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1997 TMS Annual Meeting: Thursday AM Session Abstracts

The following sessions will be held during 1997 TMS Annual Meeting on Thursday morning February 13, at the Orange County Convention Center in Orlando, Florida unless otherwise noted. To view other programming planned for the meeting, go to the Technical Program Contents page. Here, you can choose to review the program in half-day increments or session by session.


Sponsored by: MSD Materials, Synthesis & Processing Committee and Jt. SMD/MSD Composite Materials Committee
Program Organizers: L.L. Shaw, Dept. of Metallurgy and Materials Engineering, University of Connecticut, Storrs, CT 06269; E.J. Lavernia, Dept. of Mechanical and Aerospace Engineering, University of California - Irvine, Irvine, CA 92717; S. Krishnamurthy, UES, Inc., 4401 Dayton-Xenia Rd., Dayton, OH 45432-1894; E.S. Chen, U.S. Army Research Office, 4300 S. Miami Blvd., Research Triangle Park, NC 27709

Room: 340B

Session Chairpersons: Prof. Leon L. Shaw, Dept. of Metallurgy and Materials Engineering, University of Connecticut, Storrs, CT 06269; Dr. David E. Alman, U.S. Department of Energy, Albany Research Center, Albany, Oregon 97321

8:30 am INVITED

COMMERCIAL PROCESSING OF METAL MATRIX COMPOSITES: W.C. Harrigan, Jr., Alyn Corporation, P.O. Box 16249, Irvine, CA 92623

Discontinuously reinforced metal matrix composites are a class of materials that exhibit a blending of properties of the reinforcement and the matrix. The reinforcement can be ultrahigh strength whiskers, short or chopped fibers or particles. Each of the reinforcements have property or cost attributes which dictates use in a given situation. Commercial producers have concentrated on composites with particles because of cost issues. These composites have been made by a number of manufacturing techniques. These include powder metallurgy, casting and spray deposition. The technique that has consistently produced high property composites has been powder metallurgy. Recent work in this area has been on refining techniques that offer lower cost manufacturing. Scale-up of facilities to produce vacuum hot pressed composite billets has been completed with the help of DOD funds through a Defense Procurement Act Title 3 program. Several companies have been working with a CIP-Sinter process to produce lower cost billet stock. This talk will review the recent cost reduction programs and the implications of these programs on the commercialization of these composites.

9:00 am


Reactive Hot Compaction of Ni and Al powders in which one or both of the powders were preoxidized was carried out to fabricate functionally gradient composite (FGC) of NiAl with in-situ Al2O3 reinforcement. The FGC consisted of five layers with a variation of alumina content from less than 4% on one side to about 52% on the other. The gradient in the composition was obtained by stacking different powder mixtures of desired compositions. The alumina formed a continuous network around the NiAl during the compaction process. The effects of powder oxidation and heating rate on the formation of NiAl, Al3Ni and Al3Ni2 will be discussed on the basis of the DTA and microstructural studies.

9:25 am

POWDER METAL-MATRIX COMPOSITES: SELECTION AND PROCESSING: M.J. Tan and Zhang Xi, School of Mech. & Prod. Eng., Nanyang Technological University, Nanyang Avenue, Singapore 2263

There has been growing interest in the last decade in the development of metal-matrix composites (MMCs) for the aerospace industries because of their attractive physical and mechanical properties, and enhanced elevated temperature capabilities. However, some of the fabrication techniques (e.g. using powder metallurgy) for this new class of MMCs are hampered by (i) the poor distribution of the reinforcements, and (ii) the limited room temperature ductility of the composites and hence formability. This presentation reports work done to address the above two problems by (i) an analysis based on size difference of matrix and reinforcement particles, taking into account the processing parameters, and (ii) introducing an innovative way of extruding brittle composites to increase its formability. By mainly considering the size difference effect of matrix powder and reinforcement particle, a critical value of reinforcement size is proposed to predict whether a uniform distribution of reinforcement is possible in powder metallurgy of particulate reinforced metal matrix composites. A uniform distribution of reinforcement could be expected only when the reinforcement size dT is not less than a critical value dC which is a function of reinforcement size dr and volume fraction Vf and reduction ratio of secondary processing, R. In extrusion, a Front Pad Extrusion Method was used to avoid fir-tree cracking on the surfaces of extrudates, especially the brittle metal composites. By this method, the MMCs were successfully extruded without any surface cracking, and all the extrudates were found to be covered by a thin layer of the pad material. This was illustrated using a schematic flow pattern of the extrudate and pad material in the dead metal zone during extrusion. Furthermore, decreased pressure requirements were necessary for extrusions using the front pad extrusion method.

9:50 am

CHARACTERIZATION OF Cu/Cu2O COMPOSITES PRODUCED BY ELECTROCHEMICAL DEPOSITION: F.S. Miller, D.C. Van Aken, Dept. of Metallurgical Engineering, E.W. Bohannan and J.A. Switzer, Dept. of Chemistry, The University of Missouri, Rolla, MO 65409

Nanocrystalline composites of copper metal and cuprous oxide were produced at room temperature by electrodeposition from an alkaline copper lactate solution. The phase composition can be continuously changed by controlling the cathode current density. At current densities below 0.1 mA/cm2 nearly pure cuprous oxide is produced and at 2.5 mA/cm2 nearly pure copper is produced. At intermediate current densities composite structures are formed. These thin films show unique optical properties that are related to the 10 to 20 nm grain diameter of Cu2O produced by electrodeposition. During deposition of the composite material the electrode potential oscillates spontaneously at fixed current density. Microstructural information obtained by TEM indicates the formation of a metastable compound that may be related to the electrode potential oscillations. This work has been funded in part by the National Science Foundation under contract DMR-92-02872.

10:15 am BREAK

10:25 am

SPATIALLY VARIED INTERFACES AS A PROBE OF INTERFACE FAILURE MECHANISMS IN Ti-MATRIX COMPOSITES: Benji Maruyama, Wright Laboratory/NIST, 2230 10th ST STE 1, WPAFB, OH 45433; Douglas B. Gundel, Systran Co., Inc., 4126 Linden Ave., Dayton, OH 45432; Sunil Warrier, Universal Energy Systems, 4401 Dayton-Xenia Rd., Dayton, OH 45432

Spatially Varied Interfaces is a design concept for composite synthesis whereby the interface mechanical response is tailored to the composite needs by varying the interface properties in patterns of weak and strong areas. In the SiCf/Ti-alloy system, random patterns have been fabricated, along with bands, longitudinal stripes and helices. To be presented are results of transverse tensile and longitudinal fatigue crack growth experiments where selected regions of the interface are systematically strengthened or weakened, and the perturbation of the failure process is measured to gain a better understanding of the stress states and interface failure mechanisms. This work was conducted in the Metals & Ceramics Division of the Materials Directorate at Wright Laboratory.

10:50 am

THE PROPERTIES AND MICROSTRUCTURE OF Al-BASED COMPOSITES REINFORCED WITH CERAMIC PARTICLES: M. Samgorinski, S. Grenier, A. Cavasin, T. Brzezinski, G. Kim, P.G. Tsantrizos, PERMA, 1744 William, Montreal, Quebec, Canada H3J 1R4

Al-based composite materials which were produced by Powder Metallurgy (PM) and Vacuum Plasma Spraying (VPS) are presented in this article. The objective was to produce materials with low coefficients of thermal expansion (CTE), tailored to approach that of steel (13x10-6 K-1), and to improve the mechanical properties of the matrix. Composite materials based on Al are used in different fields where weight and thermal stability are key requirements, such as aerospace components, electronic packaging, high precision instrumentation, and automobile engine components. The nature, size and the relative quantities of the different reinforcing phases were considered in calculations involving the optimization of the main characteristics of the composites. Fine dispersed powders (5-20 µm) of Si3N4, AlN, TiB2, Al2O3, 2Al2O3·2SiO2, B4C and SiC were used as the strengthening phases, while pure Al, 6061 and Al-Si alloy were used as the matrix. The dimensional and relaxation stability were investigated for several composites. The influence of plastic deformation and heat treatment on the structure and properties of VPS deposited composites were also investigated. It was found that a combination of plastic deformation and heat treatment (annealing or quenching with aging) increased the mechanical properties, on average, by a factor of 1.5 to 2.

11:15 am

EFFECT OF MICROSTRUCTURAL ARRANGEMENT ON THE MECHANICAL PROPERTIES OF Ni/a-Al2O3 METAL-CERAMIC COMPOSITES: E.D. Rodeghiero, E.P. Giannelis, Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853-1501

The degree to which a ductile metallic phase can be used to toughen brittle ceramic materials is highly dependent on the microstructural dispersion of the metallic constituent, the metal's aspect ratio and characteristic size, and the amount of constraint imposed on the metal by the ceramic matrix. This talk will focus on the effect of these parameters on the mechanical properties, and in particular the fracture toughness, of Ni/a-Al2O3 composites prepared through both in-situ and conventional approaches. The composites discussed will vary from particulate toughened cermets prepared from chemical and/or powder approaches to complex, anisotropic materials containing Ni foils or fibers. Through evaluation of the experimental evidence and theoretical models, the optimum microstructural arrangement of the Ni phase in the a-Al2O3 matrix will be presented.

11:40 am

FRACTURE TOUGHNESS OF SILICON CARBIDE PARTICULATE REINFORCED ALUMINUM ALLOY COMPOSITES: A.B. Pandey, Materials Directorate Wright Laboratory, WL/MLLM, Wright-Patterson AFB, OH 45433 and Systran Corporation, 4126 Linden Avenue, Dayton, OH 45432; B.S. Majumdar, UES, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432; D.B. Miracle, Materials Directorate Wright Laboratory, WL/MLLM, Wright-Patterson AFB, OH 45433

This study is part of an overall effort to optimize the strength toughness combination in discontinuously reinforced aluminum (DRA) composites for application in aerospace structures. Two different matrix alloys were considered, namely Al-2009 and Al-7091, to represent intermediate and high strength matrices, respectively, and they were reinforced with SiC particles of 4.9 and 10.4 mm. The powders were consolidated directly via blind-die extrusion, thus reducing processing time significantly from conventional vacuum hot pressing techniques. Fracture toughness tests were performed with precracked bend bars, and the J-resistance curves were determined. Damage modes were evaluated in both tensile and fracture toughness samples, in an attempt to understand the factors that may provide intrinsic toughness improvement without significant loss of strength. The mechanical properties and damage modes were compared with control samples of unreinforced materials fabricated using an identical processing route as the composites. Data from these control materials provided an added insight that has often lacked in past frac ture toughness studies. This work was performed at Materials Directorate Wright Laboratory, Wright-Patterson AFB, OH.


Sponsored by: EPD Extraction and Processing Division
Program Organizer: Annette Revet, IMC Kalium Belle Plaine, P.O. Box 7500, Regina, SK S4P

Room: 231C

Session Chairs: Annette Revet, IMC Kalium Belle Plaine, P.O. Box 7500, Regina, SK S4P; John Hryn, Argonne National Labs, 9700 South Cass Avenue, Argonne, IL 60439-4815

8:30 am

ANALYTICAL CHEMISTRY OF ALUMINUM SALT CAKE: Donald G. Graczyk, Alice M. Essling, Edmund A. Huff, Florence P. Smith and Christine T. Snyder, Argonne Chemistry Laboratory/Chemical Technology Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439

8:50 am

QUANTIFYING THE AMOUNT OF OXIDES IN ALUMINUM: D.L. Stewart Jr., K.M. Tomaswick, Alcoa Technical Center, Alcoa Center, PA 15065

9:10 am

EXPERIMENTAL STUDIES OF PHASE RELATIONS IN THE SYSTEM H20-NaCl-KCl-MgCl2, WITH APPLICATION TO A NEW PROCESS FOR TREATING SALT CAKE: Robert J. Bodnar, Maxim O. Vityk, Fluids Research Laboratory, Department of Geological Sciences, Virginia Polytechnic Institute & State University, Blacksburg, VA 24061; John N. Hryn, Argonne National Laboratory, Energy Systems Division, 9700 S. Cass Avenue, Argonne, IL 60439; John A. Mavrogenes, Research School of Earth Sciences, The Australian National University, Canberra, Australia 0200

9:30 am

CONCENTRATION AND PRECIPITATION OF NaCl AND KCl FROM SALT CAKE LEACH SOLUTIONS BY ELECTRODIALYSIS: Kandipati Sreenivasarao, Filippos Patsiogiannis, John N. Hryn and Edward J. Daniels, Energy Systems Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois 60439

9:50 am BREAK

10:00 am

THE EVOLUTION OF ROTARY MELTING AT RECYCLAGE D'ALUMINUM QUEBEC INC.'S: DIVISION OF PHILIP ENVIRONMENTAL INC.: TWO ALUMINUM DROSS PROCESSING PLANTS: Michael W. Paget, Recyclage D'Aluminum Quebec Inc., 128 Blvd. Comeau, Baie Comeau, QB G4Z 2L6; James F. Heffron, Air Products and Chemicals, Inc., R & D #2, 7201 Hamilton Blvd., Allentown, PA 18195; Pierre Richer, Air Products and Chemicals, Inc., 2090 Steeles Avenue, Brampton, ON L6T 1A7

10:20 am

COMPLETE ALUMINUM DROSS PROCESSING TECHNOLOGY: Peter G. Schirk, CHMM, Director of Engineering & Special Projects, ALTEK International, Inc., 585 Exton Commons, Exton, PA 19341

10:40 am


11:00 am

SALT-FREE DROSS PROCESSING WITH ALUREC®--TWO YEARS EXPERIENCE: Henrik Gripenberg, M. Sc., AGA AB, S-181 81 Lidingö, Sweden; Michael Müllerthann, Dipl.-Ing., Hoogovens Aluminium Hüttenwerk GmbH, Schleusenstrasse, D-46562 Voerde, Germany


Sponsored by: LMD Aluminum Committee
Program Organizer: Harald A. Øye, Institute of Inorganic Chemistry, Norwegian University of Science and Technology, N-7034 Trondheim, Norway

Room: 230A

Session Chairperson: Halvor Kvande, Hydro Aluminium, Hydro Aluminium a.s, P.O. Box 80, 1321 Stabekk, Norway

8:30 am

APPLICATIONS OF NEW STABILITY CRITERIA TO INDUSTRIAL CELL DESIGN: R.I. Lindsay, P.A. Davidson, Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, UK

Previous models of the behaviour of interfacial waves in aluminium reduction cells lead to distinct descriptions of the physical mechanisms involved and different stability criteria. We consider the implications of these criteria for cell design. A new wave equation has recently been developed from shallow-water theory, in which the Lorentz force is expressed explicitly in terms of the fluid motion. The simplicity of this new equation leads to a general energy criterion to establish which types of motion may be unstable. By expressing the new equation in matrix form, we obtain some unexpected results. We discuss the implications of some of these results for cell design. Finally, we introduce a new sufficient condition for the stability of standing waves in a finite domain, which does not require solving the governing equations. The use of Gershgorin's theorem allows us to place a lower bound on the critical value of the background magnetic field at which an instability first appears.

8:55 am

MAGNETOHYDRODYNAMIC EFFECT OF ANODE SET PATTERN ON CELL PERFORMANCE: M. Segatz, Ch. Droste, D. Vogelsang, VAW Aluminium-Technologie, G.-v.-Boeselager-Str. 25, D-53117 Bonn, Germany

Numerical simulation of coupled bath/metal magnetohydrodynamics (MIID) and MIID stability analysis allows the optimization of anode set pattern with respect to minimal cell disturbance. The contribution of anode gas induced forces and impact on the flow field are discussed. During a complete anode set cycle the anode current distribution changes significantly due to varying anode resistances, frozen bath and different metal pad heights. Typically the largest disturbance to cell stability occurs during a short time span after the anode change. With steady-state MIID simulations immediately before and after each anode change - in sequence of the underlying set pattern - the relevant cell current and ACD distribution are determined. The impact of these parameters on cell stability is predicted with a linear MIID stability analysis for a complete anode change cycle.

9:20 am

A NEW MODEL OF INTERFACIAL WAVES IN ALUMINIUM REDUCTION CELLS: P.A. Davidson, R.I. Lindsay, Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, U.K.

We develop a new wave equation for the liquid interface in aluminium reduction cells. It differs from previous models in that the Lorentz force is expressed explicitly in terms of the fluid motion. The equation is valid both for open domains and confined domains of arbitrary shape, and its simplicity makes the instability mechanism explicit. Our new equation predicts that both travelling waves and standing waves may become unstable by the same mecha nism and that the travelling wave instabilities are distinct to those uncovered in previous investigations. We also derive a simple yet general energy criterion which shows which types of motion may extract energy from the background magnetic field. This indicates that a rotating tilted interface is particularly prone to instability, and indeed such motions are often seen in practice.

9:45 am

SIMULATION OF THE DYNAMIC RESPONSE OF ALUMINIUM REDUCTION CELLS: Imad Tabsh, COMPUSIM Inc., 1003D 55 Avenue N.E., Calgary, Alberta, Canada T2E 6W1; Marc Dupuis, GéniSim, 3111 Alger, Jonquière. Québec, Canada G7S 2M9

A comprehensive program (ARC/Dynamic) was developed to simulate the dynamic behavior of aluminium reduction cells during operation. The program uses the mass and energy balance equations to determine the transient evolution of more than 60 process variables. In addition, it simulates various operational and control policies in use during cell operation. This paper describes the use of ARC/Dynamic to study the sensitivity of the cell response to variations in the input parameters. It also looks at the cell performance under various amperage curtailment conditions such as sudden shutdown of the line or scheduled reduction in line amperage. A detailed description of the amperage fluctuation model implemented in the program is presented.

10:10 am BREAK

10:30 am

MATHEMATICAL MODELLING OF CURRENT DISTRIBUTION AND ANODE SHAPE IN PREBAKE ALUMINIUM CELLS: J. Zoric, I. Rousar, Department of Inorganic Technology, Institute of Chemical Technology, 16628 Prague 6, Czech Republic; J. Thonstad, Department of Electrochemistry, Norwegian University of Science and Technology, N-7034 Trondheim, Norway

Two approaches were used to determine the current distribution in aluminium cells with prebaked anodes, i.e., primary and secondary current distribution, the latter giving far more realistic results. Current densities obtained for secondary current distribution were used to model the changes in anode shape from the time when a new anode has been set until it achieves the typical rounded off steady state profile. Mathematical modelling of the anode consumption using current densities obtained by the solution of the Laplace equation in 2D space, showed that a constant shape was reached after 6 - 8.6 days, depending on the width of the gap to a neighbouring anode or to the sidewall/sideledge. The calculated steady state shapes were similar to the shapes of anodes taken out of a cell. The current density decreases up along the side of the anode from the nominal value at the underside (0.75 A cm-2) to a minimum near the surface of the electrolyte (0.08 - 0.28 A cm-2), depending on the geometry. The percentage of the current which passes through the sides of the anodes is of the order of 15%. The current density on the anode side facing the periferic channel increases with increasing distance to the sideledge, while the exact shape of the ledge makes little difference. The cathodic current density in the periferic channel goes down to 0.07 A cm-2 for a 30 cm wide channel.

10:55 am

MATHEMATICAL MODELLING FOR COKE BED PREHEATING OF ALUMINIUM REDUCTION CELL: Shaher A. Mohammed, R&D Dept., Aluminium Company of Egypt, Nagi-Hammadi, Egypt; Maher M. Abdulwahab, Attia A. Arif, Omar M. Dahab, Power and Energy Dept., Minya University, Egypt

Many methods are available to preheat and bake-out the cathodes of aluminium reduction cells but only few of them are widely used. Resistor coke bed with shunt rheostat is one of the most common methods to preheat the cell. To get optimum design parameters for resistance elements and preheating method, a finite element model was built to simulate the process. The effect of starting current, coke bed thickness, rate of increase of current and finally total time needed for preheating, were studied. The obtained results indicated that the practical technique used has to be subjected to some modifications in order to reach satisfactory conditions.

