length of time. The cross sections of the reaction couples were analyzed by using OM and EPMA. Two phases were formed at the interface, and the diffusion paths were glass/ZnSe/As2Zn3/Zn. The growth rates of the intermetallic layers were also determined by using as image analyzer. The growth rates followed the parabolic law for the type I and type III couples which indicated a diffusion-controlled mechanism.
4:50 pm
THE ATMOSPHERIC OXIDATION OF TELLURIUM: Marc Suys, École Polytechnique de Montréal, Dept. of Chemical Engr, C.P. 6079, centre-ville, Montréal (Québec), Canada DA, H3C 3A7; A. Roy, and J. L'Écuyer, Noranda Advanced Materials, 4950 Lévy, Saint-Laurent (Québec), Canada, H4R 2P1
Tellurium forms technologically important alloys which are being used increasingly in the semiconductor industry (CdTe,Bi2Te3). As such, control of the purity of the source TE metal is critical. Therefore, the understanding of the atmospheric oxidation of tellerium cannot be neglected, as it can be a source of oxygen incorporation in the metal, and thus in the alloys. We have studied, by X-Ray Photoelectron Spectroscopy (XPS), the oxidation of crushed tellerium under various conditions of humidity and air exposure. The rate of oxidation of tellerium is relatively slow: 30 A of tellerium dioxide is detected on the surface of a sample after 8 days of direct air exposure. Our results tend to suggest that the rate-limiting step is the transport of the oxidizing reactant to the tellerium surface. We have also observed that the oxidation reaction is dependent on the relative humidity, as has been reported previously, for thin films, by various authors.
Room: 314A
Session Chairpersons: Professor Robert O. Ritchie, Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 97420-1760 and, Center for Advanced Materials, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; Dr. Michael F. Henry, General Electric CR&D, P.O. Box 8, K1-MB229, Schenectady, NY 12309
2:00 pm INVITED
MECHANISMS OF FATIGUE FRACTURE IN METALLIC, CERAMIC, AND INTERMETALLIC MATERIALS: Robert O. Ritchie, Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 97420-1760 and, Center for Advanced Materials, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
From his early micro-mechanical modeling of fatigue-crack propagation in anti-plane shear to his later hypothesis for the existence of a fatigue threshold, Frank McClintock has made many seminal contributions to the understanding of fatigue fracture in metallic materials. In this presentation, current thinking on the mechanics and mechanisms of fatigue is examined, with particular emphasis on the similarities and differences between metal fatigue and the failure of monolithic and composite intermetallics and ceramics under cyclic loading. This is achieved by considering the process of fatigue-crack growth as a mutual competition between intrinsic mechanisms of crack advance ahead of the crack tip (e.g., alternating shear), which promote crack growth, and extrinsic mechanisms of crack-tip shielding behind the tip (e.g., crack closure and bridging), which impede it. The widely differing nature of these mechanisms and their specific dependence upon the alternating and maximum driven forces (e.g., 
K and Kmax) provide a useful distinction of the process of fatigue-crack propagation in the different classes of materials.
2:25 pm INVITED
OBSERVATIONS ON THE NUCLEATION AND MICROSTRUCTURALLY DEPENDENT CRACK PROPAGATION IN STRUCTURAL METALLIC MATERIALS: David W. Hoeppner, Department of Mechanical Engineering and Quality and Integrity Design Engineering Center, University of Utah, 3209 MEB, Salt Lake City, UT 84112
In the mid 1800's Sorby used the optical microscope to study fatigue deformation of materials and started an activity that continues with some vigor today. The early investigators of fatigue deformation wanted to learn the mechanism(s) of fatigue crack nucleation and propagation. This progress was aided by many investigators including Frank McClintock. McClintock and other investigators inspired many investigators to pursue the observation of fatigue deformation so that improved understanding of fatigue mechanisms could be attained. However, many studies that were made were "static". That is, materials were exposed to cyclic loading and then viewed with the observational technique. While this allowed some progress to be made, this did not deal with the actual deformation(s) that were occurring and thus progress in understanding fatigue was very limited. However, some investigators did mount microscopes on fatigue machines and make what became known as "in-situ" observations. Some of the contributions made will be reviewed as background of this paper. The development of the scanning electron microscope has changed the understanding of cyclic deformation response in engineering and model materials. Starting in 1970 numerous investigators around the world developed fatigue machines that were either placed in the chamber of an SEM or were attached to the SEM. Contributions of Kromp, Weiss, Strickler, Kikukawa, Jono, Aachi, Davidson, Hoeppner and others will be reviewed. In addition the past 25 years has seen the development of numerous in-situ systems. This has led to much greater understanding of fatigue crack nucleation and microstructurally dependent propagation. These studies and observations will be reviewed in the paper.
2:50 pm INVITED
DISLOCATION-CRACK INTERACTIONS DURING FATIGUE CRACK GROWTH: K. Sadananda1, N. Louat2 A. K. Vasudevan3, 1Naval Research Laboratory, Code 6323, 4555 Overlook Drive SW, Washington D. C. 20375; 2Fairfax Materials Research Inc., 5613 Marble Arch Way, Alexandria, VA 22315; 3Code 332, Office Naval Research, N. Quincy Road, Arlington, VA 22217
Fatigue crack growth occurs due to irreversibility associated with the plastic flow under cyclic load. Although crack growth occurs by plastic flow, the use of elastic fracture mechanics parameter to quantify crack growth may still be justified since material for the most part is under elastic loading, normally termed as small scale loading. In the past, concepts such as plasticity induced crack closure have crept into the literature and led to massive confusion in the literature in understanding and quantifying fatigue crack growth. We present new unifying concepts using dislocation models that accounts, load-ratio effects, so-called anomalous effects of short cracks, over-load and under-load effects, as well as concepts that connect the crack nucleation through Kitagaawa diagram.
