Room: 315B
Session Chairperson: TBA
8:00 am
PULSED LASER DEPOSITION OF ELECTRONIC CERAMIC THIN FILMS: D.B. Chrisey, J.S. Horwitz, P.C. Dorsey, L.A. Knauss, R.C.Y. Auyeung, U.S. Naval Research Laboratory, Washington, D.C., 20375-5345
Pulsed laser deposition (PLD) is a unique physical vapor deposition technique that is making available high quality thin films of complex, multicomponent materials for the design and fabrication of advanced electronic devices and protective coatings. Single phase and epitaxial thin films can be deposited in situ. by PLD. Recent applications of PLD include high temperature superconductors, ferroelectrics, magnetoresistive materials and ferrites. Ferroelectric thin films grown by PLD are currently being developed into low loss, frequency agile microwave electronics which exploit the electric field dependence of the dielectric constant. More recently, colossal magnetoresistance with DRH/RH=0 ~100,000% has been observed in thin films of rare earth manganites deposited by PLD. These materials have applications in magnetic field sensing and recording as well as electrodes in solid oxide fuel cells and room temperature microbolometers. This presentation will show recent examples applying PLD to high quality electronics ceramic thin films growth for next generation devices.
8:35 am
THERMAL BARRIER COATINGS FOR AIRCRAFT ENGINES--A PRATT AND WHITNEY PERSPECTIVE: S. Bose, Pratt and Whitney, 400 Main Street, East Hartford, CT 06108
The gas temperatures in the turbine section of Aircraft Gas Turbine Engines are hundreds of degrees higher than the melting point of the materials of construction. Exposure to such high temperatures would result in structural failure of the materials from a variety of mechanisms. Yet, in modern engines, the components, generally made a nickel and cobalt based superalloys, survive for extended periods of time. This is accomplished by devising efficient air cooling of the components and by applying Thermal Barrier Coatings (TBCs) to the substrate alloy to reduce metal temperatures to safer levels. Combustor TBCs are processed with air plasma spray (APS) ceramic on APS metallic bond coat. Vanes, exposed to higher temperature and thermal load, require electron beam physical vapor deposition (EB-PVD) ceramic on FE/A1 laminates of different layer thicknesses were produced by PVD. TEM studies showed that as deposited microstructure depends on the ratio of the nominal thicknesses of the FE and A1 layers and on the actual layer thickness. For dfe:da1=0.4mm the microstructure consisted of nanocrystals of Fe/A1 solid solution with A2 or B2 structure and A13Fe. For dfe:dA1»44nm or 2.1mm:0.7mm laminated structures were produced. The laminates consisted of layers of Fe(A2-bcc) and of solid solution of Fe in A1 with B2 (ordered bcc) structure which was formed by interdiffusion between the Fe and A1 layers. Thermodynamic modelling showed that interdiffusion and interface reaction in the as deposited materials are closely related to the overall heat of mixing. The mechanical properties of the laminates will be related to their microstructures low pressure plasma spray (LPPS) bond coat. These TBCs have allowed the components to be operated at high gas path temperatures to meet thrust, efficient and life requirements of Pratt and Whitney's gas turbine engines. Details of Pratt and Whitney's experience on various aspects of TBCs will be discussed.
9:10 am
ANALYSIS OF THERMAL SPRAY METHOD FOR COATING NANOSCALE MATERIALS: Schmuel Eidelman, Xiaolong Yang, Science Applications International Corporation, 1710 Goodridge Drive, McLean, VA
Thermal Spray (TS) system allows delivery of the plating materials to the substrates at high velocities (on the order of 1 to 1.5 km/sec) and high temperatures. The total pressure of the particle impinging on the surface can reach 10 Gpa for some of the TS systems. Lower sintering temperatures and higher ductility of nanoscale materials open a range of attractive and unique possibilities for high rate deposition of nanostructured coatings. We use a recently developed and validated three dimensional simulation capability to model the TS systems' gas and coating powder flow for the TS process analysis, to illustrate the roots of currently used TS systems' inefficiencies, and to optimize and control the coating process. Examples are given for the TS process designs with improved performance and system efficiency. The use of numerical simulation will be especially crucial for the plating with nanoscale powders.
9:30 am
ROLE OF INTERDIFFUSION AND HEAT TREATMENTS ON THE ADHESION OF PLASMA SPRAYED NiCrAlY COATINGS: C.S. Richard, G. Beranger, Universite de Technologie de Compiegne, Department de Genie Mecanique, URA 1505 du CNRS, 60206 Compiegne Cedex, France; J. Lu, Universite de Technologie de Troyes, Department de Genie des Systemes Mecaniques, 10000 Troyes, France
During service blades and vanes of stationary gas turbines are subject to different kinds of loadings like mechanical and thermal stresses as well as corrosion, oxidation and erosion. Against these phenomena, plasma spraying coatings are frequently used to protect the componenets in the hot parts of these engines. The layers are commonly deposited by Atmospheric Plasma Spraying (APS) and by Vacuum Plasma Spraying (VPS). One of the main parameters in quality of a coating is its adhesion on a Ni-based superalloy substrate. This study focused on a NiCrAlY metallic bonding layer and its adhesion on a Ni-based supralloy substrate. It looks at the influence of different spraying methods (APS and VPS) and the influence of a post heat treatment on the adhesion of the coatings. In order to determine the interface toughness, a Vickers interfacial indentation test, based on fracture mechanics method, was performed. In APS and VPS cases, the residual stresses were evaluated by a step-by-step drilling method and these were taken into account in the adhesion parameters. The results were supplemented by a microstructural study of the interface in order to understand the role of interdiffusion on adhesion.
:
9:50 am
PLASMA SPRAYED ZIRCONIA BASED COATINGS FOR USE AS AN INSULATING LAYER IN DIE CASTING: M. Giannos, CAST, CSIRO Division Manufacturing Technology, Melbourne, Victoria, Australia
10:10 am
COATING PHASES OF COMMERCIAL GALVANNEALED COATINGS: Carlos Nelson Elias, Universidade Federal Pluminense, Av. Dos Trabalhadores 420, Vila Santa Cecilia 27260-740 Volta Redonda, RJ-BRAZIL, Jorge Alcala Vera, Institutio Militar de Engenharia, Pr General Tiburcio 80, 22290 270 Rio de Janeiro, RJ
Hot-dip galvannealed steel sheet has been increasingly used in the automotive industry and more recently it has been found that a zinc-iron alloy steel sheet, such as galvannealed would provide even better results. The galvannealed steel sheet is a product with good corrosion resistance, weldability and paintability. Therefore it has been used in the automotive and appliance industries. The properties of galvannealed steel are strongly influenced by the iron content of the coating, especially galling, corrosion resistance, welding and powdering. The galvannealed steel is predominately composed of delta phase. When the soft zeta phase is present in the surface of the coating, it adheres to the die and reduces the performance of steel sheet during deformation. When the hard and brittle gamma phase is at the interface steel-coating , the galvannealed coating fails by powdering. In this work we discuss the formation of Fe-Zn intermetallic compounds in the industrial galvannealed coating.
10:30 am BREAK
10:40 am
RECENT TRENDS IN ELECTROPLATING: Brian Am Manty, Concurrent Technologies Corporation, Johnstown, PA
This paper reports on recent trends and advances in electroplating as a surface finishing technology. It includes a description of environment and worker exposure regulations that have affected the industry. New developments in water and chemical recycling equipment and techniques have substantially reduced the amount of wastes generated during electroplating. Near-zero discharges are now technically and economically feasible for many electroplating shops. Several guidance documents are available to help electroplaters reduce wastes with simple, inexpensive techniques. Alternative electroplating processes and materials are also being developed for processes requiring the use of toxic materials. On-going programs within industry and the government are aimed at reducing the use of cadmium, chromium (hexavalent), lead and cyanide. There is a substantial increase in commercial formulations for alloy electrodeposits, especially where those alloys may be used as a substitute for more toxic coatings.
11:05 am
STRUCTURE AND PROPERTIES OF FUNCTIONALLY THICK CHROMIUM ELECTRODEPOSITS FROM A TRIVALENT ELECTROLYTE - A " GREEN " TECHNOLOGY: Christian E. Johnson, Jasper L. Mullen National Institute of Standards and Technology, Gaithersburg MD 20899
Chromium is widely used as an electrochemically applied coating on metal for wear resistance, to reduce friction, or for a desired appearance. In present commercial electroplating processes, the chromium is deposited from electrolytes in which it is in the hexavalent state. With recent interest in seeking alternatives to the toxic Cr6+, a process has been developed to deposit thick chromium coatings from a non-toxic trivalent electrolyte. The coatings deposited from this electrolyte are an alloy of chromium-carbon-oxygen-hydrogen having an amorphous structure, as-deposited. However, with heat treatment they are transformed to a crystalline structure of chromium carbide in a chromium matrix. The hardness and resistance to wear increase with the transformation of this coating after heat treatment. The structure of the electrodeposited coatings, will be discussed. Property measurements of microhardness, wear and coefficient of thermal expansion will be discussed for the as-deposited and heat treated coatings.
11:35 am
COPING WITH UNINTENDED Cu ENRICHMENT DURING CONVERSION COATING OF MICROSTRUCTURALLY COMPLEX ALUMINUM: R.G. Buchheit, Sandia National Laboratories, Albuquerque, NM 87185
Copper is a major alloying element in engineering aluminum alloys. Cu is concentrated in second phase particles distributed throughout the alloy. The interaction of these particles with conversion coating solutions can result in enrichment of Cu on the treated surface. This enrichment has serious negative consequences on subsequent corrosion and adhesion properties. Direct examination using high resolution SEM shows that in 2024-T# Cu is segregated into large (2-6 micrometer) Al2CuMg particles. During surface finishing these particles experience severe dealloying and produce a fine dispersion of Cu-rich clusters that are distributed across the alloy surface facilitating galavanic corrosion during testing or service. Since redistribution of Cu across the surface is possible without ever oxidizing the Cu, mitigation schemes based on Cu complexing agent additions alone may be inadequate. However, mitigation schemes that utilize a Cu complexing agent and a sufficiently oxidizing solution can successfully prevent Cu enrichment and produce significant improvements in corrosion resistance.
Room: 340B
Session Chairpersons: Prof. Leon L. Shaw, Dept. of Metallurgy and Materials Engineering, University of Connecticut, Storrs, CT 06269; Prof. Carl C. Koch, Dept. of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695
8:30 am INVITED
PROCESSING OF CONTINUOUSLY REINFORCED Ti-ALLOY MMCS BY PHYSICAL VAPOR DEPOSITION: P. R. Subramanian, S. Krishnamurthy, and S. Keller, UES, Inc., Materials and Processes Division, 4401 Dayton-Xenia Rd., Dayton, OH 45432-1894
Fiber-reinforced titanium aluminide composites are of particular interest as candidate materials for aerospace structural applications at moderately high temperatures. Conventional techniques for fabrication of these composites pose many technical challenges, and serve as one of the barriers to the practical use of these composite systems. The present work deals with a novel vapor synthesis route, the matrix-coated fiber process, for producing Ti-alloy metal matrix composites (MMCs). In this process, the matrix alloy is directly deposited on continuous SiC fibers by hollow-cathode magnetron sputtering. The matrix-coated fibers are then consolidated to produce unidirectionally reinforced MMC panels. Details of the processing technique will be presented, along with results on microstructural evolution. Results from room-temperature mechanical evaluation of the MMC specimens will also be presented. This research is funded by the U.S. Air Force as a Small Business Innovative Research Program under Contract No. F33615-94-C-5214 . Program Monitor: Dr. Stephen W. Schwenker, USAF Wright Laboratory, Materials Directorate (WL/MLLM), Wright-Patterson AFB, OH 45433-7817.