11:20 am

HIERARCHICAL INTELLIGENT CONTROL SYSTEM FOR ALUMINUM REDUCTION CELLS: Jie Li, Yexiang Liu, Jin Xiao, Department of Metallurgy, Central South University of Technology, Changsha, Hunan 410083, China; Feng Wang, Shengwen Shi, Department of Technology, Liancheng Aluminum Plant, Lanzhou, Gansu 730335, China

A hierarchical intelligent control system for aluminium reduction cells has been developed. There are two intelligent levels in the system. The higher level built on the principle of neural network expert system, aims at analyzing medium and long-term change trends of the state of the process, calculating settings for the lower level, interacting with operators and offering operation proposals. The lower level, composed of several subsystems which are set up on the principle of fuzzy control and expert control, is used to realize short-term analyses and real-time control of the process. As the system has a hierarchical and modular structure, its design, realization and testing are simplified. Test-run results verified that, combined together in one system, the controllers have good properties of robustness and adaptability with respect to changes of operating conditions and severe disturbances.

11:45 am

DETERMINATION OF METAL CURVATURE AND IMPROVED ANODE CONSUMPTION: Jon H. Stefansson, Electrolysis Department, Icelandic Aluminium Co. Ltd., IS-222 Hafnarfjördur, Iceland; René von Kaenel, Jacques Antille, Technology Center Chippis, Alusuisse Technology & Management Ltd., CH-3965 Chippis, Switzerland

The Alusuisse ISAL smelter in Iceland does not have an in house anode plant. This makes it increasingly important to operate with small and evenly thick anode butts. Since the insertion height is calculated according to the carbon burning rate, it is important to know the difference in metal level according to the position in the pots. Two methods have been used to determine the metal upheaval. The first consists in measuring the height of many enough anode butts since the lower anode level adjusts to the metal level with time. The second method is based on mathematical modelling. Measured values have been compared to calculated values with good agreement. Insertion of the anodes according to metal level has resulted in improved gross anode consumption due to more even butt thickness and stable operation.


Sponsored by: LMD Aluminum Committee
Program Organizers: Dr. Subodh K. Das, ARCO Aluminum, Inc., P.O. Box 32860, Louisville, KY 40232; Dr. George J. Kipouros, Technical University of Nova Scotia, Department of Mining and Metallurgical Engineering, P.O. Box 1000, Halifax, Nova Scotia, Canada B3J2X4

Room: 340A

Session Chairperson: Carl Seidler, Technical Service Manager, ARCO Aluminum, Inc., P.O. Box 32860, Louisville, KY 40232

8:30 am

A NEW CASTING DEFECT HEALING TECHNOLOGY: Edwin S. Hodge, Thomas W. Reddoch, Format Industries, Inc., Knoxville, TN; Srinath Viswanathan, Oak Ridge National Laboratory, Oak Ridge, TN

A new technology is presented for healing of defects in 356 and 201 Aluminum alloys that provides economic upgrading of these cast alloys. This technology uses pneumatic isostatic forging (PIF) to provide a unique capability to produce high quality Aluminum alloy products with enhanced mechanical properties that are uniform throughout the part thus permitting higher design allowables and increased usage of Aluminum alloy castings. The fundamental mechanism underlying PIF is a single mode plastic deformation process that uses isostatic application of pressures for 10 to 30 seconds at temperature. The process can be integrated in-line with other production operations, i.e., using the latent heat from the previous casting step. The results of applying the PIF process indicate lower cost and significant improvement in me chanical properties that rival and often exceed corresponding properties of other technologies like hot isostatic pressing (HIP) and related processes. This process offers many advantages that will be described in the paper in addition to presenting case histories of property enhancement by PIF, and the mechanism for responsible property enhancement.

9:00 am

TENSILE PROPERTIES OF 319 ALLOY CASTINGS: S. Viswanathan, W. Ren, Metals and Ceramics Division, Oak Ridge National Labs, Oak Ridge, TN 378316083, G.B. Ulrich, Y12 Plant, Oak Ridge, TN 378318096; M.E. Hoover, General Motors Powertrain Division, Saginaw, MI 486055073

Plate castings of 319 alloy were made over a wide range of thermal conditions by casting in sand molds, molds with end chills, and molds with top, bottom, and end chills. The plates were sectioned along their width into coupons. Odd-numbered coupons were machined into tensile specimens and tested in the as-cast condition. Even-numbered coupons were heat treated to a T6 condition, and then machined and tested. Yield strength, Ultimate tensile strength, and ductility measured by percent elongation were plotted with respect to distance from the chill end of the plate as well as related to porosity and other microstructural features such as dendrite cell spacing. The data shows that tensile elongation is a strong function of porosity. In particular, the data indicates a threshold value of porosity below which a sharp increase in ductility is observed. These effects as well as the effect of heat treatment and dendrite arm spacing are discussed. *Research sponsored by the U.S. Department of Energy Defense Programs, Assistant Secretary, Technology Management Group, Technology Transfer Initiative under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corporation.

9:30 am

RECENT DEVELOPMENTS IN SQUEEZE CASTING OF MAGNESIUM ALLOYS AND THEIR COMPOSITES: Henry Hu, Alan Luo, Institute of Magnesium Technology (ITM, Inc., SteFoy, Quebec, Canada GIP 4N7

Squeeze casting, also known as liquid metal forging, extrusion casting and pressure crystallization, is a process in which molten metal solidifies in a die under an applied high pressure. The concept of squeeze casting was invented in Russia over 100 years ago. Later the process has been exploited in North America, Japan and Europe to produce various automotive components. With the rapid expansion of magnesium applications in the automotive industry, the development of squeeze casting technology for magnesium alloys and their composites has been motivated by incentive to produce high quality magnesium-based components. The present paper reviews recent progress in squeeze casting of magnesium alloys and magnesium-based composites. The effects of process variables on the cast structure and properties of magnesium alloys and magnesium-based composites are discussed. The significant advantages of squeeze cast magnesium alloys and magnesium-based composites are highlighted. The ongoing research work at ITM is presented.

10:00 am

CAST ALUMINUMFLY ASH COMPOSITES FOR ULTRALIGHT AUTOMOTIVE APPLICATION: P.K. Rohatgi, R.Q. GUO, Department of Materials, University of Wisconsin, Milwaukee, WI 53211

Coal fly ash, an industrial waste by-product, is produced during combustion of coal by thermal power plants. Additions of solid or hollow particles of fly ash into aluminum melt by common foundry techniques reduce the cost and density of aluminum castings while increasing their performance. Fly ash particles are very light materials with density around 2.1 to 2.3 g/cm3 for solid fly ash particles and a density as low as 0.4 to 0.8 g/cm3 for the cenospheres of fly ash which are hollow. In this paper, manufacture and some properties of aluminum-fly ash composites (Ashalloy) have been studied. Aluminum alloy-fly ash (Ashalloy) represents a candidate ultralight material for automotive application. Incorporation of cenosphere fly ash particles, which are hollow with very low density, significantly reduces the density of material. Some of the characteristics of fly ash used for making composite have been described. The fly ash particle shape, size, and density have been determined. Mechanical properties of aluminum alloy - fly ash composites made by stir casting show that the composites have similar hardness, elastic modulus as matrix aluminum alloy, and improved wear abrasive resistance compared to the matrix alloy. Several prototype components of aluminum - fly ash composites for automotive applications, small engine and electromechanical machinery have been made and are under trials.

10:30 am BREAK

11:00 am

EFFECT OF SECTION THICKNESS AND GATE VELOCITY ON EVOLVED MICROSTRUCTURE AND MECHANICAL PROPERTIES OF HIGH PRESSURE DIE CAST MAGNESIUM ALLOY AZ91D: Dr. Rodrick Esdaile, Technical Director, Austrailian Trade Commission (Austrade), Gordon L. Dunlop, CRC for Alloy and Solidification Technology (CAST), The University of Queenland, St. Lucia, Qld 4072, Australia, Morris T. Murray, CSIRO Division of Manufacturing Technology, Preston, Vic 3072, Australia

This paper investigates the change that occurs in microstructure and mechanical properties when the section thickness is varied for high pressure die cast Mg alloy AZ9lD. It has been found that yield and ultimate tensile strength increase more than would be expected with decreasing section thickness. This is explained in light of the fine microstructure in the surface layer (skin) that develops during the rapid solidification that occurs in this process. The two stage solidification sequence which leads to the evolution of the unique microstructure in die castings has been supported by evidence from solidification experiments using wedge castings and computer simulation of the shot sleeve. Two different die castings with relatively thick cross sections have been compared in terms of their porosity content and its effect on mechanical properties. Finally, the effects on mechanical properties of thick and thin specimens due to variation of casting parameters such as gate size is also discussed.

11:30 am

DUCTILE PRESSURE DIE CASTING FOR AUTOMOTIVE APPLICATIONS--A Status Report: Hubert Koch, Alois J. Franke, Aluminum Rheinfelden, GmbH, P.O. Box 1140, D79601 Rheinfelden, Germany

After three years of commercial application of low iron pressure die casting alloys for structural parts, this paper reviews industrial scale experience and looks out to further potential in alloy development. Silafront-36TM (AA 365) and Magsimal-59TM both have an iron content below 0.13 wt% ensuring good ductility of the casting while completely avoiding soldering or sticking to the die in manufacturing. This is a breakthrough in pressure die casting where during decades the soldering problem has prevented the application of ductile casting alloys. Silafront-36TM (AA 365) and Magsimal-59TM are used for suspension parts, steering wheels, space frame nodes, motor mounts etc. High pressure die casting and squeeze-casting are the processes applied. Silafront-36TM is an AlSi9Mg-type alloy that can be heat treated and welded. Magsimal-59TM is of the AlMgMnSi-type and specially designed for applications without heat treatment with extraordinary mechanical and dynamic properties. This paper describes the manufacture of the castings, the application and component properties for both alloys.


Sponsored by: LMD Aluminum Committee
Program Organizer: Jean-Claude Thomas, Aluminium Pechiney, Pechiney/Balzac, 92048 Paris la Défense, France

Room: 230C

Session Chairperson: André L. Proulx, Alcan International Limitée, 1955 Boulevard Mellon, C.P. 1250, Jonquière, Québec, Canada G75 4K8

8:30 am

ECA FOR IMPROVED CATHODE PERFORMANCE: Johan A. Johansen, Herman Gran, Elkem Carbon, P.O. Box 8040, Vagsbygd, N-4602 Kristiansand, Norway

ECA (Electrically Calcined Anthracite) is the main raw material for the carbon part of the electrolysis cells. Demand for increased potlife and more efficient cathodes (lower voltage drop) have led to use of more graphite in the carbon materials. Little has been done to improve the main raw material, ECA. The characteristics of ECA can be strongly affected by calcining conditions and selection of raw anthracites. In this study, different ECA qualities were produced in full scale calciners and the effect of improved ECA quality on cathode materials studied. A lab scale test program was established to evaluate the effect on different baked properties. Important properties for improved cathode performance, like sodium resistance, electrical conductivity and mechanical properties, can be effected by use of selected ECA.

8:55 am


The preparation of carbon paste for manufacture of cathodes and graphite electrodes requires the heating-up of the raw materials as well as the following mixing and cooling of the paste. In the last few years, a newly developed plant type has proved successful in practical operation. It consists mainly of an electric resistance heater and a high-performance mixer. The coke fractions are heated up to temperatures between 150-200°C by the resistance heater and fed into the high-performance mixer along with liquid pitch. After completed homogenization of the components, the temperature required for the moulding is achieved with greatest accuracy by addition of water and evaporation cooling. One single machine of this type replaces 8-12 conventional batch mixers. The special merits of this process are the minimal maintenance compared to conventional techniques, the reduced energy consumption, the shortened cycle time and the considerably improved environmental protection. The plant is a closed system; dusts and steams are purified in an exhaust air decontamination plant and partially reused. The plant flexibility makes it possible to prepare carbon paste for both cathodes and graphite electrodes with exactly the same equipment by only simply changing the recipe. As an example, the latest state of the art is presented as well as the most significant operating results by means of a plant which was commissioned in 1995 at a great international manufacturer of carbon and graphite products.

9:20 am

THE OXIDATION OF HETEROGENEOUS CARBON ELECTRODES AND FURNACE LINERS--PART 1: X-RAY DIFFRACTION APPLICATIONS: F. Hiltmann, SGL Carbon AG, Frankfurt-Griesheim, Germany; B.J. James, B.J. Welch, M.M. Hyland, Department of Chemical and Materials Engineering, The University of Auckland, New Zealand

The primary purpose of this study is to fully understand the role played by oxidation reactions in the degradation of carbon cathodes and furnace liners such as those used in aluminium smelting cells. While we have developed a sensitive technique for detecting oxidation at low rates, full mechanistic understanding is dependent on supplementary characterisation of the residual unreacted materials. This is complicated by the heterogeneous nature of the electrode materials. This paper presents details of the application of X-ray diffraction for studying the various component materials of these composites, namely pitch, graphite and anthracite. Also presented in this paper is supporting compositional analysis of the heterogeneous carbon samples together with element maps to indicate the distribution of typical trace elements.

9:45 am

THE OXIDATION OF HETEROGENEOUS CARBON ELECTRODES AND FURNACE LINERS--PART II: OVERALL REACTIVITY CORRELATIONS: B.J. James, B.J. Welch, M.M. Hyland, Department of Chemical and Materials Engineering, the University of Auckland, New Zealand; F. Hiltmann, SGL Carbon AG, Frankfurt-Griesheim, Germany

Using the method described previously (Light Metals, 1996) the oxidation reactions of carbon cathode materials have been characterised for onset temperature and rate of oxidation at low (less than 550°C) temperatures. Combining the results of composition and structural analysis described in Part I, correlations have been made between the inherent structure of the component materials and their onset temperature and relative rates of oxidation thus explaining the preferential nature observed in the oxidation of composite samples. Using the results of polarised light microscopy and scanning electron microscopy the relationship between bulk structure of the heterogeneous samples and their oxidation reactions has been examined with important implications for the performance of these materials in service.


Sponsored by: LMD Aluminum Committee
Program Organizer: Wolfgang A. Schneider, VAW aluminium AG, Research and Development, Georg-von-Boeselager-Str.25, D-53117 Bonn, Germany

Room: 230B

Session Chairperson: Robert B.Wagstaff, Wagstaff, N.3910 Flora Rd., Spokane, WA 99216

8:30 am

COMPREHENSIVE EVALUATION OF THREE REFRACTORY MATERIALS FOR HOT-TOP BILLET CASTING SYSTEMS AT GOLDENDALE ALUMINUM COMPANY: J. Martin Ekenes, Consultant, N.3418 Arden Road, Otis Orchards, WA 99027; Larry Bennett, Goldendale Aluminum Company, Craig Johnson, Permatech Inc.

The life of refractory components in billet hot-top casting systems is often the factor limiting mold package life. Evaluation of new materials in commercial casting operations requires careful planning in order to assure integrity in data collection. A full scale test spanning a five month period was conducted at Goldendale Aluminum Company comparing two silica based precision castable refractories and a graphite reinforced calcium-silica board. Comprehensive records facilitated testing a variety of hypotheses. This paper describes plan development, implementation, data collection, analysis, and the conclusion drawn.

8:50 am

CALCIUM CONTAMINATION OF MOLTEN Al-Mg ALLOYS BY CALCIUM CARBONATE POWDER: Dennis D. Yancey, Dept. of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; David H. DeYoung, Aluminum Company of America, Molten Metal Processing Center, Alcoa Technical Center, Alcoa Center, PA 15069

A bench-scale study has been conducted to determine the effects of melt temperature, alloy composition, and powdered calcium carbonate quantity on Ca contamination of molten Al-Mg alloys. Calcium carbonate powder is often used in ingot plants as a "caulking" material in troughs, joints, etc. to prevent molten metal leaks. Results of the study show that: (i) at melt temperatures above 1425°F, calcium carbonate markedly increases the concentration of Ca in molten Al-4.5 wt% Mg alloy; (ii) Mg is required for the reaction of CaCO3 with the aluminum melt to occur; (iii) for a given quantity of calcium carbonate, within the temperature range of 1400-1550°F, increase in melt temperature increases Ca contamination; (iv) for a given temperature of 1450°F or 1550°F and within 0.008-0.36 wt% CaCO3, increase in the quantity of calcium carbonate markedly increases both the rate of Ca contamination and the maximum concentration of Ca obtained in the melt for a 5 hour interaction period. The decomposition of calcium carbonate and the associated Ca contamination of molten Al-Mg alloy appears to be a kinetically-driven phenomenon.

9:10 am

INVESTIGATION OF THE EFFECT OF DIFFERENT METAL FEEDING SYSTEMS ON CAST STRUCTURES USING A WATER MODEL: A. Buchholz, S. Engler, M.-S. Ji, W. Schmitz, Foundry Institute, RWTH Aachen, Intzestr.5, D-52056 Aachen, Germany

Forced convection imposed by the feeding system plays an important role in the solidification of continuous casting processes. Convection modifies heat and mass transport and thus has a significant impact on the cast structure. A better understanding of the fluid dynamics promises an improvement of continuous casting processes. To investigate flow patterns and the influence of different inlet systems on cast structures a water model was designed maintaining dynamic similarity between model and real casting equipment. Sump profiles were derived from etch lines achieved from real castings. The flow patterns were studied for different metal distributors comprising horizontal, vertical, inclined spouts and diffusor bag. The effect of the different flow patterns is correlated with results of metallographic analysis. The experiments are reviewed by some aspects of numerical simulation. The results show that physical modelling remains an instructive tool to study the dynamic behaviour of transient flow phenomena.

9:30 am

PHYSICAL (BY PARTICLE IMAGE VELOCIMETRY) AND MATHEMATICAL MODELING OF METAL DELIVERY DEVICES FOR EM AND DC CASTING OF ALUMINUM: Dong Xu, J.W. Evans, Dept. of Materials Science and Mineral Engineering, University of California, Berkeley CA 94720; Daniel P. Cook, Corporate Research & Development, Reynolds Metals Company, Richmond, VA 23261-7003

A half-section water model of a pilot scale caster (at RMC, Richmond, Virginia) has been constructed at UC Berkeley. A particle imaging velocimetry (PIV) system has been assembled to measure velocities in the model for various simulated nozzle and bag geometries. The PIV system is a relatively inexpensive system using an incandescent light source, rather than the usual high-power laser. A digital camera, microcomputer and software (Optical Flow Systems) track the frame-to-frame movement of neutral-density particles in the water and provide vector maps of the velocity. Measured velocities have been compared to velocities computed using the finite element package FIDAP and show good agreement.

9:50 am


The occurrence of feathery crystals during experimental casting trials on a level pour casting unit yields a strong relationship as well to the pouring temperature as to the governing fluid flow pattern within the liquid melt pool of the billet. Three-dimensional simulations of the coupled fluid flow and heat transfer problem during the stationary phase of the level pour casting process are used to investigate the variations of the thermal field in the liquid part of the solidifying billet. The calculated flow field patterns and temperatures are discussed in dependency of casting velocity, pouring temperature and size of pouring gate. The resulting thermal gradients in the mushy zone over the circumference of the billet are correlated to microstructure analysis of the corresponding casting trials.

10:10 am BREAK

10:10 am

OPEN MOLD WITHOUT DISTORSION FOR ALUMINUM DC CASTING: MODELING AND TESTING THE OPTIMUM SHAPE AND MATERIAL: B. Hannart, Pechiney Rhenalu, Centr'Alp-BP24, F-38340 Voreppe, France; O. Bonnet, Pechiney CRV, Centr'Alp-BP27, F-38340 Voreppe, France; A. Noraz, Aluminium Pechiney, Centr'Alp-BP27, F-38340 Voreppe, France

The thermomechanical behaviour of open molds used for DC casting of aluminum slabs was analysed, and their design was optimized, in order to avoid thermal distorsion. The analysis used a thermomechanical finite element model, describing the mold geometry, the material properties, and the heat transfer between mold, molten metal and cooling water. The deformations observed during and after the casting were realistically reproduced, both in 3D and in 2D. The 2D model, allowing to test new designs in less than 10 minutes, was used to propose several solutions for reducing the residual distorsion of the mold. The different solutions were tested in industrial conditions at Aluminium Dunkerque, and mold distorsions were systematically measured. With the optimum choice of mold geometry and alloy, the residual distorsion was completely eliminated.