3:25 pm INVITED
FATIGUE FRACTURE STRIATION FORMATION AND ITS RELATION TO CRACK TIP BEHAVIOR: Campbell Laird and Pedro Peralta, Department of Materials Science and Engineering, University of Pennsylvania, 3231 Wanut Street, Philadelphia, PA 19104
The mechanisms of fatigue striation formation are reviewed in terms of ductile and brittle fracture processes. Depending on these processes, fatigue striations can show considerable morphological variations, which are explained in terms of detailed slip processes and dislocation structures as well as fracture mechanisms. The problem of striation formation during intergranular crack propagation is also treated with respect to new results obtained on bicrystals having misorientation. These results are helpful for understanding how striation formation is related to the geometry and crystallography of slip at the crack tip.
3:50 pm BREAK
4:00 pm INVITED
INFLUENCE OF MICROSTRUCTURE ON LOW CYCLE FATIGUE FRACTURE: S. L. Mannan, K. Bhanu Sankara Rao, Materials Development Division, Indira Gandhi Center for Atomic Research, Kalpakkam 603 102, India
High temperature low cycle fatigue (LCF) has been an area of great interest in the last decades because of its relevance in nuclear and aerospace industrial applications. In general, the cyclic deformation and fracture of alloys engineered for high performance applications depend critically on the stability of initial microstructure during cyclic loading and on the slip mode, both of which in turn depending on temperature, govern the cyclic stress response and the mode of crack initiation and propagation. In order to attain adequate fatigue resistance in high temperature materials, a thorough understanding of quantitative relationship between initial microstructure and the fracture mode is required. Grain size, degree of prior cold work, thermal aging that occurs prior to and during service are the major structural parameters that influence LCF of austenitic stainless steels while the size and distribution of ' and carbides control the cyclic deformation and fracture in nickel base superalloys. Low cycle fatigue studies have been conducted on 304SS to examine the effects of grain size (75, 310 and 700 µm), cold work (0, 10, 20 and 30%) and thermal aging (923K: 1000h, 3000h, 5000h) on LCF fracture over a very wide temperature range (300-1023K). Fine grained material exhibited better endurance in terms of total and plastic strain amplitudes at all temperatures. The temperature dependence of fatigue life showed a complex behaviour. Medium and coarse grained alloy displayed a continuous reduction in life with increase in temperature with recovery in life at elevated temperatures. The effects of grain size on life were rationalised on the basis of martensite transformation, dynamic strain aging, oxidation and creep in the temperature range of their operation. The superior fatigue resistance of fine grained material has been attributed to the occurrence of trangranular fracture at all the temperatures. Cold work has been found to be both beneficial and harmful for fatigue life depending on the temperature. LCF life decreased with increasing PCW at and below 823K, whereas at 923K, PCW levels greater than 10% cold work exhibited recovery in life due to the reduced incidence of intergranular cracking. Thermal aging prior to LCF testing promoted transgranular cracking and improved fatigue resistance. The influence of microstructure (A: free from carbides and ', B: peak aged spherical ' of 18 nm diameter and C: overaged spherical ' of 35 nm diameter) on strain controlled LCF behaviour of Nimonic PE-16 superalloy has been studied at 923 K. Coffin-Manson plots describing the plastic strain amplitude versus life showed that Microstructure A had maximum fatigue resistance while C displayed the least. Microstructure B showed a two slope behaviour in the Coffin-Manson plot. For this condition samples cycled at low strain amplitudes exhibited much shorter lives than would be expected by extrapolation from high strain portion of the plot. Microstructure A exhibited crack initiation in planar slip bands, followed by transgranular propagation marked by fatigue striations. In B, the fracture mode at high strains was transgranular, while at low strains propagation by both trans and intergranular (mixed mode) was observed. Alloy C displayed cleavage facets very frequently on the fracture surface, and crack propagation was mixed mode at all strain amplitudes. The microstructural dependence of LCF behaviour and fracture modes have been rationalised on the basis of operative deformation mechanisms, degree of slip homogenization and the evolving microstructure during cyclic deformation. The degree of homogeneity was assessed by slip band spacing measurements on tested samples. These studies on 304SS and Nimonic PE-16 emphasise the need for optimisation of microstructure for maximizing fatigue resistance.
4:25 pm INVITED
CORROSION FATIGUE BEHAVIOR OF METALS AND ALLOYS: David J. Duquette, Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180
The qualitative aspects of the effects of corrosion on the fatigue behavior of metals and alloys have been recognized for more than 60 years. However, for much of that time, corrosion was assumed to lower fatigue resistance, simply by either inducing stress raisers in the form of pitting, or by reducing the cross-sectional area of a component. Modern research has shown that there may be a complex synergism between corrosion and the cyclic deformation response of metallic materials. This synergism may affect precrack deformation, crack nucleation and/or crack propagation. This presentation will address this synergism, and attempt to demonstrate that neither simple corrosion models for crack initiation, nor superposition models where corrosion rates and fatigue crack propagation rates are numerically added, are adequate to represent corrosion fatigue damage.
