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. &