Room: 315B
Session Chairperson: TBA
8:00 am
TRIBOLOGICAL MEASUREMENT METHODS FOR COATINGS: Stephen M. Hsu, National Institute of Standards and Technology, Gaithersburg, MD 20899
Coatings are increasingly being used as a means to protect materials from harsh environments. As the coating technology becomes more sophisticated, the requirement for new and better measurement techniques to understand wear mechanisms and coating effectiveness soars. For functionally gradient coatings, the issue of measuring local properties vs global properties in determining the extent of compositional change necessary to achieve a particular performance level is critical. For very thin hard coatings on relatively soft substrates, the deformation and yielding of the substrate affect the coating effectiveness. This paper presents some new and novel techniques that can be used to measure the coating properties under rubbing conditions.
8:35 am
PLASMA-ASSISTED DEPOSITION OF TRIBOLOGICAL COATINGS: K. Sridharan, R.A. Breun, A. Chen, J.R. Conrad, R.P. Fetherston, J. Firmiss, J.P. Hockers, J.S. Kim, R.J. Matyi, M.M. Shamim, C. Tan, E.A. Treptow. University of Wisconsin, Madison, WI 53706
A variety of alloy and compound coatings can be synthesized using plasma-based techniques. At high target bias voltages, implantation of ions into the target can be achieved to dose levels sufficient to bring about beneficial surface modification. The range of compositions achievable, low processing temperatures and environmental cleanliness makes this technique potentially attractive for a number of applications. The paper will focus on the design and development of wear resistant coatings using the plasma source ion implantation method operated in the ion-assisted deposition mode. Results of microstructural characterization and tribological evaluation of these coatings will be presented. The work is supported by the US Army Grant No. DAAII04-94-G-0283 and NSF Grant No. DMI-9528746.
9:10 am
A COMPARATIVE ANALYSIS OF MECHANICAL PROPERTIES IN COATED SYSTEMS BY INSTRUMENTED INDENTATION: Larry Seitzman, Code 6170 Naval Research Laboratory, Washington, DC 20375
Vickers indentation was performed on a variety of coating-substrate combinations. Force-displacement curves were obtained by continuously monitoring the loading and unloading of the indentor. Different methodologies for analyzing the data (i.e. shape effect vs contact depth as well as regression vs polynomial fitting) were compared. Mechanical property profiles of the coated system were obtained from both the loading and the unloading curves, and the properties determined from both curves were compared. Analysis of the unloading curve readily yields hardness and elastic modulus data, while analysis of the loading curve yields additional information. The potential for using instrumented indentation as a quality control tool for coated systems will be discussed.
9:30 am
DAMAGE MECHANISM IN SOLID PARTICLE EROSION OF FeAl-Al203 THERMAL SPRAY COATINGS: Brian Schorr, Arnold Marder, Lehigh University, Bethlehem, PA 18015; Daniel Sordelet, Iowa State University, Ames Laboratory, Ames, IA 50011
The effect of microstructure and splat cohesion on the erosion damage mechanism of FeAl-Al203 plasma and high velocity oxy-fuel (HVOF) coatings was studied. The Al203 content in the cermet pre-sprayed powders was varied from 0-80%. Microstructural evaluation revealed a good correlation between the Al203 in the pre-sprayed powders and the final as deposited plasma coatings. In addition, increased porosity was measured as the Al203 content of the coatings increased. It was found that plasma sprayed coatings tend to fail via splat delamination due to poor cohesion and high porosity, providing accelerated weight loss compared to HVOF and wrought alloys. The addition of Al203 to the plasma sprayed FeAl increased the erosion rate of the tested coatings. Examination of the eroded surfaces revealed cracking of the Al203 which led to undercutting of the FeAl matrix. In contrast, partial removal of splats by gouging as well as cracking occurred in the HVOF coatings.
9:50 am
PLASMA NITRIDING OF TOOL STEELS: Sun K. Kim, Department of Metallurgical Engineering, University of Ulsan, Ulsan, Kyung Nam, Korea 680-749
In order to produce composite surface layers by combining nitriding and coating of titanium compounds, nitriding of tool steels to obtain only diffusion layer on surface is desirable. In this paper, results on experiments to obtain a diffusion layer with zero or minimum amount of compound layer were presented. With SKD11, SKD61 and SKH9 tool steels, experimental process parameters such as hydrogen and nitrogen gas ratios, temperature, pressure and time were changed to obtain an optimum condition.
10:30 am
MICROSTRUCTURE, WEAR RESISTANCE, AND HIGH TEMPERATURE OXIDATION RESISTANCE OF BORONIZED GAMMA-TiAl: Soosik Kim, Youngsic Yoon, Hansam Kim1, Kyeongsoon Park2,Met. Eng. Dept., Inha Univ., Inchon, Korea, 1Metall. Eng. Dept., Inha Tech. College, Inchon, Korea, 2Materials Eng. Dept., Chung-ju National Univ., Chungju, Korea
Ti-45.0 at% Al-1.6% Mn intermetallic compounds, which were fabricated by reactive sintering, were boronized in the temperature range 1150 to 1250°C under a flow of Ar gas in a graphite pack with boron carbide (B4C) powders. Energy dispersive x-ray spectroscopy (EDXS) and x-ray diffraction (XRD) were used to investigate the phase present in the coating layer. The coating layer was composed of Ti2B, TiB, and Al2Ti4C2 phases. The formation mechanism of the above compounds in the coating layer was investigated. Some vacancies were found below the coating layer. The thickness of the coating layer increased with increasing boronizing temperature and time. The activation energy of formation of the coating layer was calculated to be 320 Kj/mole. The microhardness of the coating layer was extremely high (700-800 Hv), compared to that (300-400Hv) of the substrate, improving the resistance to wear and high-temperature oxidation.
10:10 am BREAK
10:50 am
THE WEAR-RESISTANCE OF TiNi INTERMETALLICS WITH TiN COATING: H.C. Lin, H.M. Liao, J.L. He, K.M. Lin, K.C. Chen, Department of Materials Science, Feng Chia University. Taichung, Taiwan 407, China
The wear resistance of TiNi intermetallics with TiN coating was studied by wear test, hardness measurement, XRD and microstructure observation. Both TiN and Ti2Ni layers are found to form on the surface of ion-nitrided TiNi intermetallics. These layers can improve the wear-resistance of these TiNi intermetallics. The effects of nitriding temperatures, TiN/Ti2Ni thickness and applied wear-load on the wear behavior of TiNi intermetallics are investigated in this paper. Meanwhile, the major wear mechanisms in these ion-nitrided TiNi intermetallics are also discussed.
Room: 340B
Session Chairpersons: Dr. Edward S. Chen, U.S. Army Research Office, 4300 S. Miami Boulevard, Research Triangle Park, NC 27709; Dr. Douglas B. Gundel, Systran Co., Inc., 4126 Linden Ave., Dayton, OH 45432
8:30 am INVITED
INTERMETALLIC MATRIX COMPOSITES PREPARED BY MECHANICAL ATTRITION: A REVIEW: Carl C. Koch, Department of Materials Science & Engineering, North Carolina State University, Raleigh, NC 27695
The interest in intermetallic matrix composites has grown in recent years due to the realization that monolithic intermetallics would not likely satisfy the balance of properties needed for advanced aerospace systems. Processing of intermetallic matrix composites is a critical issue and a number of methods have been explored to fabricate such composites with either continuous or discontinuous reinforcements. While the latter category in general provides less improvement in mechanical behavior, this is the type of composite where mechanical alloying may provide an inexpensive processing route. Intermetallic systems to be discussed include Ni3Al, NiAl, Ti3Al, TiAl, and MoSi2. Early work on oxide dispersions in intermetallics by mechanical alloying, dispersions introduced by cryomilling, and nanocrystalline intermetallic composites will be covered by this review. The possibility of superplastic forming of nanocrystalline intermetallic matrix composites will also be considered.
9:00 am
MECHANICAL ALLOYING OF INERT GAS ATOMIZED Al-Li-Cu-Mg-Zr ALLOY/SiC SHORT FIBERS REINFORCED MMC POWDERS: S. Özbilen, Gazi University, Faculty of Technical Education, Department of Metals Education, Teknikokullar, Arkara, Turkey
MMC powders of Al-Li-Cu-Mg-Zr alloy base with variable amount SiC short filamentary reinforcement were produced in a pilot plant down-draught atomizer with a Mannessman type nozzle under Ar. Powder based alloy matrix composite powders were ground in a mechanical alloying attritor not only for introducing deformation but also to investigate the influence of this new and unique processing route on the microstructure and properties of the material system under investigation.
9:25 am
SYNTHESIS OF NANOSTRUCTURED SiC/Si3N4 COMPOSITE POWDERS THROUGH REACTION MILLING: Z.-G. Yang, L. Shaw, Department of Metallurgy and Materials Engineering, University of Connecticut, Storrs, CT 06269
In this study, synthesis of SiC/Si3N4 nanocomposite powders through reaction milling was investigated. Graphite and silicon powders were used as the source of carbon and silicon respectively, while the source of nitrogen was from either nitrogen or ammonia gases. Various compositions of the starting powder mixtures for forming nanopowders spanning from pure SiC to pure Si3N4 were investigated. It was found that nanocrystalline SiC powders could be synthesized at ambient temperature by milling silicon and graphite powders in argon atmosphere. However, the formation of SiC was retarded when milling was conducted in nitrogen or ammonia atmosphere. Crystalline Si3N4 formed only after post annealing the milled powder mixtures and the annealing temperature had a strong effect on the formation of the composite powders. Based on the results from XRD, TEM, DTA and TGA, the formation mechanisms of the composite powders will be discussed.
9:50 am INVITED
SYNTHESIS OF METAL MATRIX COMPOSITES BY MECHANICAL ALLOYING: F.H. Froes, C. M. Ward-Close, E.G. Baburaj, A. Vassel, College of Mines & Earth Research, University of Idaho, Moscow, ID 83844
Abstract not available.
10:20 am BREAK
10:30 am
AN INVESTIGATION OF THE VACUUM HOT PRESSING BEHAVIOR OF SILICON CARBIDE FIBERS COATED WITH NANOCRYSTALLINE Ti-6Al-4V: Joseph M. Kunze, Triton Systems, Inc., 114 Turnpike Road, Chelmsford, MA 01824; Haydn N. G. Wadley, Intelligent Processing of Materials Laboratory, Department of Materials Science & Engineering, University of Virginia, Charlottesville, VA 22903
The vacuum hot pressing of silicon carbide monofilaments coated with nanocrystalline Ti-6A1-4V has been studied and modeled. In the experiments, surprisingly high identification rates were observed, even at processing temperatures and pressures well below those used for processing conventional Ti-6A1-4V. From the cross sections of partially consolidated specimen, the evolution of coated fiber-fiber contacts and pore shapes were determined. The pores were found to be cusp-shaped throughout the consolidation process. Columns of coated fibers were observed to form which resulted in regions of locally high fiber volume fraction. In the model, the initial densification was based upon a micromechanical contact analysis for a metal coated fiber. Final stage densification was analyzed by modifying the Qian et al strain rate potential for a power law creeping body containing isolated cusp-shaped pores. Simulations of the VHP experiments were performed using this model which incorporated time and temperature dependent microstructure relations. Overall, the simulations compared well with the experimental density data, although the load supported by the regions of locally high fiber volume fraction resulted in the model slightly overestimating the observed densification time response.
10:55 am
MODEL-BASED SIMULATION OF THE CONSOLIDATION PROCESSING OF METAL COATED FIBERS: D.M. Elzey, R. Vancheeswaran, H.N G. Wadley, Intelligent Processing of Materials Laboratory, Department of Materials Science & Engineering, University of Virginia, Charlottesville, VA 22903
The metallization of structural ceramic fibers by physical vapor deposition, sputtering, etc., followed by consolidation (e.g. hot isostatic pressing) offers an attractive route for the manufacture of continuous fiber-reinforced metal matrix composites (MMC's). Recent models for describing the evolution of key microstructural features (such as porosity, interfacial reaction zone thickness and fiber microbending/fracture) during consolidation are described, and are combined to simulate changes in the composite's microstructural "state" during arbitrary consolidation process schedules. Results are presented for PVD Ti-6Al-4V -coated SiC monofilament fibers consolidated by vacuum hot pressing which illustrate the presence of optimal solutions to the process path planning problem. An optimization scheme is briefly described which allows identification of the consolidation process cycle providing maximum relative density with minimum fiber and interfacial damage. In addition to the process schedule, optimal quality is shown to depend strongly on the fiber/matrix combination, the initial coated fiber packing geometry and the (evolving) matrix microstructural state.