10:40 am

DIRECT CHILL CASTING OF ALUMINUM ALLOYS: INGOT DISTORSIONS AND MOLD DESIGN OPTIMIZATION: J.-M. Drezet, M. Rappaz, Laboratoire de Métallurgie Physique, Ecole Polytechnique Fédérale de Lausanne, MX-G, CH-1015 Lausanne, Switzerland

During the direct chill (DC) semi-continuous casting of aluminum alloys, the metal experiences high thermal stresses which are partially relaxed by deformation. This deformation is responsible for three main ingot distorsions: butt curl, butt swell and non-uniform rolling faces pull-in. These distortions are detrimental to the productivity of the process because they require butt sawing and more ingot scalping before rolling. On the other hand, residual stresses may induce longitudinal cracking of the cold ingots. Under pseudo steady-state conditions, i.e. after nearly one meter of casting, the solidified shell contracts towards the liquid pool (Pull-in). This contraction which amounts to about 9% at the lateral faces center is only 2% at the ingot corner. If a rectangular mold is employed, the resulting ingot is therefore concave ("bone shape"). To compensate for this non-uniform contraction of the ingot, the sides of the mold are designed with a convex shape, usually with three linear segments. Nevertheless, instead of producing flat rolling sheet ingots, such molds produce W-type ingot cross section. A comprehensive 3D mathematical model based upon the Abaqus software has been developed for the computation of the thermomechanical state of the solidifying strand during DC casting and subsequent cooling of rolling sheet ingots. Based upon a finite element formulation, the model determines the temperature distribution, the stresses and the associated deformations in the metal. This paper concentrates on the non-uniform contraction of the lateral faces and shows comparisons between computed and measured ingot cross-sections after complete cooling. Finally, the influence of the mold design on the final ingot cross-section is assessed and the use of an inverse method for mold design optimization is presented.

11:00 am

WATER COOLING IN DIRECT CHILL CASTING: PART 2, EFFECT ON BILLET HEAT FLOW AND SOLIDIFICATION: John Grandfield, Comalco Research Centre, P.O. Box 316, Thomastown, Victoria 3074, Australia

Water cooling plays an important role during DC casting. Control of the water cooling is essential for good process performance. In some cases the ability of the water cooling to remove heat limits productivity, and scrap can be generated due to variation in water cooling. The considerable work conducted to date on water cooling in DC casting is reviewed. The boiling theory is covered in a companion paper. Published measurements of cooling intensity and the affect of water cooling on the temperature distribution during casting are analysed. Various mold water system designs are discussed. The effect of variables such as water flow rate, impact velocity, composition, temperature etc are presented. Practical implications for controlling water cooling and the casting process are suggested.

11:20 am

CONSTITUTIVE MODELING OF HIGH-STRENGTH ALUMINUM CASTING: Keh-Minn Chang, Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, WV 26506; Jerry Harris, Ravenswood Aluminum Corporation, Ravenswood, WV 26506

High strength aluminum 7xxx alloys are susceptible to cracking during casting, and computational simulation is adapted to obtain better understanding and satisfactory control. Constitutive model of thermomechanical properties of the as-cast ingot is necessary for calculation of thermal stress developed after solidification. Considering the potential influence of precipitation, ingot properties are evaluated by a continuous cooling method, which allows controlled cooling at different rates to test temperatures of interest. The results indicate that thermomechanical behaviour of cast ingot remarkably differs from that of final wrought product. The relationship of mechanical properties are correlated with the microstructure of cast ingots.

11:40 am

3D ANALYSIS OF EM SEMI-LEVITATING AND FREE SURFACE PROBLEMS: M. Ramadan Ahmed, Aluminum Co. of Egypt, 48/50 Abd El-Khalek Sarwat St., Cairo, Egypt; S. El-Masry, Faculty of Engineering & Technology, Helwan, Egypt; Fawaz Moustafa, Ibrahim Moustafa, Egyptalum Company, Nag Hammady, Egypt

Developing an accurate mathematical model for the analysis of electromagnetic (EM) semi-levitating and free surface problems is still in the top of attentions for many researchers working in the field of the EM casting and others near-net-shape product applications. In this paper, a 3D iterative solution based on the Boundary Element technique coupled with a heat transfer analysis is derived for modeling an electromagnetic (EM) caster producing aluminum ingot installed in the Egyptalum Company. The main objective of this work is studying the effects of the EM screen location, the cooling system strategy and the melt withdrawal speed, and the effects of the estimated electrical setting parameters on the EM caster performance and its operation stability. The numerical results show that the location of the screen as well as the melt withdrawal speed have significant effects on the stability and the shape of the formed aluminum ingot. On the other hand, changing the supply frequency from 1500 Hz up to 2500 Hz increases the total electrical power consumed but it has no significant effect on the ingot shape. Finally, measurements showing a comparable reduction of 10% in the total electrical power consumed and a stable equilibrium free surface shape are recorded as the EM caster is tested, in the company, using those concluded setting parameters.


Sponsored by: Jt. EMPMD/SMD Chemistry and Physics of Materials Committee, MSD Thermodynamics and Phase Equilibria Committee
Program Organizers: Brent Fultz, 138-78, California Institute of Technology, Pasadena, CA 91125; En Ma, Louisiana State Univ., Dept. of Mechanical Eng., Baton Rouge, LA 70803; Robert Shull, NIST, Bldg. 223, Rm B152, Gaithersburg, MD 20899; John Morral, Univ. of Connecticut, Dept. of Metallurgy, Storrs, CT 06269; Philip Nash, Illinois Institute of Technology, METM Dept., Chicago, IL 60616

Room: 330C

Session Chairperson: Robert Shull, NIST, Bldg. 223, Rm B152, Gaithersburg, MD 20899

9:00 am INVITED

RESISTANCE BEHAVIOR OF Cr-Si-O THIN FILMS: Alan F. Jankowski, Jeffrey P. Hayes, Ronald Musket, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550; Frederic Cosandey, Chandrasekhar E. Gorla, Rutgers University - College of Engineering, P.O. Box 909, Piscataway, NJ 08855; Ronald S. Besser, Victor Westerlind and Gregory Cobai, Silicon Video Corporation, 6580 Via Del Oro, San Jose, CA 95119

Thin coatings of Cr-Si-O are assessed for use as a resistor. The submicron thick films are sputter deposited using a working gas mixture of (1-x)Ar-(x)O2. Several sintered-compacts of metal and oxide powders are commercially prepared for use as the sputter targets. The deposition process yields a range of film compositions which consist of 2-30 at.% Cr and 20-45 at.% Si as measured using Rutherford Back Scattering. A broad range of resistance values (101 to 1014 Ohm-cm) are found as measured by point contact with metal pads deposited onto the Cr-Si-O film surface. The film structure and morphology is characterized using transmission electron microscopy from which the resistance behavior can be correlated to the distribution of metallic-Cr. Thermal aging reveals metastability in the Cr-Si-O film morpholgy and resistance behavior.

9:30 am

MICROSTRUCTURE AND OPTICAL PROPERTIES OF GaN NANOCRYSTALS IMBEDDED IN A POLYMER MATRIX: M. Benaissa, Instituto Nacional de Investigaciones Nucleares, Mexico; M. José-Yacamán, Instituto de Fisica-UNAM, Mexico; K.E. Gonsalves, G. Carlson, University of Conneticut, Storrs, CT 06269

Presently, nanostructured GaN composite was prepared using a novel synthetic route. GaN nanocrystals were imbedded in a poly(methyl methacrylate) thin film matrix (GaN/PMMA) and then studied from structural and optical point of views. X-ray powder diffraction and high-resolution transmission electron microscopy were performed to analyze the microstructure while the optical properties were measured by optical absorption and photoluminescence. Microstructural analyses showed that the GaN nanocrystallites imbedded in the PMMA matrix have an average size of about 5.5 nm and crystallize in the zinc blende lattice (lattice constant a close to 0.45 nm) with some nitrogen vacancies and structural imperfections. Optical absorption measurements indicate that the band gap energy of the GaN/PMMA composite is approximately 3.51 eV.

9:50 am

ANELASTIC AND MAGNETOELASTIC BEHAVIOUR OF BULK NANOPHASE MATERIALS: E. Bonetti, L. Del Bianco, Dipartimento di Fisica and Istituto Nazionale per la Fisica della Materia, viale Berti Pichat 6/2 I-409128 Bologna, Italy

Mechanical spectroscopy techniques have been employed to investigate the anelastic and magnetoelastic behavior of bulk nanophase Fe and Fe-Al prepared by mechanical alloying and FeCuNbSiB granular alloys obtained starting from amorphous precursors through thermal treatments. The different magnetic states of the materials lead to strong modifications of the anelasticity spectra. The experimental results are presented and discussed with specific reference to the following to aspects : a) magnetoelastic coupling and giant DE effect in the FeCuNbSiB system occurring just below the nanocrystallization temperature, b) giant modulus enhancement in bulk iron and iron-aluminum alloys linked to changes of the magnetic behavior connected to grain size reduction and interfacial structure relaxation.

10:10 am BREAK

10:25 am

MAGNETIC PROPERTIES OF GRANULAR Co-Cu ULTRATHIN FILMS: A. Cabbibo, Y.D. Park, J.A. Caballero, J.R. Childress, Materials Science and Engineering, University of Florida, Gainesville, FL 32611-2066

Ultrathin (<10nm) films and multilayers of granular Co-Cu composites have been prepared by co-sputtering. Nanoscale Co particles are formed in Cu by depositing on heated substrates (TS>100C), with the usual increase in magnetic coercivity Hc, and superparamagnetic behavior above a critical blocking temperature (Tb) which depends on the partical size, shape, and local magnetic environment. We find that the confinement of the granular layer to thicknesses near the particle size induces variation in Hc and Tb due to changes in particle shape, magnetic anisotropy and inter-particle interactions. By varying the composition and thickness of both magnetic layer and interlayer, as well as the deposition conditions, one can identify conditions under which then magnetic granular layers can be fabricated with large anisotropy and therefore increased blocking temperature, without the need for post-deposition high-temperature processing. Such layers are designed to be used in magnetoresistive spin-valve multilayer structures.

10:45 am

ATOMIC STRUCTURE PECULIARITIES AND PHASE TRANSFORMATIONS IN HIGH-Tc SUPERCONDUCTING CERAMIC COMPOUNDS YBa(2)Cu(3)O(7-x): V.G. Pushin, L.I. Yurchenko, T.G. Koroleva, G.Ye. Vedernikov Institute of Metal Physics, Ural Division of Russian Academy of Sciences, S. Kovalevskaya 18, 620219 Ekaterinburg, Russia.

Recent results of high-resolution and in situ transmission and scanning electron microscopy, diffraction of X-rays and electrons, physical and mechanical tests on high T-c superconducting ceramic compounds of Yba (2)Cu(3)O(7-x), including thick ceramic films synthesided on ZrO(2), are presented. The main types of atomic structures, structural defects, secondary phase inclusions are systematized. It is shown that grain structure of ceramics in form of the polyhedral matrix crystallites divided by grain boundaries is characterized by a porosity and secondary phase inclusions, which exist inside grains and between them. In some cases the inclusions of amorphous phase were detected. The peculiarities of high-resolution TEM of investigated ceramic compounds are discussed. The pretransition phenomena and phase martensite-like transformations in high-Tc superconducting ceramics and classical high-Tc intermetallic compounds of type A15 (V(3)Si, Nb(3)Sn, V(3)Ge) and C15(V(2)Zr, V(2)Zr, V(2)Hf) are compared.

11:05 am

LOW FREQUENCY INTERNAL FRICTION STUDIES OF NANOCRYSTALLINE COPPER-IRON MATERIALS: W.N. Weins, J.D. Makinson, R.J. DeAngelis, Department of Mechanical Engineering, The Center for Materials Research and Analysis, University of Nebraska, Lincoln, NE 68588-0656

The low-frequency internal friction behavior of mechanically milled copper and copper-30 wt% iron alloys was studied over a temperature range of 100-700°K and a frequency range of approximately 1 to 3 Hz. Alloys were prepared by consolidating mechanically milled and alloyed powders using hot isostatic pressing to form compacts from which bars were machined for testing. Samples studied included unmilled copper, milled copper and milled copper-30 wt% iron. All powders were consolidated at 600°C and diffracting particle size of the consolidated material varied from 18-30 nm. The internal friction studies indicated the presence of a large grain boundary peak in all samples at approximately 300°C which increased with decreasing particle and grain size. The presence of iron appears to depress this peak and cause the occurrence of a second smaller high temperature peak in the range of 400-500°C, which is believed to be associated with iron in solid solution.

DESIGN AND RELIABILITY OF SOLDERS AND SOLDER INTERCONNECTS: Session VII: Interconnect Design and Reliability in Electronic Packages III

Sponsored by: ASM-MSD Flow and Fracture; SMD Mechanical Metallurgy; EMPMD Electronics Packaging and Interconnection Materials Committees
Program Organizers: Dr. R.K. Mahidhara, Tessera Inc., 3099 Orchard Drive, San Jose, CA 95134; Dr. D.R. Frear, Sandia National Laboratory, Mail Stop 1411, Albuquerque, NM 87185; Professor S.M.L. Sastry, Washington University, Mechanical Engineering Dept., St. Louis, MO 63130; Professor K.L. Murty, North Carolina State University, Materials Science and Engineering Dept., Box 7909, Raleigh, NC 27695; Professor P.K. Liaw, University of Tennessee, Materials Science and Engineering Dept., Knoxville, TN 37996; Dr. W.L. Winterbottom, Reliability Consultant, 30106 Pipers Lane Court, Farmington Hill, MI 48331

Room: 332

Session Chairperson: Dr. Zequn Mei, Hewlett-Packard Co., Electronic Assembly Development Center, 1501 Page Mill Road, Mail Stop 4U-3, Palo Alto, CA 94304; Professor K.M. Leung, Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Kong Kong

8:30 am INVITED

QUALITY AND RELIABILITY OF BGA AND SMT COMPONENTS: Reza Ghaffarian, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109

Spacecraft electronics including those at the Jet Propulsion Laboratory (JPL), demand production of highly reliable assemblies. JPL has recently completed an extensive study, funded by NASA's code Q, of the interplay between manufacturing defects and reliability of ball grid array (BGA) and surface mount electronic components. More than 400 test vehicles were assembled using ceramic and plastic BGAs, LCCs, J-leads, and gull wing components. These were subjected to thermal cycle testing and solder joint defects were logged prior to testing and solder damage propagation over time was documented. These findings offer valuable information to designers and quality assurance personnel alike on package robustness as well as in better understanding the defects that can actually lead to failure.

8:55 am INVITED

SOLDER JOINT RELIABILITY AND LIFE PREDICTIONS FOR VARIOUS SMALL OUTLINE PACKAGES MOUNTED ON FR-4 BOARDS: Suresh Golwalkar, Timothy Rothman, Paul Boysan and Robert Surratt, Intel Corporation, 1900 Prairie City Road, Folsom, CA 95630

TSOP or Thin Small Outline Packages have gained wide spread market acceptance throughout the electronic industry. This innovative and small footprint package was designed to fill a need created by the form factor specified for use in PCMCIA standard memory cards. However, with the broad and rapidly escalating acceptance of Flash products in the marketplace, this small outline package is being considered for a multitude of other use conditions. The small form factor of TSOP and accordingly short stiff lead form construction, requires further scrutiny in certain situations - specifically, applications requiring 20+ year lifetimes or others using 60 mil thick multi-layer FR-4 PCB's subject to extreme thermal cycling. Solder joint reliability is predominantly determined by two separate factors. The first being the surface mount process itself. Without a good initial solder joint, you can not expect good solder joint reliability. This fine pitch package (0.5 mm) requires different considerations than the existing 50 mil (1.27 mm) pitch type components. IR reflow profiles, solder volumes, and land pad layouts all contribute to proper fillet formation and a defect free solder joint. One must start with a good SMT process to have reliable solder joints. Second, is the use condition itself. Package/board configuration, operation conditions and thermal cycling of the board, drive solder joint reliability. In order to determine if TSOP is the correct package for a given application, various graphical presentations of failure rate versus service life are included in this paper. Solder joint evaluations were performed using various temperature cycle conditions. Data was taken using 64 mil thick FR-4 boards of various layer count and 20 mil thick 4 layer memory cards using 32Id, 40Id TSOP and 44Id PSOP packages. Temperature cycle conditions A, B and C were performed and Weibull probability plots were developed for each condition. Acceleration factors for solder joint fatigue is given by Norris and Landsburg equations. These include frequency transformations, temperature swing transforms, and a factor for variation of isothermal fatigue characteristics of solder joints between test and operating conditions. These equations yield use condition graphs. The graphs provided, show four different operational temperature swing conditions. Express, industrial, consumer, and computer conditions are depicted according to the IPC standards for these use variables. The extreme of the temperature swing and the frequency of swings per day, modulate the solder joint reliability. We have included both temp cycle condition A and B test data and modeled projections based on those. We feel that condition A more directly simulates real life use condition. Conditions B and C were used as highly accelerated conditions to obtain (trends only) swifter, but preliminary, failure predictions. As can be seen from temp cycle A cycling data, 50% failure point takes approximately six months to complete. PSOP data has ben included for completeness. As can be observed from the data, PSOP solder joint reliability, is oustanding for any application and any temperature range.

9:20 am INVITED

DEFORMATION ANALYSIS ON FLIP CHIP AND CSP SOLDER INTERCONNECT BY MICRODAC: D. Vogel1, J. Auersperg2, A. Schubert1, B. Michel1, H. Relchl1; 1Fraunhofer Institute for Reliability and Microintegration Berlin, Dept. Mechanical Reliability and Micro Materials, Gustav-Meyer-Allee 25, 13355 Berlin, Germany; 2Technical University Berlin, Forschungssohwerpunkt Technologien der Mikroperipherik, Gustav-Meyer-Allee 25, 13355 Berlin, Germany

In order to enhance thermo-mechanical life time of solder interconnects in flip chip and CSP assemblies the design of new products is optimized by the help of Finite Element (FE) simulations. Solder stress reduction is achieved selecting proper materials and assembly geometry. Life time estimations and trends can be obtained by fatigue models, e.g. a Coffin-Manson approach, utilizing calculated stress and strain distributions. The performance of FE modeling depends on the quality of the provided input data, i.e. on load conditions, geometrical layout, constitutive material laws and on material parameters. Lacking data necessarily leads to simplifications. Consequently, comparable strain and stress measurements are requested to make FE results reliable. Often Moire deformation measurements are utilized for microelectronics purposes to obtain data for comparison with FE findings. Unfortunately, the method is faced with difficulties, if very small structures like single bumps have to be investigated and resolved. The new microDAC method applied in this work can overcome these problems. The underlying measurement principle is a correlation based computer algorithm. It allows to track local object pattern during load. A set of local patter displacements is treated to get strain and shear fields over the object surface. Until now thermal and/or mechanical load on flip chip and CSP specimens is realized inside scanning electron microscopes, as well as for optical and laser scanning microscopes. The picked up images for different load states are processed by the microDAC computer code. Measurements have been accomplished for flip chip and chip scale package solder interconnects. E.G., strains inside eutectic PBSn bumps of flip chip assemblies with highly filled underfill material have been determined by microDAC. Bump stresses were caused by the thermal mismatch between a low cost FR-4 substrate and the silicon die, heating up the assembly from room temperature. Measured deformation fields have been compared with FE results. The main strain features of FE simulation and microDAC measurement results correspond with each other. The hard underfill obstructs the shear of corner bumps. Consequently, shear strains (xy of corner bumps should not necessarily be a major reason of solder fatigue. Solder strains (xx in the perpendicular to the board direction are quite high. Their amount exceeds the value of unrestricted thermal strain of solder or underfiller material between a half and one order of magnitude. So, this strain component can significantly contribute to bump fatigue. Calculated (xx strains are at least three times lower than measured on the real component. The reason is assumed to be a anisotropic thermal expansion of the thin underfill layer. So, solder fatigue estimations only based on FE strain values can result in significantly higher life time values than realistic reached.