9:00 am
COMBUSTION CHEMICAL VAPOR DEPOSITION (CCVD) OF LaPO4 MONAZITE ON ALUMINA FIBERS FOR CERAMIC MATRIX COMPOSITES: T.J. Hwang, M.R. Hendrick, H. Shao, H.G. Hornis, A.T. Hunt, Micro Coating Technologies, 430 Tenth Street, Suite N-108, Atlanta, GA 30318
It has been demonstrated that monazite compounds can serve as an oxidation protection and crack deflecting interface coatings to improve the strength and toughness in oxide-oxide ceramic matrix composite. In this study, lanthanum phosphate LaPO4 (monatize) was coated on alumina fibers (Nextel 610) using the combustion chemical vapor deposition (CCVDSM) method in the open atmosphere. This study has shown that the CCVD is feasible for applying a dense LaPO4 coating while moving the fiber tows through the deposition zone. A systematic stoichiometry study showed that monazite was the predominate phase in the film. Deposition temperatures were controlled to prevent degradation of fibers while maintaining an optimal deposition rate and coating quality. Several interlayer materials were investigated to minimize the reaction and recrystallization of the A12O3 fibers. Since a vacuum chamber is not required for the CCVD process, large scale, continuous coating of fibers is possible.
9:25 am
DENSE TITANIUM MATRIX COMPOSITE MONOTAPE FROM E-BEAM METAL COATED FIBERS: Herve Deve, Metal Matrix Composites Program, 3M Center, Bldg 60-1N-01, St Paul, MN 55144-1000
The high temperature specific strength and stiffness of titanium matrix composites (TMC's) make them very attractive for the next generation of jet engine components. Significant efforts are now underway at 3M to reduce the cost of TMC's; bring them to a production status; and offer the customer a TMC precursor that will be easy to integrate into titanium components. The recent advances in the production of metal coated fibers by electron beam evaporation have allowed the development of continuous dense monotape. Dense TMC monotape will facilitate the fabrication of complex curved parts such as rings. A dense monotape is a single composite ply made by roll-bonding cylindrical metal coated fibers. Continuous roll-bonding allows the low-cost fabrication of TMC tape that do not contain organic binders. Monotapes have been produced that are typically 200 =B5m thick by 10 mm wide and greater than 30 meter long. The flexible composite tape can be easily laid-up on flat or curved parts. Final bonding of the component requires a HIP or diffusion bonding cycle without the complex removal of organic binders. TMC rings with a nearly perfect fiber distribution were fabricated to illustrate the simplicity of use of TMC monotapes.
9:50 am
REACTIVE SPRAY ATOMIZATION AND DEPOSITION OF ALUMINUM ALLOYS: MODELING DISPERSOID VOLUME FRACTION AND SIZE DISTRIBUTION: J.-P. Delplanque, E.J. Lavernia, R.H. Rangel, Department of Mechanical and Aerospace Engineering, Department of Chemical and Biochemical Engineering and Materials Science, University of California, Irvine, California 92697-2575
Reactive spray atomization and deposition combines atomization, chemical reaction and consolidation into a single step. It offers a unique opportunity for in-situ, continuous control over alloy composition and chemical reaction between atomized droplets and reactive atomization gas. During reactive spray deposition a molten alloy is atomized by using a reactive gas mixture. The atomized droplets are subsequently deposited on a substrate. Chemical reactions occur between the matrix material and the reactive gas during both atomization and deposition. By carefully selecting alloying additive and reactive gas combinations on the basis of containing in-situ dispersoids such as carbides, nitrides, and oxides, leading to grain refinement. The volume frac tion and the size distribution of the dispersoids is critical to the grain refinement mechanisms. The primary goal of the present work is to define a model to estimate these characteristics. The materials considered are aluminum alloys while target dispersoids are primarily oxides. These may be obtained by the reaction of oxygen containing atomization gas mixtures with molten alloy droplets or with minor alloy additives which exhibit a high affinity for oxygen. Droplet position and velocity histories are obtained from the numerical solution of the one-dimensional equation of motion. The energy equation inside the droplet is solved numerically using finite-differences to predict the spatially resolved temperature field. The solid/liquid interface progression rate is estimated using a power law. The effect of the dispersiods on the achievable undercooling is included. This model is then used to determine the parameters controlling the volume fraction and the size distribution of the dispersiods.
10:15 am BREAK
10:25 am INVITED
PLASMA SPRAYED MULTI-LAYERED AND FUNCTIONALLY GRADED MATERIALS: H. Herman, Department of Materials Science and Engineering, State University of New York, Stony Brook, NY 11794
Multi-layered (MLM) and functionally graded (FGM) composites display discrete or continuously varying compositions of metals, ceramics and polymers and/or microstructures over definable geometrical orientations and distances. Plasma spray offers a flexible and economic means for producing non-uniform composites and is used to apply layered and graded deposits to enhance the survivability of thick ceramic coatings (e.g., TBCs). These "graded coatings" are primarily applied to reduce CTE mismatch-related failure. The versatility of plasma spray allows the processing of a wide range of high performance materials, including most metals and refractory ceramics, under a controlled atmosphere if desired. Using plasma spray, it is possible to deposit multiple constituents simultaneously, thus providing a unique means of producing FGMs. Plasma spray MLM/FGM production will be discussed and the characteristics and properties of two FGM systems, Ni-Al2O3 and NiCrAlY-ZrO2, will be presented. This research is supported by NIST-Caterpillar Advanced Technology Program and the INEL University Research Consortium.
10:55 am
SPRAY FORMING OF TiB2 REINFORCED GAMMA TITANIUM ALUMINIDE ALLOYS: B. Li, E.J. Lavernia, Department of Chemical Engineering and Materials Science, University of California at Irvine, Irvine, CA 92697-2575
Gamma titanium aluminide composite with a nominal composition of Ti-47Al-2Nb-2Mn + 0.08 wt.% TiB2 was spray formed using a skull melting technique. Microstructure characteristics of as-received and spray formed Ti-47Al-2Nb-2Mn + 0.08 wt.% TiB2, along with the oversprayed powders, were examined by optical microscope and SEM, and rationalized on the basis of numerical analysis.
11:20 am INVITED
SOL-GEL SYNTHESIS OF CERAMIC MATRIX COMPOSITES: E.D. Rodeghiero, E.P. Giannelis, Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853
Sol-gel techniques provided new and powerful means by which to synthesize oxide-based ceramic matrix composites. The advantages of sol-gel approaches relative to conventional powder processing are numerous. First, sol-gel synthesis can achieve extremely fine (nanoscale) microstructures with high degrees of dispersion between the matrix and reinforcement phases. In addition, the chemical compositions of the various phases can be precisely controlled. Furthermore, gel-derived composites are also highly uniform, as a result of eliminating powder mixing and segregation problems. Finally, sol-gel synthesis can reduce consolidation temperatures significantly, leading to more efficient, economical processing. This talk will present the results of our work in synthesizing both Ni/
-Al2O3 metal-ceramic composites and SiC(whisker)/-Al2O3 ceramic-ceramic composites. The unique physical and mechanical properties of these composites in their various forms will be discussed, as well as their potential applications.
11:50 am
NANOCOMPOSITE MATERIALS VIA CHEMICAL ROUTES: Kenneth E. Gonsalves, X. Chen, Department of Chemistry & Institute of Materials Science, University of Connecticut, Storrs, CT 06269
The formation of an AlN/Polyimide (PI) nanocomposite was achieved by the rapid solidification of the precursor suspension, followed by compression molding. Such an approach for nanocomposites exhibits improved homogeneity with ultrafine fillers and allows a tailorable composition and property at the nanoscale level. AlN/PI nanocomposites with an increased ceramic loading up to 50% by volume were attained and their thermal and mechanical properties, along with the compositional effects, were investigated.
Sponsored by: LMD Aluminum Committee
Room: 230D
Session Chairman: Jean Doucet, Alcan International Limited, 1188 Sherbrooke Street West, Montreal, Quebec, Canada H3A 3G2
Program Organizer: F. S. Williams, Alcoa Alumina & Chemicals L.L.C., Point Comfort, TX 77978-0101
8:30 am
REDUCTION OF THE MOISTURE CONTENT IN MRN BAUXITE, BY TREATMENT WITH DEWATERING AID: Carlos Estevam da Silva, Marcos Fernando Dias Moreira, Mineracão Rio do Norte S.A. , Porto Trombetas, PA 68275-000 Brazil; Luis Gustavo Esteves Pereira, Mauro Pinto dos Reis, Nalco Brasil Ltda, Av. das Nacões Unidas, 17891 - 11o. Andar, Sao Paulo, - SP - 04795-100 - Brazil
MRN must sell their bauxite at a maximum of 12% moisture content to avoid paying a penalty. To meet this target it is necessary to mix dried and wet bauxite; however, that mixing is very costly because of the high drying cost. Thus MRN and NALCO BRASH have worked together to develop a chemical program to reduce the moisture content of wet bauxite. A large number of dewatering aid products were tested on a lab scale. Two products were selected and tried in pilot plant scale. Finally the product 95DW121 was selected and tried on an industrial scale. The industrial trial was run for three months in the fine and superfine plants with the results that the bauxite moisture was reduced around three percentage points with a dosage rate of 80 g/t.
8:55 am
BQUANT: COST-EFFECTIVE CALCULATIONS OF BAUXITE MINERALOGY: Frank M. Kimmerle, Frank Feret, Alcan International Ltd., Arvida Research and Development Centre, P. O. Box 1250, Jonquière, QC, G7S-4K8; Barbara Feret, BF Simulation, 3099 St. Patrick St., Jonquière
Routine elemental analysis of the major and minor oxides in alumina-bearing minerals, using modern XRF instrumentation yields better than 0.1% reproducibility at a rate exceeding 100 samples per day. However, the mineralogy required to evaluate the amount of recoverable alumina or other Bayer plant parameters has been far less readily accessible. Empirical fits between elemental composition and simulated plant digests are limited to narrow composition ranges in particular geological deposits. Interpretation of X-ray diffractograms is notoriously slow, influenced by crystallite size, amorphous phases, and preferred orientation effects. Instead, using non-linear programming, the BQUANT software provides quantitative phase analysis based on an elemental mass balance. It can even deal with overburden, clay bottoms and is independent of the exact nature of the geological deposit. Given its rapidity, it is particularly useful for estimating the potential of new deposits. Given its accuracy, it greatly facilitates mine exploitation control.