4:50 pm INVITED
THE EVOLUTION OF A CONSTITUTIVE RELATION FOR FATIGUE CRACK GROWTH: Arthur J. McEvily, Department of Metallurgy and Institute of Materials Science, U-136, University of Connecticut, Storrs, CT 06268
Load sequence effect can exert a strong influence on the rate of fatigue crack growth. For example, a large spike overload can result in a period of crack growth retardation after the overload. In order to calculate the number of delay cycles resulting from such an overload, a constitutive equation is needed, and it has been proposed that the following equation provides a generally valid constitutive relationship for the rate of fatigue crack growth: da/dN = A (Keff - Keffth)2 where a is the crack length, N is the number of cycles, A is a material constant, Keff is the effective range of the stress intensity factor, Keffth is the effective range of stress intensity factor at threshold. This equation can only be used if crack closure effects are accounted for. Examples of the use of the equation to calculate the number or retardation cycles following an overload as a function of specimen thickness will be given. In addition, the application of the equation to the study of short crack growth involving high-low and low-high load sequences will also be demonstrated.
5:15 pm INVITED
MICROMECHANICS OF FATIGUE AND FRACTURE IN LAMELLAR TiAl: Bimal K. Kad, Robert J. Asaro, Department of Applied Mechanics & Engineering Sciences, University of California at San Diego, La Jolla, CA 92093
While phenomological correlations, or simple rules of mixtures, are an important initial step in predicting the composite bulk response, the complexities of inhomogeneous deformation in layered morphologies, strain partitioning and incompatibilities between the respective micro-constituents, and discrete interface slip characteristics present formidable challenges for microstructural design. Thus, finite element based numerical procedures, incorporating phyically based crystal plasticity models, are employed to study the evolution of non-uniform deformation, under monotonic and fully reversed 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 data measurements. Such an effort is particularly desirable to help track various aspects of plastic anisotropy of specific layers, and micro-constituents are implicit in polycrystalline aggregates. We will present several examples of experimentally observed, and numerically computed results, to identify hot spots for strain localization in fully reversed loadings, and prescribe microstructural remedies to alleviate such effects.
5:40 pm
STEADY-STATE FATIGUE CRACK GROWTH IN COMPOSITE LAMINATES: J. Tong, Department of Mechanical and Manufacturing Engineering, University of Portmouth, Anglesea Building, Anglesea Road, Portmouth PO1 3DJ, UK
Matrix crack growth behaviour under mechanical fatigue loading has been studied in a quasi-isotropic GFRP laminate. Detailed experimental observations have been made on the growth of individual cracks and the accumulation of cracks in ±45°C as well as 90° plies. The results show that when the crack length is sufficiently long compared with the layer thickness, the growth of fatigue cracks in off-axis layers is essentially independent of crack length, a phenomenon termed as steady-state cracking. A generalised plane strain finite element model has been constructed and used to relate the crack growth rate to the associated strain energy release rate. A good correlation has been achieved which indicates that strain energy release rate may be the appropriate parameter to characterise stable matrix growth behaviour in composite laminates.
Room: 330B
Session Chairperson: Professor Jose Luis Estrada Haen, Instituto Politecnico Nacional, Unidad Profesional Adolfo Lopez Mateos, Mexico
2:00 pm KEYNOTE
EXPERIMENTAL BASED DETECTION OF THE SPLASH LIMITS FOR THE NORMAL AND OBLIQUE IMPACT OF MOLTEN METAL PARTICLES ON DIFFERENT SURFACES: M. Berg, J. Ulrich, Universitat Bremen, SFB 372,Verfahrenstechnik/FB4, Postfach 330440, D-28334 Bremen, Germany
Understanding of the impact of single molten metal particles contribute to reduce the overspray during the spray deposition processes. The impact of molten Pb- and Sn-particles with a flat solid surface is investigated experimentally. The impact process is monitored by a high speed video system. At each measurement all temperatures (particle, target, and ambient) are taken as the weight of the particle before and after impact. By means of the image processing, the final diameter of the splat is found and evaluated regarding physicla properties, impacting diameter, impact power, and target surface roughness. By the weight difference of a particle before and after the impact, amount of splashing material is detected. The impact diameter, the impact speed, and the spreading diameter are also observed by the high speed, and the spreading diameter are also observed by the high speed video system. The results are presented in the form of diagrams with dimensionless numbers such as the ratio of the maximum spreading diameter, d, to the initial particule diameter, D. Other numbers such as Weber, We, or Reynolds, Re, in connection with d/D ratio give the possibility of comparing all experimental results with each other. A critical dimensionless number above which splashing exists has been discussed.
2:30 pm
MICROSTRUCTURE CHARACTERIZATION OF AL-SI AND AL-MMCS PROCESSED BY SPRAY ATOMIZATION AND DEPOSITION: Jose Luis Estrada, Enrique Nicolas, Instituto Politecnico Nacional, Unidad Profesional Adolfo Lopez Mateos, MEXICO; Enrique J. Lavernia, Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92717
The spray atomization and deposition process is described as applied to Al-Si alloys and Al-Si metal matrix composites. This process shown to be similar to powder metallurgy (P/M) in that advanced alloys can be manufactured. However, many difficulties inherent in P/M are avoided, including oxide film formation and the need for degassing. In the spray atomization and deposition process atomized droplets exist for only a few milliseconds before being deposited to form high density preforms. The primary metallurgical characteristics of Al-12w/oSi, Al-17w/oSi, Al22w/oSi and Al-alloy based MMCs reinforced with SiC particulates preforms are presented. Characterization of the preforms consisted of the description of the production technique, descriptions of the microstructures by light microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Auger electron spectroscopy. The volume percentage of reinforced particles was determined. Both the spray deposited Al-Si alloys and the Al-Si metal matrix composites exhibited a rapid solidified matrix microstructure and the spray deposited MMCs a relatively uniform distribution of reinforcements.