9:45 am INVITED

RELIABILITY FORMULATION FOR ELECTRONIC INTERCONNECTIONS: Eugene Atwood and Horatio Quintone, IBM Microelectronics, B/330-81A, Route 52, East Fishkill Facility, NY 12533

This paper describes a novel reliability methodology, supported by data, which includes a rigorously derived stochastic formulation. As an introduction to this topic, the paper reviews and critiques methods currently used in the field of electronic interconnection reliability and presents supporting data illustrating the arguments set forth. Plausible physical explanations are presented for each of the factors used in the IBM modified Coffin-Manson acceleration model. The acceleration model is challenged because of its form which assumes linearly independent factors. A review of the log normal and extreme value distributions, commonly used to model system reliability of electronic interconnects, highlights deficiencies and violations of some of the basic mathematical axioms i.e., "closure property". Additionally we present a refutation of "theoretical derivations" that have put forward to establish the validity of the log normal distribution as a model of fatigue fracture mechanisms. With regard to the main topic: today's thermal environments can no longer be defined by simple periodic functions, i.e., a fixed frequency and amplitude, but instead they tend to be "highly no-periodic" and of random nature. The randomness can be a result of the synergy between operating systems, software, use patterns and CMOS technology, e.g. temperature fluctuation patterns resulting from power management schemes defined in today's electronic devices. Present reliability formulations are not tailored to deal with this randomness. A rigorous formulation is presented that accounts for non-deterministic environments. The method treats the problem stochastically including the use of a novel distribution for time-to-fail, SCRIP (Statistics of Crack Initiation and Propagation) developed by the authors et al, and other system reliability formulations. An additional methodology is proposed which formulates electronic interconnection reliability in the presence of these random environments and extends the use of cycle/time based reliability assessments commonly used in the industry. The method consists of performing a series of renormalizations by discrete auto correlation and convolution integrals which are used to determine to determine the spectral power density function of the random environment.

10:10 am INVITED

SOME PHYSICS, KINETICS AND EMPERICAL RELATIONSHIPS RELATED TO FAILURE OF SOLDERED JOINTS: Barry Schlund, Reliability Engineering Department, M/S H2121, Motorola GSTG, 8201 E. McDowell Road, Scottsdale, AZ 85252

The primary purpose of this paper is to provide the physical reasons behind what appears to be many self-contradictions encountered in solder reliability testing and experience. This is accomplished by presenting the underlying physical aspects of solder reliability, including workmanship, metallic and intermetallic bonding, interface mechanisms, diffusion, vacancy and void formation, work-hardening and softening, as well as smooth versus chaotic stress-strain behavior. Also discussed, is the criterion for successful application of finite element analyses in fatigue life calculations. It is hoped that this work will help bridge the gap between practitioners with opposing beliefs, for example those who believe in chaotic stress-strain behavior versus those who believe in smooth behavior. General guidelines for estimating the appropriate input conditions in the absence of accurate life profiles are provided. The use of the tool is demonstrated with several examples. These include: Thin Outline packages, Quad Flat packs, J-leaded components, and leadless Chip Carriers. A comparison of observed failures and calculated times to failure is provided.

10:35 am BREAK

10:45 am INVITED

COMBINED HEAT TRANSFER AND THERMAL LOAD ANALYSIS FOR FATIGUE LIFE PREDICTION OF SOLDER JOINTS OF RESISTORS: Hasan U. Akay, A. Bilgic and N. H. Padyar, Department of Mechanical Engineering, Purdue School of Engineering and Technology, IUPUI, Indianapolis, IN 46202

Despite the studies performed in the last two decades to understand the fatigue behavior of the solder joints used in the electronic packages, the problem still draws big attention among the electronic package manufacturers. Fortunately, the studies performed provided a great improvement in the information about the behavior of the solder material under low-cycle-fatigue conditions. Based on the available information about the mechanical and fatigue behavior of solder material under thermal loads, the present authors developed the volume-weighted averaging technique for the fatigue life prediction of solder joints (A. Bilgic, "Fatigue Life Prediction Methods for Thermally Loaded Solder Joints Using the Finite Element Method", Master of Science Thesis, Purdue University, Indianapolis, IN) and H. U. Akay, N. H. Padyar and A. Bilgic, Fatigue Life Predictions for Thermally Loaded Solder Joints Using a Volume-Weighted Averaging Technique, ASME Journal of Electronic Packaging, 1996 (in Review). The method consists of calculating the stresses and strains generated within a specific package by use of the finite element method and then correlating the calculated stress-strain response to the fatigue life by use of an energy-based fatigue life prediction criterion. The method was used to predict the fatigue lives of several arbitrary solder joints and the predictions were compared with the experimental data. The predictions were very encouraging. It is stated that the method does not differentiate between leadless and leaded solder joints or the loading applied on the packages. In addition, the method is very mesh-insensitive, implying that the number of nodes and finite elements used in the mesh has no major effect on the predictions. In this study, we extend our method to the fatigue life prediction of three-dimensional solder joints of resistors. The heating is provided by the power loading applied on the resistor. The differential thermal expansions within an assembly causes the thermal strains and stresses, as in the case in chip carriers. The analysis is performed in two steps: 1) A heat transfer analysis is performed to determine the spatial variations of temperatures during a power loading cycle; 2) Thermal stress analysis is performed to determine the thermal stresses and strains developed during the structure. The stress-strain response against the applied power loading is then used to predict the fatigue life using the previously developed volume-weighted technique and the fatigue life prediction criterion. The predictions are compared with the experimental data provided by others.

11:10 am

MECHANICAL PROPERTIES OF SN-AG COMPOSITE SOLDER JOINTS CONTAINING COPPER-BASED INTERMETALLICS: S.L. Choi, J.L. McDougall, T.R. Bieler, K.N. Subramanian, Dept. of Materials Science and Mechanics, Michigan State University, East Lansing, MI 48824

11:30 am

RELIABILITY OF A CHIP SCALE PACKAGE: Steve Greathouse*, Rao K. Mahidhara**, Vern Solberg**, Joe Fjelstad**, Tom DiStefano**, *Intel Corp., CH6-315, 5000 W. Chandler Blvd., Chandler, AZ 85226; **Tessera Inc., 3099 Orchard Drive, San Jose, CA 95134

Post stress reliability for Chip Scale Packages and their interconnects has been lacking in the industry. An evaluation of the Tessera µBGA package through the solder screening process, reflow profile, and resultant reliability data is given. Reliability data is compared to industry standard goals for stress ing. Further discussion of solderability methods and solder ball integrity via ball shear is also given.

11:50 am

CRATERING IN 90:10 Pb:Sn CAST COLUMNS FOLLOWING SHEARING IN CAST COLUMN GRID ARRAY (CCGA) PACKAGES: M. Nemiroff1, K. Economy2, Y. P. Geng3, T. H. Hao4, 1Cadence Corp., 10850 Via Frontera, San Diego, CA 92128; 2UNISYS Corp., 10850 Via Frontera, San Diego, CA 92128; 3Institute for Mechanics and Materials, University of California, San Diego, CA 92093; 4China Textile University, Shanghai, China

Void-like features have been observed on sheared surfaces on 90:10 Pb:Sn columns in ceramic cast column grid array (CCGA) packages. The feature sizes are typically 3-5 mils across. These features are not voids. They are crater-like fractures caused by the shearing tool. Shearing with a heavy tool causes extensive cratering. Shearing the columns with a razor blade produces far fewer, if any, of these void-like features. These craters are a concern since they can be mistaken for voids which affect the reliability of CCGA devices. The surface of these features are devoid of large (greater than 2-3 micron) tin-rich regions normally in the bulk of the column. The tin-rich regions have lower toughness than the Pb-rich matrix in the two-phase 90:10 Pb:Sn cast column. Cratering can be explained as a mechanism where the shearing tool creates a crack that propagates around these tin-rich regions. Micromechanical models have been established to simulate crack propagation (a) through and (b) around the tin-rich area. The results show that the energy released for case (b) is less than that of case (a) even though case (b) has a longer crack path.

12:10 pm INVITED

EXPERIMENTL STUDIES OF SMT SOLDER JOINT RELIABILITY: K. M. Leung, Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Kong Kong

SMT solder joints between ceramic chip carriers and printed circuit boards are found in general to suffer large thermal strains and stresses during device operation under repeated power cyclings. A comprehensive study of the thermomechanical behavior of SMT solder joints has been performed under power cycling using different techniques of optical interferometry. This paper will discuss the detailed analysis of these experimental measurements and its implication on fatigue life estimation of SMT solder joints. Other major experimental studies on solder joints reliability performed at the City University will be reviewed as well.


12:30 pm


A thin layer of 6.0 to 8.0 microinches (0.1 to 0.2 microns) of electroless palladium deposited directly on the copper surface of a printed wiring board has exhibited excellent solderability. This new surface offers a series of advantages over the traditional Hot Air Solder Leveling (HASL). It is flat, coplanar, which is a must for successful screen printing of fine featured devices. It is lead free and environmentally friendly. Other than being solderable it is also wire bondable and has applications as a viable surface finish for contact switching or compression contacts. Characteristics of palladium are discussed. Data of solder joint reliability is presented. The data includes an in depth EDX analysis of metallurgy of the interface between palladium coated copper pads and the solder forming the joint, under various accelerated aging conditions. The solder joint has been subjected to 2000 thermal cycles per IPC standard testing procedures. The results indicate no impairment in resistivity of solder joint integrity.

12:50 pm

RELIABILITY EVALUATION OF CHIP SCALE PACKAGES BY FEA AND MICRODAC: J. Auersperg1, D. Vogel2, J. Simon1, A. Schubert2, B. Michel2, 1Technical University Berlin, Forschungssohwerpunkt Technologien der Mikroperipherik, Gustav-Meyer-Allee 25, 13355 Berlin, Germany; 2Fraunhofer Institute for Reliability and Microintegration Berlin, Dept. Mechanical Reliability and Micro Materials, Gustav-Meyer-Allee 25, 13355 Berlin, Germany

Chip Scale Packaging is one of new hot topics in electronic packaging where Chip Scale Packages are defined by size, which should be nearly chip size. Different types of CSPís have been developed. They may be classified by the technological concept, e.g. waferlevel (including molding), flip chip with interposer (rigid, flex) and the well known (BA. The mechanical reliability mainly is determined by the packaging technology. The package design has to compensate stresses caused by the thermal mismathc between its components. Different CSPís approaches were analyzed by thermomechanical Finite Element Analysis simulating a thermal cycling process with respect to the complex mechanical behavior of the different materials used, e.g. the creep effect in solder joints, the temperature dependence of material parameters, the visco elastic behavior of underfill materials. The results will be discussed from the aspect of an estimation of the mechanical reliability. Several types of SCPís with a great variety of materials used are evaluated in such a way. The sensitivity of the related values to changes of material and geometrical parameters was used to enhance the thermo-mechanical life time. Experimental methods are applied to obtain accurate input data for the FEA. The comparison of the results from FEA with those obtained from microDAC strain measurement method helps to fit the model data utilized in numerical simulations for more realistic physical models and makes the FE results reliable. This work is part of a national CSP project with partners from German industry.

INTERNATIONAL SYMPOSIUM ON RHENIUM AND RHENIUM ALLOYS: Session IX: Processing, Structure and Properties of Rhenium and Its Alloys (Part III)

Sponsored by: SMD Refractory Metals Committee and MDMD Powder Materials Committee
Program Organizer: Dr. Boris D. Bryskin, R&D Manager, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036

Room: 232C

Session Chairperson: Dr. John A. Shields Jr., Climax Specialty Metals, 21801 Tungsten Road, Cleveland, OH 44117; Dr. Omar Es-Said, Loyola Marymount University, Los Angeles, CA 90045-2699

8:30 am

STRUCTURES AND PROPERTIES OF Mo-Re ALLOYS: Fumio Morito, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305, Japan

It is well known that MO-Re alloys exhibit superior properties among Mo based alloys. However Re effect on the structures and properties of Mo has not well understood. The current state of Mo-Re alloys was therefore reviewed not only in the field of high temperatures but also in the application of high performance. Focusing on the effect of Re concentrations in Mo, the structures and properties of the welds produced by electron beam welding were investigated. Bend and tensile behaviors of the welds were evaluated. Microstructures and fracture surfaces of the welds were examined in details by SEM/EDX and TEM. Furthermore formation and distribution of sigma-phase in Mo-Re welds were studied. A role of signa-phase on the structures and properties of Mo-Re alloys was also discussed.


8:50 am

THE ORIGIN OF THE INHOMOGENEOUS RHENIUM DISTRIBUTION IN POTASSIUM DOPED W-Re ALLOYS: I. Gaal, Research Institute for Technical Physics of the Hungarian Academy of Sciences, H-1325, P.O. Box 76, Budapest, Hungary

8:50 am

MECHANICAL ALLOYING OF W-25wt.%Re POWDER: F.H. Froes, C.R. Clark, C. Suryanarayana, E.G. Baburaj, Institute for Materials and Advanced Processes, University of Idaho, Mines Building, Room 321, Moscow, Idaho 83844-3026; Boris D. Bryskin, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036-0245

Mechanical alloying (MA) of well characterized elemental W (75 wt.%) and Re (25 wt.%) was carried out in a SPEX Mill at ambient temperature for 1,3,5 and 10 hours. Milled products were examined for structural, chemical and morphological details using x-ray diffraction, scanning electron microscopy and transmission electron microscopy. XRD patterns showed continuous decrease in the intensity of Re peaks, with increasing MA time. However the Re peaks continued to be present even after 5 hours of milling. Ten hours of milling showed complete dissolution of Re, as observed by the complete absence of Re peaks in association with W peak shift in accordance with the dissolution of Re in W. Extensive reduction in particle size and chemical homogeneity of the alloy could be established by microstructural and chemical analysis using SEM and TEM. After pressing and sintering of pellets, tests revealed a significant amount of contamination by iron through milling.

9:10 am

THE KEY POINT OF TUNGSTEN-RHENIUM ALLOYS PROCESSING: Ms. Song Lin, 62 Amethyst Way, Franklin Park, NJ 08823

Tungsten-Rhenium alloys have won an important application in various modern technical fields and achieved great economic- technical effects and primarily produced by powder metallurgy. Nevertheless, the practical uses of tungsten-rhenium alloys sometimes are limited due to some difficulties encountered in their processing and applications. The common troubles are as follows: 1). The inhomogeneity of the alloy's composition. 2). The bubbling effect, during sintering of alloy rods. 3). Breaks occurred in winding formation of the alloy wire. 4). The formation of brittle second phases in the alloy. With the purpose to improve the properties of Tungsten Rhenium alloys. A systematic investigation of above mentioned problems are summarized.

9:50 am BREAK

9:30 am BREAK

9:50 am

MECHANICAL BEHAVIOR OF DILUTE Mo-Re ALLOY: R.W. Buckman, Jr., Refractory Metals Technology, Pittsburgh, PA 15236

The creep-rupture life of unalloyed molybdenum at 0.65Tm is only increased by an order of magnitude with up to 50% Re addition. A proprietary process, developed for unalloyed molybdenum, results in an increase in creep-rupture life at 0.65Tm by 4-5 orders of magnitude. A Mo-14Re alloy processed by a similar method exhibits comparable creep rupture strength while recrystallized material retains a DBTT significantly below room temperature.

10:10 am

THE INFLUENCE OF RHENIUM ON STRUCTURE AND STRENGTH CHARACTERISTICS OF THE HIGH-TEMPERATURE STRENGTH EUTECTIC CHROMIUM BASED ALLOYS: L.V. Artyuh, O.A. Bilous, A.A. Bondar, M.P. Burka, S.A. Firstov, N.I. Tsyganenko, T. Ya. Velikanova, Frantsevich Institute for Problems of Materials Science, 3 Krjijanovskogo Str. 252680 Kiev, Ukraine

In our Institute some data were obtained that chromium-carbide eutectic cast alloys have prospects promising. The eutectic (CR)+(TiC) alloy has Vickers hardness about 100 Kg/mm2 at 1000°C and is harder than traditional commercial alloys on the base of iron, cobalt or nickel in some times about 1000°C. And what is more that the latter is able to be machined with the former at high temperature. Produced from (Cr)+(TiC) swages allowed to carry out isothermic swaging of high-temperature strength X220BX alloy (the Ni-based material for vane gas-turbine engine) in air at 1150°C and 200 Mpa stress. Molybdenum additions to the eutectic (Cr)+(TiC) alloy were determined to increase high temperature hardness to 1000°C up to 200-300 Kg/mm2. Continuing development the effect of rhenium on the structure and high-temperature hardness of eutectic two-phases (Cr)+(TiC) alloys in Cr-Ti-C and Cr-Mo-Ti-C systems was examined in this investigation. The rhenium additions being 5, 10 and 20 at. & were shown to lead to the formation of limited quantity of third phase, (Cr23C6). Highly dispersed eutectic structure became more homogeneous. According to microprobe analysis the rhenium (as molybdenum) is predominatly dissolved in chromium matrix. High-temperature hardness was determined to be increased already with 5 at.% Re additions. The develop is about 100 kg/mm2 at 300-800°C and about 40 Kg/mm2 at 1000°C. It became higher with increasing rhenium content up to 20 at.%. The hardness of five-component alloys was always more than four-component at the whole temperature interval. The maximum was found at maximum rhenium content (450 Kg/mm2 at 900°C). to our mind the develop was achieved due to solid solution strengthening of chromium matrix (well-known "rhenium effect"). The determined of hardness allows to estimate the strength characteristics using the =HV/3 connection. Therefore the eutectic (Cr)+(TiC) alloys with rhenium alloying are believed to become more perspective for application.

10:30 am

HIGH-RHENIUM BINARY AND TERNARY ALLOYS WITH TUNGSTEN AND MOLYBDENUM FOR SERVICE IN NITROGEN- AND HYDROGEN-CONTAINING ENVIRONMENTS: K.B. Povarova, N.K. Kasanskaia, O.A. Bannikh, I.D. Marchukova, V.L. Likov, Baikov Institute of Metallurgy, Russian Academy of Sciences, Leninskii Pr. 49, 117334 Moscow, Russia

Microstructure, fracture mode and mechanical properties of vacuum melted binary WR-27VM, MR-47VM alloys and ternary MWR-10/45VM alloy both deformed and recrystallized are investigated in the temperature range of 20-1200°C. Conditions for o-phase precipitation hardening are found. The effect of a-phase on the low-temperature ductility and low and high-temperature strength is estimated. Corrosion resistance at 400-1000°C and features of the chanses in surface layer composition in products of ammonia thermal dissotiation are investigated. It is shown that ternary alloy has high low-temperature ductility and strength and moderate high temperature strength as these of MR-47VM as well, as high corrosion resistance in ammonia dissotiation products close to that of WR-27VM. Mechanisms of surface layer composition changes in corrosion atmosphere are discussed.

10:50 am

THE SYNTHESIS OF W-Re POWDER ALLOYS: V.V. Panichkina, V.V. Skorokhod, Frantsevich Institute for Problems of Materials Science, 3 Krjijanovskogo Str. 252680 Kiev, Ukraine

The fine particle powder technology was used for the production of W-Re alloys. Single phase W-Re powders were obtained by co-reduction of fine particle W-Re oxide blends. The homogeneous disperse W-20%Re powders and the single phase W-80%Re intermetalide powder with particle size in range of 1- 4 µk were synthesized. W-20%Re powder was mixed with the W powder of the same dispersion in order to obtain W-2%Re alloy. The -phase would not be formed during the sintering because Re in blend is in form of the prealloyed W-20%Re powder. The synthesized W-2%Re ingots were rolled in 2-3 mm sheets. The mechanical characteristics and the structure of the material were investigated. The sheets had higher plasticity due to the 2%Re alloying. The W-80%Re alloy powders were successfully used for the production of long working time impregnated cathodes.