11:20 am
MODEL-BASED SIMULATION OF THE CONSOLIDATION PROCESSING: R.Vancheeswaran, H. N. G. Wadley, Intelligent Processing of Materials Laboratory, Department of Materials Science & Engineering, University of Virginia, Charlottesville, VA 22903
The performance of fiber reinforced titanium matrix composites (TMC) made by consolidation of spray deposited monotapes is strongly influenced by the processing conditions used. This high temperature consolidation step must simultaneously minimize fiber microbending/fracture, the interfacial reaction product layers at the fiber-matrix interface and at the same time eliminate matrix voids (i.e. increase the relative density). These three microstructural variables have conflicting dependencies upon the consolidation process variables (temperature, pressure and time), and it has been difficult to identify process pathways by trial and error that lead to composites of acceptable quality (where the fiber damage and reaction layer thickness are kept below some bounds, while matrix porosity is eliminated). Models for predicting the microstructure's dependence upon process conditions (i.e. the time varying temperature and pressure) are combined with consolidation equipment dynamics to simulate the microstructure evolution and to assess the relative "processability" of several silicon carbide fiber/titanium alloy matrix systems during their consolidation. We introduce the idea of process failure surfaces and show how this simulation tool in conjunction with a model predictive control (algorithm), is able to design "locally" optimal process cycles that minimize fiber damage, reaction product layer thickness and porosity. The approach is then used to path plan process schedules that will steer away from these damage surfaces for a variety of TMC systems.
11:45 am
STUDIES ON SINTERED ZIRCON-REINFORCED ALUMINUM ALLOY MATRIX COMPOSITES: J. U. Ejiofor, Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487; B.A. Okorie, Department of Metallurgical and Materials Engineering, Enugu State University of Technology, P.M.B. 01660, Enugu, Nigeria; and R. G. Reddy, Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487
Zircon, ZrSiO4, is a thermally stable mineral. Owing to its abundance, high hardness, excellent abrasion/wear resistance and low coefficient of thermal expansion, researchers are investigating its use for medium strength, tribological applications. In the present study, the conventional low-cost, double compaction powder metallurgy route in the synthesis of Al-13.5Si-2.5 Mg alloy(wt%) reinforced with ZrSiO4, was investigated. The mechanical, physical and tribological properties were determined following the development of optimum conditions of compaction and sintering. At 0.15Vf, the UTS, 0.2%Y.S. and hardness improved by 4%, 12.8% and 88% respectively while the adhesive wear rate and the coefficient of friction reduced by 99.55 and 35.5% respectively. At a critical volume fraction of zircon, between 0.03 and 0.05, a significant improvement in wear resistance was observed. The use of optical microscopy, EPMA, SEM and x-ray analysis revealed the phases and possible reactions at the matrix-reinforcement interface, fracture mode and compositions of fractured surfaces which are related to measured mechanical properties and, the influence of the reinforcement phase on wear rate. Further structural analysis showed that the improvement in mechanical properties is attributed largely to the load-bearing ability and intrinsic hardness of zircon than to particulate dispersion effects. An attempt was made to model the strength of the composites.
Room: 230D
Session Chairman: David Riner, Reynolds Metals Co., PO Box 9911, Corpus Christi, TX 78469
8:30 am
OPTIMIZATION OF ALUMINA PLANT OPERATION WITH RESPECT TO MARKET CONDITION: P. Das, National Aluminium Company Ltd., Damanjodi, Dist. Koraput, Orissa 763008, India
In international markets, wide fluctuations of alumina prices have been found to be a common phenomenon over the years. It has been observed that almost all the buoyant cycles have essentially been followed by recessionary market conditions. Hence, during the periods when alumina prices are relatively low, for survival it becomes obligatory on the part of the management to strike an operational philosophy suitable for achieving minimum cost of production. However, during buoyant market conditions it is wise to make attempts for maximization of production by suitable optimization of process parameters even if there is a marginal increase in unit cost of production. Since such attempts are directly related to the profitability of the organization, a careful study should be made taking into consideration all interrelated factors. This paper highlights the areas of an alumina plant where changes in process parameters, permissible on technoeconomic consideration, could be made for optimization of production and profitability.
8:55 am
DEVELOPMENT OF SOFTWARE FOR BAYER PROCESS ALUMINA PLANTS: C. Misra, V. Soi, Alumina Technology Associates, 714 Pine Valley Drive, Pittsburgh, PA 15239
PC based software packages have been developed to assist in the operation and management of Bayer process alumina plants. Software packages for digestion, residue washing and precipitation areas have been designed for use by plant operators to formulate operating policy and are integrated with existing or new process control systems. As example, important features and structure of software developed for the precipitation system are discussed in more detail.
9:20 am
DYNAMIC MODELING OF YIELD AND PARTICLE SIZE DISTRIBUTION IN CONTINUOUS BAYER PRECIPITATION: Jerry L. Stephenson, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069; Chris Kapraun, Alcoa Alumina & Chemicals, L.L.C., Point Comfort Operations, State Highway 35, Point Comfort, TX 77978
Process engineers at Alcoa's Point Comfort refinery are using a dynamic model of the Bayer precipitation area to evaluate options in operating strategies. The dynamic simulator, a joint development effort between Point Comfort and Alcoa Technical Center, predicts process yield, particle size distributions, and occluded soda for a given flowsheet of the precipitation and classification circuit. In addition to rigorous material and particle population balances, the model includes mechanistic kinetic expressions for particle growth, agglomeration, nucleation, and attrition. The kinetic parameters have been tuned to Point Comfort's data with excellent matches between the model results and plant data. The model is written for the ACSL package with specially developed input/output graphical user interfaces which provide a user-friendly tool. Features such as a seed charge controller enhance the model's usefulness for evaluating operating conditions and process control approaches.
9:55 am
INCREASING THE ACTIVITY OF SEED USED FOR PRECIPITATION OF THE SODIUM-ALUMINATE LIQUOR: Bi Shiwen, Yang Yihong, Fu Gaofeng, Wen Jie, Ju Aihua, Department of Nonferrous Metallurgy, Northeastern University, Shenyang, 110006, China
The activity of seed is one of the most important factors in the precipitation of the sodium-aluminate liquor. The industrial aluminumoxide-hydrate is treated with sulfuric acid to increase its activity, and then it is used as the seed of precipitation. It is demonstrated that the seed has the ability to increase the rate of precipitation. The reason of this phenomenon is analyzed.
10:10 am BREAK
10:30 am
SECONDARY NUCLEATION OF ALUMINUM TRIHYDROXIDE IN BAYER SODIUM ALUMINATE SOLUTION: Xue Hong, Bi Shiwen, Shuai Shiwu, Yan Yihong, Li Dianfeng, Department of Nonferrous Metallurgy, Northeastern University, China; Chen Wankun, The Great Wall Aluminum Company of China
In this paper, secondary nucleation of aluminum trihydroxide in Bayer sodium aluminate solution was discussed by picture analysis and scanning electron micrograph. The effects of temperature, seed size and aluminate concentration on secondary nucleation are determined with growth time. As this study has shown, the nucleation rate depends upon the experimental conditions of supersaturation, temperature and seed size or surface area. The nucleation can promote the formation of relatively large particles under an opportune condition.
10:55 am
BAYERITE - ALUMINIUM TRIHYDROXIDE: Maurycy M. Pyzalski, Technical University of Mining and Metallurgy, Faculty of Ceramics and Material Engineering, Ave. Micklewicz 30, A-3, 30 - 059 Cracow, Poland
The physico-chemical properties of Bayerite, which was obtained in semi-commercial scale using new technology, were investigated in detail. The properties of another polymorphic form of aluminum trihydroxide, i.e., hydrargillite (Gibbsite) obtained by means of Bayer's and Grzymek's methods were also evaluated in a similar way. The results thus obtained allow characterization of the properties of hydroxides. They also put a new light on their formation and polymorphism.
Room: 230A
Session Chairperson: Jeff Keniry, Comalco Research, 15 Edgars Road, Thomastown, VIC 3074, Australia
8:30 am
UNDERSTANDING BOUNDARY-LAYERS: Warren Haupin, 2820 Seventh Street Road, Lower Burrell, PA 15068
Understanding the physics and chemistry of boundary-layers, the thin stagnant zones that form at each bath interface, clarifies many cell phenomena. A non-wetting boundary at the anode causes the anode effect. The effect of bath velocity on the boundary-layer thickness and its effect on the heat transfer coefficient coupled with bath temperature and bath composition explains the formation and loss of frozen ledge and its relationship to heat losses from the cell walls. Similarly, the boundary-layer at the bath-aluminum interface ex plains cathodic overvoltage, the sodium content of the aluminum, current efficiency and the relationship of each to metal pad stability (magneto-hydrodynamic stability).
8:55 am
ON THE COMPOSITION OF SOLID DEPOSITS FROZEN OUT FROM CRYOLITIC MELTS: Asbjørn Solheim, Lisbet I. R. Støen, SINTEF Materials Technology, N-7034 Trondheim, Norway
Thermodynamically, the primary crystallization product formed by cooling a melt containing cryolite, AlF3, Al2O3 and CaF2 is expected to be cryolite with minor amounts of CaF2 and AlF3 in solid solution. In practice, however, any deposit frozen out from such melts may contain considerable amounts of bath constituents other than cryolite. The factors governing the composition of the freeze are studied theoretically and by experiment. Besides solid solution, the composition depends on two factors, 1) diffusion of bath constituents from the surface of the deposit towards the bulk of the melt, and 2) dendritic crystal growth with subsequent trapping of bath between the crystals. The condition which gives dendrite formation is formulated. Based on this criterion, a deposit frozen out from melts containing excess AlF3 and alumina would contain more AlF3 than a deposit frozen out from a melt containing excess AlF3 alone. This was confirmed by experiment.
9:20 am
THE GAS UNDER ANODES IN SMELTING CELLS. Part I: MEASURING AND MODELLING BUBBLE RESISTANCE UNDER HORIZONTAL DE-ORIENTED ELECTRODES: T. M. Hyde, B. J. Welch, Department of Chemical Engineering, University of Auckland, New Zealand
With a continuing drive to reduce energy and the tighter operating tolerances of modern aluminium smelting cells, there is an ever increasing need for a precise cell voltage equation. Precise correlation exists for the electrical conductivity in smelting cells, the reverse is not the case for the added resistance effect of gas bubbles. Where it has been allowed for, the models used have been based on those proposed for vertically oriented electrodes. Furthermore the measurements on which the model is based can be influenced by other electrochemical changes while the shape and dispersion and gas bubble differ from those expected in aluminium smelting cells based on model studies. An apparatus and high speed switching data acquisition technique have been developed to allow the ohmic resistance of a molten salt electrolyte to be isolated from all other contributors. Ceramic objects of known geometry, size and volume, rest in the electrolyte immediately under the upper electrode (anode) thus simulating gas bubbles. The technique developed enables the measurement of the direct increase in resistance due to the introduced volume of non-conducting simulated gas. The bubble parameters examined included volume, electrode coverage, depth and shape. The resulting data have been tested against existing models.
9:45 am
THE GAS UNDER ANODES IN SMELTING CELLS. Part II: GAS VOLUME AND BUBBLE LAYER CHARACTERISTICS: R. Aaberg, V. Ranum, The Norwegian University of Science and Technology, 7034 Trondheim, Norway; K. Williamson, B. J. Welch, Department of Chemical & Materials Engineering, The University of Auckland, New Zealand
Recent physical models have suggested that the gas bubbles formed under anodes in smelting cells tend to coalesce and release as large bubbles predominantly. Whilst it is well established that the gas bubbles increase the cell resistance, and correlations proposed include the gas volume or bubble layer depth and surface coverage. However, the volume and degree of coverage of the electrodes have been subject to speculation rather than accurate measurements. In this investigation, using a larger than normal laboratory cell, it has been confirmed that the gas released is consistent with the physical models with most of the gas being evolved in discreet large bubbles. The release frequency is similar to the dominant frequency found in operating cells. The average gas volume under an anode prior to release is between 0.4 and 0.5 cm3 per cm2 of electrode. From combined resistance studies it has been calculated that approximately two thirds of the anode is covered with gas at release with an average bubble thickness of 5 mm.
10:10 am BREAK
10:30 am
MICROPYRETICALLY SYNTHESIZED POROUS NON-CONSUMABLE ANODES IN THE Ni-Fe-Cu-Al SYSTEM: J. A. Sekhar, H. Deng, J. Liu, International Center for Micropyretics, Department of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH 45221-0012; V. de Nora, MOLTECH S.A., 9, Route de Troinex, 1227 Carouge, Geneva, Switzerland
A micropyretically synthesised porous Ni-Fe-Cu-Al intermetallic composite electrode has been developed for use as a non-consumable anode in the Hall Héroult cell. The oxidation behavior in air and under electrolysis conditions have been studied. The electrode is noted to be resistant to the corrosive conditions encountered during electrolysis for up to 300 hour tests in 10 Amp and 100 Amp cells. The synthesis procedures for the manufacture of the electrodes and the beneficial influence of the pores are discussed. Preliminary results on the metal contamination during electrolysis are also presented.
10:55 am
APPLICATION OF NONEQUILIBRIUM THERMODYNAMICS TO THE LEDGE SURFACE OF ALUMINIUM ELECTROLYSIS CELLS: Ellen Marie Hansen, Signe Kjelstrup, Department of Physical Chemistry, The Norwegian University of Science and Technology, N-7034 Trondheim, Norway
Nonequilibrium thermodynamics for surfaces has been applied to the interface ledge-electrolyte in aluminium electrolysis cells. The method describes the interface as a layer of finite thickness 
, having a bath-like part and a ledge-like part, with properties differing from the bulk properties. The method can explain the heat transfer coefficient for the interface in a new way, namely as a combination of the thermal conductivities in the two parts of the interface. Examples are given to show how the temperature "jump" between the two bulk phases may either be located in the ledge-like part of the interface, in the bath-like part, or in both. In analysis of ledge growth, the possibility of different surface temperatures should be taken into account, because this temperature may, together with the temperatures close to the interface on both sides, determine the rate of freezing or melting. It is also shown how the simple steady state model can be expanded into a dynamic one.