2:50 pm
TUNGSTEN BORIDE SYNTHESIS IN BURNING: S.V. Nikolenko, V.V. Gostischev, Institute of Materials, Far Eastern Branch of the Russian Academy of Sciences, Khabarovsk, Russia
Nowadays, a great theoretical and practical interest is observed towards tungsten boride, that can be explained by its' specific physical, chemical and mechanical properties. This paper discusses the process of tungsten boride extraction by alumothermy from the tungsten-containing mineral (sheelite concentrate) derived from the original product by enriching. The experiments were conducted in air and vacuum. The study of the extracted products has shown that their composition differs and depends on the synthesis conditions. For example, if we use B2O3, in relation W:B=1:2; 1:3; 1:4, as a boride element, then we get the lower borides as the synthesis products: W2B, WB and metallic tungsten. The use of boron oxide with coal gives W2C together with W2B5. Including boron carbide guarantees that we shall receive the higher boride W2B5, independently from the environment of the reaction, due to the high speed of the burning. The conducted set of experiments, shows the possibility of synthesizing tungsten boride-base powders from the enriched mineral raw materials, which can be used for electro-spark and laser deposition of wear and heat resistant harding coats on construction and instrumental steels.
3:10 pm
POROSITY AND OXIDE DISTRIBUTION IN SPRAY FORMED Al-Cr-Zr ALLOYS: M. Baker, A. Hellwig, A.F. Norman, P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK
In spray formed Al alloys porosity is common and typically about 2 to 8% depending on alloy and product form and the oxygen content is typically less than the level of oxygen in commercially produced RS/PM Al alloys. There is no experimental evidence available about the distribution of Al2O3 in spray formed Al alloys. We have studied the size and distribution of pores and the distribution of oxides in spray formed Al-Cr-Zr alloys. The fracture surfaces of the as sprayed and forged deposits were examined by AES and SAM. Cratered regions on the in situ fracture surfaces were identified and a localized 2nm thick Al2O3 film on their surface was measured by high resolution AES. The fracture path followed areas rich in Al2O3.
3:30 pm BREAK
3:50 pm
STUDY OF MICROSTRUCTURE AND PROPERTIES OF SPRAY FORMED Al-Cr-Zr ALLOYS: A.F. Norman, P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK
The technical problems and cost associated with the multi-step PM processing of RS Al alloys have hindered their successful development. Spray forming can obviate these problems by means of the integral inert gas atomisation and deposition operation in which the alloy exists in particulate form only for a few milliseconds. Spray forming experiments have been performed on Al-Cr-Zr alloys studied previously by the combined RS/PM route. The microstructure and the tensile properties of the forged and heat treated deposits will be compared with the RS/PM alloy. The latter exhibits superior properties, not matched by the spray formed alloy.
4:10 pm
ABOUT SELECTION AND DESIGN OF ELECTRODE MATERIALS FOR ELECTRO-SPARK ALLOYING OF STEELS: A.D. Verkhoturo, S.V. Nikolenko, Institute of Materials, Far Eastern Branch of Russian Academy of Sciences, Khabarovsk, Russia
Earlier, we have proposed several parameters of selecting and designing electrode materials for electro-spark alloying (ESA) of metallic surfaces. These parameters were developed according to the necessity of achieving the maximum depth, continuity, the least stress in the alloyed layer (AL), as well as the least roughness. However, the developed principles account only for the "geometrical" characteristics of AL, without accounting for the technological characteristics, and the current manufacturing demands: higher productivity of the ESA process, creating the optimal conditions for the AL forming. Considering all of the above this paper discusses: 1) The scientific principles of designing and selecting the multi-component electrode materials, that account for the electrode space composition, as well as the composition-structure-characteristics relationship of electrode materials on the physical-chemical characteristics of AL and allowing to decrease fragile destruction of electrode material in the total erosion phenomena. 2) "Technological" scheme of AL forming, that accounts for effect of physical-chemical properties of electrodes, parameters of ESA process on physical-chemical and exploitational properties of AL and allowing to receive coatings with given characteristics. According to these principles several new electrode materials have been created, using tungsten carbide and titanium base with self-fluxing and mineral additives that allow to greatly increase wear and heat resistance of construction and instrumental steels.
4:30 pm
CHARACTERIZATION OF CONTINUOUS PRODUCTION OF ALUMINUM ALLOYS DURING LINEAR SPRAY ATOMIZATION AND DEPOSITION: Y. Zhou, E.J. Lavernia, Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92697-2575; S.W. Lee, V.G. McDonell, G.S. Samuelsen, Dept. of Mechanical Engineering and Aerospace, University of California, Irvine, CA 92697-2575; R.L. Kozarek, Processing Design and Smelting Division, Aluminum Company of America, Alcoa Center, PA 15069
The linear spray atomization and deposition is a potential near-net shape technique for continuous production of aluminum alloys. Possible benefits of linear spray atomization and deposition are: a) deposit geometry improvement, b) high productivity, c) high aspect ratio, and d) low overspray yield. In the present study, characterization of metal sprays using phase Doppler particle analyzer (PDPA), such as droplet velocity distribution, droplet size, droplet size distribution and spatial distribution, was carried out. The droplet size distribution of aluminum alloy powders were also studied using the mechanical sieving method to compare with the results obtained using PDPA. The plot of the axial velocity with droplet diameter reveals the relationship that smaller droplets have higher axial velocity than do lager droplets. The results also indicate that the axial velocity exhibit the bimodal behavior when atomization pressure approaches a certain critical value and this bimodal behavior behaves increasingly with higher atomization pressure. The Sauter mean diameter obtained using PDPA and the mass median diameter using the mechanical sieving show a decreasing trend with increasing atomization pressure.