11:10 am

NEW METHODS OF IMPUTTING RHENIUM AND MANUFACTURE OF TUNGSTEN-AND MOLYBDENUM-RHENIUM ALLOYS: V.V. Khaydarov, P.S. Maksudov, V.I. Pack, A.A. Pirmatov, Uzbek Refractory and Heat Resistant Metals Integrated Plant, 702119 Chirchik, Tashkent Region, Republic of Uzbekistan

Uzbek Refractory and Heat Resistant Metals Integrated Plant is a complex enterprise infield of manufacture tungsten, molybdenum, rhenium, and alloys on their basis. There is a special technology of imputing rhenium from molybdenum concentrates, which contains from 300 GR. to 700 GR. rhenium per each 1 ton of concentrate at the enterprise. Moly concentrates are manufactured by method of nitrogen acid imputing. In this case basic point of rhenium transferring into liquids which contains molybdenum, rhenium and nitrogen and sulfur acids. Using such types of liquids, there are well known methods such as extraction and distilled rectification methods of imputing rhenium. And all above mention of methods have low effect. That is why researching in field of sorption technology of imputing rhenium from nitrogen-sulfur liquids. Researching of wide range of low, middle and high basis of anionites determined that the best one is vanil-peridium resin. Using such type of resin in industry we achieved 80% imputing rhenium as ammonium perrenatum. There is wide range of utility possibilities now we can use our own rhenium and produce powder alloys on basis of tungsten and molybdenum. Tungsten alloys are: BP-3; BP-S; BP-20. Molybdenum alloys are: MKP-16; MP-47. Wire produced from tungsten and molybdenum alloys using in thermometry and tube building industry as they have hardest characteristics.


THE STRUCTURE AND PROPERTIES OF THE ALLOYS OF Re-Cr-C TERNARY SYSTEM: T. Ya. Velikanova, A.A. Bondar, A.V. Grytsiv, Frantsevich Institute for Problems of Materials Science, 3 Krjijanovskogo Str. 252680 Kiev, Ukraine

Existence of the rhenium effect improving the mechanical properties of the multycomponent chromium alloys (containing the rhenium and carbon together with other elements) specifies our interest in Re-Cr-C ternary system. Constitution and properties of more than 40 alloys prepared by arc melting were investigated by metallography, x-ray diffraction, microprobe and differential thermal analyses and Pirani-Altertum method in total concentration range. Rhenium raises the melting point of bcc chromium based phase (up to 2284°C in binary system Re-Cr). The maximum temperature of melting for the carbon and rhenium saturated chromium in equilibria with (Cr,Re)23C6 and (-Re3Cr2) amounts to 1650°C and appear more high then melting temperature for binary alloys containing Cr and Cr23C6 phases (1581°C). Ternary alloys of this two phase field have higher strength and ductility than binary ones. It is in according to data about existence rhenium effect in chromium based alloys. Essential singularity of Re-Cr-C system is immensely high combined solubility of the chromium and carbon in rhenium at high temperatures (about 50 at% Cr at 30 at% C: and 1710°C) and significant solubility of rhenium in chromium carbides (the most solubility Re in Cr23C6 amounts to 18, in Cr7C3 and Cr3C2 ones do 8 and 6 at.% at, 1655, 1710 and 1760°C, respectively ). Rhenium based solid solution forms equilibria with carbon, solid solutions of rhenium in chromium carbides and (-Re3Cr2) and thus it specifies the constitution of Re-Cr-C ternary system.


Sponsored by: SMD Refractory Metals Committee and MDMD Powder Materials Committee
Program Organizer: Dr. Boris D. Bryskin, R&D Manager, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036

Room: 231A

Session Chairpersons: R.W. (Bill) Buckman Jr., Refractory Metals Technology, P.O. Box 100551, Pittsburgh, PA 15236; Dr. Lynn B. Lundberg, Materials Consultant, 2832 W. 33rd N., Idaho Falls, ID

8:30 am

RHENIUM AS AN ALLOY ADDITION TO THE GROUP VA METALS: R.W. (Bill) Buckman Jr., Refractory Metals Technology, P.O. Box 100551, Pittsburgh, PA 15236

The anomalous effect rhenium has on the ductility of the Group VIA elements Mo, W, and Cr is not observed in the Group VA metals Ta, Nb, and V. The low temperature ductility of the Group VA elements is significantly impaired at rhenium additions greater than about 3 atom percent. However, rhenium has been shown to significantly improve the high temperature creep strength of tantalum alloys and the effect is saturated at about 1.5 atom percent rhenium, a level which does not alter the ductile-to-brittle transition temperature of tantalum alloys significantly.

8:50 am

UNDERCOOLING EXPERIMENTS ON RHENIUM AND RHENIUM ALLOYS BY DROP-TUBE PROCESSING: Bernard Vinet and Sandrine Tournier, Commissariat á l' Énergie Atomique, DTA/CEREM-Département d'Étude des Matériaux, 17 rue des Martyrs, 38054 Grenoble cédex 9, France

Solidification of deeply undercooled melts can lead to the same variety of solid state metastabilities as do methods of rapid quenching of the liquid onto cold substrates. Since undercooling is realized at slow cooling rates, containerless processing is often needed to avoid external nucleation sources. In such a way, refractory materials are studied by letting single droplets fall through an evacuated high drop-tube as for instance the 48 metre high facility built in Grenoble. In this contribution, an overview is proposed on the most interesting results obtained so far for rhenium and rhenium alloys. Undercooling experiments have been realized on refractory binary alloys showing complex (D8b, type CrFe, 30 atoms per cell) and X (A12, type -Mn, 58 atoms per cell) phases in the equilibrium phase diagram. The studied systems associate a b.c.c. (W, Ta, Mo, Nb) transition metal with a h.c.p. metal, rhenium in the event (Tc, Os and Ru should also be considered if only from a phenomenological point of view). A favoured primarily formation of the metastable bcc-structure instead of the direct formation of the stable phase is obtained in the case of the Re-W system. Moreover, a double recalescence phenomenon is obtained in a composition range between 65 and 82 at% W. This result is discussed in connection with the appearance of the metastable A15 phase. In the case of the Re-Ta system, it is shown that the% phase nucleates from the melt.

9:10 am

PHYSIKO AND CHEMICAL PRINCIPLES OF RHENIUM ALLOYS DEVELOPMENT: K.B. Povarova, M.A. Tylkina, Baikov Institute of Metallurgy, Russian Academy of Sciences, Leninsky Pr. 49, 117911 Moscow, Russia

Physiko-chemical principles of rhenium alloys development are considered and examples are shown of application of these principles to the development of conventional and advanced rhenium alloys. The features of physiko-chemical interaction of rhenium with elements of Periodic table in binary, temary and more complicated alloy systems are analysed. Special attention is given to the theoretical analysis of experimental "composition-property" diagrams. The role of electronic structure is discussed as concerns the effect of the chemical composition on some physical and mechanical properties of Cr- Moe, or WRe-based solid solutions. The stability is estimated of solid solutions, intermetallic compounds, and interstitual phases in rhenium alloys, as well as the tendencies and rates of diffusion processes in multi component heterogenious rhenium alloys. Special rhenium effects responsible for decreasing of cold brittleness phenomena in IV group metals are discussed as well as high strain-hardening rates of W-and Mo-alloys with Re. Application of Re-contained alloys are observed.

9:30 am

THE RHENIUM EFFECT IN W- AND Mo- BASE ALLOYS: THE EXPERIMENTAL REGULARITIES AND THE PHYSICAL NATURE: A.D. Korotaev, A.N. Tyumentsev, Yu. I. Pochivalov, Siberian Physical & Technical Institute, Revolution Sq. 1, 634050 Tomsk, Russia

The experimental data on the rhenium effect and related phenomena, such as the solution softening, the elastic twinning and superelasticity, the high strengthening capacity of Mo-Re alloys, allowing a strength of 9000 Mpa, etc., are critically reviewed. Particular attention is given to the authors' results on the high ( 4 at.%) solubility of oxygen in Mo-Re alloys, to the segregation of the interstitial on the structure defects, and to the contribution of these factors to the increase of the plasticity. Some considerations are advanced on the reason for the increase in plasticity for alloys with a rhenium content of 5-10 at.%. The effect of the rhenium alloying on the decrease in the mobility of screw dislocations and the contributions of the Peierls forces to the increase in plasticity are discussed. The problem of the formation of local composition irregularities with an atomic short-range order and a type A15 lattice and the relevant experimental data are considered. It is supposed that the grain bulk-to-boundary strength ratio is important for high temperature (1300 K) strength and plasticity of Mo-Re alloys to be attained.

9:50 am BREAK

10:10 am

THE SOLUBILITY OF OXYGEN IN RHENIUM-ALLOYED MOLYBDENUM: A.D. Korotaev, A.N. Tyumentsev, V.V. Manako, Siberian Physical & Technical Institute, Revolution Sq. 1, 634050 Tomsk, Russia

The regularities of the phase transformations and the variation of the composition of Mo-Re-base alloys in the process of oxygen diffusion alloying were investigated. It has been found that the alloying with rhenium to a concentration of 47 wt.% increases (to 4 at.% and more) the solubility of oxygen, reduces (by 2-3 orders) its diffusion coefficient in molybdenum, and prevents the increase in the oxygen solubility at dislocations and small-angle boundaries of the substructure and the segregated enriching of intergrain boundaries with oxygen. For the Mo-Re alloys subjected to solid-solution hardening with oxygen it has been found that the phenomenon of mechanical twinning is suppressed and the characteristics of the dislocation structure are changed on plastic deformation. Moreover, in the solid solutions of the Mo 47% Re alloys, local regions of the short-range order or type Mo3ReOx complexes with the A15 structure, stabilized as a result of the diffusion of oxygen atoms, are observed. The role played by the regularities revealed in the realization of the rhenium effect is discussed.

10:30 am

THE ROLE OF PRECIPITATES OF CLOSE PACKED PHASES IN THE "RHENIUM EFFECT": Yu. N. Gornostyrev , M.I. Katsnelson, Institute of Metal Physics, 620219 Ekaterinburg, Russia; A.V. Trefilov, Kurchatov Institute, 123182 Moscow, Russia

The connection of "rhenium effect" (simultaneous increase of the strength and plasticity in W, Mo, Cr by adding rhenium at a concentration close to the solubility limit) with the peculiar structural state of corresponding alloys is discussed. The hypothesis is suggested, according to which the main factor for the appearance of the rhenium effect is the formation of dispersed close packed (of Frank-Kasper type) phases such as W3Re with A15 structure or distorted -phase. The general problem of the appearance of dispersed Frank-Kasper phases near the instability boundary of BCC lattice in transition metal alloys is considered in the framework of a simple crystallogeometrical model. It is shown that the precipitates of the phases in BCC host may provide the increase of the solubility of interstitial impurities. The replacement of carbide phases by the precipitates of the Frank-Kasper phases may lead to the improvement of mechanical properties of the alloys.

10:50 am

LOW- AND HIGH-RHENIUM TUNGSTEN ALLOYS: PROPERTIES, PRODUCTION, AND TREATMENT: K.B. Povarova, O.A. Bannych, E.K. Zavarzina, Baikov Institute of Metallurgy, Russian Academy of Sciences, Leninsky Pr. 49, 117334 Moscow, Russia

Author's experimental data on the effect of rhenium on the microstructure and some physical and mechanical properties of W-Re alloys, including molybdenum-containing alloys and alloys strengthened by interstitial phases are discussed. On the base of these data as well as on literature data, low-alloyed and high alloyed W-Re-alloys for different operating conditions are developed. Advantages and disadvantages of the vacuum melting and powder metallurgy processes for production of these alloys are discussed. The ways for increase in purity and improve of homogeneous distribution of rhenium in sintered PM-alloys are discussed too. Analysis of numerous experimental data on the effect of plastic deformation and heat treatment on microstructure, fracture mode and mechanical properties of the rhenium alloyed materials shows the possibility to predict mechanical properties of deformed alloys during their thermo-meohanical treatment and for operating in the wide temperature range.

11:10 am

DISPERSION AND SUBSTRUCTURE HARDENING OF Mo-Re BASE ALLOYS: A.N. Tyumentsev, A.D. Korotaev, Yu. P. Pinzhin, Siberian Physical & Technical Institute, Revolution Sq. 1, 634050 Tomsk, Russia

Using the literature and original data on the phenomenon of internal oxidation (IO) in low alloys based on Mo and Mo-47% Re, the basic mechanisms of this phenomenon and the scientifc principles for controlling the parameters of the heterophase structure formed on IO are discussed. On this basis, new methods for dispersion and combined dispersion and substructure hardening of type Mo-47% Re - Zr alloys have been developed and used. These methods provide a depth-uniform distribution of the ZrO2 oxide stable until 2500K and a high recrystallization temperature (2300K). The resulting high-strength state is stable to heat with the large plasticity margin retained. Based on the study of the regularities and mechanisms of the plastic deformation and destruction of internally oxidized Mo-Re-base alloys, the hardening mechanisms with IO and the potentialities of the methods developed for increasing the heat resistance of the Mo-Re-base alloys have been analyzed.

11:30 am

"RHENIUM EFFECT" ON THE IMPROVING OF MECHANICAL PROPERTIES IN Mo, W, Cr AND THEIR ALLOYS: Yu. V. Milman, G.G. Kurdumova, Institute for Problems of Material Science, 3 Krzhizhanovsky Str., Kiev 252180,Ukraine

The current state of science and mechanical properties improving for Cr, Mo and W alloyed by Re (so-called "rhenium effect") is reviewed. The main possibilities for increasing low-temperature plasticity of Cr, Mo and W by Re additions are closely connected with electron structure change during alloying; that is, plasticity is increased when alloying essentially changes the electron structure by disturbing the optimum conditions of the resonance covalent bond and changing the filling of energy bands. The observed growth of the density of electron states at the Fermi level N(EF) is accompanied by lowering of Peierls stress, decrease of staking fault energy ( SFE), increase of activation volume and interstitial solubility, and the involvement of an additional deformation mechanism - twinning. The increase of N(EF) should not be very sharp for SFE and interstitial solubility to have the optimum value. SFE has to be lowered so that twinning can occur, but the mobility of dislocation screw components should not be impeded. Lowering of SFE is accompanied by growth of activation volume and increase of stress relaxation rate at concentrators. The increase of interstitial solubility should be sufficient to diminish the tendency to impurity segregation on dislocations as well as on grain and subgrain boundaries, but not so great as cause the abrupt hardening of a solid solution . The experimental results devoted to the influence of Re additions on the dislocation structure, mechanical properties and fracture mechanisms are discussed.

INTERNATIONAL SYMPOSIUM ON RHENIUM AND RHENIUM ALLOYS: Session XI: Single Crystal Technology--Rhenium and Rhenium Containing Alloys

Sponsored by: SMD Refractory Metals Committee and MDMD Powder Materials Committee
Program Organizer: Dr. Boris D. Bryskin, R&D Manager, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036

Room: 232B

Session Chairpersons: Dr. Amber M. Dalley, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA 15904; R.H. Titran, NASA Lewis Research Center, 21000 Brookpark Road, Mail Stop 49-1, Cleveland, OH 44135

8:30 am

DEVELOPMENT AND TURBINE ENGINE PERFORMANCE OF THREE ADVANCED RHENIUM CONTAINING SUPERALLOYS FOR SINGLE CRYSTAL AND DIRECTIONALLY SOLIDIFIED BLADES AND VANES: Robert W. Broomfield, David A. Ford, Harry K. Bhangu, Rolls-Royce Plc., Derby and Bristol, U.K.; Malcolm C. Thomas, Donald J. Frasier, Phil S. Burkholder, Allison Engine Company (Rolls-Royce plc), Indianapolis, IN; Ken Harris, Gary L. Erickson, Jacqui B. Wahl, Cannon-Muskegon Corporation (SPS Technologies Inc.), Muskegon, MI 49443

Turbine inlet temperatures over the next few years will approach 1650°C (3000°F) at maximum power for the latest large commercial turbofan engines, resulting in high fuel efficiency and power levels approaching 442 kN (100,000 lbs). High reliability and durability must be intrinsically designed into these turbine engines to meet extended over-water, large twin engine aircraft (ETOPS) certification requirements. This level of performance has been brought about by a combination of advances in air cooling for turbine blades and vanes, design technology for stresses and airflow, single crystal and directionally solidified casting process improvements, the development and use of rhenium (Re) containing high y' nickel-base superalloys with advanced coatings, including full-airfoil ceramic thermal barrier coatings. Re additions to cast airfoil superalloys not only improve creep and thermo-mechanical fatigue strength but also environmental properties, including coating performance. Re dramatically slows down diffusion in these alloys at high temperature turbine operation conditions. A team approach has been used to develop a family of two single crystal alloys (CMSX-4. containing 3% Re and CMSX.-10 containing 6% Re) and a directionally solidified, columnar grain alloy (CM 1 86LC. containing 3% Re) for a variety of turbine engine applications. A range of critical properties of these alloys are reviewed in relation to component turbine engineering performance through engine certification testing and service experience. Industrial turbines are now commencing to use this aero developed turbine technology in both small and large frame units in addition to aero-derivative industrial engines. These applications are demanding with high reliability required for turbine airfoils out to 25,000 hours. with perhaps greater than 50% of the time spent at maximum power. Combined cycle efficiencies of large frame industrial engines is scheduled to reach 60% in the U.S. ATS program. Application experience out to a total 2 million engine hours and 28,000 hours individual blade set service for CMSX-4. first stage turbine blades is reviewed for a small frame industrial engine.

8:50 am


The major use of Rhenium is in catalysts primarily in the petrochemical industry. However, due to increased demands in high temperature turbine applications, Re is becoming a critical alloying element primarily in nickel base, single crystal superalloys. As a member of the refractory metal family of elements, Re is a higher cost member, in pat due to the expense associated with production. This paper briefly address the new significance of Re in superalloy applications, where its use was practically non-existent in polycrystalline alloys. Also included is an overview of the raw materials from which Re is processed as well as the production techniques currently in use.

9:10 am

MECHANICAL PROPERTIES OF Mo-Re SINGLE CRYSTALS AND BICRYSTAL ALLOYS: A. Yastrebkov, Yu. Aleynikov, O. Petrova, and Yu. Ivakin, RI SIA "LUTCH", 142100 Podolsk, Moscow Region, Zheleznodorozhnaya 24, Russia

Rhenium influence (at content up to 30 at.%) on the character of the change of the crystal and intercrystalline boundary mechanical properties was studied using single crystal and bicrystal alloy specimens produced by electron beam zone melting. Tensile tests of single crystals were carried out at 20°C, their impact strength was studied at temperatures from -200°C up to +300°C, the depth of microcracks appearing at electrodischarge treatment and hardness was measured. Bicrystal specimens of the alloys having 5,10 and 2Q at.% of Re were tested for impact strength at 20°C, microcrack depth in the crystals and on the intercrystalline boundaries after electrodischarge treatment was studied. Disorientation angle ranges of the twist intercrystalline boundaries were 7-9° and 18-21°. It is shown that alloying strengthens crystals and improve their ductility. Single crystal strengthening has not monotonous nature. Minimum of hardness, ultimate strength and yield strength was observed at 3-4 at.% of Re. The alloying decreases microcrack depth after electrodischarge treatment both in crystals and on the intercrvstalline boundaries however the depth of the last ones is always more.