11:20 am
PHYSICO-CHEMICAL PROPERTIES OF Na3AlF6-AlF3-LiF-CaF2 SYSTEM UNDER THE SAME SOLVABILITY OF Al2O3: Li Dexiang, Chen Jianshe, Li Guohua, Department of Nonferrous Metallurgy, Northeastern University, Shenyang, 110006, China; Ma Xiufang, Beijing Nonferrous Metal Research Institute, Beijing, China
The concept of properties of electrolyte melts under the same solvability of alumina at nonequal temperature, that is, the properties of melts under equal solvability of alumina dissolving in the electrolyte at the temperature which is 20°C above the liquidus, were put forward. Based on this theory, the physico-chemical properties, such as the initial crystallization temperature, solvability of alumina, conductivity, density of (2.23-3.0) NaF·AlF3 - (0-5%) LiF - (0-15 %) CaF2 system were studied. The results will provide more scientific basis for choosing the optimum electrolyte composition in aluminium electrolysis.
11:45 am
MEASUREMENTS OF HF IN STACKS AND POT ROOMS USING A REMOTE SENSING EYE-SAFE LASER INSTRUMENT: H.I. Schiff, Unisearch Associates, Inc., 222 Suidercroft Rd., Concord, Ontario, Canada L4K 1B5
A remote sensing system for continuous measurement of HF and other gases has been developed based on eye-safe turnable gases. The laser, its controls and data acquisition system are contained in a small instrument which can be located anywhere in the plant, such as the control room. The optical beam is transported to one or more stacks or ducts by fibre optics which may be kilometres in length. It is then directed across the stack and returned by a retroreflector to the same optical fibre and retroreflector combination for pot-room or roof-top monitoring. The use of optical multiplexing permits a single instrument to make simultaneous measurements at a number of locations providing a very cost effective system which can operate in any environment. Systems have been installed in four Canadian smelters and one in the UK. Examples of some of the measurements made with these systems will be presented.
Room: 232A
Session Chairs: J.M. Toguri, Dept of Metallurgy and Materials Science, Univ. of Toronto, 184 College Street, Toronto, Ontario, Canada, M5S 1A4; U. Pal, Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Room 4-134, Cambridge, MA 02139
8:30 am
MEASUREMENT OF GAS COMPOSITIONS USING SOLID ELECTROLYTES: R.V. Kumar, D.J. Fray, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, United Kingdom
Sensors are required to measure gaseous species such as SOX, NOX, HCl, and water vapour at elevated temperatures. There are very few solid electrolytes which respond to these gases, and furthermore, the species are usually present with other gases to which the electrolyte may respond. In addition, for long periods of operation, a stable reference is required. In order to meet these challenges, sensors consisting of two electrolytes in intimate contact have been developed. To measure HCl, a proton-conducting electrolyte is interfaced with strontium chloride. The reaction for the cell: (-) Pt, Air + HCl(g))/SrCl2//SrCeO3 + 10 mole % Nd2O3// Air + HCl(g), Pt(+). At the various interfaces, the reactions are: anode: 2Cl- + SrHCl = SrCl2 + HCl(g) + 2e-interface: 2H+ + 2Cl- = 2HCl(interface) cathode: HCl(interface) + SrCl2 + 2e- = SrHCl + 2Cl- overall cell reaction: HCl(interface) = HCl(g). The net result is that the potential is independent of the oxygen potential of the gas and the reference is given by the interaction of the two electrolytes. There is no need for an external reference which overcomes the problems of forming gas thigh seals at elevated temperatures. Other examples of this approach for the measurement of SOX, NOX, CO2, and H2O will be given.
8:55 am
DEVELOPMENT AND APPLICATION OF OXYGEN SENSORS IN COPPER METALLURGY: S. Seetharaman, Du Sichen, A. Jakobsson, Division of Theoretical Metallurgy, Royal Institute of Technology, S-100 44 Stockholm, Sweden
Oxygen concentration cells with stabilized zirconia electrolytes are widely used today to measure the activity of oxygen in liquid metals. In the case of liquid copper, the activity of oxygen in the molten metal as well as the effect of a third element on the same have been extensively studied using galvanic cells of the type (-) Pt, W or cermet / Cu-O-M // ZrO2 (stabilized) // AO, A / Pt (+, where M is the third element in molten copper and AO / A represents a suitable oxide/metal reference electrode. The effect of a number of "third elements" like Mn, Zn, As, Se, and Te on the oxygen activity in liquid copper have been studied by this method. The Mn and Zn interact very strongly with oxygen in Cu ( ), while, in the case of arsenic, the interaction parameter is nearly zero. The behavior of Se and Te in liquid copper with respect to the effect on the activity of oxygen is unique. At oxygen levels of the order of 10-4, these elements lower the activity coefficient of oxygen in the melt, while, at lower oxygen levels, the interaction parameter values are positive. These results are discussed in the light of some of the theoretical models for solute interactions in liquid metals. The application of these sensors in flash smelting, converter, and casting sections of copper production are discussed along with their implications on process optimization.
9:20 am
APPLICATION OF RAMAN SPECTROSCOPY TO HIGHTEMPERATURE ANALYTICAL MEASUREMENTS. J.P. Young, S, Dai, Y. Lee, H. Xiao, Chemical and Analytical Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 378316142
There are numerous analytical applications of scatteremission and absorption spectroscopy to liquids and solids in the temperature range of 0° to 350°C; process control is made impossible by using fiberoptic probes and Raman spectroscopy, for example, in these measurements. We have developed a unique allsilica fiberoptic probe which can have analytical applications in the temperature range where silica is a solid, 0° to 1600°C, and in chemical situations where it is inert. We have also developed techniques to use the ratio of the Stokes/antiStokes Raman emission of diamond to measure temperature in the range of 400 to 1000°C. We will discuss our results of such measurements in molten chloride and fluoride salts, other liquids, and solids. We will also describe our plans for temperature measurements by Raman spectroscopy through optical fibers in the range of 1000 to 2500°C, a range that can include molten metals such as steel.
9:45 am
SOLID STATE CURRENT-POTENTIAL SWEEP SENSOR FOR THE IN-SITU MONITORING OF COMPOSITION AND TRANSPORT PROPERTIES IN HIGH TEMPERATURE METALLURGICAL SLAGS: S.C. Britten, V. Stancovski, U. Pal, Dept of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 4-134, Cambridge, MA 02139
An in-situ solid-state electrochemical technique for measuring the concentrations of easily dissociable oxides in slags at temperatures between 1200 to 1600°C is being developed. The technique consists of using a stabilized zirconia solid electrolyte, which conducts oxygen ions, to separate a reference gas compartment from the slag of interest. Using a potentiostat, a direct current potential sweep is applied between the inner and outer compartments of the electrolyte, driving oxygen ions from the slag into a reference gas. With the use of open circuit reference electrodes, the resulting magnitude of the current potential profile reveals the concentration of dissociable oxides such as those of iron, manganese, and chromium. The open circuit potential recovery indicates the type of oxide present and its thermodynamic activity within the slag. The technique should therefore determine multiple properties of several different oxides with only one measurement. The limits imposed by the electronic short-circuit property of the zirconia electrolyte on the sensitivity of the technique are also under investigation.
10:10 am BREAK
10:20 am
APPLICATIONS OF SENSORS IN MOLTEN SALT TECHNOLOGY FOR METAL PROCESSING: P.T. Velu, R.G. Reddy, Dept of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487
The use of emf measurements to derive classical thermochemical data has been in use for many years. The reaction associated with electrochemical process is harnessed in a galvanic cell and energy involved measured in terms of electromotive force. The property requirements of sensor electrodes used differ for various aqueous, molten salt, and solid electrolyte systems. The electrodes for molten salt electrolytes need special care for construction. This paper describes the studies carried using an Ag/AgCl reference electrode. This electrode was used to measure the solubility of compounds in molten salt electrolytes. The results obtained using this electrode are in excellent agreement with the values from chemical analysis method.
10:45 am
NOVEL SOLID STATE SENSOR FOR MEASURING ARSENIC IN MOLTEN METALS: G.M. Kale, Dept of Mining and Mineral Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom; D.J. Fray, Dept. of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3 QZ, United Kingdom
A novel solid state sensor for measuring arsenic dissolved in molten metals has been developed based on a novel solid electrolyte conducting K+ ions. The solid state sensor can be schematically represented as: (-)Mo, Zn-As/ /K-323 SE/ /K-
Fe2O3+Fe2O3+02, Fe-Cr(+). The open circuit emf of the above sensor was measured in molten zinc containing less than 0.1 wt % As at a temperature of 823K. The emf of the sensor was found to vary linearly as a function of 1nXAs, where XAs is the mole fraction of As in An(1). The ionic conductivity of the novel solid electrolyte (K-323) was measured over a range of temperature (370<T<770K) using a vector impedance analyzer. The K+ ion conductivity of K-323 at 823K was found to be 1 X 10-3
-1cm-1. The performance of these arsenic sensors is currently being evaluated in plants in the United Kingdom and Germany.
11:10 am
MEASUREMENT OF NITROGEN AND SULPHUR IN MOLTEN METALS USING SOLID ELECTROLYTES: Y.C. Avniel, T.E. Warner, D.J. Fray, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, United Kingdom
One of the major problems of the iron and steel industry is the presence of phosphorus, sulphur, nitrogen, and silicon. Careful control and removal of these elements is required, and an on-line measurement of the concentration during removal would greatly improve the efficiency of the process. The oxygen content of molten metals is usually measured by using a sensor based upon stabilized zirconia, in which the oxygen ion is mobile. However, for nitrogen and sulphur, stable ionically conducting solid electrolytes for nitrogen and sulphur do not exist. The approach adopted in this work is to use electrolytes which conduct alkali and alkaline earth elements. For example, when a sodium ion conducting electrolyte is placed in a situation where sodium is not present, the sodium comes to equilibrium with the species which forms the most stable compound with sodium. Examples are given where sodium, strontium, and calcium beta alumina respond to sulphur and oxygen. Regions of response to a given species depend upon the concentration of other species in the melt and the standard free energy of formation of the various compounds. In the case of nitrogen measurement, it proved necessary to develop a new electrolyte, based upon rare earth oxides, in which nitrogen is soluble in the anion lattice. Results are presented for the measurement of sulphur and nitrogen partial pressures and for these species in molten iron and steel.
Room: 231A
Session Chairperson: D.B. Dreisinger, University of British Columbia, Department of Metals and Materials Engineering, 309-6350 Stores Road, Vancouver, B.C., Canada
8:30 am
INDUSTRIAL IN-PULP Co-Ni ALLOY ELECTRO-WINNING AT THE GECAMINES-SHITURU PLANT: K. Twite, J.-M. Dereydt, K. Mujinga, Gecamines Shituru Plant/Likasi, Bd. du Souverain 30, 32, B1170 Brussels, Belgium; P. Louis, Union Miniere, Allée de la Frènaie, B 1300 Wavre, Belgium
GECAMINES is a large mining concern and the world's leading cobalt producer having some of the richest cobalt deposits in the world. Cobalt is associated in the ore with copper as sulphides and oxides and in some locations with nickel too. Specific hydrometallurgical processes have been developed by GECAMINES which had done an important contribution to the development of the cobalt hydrometallurgy. In the Shituru plant, cobalt is obtained from an unique in-pulp electrolysis process, while in Luilu, cobalt is electrolyzed in a clear acidic solution giving a purer deposit. In the beginning of 1996 Shituru started the treatment of mixed Cu-Co-Ni Shinkolobwe hydrates obtained as by-product of an uranium solvent extraction plant. A typical analysis of this feedstock is: Cu: 2%, Co: 8%, Ni: 4%. The nickel sulfide depolarized cementation process developed previously by GECAMINES was inefficient to treat such a high level of Nickel contamination and it was decided to produce alloyed Cobalt-Nickel cathodes in the Shituru tankhouse. As anticipated from laboratory tests as previous studies and publications, a lower Ni/Co in the deposit was obtained compared to the Ni/Co ratio solution, despite the nickel reversible electrochemical potential is somewhat higher than the one of cobalt (-0.25 V vs -0.28 V). In this paper, the process flow-sheet and production data are given. Cobalt alloy with 5 - 20 % Ni was obtained at a production level of 300 t per month. The process developed is a first industrial realization in this way, bringing a new contribution to cobalt hydrometallurgy.
8:55 am
ELECTROLYTIC PROCESSING OF MANGANIFEROUS SILVER ORES IN ACIDIC NITRATE MEDIUM: O. Rutten, S. Van Sandwijk, G. Van Weert, Department of Raw Materials Technology, Delft University of Technology, Mijnbouwstraat 120, 2628 RX Delft, The Netherlands
Cathodic and anodic reactions in the acidic nitrate medium were studied in reference to the electrolytic production of manganese dioxide from pyrolusite (Mn02) ores by reductive leaching. Two USA ores were investigated. The reductant for Mn02 is produced cathodically and can either be nitrous acid or nitrogen oxide gas. In this work emphasis was placed on the nitrous acid leach. Manganese and silver are solubilized, iron is not. Cathodic regneration of nitrous acid was investigated in the range of 0.5 to 3.0 M nitric acid, 0.0 to 0.1 nitrous acid on graphite, platinum and platinized titanium cathodes at 20 to 80°C. It was established that the formation of the nitrosyl ion (N0+) is a prerequisite for the cathodic reduction of nitric acid. At cathode potentials < +700 mV (SHE), cathodic reduction of nitrous acid to nitric oxide takes place. Anodic deposition of manganese is as flaky -Mn02, similar to that produced in sulphate electrolytes. A conceptual flowsheet is presented and discussed.