4:50 pm
SPRAY ATOMIZATION AND DEPOSITION OF GAMMA TITANIUM ALUMINIDE ALLOYS: B. Li, E.J. Lavernia, Department of Chemical Engineering and Materials Science, University of California at Irvine, Irvine, CA, 92697-2575
Spray forming of gamma titanium aluminides had been investigated experimentally and numerically. Three different nominal compositions had been successfully spray formed. The microstructure of spray formed Ti-47Al consists of fine, equiaxed fully lamellar 2+ structure, with an average linear grain size of 60 µm and an average interlamellar spacing of 0.3 µm. These microstructural characteristics led to a higher creep resistance, in a temperature-stress regime of 780 to 850°C and 180 to 320 MPa, relative to fully lamellar -TiAl obtained through conventional casting + heat treatment processes. A two dimensional modeling of the momentum and thermal behavior of atomized droplets of -TiAl predicted that the two dimensional droplet size distribution in the spray cone changes from being heterogeneous to being almost homogeneous as axial flight distance increases. The modeling results also indicated that the two dimensional distribution of the fraction solidified in the spray cone is heterogeneous. The fraction solidified in the spray at any given axial distance increases with increasing radial distance from the spray axis.
5:10 pm
COARSENING KINETICS OF SOLID PARTICLES IN THE SPRAY-FORMED ALUMINUM ALLOY PREFORMS: Ram B. Bhagat, Maurice F. Amateau, The Pennsylvania State University, Applied Research Laboratory, P.O. Box 30, North Antherton Street, State College, PA 16804
The coarsening kinetics of solid particles in the semi-solid aluminum alloys have been reported to follow a parabolic or a cubic law. Considering the gas-dynamic nature of the spray forming process, the high-velocity impact on the substrate is most likely to cause extensive deformation of the semi-solid and even the fully solidified droplets leading to dendrite fragmentation and grain multiplication followed by homogenization and coarsening both during the solidification and subsequent cooling until the temperature falls to a low value. In this investigation, we have developed a growth kinetics relationship based on our experimental results of the heat treatment of select spray-formed aluminum alloys. The calculated rate constant (as a function of temperature) is used in conjunction with a two-dimensional finite element analysis for transient heat transfer to determine the growth of a solid particle in the semi-solid state at any time. The results of this study are useful in understanding the kinetics of grain growth and in obtaining equiaxed, fine-grained microstructures in the aluminum alloys.
Room: 330G
Session Chairperson: Jeff Rickman, Dept. of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18105-3195
1:30 pm INVITED
ESTIMATION OF GRAIN BOUNDARY ENERGETICS FROM MICROSTRUCTURAL DATA: Brent Adams, W.W. Mullins, Dept. of Materials Science and Engineering, Carnegie-Mellon University, Pittsburgh, PA 15213-3890; David Kinderleherer, Mathematics Department, Carnegie-Mellon University, Pittsburgh, PA 15213
Abstract not available.
2:10 pm
THE RELATIONSHIP BETWEEN GB SEGREGATION AND FRACTURE STRENGTH: R.G. Faulkner, L.S. Shvindlerman, Institute of Polymer Technology and Materials Engineering, Loughborough University, Loughborough, Leics LE11 3TU, Institute for Solid State Physics, Russian Academy of Science, Chernogolovka, 142432, Moscow, Russia
A thermodynamic analysis is performed of the effects of segregation and grain boundary structure on grain boundary free energy in metallic solids. This leads to a definition of the reduction in grain boundary free energy caused by a given level of segregant. In turn this allows the prediction of grain boundary fracture strength assuming a ductile material intergranular fracture mechanism as proposed by McMahon and Vitek. The net result is that intergranular fracture strengths can be predicted as a function of the segregation patterns existing for the material's specific thermal history, the grain boundary sigma value, and the interplanar spacing on the boundary plane. A knowledge of the binding energy of the segregant atoms to the boundary is required but this is shown to be calculable on the basis of atomic misfits for metallic lattices. The results are compared with available data from Lim and Watanabe on GB fracture in Al-Sn-Zn materials.
2:30 pm
THE ROLE OF GRAIN BOUNDARY ARBON FILMS IN THE RATE-DEPENDENT, INTERGRANULAR FRACTURE OF NICKEL-COPPER: MarjorieAnn E. Natishan, Matthew Wagonhoffer, Mechanical Engineering Department, University of Maryland, College Park, MD 20742
As part of an ongoing investigation to bound the service conditions of intergranular failure in nickel-copper alloy K-500 containing grain boundary precipitates of carbon, previously tested stress-rupture specimens were examined to document and characterize the deformation associated with grain boundary failures. Of particular interest was defining the role of the grain boundary carbon precipitates in the rate-dependent intergranular fracture process under ambient conditions. The failed creep/stress rupture specimens were sectioned perpendicular to the fracture surface and prepared for optical and electron microscopy of the microstructure adjacent to the primary fracture. High resolution microscopy revealed voids opened along the grain boundaries at carbon precipitate/nickel grain boundary interfaces. It is postulated that voids nucleate along these interfaces due to the combined driving force of the applied local stress resulting from dislocation accumulation at grain boundary/carbon interfaces and vacancy diffusion to these high energy sites. The intergranular failure then results from crack propagation along intergranular paths weakened by void formation.