9:20 am
MONITORING OF HEAT EXCHANGER PERFORMANCE THROUGH THE SCALING FACTOR: Eugènio C. G. Azevedo Jr., Carlos Eduardo A. Batista, Alumar-Consórcio de Alumínio, BR 135 - Km 18, Distrito Industrial de Pedrinhas CEP 65095.050 - São Luis/MA - Brasil
The ALUMAR Refinery was designed to maximize heat recovery, and therefore minimize process steam requirements. Since the increase of alumina production from 0.5 to 1.2 million tons per year, the heat exchangers became a strategic point in the refinery performance. An objective has been to create a tool to improve the performance of the heaters. A continuous method of monitoring individual heaters was developed of calculating the scaling factor using the principles of the heat transfer theory. This paper describes the method and the steps to achieve a significant improvement in the identification and troubleshooting of heat transfer related problems. This method also proved to have a positive effect on the operation and maintenance planning of the heat exchangers in the refining.
9:45 am
THE PRECIPITATION MECHANISM OF SODIUM ALUMINOSILICATE SCALE IN BAYER PLANTS: J. Addai-Mensah, A.R. Gerson, K. Zheng, A. O'dea, R. St. C. Smart, Ian Wark Research Institute, University of South Australia, The Levels, Adelaide, 5095, Australia
During the dissolution of bauxite ores by caustic soda, a serious and unwanted downstream precipitation of sodium aluminosilicate may occur in heat exchangers, due to the presence of silica impurity dissolved in the Bayer liquor. To date, the mechanism of nucleation and growth of scale occurring on heat transfer surfaces is not fully known. This paper presents the results from studies carried out to investigate the mechanism of formation of sodium aluminosilicate scale on metallic surfaces under conditions close to those in alumina refineries. It is shown that the scale formation may involve two aluminosilicate dimorphs: sodalite and cancrinite. The extent of solution desilication and scale growth was observed to be strongly temperature and carbonate impurity concentration dependent.
10:10 am BREAK
10:30 am
ASPECT OF DEEP DESILICATION WITH LIME AGENT: Qingwei Wang, Gengyou Tian Zhengzhou, Light Metals Research Institute, Shangjie District, Zhengzhou City, Henan, 450041, China; Chongyu Yang, Central South University of Technology, Changsha City, Hunan, 410083, China
The formation of hydrogarnet (CAS) with low solubility is the essence of desilication of the sodium aluminate solutions with lime addition. The mechanisms of formation of hydrogarnet were studied. It is indicated that desilication with formation CAS is in a form of SCM-type model, i.e. the unreacted core model for spherical particles of unchanging size. The reaction is controlled by diffusion through outer layer. A mathematical model of the kinetics of the process has been developed.
10:55 am
A STUDY OF DESILICATION OF ALUMINATE SOLUTION WITH HCAC : Peng Zhihong, Li Xiaobin, Department of Metallurgy, Central South University of Technology, Changsha, Hunan, 410083, China
Because the sintering process is very important in the Chinese alumina industry, it is important to understand and improve on desilication of aluminate solutions from the sintering process. This paper presents a thorough study on a new method of desilication utilizing HCAC (4CaO·Al2O3·mCO2·mH2O) both in theory and practice. The reaction thermodynamics and kinetics study reveal the reaction laws during synthesis of HCAC and desilication with HCAC. All levels of tests and applications indicate that the desilication effect of HCAC is superior to lime. It can achieve lower silica concentrations in the purified solution under the same amount of lime addition. At the same target silica concentration it can decrease the amount of lime addition about 44% and reduce the loss of alumina about 30%. The new method has achieved satisfactory results in the plant after replacing the old method of desilication with lime in Shangdong Aluminium Corporation. It sets a new path for sintering processes in China by improving alumina product quality, decreasing energy consumption, and raising the target of technology and economy.
Room: 230A
Session Chairperson: Jerry Johnson, Alumax Inc., Intalco Plant, P.O. Box 937, Ferndale, WA 98248
8:30 am
COMMISSIONING OF ALUSAF HILLSIDE SMELTER REDUCTION POTS: Jean-Paul Aussel, Jean-Claude Frison, Aluminium Pechiney, Licensing Department, BP 7, FR-38340 Voreppe, France; Shaun Kroutz, Gideon Stander, Alusaf Hillside Smelter, P.O. Box 897, RSA 3900 Richards Bay, Republic of South Africa
From the 18th of June 1995 to the 21st of June 1996, Alusaf Hillside Smelter started the 576 AP30 reduction pots of its two potlines. The promising results achieved by the first stabilized pots allowed the Process management team to finely tune the potlines around 310 kA and to achieve current efficiency in excess of 95.5% and energy consumption very close to 13000 kWh/t during the first half of 1996. The results of these first 6 months of operation of the first full potline are discussed. It includes data on the raw materials, the organisation and the training programs of the Reduction Department which were all instrumental in engineering this success. The evolution of the Reduction Process parameters and results described in the paper will be updated for the final presentation with the available data of both potlines.
8:55 am
FROM 110 TO 175 kA: RETROFIT OF VAW RHEINWERK. PART I: MODERNIZATION CONCEPT: D. Vogelsang, I. Eick, M. Segatz, Ch. Droste, VAW Aluminium-Technologie, G.-v.-Boeselager-Str. 25, D-53117 Bonn, Germany
Modernization of the 210,000 tpy VAW Rheinwerk smelter includes installation of point feeder, alumina conveying system, state-of-the-art pot control system and forsees an increase in amperage of up to 175 kA. For the modernized pots, concepts for the potlining as well as for improvements of the busbar system were developed, based solely on computer simulations. For the layout of the potlining a new three-dimensional thermoelectric cell model was applied that allows prediction of side ledge countours as well as heat and voltage balances. Based on this model the choice of semi-graphitic vs. fully graphitized cathode blocks was evaluate with respect to the anticipated increase in system amperage. Temperature fields and side ledge contours predicted are in good agreement with measurements. The busbar system, designed originally for a current load of 110 kA, was improved in a very efficient manner to cope with the higher amperage. Magneto-hydrodynamic simulations predicted and plant measurements demonstrated significant improvements in cell stability and performance.
9:20 am
FROM 110 TO 175 kA: RETROFIT OF VAW RHEINWERK. PART II: CONSTRUCTION & OPERATION: J. Ghosh, A. Steube, B. Levenig, VAW Aluminium AG, Koblenzer Str. 122, D-41468 Neuss, Germany
Construction, start-up and operation of ten retrofitted 165 kA prebaked pilot cells in the Rheinwerk smelter are described. The excellent performance of these pots led to the DM 40 Mill. investment decision to retrofit all three potlines. The hot-change of cells during full potline operation minimizes production losses. The pilot cells are equipped with improved steel shells and lining, modified busbar system and modern pot controller and point-feeding system. To evaluate the most cost-effective solution with best performance, four cells are provided with two point feeders and six cells with three point feeders. The new-developed VAW-ELAS process controlling system with improved algorithms and a user-friendly graphical interface allows system atic surveillance and interpretation of all pot parameters and has a major contribution to the highly improved pot performance.
9:45 am
DEVELOPMENT OF A 200 kA REDUCTION CELL TECHNOLOGY - CD200: Geoff Bearne, Mark Dunn, Comalco Research Centre, P.O. Box 316, Thomastown 3074 Australia; Mike Roberts, Yousuf Ali Mohammed, Head of Technology Development Reduction, Dubai Aluminium Co. Ltd., P.O. Box 3627, Dubai, United Arab Emirates
In 1990, Comalco and Dubai Aluminium Co. Ltd. (Dubai) joined forces to develop a modern high amperage reduction cell design known as the CD200. This technology was aimed at the 190 to 200 kA operating range. It was designed to be compatible with future expansion plans at Dubai as well as at the Comalco managed New Zealand Aluminium Smelters Ltd. (NZAS) plant, while remaining within the scope of the present anode design. The cell incorporated a cathode lining design and alumina feeding technology which had been successfully demonstrated at NZAS. The bus bar system was developed using computer modelling at the Comalco Research Centre (CRC). Dubai provided the financial investment and operational experience as well as improvements in process control strategies. Five cells were installed in Dubai's potline 4 and these have operated since 1991. During the last five years, there have been changes to the bus bar design and cathode lining, introduction of larger anodes and further enhancements of the process control systems and operating practices. As a result, the operational performance and the power efficiency of the prototype cells have met or exceeded all targets. Subsequently, the technology has been selected for expansions at both NZAS and Dubai. NZAS has installed 48 cells to be operated at 190 kA, with commissioning from mid 1996. 2 is installing 240 cells to be operated at 195 kA, with start up scheduled in September 1996.
10:10 am BREAK
10:30 am
AN ANALYSIS OF THE ELECTRICAL PREHEAT TECHNIQUE BASED ON THE START-UP OF THE CD200 PROTOTYPES AT DUBAI ALUMINUM CO. LTD: Mark R. Dunn, Comalco Research Centre, P.O. Box 316, Thomastown 3074 Australia; Q.M.I. Galadari, Dubai Aluminum Co. Ltd., P.O. Box 3627, Dubai, United Arab Emirates
In 1991 the Dubai Aluminum Co. Ltd. And Comalco Research & Technology set up a joint project to develop a 200 kA cell in a facility attached to the end of Dubai's potline 4 (then under construction). One aspect of this project was the development and assessment of a suitable electrical preheat practice, based on Dubai's current methods. This paper reports on the process used and the extensive monitoring that took place during the preheats. The effect of current distribution control was also quantified in terms of cathode temperature variation.
10:55 am
ELECTRIC POWER CONTRACTS AND OTHER FACTORS AFFECTING SMELTER ECONOMICS: Nolan E. Richards, 117 Kingswood Dri., Florence, AL 35630; Helge O. Forberg, 8A Quail Ridge Court, Owensboro, KY 42303
The cost of electric power for smelters varies from less than 15% to more than 35% of operating costs. For a smelter with a high power rate, it becomes important to obtain a premium in the market for finished products, produce a higher proportion of premium grade metal, increase volume supplemented with purchased scrap, reduce other cost factors or negotiate a power contract that would allow power modulation. The large difference in cost of power demand between a peak period, normally between 6 p.m. and 10 p.m., and the no-peak period can give some smelters the opportunity to negotiate advantageous contracts for reductions in demand of 20-30% during the peak period. Provided the smelter can implement the changes necessary in the operating procedures to maintain control of potroom operations during the modulations, the decreased power rate can have a substantial beneficial affect on the plant's economics. Some of the strategies and major changes which could be considered for a reduction plant to improve economics are discussed in this paper.