9:20 am
A NOVEL ELECTROMETALLURGICAL PROCESS FOR THE TREATMENT OF REFRACTORY GOLD CONCENTRATES: N. de Jager, M.J. Nicol, University of the Witwatersrand, School of Process and Materials Engineering, Johannesburg, South Africa
In order to liberate gold from refractory gold ores and concentrates it is necessary to oxidize the surrounding sulphide minerals, typically pyrite and arsenopyrite. Traditional methods of oxidation include pressure leaching, roasting and bacterial oxidation. In recent years, bacterial oxidation has found increasing favour, although it is by no means completely satisfactory and is subject to large residence times. It is also extremely sensitive to operating conditions. Similarly, pressure leaching and roasting have their own particular disadvantages. A novel process has been developed as an alternative to the traditional methods whereby electro-generated ferrate [iron (VI)] ions in alkaline solution are used to oxidize a pyrite concentrate. This process has been observed to proceed fairly rapidly and could prove to be a more economically viable process, as well as being more environmentally acceptable. As an added benefit, operating in an alkaline environment is advantageous for downstream cyanidation processes. Iron (VI) is a relatively unknown species, due mainly to its instability in acidic solutions. However in alkaline solution it has been observed to be sufficiently stable for use as an oxidant when kept under the correct conditions. Iron (VI) is most conveniently manufactured electrolytically via the dissolution of high-carbon iron anodes in strongly alkaline solutions. Some literature has been published on the electrolytic generation of iron (VI) and relatively high efficiencies have been observed by both the authors and other researchers. This study utilizes both electrochemical techniques and leaching experiments to examine the kinetics and mechanism of the oxidation of pyrite by iron (VI). Cyclic voltammetry, rotating disk voltammetry and potential step experiments have been used to investigate the mechanism and kinetics of the oxidation process. Other potentiodynamic and poteniostatic techniques have also been employed. Leaching experiments have been used to provide a more detailed investigation into the kinetics of the process.
9:45 am
ELECTROLYTIC RECOVERY OF MERCURY FROM LOW CONCENTRATION BRINE SOLUTIONS: M. Rockandel, Universal Dynamics Ltd., Vancouver, Canada
Universal Dynamics Ltd. of Vancouver, Canada has developed, patented and commercialized the "REMERC" process for the treatment of mercury contaminated sludges and soils. Mercury is extracted into an acidified and oxidizing, sodium chloride brine solution. REMERC was initially developed to treat mercury contaminated EPA listed wastes (K106) generated by the chlor-alkali industry. More recent work has expanded the capability of REMERC to include remediation of mercury contaminated sites, equipment and building materials. In the process mercury is currently recovered from solution by cementation on iron powder in an agitated reactor. The process recovers high purity elemental mercury (99.9% purity). Cementation typically recovers about 90-95% of the mercury in 30 minutes. Higher recovery is not necessary because of the recirculation of the leach solution. When treating highly contaminated chloralkali wastes (5-13% mercury content), REMERC will reduce the mercury laden solutions from 400-1,000 mg/l mercury to 50-100 mg/l. In the treatment of less concentrated wastes (<1,000 mg/kg mercury) such as those encountered in site remediation, the treated solutions will generally contain 10-20 mg/l mercury. Cementation while being simple and able to achieve the required recovery has the undesirable properties of; requiring a solid-liquid separation and adding iron to solution which must be precipitated, ultimately increasing the weight of residue to landfill. The potential advantages of electrolysis were recognized early in the development of REMERC. Mercury electrolysis is well known in gold and chloralkali processing. Initial testwork utilized a liquid mercury cathode and a coated titanium anode both common to chloralkali producers. The mercury cathode appeared susceptible to polarization and solution impurities significantly affected performance. Agitation of the mercury pool improved performance but it was still not possible to achieve the reduction objectives. Current efficiencies were low, near 10%, and it was apparent that a relatively large cathode pool would be required to limit the current density. A number of electrode combinations with and without a membrane were then tested in a vertical electrode configuration but the desired performance was not obtained. In 1995 Universal Dynamics working with Dremco Ltd. of Arizona, USA began the development of a plate and frame style electrolytic cell. The objective of the electrolytic process was to achieve similar removals to those obtained by cementation, while producing high purity elemental mercury (>99.9% purity) and chlorine at the anode. Although current efficiency is a relatively minor concern the design objective was to achieve at least 50% CE. The current efficiency goal would require operation of the cell at current densities approaching the limiting current flow. The final cell current densities would therefore be in the range of 0.1 - 1.0 A/m2. Operation of a laboratory scale cell has demonstrated that the operating objectives can be achieved with a cell consisting of closely spaced shiny titanium cathodes and ruthenium oxide coated titanium anodes. Numerous variables were observed to be important including; inter electrode velocity, current density, pH and chlorine stripping. The cell has been tested on solutions generated by two REMERC operations, solution produced during site remediation pilot testing and on more highly concentrated solutions generated by oxidation of calomel generated at Cominco Metals, Norzink facility in Trail, B.C.
10:10 am BREAK
10:30 am
RECOVERY OF Cu2+ AND Cd2+ FROM DILUTE AQUEOUS SOLUTIONS BY ION FLOTATION AND ELECTROLYSIS: F.M. Doyle, University of California at Berkeley, Department of Materials Science and Mineral Engineering, Berkeley, CA 94720-1760; K. Sreenivasarao, Argonne National Laboratory, Energy Systems Division, Argonne, IL 60439
Copper and cadmium metal has been recovered from dilute (3 X 10-4 mol/dm3) chloride solutions by ion flotation with dodecysulfate, followed by electrolysis. This approach should facilitate treatment of effluents too dilute for effective direct electrolysis. The adsorption density of metal dodecylsulfate complexes on bubble surfaces was estimated from surface tension data, and compared well with experimentally-observed metal removal kinetics, and ultimate recoveries. Copper and cadmium were recovered by electrolyzing the foamate, using steel wool cathodes and a graphite anode. The stability constants of the copper and cadmium dodecysulfate complexes are estimated, and used to analyze the thermodynamics of electrolysis. Dodecysulfate was unaffected by the electrolysis process, and hence could be recycled to ion flotation. A conceptual flowsheet for an overall effluent-treatment process is presented.
10:55 am
NITROX METALS CORPORATION'S PROCESS FOR DIRECT LEACHING OF COPPER CONCENTRATES: R.N. O'Brien, E. Peters, Vancouver, B.C., V6N 2G1
It has been discovered that copper concentrates can be leached in strong (40-60%) sulfuric acid with air as the primary oxidant, if nitric acid is present as a catalyst. Chalcopyrite is rapidly decomposed at temperatures well below the boiling temperature of the lixiviant (150C.) and the resulting copper and ferric salts are precipitated as CuSO4 H2O or CuSO43 H2O and FeH(SO4)24H2O. Other metal sulfides such as zinc, lead, nickel, etc. are also converted to sulfates that are nearly insoluble. Sulfur is partially converted to elemental and partially to sulfuric acid. Reduction products of nitric acid can be recovered from the distillate with good recovery. Conversion of as-received copper concentrates is largely complete in about 1 hour. A number of process flow sheets are possible, and one that utilizes existing solvent extraction and electrowinning technology is considered economically feasible. This flow sheet involves (a) separation of metal sulfates and unleachable residues from excess acid by centrifuge, (b) water leaching of salts with partial neutralization (with limestone) of excess acid, to a tenor of 10 g/l Cu2+, (c) solvent extraction of copper using one of the LIX reagents, and (d) precipitating most of the ferric iron from raffinate with more limestone, so that it can be used as recycled water in step (a). Gold and silver are retained in a water insoluble small volume residue also containing any elemental sulfur formed, while minor elements like arsenic, antimony, etc. are retained by the strong sulfuric acid that is centrifuged from solids in step (a). These can be removed from this solution using methods previously developed for the purification of copper electrorefining electrolytes.
11:20 am
ACID RECOVERY AND PURIFICATION USING ABSORPTION RESIN TECHNOLOGY: M. Sheedy, Prosep Technologies Inc., Pickering, Ontario, Canada
Strong mineral acids, principally sulphuric, are widely used as electrolytes for the electrorefining and electrowinning of metals. Impurities in these electrolytes are controlled by continuously bleeding solution form the tank house. In addition to the contaminant these bleed streams contain high levels of sulphuric acid and the metal being recovered. Subsequent treatment of these bleed streams often requires neutralization which generates large volumes of solid waste. Absorption resin technology employing a novel ion exchange technique known as Recoflo allows the separation of the mineral acid from dissolved metal salts. The recovered acid is suitable for recycle back to the electrolyte circuit. The metal salt and other contaminants leave the process free of sulphuric acid. In this process, known commercially as the APU, ion exchange resin is used to sorb sulphuric acid while excluding the metal salts. The purified acid is then removed by washing the resin with water. The process has been extensively used for the recovery of waste pickling acids in the steel industry and anodizing solutions in the aluminum industry. In the mining industry the process has been successfully evaluated for the separation of excess sulphuric acid from copper electrolytes, the removal of magnesium and manganese contaminants from zinc electrolytes, and antimony, bismuth and nickel from copper electrolytes.
11:45 am
ELECTRODEPOSITION OF THIN MULTILAYER MAGNETIC MATERIALS: Z. Liu, K.C. Liddell, Washington State University, Department of Chemical Engineering, Pullman, WA 99164-2710
High-quality multilayers exhibiting giant magnetoresistance have been made by electrodeposition. The thickness of the individual layers was varied by changing the duration of the deposition pulses. Smooth and adherent layers as thin as 1A were made and characterized.
Room: 340A
Session Chairperson: Dr. Subodh K. Das, ARCO Aluminum, Inc., P.O. Box 32860, Louisville, KY 40232
8:30 am
PREDICTING THE FORMABILITY OF ALUMINUM AUTOBODY SHEET ALLOYS: J. Daniel Bryant, Tatsuhito Koya, Armand J. Beaudoin, Reynolds, Metals Corporate Research and Development, Fourth and Canal Streets, P.O. Box, 27003, Richmond, VA 23261
While aluminum alloys based on the Al-Si-Mg-Cu system are currently being used in the production of a number of automotive body panels, the continuing demands for improved formability in these alloys have led alloy developers to the study of novel compositions and processing practices. Predicting stamping performance for a wide range of alloy variants, however, remains a difficult problem. Uniaxial tension tests, while providing reproducible assessments of mechanical behavior, are performed in a strain state that is quite different from that encountered in most stamping operations. As such, more elaborate, and often and less reproducible, methods of assessment are often employed, such as limiting dome height measurements and the construction of forming limit curves. In the present work, we have analyzed the tensile behavior of a series candidate alloys and used these data to predict the forming limit curve over a range of strain states. Using a modified form of the Voce work-hardening model, a Marciniak-Kuczinski simulation has been constructed and used to predict the forming limit curve minimum (FLC0). These predictions are then related to experimentally determined forming limit curve data for the candidate alloys. The comparison of predicted and measured forming limit curve data indicates that the model can be successfully used to predict mechanical behavior under a state of plane strain using uniaxial tensile data. The results of the model indicate that the slope of the work-hardening curve, particularly at high strain values, is intimately related to the forming limit curve minimum. These correlations provide alloy developers with an inexpensive method of comparing the formability new alloy variants by more thoroughly exploiting the data concealed within the full uniaxial tensile curve.
9:00 am
TOOL WEAR DURING MACHINING OF AA356 ALUMINUM ALLOYS: Zhongnan Dai, J.G. Morris, Light Metals Research Labs, Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506
As a casting material, AA356 Aluminum alloy is widely used in the automotive industry. During machining, the tool wear mechanism for this alloy is significantly different from that for steel. For different as-cast metallurgical microstructures, materials with harder dispersed particles and stronger matrices show higher resistance to seizure because of an increase in the pressure requirement above which seizure occurs. This results in better machinability. On the other hand, hard particles act as small cutting edges on the tool materials, thereby causing tool wear due to the particle's abrasive characteristics. The wear characteristics of cutting tools were investigated in this study. Scanning electron microscopy, optical microscopy, EDX analysis were used to identify wear mechanisms. The results obtained show that there are a number of different wear mechanisms that contribute to tool damage, and hence, to tool-life. The role of the as cast microstructure on tool wear was also studied in order to determine under what structural states tool wear would be reduced.