2:50 pm
ATOMISTIC STUDIES OF SEGREGATION AND FRACTURE IN Al-Mg ALLOYS: X.Y. Liu, J.B. Adams, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 105 South Goodwin Avenue, Urbana, IL 61801
High Mg content (>5%) Al-Mg alloys are known to cause edge cracking during the hot working. We investigated one possible explanation, that Mg segregation to grain-boundaries can embrittle them. The extent of Mg segregation to a wide variety of grain-boundaries in Al alloys with 10% Mg is determined with the EAM. These results are consistent with our previous surface segregation studies, which are consistent with experimental studies of surface segregation. The Griffith ideal work of fracture is determined by rigidly cleaving both pure Al and Al-Mg alloys; the presence of 20-40% Mg at interface is found to lower the work of adhesion by 10%. Segregation of Mg to surface (for slow fracture, i.e., below the threshold for catastrophic failure) suggests a further reduction of 20% in the work of adhesion. Dynamic studies of fracture are also carried out with Molecular Dynamics, to determine the effect of plastic deformation.
3:10 pm BREAK
3:30 pm INVITED
ATOMISTIC SIMULATION OF NANOCRYSTALLINE MATERIALS: S.R. Phillpot, P. Keblinski, D. Wolf, Materials Science Division, Argonne National Laboratory, Argonne, IL 60439; H. Gleiter, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany
Molecular-dynamics simulations have been used to synthesize and characterize fully dense, three-dimensional, "relaxed" nanocrystalline fcc metals and silicon. The high-energy grain boundaries in these nanocrystalline materials are found to be highly disordered. In the case of silicon the structures of the highly-constrained grain boundaries, triple lines and point grain junctions were found to be highly disordered and similar to the structure of amorphous silicon. Computer simulations of the behavior of an idealized model nanocrystalline material expose important parallels that exist in the dynamical properties of nanocrystalline materials and glasses. Both types of heavily disordered, metastable microstructures exhibit low- and high-frequency lattice-vibrational modes not seen in the perfect crystal, giving rise to similar thermodynamic properties at low temperatures, most notably a pronounced anomaly in their specific heats and a free-energy based phase transition from the nanocrystalline state to the glass below a critical grain size. Based on a free-energy argument, we suggest that below a critical grain size nanocrystalline materials should be unstable with respect to the amorphous phase. Work supported by the U.S. Department of Energy, BES Materials Sciences, under Contract W-31-109-Eng-38 and by the A. v. Humboldt and Max-Planck Foundations (Max-Planck Research Award program).
4:10 pm
THE EFFECT OF GRAIN BOUNDARY CHARACTER ON TIME DEPENDENT CRACK PROPAGATION IN A Ni-BASE SUPERALLOY: P.F. Browning1, M.F. Henry1, K. Rajan2, 1General Electric Corp. Res. & Dev., P.O. Box 8, Schenectady, NY 12301; 2Rensselaer Polytechnic Institute, Dept. of Materials Engrg., Troy, NY 12180
An investigation of the effect of grain boundary character in the Ni-base superalloy Rene 88DT on environmentally assisted crack propagation in high temperature, gaseous environments will be presented. When tested at elevated temperature under hold time fatigue or sustained loading conditions in gaseous environment, crack propagation can occur intergranularly in this alloy, and hence may be influenced by grain boundary character. Automated microanalytical techniques have been applied to the crack tip area, with the intent of determining whether intergranular cracking occurs more readily along certain types of grain boundaries. The Coincident Side Lattice approach has been taken to characterize the misorientation between adjacent grains.
4:30 pm
DYNAMIC EMBRITTLEMENT IN BERYLLIUM-STRENGTHENED COPPER: Ranjani C. Muthiah, C.J. McMahon, Jr., University of Pennsylvania, Philadelphia, PA; Amitava Guha, Brush Wellman Inc., Cleveland, OH
Dynamic embrittlement refers to the quasi-static diffusion-controlled decohesion, usually along grain boundaries, that can occur when a high-strength alloy is stressed in the presence of surface-absorbed impurities. Oxygen-induced cracking of nickel-based alloys at high temperatures (relevant to gas turbine engines) is thought to be an example of this phenomenon. A precipitation-hardened Cu-0.26%Be, which can be heat-treated to a wide range of strengths, is being used as a low-temperature model material for dynamic embrittlement. This alloy was found to be resistant to cracking at 200°C in an inert atmosphere but was highly susceptible to grain boundary cracking in air. Preliminary tests indicate that the failure time is highly stress-dependent, but there is an incubation time for the cracking, presumably related to crack nucleation. Crack growth rate studies are being done to eliminate the effect of the variable nucleation time. The oxygen partial pressure and yield strength dependence of the cracking mechanism are also being studied.
4:50 pm
ATOMIC-SCALE SIMULATIONS OF GRAIN-BOUNDARY FRACTURE: F. Cleri, ENEA, Divisione Materiali Avanzati, Centro Richerche Casaccia, CP 2400, 00100 Roma A.D., Italy; S.R. Phillpot, D. Wolf, Materials Science Division, Argonne National Laboratory, 9700 S. Cass Ave., Argonne, IL 60439; S. Yip, Department of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, MA 02138
The results of fully atomistic simulations of grain-boundary fracture are presented. Microcracks were placed in the interface plane of symmetric-tilt grain boundaries (STGBs) for an fcc system described by a smoothed Lennard-Jones potential uniaxially loaded in pure mode-I. Proper treatment of boundary conditions was ensured, as demonstrated by the good agreement of crack propagation energy and stress fields with the continuum-elasticity solutions for the bulk reference crystal. The ductile vs. Brittle response of different STGBs was investigated as a function of the grain-boundary structure. A directional toughness effect was observed and compared to available experimental data and continuum-elasticity-based theoretical treatments. Extensive comparison with the Peierls-Nabaro-Rice model of dislocation nucleation from a crack tip was carried out, showing that some of the assumptions of the model need to be reconsidered in the case of interfacial fracture. *Word of FC was partly supported by Italian National Research Council (CNR), grant AI93.02171.11. Work of SRP and DW was supported by the US Department of Energy, BES-Materials Sciences under Contract W-31-109-Eng-38.