11:20 am
CAPACITY CREEP - THE HIDDEN POTENTIAL GROWTH OF ALUMINIUM SMELTING CAPACITY: K. J. Driscoll, CRU International, Ltd., London WC1X 0AD, England
Given the lack of firm expansion plans for aluminium smelting capacity over the next few years, many people are expecting a smelter bottleneck to develop towards the end of the century. However, CRU believes that a potential source of capacity growth, which we call "capacity creep", is being ignored. As well as new greenfield and brownfield expansions which might fill the new capacity requirements, incremental production gains at existing smelters can be achieved through lower cost upgrades or improvements in operational efficiencies. Indeed, we believe that such capacity creep has historically added around 0.50-0.75% per year to industry capacity, although many of these capacity increases remain undocumented. This paper will present the results of an extensive study of the potential for growth in aluminium smelting capacity, in which we will review how and where capacity creep has occurred, and show that the potential for further capacity creep remains substantial.
11:45 am
ORGANISATION AND INFORMATION SYSTEMS: WHERE INTEGRATION COMES: S.A. Ferre, Aluminium Péchiney, 235 Avenue Alsace Lorraine, 73007 Chambery Cedex, France; P.W. Cowie, Alusaf Limited, 9 West Central Arterial, P.O. Box 897, Richards Bay 3900, Republic of South Africa
Managing an aluminium plant within a concurrential environment demands a greater use of leading edge technology. This technology is of course related to the smelting process but also deals with the organisation scheme and the information provided. During the engineering phase and the construction phase of the Alusaf smelter, Aluminium Pechiney has provided Alusaf with the AP30 technology and has elaborated an organisation with its SA partner. The design and the construction of the information systems have been done in partnership between AP and Alusaf. The information system is based on the use of the state-of-the-art technology and more important is really designed to fit the organisation and to evolve with it. It is built using the 4 classic levels of the CIM model. It takes advantage of packages as SAP R/3 and Microsoft Office Suite tools for routine processes and uses specific developments defined by AP and is used by Alusaf to implement value-adding processes.
Room: 232A
Session Chairs: S. Viswanathan, Oak Ridge National Lab., Oak Ridge, TN 37831-6083; J. Chun, Dept of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
8:30 am
USE OF IMAGING PYROMETRY SENSOR IN METALLURGICAL PROCESSES: C. Lorenson, Quadtek, 14737 NE 87th St., Redmond, WA 98052
The Spyrometer imaging pyrometer brings a new dimension of imaging capabilities to temperature measurement technology by combining a high temperature video camera with scanning optical pyrometry. This gives operators the ability to observe process conditions while measuring the temperature of virtually any object or region in the field of view. Since the lens tube of the camera can be air or water cooled, it is possible to insert the optical lens tube inside furnaces giving very good view of many different types of metallurgical processes. Specific benefits in process knowledge and maintenance tasks for electric arc melting furnaces, anode furnace and casting wheels, flash smelters, reheat furnaces, and torpedo ladles in different types of metal industries will be discussed.
8:55 am
A COMPUTED TOMOGRAPHY SENSOR FOR SOLIDIFICATION IN METAL CASTING: J. Chun, N. Saka, M.H. Hytros, D. Kim, Dept. of Mechanical Engineering, R.C. Lanza, I.M. Jureidini, Dept of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
We have developed a novel method, using X-ray photons and computed tomography (CT), for distinguishing the solidification front in metal casting processes directly and nondestructively. Depending on the metal, the density of the liquid and solid phases may differ anywhere from 4 to 12%. Computed tomography provides an excellent means of mapping this density difference into a two- or three-dimensional image. Using a Co60 radioisotope and a NaI scintillation detector, CT image reconstruction was performed on pure tin metal in a two-phase state. In addition, CT image reconstruction was done using a 6 MeV linear accelerator and CdWO4 scintillation detector array on pure and alloyed aluminum metals while they underwent solidification. As the speed of the data acquisition and image reconstruction improves, this sensor technology offers the possibility of real-time performance and eventual feedback control for the metal casting process.
9:20 am
LASER ULTRASONIC SENSING OF SOLID-LIQUID INTERFACES DURING BRIDGMAN SINGLE CRYSTAL GROWTH: H.N.G. Wadley, Y. Lu, D.T. Queheillalt, Intelligent Processing of Materials Laboratory, School of Engineering and Applied Science, University of Virginia, Charlottesville, VA 22903
Using a 3-D ray tracing methodology combined with laser ultrasonically measured elastic constant data near the melting point, ultrasonic propagation in cylindrical single crystal bodies containing either a convex or a concave solid-liquid interface have been simulated and used to design new sensing concepts. Ray paths, wavefronts, and time of flight (TOF) of rays that travel from a source to an arbitrarily positioned receiver have been calculated. Experimentally measured TOF data have been collected using laser generated/detected ultrasound on model systems with independently known interface shapes. Both numerically simulated data and experimental results have shown that the solidification (interfacial) region can be identified from ultrasonic transmission TOF data. Ultrasonic sensing in the diametral plane is the preferred sensing configuration. Since convex and concave solid-liquid interfaces result in distinctively different TOF data profiles, the interface shape (convex or concave) can be readily determined from the TOF data. When TOF data collected in the diametral plane are used in a nonlinear least squares algorithm, the interface curvature has been successfully reconstructed and ultrasonic velocities of both the solid and liquid obtained, the reconstruction errors were found to be less than 5%.
9:45 am
EDDY CURRENT SENSORS FOR MONITORING THE NUCLEATION AND GROWTH OF Cd0.96Zn0.04Te BULK CRYSTALS: Haydn N.G. Wadley, K.P. Dharmasena, Bill W. Choi, Intelligent Processing of Materials Laboratory, School of Engineering and Applied Science, University of Virginia, Charlottesville, VA 22903
Non-contact eddy current sensing methods have been developed and applied to Cd0.96Zn0.04Te crystal growth to obtain a better understanding of the melt, solid nucleation, and the growth process. The application of this sensor approach relies on a large difference in liquid and solid electrical conductivities near the melting point and requires knowledge of the relationships between the electrical conductivity, melt composition, and temperature. Using a multi-frequency encircling eddy current sensor, the electrical conductivities of three different Cd1-yZnyTe (y = 0.00, 0.045, and 0.08) alloys were measured as a function of temperature in a laboratory-scale vertical Bridgman furnace. The measured solid and liquid electrical conductivities were then used in electro-magnetic finite element models to analyze the multifrequency responses of eddy current sensor designs during the simulated growth of a crystal. Three eddy current sensors were fabricated and installed in a vertical Bridgman furnace and used to monitor many Cd0.96Zn0.04Te growth runs One sensor was placed in the vicinity of the ampoule tip to detect undercooling/spontaneous nucleation and two other sensors ("absolute" and "differential" designs) placed to monitor the movement/curvature of the liquid-solid interface during crystal growth. The sensor data was used to characterize the initial melt state, detect the onset of nucleation, determine the growth velocity, and identify the shape of the interface.
10:10 am BREAK
10:20 am
ADVANCES IN SENSING COMPOUND SEMICONDUCTOR CRYSTAL GROWTH: J.P. Wallace, Casting Analysis Corp., RT 2 BOX 113, Weyers Cave, VA 24486
Monitoring compound semiconductor crystal growth using multifrequency eddy currents for sensing illustrates some of the extreme problems of measurement and interpretation of that are not often seen in metallic systems monitored through solidification. Using sensor arrays and scanning have produced a qualitative and quantitative basis for understanding some of the high temperature electrical conductivity mechanisms. The implications of these measurements of electrical conductivity variations are important in that they reflect the complex states of stress that will occur on cooling and heat treating following crystal growth. In particular, for the CdTe and the CdZnTe system, the measurements provide some proof of where the changes in majority defect types occur. The complex nature of the melt and the cooling solid coupled with the growth interface data provide a basis for analyzing the major events during growth and cool down.
10:45 am
GAUGING OF HOT TUBE, BAR, AND WELDS BY MULTIFREQUENCY EDDY CURRENT: J.P. Wallace, Casting Analysis Corp., C. Iheagwara, Magnetic Analysis Corp., RT 2 Box 113, Weyers Cave, VA 24486
Refinements in sensor design have produced low-cost rugged elements acting as loops coupled with stable detection hardware. This has allowed direct dimensional gauging of nonferrous and ferrous products above the curie point for absolute dimensions and electrical conductivities independently. The software was developed for the analysis of electrical conductivity profiles in CZ silicon crystal growth, then refined for the monitoring of bar properties, and then tube properties. Since in most metal working operations, speeds at the minimum of a few hundred feet per minute are encountered, the design of the gauge was optimized for a rapid measurement. Independently extracting electrical conductivity provides data in some metal system for determining the temperature of the monitored product. Applications in ferrous heat treatment will be discussed.
11:10 am
A REMOTELY OPERABLE SENSOR FOR PRECISION SURFACE MAPPING USING COHERENT FREQUENCY MODULATED (FM) LASER RADAR: M.M. Menon, R.E. Barry, P.T. Spampinato, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6305; A. Slotwinski, Coleman Research Corporation, Springfield, VA 22150; M.A. Dagher, Rockwell International Corporation, Canoga Park, CA 91303
A coherent FM laser radar based sensor is being developed for remote metrology of plasma facing material surfaces in the International Thermonuclear Experimental Reactor (ITER). The sensor is capable of three-dimensional mapping of the surface under examination, based on a series of precise range measurements. Sub-millimeter accuracy at large ranges (15 m) has been achieved. Other features that are being incorporated include the ability to operate under adverse environmental conditions involving a combination of very high gamma radiation (3x106 rad/h), ultra-high-vacuum (<10-7 torr), and high temperature (200°C). The paper will describe the basic principles of the sensor, together with experimental results obtained with the sensor. The paper will also outline the broad capabilities of the sensor, including its ability for remote rendering of "visual quality" images without the need for any external illumination. Research sponsored by the Office of Fusion Energy, U. S. Department of Energy, under contract DE-AC05-96OR22464 with Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp.
Room: 231A
Session Chairperson: R.S. Kunter, Advanced Sciences Inc., 405 Urban Street, Suite 401, Lakewood, CO 80228
8:30 am
THE USE OF FRACTAL DIMENSION WITH AN AGGREGATION MODEL TO CHARACTERISE COPPER ELECTRODEPOSITION IN THE PRESENCE OF THIOUREA: S.P. Fox, S.A. Godorr, A.W. Bryson, School of Process and Materials Engineering, Private Bag 3, Wits 2050, South Africa
This work is an extension of a previous investigation on the development of surface roughness during electrodeposition of copper. A comprehensive model based on diffusion and migration in a force field together with surface diffusion and sticking probabilities is used to generate profiles which are compared to those produced experimentally. The roughness is characterized by using the technique of fractal geometry which is shown to describe both qualitatively and quantitatively the development of surface morphology during electrodeposition. The work is extended to the deposition of copper in the presence of various concentrations of thiourea. The development of roughness is observed experimentally on the edge of a thin copper disc mounted between two glass plates. This enables photographs to be taken at various stages during growth. The surface outline is digitized using an image analyzer which enables the fractal dimension to be determined as growth proceeds. As expected the presence of thiourea at low concentrations produces a fractal dimension which is closer to unity (i.e. the surface becomes smoother). The original model is modified to include diffusion and migration of thiourea to the surface. It is postulated that the presence of thiourea on a surface site changes the sticking probability of discharged copper ions at this site. This results in increased surface diffusion of the copper, which in turn produces a smoother deposit. Extensive experimental results are presented which show that the model adequately predicts the effect of changes in thiourea concentrations over a wide range of conditions including those that are of relevance in electrorefining practice.