9:30 am

THE RHENIUM IMPACT ON THE MASS TRANSFER IN Mo-Re SINGLE CRYSTALS UNDER SHOCK LOADING: S.V. Divinski, L.N. Larikov, M.N. Belyakova, V.V. Zholud, V.F. Mazanko, Institute of Metal Physics, National Academy of Sciences, 36 Vernadsky Str., Kiev-142, 252142, Ukraine

An abnormally high depths of marked atom penetration at shock loading have been discovered for Fe and then were observed for a number of metals. In this work, this phenomenon is thoroughly investigated for the Mo-Re single crystals. It was found that Re moderates substantially the mass transfer. The derth of penetration of the Ni-63 isotopes decreases to 17 and 3 percents of that value for pure Mo if the Re content is 10 and 17 at.%, respectively. These results are discussed in a framework of Re impact on generation and migration of interstitials under movement of jugged screw dislocations. Moreover, the Re alloying increases the contribution of twinning to the plastic deformation. A computer model of enhanced mass transfer at shock loading has been proposed and the Re impact was numerically studied.

9:50 am BREAK

10:10 am

STRUCTURE EVOLUTION IN RHENIUM SINGLE CRYSTALS AT ROLLING AND ANNEALING: S.V. Divinski, L.N. Larikov, M.N. Belyakova, V. Rafalovski, Institute of Metal Physics, National Academy of Sciences, 36 Vernadsky Str., Kiev-142, 252142, Ukraine

Structure of Re single crystal with the {0001}<1120> orientation subjected to rolling has been investigated. Initial orientation is unstable and single crystal is transformed to polycrystalline state. This texture evolution has been analyzed by a computer model. A good agreement with experiment has been achieved. Strain dependence of density of the Re crystal reveals abrupt increase at about 22% of strain, although visible cracks at external surface appear only at ~30% of strain. The last value corresponds to pronounced intensifying of the subsequent recrystallization under annealing. Influence of rotational deformation modes have been numerically studied and their substantial impact on axial textures of Re was predicted.

10:30 am

EFFECTS OF THE RHENIUM ADDITIONS ON THE STRUCTURE AND MECHANICAL PROPERTIES OF THE TUNGSTEN SINGLE CRYSTALS: O.A. Bilous, V.N. Minakov, D. Ye. Ovsienko, E.I. Sosnina, V.I. Trefilov, I.N. Frantsevich Institute for Problems of Material Science, Institute for Physic of Metals, 3 Krzhizhanovsky Str., Kiev 252180, Ukraine

The structure and mechanical properties of single crystals W and binary alloys W-Re that were grown by electron beam zone technology with low carbon concentration (10-6÷10-7Torr) in the direction axis <100>±(1÷1.5). The yield stress and the ductile-brittle transition temperature of the W and W-Re single crystals of the specimens that were cut normally to the direction of crystals growing have been determined to be lower than in parallel cut ones. That is determined by dislocation structure anisotropy of single crystals. Alloying tungsten single crystal with rhenium results in considerable decrease of cold brittleness temperature Tb was shown. The most effective are the lowest rhenium concentration. Thus, adding of o.1 at.% Re decreases Tb from -40°C and 4.3 at.% Re only to -60°C in parallely cut specimens, for example. It should be marked, yield stress grows proportionally the rhenium content in alloys.

10:50 am

STRUCTURE AND PROPERTIES STABILITY OF Re-SINGLE CRYSTALS UPON VACUUM ANNEALING AND THERMOCYCLING: G.S. Burkhanov, V.M. Kirillova, Baikov Institute of Metallurgy, Russian Academy of Sciences, Leninsky Pr. 49, 117911 Moscow, Russia; B.D. Bryskin, Rhenium Alloys, Inc., 1329 Taylor Street, P.O. Box 245, Elyria, OH 44036-0245

Electro-beam zone melting was used to grow high purity Re single crystals with different crystallography orientations. Thermo-electrical moving force (t-c.m.f.) of Re-single crystal was found to insignificantly increase upon 4 h vacuum annealing at 2000°C. In this case anisotrophy of Re-single crystal t-e. m.f. substantially increased. Comparison between Re-single and polycrystals showed that electrical properties of single crystal were stable in contrary of that of the polycrystal. Structure, hardness and specific electrical resistivity of Re-single crystal were established to insubstantially increase upon thermocycling (1600-400°C, 300 cycles). Specimens as 5x5 mm2, 100 mm rectangle (with two sides parallel to basic plane) were cut from Re-single crystal ingot. The shape of this specimens was unchanged upon above mentioned thermocycling. Explanation of stability of Re-single crystal and its application were discussed.

11:10 am

USAGE OF EB FLOATING ZONE MELTING FOR PRODUCTION OF RHENIUM ALLOYS WIRE: A.V. Elutin, I.A. Yudin, State Research Centre-State Institute of Rare Metals-GIREDMET, 5 B Tolmachevsky Per., Moscow 109017, Russia

In the eighties in the former USSR some efforts were made to create modern equipment for producing single crystals of refractory metals by electron beam (EB) floating zone melting. Using this EB furnaces, single crystals of tungsten, molybdenum, tantalum, niobium and rhenium were produced. Dimen sions of crystals were up to 35-40 mm in diameter for tungsten and up to 110 mm for niobium. This report contains experimental data in studying process of growing single crystals of rhenium containing alloys based on molybdenum and tungsten, such as Mo48%Re alloys and W-27%Re and polycrystalline as cast rods and bars. It was found that this method is very efficient for producing calibrated bars from these alloys which can be used in wire production without mechanical treatment. This technology provides very high yield of metals.

11:30 am

GROWTH FEATURES OF W-Re SINGLE CRYSTALS UPON PLASMA ARC MELTING: G.S. Burkhanov, V.M. Kirillova, Baikov Institute of Metallurgy, Russian Academy of Sciences, Leninsky Pr. 49, 117911 Moscow, Russia; B.D. Bryskin, Rhenium Alloys, Inc., 1329 Taylor Street, P.O. Box 245, Elyria, OH 44036-0245

Plasma-arc welding was used to grow high purity W-Re single crystals in a wide concentration range (1-20 wt.% Re). Relationship between solidification (growth rate "R", temperature gradient in liquid phase - ''GL', Re concentration - "Co") and growth structure (cellular, dendritic, single- and polycrystalline) of W-Re alloys was determined and shown as "Co - GL/R _"' diagram. Effect of crystallographic instability was discovered for (W-Re) single crystals with [110] and [111] orientation which were changed to preferable [100] growth orientation upon growing. The reason of this orientation and its dynamics were examined. W-Re single crystals of 1st melt were characterized by considerable misorientation of 1st order subgrains from seed to the top of ingot and "striped" microstructure. Such structure and instability of crystallographic growth were examined by concentration undercoolings. The ways for improving of W-Re single crystals structure perfection are suggested.


11:50 am

METHOD FOR PRODUCING HIGH-PURITY RHENIUM FOIL: A.V. Elutin, K.S. Kovalev, T.B. Danilina, State Research Centre-State Institute of Rare Metals-GIREDMET, 5 B. Tolmachevsky Per., Moscow 109017, Russia


Sponsored by: Jt. EPD/MDMD Synthesis, Control, and Analysis in Materials Processing Committee, EPD Process Fundamentals, Aqueous Processing, Copper, Nickel-Cobalt, Pyrometallurgy, Lead, Zinc, Tin Committees, MSD Thermodynamic & Phase Equilibria Committee
Program Organizers: R.G. Reddy, Department of Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, AL 35487-0202; S. Viswanathan, Oak Ridge National Lab., Oak Ridge, TN 37831-6083; P.R. Taylor, Department of Metallurgical and Mining Eng., University of Idaho, Moscow, ID 83743

Room: 231B

Session Chairpersons: R.G. Reddy, Department of Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, AL 35487-0202; J. Hryn, Blvd. 362, Argonne National Labs, 9700 S. Cass Ave., Argonne, IL 60439

8:30 am

A MATHEMATICAL MODEL TO CHARACTERIZE, THE DISSOLUTION OF SULFIDES IN CuCl2-CuCl-FeCl3-FeCl2-NaCl-HCl- H2O SYSTEM: CUPRIC CHLORIDE LEACHING OF SYNTHETIC NiS: R.C. Hubli, T.K Mukherjee, C.K. Gupta, Bhabha Atomic Research Centre, Trombay, Bombay 400085, India, S. Venkatachalam, Department of Met. Eng. and Matls. Sci., I.I.T. Bombay, India; R.G. Bautista, Mackay School of Mines, University of Nevada, Reno, NV 89557

Simulation of sulfide dissolution in cupric chloride media using the partial equilibrium approach has been investigated under different process conditions. The following observations may have a significant bearing on the dissolution behavior: The amount of cupric-chloro-hydroxy complexes is low, <1% of total Cu(II), when the pH of the lixiviant is around 1.5 but increases at lower H+ concentrations. Under aerated conditions the hydrolysis is higher and control of pH during the dissolution process is necessary, the total initial Cu(II) concentration higher than 0.50 M does little to enhance dissolution but may entail a higher loss of "free" copper, the optimum temperature for cupric chloride leaching is around 373-378K (100-105°C) and the presence of small amounts of ferric ion results in increasing the initial rate of dissolution as well as suppressing the hydrolysis of copper.

*Acknowledgments: This investigation forms a part of the INDO-US collaborative research programme supported by the Department of Science and Technology, Government of India and the NSF, USA under NSF Grant No. INT-9103106.

8:55 am

LEACHING OF A CHALCOCITE CONCENTRATE WITH CUPRIC CHLORIDE-OXYGEN: M.C. Ruiz, S. Honores, R. Padilla, Department of Metallurgical Engineering, University of Concepcion, Casilla 53-C, Concepcion, Chile

This work outlines the results of leaching studies on a copper concentrate containing chalcocite (CU2S) and digenite (Cu9S5) with an acid saline solution of cupric chloride oxygenated at ambient pressure. The variables studied included the stirring speed, concentration of cupric ions, concentration of HCl, concentration of chloride ions, oxygen flow rate, temperature and time. The leaching system was found to be very effective for the dissolution of the concentrate. Over 95% of the copper was dissolved in 30 minutes with negligible dissolution of iron. The dissolution of copper increased with the stirring speed up to about 400 rpm and depended little on the total chloride concentration. The oxygen flowrate affected the dissolution of copper only below 0.09 l/min. The concentration of HCl did not influence tile dissolution providing its was sufficient to avoid the precipitation of copper oxychloride. The study of the effect of the temperature showed a maximum in copper dissolution around 90°C.

9:20 am

ELECTROCHEMICAL STUDY OF PYRITE OXIDATION IN CHLORIDE SOLUTION: H.K. Lin, Mineral Industry Research Laboratory, 212 O'Neill Building, University of Alaska Fairbanks, Fairbanks, AK 99775-7240; W.C. Say, Department of Material Science, National Taipei Institute of Technology, Taipei, Taiwan

Pyrite oxidation in chloride solution was investigated with cyclic voltammetry, ac impedance and potential step techniques. The pyrite oxidation in quiescent electrolytes is irreversible and controlled by diffusion. Depression of the semi-circle in the complex plane plot has been explained mathematically based on the concept of the equivalent circuit. When the semicircle is depressed, the mathematical formula indicates that the reaction resistance should be obtained from the intersection of the semi-circle with Z'-axis instead of the semi-circle diameter. The peak charging current densities at 1.10 and 0.90 V vs. SHE obtained from the equivalent circuit coupled with the ac impedance measurements match the peak current densities obtained with the potential step measurements.

9:45 am

LEACHING OF CHALCOPYRITE IN CuCl-NaCl-O2 SYSTEM: R. Padilla, D. Lovera, M.C. Ruiz, Department of Metallurgical Engineering, University of Concepcion, Casilla 53-C, Concepcion, Chile

The leaching behavior of chalcopyrite concentrate in acidic CUCl2-NaCl-O2 solutions was investigated. Experiments were conducted under continuous flow of oxygen at atmospheric pressures. The results indicated that among the variables temperature has the largest influence on the dissolution of chalcopyrite in this medium, and high dissolution can only be obtained at temperatures near the boiling point of the solution. It was also found that the stirring speed did not influence appreciably the dissolution of chalcopyrite and that an increase in the oxygen flow rate in the leaching reactor increased the dissolution of chalcopyrite. The total chloride concentration affects markedly the dissolution of chalcopyrite up to about 4 M. Copper dissolutions of about 85% were obtained in leaching chalcopyrite of size fraction -65+100# Tyler at 100°C in 2 hours.

10:10 am BREAK


Sponsored by: LMD - Reactive Metals Committee
Program Organizers: R.G. Reddy, Department of Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, AL 35487-0202; J. Hryn, Blvd. 362, Argonne National Labs, 9700 S. Cass Ave., Argonne, IL 60439

10:20 am

VAPOR PRESSURE STUDIES OF THE SALT FLUX PHASES: S. Wang, ASARCO Inc., Technical Services Center, 3422 South 700 West, Salt Lake City, UT 84119; R.G. Reddy, Department of Metallurgical and Materials Engineering , The University of Alabama, Tuscaloosa, AL 35487

Physical and chemical properties of the salt flux phase play a significant role in the recycling of UBC and aluminum melting processes. Particularly, the knowledge of several properties such as salt vapor pressure, melting temperature, loss of aluminum, corrosion of refractories are useful for the performance improvements in aluminum industry. In this paper, vapor pressure of sodium and potassium salt fluxes were studied in the pure, binary and ternary systems. The experimental results of vapor pressure studies are presented and the potential application I the industry to the efficiency and the operating advances are discussed.

10:45 am

COMPLEXES OF NIOBIUM (IV,V) IN LiF-NaF-KF MELTS WITH VARYING O2- CONCENTRATIONS: Flemming Matthiesen and Pia Tolstrup, Jensen Kernisk Lab. A, DTU, 2800, Lyngby, Denmark; Terje Ostvold, Institutt for Uorganisk Kjemi, NTNU, Gloshaugen, 7034, Trondheim

The ternary eutectic LiF-NaF-KF (FLINAK) melt at 700°C was used as a solvent for a study of Nb(IV,V)-O-F complexing. The motivation for this study is the electroplating mechanism of Nb from such melts. A 1.8 mol% Nb2O5 solubility is observed in this melt. The dissolution mechanism is K+ +Nb2O5=NbO2Fx1-x+KNbO3(s)+xF-. When Na2O or SrO is added to FLINAK containing 1 mol% Nb(V), a constant concentration of Nb and a concentration of O2- given by the added oxide up to nO/nNb=2 is observed. For 2 < nO/nNb < 3, the NbO2Fx1-x complex reacts to form KNbO3(s). The solubility data of this compound is matched by literature data. By further additions of O2-, this solid reacts to form NbO43- type complexes. When Na2O is added to FLINAK containing 1 mol% Nb(IV), a constant concentration of Nb and a concentration of O2- given by the added oxide up to nO/nNb=1 is observed. Above this ratio some Na2O still dissolves, but an unknown compound precipitates. At nO/nNb=2 the O2- and Nb(IV) concentrations decrease with increasing oxide additions and reaches a minimum at NO/nNb=3 and probably K2NbO3(s) is formed. Up to nO/nNb=3 the melts are coloured, but changes to colourless (white solids when cooled) at nO/nNb>3. A melt containing a complex of the type NbO42- is probably formed at these high oxide concentrations. Na2O is now completely soluble in the melt.

11:10 am

KINETICS OF ERBIUM OXIDE CORROSION IN MOLTEN CERIUM: C. Lensing, D.L. Olson, B. Mishra, Center for Welding, Joining and Coatings Research, Department of Metallurgical & Materials Engineering, Colorado School of Mines, Golden, CO 80401

The compatibility between erbium oxide and molten cerium was investigated to understand the high temperature corrosion mechanisms and to provide kinetic data. High and low density erbium oxide samples were immersed into molten cerium at temperatures ranging from 850 to 975°C for 16 to 128 hours. A parabolic rate dependence for corrosion scale formation was observed as well as an intergranular penetration of cerium into erbium oxide was noted. Activation energy for the complete corrosion process is 38.5 kCal/mole. Two reaction layers formed for the cerium system, viz. cerium oxide particle layer and a layer of erbium oxide-cerium oxide solid solution.

11:35 am

DEVELOPMENT OF PROCESSING METHODS FOR STAINLESS STEEL-ZIRCONIUM NUCLEAR WASTE FORMS ALLOYS: S.M. McDeavitt, D.P. Abraham, Argonne National Laboratory, Chemical Technology Division, 9700 South. Cass Avenue, Argonne, IL 60439

Stainless steel-zirconium waste form alloys are being developed at Argonne National Laboratory for the immobilization of metallic materials left behind following the electrometallurgical treatment of spent nuclear fuel. The metal waste form comprises fuel cladding, noble metal fission products (e.g., Ru, Rh, Pd, Zr, and Tc), and other metallic constituents. These metallic wastes are not generated in the electrorefiner; they are present with the spent fuel before treatment. The nominal compositions stainless steel- 15 wt% zirconium and zirconium-8 wt% stainless steel are the baseline alloys for stainless steel-clad and Zircaloy-clad fuels, respectively. The selection process for the baseline compositions will be described and the subsequent development of basic alloying procedures will be reviewed (e.g., alloying temperatures, molten metal containment, and heating method). Other process-related issues still under development include microstructural refinement through annealing and molten salt fluxing for surface purity and composition control.

RECENT ADVANCES IN FRACTURE--A Symposium Dedicated to Emeritus Professor Frank A. McClintock: Session VII: Fracture at High Temperature

Sponsored by: MSD Flow and Fracture; SMD Mechanical Metallurgy Committees
Program Organizers: Dr. R.K. Mahidhara, Tessera Inc., 3099 Orchard Drive, San Jose, CA 95134; Dr. A.B. Geltmacher, Naval Research Laboratory, Code 6380, 4555 Overlook Drive SW, Washington DC 20375; Dr. K. Sadananda, Naval Research Laboratory, Code 6323, 4555 Overlook Drive SW, Washington DC 20375; Dr. P. Matic, Naval Research Laboratory, Code 6380, 4555 Overlook Drive SW, Washington DC 20375

Room: 314A

Session Chairpersons: Professor Amiya K. Mukherjee, Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616; Professor Kenji Higashi, Department of Mechanical Systems Engineering, Osaka Prefecture University, Sakai, Osaka, Japan

8:25 am INVITED

MODELLING OF CREEP CRACK GROWTH: George R. Webster, Department of Mechanical Engineering, Imperial College, London, SW7 2BX, UK

Failure in high temperature components which suffer creep can occur by net section rupture, crack growth or some combination of both processes depending on the loading conditions. Failure by crack growth is most likely to occur from sites of stress concentration or in components which contain an initial defect. In many practical situations, cracking is preceded by an incubation period, or at least a transient region of very slow growth, prior to the onset of steady state behaviour. This transient region can occupy the majority of life and it is important that it is taken into account to obtain reliable lifetime predictions. In this presentation non linear fracture mechanics concepts will be used to predict the behaviour. A model involving the build up of damage in a process zone at a crack tip will be employed to describe an incubation period, the transient region and steady state crack propagation rates. The role of superimposed fatigue loading will be examined. The analysis will be applied to characterize high temperature crack growth in polycrystalline, directionally solidified and single crystal materials.

8:50 am INVITED

INTERFACIAL DECOHESION FROM SURFACE - ABSORBED EMBRITTLING ELEMENTS: R.C. Muthiah1, Y. Xu2, C.J. McMahon1 and J.L. Bassani2, 1Department of Materials Science and Engineering; 2Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA

Motivated by problems in high-temperature cracking in superalloys exposed to an oxidizing environment, McClintock and Bassani (1981) developed a model that considered the diffusion along a grain boundary due to a concentration gradient alone and the resulting decohesion in the presence of the time-dependent crack-tip stresses. More recently, Bika and McMahon (1995) extended their ideas to include the influence of the crack-tip stress gradient on the diffusion process. In this paper we develop a model where diffusion is driven both by concentration and stress gradients while those stresses are directly influenced by cracking process. The formulation utilizes a cohesive zone model that couples creep deformation, diffusion, and damage ahead of a crack to predict the cracking due to dynamic embrittlement. This cracking process is being studied experimentally in systems in which the surface-active embrittling element comes either from the material itself, i.e., from surface segregation, or from the surrounding atmosphere. Both polycrystalline and bicrystal specimens are being employed. We have found that a precipitation-hardened copper-beryllium alloy makes an ideal model material for the study of stress-driven oxygen-induced embrittlement in high-strength alloys. The effect of varying the diffusion coefficient as function of direction in bicrystals is being investigated in a copper-tin alloy, in which the embrittlement comes from surface-segregated tin.