9:30 am
THE EFFECTS OF PREAGING TREATMENTS ON FORMABILITY AND PAINT BAKE RESPONSE IN ALUMINUM AUTOBODY SHEET ALLOYS: J. Daniel Bryany, Reynolds Metals Company, Corporate Research and Development, Fourth and Canal Streets, P. O. Box 27003, Richmond, VA 23261
The use of heat treatable aluminum alloys for automotive body panels is presently increasing, due to aluminum's attractive combination of low density and compatibility with current production methods. In these applications, the automotive paint bake cycle is used to impart a modest artificial aging response, referred to as the paint bake response (PBR), in the alloys following stamping. Unfortunately, the short duration of the paint bake cycle (as dictated by production demands) is generally insufficient to exploit more than a small fraction of the age hardening potential of the alloys. Reynolds Metals Company has developed a thermal treatment which has been shown to be effective in increasing the paint bake response by up to a factor of four, while at the same time improving the formability of alloys and reducing the natural aging rate. Through the use of atomic resolution microscopy and differential thermal calorimetry, the mechanism of pre-aging can be shown to be the result of changes in the precipitation sequence of metastable variants of Mg2Si, resulting in an increase in the precipitation kinetics during the paint bake cycle and a finer distribution of strengthening precipitates in the painted component. Through the use of pre-aging, our research has shown that 6XXX autobody sheet alloys may be produced which have both superior stamping performance as well as higher strengths in the stamped and painted components, resulting in automotive body panels with up to 50% higher dent resistance.
10:00 am
THE EFFECT OF THE DISPLACEMENT CONTROL ROUTINE ON THE ELONGATION TO FAILURE AND FAILURE MORPHOLOGIES IN SUPER PLASTIC AA 5083: A.L. Lund, S.G. Pitman, M.A. Khaleel, M.T. Smith, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352
It has been noted in the literature that superplastically formed Al alloys fail by cavitation. The morphology of the final cavitated fracture region may be important in determining optimum forming conditions, by determining whether failure occurs parallel or perpendicular to the principal stresses. In addition, the displacement control routine may have a large effect on the total elongation that can be expected during forming operations. Tests were performed to evaluate failure in a AA5083 base alloy, by the following methods: 1) uniaxial tension tests at a constant true strain rate were interrupted at 80%, 60,G, 40%, and 5% of the maximum load, and microstructurally evaluated to identify the failure path and 2) tests were performed with various displacement control routines, and the elongation to failure was measured. The following displacement routines were used: smooth test, two-step strain test, multi-bump strain rate tests with various sizes of bumps scheduled at various intervals, and variable load oscillation tests.
10:30 am BREAK
11:00 am
EVOLUTION OF ALUMINUM MICROSTRUCTURES IN THE ALUMINUM EXTRUSION PROCESS: Woiciech Z. Misiolek, Aluminum Processing Program, Rensselaer Polytechnic Institute Troy, New York 121803590
The final microstructure and its uniformity is responsible for the physical properties and surface quality of the extruded profiles. Extrusion is time dependent process and its deformation variables such as, deformation zone and dead zone geometry as well as extrusion speed and temperature, change in time. The final microstructure depends on the above mentioned extrusion parameters as well as billet microstructure and post processing treatment. Metal flow conditions are influenced by the process parameters. Both physical and numerical process modeling techniques have been applied to predict metal flow behavior during extrusion through dies with different geometries. Additional information, allowing understanding of microstructure evolution, can be obtained from the crystallographic characterization of the typical deformation zone regions such as dead metal zone, main deformation zone and recrystallized zone on the billet-container interface using the electron backscattering diffraction (EBSD) technique. This technique has been utilized to follow in detail the orientation aspects of the deformed grains in extruded aluminum. This analysis provides information which can be used in the die and process design to improve metal flow uniformity and therefore the microstructure of the final product. It also allows prevention of the typical extrusion defects like surface tearing.
11:30 am
METALLURGICAL SAMPLE PREPARATION AND IMAGE ANALYSIS TECHNIQUES USED FOR THE EVALUATION OF AUTOMOTIVE MATERIALS: Matthias Hoffman, George A. Blann, Buehler Ltd., 41 Waukegan Rd., P.O. Box One, Lake Bluff, IL 60044; William R. Creech, BMW Manufacturing Corp., Greer, SC
This paper focuses on the commercial application of aluminum alloys and composite materials used in the automotive market. Today's automotive materials require a high degree of reliability. Therefore, efficient and accurate material testing and characterization methods are essential. Automotive alloys and composite materials often times are evaluated for microstructural properties. This work focuses on the developments in the metallurgical Q & A and research lab by highlighting the latest advancements using automated and semi-automated sample preparation techniques. The interpretation and quantitative analysis of these microstructures Ts accomplished by utilizing automated image analysis techniques. Image Analysis allows for an efficient as well as accurate analysis of dimension measurements, constituent analysis, porosity measurements, etc.
Room: 230C
Session Chairperson: Boris M. Triko, Aluminum Company of America, 1000 Riverview Tower, 900 South Gay Street, Knoxville, TN 37902-1848
8:30 am
GREEN PASTE POROSITY AS AN INDICATOR OF MIXING EFFICIENCY: Per Stokka, Norsk Hydro Research Centre, N-3901 Porsgrunn, Norway
Variations in green paste porosity were studied as a function of pitch content and mixing parameters. Porosity in paste from paste plants operating with different mixing systems, was measured and used to indicate the efficiency of the mixing. Changes in paste porosity during remixing in the laboratory were also studied.
8:55 am
POTENTIALITIES IN THE PASTE PLANT: S. Wilkening, VAW Aluminium-Technologie GmbH, P.O. Box 2468, 53114 Bonn, Germany
Over the last decade much progress in paste plant technology originated from computerized process control, improved process philosophy and P & ID's as well as full level 2 operation. This paper will focus on materials aspects to get out more from the intrinsic properties of coke and pitch. Proposals will be made how to utilize in a better way the structural properties of petroleum coke and the fluid and carbonization properties of binder pitch. Potential changes in equipment and lay-out will also be discussed.
9:20 am
VERTICAL ANODE CRACKING - THE VALCO EXPERIENCE: Norbert A. Ambenne, Volta Alumium Company Ltd (VALCO), P.O. Box 625, Tema, Ghana, West Africa
During the period 1990 - 1995 the VALCO aluminum smelter experienced a serious anode cracking problem. Approximately 12 % of the anodes split mainly along a particular set of anode stubs. About half of these splits resulted in carbon pieces falling into the reduction cell with attendant operating difficulties. This cracking phenomenon started when the plant was converted from 41.5 to 48 inches longer anodes with the extra length added to one end of the anode. Results of the investigations revealed that several operating variables contributed to anode cracking in varying degrees. These factors include mix profile in anode former mold, anode stub-to-gap ratio, anode setting practices, pot condition, anode symmetry, and moisture content in anode aggregate. This paper discusses these factors and how they affected anode cracking at Valco.
9:45 am
AN APPROACH FOR A COMPLETE EVALUATION OF RESISTANCE OF A MATERIAL TO THERMAL SHOCK (PART 1): APPLYING TO THE CASES OF ANODES AND CATHODES: Christian Dreyer, Bernard Samanos, Aluminium Pechiney, LRF BP 114, 73303 Saint Jean de Maurienne, Cedex, France
The aim of this article is to describe a new method for characterizing a material in terms of resistance to thermal shock. Such characterization takes into account the criteria of thermal shock resistance to initiation (Kingery criterion) and propagation (Hasselman criteria). It can be applied equally well to hard or soft thermal shock. This new approach has the following main advantages : 1) characterization of the material in terms of thermal shock is complete, 2) thermal shock tests or empirical formulae, the validity of which are often hard to establish, become unnecessary. Examples of the use of this new approach are presented for anodes and cathodes.
10:10 am BREAK
10:30 am
AN APPROACH FOR A COMPLETE EVALUATION OF RESISTANCE OF A MATERIAL TO THERMAL SHOCK (PART 2): APPLYING TO AN INDUSTRIAL PROBLEM AT ALBA: Bernard Samanos, Christian Dreyer, Aluminium Pechiney, LRF BP 114, 73303 Saint Jean de Maurienne Cedex, France; A. Hameed, G. Abbas, Jaffar G. Ameeri, Aluminium Bahrain, 570 Manama, Bahrain
This article presents in detail the steps taken to successfully resolve the problem of anode breakage due to thermal shock et ALBA. These steps can be essentially characterized as follows: 1) establishment of a method of accounting for anode breakages, 2) parametric studies on benchscale anodes, 3) effects on the process. Characterizing anodes in terms of resistance to thermal shock, following the method described in Part 1, allowed us to appreciate the importance of each of the adjustable parameters of the process. The applied solution draws on a new grain size distribution formulation.
10:55 am
ANODE PROPERTY DEVELOPMENT DURING HEAT TREATMENT: Mona Jacobsen, Department of Thermal Energy and Hydro Power, the Norwegian Institute of Science and Technology, N-7034 Trondheim, Norway; Oyvind Gundersen, Department of Engineering Cybernetics, The Norwegian Institute of Science and Technology, N-7034 Trondheim, Norway
Change of weight, density, permeability and porosity of anode specimens were measured after being baked to temperatures between 300 and 1250°C. Test specimens were cut from a green anode and analysed prior to the baking to study green property variations. Density variations in the green anode were significant and influenced the permeability measured in the green specimens. In mathematical modeling of the baking process, anode property models for description of heat and mass transport phenomena in the anodes are required. As basis for the derivation of the property models, the anode was considered to be a composite medium consisting of pitch coke, filler coke and pores. The filler coke was divided into a coarse and fine size fraction. The fine fraction mix with the binder pitch to constitute the binder matrix. It was assumed that the binder matrix was uniformly distributed on the surface of the remaining coarse filler particles. The models were compared and verified against the data.
11:20 am
ANODE IMPREGNATION SYSTEM FOR ALUMINIUM REDUCTION CELLS: Georges Berclaz, Avenue St-François, 3968 Veyras/Sierre, Switzerland; Vittorio de Nora, Jean-Jacques Duruz, Gaynor Johnston, MOLTECH, 9 Route de Troinex, CH 1227 Carouge-Geneva, Switzerland
The minimization of anode carbon consumption in aluminium reduction cells has an important technical, environmental and economical impact. The basic anode elements, such as coke and pitch, do not always have the desired properties and there is an increasing need to protect the anodes against oxidation by air and CO2. A solution based on boric acid impregnation of the upper part of the anode has been tested at the industrial scale. Anodes have been impregnated using specially designed equipment to place the protection in the appropriate part of the anode and to avoid metal contamination. Results are shown for different levels of impregnation. Comparison to metal spraying protection is also analyzed.
Room: 230B
Session Chairperson: Seymour G.Epstein, The Aluminum Association Inc., 900 19th St., N.W., Washington, DC 20006
8:30 am
UPDATE ON MOLTEN METAL INCIDENT REPORTING: S.G. Epstein, The Aluminum Association Inc., 900 19th St., N.W., Washington, DC 20006
Millions of pounds of molten aluminum are handled every day, safely and without incident, in nearly every segment of the aluminum industry. However, there are inherent hazards in handling any molten material and explosions involving molten aluminum and water or other oxidizing contaminants continue to occur in plants throughout the world. While these are infrequent events that often result in little or no damage to equipment or injury to personnel, an awareness of the possible consequences of an explosion is critical to maintaining a safe casthouse. The aluminum industry has made an extensive effort to gain an understanding of molten metal explosions, the factors that promote them, and how they might be prevented. The effort has included laboratory studies, conducted over the past 45 years, and thorough investigations of plant incidents. As part of this effort, the Aluminum Association established in 1985 a world-wide molten metal incident reporting program to obtain and share information on plant incidents. Presently, there are more than 230 participants in the program representing about 300 plants located in about 20 countries. Findings from the nearly 1200 reports submitted to date are reviewed in this paper.
8:55 am
INVESTIGATION OF COATINGS WHICH PREVENT MOLTEN ALUMINUM/WATER EXPLOSIONS - PROGRESS REPORT: R.T. Richter, D.D. León, T.L. Levendusky, Aluminum Company of America, Alcoa Technical Center, Alcoa Center, PA 15069
The aluminum industry has used Porter International 7001 (Tarset Std.) successfully as a protective coating in casting pits for over 20 years to prevent molten aluminum and water explosions until it was withdrawn from the market in 1994. The Aluminum Association contracted with Alcoa in 1995 to identify and test alternate coating materials which would be an acceptable replacement for Tarset Std. This paper will report the status of the program which was initiated in September 1995 and will be concluding in late 1996. Included in this paper are the screening and selection processes of the candidate coatings, results of initial molten aluminum/water explosion tests and the selection of the best performers for final explosion tests.
9:20 am
PROMOTING AWARENESS OF POTENTIAL HAZARDS IN ALUMINUM SCRAP: D.C. Pierce, C.H. Kenney, Reynolds Metals Company, 6601 West Broad Street, Richmond, VA 23261
There are a variety of potential safety hazards in any industrial activity and this includes the melting of aluminum scrap. The source of most hazards in scrap aluminum is the moisture or contamination that the scrap contains. Melting internal or purchased scrap remains the prevailing cause of molten metal incidents today. Everyone who handles scrap aluminum, from the first collection through to the melting, needs to be aware of the potential hazards. Facilities need to use a variety of approaches to increase safety awareness in all the operations. Scrap collectors, suppliers and brokers must be mindful of what the scrap hazards are, and the receiving plants must take steps to keep the hazards out of their casthouses. One of the new tools that plants have available is a fax-notification system operated by the Aluminum Association for information on scrap that has been rejected by another facility for safety or health reasons. This system is felt to offer an important safety enhancement, because scrap dealers have been known to resell unsafe scrap after it has been rejected. Although the Scrap Rejection Notification System is currently operational, its success will be measured by how infrequently it is needed.