8:55 am
DIRECT RECOVERY OF METALS FROM LOADED ORGANIC SOLVENTS: A REVIEW OF RECENT METHODOLOGIES: L.M. Abrantes, A.P. Paiva, Universidade de Lisboa, Faculdade de Ciências, Departamento de Quimica, Lisboa, Portugal
The application of hydrometallurgical methods to the recovery of metal values from ores and concentrates has been receiving a growing interest, either from researchers or from the mining industry. For the concentration/purification of the relatively low concentrated metallic solutions resulting form the leaching of those raw materials, a well established technique often used is solvent extraction (SX); the loaded organic solvent is then conventionally contacted with a suitable aqueous medium, the metal in its final form being usually recovered form this solution by electrowinning. Methods dealing with the direct stripping of metals from loaded organic extractants have recently been investigated, as an efficient stripping is sometimes difficult to achieve for some solvents. Amongst these innovating processes, the electroreductive stripping (2-phase electrolysis) and cementation (galvanic stripping) must be emphasized, the related research works being cautiously reviewed in the present paper. Particularly, the possibility of use of a 2 phase electrolysis to recover basic and precious metals is more extensively discussed. Examples are given for the recovery of copper and silver from suitable organic media, namely by direct application of an electrical potential to a mixture of a silver loaded organic phase containing Cyanex 471X - obtained by SX - and a stabilized sodium thiosulfate solution. The overall efficiencies of these one-step techniques are analyzed and compared with the results obtained by conventional stripping procedures. The purity of the cathodic deposits is also considered. The recovery of silver by galvanic stripping involving iron and zinc powders is also preliminarly evaluated, using a similar organic solution as described above. The influence of temperature on the efficiency of the process is also studied, either for concentrated or more diluted organic silver solutions. The literature data and the results reported here on the application of both methods for direct metal recovery from organic phases show promising advantages over the conventional procedures, encouraging a research effort to optimize and establish these alternative processes.
9:20 am
KINETICS MECHANISM OF GOLD ELECTROWINNING: J.A. Garcia, Universidad Nacional de San Juan, Argentina, C. Hecker, Universidad de Concepcion, Chile, E. Larenas, Concepcion, Chile
To determine the kinetic reaction mechanism, electrochemical experimental techniques of stationary polarization, linear voltammetry and faradaic impedance were used. Gold electrodeposition experiments were realized using an electrolysis cell, provided by a rotary disk of vitreous carbon and or platinum counter electrode of platinum mesh and reference electrode. Using an automatic measurement system voltammograms and Nyquist faradaic impedance spectra were obtained. In this paper, responses for different cases were analyzed through faradaic impedance criteria, considering several kinds of diagrams obtained. The importance diffusion influence of aurocyanide ions and adsorption as controlling steps previous charge transfer was verified. A model of proposed mechanism is discussed.
9:45 am
AN INVESTIGATION ON GOLD ELECTROWINNING FROM ACIDIC THIOUREA SOLUTIONS: C.M. Juarez, A.J.B. Dutra, Federa University of Rio de Janeiro, Metallurgical and Materials Engineering Program, Rio de Janeiro, Brazil
The use of thiourea as a gold leaching reagent has been extensively studied by many researchers, and it has proved to be promising for some cases as refractory gold ores and electronic gold scraps. Otherwise, the recovery of gold from these solutions did not receive so much attention. In this paper, the electrowinning of gold in acidic thiourea solutions was studied by voltammetry, chronopotentiometry and electrochemical impedance in a conventional three-electrode cell with a rotating disc electrode. These electrochemical techniques can provide valuable kinetic information to electrowinning practice. Results have shown that gold electrowinning should be carried out at low current densities in order to avoid cathode passivation and side reactions, as formamidine disulfide reduction and hydrogen evolution at higher overpotentials.
10:10 am
ELECTROCHEMICAL ASPECTS OF THE DISSOLUTION OF GOLD IN CYANIDE ELECTROLYTES CONTAINING LEAD: D. Mussatti, J. Mager , G.P. Martins, Colorado School of Mines, Department of Metallurgical and Materials Engineering, Golden, CO 80401
The role of lead (Pb), at low concentrations in high pH cyanide electrolytes, on the dissolution behaviour of gold has now been a topic of scientific and industrial concern for over 50 years. The recent paper by Kondos et al at CANMET (1995) attests to this continuing interest and apparent importance. Nevertheless, the mechanism(s) by which this (and other heavy metal) component influences the electrodics of this electrochemical system has still not been unequivocally demonstrated. Instead, several plausible hypothesis, by pioneering researchers in this field, have been advanced and reiterated over the ensuing years. While it is generally accepted, based on electrode potential calculations, that co-reduction of lead on the gold surface may occur due to cementation (contact reduction) the cemented lead has never been characterized. The subject matter is confounded further when sulfide (or hydrosulfide) species are also a consitutent of the electrolyte. The work to be presented re- examines the role of lead and sulfide in this system, by considering the species distribution of these components and by conducting potentiodynamic studies in conjunction with surface analyses of a gold (and lead) electrode.
10:30 am
STUDY ON WASTEWATER TREATMENT OF CHEMICAL PLATING SOLUTION USING RECOVERING PROCESSES: Y. Kumagai, National Institute of Material & Chemical Research, Laboratory of Organic Materials, Tsukuba, Japan; F.A. Souza, Federal University of Minas Gerais, Department of Metallurgical Engineering, Belo Horizonte, Brazil
Electroless plating processes or chemical deposition processes, have been used in many fields such as automobile and electronic industries. These solutions must be disposed or treated even when the components already have high performance and concentrations. Commonly, in these kind of solution among others components, metal ions are in very high concentrations. The cost of the plating process becomes higher and is very difficult to keep the environmental regulations. The main objective of this study was to investigate the ways to recover the bath components, among them, the metal ion, in order to decrease the cost of the process as well as to meet the environmental regulations. Specifically, in this study was investigated the way to recover, from the exhausted bath, the nickel ion, sulfate ion, phosphite ion and organic compounds. In this case, was investigated a solution for electroless for nickel deposition. The metal ion was recovered from the wastewater by chemical plating onto mica powder surface. The phosphite and sulfate ions were recovered from the wastewater by precipitation as calcium salts. The organic acids were recovered by solvent extraction. These recovery process, used for the metal ion, is particularly important because many studies are investigating the use of mica coated with metal in the development of new composite materials.
10:55 am
THE EVALUATION OF FOAMING BEHAVIOUR OF SURFACTANTS FOR ACID MIST CONTROL IN METAL ELECTROLYSIS PROCESSES: A.M. Alfantazi, D.B. Dreisinger, University of British Columbia, Department of Metals and Materials Engineering, Vancouver, B.C., V6T 1Z4, Canada; J. Synnott, M. Boissoneault, Falconbridge Ltd., Kidd Creek Division, P.O. Bag 2002, Timmins, Ontario, P4N 7K1 Canada
Acid Mist Generation is a major concern in zinc, copper and nickel electrowinning industry and there is a strong environmental drive to control its emission in the work environment. Foaming reagents are typically added to the electrolyte to alleviate this problem. In zinc electrowinning, licorice and saponin are examples of foaming reagents used for this purpose. In order for the foaming reagent to be effective, its foaming behaviour must be determined. In this work, a test procedure was developed to study the foaming characteristics of various surfactants for use as foaming agents to control acid mist in aqueous metal electrowinning. This new test was termed a "mini-flotation test" and it was used to study the foaming behaviour of a large number of reagents in an industrial zinc electrolyte under simulated zinc electrowinning conditions (gas sparging). In addition, the influence of important parameters such as current density, electrolyte temperature, reagent addition level and sulfuric acid concentration on the foaming characteristics of the electrolyte for each surfactant were investigated. This study has identified the most important factors that influence foam formation, growth and stability. This method could be used as a process control measure for reagent addition in the cellhouse by generating a calibration curve for the optimum electrolyte conditions.
11:20 am
ELECTROWINNING COBALT FROM SULPHATE SOLUTIONS: K.C. Lenthall, A.W. Bryson, Mintek, Private Bag X3015, Randburg, 2125, Republic of South Africa
The effects of operating parameters on cobalt electrowinning from sulphate solutions were investigated. Experiments were carried out in a divided five-litre cell holding two anodes and a single cathode (150 by 105 mm). The cell was operated in a continuous manner and the catholyte conditions (pH and temperature) were controlled. The following parameters were chosen as a base for the investigation: cobalt feed concentration 90 g/l, catholyte pH 2.5, temperature 65°C, current density 250 A/m2. The feed flow-rate was set to achieve a Co of 30 g/l. The cobalt concentration in the catholyte was varied from 25 to 65 g/l and the current efficiency was found to increase linearly from 90 to 96. Varying the catholyte pH from 2 to 2.75 caused efficiency to increase linearly from 91 to 98%, but above pH 2.75 the rate of increase slowed. Efficiency remained at 95% between 35 and 65°C. Cathodic current density was varied between 150 and 350 A/m2 and did not affect efficiency. Only temperature and catholyte H+ were found to affect the nature of the deposit. Below pH 2.5 many small pits occur. Above this pH, the deposit is shinier and has fewer, though larger, pits. The temperature of the catholyte has a marked effect on the deposit since pitting on the metal decreases dramatically below 50°C. In order to simulate realistic cell behaviour, control of catholyte pH was relaxed. The feed flow-rate was varied from 2.2 to 4.5 ml/min, corresponding to a Co of 30 to 60 g/l. The catholyte pH and cobalt concentration were both found to increase with increasing flow-rate, which caused an increase in efficiency from 82 to 99%. The cell is modeled by considering (i) the transport of H+ across the diaphragm, (ii) the effect of Co and H+ on efficiency using Wark's Rule, (iii) the overall mass balance across the cell.
Room: 230C
Session Chairperson: Lester Mc Coy, Great Lakes Carbon Corporation, P.O. Box "C", Port Arthur, TX 77640
8:30 am
CORRELATION OF COKE PROPERTIES, ANODE PROPERTIES, AND CARBON CONSUMPTION: C.T. Leach, D.G. Brooks, R.E. Gehlbach, Manufacturing Technology Laboratory, Reynolds Metals Company, 3326 East Second Street, Muscle Shoals, AL 35661-1258
Researchers often use calcined coke and anode core properties to predict carbon consumption in aluminum reduction cells. This study compared laboratory analysis data and production data from 1992 through 1995 at RMC's Lake Charles Carbon Company and Baie Comeau Reduction Plant. During this period, carbon plant operations produced anodes with a range of properties using various calcined cokes. The results indicate that calcined cokes having a relatively wide range of properties can produce quality prebake anodes that yield low, stable carbon consumptions. Some coke and anode properties that are considered important quality parameters had little or no detrimental effect on carbon consumption. Correlations exist between certain coke and anode properties during time periods where the properties changed significantly.