Room: 330F
Session Chairpersons: L. Christodulou, Imperial College, Prince Consort Rd., London SW7 2BP; O. Senkov, University of Idaho, Moscow, ID 83844-3026
2:00 pm
REACTIVE PROCESSING OF ALUMINIUM METAL-MATRIX COMPOSITES: M.J. Capaldi1, J.L.F Kellie2, and J.V. Wood1, 1Department of Materials Engineering and Materials Design, University of Nottingham, UK; 2 London & Scandinavian Metallurgical Co Ltd, Rotherham, UK
Two distinct processes have been used to produce in situ reactions in aluminium in order to form composites with varying amounts and types of additive. The first involves fluoride salt reactions which result in the production of TiB2 particulate finely distributed in a wide range of aluminium base alloys (both cast and wrought). The particulate concentration is limited to about 12 vol% before problems of inclusion entrapment and porosity become evident. Brief details of the process and properties after conventional and pressure die casting will be reported. The second process uses a self-propagating high temperature synthesis reaction to make carbides, nitrides, borides or mixtures. A particular reaction to be reported will be for A1+TiC. Details of the SHS reactions involved will be correlated with processibility and properties.
2:20 pm
REACTIVE MILLING AND SINTERING OF ALUMINIUM BASE POWDER METALLURGY COMPONENTS: C.C. Degnan, J.V. Wood, Department of Materials Engineering and Materials Design University of Nottingham, UK
A form of mechanical alloying has been employed to create a range of structures in aluminium +X powders. The emphasis has been on partial mixing so that the energy of mixing can subsequently be utilised during sintering. A similar process has been employed to make intermetallica and sintering aids. The prime objective of the work is to allow conventional pressing and sintering to be employed for making high strength structurally sound powder metallurgy components.
2:40 pm
THERMOMECHANICAL STUDY IN COMBUSTION SYNTHESIZED Ti-Ni SHAPE MEMORY ALLOY: F.M.H. Zarandi, K. Sadrnezhaad, Sharif University of Technology, Tehran, Iran 11365-9466
The thermal explosion mode of self-propagating high-temperature synthesis, by which time and energy can be saved and the cast product has the least interstitial contamination and high homogeneity, is used to successfully producing Ti-Ni shape memory alloys. The specimens, after hot and cold rolling, are solution treated and aged. The Rhombohedral(R)-phase transformation is observed in the Ti-50.03 at%Ni alloy. MS(1) and TR(2) have their maximums at aging temperatures of 773 and 723 k, respectively, and rise with Ni-contents. The rate of rising of TR, in aged specimens, depends on the composition and in the Ti-50.33 at%Ni alloy, in spite of the Ti-50.23 at%No alloy, MSis more than AS(3).After cold rolling of solution treated specimens, more than 50 percent reduction in thickness, and aging treatment the rate of variations of MSand AS versus aging temperature decreases and up to aging temperature of 723 k, TR is higher than that is in the not cold worked specimens. Also variations of MSwith amount of old working strains does not show uniform behaviour. All Round Shape Memory Effect occurs completely in the Ti-50.33 at%Ni alloy. 1: Start temperature of martensitic transformation; 2: Start temperature of R-phase transformation; 3: Start temperature of reverse martensitic transformation.
3:00 pm
STRUCTURAL METAL FOAMS FROM BONDED ALUMINIUM ALLOY HOLLOW SPHERES: N.E. Naxter, J.K. Cochran, T.H. Sanders Jr., Georgia Institute of Technology, Atlanta, GA 30332-0245
The demand for ultra low density structural materials that are economical is increasing. The feasibility of bonding monosized hollow spheres at points of contact to fabricate net-shaped foams with isotropic properties has been demonstrated. Currently, research efforts are focusing on adapting existing technology developed at Georgia Tech to fabricated low density hollow metal spheres. Spheres are fabricated directly from the melt using a coaxial nozzle process. Molten aluminium is injected through the outer orifice of the nozzle with gas passing through the centre orifice. As instabilities form on the liquid jet, surface tension serves to pinch off hollow monosized spheres Parameters such as melt and nozzle temperature, liquid and gas flow rates, and temperature gradient of the drop zone are controlled. As in-depth study relating sphere cooling rates to microstructural evolution and corresponding mechanical properties has been undertaken and the results of these investigations will be the subject of this presentation.
3:20 pm
EFFECT OF THE FABRICATION METHOD ON THE AGING BEHAVIOR OF 6061 Al COMPOSITES REINFORCED WITH 20 VOL% SiC WHISKERS: S. Ryu1, Y. Choi2, S.S. Cho3, H. Kwon3, S.I. Hong4, 1Tongyang Nylon Co. Ltd., Ulsari Kyungnam, Korea; 2Sunmoon Univ., Asari, Chungnam, Korea; 3Kookmin University, Seoul, Korea; 4Chungnam National University, Taedok Science Town, Taejon, Korea
Age hardening behaviors of SiC whisker reinforced composites with 6061 Al matrix fabricated by powder metallurgy and squeeze casting were investigated to examine the effect of the fabrication method on the aging kinetics. In squeeze cast composite, numerous triangular particles which is believed to be MgAl2O4 were observed at Al/SiC interfaces whereas no visible interface particles were observed in P.M. composites. P.M. composites showed faster age hardening and reached the maximum hardness earlier than in squeeze cast composites. The decrease of the aging kinetics in squeeze cast 6061 Al matrix composites compared to that in P.M. composites is thought to result from more severe depletion of Mg atoms due to interfacial reactions in squeeze cast composites. The uniformity of whisker distribution is suggested to influence the general aging behavior through its effect on the local dislocation density. Data on the aging kinetics and the interfacial reactions in other Al alloys were also examined to study various factors which can influence the aging kinetics.