9:45 am BREAK
9:55 am
NEW GUIDELINES FOR SOW CASTING AND MELTING: G.N. Chaffin, Quality Challenges, Midlothian, VA 23112; J.E. Jacoby, Consultant, 3398 North Hills Road, Murrysville, PA 15668
The aluminum industry has experienced many incidents of explosions as a result of wet or contaminated sows being charged into molten metal. The presence of moisture in the cavity of a sow is often impossible to detect and therefore the sow is assumed to be safe. However, this undetected moisture can cause a serious explosion if it is submerged into molten aluminum. The Aluminum Association has prepared guidelines for sow casting, inspection and melting to help facilities protect themselves from the potential hazards associated with melting sows. The guidelines and this paper consider mold designs, casting, transportation & storage, inspection and melting operations. Recommendations are offered which can be used in conjunction with each plant´s practices. The recommendations can help both the casting facility and the melting plant work toward a decrease in the possibility of an incident involving the melting of sows.
10:20 am
THE SEARCH FOR PROTECTIVE CLOTHING FOR WORKERS EXPOSED TO THE HAZARDS OF MOLTEN ALUMINUM AND MOLTEN BATH: Ronald R. McHaney, Kaiser Aluminum and Chemical Corporation
Burns are one of the leading causes of work injuries within the aluminum industry. Some physical and chemical properties of molten aluminum - low emissivity and viscosity - contribute to the potential for injury-producing incidents. Other properties, including high heat of fusion and shrinkage characteristics during cooling, add complexity to the task of identifying suitable protective clothing for workers exposed to the hazards of molten aluminum and bath. This presentation will address the initiative to identify protective clothing for workers exposed to those hazards and the progress that has been made including the development and application of the American Society for Testing Materials (ASTM) designation: F955, "Standard Test Method for Evaluating Heat Transfer Through Materials for Protective Clothing Upon Contact with Molten Substances". In addition, I will discuss the need to consider worker comfort and the potential for heat stress in the selection process.
10:45 am
PANEL DISCUSSION: All Speakers
Room: 240A
Session Chairperson: John Grandfield, Comalco Research Centre, P.O.Box 316, Thomastown, Victoria 3074, Australia
8:30 am
MODELLING OF SOLIDIFICATION IN Al-ALLOYS: Nigel Saunders, Thermotech Ltd., The Surrey Research Park, Guildford GU2 5YG, and IRC in Materials for High Performance Applications, University of Birmingham, Birmingham B15 2TT, United Kingdom
Solidification in Al-alloys is a complex process usually occuring under non-equilibrium conditions with the possible formation of metastable low melting point eutectics and non-equilibrium phases. However, it has recently been shown that it is possible to use thermodynamic phase diagram calculations to simulate the non-equilibrium solidification of complex Al-alloys under so-called 'Scheil' conditions. Excellent results can be obtained for features such as fraction solid transformed as a function of temperature, phase formation, latent enthalpy and Cp of solidification etc. All of these features are important input into modelling of solidification processing particularly for software packages which simulate heat flow during casting. The paper will present the results of 'Scheil' simulations for a wide range of commercial Al-alloys showing comparison with experimental results for fraction solid transformed and phase formation. The use of subsequently derived Cp and heat evolution parameters in casting simulation packages will be discussed and examples of its application shown.
8:50 am
THE APPLICATION OF EFFICIENT PARALLEL PROCESSING TO FINITE ELEMENT MODELING OF FILLING, SOLIDIFICATION, AND DEFECT PREDICTION FOR ULTRA-LARGE SHAPE CASTINGS: David Snyder, Aluminum Company of America, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069; David Waite, Consultant, Coralville, IA; Alpesh Amin, HP/Convex Corporation, Atlanta, GA
Finite element modeling has become widely to used simulate the filling, solidification, and defect formation in casting processes. For extremely large, complex parts, typical of automotive structural applications, the high cost of tooling makes process modeling an extremely useful tool. However, as the size and complexity of casting part geometry increase, the computational requirements for modeling become formidable. To address the challenge for modeling ultra-large shape castings, a finite element code was developed to efficiently take advantage of shared-memory parallel computing systems. This paper gives a brief description of the mathematical models which describe the casting processes. The implementation of the models and the numerical issues regarding memory architecture, parsing of computations, cpu synchronization, and overhead minimization for parallel processing are discussed. Examples are presented for filling and solidification analyses of permanent mold, tilt-pour, and die casting models run on an 8-CPU HP/Convex SPP-1000 computer.
9:10 am
IN-SITU TEMPERATURE MEASUREMENTS IN LOW PRESSURE PERMANENT MOLD CASTING: Florence Paray, Joe Gruzleski, Department of Mining and Metallurgical Engineering, McGill University, 3450 University Street, Montreal, Quebec, Canada H3A 2A7; Joe Clements, Grenville Castings Ltd., Merrickville, ONT, Canada K0G 1N0; Bahadir Kulunk, Timminco Metals, Research and Development Center, Haley, ONT, Canada K0J 1Y0
The low pressure casting process has an increasing popularity as it allows a rapid production of components close to the final "near net shape" with a very good casting yield. Depending on the property requirements of the final product, it is often necessary to control casting soundness. Internal porosity can cause a loss of pressure tightness, a critical factor in parts such as engine blocks and manifolds which are required to keep various gases and fluids. The development of criteria functions should allow the prediction of the thermal conditions required to maintain porosity below some critical predetermined level. In order to determine criteria functions, it is necessary to acquire thermal data during casting solidification. A low pressure casting machine and die were instrumented to obtain "in situ" thermal analysis curves during the solidification of flat plates of thickness varying from 1/8" to 3/4" in Sr modified and unmodified 6290, 356 and 319 alloys. The paper describes that effort and some of the results obtained.
9:30 am
A TECHNIQUE FOR THE ESTIMATION OF INSTANTANEOUS HEAT TRANSFER AT THE MOLD/METAL INTERFACE DURING CASTING: Michael Trovant, Stavros Argyropoulos, Department of Metallurgy & Materials Science, University of Toronto, 184 College Street, Toronto, Ontario, Canada M5S 3E4
Many current advancements responsible for improving the accuracy of solidification algorithms have resulted from the incorporation of additional complex casting related phenomena into the numerical calculation scheme. More recently, however, the proper specification of boundary conditions has been found to play a critical role in limiting model inaccuracy. Of particular interest to casting are the temperature boundary conditions, which when adopted by many models appear to be the most troublesome. Temperature boundary conditions can vary significantly with time and position along the face of the casting and accurate heat transfer coefficients are notoriously difficult to obtain experimentally for all points on the mold/metal interface, especially when the influence of thermal contraction is acknowledged. A novel technique which minimizes the error associated with selecting boundary conditions without experimentation is proposed. Advanced knowledge of the air gap formation and its correlation to the heat transfer coefficient at the mold/metal interface is used to formulate a coupled mathematical model which determines the increase of the air gap and predicts the instantaneous cooling conditions at a given mold wall. The objective is to allow the modeler to estimate effect of thermal contraction on the heat loss at mold/metal interfaces without resorting to experimentation.
9:50 am
MECHANISM OF DENDRITE FRAGMENTATION IN CASTINGS: Shan Liu, Shu-Zu Lu, A .Hellawell, Michigan Technological University, Dept. of Metallurgical and Materials Engineering, Houghton, MI 49931
A temperature gradient stage was designed with a controlled deceleration mechanism to simulate the columnar growth in castings/ingots where the growth velocities and temperature gradients at a dendritic front undergo a continuous decrease during solidification. Transparent materials of SCN-H2O and NH4Cl-H2O systems were used so that the solidification process with various decelerations could be directly observed and video recorded. It is observed that fragmentation of secondary arms is directly related to the deceleration and this provides an intrinsic resource for the formation of equiaxed grains in castings where convection may be available for transportation of the fragments to the open liquid. The responses of a dendritic array to the deceleration, including primary spacing adjustment and tip radius adjustment etc., are also observed and discussed.
10:10 am BREAK
10:20 am
THE VISUALIZATION OF THE PARTICLE CONTENT OF LIQUID ALUMINUM ALLOYS: N.D.G. Mountford, A. Simionescu, I.D. Sommerville, Department of Metallurgy & Materials Science, University of Toronto, Toronto, Ontario, Canada M5S 3E4
Aluminum alloys can contain heterogenous impurities which will affect the strength of the final product and result in either failure during manufacture or in service. Pulsed ultrasound, conveyed down metal guide-rods from energized piezo-electric crystals, is passed into the liquid metal and reflections from any impurities can be recorded by special counting devices. Small particles of the order of 10 to 15 µm can be resolved and their behaviour such as in settling recorded. Sequential tests using particles of identified size and distribution such as SiC and TiAl3 demonstrated the systems reproducibility. Such changes in composition resulting from imposed turbulent transfer with the associated pick up of very small oxide particles could also be shown. The effect of "sludge" formation such as that found in die-casting applications due to intermetallic phase precipitation could also be measured. This could be of value in process control of die casting systems. The developed system is adaptable to on line quality measurement and the recording of molten aluminum cleanliness in crucibles, ladles, furnace wells, launders and other transfer systems.
10:40 am
FRACTAL ANALYSIS: POROSITY IN ALUMINUM CAST ALLOY: Bo-Tao Lee, Shu-Zu Lu, A. Hellawell, Michigan Technological University, Dept. of Metallurgical and Materials Engineering, Houghton, MI 49931
Porosity is a very common defect in Al-Si cast alloy. To examine the porosity, a fractal analysis was conducted to characterize the pores using two numbers, Fractal Dimension, D, and Shape Factor, 
. This analysis was based on the measurement of perimeters/areas of all individual pores using an image analyzer with changing magnifications. The result indicates that two types of pores, i.e., rough/shrinkage pores and smooth/hydrogen pores, can be distinguished by these fractal numbers. The shrinkage pores show a larger value of fractal dimensions whereas the hydrogen pores have a fractal dimension close to one. Combined with analysis for silicon particles, it is suggested numerically that shrinkage pores are more likely associated with the silicon phase that is not well modified, showing a rather coarse flake structure, and the hydrogen pores are in the regions where modification was well done with fine silicon particles.
11:00 am
NUMERICAL SIMULATION OF DIE FILLING IN SEMISOLID METAL PROCESSING: Andreas N. Alexandrou, François Bardinet, Mechanical Engineering Department, Worcester Polytechnic Institute, Worcester, MA 01609; Willem Loué, Pechiney CRV, Centre de Recherche de Voreppe BP27, 38340 Voreppe, France
Semisolid Metal Processing is gaining interest very rapidly. This manufacturing approach offers distinct advantages over other near-net-shape technologies, like a more homogenous microstructure and less porosity and thus excellent mechanical properties. A perfect control of the die filling during processing is however necessary, especially in the case of semisolid forming of aluminum, where a non-controlled die filling can lead to oxide inclusions. Numerical simulation would be a powerful tool, as it would allow to predict die filling and the optimization of die design. However, the constitutive behaviour of such semisolid metals is rather complex. Their non-Newtonian behaviour does not depend only on the volume fraction of liquid, but also on the metal´s history prior to processing and the processing conditions. In this paper, a Bingham power-law relation is presented, capable of describing correctly the rheological behaviour of the semisolid metal. This constitutive equation is then introduced in a modified version of the casting simulation package SIMULOR. Simulation results on the filling of a 2-D cavity under various conditions are shown. Issues related to die design of dies, using numerical simulation will also be addressed.
11:20 am
SOLIDIFICATION PROCESSING OF ALUMINUM CASTING ALLOY REINFORCED WITH CERAMIC MICROSPHERES FOR THIXOFORMING: P.D.D. Rodrigo, K. Xia, N. Setargew, Materials Group, Department of Mechanical and Manufacturing Engineering, University of Melbourne, Parkville, Victoria, Australia 3052; P. Fitzgerald, G. Withers, Cyco International, 1297 Nepean Highway, Cheltenham, Victoria, Australia 3192
A cast aluminum matrix composite based on an Al-Si-Mg alloy has been developed. The reinforcement was in the form of hollow microspheres, a ceramic by-product from coal power stations. The particles were incorporated into the aluminum alloy melt by mechanical stirring either in the semisolid state or full liquid state. The composite melt was cast from full liquid temperature to produce slugs for thixoforming. A variety of compositions, reinforcement volume fractions and processing parameters were used. The as-cast microstructure consisted of fine, equiaxed dendritic primary grains in a matrix of secondary grains and eutectic phases. The primary dendritic grains evolved to become non-dendritic after reheating the slugs to semisolid temperature. The slugs were subsequently thixoformed at a temperature corresponding to a primary solid fraction of about 50% into thin plates and alternator pulleys. Special wear tests on the pulleys showed that they were comparable to steel pulleys. The material is potentially suitable for those applications demanding good wear resistance, light weight and low cost.