8:55 am
QUANTIFICATION OF THE INFLUENCE OF NICKEL ON REDUCTION CELL ANODES: Max Casada, Venco, P.O. Box 577, State Route 2, South Moundsville, WV 26041; Jeff Rolle, A.J. Edmond Co., 1530 West 16th Street, Long Beach, CA 90813; Chris Eppig, Dr. Steve Paspek, BP Oil Company, 4440 Warrensville Center Road, Cleveland, OH 44128-2837; Zeno DeMori, ORMET, P.O. Box 176/State Route 7, Hannibal, OH 43931; Gary Force, BP Oil Company, 200 Public Square, Cleveland, OH 44114; Jaime Mora, Juan Turpial, Venalum, CVG Industria Venezolana De Aluminio, C.A., Zona Industrial Matanzas, Estado Bolivar, Venezuela; David Hester, Conoco Inc., 1000 South Pine, Ponca City, OK 74602; Mirna Chirinos, Francisco Perez, Alcasa, CVG Aluminio Del Caroni S.A., Zona Industrial Matanzas, Estado Bolivar, Venezuela; Julio Velasco, Venco URB Villa Asia, Calle Bombay Manz. 27, #10, Puerto Ordaz, Bolivar, Venezuela; Eli Epstein, Don Pirolo, Venco, 600 N. Dairy Ashford, Houston, TX 77252
The concentration of various metallic compounds in crude oils and in the resulting petroleum coke has continued an upward trend as crude reserves continue to change and tend toward being increasingly heavy and sour. Traditionally labeled as a catalyst, nickel has been included with vanadium in the evaluation of its effects on anode reactivity. In 1995, a Task Force was formed to quantify the influence of nickel on reduction cell anodes as existing information in the literature did not address specifically the affects of varying concentrations of nickel on anodes. The task force prepared resid with identical properties with the exception of nickel content. These resids were then coked, calcined, and formed into anodes in as identical a process as possible. Finally, the anodes were baked and tested to determine the effects on their performance characteristics. The results and conclusions drawn from this process will be communicated in this paper.
9:20 am
VIBRATED BULK DENSITY (VBD) MEASUREMENT OF CALCINED COKE AND BINDER CONTROL IN PREBAKED ANODE PASTE : A CASE STUDY: Luc Duchesneau, Roland Lessard, André Gendron and Germain Brassard, Alcan International Limited, Arvida Research & Development Centre, 1955 Mellon Blvd, P.O. Box 1250, Jonquière, Québec, Canada G7S 4K8
Vibrated bulk density is used to establish the binder content in prebaked anode paste. Alcan adopted the calcined coke VBD analytical method from Collier Carbon in 1961 with slight modifications. Recent paste quality problems (sticking in baking furnaces) were associated with a lack of precision in the VBD. The apparatus was identified as the main cause of imprecision (irregular flow when feeding the cylinder with the vibrating spatula, increase of table vibration amplitude over time and cylinder holding system) and an improved semi-automatic version was constructed. This communication describes the critical parts of the apparatus and their impact on the quality of the results. It also discusses calibration approach, analytical performance achieved (a four-fold improvement in reproducibility sigma = 0.003) and the impact on the paste production control.
9:45 am
PETROLEUM COKE DEOILING FOR PROPERTIES DETERMINATION: R.E. Gehlbach, C.T. Leach, and V.A. Benoît, Reynolds Metals Co., 3326 E. Second Street, Muscle Shoals, AL 35661-1258
The presence of petroleum-based dedusting agents applied to calcined petroleum coke for control of fugitive dust precludes obtaining correct analytical results when certain tests are performed. Removal of various dedusting agents in commercial use is difficult and the process (es) employed may also affect the properties obtained. Results are presented for studies of thermal, solvent extraction, and vacuum deoiling methods and their effectiveness for several surface-sensitive tests. While all methods are observed to remove virtually all of the dedusting agents, different types of residues or decomposition products remain on the coke particles and adversely affect test results. Depending on the particular properties to be determined and the desired accuracy of the results, more than one technique may be required.
10:10 am BREAK
10:30 am
EFFECTS OF IRON AND SULPHUR ON THE AIR- AND CO2-REACTIVITY OF COKES: Trygve Eidet, Department of Electrochemistry, Norwegian Institute of Technology, Elkem ASA, Research, PO Box 8040 Vaagsbygd, N-4602 Kristiansand, Norway; Morten Sorlie, Elkem ASA, Research, PO Box 8040 Vaagsbygd, N-4602 Kristiansand, Norway; Jomar Thonstad, Department of Electrochemistry, Norwegian Institute of Technology, N-7034 Trondheim, Norway
The aim of this work was to investigate the effects of inorganic impurities on the reactivity of cokes and anode materials and at the same time to avoid the uncertainties that are introduced by the often complex background impurity content in industrial anode cokes. An aromatic distillate fraction from the production of coal tar pitch was used as coke precursor and cokes with controlled amounts of impurities were produced in a laboratory coker. Iron was added to the coke precursor as iron (III) acetylacetonate, and sulphur as dibenzothiophene. These organic substances dissolve in the precursor. The effects of iron and sulphur on the reactivities of cokes were measured in air at 500°C and in CO2 at 960°C. Surface studies (SEM, EDX) showed the topography of the surface, what iron phases were present and indicated the impact of iron and sulphur on the reaction.
Room: 230B
Session Chairperson: Stuart R. Thistlethwaite, London & Scandinavian Metallurgical Co. Ltd., Fullerton Road, Rotherham, South Yorkshire, S60 1DL, England
8:30 am
AlTiB GRAIN REFINER - THE CONSISTENT INGREDIENT: P.C. van Wiggen, KBM Master Alloys
The use of AlTiB grain refiners for a precise control of the metallurgical cast structure has become an integral requirement in the manufacture of present day products. A permanent high standard in the quality and consistency of grain refiners is essential especially when considering their radical impact on the production result. This paper will discuss the consistency of grain refiners in terms of the composition, the production route and the required grain refiner properties. Particular attention will be given to an in-depth comprehension of the AlTiB microstructure. The above will be illustrated by microstructures and further supported by a selection of SPC data, process capabilities and (particle) distribution figures taken from various grain refiners. Information concerning recent advancements in the characterisation and process development of AlTiB grain refiners will also be incorporated in this paper.
8:50 am
EFFECTS OF TRANSITION METALS ON THE POTENCY OF TiBAl GRAIN REFINERS: A. Green, M.A. Kearns, London & Scandinavian Metallurgical Co. Ltd., Fullerton Road, Rotherham, South Yorkshire, S60 1DL, England
TiBAl grain refiners are known to be susceptible to fading and poisoning phenomena which can limit their effectiveness in some practical situations.The long-term fading behaviour of good and bad TiBAl grain refiners in 99.7% Al is presented as a function of temperature in the presence of Zr and other transition metals. It is shown that fade occurs more rapidly at higher temperatures and that the effects of Zr and other transition metals display a complex behaviour as a function of temperature. The observations are explained in terms of recent theories on the behaviour of TiBAl grain refiners which propose that potent TiB2 nuclei have TiAl3 layers present on certain facets. It is shown that the reported behaviour is consistent with interactions occurring between transition metals and the potent aluminide layer. Results are discussed in terms of key stages in the production of TiBAl grain refiners and lessons for the use of TiBAl in the aluminium industry are highlighted.
9:10 am
DEVELOPMENT OF AN IMPROVED AlTiC MASTER ALLOY FOR THE GRAIN REFINEMENT OF ALUMINIUM: W. Reif, Institute of Material Science, Technical University Berlin, Str. des 17.Juni 135, D-10621 Berlin, Germany; A. Green, London & Scandinavian Metallurgical Co. Ltd., Fullerton Road, Rotherham, South Yorkshire, S60 1DL, England; P.C. van Wiggen, KBM Master Alloys B.V., Klosterlaan 2, 9936 TE Delfzijl, The Netherlands; W.Schneider, VAW aluminium AG, Research and Development, Georg-von-Boeselager-Str.25, D-53117 Bonn, Germany; D. Brandner, Hoogovens Aluminium-Walzprodukte GmbH, Carl-Spaeter-Str.10, D-56070 Koblenz, Germany
The commercial AlTiB master alloys for grain refinement of aluminium contain TiB2 particles, which can be coarse and have the tendency to agglomerate in the melt. As a result of this, quality problems in different products occur.In Zr and Cr containing alloys TiB2 interacts with these elements leading to inhomogenous grain structure. In order to avoid the above mentioned disadvantages of the grain refinement with TiB2, a co-operative research programme has been carried out, to develop an improved AlTiC grain refiner. The main objectives of the project were: Development of an efficient AlTiC master alloy. Fundamental research to understand the mechanism of an AlTiC grain refiner. Evaluation of test methods for determination of the grain refining efficiency and agglomeration behaviour of TiC as standard test methods. Production scale testing of the developed AlTiC master alloy. The paper presents the results with respect to the above mentioned objectives.
9:30 am
THE DEVELOPMENT OF A COMMERCIAL Al-3% Ti-0.15% C GRAIN REFINING MASTER ALLOY: A.J.Whitehead, S.A.Danilak, Shieldalloy Metallurgical Corporation, Newfield, NJ 08344; Douglas A. Granger, Aluminum Company of America, Alcoa Technical Center, Alcoa Center, PA 15069
An Al-3% Ti-0.15% C master alloy has been developed and is now being used for ingot grain refinement in Alcoa. A description is given of the development of the high ratio Al-6% Ti-0.02% C master alloy and the progression from this alloy to the more acceptable lower ratio Al-3% Ti-0.15% C alloy. Acceptance for commercial use came only after extensive metallurgical characterization and evaluation of the grain refining performance, including the impact of alloy type and the presence of tramp elements. Details of the production, testing and characterization of this new grain refining master alloy are discussed.
9:50 am
THE GRAIN REFINEMENT OF Al-Si FOUNDRY ALLOYS: J.A. Spittle, J.M. Keeble, IRC for Materials in High Performance Applications, Department of Materials Engineering, University of Wales Swansea, Swansea SA2 8PP, United Kingdom
Whereas small concentrations of Si have been shown to enhance the grain refinement of aluminium by addition of an Al-Ti-B master alloy grain refiner, increasing Si contents in excess of 2-3% result in a continuous increase in primary aluminium solid solution grain size. Two explanations of these observations have been proposed to date based on the influence of Si on either the nucleation or growth of the aluminium primary crystals. Neither of these explanations appears to fit all the available grain size data. In an attempt to further clarify the origin of the Si coarsening effect, grain size studies have been performed on Al-Si and Al-Zn alloys as a function of solute content. It appears that the coarsening is a result of the influence of the Si content on aluminium grain nucleation. A coarsening mechanism is suggested based on the coupled influence of Si level on melt undercooling and primary phase freezing range.