3:40 pm BREAK
4:00 pm
SOLIDIFICATION BEHAVIOURS AND POWDER MAKING MECHANISMS OF THE EMULSIFIED METALLIC POWDERS: Chang-ki Min, Kyong-tae Nam, Woo-young Yoon, RASOM, Dept. of Metallurgical Engineering, Korea University, 1,5 Ka, Anam-dong, Sungbuk-ku, Seoul, 136-701, Korea
New metallic powder making processes, named "Centrifugal Emulsification Process (CEP)" and "Mixer and Settler (MS)" have been developed to synthesize rapid solidified metallic powders. The underlying principle of CEP and mS was to emulsificate the liquid metals with inorganic oil (or salt) using centrifugal force. Through CEP and mS processings, the high temperature metals as well as the low temperature alloys are fabricated. The mean particle size and size distribution could be controlled by various processing parameters that could be managed easily. The morphology of the particles could also be customized using spherodization vs. Solidification time ratio in CEP. The powder formation mechanisms in CEP and MS were rationalised through the energy balance between the input energy by centrifugal force and the increment of total surface energy of metallic liquids. The calculated mean size of powders agrees relatively well with that of the experiments. Also, the effects of rapid solidification undercooling, solidification rate and crystallisation behaviours can be evaluated effectively through the processes. The possibility of the customised not only size and morphology control but microstructure control was also shown. Both of the new methods can be applied to continuous powder making processes without oxygen contamination.
4:20 pm
Ti-6A1-4V HOLLOW SPHERE FOAMS: C. Uslu, J.K. Cochran, K.J. Lee* and T.H. Sanders, Jr, Georgia Institute of Technology, Atlanta, GA 30332-0245: *Ceramic Fillers, Inc., Atlanta, GA 30318
Structural foams, formed to near-net-shape by bonding monoxides hollow metal spheres at points of contact, offer the possibility of strong, light-weight, reasonably priced materials. The technology of making titanium hollow sphere foams has been developed using the coaxial nozzle powder slurry technique. Titanium hydride hollow powder spheres of 3 mm diameter and 20 mm wall thickness were fabricated from a high solids content acetone slurry. The powder shells were controlled atmosphere sintered and point contact bonded using the initial alloy hydride powder to form hollow sphere foams that were 20% of theoretical density. The sphere wall microstructures obtained by pressureless, solid-state sintering of the hydride alloy were compared to the conventional alloy microstructures and quantitative measures of sintering kinetics were established. Initial mechanical properties such as compressive yield strength and modulus will also be considered.
4:40 pm
METAL FOAMS FROM FUGITIVE BURNOUT: A.R. Nagel, J.K. Cochran, T.H. Sanders, Jr, K.J. Lee*; MSE-Georgia Institute of Tech Atlanta GA, 30332-0253; Ceramic Fillers Inc., Atlanta, GA
Metallic foams are being made from powders using naturally occurring organic fugitive burnout material. Most forms are fabricated by introducing pores from a gas phase into a liquid system. This tends to produce pores of irregular cell size due to pore coalescence. The object of this effort is to introduce porosity utilising a fugitive solid phase to allow greater precision in forming pore systems. The foams being investigated are nickel and titanium alloys formed from slurries with starches as the fugitive materials. Starches are inexpensive and clean burning sacrificial materials. Because replication of fugitive starches requires fine particle size powders, brittle precursor powders (i.e. metal hydrides or oxides) are initially used to form the foam and subsequently decomposed or reduced to form metallic foams. Using particle packing and theological theories, the percolation value of closed cell porosity should be increased, and the microstructure of the foam should be made more uniform. Porosity and mechanical properties are being characterised for comparison to other forma geometries.
5:00 pm
MODELING AND CONSOLIDATION OF NANOCRYSTALLINE ALUMINUM: J.S. Idasetima, R.B. Bhagat, M.F. Amateau, The Pennsylvania State University, Applied Research Laboratory, Box 30, New ARL Building, State College, PA 16804
The consolidation of nanograined powder metals presents a major problem of grain growth to micrometer size thereby lowering the potential benefits expected of the nanocrystalline microstructures. The aim of this investigation is two fold: (a) to present our results of consolidating nanograined alumium powder in conjunction with process modeling using Ashby's HIP program. The preliminary modeling results suggest that the nanograined aluminum powder can be consolidated into full density with minimal grain growth without using any grain growth inhibitor by optimizing combined sintering and vacuum hot pressing. The predicted hot pressing temperature for aluminum nanopowders (20-200 nm) ranges from 300 to 400 K for a fixed pressure of 19 MPa; time being less than 10 minutes. Boundary diffusion mechanisms dominate in both stage 1 and stage 2 of the densification. The as-received nonograined powder and the fabricated specimens have been characterized by optical, scanning, and transmission electron microscopy, x-ray diffraction and microprobe analysis. Density and microhardness of the consolidated specimens are also reported and discussed.
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