Room: 330C
Session Chairperson: Walter W. Milligan, Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931
9:00 am INVITED
SYNTHESIS AND MECHANICAL PROPERTIES OF NANOCRYSTALLINE INTERMETALLICS AND MULTIPHASE MATERIALS: J.A. Eastman*, M. Choudry*,**, M.N. Rittner***, C.J. Youngdahl*,***, M. Dollar**, J.R. Weertman***, R.J. DiMelfi****, and L.J. Thompson*, *Materials Science Division, Argonne National Laboratory, 9700 S. Cass Ave., Bldg. 212, Argonne, IL 60439, **Mechanical, Materials, and Aerospace Engineering, Illinois Institute of Technology, Chicago, IL 60616, ***Materials Science and Engineering Department, Northwestern University, Evanston, IL 60208, ****Reactor Engineering Division, Argonne National Laboratory, Argonne, IL 60439
The mechanical behavior of nanocrystalline intermetallic and multiphase materials has been investigated using disk bend, tensile, and compression techniques. Materials such as NiAl, TiAl, Al-Al3Zr, and Cu-SiOx were synthesized by the gas-condensation technique using electron beam heating. Disk bend tests of nanocrystalline NiAl and TiAl showed evidence of improve ductility at room temperature in these normally extremely brittle materials. In contrast, tensile tests of multiphase nanocrystalline Al-Al3Zr samples showed significant increases in strength, but substantial reductions in ductility with decreasing grain size. Results from compression tests of nanocrystalline Cu and Cu-SiOx will also be described. Implications for the operable deformation mechanisms in these materials will be discussed. *This work was supported by the U.S. Department of Energy, BES-Materials Science, under Contract W-31-109-Eng-38, the Alcoa Corporation, and by AFOSR Grant # FY9620-92-J.
9:30 am
INFLUENCE OF PROCESSING ON INTERNAL STRUCTURE OF NANOCRYSTALLINE Ni: B.R. Elliott, and J.R. Weertman, Northwestern University, Evanston, IL , Metallurgy Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-0001
Different processing routes can vary the internal structure of nanocrystalline compacts. As a result a single grain size measurement is insufficient to interpret mechanical property results. Blind comparison between samples with different processing histories may be hazardous since their internal structures (grain size distribution, grain boundary character, pore size distribution, adsorbed or chemically bonded impurities) are shown to vary. In particular, annealing samples to grow the grain size for producing Hall-Petch plots is shown to drastically change the pore size distribution and density in powder compacted samples that are not outgasssed prior to compaction. Improvements in processing, particularly compaction procedure, are illustrated by microscopy, XRD, SANS, PGAA, FNAA, archimedes density, and indentation tests. It is shown that with care and knowledge of the process inert gas condensed and compacted samples can be produced with few extrinsic defects.
9:50 am
MECHANICAL PROPERTIES OF NANOCRYSTALLINE Ni: B.R. Elliott, J.R. Weertman, Northwestern University, Evanston, IL
The influence of improved processing on the internal structure of n-Ni has lead to improved mechanical properties. Correlation between the internal structure (including grain size, pore size distribution, and impurities) and results of a variety of mechanical properties measurements will be presented including hardness, tensile and compression tests. Some comparison will also be made between samples produced by traditional inert gas condensation (IGC) and the newer jet blown arc IGC. (JBA-IGC). Possible deformation mechanisms will be discussed in light of the structure and property measurements.
10:10 am
A CRITICAL ASSESSMENT OF THE WILLIAMSON-HALL METHOD FOR THE DETERMINATION OF RESIDUAL STRESS IN NANOCRYSTALLINE STRUCTURES: F.S. Miller, D.C. Van Aken, Metallurgical Engineering, E.W. Bohannan, J.A. Switzer, Chemistry, The University of Missouri-Rolla, Rolla, MO 65409
An important aspect of the processing<>microstructure<>property relationships is the characterization of nanocrystalline structures by x-ray diffraction. The Williamson-Hall analysis is often used to deconvolute the line broadening effects of grain size and residual stress. In this study, Cu/Cu2O nanocrystalline films were produced by electro deposition. This technique produces a composite structure consisting of pure Cu and Cu2O grains each with diameters in the range of 10 to 20 nm. Electro deposited films were characterized by x-ray diffraction to determine both grain size and residual stress. The Williamson-Hall analysis was tested by direct measurement of the grain size by TEM and by using thermal treatments to vary the state of residual stress in the films.
10:30 am BREAK
10:45 am
MECHANICAL PROPERTIES OF Cu/Ag MULTI-LAYER COMPOSITES: Qing Zhai, Augusto Morrone, Fereshted Ebrahimi, Materials Science & Engineering, University of Florida, Gainesville, FL 32611
When materials microstructure reaches nanometer scale, their properties often appear to be unusual, which cast much consideration these days. Specifically, the extraordinarily high strength has been the subject of many recent investigations. The nanomaterials discussed in this paper is a Cu/Ag multi-layered composite, which is produced by electrodeposition in a single-bath cyanide solution. In this paper the effects of copper layer thickness and heat treatment on interfacial structure and mechanical properties of Cu/Ag multi-layered composites are presented. Tensile testing was used to investigate the mechanical properties of the samples. SEM, X-ray diffraction and TEM were used to analyze the relation between the mechanical properties and microstructure of these composites.
11:05 am
STABILITY OF NANOCRYSTALLINE ALLOYED AND MULTILAYER PVD NITRIDE FILMS: R. A. Andrievski, Institute for New Chemical Problems, Russian Academy of Sciences, Chernogolovka, Moscow Region, 14232 Russia
The alloyed and multilayer films of TiN, ZrN, NbN, and CrN with nanocrystalline structure prepared by arc deposition were investigated by XRD, electron microscopy and microhardness measurements. A general tendency of the microhardness to increase with decreasing layer thickness was found in TiN-NbN(ZrN) systems. The unmonotonous change has been revealed in TiN-CrN one. The influence of spinodal decomposition, recrystallization, and heterodiffusion on the films' properties is also demonstrated and discussed in detail. R.A.Andrievski, 1 A.Anisimova, V.P.Anisimov et al, Thin Solid Films 261(1995) 83.
Session Chairperson: M.A. Self, Mechanical Engineering Dept., Tuskegee University, Tuskegee, AL 36088
8:30 am
DOUBLE CANTILEVER BEAM TEST APPLIED TO MODE I COMPOSITE DELAMINATON: A COMPARISON OF ANALYSIS METHODS FOR FIBER BRIDGING MATERIALS: W. Richards Thissell, Anna K. Zurek, Los Alamos National Laboratory (LANL), MST-5, G755, Los Alamos, NM 87545; Frank Addessio, Todd O. Williams, T-3, B-216, Los Alamos, NM 87545
The double cantilever beam (DCB) test is widely used to characterize the mode I delamination and bridging behavior of laminated continuous fiber composite materials. Many composite systems exhibit significant large scale fiber bridging that is not included in the derivation of the analysis methods. The bridging contribution to fracture energy is statistical in nature. A comparison is made of several analysis methods for applicability to systems exhibiting significant fiber bridging. A general DCB analysis method is described that takes into account loading pin effects, material orthotropy, crack root inelasticity, and large scale deformation behind the crack faces. Some material system specific characteristics that lead to enhanced fiber bridging are described.
8:50 am
HYGRO-MECHANICAL BEHAVIOR OF A CLASS OF SWELLING-TYPE THREE-DIMENSIONALLY BRAIDED COMPOSITES: Surya R. Kalidindi, Abdel Abusaifeh, Materials Engineering Department Drexel University, Philadelphia, PA 19104
A new class of swelling-type composite materials using three-dimensionally braided graphite or Kevlar fibers have been designed and processed for potential applications in bone implants. These composites derive their swelling from the hydrophillic nature of the matrix material used in their production. A combined experimental and modeling study was undertaken to study the hygro-mechanical behavior of this class of materials. The properties of interest included the swelling strains, elastic properties, yield strengths, and impact strengths. Note that these properties for the braided composites are highly anisotropic. Furthermore, the mechanical properties are strongly affected by the amount of absorbed water. Cylindrical samples of braided composites were produced with varying fiber volume fractions, braid angles, fiber type (graphite and Kevlar), matrix cross-linking (to control the degree of swelling in the composite), and fiber architecture (uniaxial, rectangular braided, and circular braided). Swelling strains at saturation were measured in these samples. Simple compression tests were performed on these samples in at least two principal material directions in both dry and saturated conditions. Elastic moduli and yield strengths were extracted from these tests. Cylindrical samples of the matrix material (without fibers) were also produced and utilized to fully characterize the hygro-mechanical behavior of the matrix material. Constitutive models have been proposed to predict the various hygro-mechanical properties of the 3-D braided composites in both dry and saturated states as a function of the fiber and matrix properties, fiber volume fraction, and fiber orientations. A weighted average of the currently employed isostrain and isostress models in literature for this class of materials was found to consistently yield better predictions for the anisotropic elastic moduli, when compared to the predictions of either of these models. The weighting factor was found to be dependent primarily on the fiber and matrix materials (i.e. independent of the type of loading, fiber volume fraction, and fiber orientation) and has been interpreted as an interaction parameter between the various fiber and matrix systems. These models were then extended to predict the swelling behavior and yield strengths of the 3-D braided composites. The accuracies of the proposed models were evaluated by comparisons against experimental measurements described above as well as the predictions from a finite element simulation of the response of a representative unit-cell of the braided composite. These comparisons revealed that the proposed models are reasonably accurate in their predictions.
9:10 am
RF MAGNETRON SPUTTERING OF MoSi2 + X SiC COMPOSITE TO FIIMS: S. Gonodaryan1, J.J. Moore1, T.R. Ohno2, 1Advanced Coatings and Surface Engineering Laboratory, Dept. of Met. and Materials Eng., Colorado School of Mines; 2 Dept. of Physics, Colorado School of Mines, Golden, CO 80401-1887
A critical component of a prototype coating system being developed to protect molybdenum against high temperature oxidation (i.e. at 1600°C for 500 hours) is a functionally graded layer based on MoSi2 + x SiC (where x is the variable mole fraction of SiC in the film). Different approaches for synthesizing composite films include sputtering from elemental or compound targets, reactive sputtering, and direct sputtering of composite targets. This paper will explore the feasibility of synthesizing composite films by RF magnetron sputtering of a composite target. Results of compositional depth profiling using Auger Electron Spectroscopy, microstructural evaluation and X-Ray diffraction analyses of the films will be presented. In particular, the diffusion of silicon and carbon in to the substrate will be characterized using a "ball-cratering" technique followed by auger electron spectroscopy (AES). This technique will help to overcome the disadvantages associated with ion-beam sputtering during depth profiling (e.g. different sputter yields for the constituent elements, interface broadening effects, etc.).
FATIGUE OF MONOLITHIC NIOBIUM AND BNIOBIUM-BASED "IN-SITU" COMPOSITES: William A. Zinsser, Jr. and John J. Lewandowski, Department of Materials Science and Engineering, Case Western University, Cleveland, OH 44106
9:30 am
EFFECT OF COMBINED LOADING ON CRACK-TIP DEFORMATION IN GRAPHITE/EPOXY COMPOSITES: M.A. Seif, C.M. Hargrove, Mechanical Engineering Dept., Tuskegee University, Tuskegee, AL 36088
An experimental investigation of the crack displacement and failure modes of graphite/epoxy plates [0/±45/90]2s under tensile loading with central cracks at various angles (15°, 30°, 60°, 75°, and 90°) was carried out. A mixed mode state of stresses developed at the center of the crack as a result of the crack orientation. Laser Speckle technique, a high sensitive noncontact technique, was employed to measure Crack Opening Displacement (COD) and Crack Shearing Displacement (CSD) of the crack emanating from the normal and tangential stresses at the crack center. Damage zones of the material at different crack orientation were examined and evaluated. The critical stress intensity factors for mode I and mode II were obtained from COD and CSD at failure. Detail studies were performed to investigate the behavior of the material during loading application and the effect of the angles on the stress distribution. The data obtained were compared with the Linear Elastic Fracture Mechanics (LEFM) solutions. The comparisons suggested a correlation within ±8 percent deviation. It was concluded from this investigation that the theoretical analysis could be applied to obtain the fracture properties of graphite/epoxy composites.
9:50 am
INCREASING THE OFF-AXIS AND MONOLITHIC STRENGTHS IN CONTINUOUS FIBER REINFORCED ALUMINUM MATRIX COMPOSITES: Colin McCullough, Paul R. Nisson*, Steven R. Pittman Bill E. Birkholz, MMC Program, 3M Company, St. Paul, MN 55144-1000; *3M/MMC Production Plant, Middleway, WV 25430
Tremendous progress has been made in the properties of aluminum alloys reinforced with 60-70 vol. % of continuous alumina fibers, with tensile strengths routinely averaging 250 ksi (1.7 GPa) in the longitudinal direction. The choice of matrix and its resulting microstructure is critical in obtaining such strengths and the matrices used at 3M to date are a pure Al and an Al-2%Cu alloy. This leads to design considerations in composite performance (transverse and shear strengths) and in any unreinforced areas. To date, the pure Al and Al-2%Cu matrix composites have transverse strengths of 25 ksi (170 MPa) and 40 ksi (275 MPa) respectively. While these values have applications, higher strengths may be desirable. Also unreinforced areas could benefit greatly from higher yield strengths. Use of traditional higher strength alloys is seriously restricted due to both the reactivity with the fiber and their segregation behavior which dramatically reduces longitudinal strength. How ever a new aluminum alloy matrix composition promises to combine all the desired features of the matrix. Data will be presented showing retention of high longitudinal strengths while also achieving much higher transverse and monolithic strengths. The specifics of this system will be discussed as well as directions for optimization.