10:10 am BREAK
10:20 am
MODIFICATION OF SILICON IN EUTECTIC AND HYPER-EUTECTIC Al-Si ALLOYS: Ben Heshmatpour, Shieldalloy Metallurgical Corporation, 12 West Boulevard, P.O. Box 768, Newfield, NJ 08344
Refining of eutectic silicon in hyper-eutectic and eutectic Al-Si alloys is accomplished by using phosphorus-bearing additives. Commercially available copper-phosphorus (CuP) in a variety of forms and concentrations is widely used for this application. Large addition rates are needed for effective silicon modification via CuP. The recently developed ferro-phosphorus (FeP) based tableted product provides significant performance and cost advantages while requiring much smaller addition rates, lower alloy temperature, and short contact times. This paper compares the results for refinement of A390.1, B390.1, and 339.1 alloys using CuP and tableted FeP.
10:40 am
EFFECTS OF RESIDUAL TRANSITION METAL IMPURITIES ON ELECTRICAL CONDUCTIVITY AND GRAIN REFINEMENT OF EC GRADE ALUMINIUM: R. Cook, M.A. Kearns, P.S. Cooper, London & Scandinavian Metallurgical Co. Ltd., Fullerton Road, Rotherham, South Yorkshire, S60 1DL, England
Removal of transition metal impurities is a key step in production of high conductivity EC grade Aluminium. Titanium and Vanadium in particular are generally removed by adding an excess of Boron to precipitate stable borides before decanting the treated metal. It is nevertheless advantageous to add sufficient grain refiner to avoid hot cracking of the cast bar without jeopardising electrical conductivity. We report here a study of the effects of residual Vanadium on the efficiency of different grain refining additives and electrical conductivity of the product. It is shown that Vanadium must be below a threshold figure to give adequate grain refinement at levels which do not compromise conductivity. The effects of residual Fe and Si impurities on grain refinement and conductivity are also described and their role is discussed in terms of constitutional supercooling effects. The relevance of the results to the manufacture of EC grade wire is discussed.
11:00 am
EXPERIMENTAL MEASUREMENT OF ELECTRICAL CONDUCTIVITY OF ALUMINUM ALLOYS AT ELEVATED TEMPERATURES: Raphaël Craen, Nagy El-Kaddah, Department of Metallurgical & Materials Engineering, The University of Alabama, P.O. Box 870202, Tuscaloosa, AL 35487-0202; Willem Loué, Péchiney CRV, Parc Economique Centr'Alp-BP27, 38340 Voreppe, France
The knowledge of the electrical conductivity of aluminum alloys is critical for the analysis and computer simulation of induction heating and melting operations as well as electromagnetic casters. While accurate conductivity data are available for pure aluminum, there is a paucity of data for aluminum alloys, particularly at elevated temperature. This paper describes an eddy current technique for measuring the electrical conductivity of metallic specimens at high temperatures. In this technique, which is based on measurement of the electric energy dissipation (Joule Heating), the electrical conductivity is determined from measurement of the heating rate of the specimen. The measurement is made by subjecting an insulated cylindrical specimen to a uniform axial alternating magnetic field, and measuring temperature of the specimen during heating. The method requires no contact with the specimen, and is capable of providing electrical conductivity data to the melting point of the specimen with an error of less than five percent. Upon validating the technique using pure aluminum, measurements have been conducted on Al-Mg (5182) and Al-Li (8090) wrought alloys, and on foundry and rheocast Al-Si (357) cast ingots. The results show that electrical conductivities of Si and Mg alloys are about one half of pure aluminum, and the microstructure of Al-Si 357 alloy has little effect on the electrical conductivity of the alloy. The Li containing alloy exhibited a much lower conductivity than Si and Mg alloys. Expressions are presented for the conductivities of these alloys up to 450°C.
11:20 am
DETECTION OF SOLIDIFICATION REACTIONS USING HEAT PIPE TECHNOLOGY
REPLACEMENT: Panel Discussion on Attic Grain Refiner
11:40 am
COMPUTER-AIDED COOLING CURVE ANALYSIS (CA-CCA), APPLIED TO AN Al-Si SYSTEM: M.A. Ramirez A., J.C. Escobedo B., A.H. Castillejos E., A. Flores V., F.A. Acosta G., Centro de Investigación y de Estudios Avanzados del IPN, Unidad Saltillo, P.O.Box 663, 25000 Saltillo, Coahuila, México
The computer-aided cooling curve analysis is a new method for thermal analysis that can be used in foundries of low budget and with small investment. This method tries to simulate the classic differential thermal analysis method (DTA) by using only an acquisition data system coupled to numerical methods in micro-computers. The kind of information provided by this technique includes thermodynamical and thermophysical data, heat transfer parameters, solidification kinetics, and microstructure features. All this information is more than that obtained with the classic DTA, and it is necessary in order to get a real comprehension of the solidification process. CA-CCA has been applied to the study of an Al-Si system to try to characterize it and to predict microstructure, because it is possible with this technique to obtain the evolution of solid during the solidification process and the segregation behaviour of this system.
Room: 330C
Session Chairperson: Robert Shull, NIST, Bldg. 223, Rm B152, Gaithersburg, MD 20899
9:00 am INVITED
STRUCTURE, MECHANICAL PROPERTIES, AND FRACTURE IN NANOPHASE SILICON NITRIDE: MILLION ATOM MOLECULAR DYNAMICS SIMULATIONS ON PARALLEL COMPUTERS: Rajiv K. Kalia, Aiichiro Nakano, Andrey Omeltchenko, Kenji Tsuruta, Priya Vashishta, Concurrent Computing Laboratory for Materials Simulations, Physics and Astronomy, Computer Science, Louisiana State University, Baton Rouge, LA 70803
Structure, mechanical properties, and dynamic fracture in nanocluster-assembled silicon nitride are investigated with molecular-dynamics (MD) simulations involving 1.08 million particles. The simulations reveal that intercluster regions in the consolidated nanophase Si3N4 are highly disordered with 50% undercoordinated atoms. These disordered interfacial regions deflect cracks and give rise to local crack branching. As a result, the nanophase system is able to sustain an order-of- magnitude larger external strain than the crystalline Si3N4. We also investigate the morphology of fracture surfaces in nanophase Si3N4. The MD results for roughness exponents are very close to experimental values [P. Daguier et al., Europhys. Lett. 31, 367 (1995)] even though the materials and length scales are very different.
9:30 am INVITED
THERMAL CONDUCTIVITY OF NANOPHASE CERAMICS: Paul G. Klemens, Physics, University of Connecticut, Storrs, CT 06269-3046
Heat conduction of insulators is by lattice waves (phonons), which have a wide frequency spectrum. The mean free path of phonons is limited by anharmonic intereactions and by scattering, principally scattering by point defects, and by grain boundaries and other etended imperfections. Point defects reduce the mean free path and the contribution to the conductivity of high frequency phonons; grain boundaries that of low frequency phonons. These reductions in conductivity will be discussed. They are additive in materials of micron-sized grains, but not in nanophase materials, where the frequency ranges of phonons affected by point defects and by grain boundary scattering may overlap. The effect of phonon scattering on the thermal conductivy will be discussed with reference to solutes, non-stoichiometry, grain size, and radiation damage.
10:00 am
A SIMULATION STUDY ON THE MELTING OF NANOCRYSTALLINE PLATES AND SPHERICAL CLUSTERS: J.K. Lee, Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931; B.K. Cheong, W.M. Kim, S.G. Kim, Materials Design Laboratory, Korea Institute of Science and Technology, Seoul, Korea
As an emerging mass-data storage technology, phase change (PC) optical recording makes use of the difference in reflectivity between the amorphous and crystalline state of chalcogenide thin films. The amorphous state is obtained via laser melting and subsequent rapid cooling. For a better understanding of the melting behavior of such nanocrystalline plates, a Lennard-Jonesian fcc solid is studied using the method of molecular dynamics. Unlike the bulk case, it is shown that a plate melting is accompanied by a gradual change in both the volume and enthalpy. The melting point of a plate decreases as a function of h**(-n), where h is the thickness and n is 0.7. If the thickness becomes 15 lattice parameters, the melting point reaches a plateau. (111) plates show slightly higher melting points than those for (100) plates. The melting points of spherical clusters with radii ranging from 1.4 to 6.4 lattice parameters show a r**(-n) dependence, where r is the radius and n is 0.75.
10:20 am BREAK
10:35 am
EVIDENCE FOR THERMODYNAMIC STABILIZATION OF GRAIN BOUNDARIES IN Pd1-xZrx: C.E. Krill, H. Ehrhardt, R. Birringer, Unversität des Saarlandes, FB10 Physik, Postfach 151150, Gebäude 43, D66041 Saarbrücken, Germany
The rate of grain growth in a crystalline material is proportional to both the mobility and energy of its grain boundaries. Standard techniques for hindering grain growth, such as solute drag, are kinetic in nature: that is, they aim to reduce the mobility term. A thermodynamic approach, however, should be just as effective: a reduction in grain-boundary energy would be accompanied by a corresponding decrease in the driving force for grain growth. According to the Gibbs adsorption theorem, grain-boundary energies can be reduced by introducing a component that tends to segregate to the grain boundaries. We have investigated ball-milled solid solution of Pd1-xZrz for signs of improved stability against grain growth with increasing Zr concentration; the growth rate is observed to drop to very low values for x greater than 0.2. Differential scanning calorimetry has been used to estimate the concentration dependence of the grain-boundary energy, thereby isolating the themodynamic contribution to grain-growth stability from that due to solute drag.
10:55 am
VIBRATIONAL DENSITY OF STATES OF NANOCRYSTALLINE Ni3Fe PREPARED BY HIGH ENERGY BALL MILLING: H. Frase, L.J. Nagel, J.L. Robertson, B. Fultz, California Institute of Technology, mail 138-78, Pasadena, CA 91125; Oak Ridge National Laboratory, Solid Sate Physics Division, P.O. Box 2008, Oak Ridge, TN 37831
We performed inelastic neutron scattering experiments on two states of Ni3Fe: 1) as-milled, when the material had a characteristic nanocrystallite size of 9 nm, and 2) annealed, when the material had a characteristic crystallite size of 30 nm. The nanophase material showed an enhancement by a factor of 2 in its density of states at energies below 15 meV, and some broadening of its longitudinal peak at 33 meV. The large enhancement in the density of states at these low energies appears to require coupling between inter- and intra-crystallite vibrational motions. The inter-crystalline modes would be associated with the vibrations of the crystallites themselves. These measured changes in vibrational DOS predict a difference in vibrational entropy of the bulk and nanocystalline Ni3Fe of about 0.18 kB/atom at high temperatures, with the nanocrystalline materials having the larger vibrational entropy. This work was supported by the U.S. Department of Energy under contract DE-FG03-86ER45270.
11:15 am INVITED
FUNCTIONAL CERAMICS USING NANOMETER-SIZED MATERIALS: Manu Multani, Tata Institute of Fundamental Research, Bombay 400 005, India
Working with a range of current ceramic materials with a wide variety of applications, it is shown that considerable improvements can be obtained when one starts with Small Solid State Systems (S4) Materials studied range from doped ZnO varistors, PZT piezoelectrics, YIG microwave materials, and the new superconductors. General principles underlying these changes are shown to be dependent on the dispersion relations of phonons and wavevectors (for ferroelectrics) and magnons and wavevectors (for ferromagnetics). Another S4 rule that we have found applicable for most oxides is the tendency towards higher symmetry and increasing unit-cell-volume with decreasing size of the S4s. These changes may usher in phase transformation(s) and size dependent phase transition temperatures.