9:15 am INVITED

STRESS INDUCED ELECTRICAL FIELDS AND THEIR INFLUENCE ON HIGH TEMPERATURE FRACTURE IN CERAMICS: Rishi Raj, Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853

High temperature fracture in ceramics is nearly always controlled by the nucleation and growth of intergranular cavities. The mechanism of growth is stress induced diffusion of point defects. In ceramics the point defects are charged and therefore, their movement can be influenced by local electrical fields. Internal fields can arise near interfaces as a result of net segregation of charged defects to the interfaces. These electrical fields can, in turn, change the defect concentration, thereby, the self diffusivity in the nanoscale region adjacent to the interface. I will discuss, and present results from fundamental experiments that show how these fields can be influenced by applied stress and how these fields participate in the fracture kinetics. Further consideration leads us to speculate on the use of externally applied electrical fields to control nucleation and growth of cavities at grain boundaries.

9:40 am INVITED

CRITICAL ASSESSMENTS OF CAVITATION FAILURE PROCESS IN HIGH STRAIN-RATE SUPERPLASTIC MATERIALS: Kenji Higashi1, M. Mabuchi2 H. Iwasaki3, 1Department of Mechanical Systems Engineering, Osaka Prefecture University, Gakuen-cho, Sakai, Osaka 593, Japan; 2National Industrial Research Institute of Nagoya, Hirate-cho, Kita-ku, Nagoya 462, Japan; 3Department of Materials Science, Himeji Institute of Technology, Shosha, Himeji, Hyogo 671-22, Japan

A new accommodation process for high-strain rate superplastic flow is analyzed from a viewpoint of the relaxation of stress concentrations at triple junctions of grain boundaries for the alloys and around reinforcement particles for the composites resulting from sliding at boundaries and interfaces. A special process by an accommodation helper such as a liquid phase is required to continue superplastic flow when the stress concentration is insufficiently relaxed by diffusional flow and/or diffusion-controlled dislocation movement under the given deformation conditions. A liquid plays an important role as an accommodation helper in the accommodation mechanisms of high strain-rate superplasticity, that is, in an assistance to relax stress concentrations caused by sliding. However, the presence of a liquid phase does not always lead to the high strain-rate superplasticity. The critical conditions such as optimum distribution, thickness and volume in liquid phase are discussed based on the observation results by transmission electron microscopy and cavitation behavior. Cavitation behavior at various conditions for liquid phases are investigated by a quantitative analysis for high strain rate superplastic materials. It is suggested from theoretical analysis that diffusion-controlled cavity growth is limited and the plastically-controlled cavity growth is dominant when stress concentrations at triple junctions of boundaries and around reinforcements are relaxed by the presence of a liquid phase, so that the cavity growth is significantly slow in a small cavity size range. This view was in agreement with the experimental data of the cavity growth rates.

10:05 am INVITED

ROLE OF DIFFUSIONAL RELAXATION IN FRACTURE OF ALUMINUM MATRIX COMPOSITES DURING CREEP AND SUPERPLASTICITY: Rajiv S. Mishra and Amiya K. Mukherjee, Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616

Reinforcement of metallic matrix with second phase ceramic particles can lead to significant increase in creep strength. Some of these composites also exhibit high strain rate superplasticity. The diffusional relaxation of stresses during creep and superplastic deformation plays an important role. For example, the creep fracture behavior depends on the diffusional relaxation rate. Diffusional relaxation models can be used to calculate the critical creep rate. Below the critical creep rate intergranular fracture is observed, whereas above the critical creep rate transgranular fracture is observed. These observations can be explained on the basis of metal/ceramic interface decohesion. The importance of early onset of interfacial cavitation in the analysis of creep data to obtain mechanistic interpretation is discussed. The change in high strain rate superplasticity mechanism with the size of reinforcement is also explained using the diffusional relaxation models.

10:30 am BREAK

10:40 am

CREEP FRACTURE DURING SOLUTE-DRAG CREEP AND SUPERPLASTIC DEFORMATION: Eric M. Taleff*, Donald R. Lesuer** and Chol K. Syn**, *Department of Aerospace Engineering and Engineering Mechanics, The University of Texas, Austin, TX 78712; **Manufacturing and Materials Engineering Division, Lawrence Livermore National Laboratory, Livermore, CA 94550

Creep fracture has been studied in Al-Mg and Al-Mg-Mn alloys undergoing solute-drag creep and in micro-duplex stainless steel undergoing superplastic deformation. Failure in these materials can be controlled by two mechanisms, neck formation and cavitation. The mechanism of creep fracture during solute-drag creep in Al-Mg is found to change from necking-controlled fracture to cavitation-controlled fracture as Mn content is increased. Binary Al-Mg material fails by neck formation during solute-drag creep, and cavities are formed primarily in the neck region due to high hydrostatic stresses. Ternary alloys of Al-Mg-Mn containing 0.25 and 0.50 wt pct Mn exhibit more uniform cavitation, with the 0.5Mn alloy clearly failing by cavity interlinkage. Failure in the micro-duplex stainless steel is controlled by cavity growth and interlinkage during superplastic deformation. Cavitation was measured at several strains, and cavitation is found to increase as an exponential function of strain. An important aspect of cavity growth in the superplastic stainless steel is the long latency time before cavitation occurs. For a short latency period, cavitation acts to significantly reduce ductility below that by neck growth alone. This effect is most pronounced in materials with high strain-rate sensitivity, for which neck growth occurs very slowly.

11:05 am

FAILURE BEHAVIOR OF DUCTILE LAYERS IN LAMINATED COMPOSITES: S. Bulent Biner, Ames Laboratory, Iowa State University, 208 Metals Development Building, Ames, IA 50011

In this study, the failure of the ductile layers from collinear, multiple and delaminated cracks that occur in laminated composite systems was studied using a constitutive relationship that accounts for strength degradation resulting from the nucleation and growth of voids. The results indicate that in laminated composites, void nucleation and growth ahead of cracks occur at a much faster growth rate due to evolution of much higher stress values at the interface region. Except for short crack extensions, collinear and multiple cracks develop crack resistance curves similar to that seen for a crack in the ductile layer material as in homogenous isotropic cases. For delaminated crack cases, the fracture behavior is strongly influenced by the delaminating length. The resistance of the ductile layers to crack extension can be significantly reduced by short delamination lengths; however, for large delamination lengths the resistance to crack extension becomes greater than that seen for the ductile material.

11:25 am

HIGH TEMPERATURE CRACK GROWTH UNDER MIXED-MODE CONDITIONS: William E. Churley and James C. Earthman, Department of Chemical and Biomedical Engineering, University of California, Irvine, CA 92717

Results from finite element analyses have long been used to model high temperature crack growth processes beginning with the pioneering work of Bassani and McClintock. Recently, finite element results have been used to to study the mechanisms of high temperature crack growth under mixed-mode loading. Experimental studies of this failure process in high temperature alloys and intermetallics have been performed by measuring crack growth direction and crack growth rate in specially designed specimens under Mode I, Mode II and a range of mixed-mode loading conditions. The focus has been on how certain multiaxial stress parameters determined from finite element results can be used to predict both the crack paths and crack growth rates observed experimentally. This approach has led to a better understanding of the dominant crack growth processes in the high temperature materials investigated.

11:45 am

ON VOID GROWTH IN VISCOPLASTIC SOLIDS UNDER CREEP-FATIGUE CONDITIONS: Raj Mohan and F.W. Brust, Engineering Mechanics Department, Battelle Memorial Institute, Columbus, OH 43201 USA

The growth of intergranular voids in elastic-viscoplastic solids is studied using an axisymmetric micromechanical model. Numerical unit cell calculations are performed under remote slow as well as fast cyclic loading. Among the many issues examined include the effect of initial void shape, the effect of on boundary diffusion, the effect of primary creep mechanism, the effect of stress triaxiality as well as the role of elastic accommodation. The results of the study demonstrate that the void growth history and void shape evolution are significantly affected by stress triaxiality, material nonlinearity and initial void shape. The importance of accounting for primary creep mechanism, in addition to secondary creep (power-law creep) is demonstrated for cyclic loading conditions. The analyses shed some light on experimentally observed peculiar behavior under balanced cyclic loading.

12:05 pm

TWO PARAMETER CHARACTERIZATION OF CRACK TIP FIELDS UNDER THERMOMECHANICAL LOADING: Noel P. O'Dowd, Department of Mechanical Engineering, Imperial College, London, SW7 2BX, United Kingdom

Two parameter approaches (K-T, J-Q) have been used to account for constraint and geometry in fracture under mechanical testing. This paper examines the effect of thermal loading on the near tip constraint. Finite element analyses of representative thermal loading which give rise to high and low constraint fields (high and low T and Q) have been conducted. As in previous analyses linear elastic, power law hardening materials have been examined. Following the thermal loading the structure is subjected to mechanical loading, both tension and bending dominated to assess the effect on the near tip constraint. On subsequent mechanical loading it is observed that the two parameter structure of the fields is maintained and the values of Q stress have been obtained from the analyses. The thermal loading initially has a strong effect on the Q value but at higher loads when the mechanical loading dominates, this effect is much weaker. The ability of a combined thermo-mechanical T stress approach to characterize the variation in constraint is assessed.

12:25 pm

HIGH TEMPERATURE FRACTURE OF 6061/Al2O3 MMC'S DEFORMED AT HIGH STRAIN RATES: P. Ganguly and Warren J. Poole, Department of Metals and Materials Engineering, The University of British Columbia,, 309-6350 Stores Road, Vancouver, B.C., V6T 1Z4 Canada

The deformation of the particulate reinforced metal-matric composites (PRMMC) at high temperatures and high strain rates is of critical importance for a number of industrial forming applications, such as hot rolling and hot extrusion. The ductile fracture mechanism in this regime is the classic void nucleation, growth and coalescence, with the void nucleation arising from particle fracture or decohesion of the matrix-particle interface. To predict the onset of damage, it is important to be able to estimate the stress and strain states in and around the reinforcing particles. However, the situation is complicated by relaxation processes in the matrix, which tend to lower the stresses in the particles and at the matrix-particle interface. Furthermore, at large volume fractions (>0.25), the interaction between adjacent particles becomes significant resulting in substantially larger hydrostatic stresses which can aid or deter the formation of the voids depending on whether the hydrostatic stresses are compressive or tensile. The present work aims at studying the failure of PRMMC at high temperature (200°C to 550°C) and moderately high strain rates (0.1 to 10 s-1). Collar compression testing will be used to evaluate the ductility of these materials. The deformation of the macroscopic sample (i.e. w/o the explicit presence of the particles, but with the mechanical properties of the composite) has been modelled using the FEM code ABAQUS. The deformation at the particle length scale has been then determined by imposing the boundary conditions from the macroscopic model on a unit-cell FEM model with single or multiple particles. Metallographic examination of the fracture sites has also been conducted to aid the interpretation of the fracture mechanism.

12:45 pm

ON THE MECHANISMS AND TOUGHNESS OF DUCTILE FRACTURE: Alexander D. Vasilev and S. A. Firstov, Francevich Institute for Problems of Materials Science, 3 Krjijanivskoho str., Kyiv-142, UA-252680, Ukraina

The mechanism of ductile fracture of metallic and some ceramic materials subjected to uniaxial and bending loading in a wide temperature range as well as fracture toughness, and its temperature and structural dependencies are discussed. The main instrument that was used to formulate the ductile fracture mechanism was scanning and transmission electron microscopy of single and polycrystalline, and strengthened by particles, materials. On the basis of study of fracture surfaces of pre-deformed pure particleless materials, the mechanisms of void nucleation, growth and coalescence of voids was found. The pore in particleless materials nucleate along the boundaries of dislocation cellular structure that formed in a course of deformation preceding fracture. The nucleation of pores and subsequent delaminations along the cell and grain boundaries is the main reason of the fracture toughness increase of pre-deformed materials. With the longitudinal cleavage technique it is shown that the intergranular pores nucleate first of all. The decrease of grain size promotes to the transition from cleavage to ductile, by void coalescence, fracture. In materials strengthened with particles there is the temperature region where particles, even with weak interface, do not play the preferable sites of pores nucleation. In those materials, two kinds of ductile, by void coalescence, fracture mechanism may be determined. It is shown that the same mechanism of pores nucleation is valid in ionic (NaCl) single crystals but at temperature above 0.6 of melting temperature. In partially stabilized zirconia single crystals some dislocation plasticity arises at temperature above 1300°C and results in delaminations along interdomain boundaries that points out the same mechanism of pores nucleation. In silicon nitride ceramics the dimple-like, the so-called foam-like, fracture may be found as a result of decomposition of silicon nitride into silicon oxide and gases at temperature above 1000°C. To estimate the fracture toughness of materials failed by ductile manner, the formula: where is the yield stress, is the elastic modulus and is the diameter of the dimples, is proposed. It is shown also that toughness of ductile fracture decreases with temperature and is proportional to the root square of the yield stress. All the conclusions are proven using fractographical data.


Sponsored by: MDMD Shaping and Forming Committee, Jt. EPD/MDMD Synthesis Control & Analysis in Materials Processing Committee
Program Organizer: Dr. Prabir K. Chaudhury, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA, 15904; Prof. Enrique J. Lavernia, Department of Chemical Engineering and Materials Science, University of California, Irvine, CA

Room: 330B

Session Chairperson: Dr. D.J. Chellman, Lockheed Martin Aeronautical Systems, Marietta, GA 30063

8:30 am KEYNOTE


Advanced materials produced by the Osprey Process are satisfying an ever wider range of applications. The driving force for process substitution may be either cost, property improvement or novel materials which are unobtainable using any other production route. This paper will discuss examples of spray-formed materials in the aerospace, automotive, metal processing and electronic industries. In each case, the reasons for the successful commercial application of the materials will be discussed. In addition, details of the requirements for large-scale production of spray-formed alloys and process developments to reduce costs and improve product reproducibility will be given. Post processing of the as-sprayed products to satisfy customer requirements will also be covered.

9:00 am

NAVY RESEARCH AND DEVELOPMENT IN METAL SPRAY FORMING: Richard Rebis, Materials Engineer, Naval Surface Warfare Center, Carderock Division (NSWC-CD), Code 6120, Bethesda, MD 20084-5000; Craig Madden, Director, Manufacturing Programs, NSWC-CD, Code 7206, Bethesda, MD 20084-5000; Patricia Mahoney, Mechanical Engineer, NSWC-CD, Code 7220, Bethesda, MD 20084-5000

The Metal Spray Forming Technology Group of the Naval Surface Warfare Center, Carderock Division (NSWC-CD) has conducted research in support of Navy and private industry programs. In the spray forming process, a liquid stream of molten metal is atomized into a spray of semi-solid, semi-liquid particles and the metal spray is subsequently collected onto either a cylindrical or flat substrate that is rotating and translating underneath the spray. Spray forming produces a characteristic fine equiaxed, nearly-full dense microstructure in a near net shape product which can be subsequently processed. NSWC-CD has both non-reactive and reactive metal (titanium) R&D spray forming facilities. The non-reactive facility has a 300 lb. Melt capacity and is used to produce nickel, steel, or copper alloy parts. Over 380 runs have been conducted on this R&D plant since 1988. This facility is also used to produce prototype parts in support of the Navy Manufacturing Technology spray forming plant, which is currently operated by Babcock & Wilcox. In 1995, NSWC-CD installed a Reactive (Titanium) Metal Spray Forming Facility. The facility utilizes cold wall "skull" induction melting to produce up to 75 pounds of molten titanium (7000) cm3, 424 in3) for spray deposition. Recent results from both plants will be presented.

9:20 am

PLASMA SPRAY FORMING OF COMPOSITES: APPLICATIONS AND MARKET ANALYSIS: R.S. Thakur, Materials Procurement Division, Hindustan Motors Company, Indore, India; M. Sisodia, M.K. Bhargava, Dept. of Metallurgical Engineering, Malaviya Regional Eng. College, Jaipur, India 302017

Plasma Spray Forming is a droplet deposition method which involves the steps of melting, rapid solidification, and consolidation into a single operation. The advancement of technology enables the processing a wide range of metals, intermetallics, and ceramic matrix composites. The advent of Vacuum Plasma Spraying (VPS), which has opened a new dimension in Plasma Spray Forming of these materials, is outlined. The main considerations are being given to fiber reinforced metal matrix composites (MMCs) and ceramic matrix composites for their potential uses in different industrial fields, especially in making automotive engine components like pistons, cylinder liners etc. A brief case study specifically based on its annual production, cost factors, and marketing survey are discussed at length.

9:40 am

THE INFLUENCES OF AGING PRACTICE ON THE MICROSTRUCTURE AND TENSILE PROPERTIES OF SPRAY CAST Al-3Li-1Cu-0.6Mg-0.3Zr ALLOY SHEET: D.L. Yaney, Lockheed Martin Missiles and Space, Palo Alto, CA 94304; D.J. Chellman, Lockheed Martin Aeronautical Systems, Marietta, GA 30063

A spray cast aluminum-lithium alloy with nominal composition Al-3Li-1Cu-0.6Mg-0.3Zr (wt.%) has been successfully processed into 0.090 in. thick sheet. Following solutionizing at 540° C, selected combinations of quenching, stretching and aging treatments were evaluated in terms of their effect on the tensile properties of the final sheet product. Transmission electron microscopy was used to characterize the microstructural changes introduced by variations in aging practice. Although the maximum attainable yield strength was observed to increase with decreasing aging temperature, the double aging treatment of 3 hours at 170°C followed by 26 hours at 190°C, originally investigated by Gregson and Flower for similar direct chil cast Al-Li alloys, was shown to be effective in minimizing the in plane anisotropy frequently observed in Al-Li-Cu-Mg-Zr sheet products.

10:00 am BREAK

10:20 am

PROPERTIES OF SPRAY FORMED NON-HEAT TREATABLE ALUMINUM ALLOYS: M.F. Amateau, H. Patts, T.J. Eden, The Pennsylvania State University, Applied Research Laboratory, P.O. Box 30, North Antherton Street, State College, PA 16804

Non-heat treatable aluminum alloys rely on a combination of solid solution hardening and plastic deformation to achieve usable strength. The Al-Mn and Al-Mn-Mg alloys (3000 series) are used in applications requiring a high degree of deep drawing capability. Improved formability an drawability require high degree of ductility which depends upon rolling texture, recrystallization texture, grain size uniformity, and grain morphology. Spray metal forming produces a very fine and controlled starting microstructure which can have a profound effect on subsequent mechanical working and heat treatments. DC cast and spray metal formed Al-Mn and Al-Mn-Mg alloys were deformed to various amounts after which, microstructure and crystallographic texture were determined via x-ray diffraction pole figures. Subsequent recrystallization treatments were applied to evaluate the effect of the spray formed microstructure on recrystallization texture, recystallization kinetics, grain size, grain uniformity and mechanical anisotropy.

10:40 am

WEAR MECHANISMS IN SPRAY FORMED SILICON-ALUMINUM ALLOYS: D.S. Lee, M.F. Amateau, J.C. Conway, The Pennsylvania State University, Applied Research Laboratory, P.O. Box 30, North Atherton Street, State College, PA 16804-0030

Aluminum-silicon alloys, especially hypereutectic silicon compositions are finding increasing use in automotive components that are subjected to sliding contact. Conventional DC casting methods for processing these alloys result in unsuitably large primary silicon particles for subsequent extrusion and forging. Three spray cast hypereutectic aluminum-silicon alloys were processed to various states of extrusion, heat treatment and over aging. Wear measurements have been performed using the pin-on-ring configuration in the unlubricated condition sliding velocities of 4.46 m/s. The ring mating surfaces were grey iron. As cast B390 aluminum alloy was also wear tested for a standard of comparison. The worn surfaces were examined by scanning electron microscopy, electron beam microprobe analysis, and cross section microscopy to determine the nature and mechanism of wear.