10:10 am BREAK
10:20 am
STRUCTURE AND PROPERTIES OF ALUMINUM BASED PARTICULATE COMPOSITES SYNTHESIZED BY MECHANICAL ALLOYING: J.M. Molnar, T.H. Courtney, Department of Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931
Aluminum-based particulate composites have potential application in services requiring high strength combined with low density. We have used mechanical alloying followed by hot isostatic pressing (HIPing) to fabricate a series of Al-Si-C particulate composites. Pure Al or Al-Si eutectic powder was mixed with graphite and SPEX milled for varying times. Consolidation of the mechanically alloyed powders was done by HIPing at 180MPa (26 ksi) which resulted in a fully dense composite. Aluminum carbide (Al4C3) is formed during consolidation. Formation of SiC is a possibility as well. Maximum hardnesses following HIPing correspond to an approximate yield strength of 990 MPa (144 ksi). Properties as they depend upon processing conditions and the resulting microstructure are discussed. This work was supported by the Army Research Office.
10:40 am
THERMOMECHANICAL PROCESSING OF SUPERPLASTIC SICP/6061 ALUMINUM ALLOY COMPOSITE MADE BY A VORTEX METHOD: Tsunemichi Imai1 and Takeo Hikosaka2, 1National Industrial Research Institute of Nagoya, 1 Hirate-cho, Kita-ku, Nagoya 462, Japan; 2Industrial Research Institute, Aichi Prefectural Government, Nishishinwari Hitotsugi, Kariya City, Aichi 448, Japan
Thermomechanical processing to produce the HSRS for the SiC/6061 Al alloy composite fabricated by a vortex method before squeeze casting and extrusion was investigated. The SiC/6061 A1 composites hot-rolled in rolling strain per passes of 0.05~0.3 and at 573K indicate the m value of 0.4~0.6 and the total elongation of 200~300% in the strain rate of 0.08~1.3 s-1 and at 853K. The total elongations of the composite hot-rolled at 523 and 623K decrease to less than 150%. The flow stress of the composite heat treated by T6 after rolling increased and the total elongation decreased as compared with those of the composite without T6 due to reaction between SiC and matrix. The fracture surface of the composite has a partially liquid phase and filaments and it is thought that an interfacial sliding at the liquid phase contributes to the HSRS in addition to grain boundary sliding in the SiC/6061 Al composite fabricated by a vortex method.
11:00 am
COMPATIBILITY OF SEVERAL REINFORCEMENTS WITH Ti-Al AND DEVELOPMENT OF THE COMPOSITES: Chikura Fujiwara, Nagoya Aerospace Systems Works, Mitsubishi Heavy Industries, Ltd., 10, Oye-Cho, Minato-Ku, Nagoya, 455 Japan
Titanium aluminide matrix composites have received considerable attention due to their potential to have high specific strength and stiffness at high temperature. And SiC fibers are considered to be promising candidates for reinforcement of the composites. SiC/TiAl composites, however, are difficult to be fabricated in good state because of severe reactions at the interface being taken place during fabrication process. One of the most effective means to suppress the excessive reaction is to apply the diffusion barrier coating on the surface of SiC fiber. Another solution to fabricate a TiAl matrix composite is to apply the reinforcement which has good compatibility with matrix, TiAl. Several candidates for diffusion barrier coating between SiC fiber and TiAl were evaluated, then W and HfC showed excellent effects on suppress excessive interfacial reaction, while other candidates such as Al2O3, Zr, B2, Ce2O3 were not effective. Based on these results, a desirable interface model of organic polymer derived SiC reinforced TiAl composite is proposed. Other fibers were evaluated as reinforcements of TiAl matrix composites. Then it was found that W, W-Re, Re were good in compatibility with TiAl and consolidated with TiAl in good state. As a result, W-3%Re/TiAl showed 680 Mpa at 1373K.
11:00 am
THE EFFECT OF MATRIX MICROSTRUCTURE ON THE MECHANICAL PROPERTIES OF Ti3Al/TiB PARTICULATE COMPOSITES: Satoshi Emura, Masuo Hagiwara and Yoshikuni Kawabe*, National Research Institute for Metals, 1-2-1 Sengen Tsukuba Ibaraki 305 Japan; *Chiba Institute of Technology, 2-17-1 Tsudanuma Narashmo Chiba 275 Japan
Ceramic particulates reinforced composite is considered to be an effective way for improving the mechanical properties of Ti alloys and Ti-A1 intermetallics. In the present study, Ti-24Al-llNb(at%)/l0wt%TiB in-situ composites were prepared by the blended elemental powder metallurgy method. The tensile and high cycle fatigue properties of the composites were found to be much superior to those of the unreinforced matrix. Modification of the matrix microstructure was performed by annealing the composite at 1573K and air cooling, which resulted in a very fine 2+ microstructure. The mechanical properties, particularly the fatigue property, were further improved by this microstructural modification technique.
11:20 am
A STRUCTURE DESIGN OF CARBON FIBER REINFORCED ALUMINUM MATRIX COMPOSITE: Jiwen Wang ,Geyang Li, Tao Hong, Pengxing Li, Anjing Yang, Dept. of Mat. Sci., Shanghai Jiao Tong University, Shanghai, 200030, China
A process which combines fiber coating and particles hybridizing together has been utilized for the structural optimization of carbon fiber reinforced aluminum matrix composite. SiC coating was derived by Sol-gel method and SiC particle hybridizing was processed in Sol-gel solution simultaneously. Squeeze-cast process was used to get bulk composite materials. SEM analysis of the material showed a well fiber distribution in Al matrix by particles hybridizing. Mechanical properties of the composite were improved especially for the axial strength. HRTEM research indicated the coating to be an effective barrier of the interface reaction. C/Al interfacial reaction was also studied meantime which revealed that pan-based carbon fiber reacted heavily with aluminum matrix. The nucleation and growth of the reactants were discussed.
Room: 332
Session Chairperson: Sung K. Kang, IBM Corp., T.J. Watson Research Center, Room 37-250, P.O. Box 218, Yorktown Heights, NY 10598; Professor Jorma Kivilahti, Helsinki University of Technology, Materials and Manufacturing in Electronics, Vuorimiehentie 2A, Fin-02150 Espoo, Finland
8:30 pm INVITED
FLIP CHIP SOLDER INTERCONNECTIONS--A RELIABILITY PERSPECTIVE: Karl Puttlitz, IBM Microelectronics, B/330-1AX44-173, GFKA, Rt. 52, Hopewell Junction, NY 12533
The solder ball flip chip or so-called C-4 connection was introduced by IBM nearly three decades ago as an alternative to manual wire bonding whose productivity and reliability were not acceptable at the time. A very large data base indicates that flip chips are the most reliable interconnection scheme in the industry since its inception. Moreover, the combination of C-4 mounted die and alumina multilayer ceramic (MLC) substrates provided the highest overall package reliability. This paper will discuss several key technical attributes such the joint controlled collapse feature, self-centering and throughput which is independent of die I/O count. Joint design, process, compositional and metallurgical factors will be discussed in the context of the very significant effect they have on reliability as well. Flip chip technology is flexible, having been successfully utilized with several generations of chip carriers. Important also is the ability to predict the thermal-mechanical (fatigue) behavior of C-4 joints. When attached to ceramic carriers, the failure rate of flip chip joints obey a distance-from-neutral point (DNP) dependence defined by the Coffin-Manson (C-M) relationship. Modifications to the C-M relationship necessary for this application will also be discussed. It will be shown that the technology is sufficiently extendible to satisfy the trends of smaller, lighter, faster, denser, etc. which are expected to continue in the future. New developments such as chip underfill and future trends including DCA and their reliability implications will also be discussed.
8:55 am INVITED
A NEW RELIABILITY ASPECT OF HIGH DENSITY INTERCONNECTIONS: Jorma Kivilahti, Helsinki University of Technology, Materials and Manufacturing in Electronics, Vuorimiehentie 2A, Fin-02150 Espoo, Finland
Increasing importance of portability in telecommunication and consumer electronics is activating the research and development work on reliable, cost-effective fine-pitch interconnections and substrate technology alternatives. However, high density interconnections may produce increasing difficulties, e.g. in paste printing, component alignment and acceptable residual levels. Moreover, increasing microjoint densities are related to decreasing solder joint volumes, and therefore, it is even more likely that the whole solder volume will take part in the reactions, for example, between a solder, Flip Chip (FC) bump and substrate metallisation. Similar consequences of the miniaturization are encountered in the bump-limiting metallurgy; the total volumes (or thicknesses) of the diffusion barriers and adhesion layers and the original filler, alike, can transform into the matrix of intermetallics, which due to their inherent brittleness make the microjoints mechanically too weak to withstand thermal stresses. Accordingly, for confirming adequate reliability of microjoints it is essential to have better understanding and control on metallurgical compatability of dissimilar materials being in contact with each other. In this communication results of metallurgical studies on various FC bump-solder-substrate metallization reactions are presented. As specific examples, the bump-solder-substrate interactions have been studied experimentally with Au- as well as with Ni-bumped test chips, which were reflow-soldered with the eutectic SnPbAg filler at 235°C for various times onto Au/Ni- and Cu-conductors on the FR-4 substrates. The electrical properties, structural integrity and evolution of microstructures (i.e., intermetallics, Pb-rich solution or eutectic structure) of reflow-soldered Flip Chip joints were examined in detail with the conventional tests and materials characterization methods. For studying the metallurgical compatibility and controlling the reaction kinetics between Au, Ni and eutectic SnPb and SnPbAg, the wedge-shaped diffusion couple experiments which more clearly illustrate the effect of solder layer thickness on the volume fraction of the intermetallics in the microjoints, were conducted using the RMA flux as well as a vacuum furnace. The thermodynamics of the AuSnPb, NiSnPb and CuSnPb systems were critically modeled and used for rationalizing the observed bump-solder-substrate reactions in the Flip Chip joints as well as in the diffusion couples. On the basis of metallurgical considerations a new Pb-free solution to this "small-volume-problem" is also addressed.
9:20 am INVITED
EFFECT OF FLUX TYPE AND SURFACE COATING ON THE WETTING FORCE BETWEEN COPPER AND EUTECTIC Pb-Sn SOLDER: Guna Sevaduray, Wayne Lee and Selgon Yee, Department of Materials Engineering, San Jose State University, San Jose, CA
9:45 am INVITED
A STUDY ON THE SOLDER JOINT RELIABILITY OF THE OPTOELECTRONIC PACKAGING WITH FLIP-CHIP BONDING: Jong Tae Moon, G.J. Joo, M K. Song, K.E. Pyun, H.M. Park, Semiconductor Research Division, Electronics and Telecommunications Research Institute, 161 Kajonj-Dong, Yusong-Gu, Taejeon, 305-350, Korea
The optical transmitter and receiver modules were fabricated by applying flip chip bonding process. It was possible that the degree of alignment accuracy controlled below 1 µm by the force of solder self-alignment. To minimize parasitic capacitance and inductance induced from the solder joint, the reflowed solder ball on Si substrate was varied from 100 µm to 5 µm. The Pb-In, Pb-Sn, In-Sn and In-Ag alloys as the bonding materials were deposited above UBM on the Si substrate by using thermal evaporation method. During the reflowing process, the behavior of solder ball formation, and the intermetallic compounds between the UBM and solder composition were inspected with various heating rates and the use of flux. During the flip chip bonding process, the solder joint shape and the gap between Si substrate and optical devices were controlled by means of a various temperature profiles and bonding force. The solder joints reliability of the flip chip bonded optical submodules were evaluated by shear, thermal shock, and thermal cycling test. In the case of the thermal shock test, the range of temperature was from 25°C to the liquid N2. Thermal cycling numbers were 1000 cycles from -40°C to 120°C. These samples were analyzed by optical microscopy, SEM/EDS and TEM.
10:10 am INVITED
RELIABILITY CHALLENGES AND MODELING OF MINIATURIZED SOLDERED ASSEMBLIES: Jean-Paul Clech, EPSI Inc., P.O. Box 1522, Montclair, NJ 07042
Miniaturized electronic packages have emerged that bring about new reliability challenges and, in some cases, have revived the concerns of Leadless Chip Carriers (LCCCs) on organic substrates: 1) most of these packages are leadless; 2) their Coefficient of Thermal Expansion (CTE) is low because of the high silicon contents of shrinking or disappearing packages; 3) the assembled packages may have a low stand-off height (for miniaturization purposes); 4) typical assemblies are very fine-pitch with micro-solder joints having smaller load bearing or crack propagation areas than conventional surface mount assemblies. The above attributes may be detrimental to long term solder joint integrity and suggest that reliability be looked at carefully, more so than with conventional surface mount assemblies. This talk will present thermal stress and reliability models that can help tackle those problems and ensure that assembly reliability is built-in during the early stages of product design. Two examples of engineering models of miniaturized assemblies will be discussed that enable rapid assessment of the impact of package geometry and materials on assembly reliability. The first example is a model of flip-chip assemblies with underfill. The model quantifies the solder joint relief provided by the underfill layer and its effect on assembly stiffness. The mechanics of flip-chip with underfill are unique since they involve an increase in assembly stiffness to provide for solder joint strain relief. The analysis is that of a multilayer structure (board/underfill/die) that deforms under thermal loads and 'external' forces and moments exerted by the solder joints. Predicted shear strains in the underfill layer are in good agreement with moiré measurements. In the limiting case where the shear modulus of the encapsulant is very low, the