11:00 am

THE USE OF TUNGSTEN BORIDE AS POWDER ELECTRODE MATERIAL FOR ELECTRO-SPARK ALLOYING OF STEELS: S.V. Nikolenko, Institute of Material Science, The Far Eastern Branch of Russian Academy of Sciences, Khabarovsk, Russia

The current development of technology is followed by the more and more complex demands for construction materials. In many cases the use of a combined material that has both the necessary hardness of the base and the high resistance of the outside layer to the environmental factors and wear is most efficient. This can be achieved by applying different kinds of protective coatings. Electro-spark alloying is one of perspective methods of coating deposition. This paper discusses the process of depositing the tungsten boride base composite powder material using a powerful impulse discharge, developed in a semi-closed volume with an electric field, accomplished by interaction of the powder units with the discharge plasma fed into the electrode space in gaseous environment. The process is conducted on a "Rasryad-3A" set, designed for coating with powder electrode materials.

11:20 am

GEOMETRICAL ASPECTS OF THE SPRAY FORMING PROCESS: B. Cantor, Department of Materials, Oxford University, Parks Road, Oxford OX1 3PH, UK

This paper describes a number of geometrical aspects of the shaping, heat flow, and microstructure in materials manufactured by different variants of the spray forming process. In particular that paper will discuss: (i) the transition from an initial chilled structure to a bulk equiaxed structure as spraying proceeds; (ii) the difference between thermal sprayed splat microstructures and incremental solidification; (iii) the effect of steps and other features on the substrate; and (iv) multiple sprays and multipassing with a single spray and their effect on banded structures.

11:40 am

AN INVESTIGATION OF THE CYCLIC FATIGUE AND FRACTURE BEHAVIOR OF SPRAY ATOMIZED AND DEPOSITED ALUMINUM-SILICON ALLOY: S. Anand, T.S. Srivatsan, Department of Mechanical Engineering, The University of Akron, Akron, OH 44325-3903; E.J. Lavernia, Department of Chemical and Biochemical Engineering and Materials Science, University of California, Irvine, CA 92697

In this study an Al-17Si-4.5Cu-0.6Mg was synthesized utilizing the spray atomization and co-deposition technique to modify the distribution of the silicon phase in the alloy matrix. Detailed microstructural characterization studies were done using optical and electron microscopy observations with an emphasis on understanding the influence of spray deposition processing on distribution of the silicon phases in the alloy deposition processing on distribution of the silicon phases in the alloy matrix. Specimens of the aluminum alloy were cyclically deformed under stress-amplitude control over a range of amplitudes. The mechanisms and micro-mechanisms governing cyclic stress response and fatigue life of the alloy will be highlighted, compared with a conventional ingot metallurgy processed counterpart, and discussed. The kinetics governing the cyclic deformation characteristics and fracture processes of the spray processed and conventional ingot metallurgy processed alloys will rationalize in light of mutually interactive influences of microstructural effects, nature of loading, matrix deformation characteristics, macroscopic aspects of fracture, and ductility of the material. *Research supported by National Aeronautics and Space Administration (Langley, Virginia) (Grant Number: NAGI-1619), with material support from Reynolds Company (Richmond, VA).

SYNTHESIS OF LIGHT-WEIGHT METALLIC MATERIALS II: Session VII: Casting, Spray Forming, and Plasma Processing

Sponsored by: MSD Synthesis/Processing Committee
Program Organizers: C.M. Ward-Close, Structural Materials Center, R50 Building, Defense Research Agency, Farnborough, Hampshire, GU14 6TD, United Kingdom; F.H. Froes, University of Idaho, Institute for Materials and Advanced Processes, Mines Bldg 204, Moscow, ID 83844-3026; D.J. Chellman, Lockheed Aeronautical Systems Co., Lockheed Corporation, Marietta, GA 30063-0150; S.S. Cho, Vice President of Rapidly Solidified Materials Research Center, (RASOM), Chungnam National University, Taedok Science Town, Taejon 305-764 Korea

Room: 330F

Session Chairpersons: A.K. Ghosh, University of Michigan, Ann Arbor, MI; J.V. Wood, Department of Materials Engineering and Materials Design University of Nottingham, UK

8:30 am


Very recently the major break-through in spray forming of high performance aluminium has been achieved. After many years of intensive alloy and process development, the first long time volume application could be realised. The use of PM aluminium for cylinder liners in gasoline passenger car engines gives strong improvements in the system of piston, piston rings and liner running surface. Furthermore the engine emissions have been reduced drastically. Based on the progress made with respect to technical and economical aspects this first volume production will have great impact on other application in automotive and aircraft industries or for leisure equipment. The paper describes the state of the art spray forming of aluminium based alloys under technical and metallurgical aspects. Examples will be given several applications in different market sections with functionally relevant test results. Finally the economical situation of spray forming will be discussed in comparison to competitive technologies.

8:50 am

FABRICATION OF LOWER THERMAL EXPANSION ALUMINIUM ALLOYS BY SPRAY-CASING PROCESS: Chong-Sung Park, Hyun-Hp Park, Myung-Ho Kim, R.A.S.O.M., Department of Metallurgical Engineering, Inha University, Inchon 402-751, Korea

Spray-casting process is becoming increasingly attractive as an alternate production route for particulate reinforced metal matrix composites, and the coefficient of thermal expansion (CTE) of the composites can be controlled by altering the level of reinforcement. In this study, performs of Al-Si matrix composites reinforced with SiCp were fabricated by spray-casting process, and the coefficient of thermal expansion (CTE) of the composites were investigated using thermal mechanical analysis (TMA) after hot-extruded. It was found that the CTE of the composite with SiCp reduced with increase in volume fraction of SiC particles, and the Al-Si performs without SiCp also exhibited reduced CTE compared to mold-cast specimen. The effect of the grain and Si phase size, and the aspect ratio of Si phase, as well as the volume fraction of the SiCp on the CTE of the Al-Si composite have also been examined.

9:10 am

PRODUCTION OF CONTINUOUS POLYCRYSTALLINE Al-Cu RIBBONS BY PLANAR FLOW CASTING AND SOLIDIFICATION STRUCTURES: Department of Metallurgical Engineering, Yonseu University, 134 Shinchon-dong, Seodaemun-gu, Scoul, Korea

The geometry and microstructures of ribbons spun by planar flow casting have been investigated as functions of processing parameters adapting various kinds of crucial material and slot design. Microstructural transitions from segregation free zones to cellular/dendrite regions increased with increasing wheel velocity and the superheat of molten metal before ejection. X-ray diffraction spectra indicated an increasing tendency towards a (200) preferred orientation on the wheel-side surface of the ribbon with increasing the superheat of molten metal. A model based on a two-dimensional cellular automaton technique coupled with the control volume method was developed for the prediction of dendrite grain structures in planar flow casting. The calculated grain structures were in good agreement with those obtained from experimentation.

9:30 am

COLUMNAR-EQUIAXED TRANSITION OF SOLIDIFICATION STRUCTURES IN SQUEEZE CASTING: I.S. Cho, C.P. Hong; RASOM, Department of Metallurgical Engineering, RASOM Yonsei University 134 Shinchon-dong, Seodaemun-ku, Seoul 120-749, Korea

The CET(Columnar-Equiaxed Transition) of solidification structures in squeeze casting of Al-Cu alloys was investigated. The interfacial heat transfer coefficient between the casting and the mold was evaluated using an inverse problem method. Solidification sequences in squeeze casting were simulated using the calculated interfacial heat transfer coefficients. The cellular automaton coupled with the control volume method was developed for the predication of solidification grain structures and was applied to evaluate the CET in squeeze casting. The effects of casting process variables, such as pressure, pouring temperature, mold temperature and inoculation on the CET in squeeze casting were investigated. The solidification parameters, solidification rate and thermal gradient at the solidification front, were also analyzed in regard to their effects on the CET. The calculated results were also compared with those obtained experimentally.

9:50 am

SEMI-SOLID PROCESSING OF A356 Al ALLOYS: C.P. Chen, C.-Y.A. Tsao, Department of Materials Science and Engineering National Cheng-Kung University Tainan, Taiwan

A356 Al alloys were synthesised and processed in the semi-solid state. The alloys with a non-dendrite structure were synthesised via electromagnetic stirring in the semi-solid state and then subsequently cast into billet form. The billets with non-dendrite structure were then reheated to semi-solid re gime and isothermally upset-deformed. The effects of the solid fraction during semi-solid deformation, deformation rate, and deformation temperature on the morphology, macrostructure, and stress-strain relationships of semi-solid deformed billets were investigated and compared to those of conventional deformed billets. A phenomenological model was developed to help explain the different behaviours of the semi-solid deformed billets.

10:10 am BREAK

10:30 am

COMPARISON BETWEEN PLASMA PROCESSED NANOCRYSTALLINE Fe AND ITS PRECURSOR IN POWDER AND COMPACT FORMS: Xiaofu Chen, E.G. Baburaj, Wenxian Zhu*, Patrick R Taylor*, F.H. (Sam) Froes, Peter C. Kong+, Institute for Materials and Advanced Processes (IMAP); University of Idaho, Moscow, ID-83844-3026, USA. *Department of Metallurgical and Mining Engineering, University of Idaho, Moscow, Idaho, 83844-3024 USA; +Lockheed Idaho Technologies Company, Idaho Falls, Idaho 83415-2210

Nanocrystalline Fe powder has been produced from 1-4 mm size initial powder, using non-transferred arc plasma processing. Both the processed and initial powders have been consolidated by HIPing at different temperatures to determine the lowest possible processing temperature-time combination which gives rise to full densification. The fine powders and consolidation products have been characterised in detail for particle size, structure and morphology by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and the results have been used as feed-back to improve the processing conditions. The particle size of plasma processed Fe powered is in the range of 10-50 nm. The temperature dependent grain growth of plasma processed and starting Fe powders have also been examined in this study.

10:50 am

STUDY OF MICROSTRUCTURE AND PROPERTIES OF SPRAY FORMED Al-Cr-Zr ALLOYS: A.F. Norman, P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK

The technical problems and cost associated with the multi-step PM processing of RS Al alloys have hindered their successful development. Spray forming can obviate these problems by means of the integral inert gas atomisation and deposition operation in which the alloy exists in particulate form only for a few milliseconds. Spray forming experiments have been performed on Al-Cr-Zr alloys studied previously by the combined RS/PM route. The microstructure and the tensile properties of the forged and heat treated deposits will be compared with the RS/PM alloy. The latter exhibits superior properties, not matched by the spray formed alloy.

11:10 am

EFFECT OF ALLOY ELEMENTS ON THE DAMPING CAPACITY OF SPRAY CAST Al-Zn ALLOY: B.C. Moon, Z.H. Lee, Department of Materials Science and Engineering, RASOM, Kaist, Korea

Damping capacity of a material refers its ability to dissipate vibrational energy into thermal energy. In Al-Zn system, damping originates form the interfacial friction between two phases and the damping capacity is proportional to the interfacial area. The microstructure of spray cast alloys are very different from the cast alloys and the damping characteristics of spray cast Al-Zn alloys is expected to be also different. In this study, the effect of third element on the damping behaviour of spray cast Al-Zn alloys was studied. Al-Zn-X alloys were made by spray cast and mold cast. Third elements were Cu, Mg and Mn. Uniformly rolled cast and sprayed specimens were solution treated then quenched by water. Specimens were aged at room temperature for 24 hours. Damping capacity was measured by logarithmic decrement of freely decayed vibration of cantilever beam. Damping capacity of spray cast alloys was higher than cast alloys. Dilute tried elements increased the hardness but decreased the damping capacity alightly.

11:30 am

PRODUCTION OF CONTINUOUS POLYCRYSTALLINE Al-Cu RIBBONS BY PLANAR FLOW CASTING AND SOLIDIFICATION STRUCTURES: S.M. Lee, K.Y. Lee, C.P. Hong; RASOM Department of Metallurgical Engineering, Yonsei University 134 Shinchon-dong, seodaemun-ku, Seoul 120-749, Korea

The geometry and microstructures of ribbons spun by planar flow casting have been investigated as functions of processing parameters adapting various kinds of crucible material and slot design. Microstructural transitions from segregation free zones to cellular/dendritic regions were obsened in Al-Cu alloys. The thickness ratio of columnar layer increased with increasing the wheel velocity and the superheat of molten metal before ejection. X-ray diffraction spectra indicated an increasing tendency towards a (200) preferred orientation on the wheel-side surface of the ribbon with increasing the superheat of molten metal. A model based on a two dimensional cellular automaton technique coupled with the control volume method was developed for the prediction of dendritic grain structures in planar flow casting. The calculated grain structures were in good agreement with those obtained experimentally.

11:50 am

OPERATING PARAMETERS FOR THE CONTINUOUS UNIDIRECTIONAL SOLIDIFICATION OF A 1% Si ALUMINUM ALLOY DRAWN TO FINE WIRE: M.H. Kim, Chungbuk National University and RASOM, Cheongju Korea; T.S. Song, Chungbuk National University, Cheongju, Korea; H.H. Jo, Korea Academy of Industrial Technology, Incheon, Korea; C.S. Kang, Seoul National University, Seoul, Korea; C.R. Loper, Jr., The University of Wisconsin-Madison, Madison, WI

Previous studies have demonstrated the technique of producing continuous cast, directionally solidified castings of a limited number of alloys. These procedures have been successful when the casting conditions are established so that the solid-liquid interface is maintained outside of the mold by insuring a mold temperature in excess of the liquidus temperature and a solid-liquid interface located near enough to the mold so that the molten metal surface tension is able to support the liquid phase. Rods varying from 3 to 10 mm. (0.12 to 0.39 in.) D. have been successfully cast in this manner. This study has expanded that technique to a 1% Si aluminum alloy, and the casting, and the casting conditions which would enable production of an 8 mm. (0.31 in). D. rod having a mirror surface with a highly longitudinally oriented microstructure have established. Furthermore it was demonstrated that this alloy could be wire drawn, without the need of intermediate recrystallization or stress relief, to produce wires of 0.14 to 0.10 mm. (0.0055 to 0.0039 in) D.


Sponsored by: EPD Copper, Nickel, Cobalt Committee
Program Organizers: Norbert L. Piret, Piret & Stolberg Partners, Im Licht 12, D-47279 Duisburg, Germany; Ivan M. Santos Moraes, Caraiba Metals, Dias D'Avila, Bahia, Brazil

Room: 340D

Session Chairpersons: N.L. Piret, Piret & Stolberg Partners, Im Licht 12, D-47279 Duisburg, Germany; Ivan M. Santos Moraes, Caraiba Metals, Dias D'Avila, Bahia, Brazil

8:30 am INVITED

ASPECTS OF IMPURITIES CONTROL AT CARAIBA METALS ELECTROREFINERY: Jose Luiz Rodrigues Bravo, Caralba Metais S.A.(CMSA), Via do Cobre N° 3700, A.l.O. - Copec, Dias D'Avila - Bahia - Brazil

The production of electrolytic copper with assured quality corresponding to international standards in a conventional electrorefinery of a custom smelter, is a hard and cautious task, if no advanced technologies for selective control of electrolyte impurities are available. The improper control of the amount of As, Sb and Bi in the anode that enter de tankhouse, attributable either to a bad schedule of concentrate input or to the unavailability of clean concentrates from the international market, as well as the lack of means to maintain the suitable level of these elements in the electrolyte together with other operational circumstances, can result in off-grade copper, as well as affect the starting sheet quality chemically and physically. This paper presents in a practical way the relationship between the operational conditions and the cathode and starting sheet quality produced at CMSA, covering the period of the last five years of operation, discusses the technologies available in the market for antimony and bismuth removal and compares the results of testwork, achieved in the laboratories of CMSA, using two resins not associated with patented technologies.

9:00 am


Asarco operates one of the largest individual copper electrorefineries in the world at Amarillo, Texas. The feed is a mixture of anodes from Asarco smelters and copper purchased from various primary and secondary sources. The variation in feed makes it imperative that the refinery practices state-of-the-art quality control to minimize the effects of unwanted impurities. In late 1993, a plant designed to significantly reduce the antimony and bismuth levels in the electrolyte was commissioned. The purification plant uses ion exchange technology in conjunction with a novel stripping system developed by Zeneca Specialties, which permits the recycling of the eluant. Thereby, the extremely high costs of stripping with conventional reagents are avoided. In addition, the environmental impact of treating the eluant for recovery of antimony and bismuth is minimized. This paper outlines the development of the technology and, in particular, describes the operational practices and improvements at Amarillo since the commissioning of the plant.

9:30 am INVITED

BLEED-OFF TREATMENT OF HK-SECONDARY COPPER ELECTROREFINERY: Dr. R.F. Dobner, Huttenwerke Kayser AG, Posffach 1560, D44505 Lunen

After a short introduction of the electrolysis process at HK and explanations concerning the anodes used, the regulation and buffering of bleed will be described and the principles of technology for processing of bleed will be presented. Modernization aspects, especially installation equipment, and the different types of evaporators used will be described in detail. Besides experience made with acid-resistant materials - stainless steel, enamel, plastics - will be reported. Environmental aspects such as water and air pollution will be outlined briefly and in conclusion the quality of products obtained as well as quality control will be presented.

10:00 am BREAK

10:20 am INVITED

PROCESS OPTIONS IN THE TREATMENT OF COPPER REFINERY ELECTROLYTE BLEED: James E. Hoffmann, Jan H. Reimers & Associates USA Co., P.O. Box 420545, Houston, TX

This paper will briefly review the conventional technologies employed for the treatment of copper refinery electrolyte bleed. The distinction between decopperizing and electrolyte purification will be emphasized. The strengths and weaknesses of conventional practice will be reviewed and a number of process options to address the weaknesses of present process technology will be described and evaluated. The effect of process selection upon energy consumption and the environmental aspects of process effluent control will be discussed.

10:50 am

IMPROVING THE QUALITY OF THE NICKEL SULFATE HEXAHYDRATE PRODUCED AT CARAIBA BY APPLYING THE QUALITY FUNCTION DEPLOYMENT METHOD (Q.F.D.): Ivan Marcelo Santos Moraes and Group of Q.F.D., Caraiba Metais S.A., Via do Cobre N° 3700, A.l.O. - Copec, Dias D'Avila - Bahia Brazil, CEP 42800-000

Caraiba Metais has a plant for the purification and the crystallization of the crude nickel sulfate removed from its copper electrolyte purification system. In November 1994, an interdepartmental group was formed to study the Q.F.D method, through its application on the improvement of the quality of the nickel sulfate hexahydrate. The team, formed with representatives of the following areas: production, technology, marketing, sales, maintenance, laboratory and TQC office, had also the task of checking the applicability of the method to other products of the company. This paper describes the main steps such as the survey of customer's demands, the preparation of the quality matrix, the planned and the designed quality and the consequent identification of the engineering bottlenecks. It is also shown how these bottlenecks were studied and solved. The application of the method allowed the team to identify means of increasing the production capacity by 40%, to improve the intrinsic quality of the product (including packaging), and to increase the reliability of the process.

11:20 am

COPPER SULFATE RECOVERY USING FLUIDIZED BED CRYSTALLIZATION: Martin Schranz, Robert J. Farrell, Swenson Process Equipment Inc., 15700 Lathrop Ave., Harvey, IL 60426

Copper sulfate pentahydrate is recovered from the spent etchant waste stream of a printed circuit/wiring board manufacturing facility. The fluidized bed crystallizer contains submerged cooling surfaces (through which a coolant is passed) which are bathed in a stream of air. The air bubbles provide agitation which improve heat transfer, reduce fouling and maintain crystals in suspension. The recently patented fluidized bed crystallization apparatus (US 5,523,064) has significant advantages when compared to a conventional surface cooled crystallizer including capital cost, ease of operation and production of larger more uniform crystals.

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