Room: 340D
Session Chairperson: Anthony D. Rollett, Materials Science & Engineering Dept., Carnegie Mellon University, Pittsburgh, PA 15213
8:30 am INVITED
CURRICULUM DESIGN; INPUTS AND OUTPUTS: Richard Heckel, Dept. of Metallurgy and Materials Engineering, Michigan Technological Univ., 1400 Townsend Drive, Houghton, MI 49931
Undergraduate engineering curricula are designed by faculty committees in accord with accrediting guidelines for content, logical course sequencing and practical limitations for scheduling faculty and laboratory resources. Presently, engineering education is receiving intense scrutiny due to several decades of large tuition increases, continuous enrollment declines since the early '80s, constraints in external research support and decreases in the number of employment opportunities for graduates. These trends have already resulted in proposals for new curriculum designs which would, for example, reduce credits needed for graduation, sacrifice discipline-specific content and increase multidisciplinary activities. Presumably, such curricula would broaden appeal, increase engineering enrollments, widen the range of career opportunities and stimulate interest in industrial interactions. Can such curricula provide the optimum balance between the new educational boundary conditions and quality engineering education? To what extent should curriculum design emphasize graduate/employer feedback, student/parent expectations, instructional philosophy/methodology and general skill development (communication, self-directed learning, open-ended problem solving, ethical decision making, etc.)? Tradeoffs and opportunities associated with these issues will be discussed.
9:00 am
THE MATERIALS SCIENCE AND ENGINEERING CORE CURRICULUM AT VIRGINIA TECH: R.W. Hendricks, R.S. Gordon, Virginia Tech, MSE Dept., Blacksburg, VA 24061-0237
We have developed a core curriculum for an ABET-approved Materials Science and Engineering curriculum incorporating 8 required core courses, options in each of the 5 principle fields (ceramics, composites, electronic materials, metallurgy and polymers), and developed an integrated "across-the-curriculum" approach to writing and communication, ethics, and statistics. Our required core courses, each with laboratory, include physical ceramics, physical metallurgy, electronic materials, and polymer engineering. These "material specific" courses are supported by three material-independent courses including X-ray diffraction, thermodynamics and transport processes, and by a capstone engineering design course based on a research project. Oral, written, and graphical communication, statistics, and ethics and integrated in a manner such that the student is led from fundamental concepts through to sophisticated interpretation of each topic. The student is exposed to these "across-the-curriculum" topics during each semester of the three year program of study beginning with the sophomore year.
9:25 am
MATERIALS SCIENCE AND ENGINEERING: THE NEW UNDERGRADUATE CURRICULUM AT DREXEL UNIVERSITY: Alan Lawley, Dept. of Materials Engineering, Drexel University, Philadelphia, PA 19104
In 1994 the new undergraduate Drexel Engineering Curriculum was implemented, emphasizing 'up front' engineering, computer and communication skills, life long learning and teamwork. This common core in the first two years reflects many of the tenets and the philosophy of the E4 experiment ('Enhanced Educational Experience for Engineering Students') which began in 1988. Concurrently, the Department of Materials Engineering has been proactive in the Gateway Coalition, a major component of which is to build on E4 by focusing on the upper level curriculum via the development of advanced engineering science courses. Our new undergraduate major, enacted in 1995, reflects the maturing of the E4 experiment into the core Drexel Engineering Curriculum and the integration of selected engineering science courses (developed under the Gateway Coalition) into the curriculum at the upper level. Evolution of the new curriculum is discussed, including the development of modules in materials education.
9:50 am
MATERIALS SCIENCE AND ENGINEERING CURRICULA; RETHINKING THE CORE CONTENT - THE CASE FOR A 128 HOUR CORE: Richard L. Porter, Campus Box 7904, North Carolina State University, Raleigh, NC 27695-7904
Most materials educators agree that three major components constitute the undergraduate materials science and engineering curriculum; that presented in the first 2-3 semesters (generally the basic sciences), the real "core," and finally the obligatory senior design or capstone experience. Scattered throughout will be the necessary humanities and social sciences, maybe a communications course or technical writing course. It is assummed that the mathematics, chemistry, physics, and writing have been properly and correctly introduced and students' have mastered the content. There are several problems with this approach; little if any experiential learning, little if any contextual learning for the basic sciences, little integration of engineering sciences with the basic sciences, and in many cases a disconnected core. Although all curricula meet and or exceed ABET criteria, there is little accountability for the actual content and methodology of presenting the material. This paper discusses the entire curricula in context with the intended outcome for materials science and engineering and encourages curricular designers to rethink the entire learning experience, not to simply add more courses for short term accomplishments. At North Carolina State University, our approach has been to introduce different models for first year engineering, ranging from a hands-on engineering experience linked with freshmen writing, an integrated approach pulling together math, chemistry, and physics, with a year year engineering overview, and recently a new freshmen course linked with the computer literacy course and including a weekly small-group problem solving session. Concurrently, we have administered an attitudes survey at the beginning of the year and again at the end of the semester and year. Students enrolled in these special courses report a greater interest in engineering as a problem solving discipline, they view engineering as an iterative process, and report a higher degree of satisfaction with their first year experiences. Finally, a curriculum will be presented and discussed that builds upon the fundamental basic sciences and integrates the curriculum rather than present it as a linear combination of sub-disciplines.
10:15 am INVITED
INDUSTRIAL EXPECTATION OF A MATERIALS EDUCATION: AN AUTOMOTIVE VIEW: R. Heimbuch, D. Mattis. J. Hall, General Motors, 30300 Mound Road, A/MD-36, Warren, MI 48090-9040
Competitive pressures have caused the automotive industry to critically examine and modify their engineering processes. The new engineering processes have put a higher value on certain skill sets than in the past. The need for technical competence has not changed - it is a given. The question for the Education Community is how to maintain a strong balanced technical framework while developing other critical skills. The goal should be to enhance the effectiveness of the student as he or she moves into and through their professional career. The authors will share their views around the critical question of "balance" and "critical skills".
10:45 am
RESTRUCTURING UNDERGRADUATE EDUCATION AT ILLINOIS INSTITUTE OF TECHNOLOGY; CASE STUDY: METALLURGICAL AND MATERIALS ENGINEERING PROGRAM: Marek Dollar, Mechanical, Materials and Aerospace Engineering Dept., Illinois Inst. of Technology, Chicago, IL 60616.
There is a broad recognition at IIT that we live in a time of revolutionary change in undergraduate education. In response, we are developing new ways to recruit and retain a diverse student body, seeking educational relationships with industry, experimenting with new approaches to teaching and learning, and positioning ourselves to meet ABET engineering criteria for the year 2000. The key elements of the undergraduate education restructuring will be presented. They include, but are not limited to, such initiatives as: Interprofessional Projects, project-oriented learning that teams students from different disciplines and professions and constitutes a new instructional tool though which students learn concepts of teamwork, communication and problem solving; Introduction to the Professions, a freshman-level course that in an innovative way bridges the gap between high school experience and the university's environment; Writing Across Curriculum, an institutional structure for integrating writing into engineering courses. Our attempts to increase computer competence, introduce multimedia in the classroom and create undergraduate research opportunities will also be discussed.
11:10 am
EFFECTIVE USE OF A SMALL FACULTY FOR MAINTENANCE OF A COMPREHENSIVE MATERIALS ENGINEERING PROGRAM: Jeffrey W. Fergus, Materials Research and Education Center, 201 Ross Hall, Auburn University, AL 36849
A recent analysis of the materials/metallurgical engineering programs at U.S. universities shows that these programs can be divided into three, approximately equal, groups in terms of faculty size. Specifically, there are 24 programs with 21-90 faculty, 23 programs with 13-20 faculty and 25 programs with 3-12 faculty. The small number of faculty in this latter group presents challenges in terms of maintaining a comprehensive (undergraduate, graduate, research) materials program. This presentation will relate experience with the materials engineering program at Auburn University, which has 7 full-time faculty, in meeting these challenges. In addition, the contribution of these small programs to the materials engineering discipline as a whole will be discussed.
11:35 am
TITLE TBA: Samuel Allen, Dept. of Materials Science and Engineering, Mass. Inst. of Technology, Cambridge, MA 02139
Room: 332
Session Chairpersons: Judy Glazer, Hewlett-Packard Co., Electronic Assembly Development Center, Mail Stop 4U-3, 1501 Page Mill Road, Palo Alto, CA 94304; James F. Maguire, Boeing Co., P. O. Box 3999, Defense & Space Systems Group, Mail Stop 3W-97, Seattle, WA 98124
8:30 am INVITED
DESIGNING WITH Pb-FREE SOLDERS: Walter L. Winterbottom, Reliability Consultant, 30106 Pipers Lane Court, Farmington Hill, MI 48331
As the global competition in the transportation industry intensifies, the focus on quality and time-to-market have become major driving forces in product design and dominant forces in the market place. Although the current design/development process as practiced in the industry provides a time tested path for new products, leadership in these areas seems to be elusive. A York Times article (March, 1991) notes that Consumers Report ranks the reliability of new American models at about the level of the average Japanese models. In 1988, the Material Systems Reliability Department was organized in the Materials Research Laboratory of Ford Research with the mission to evaluate existing, and develop if necessary, design methodologies capable of the task of providing world leadership in both quality and time-to-market. It was apparent from the outset that a life-cycle design approach must be used to contain reliability, cost, and environmental considerations in a time efficient manner. Further, it became increasingly apparent from the Department's failure mode/root cause identification and testing assistance activities that these issues have to be designed into a product rather than being assured by extensive prototype testing programs. A Design-for-Reliability methodology based upon the development of analytical prototypes which has the capability to fulfill the requirements for world leadership. The methodology is based upon the definition of system failure modes and mechanisms, system model development with verification capable of reliability prediction early in the design process prior to the building and testing of prototype hardware. This 'preventive' approach is based upon quantitative reliability estimates as a key design metric for use in assessing design alternatives. In simplest terms, the approach emphasizes the need to consider products as material systems whose reliability must be thoroughly understood early in the design and development process. The traditional 'build, test, and fix' design approach must be replaced with an approach that relies upon analytical prototypes leading to a single, optimized, prototype hardware build. In the presentation, the Design-for-Reliability approach will be illustrated using electronic packaging design with lead-free solder interconnects as example.
8:55 am INVITED
DESIGN OF NEW SOLDER ALLOYS THROUGH MICROSTRUCTURE CONTROL: Sungho Jin, Lucent Technologies, Bell Laboratories, Room 1A-123, 700 Mountain Avenue, Murray Hill, NJ 07974
The mechanical properties of solder alloys and reliability of solder joints are significantly affected by microstructural features such as grain size, phase distribution, and precipitate morphology. A finer grain size, smaller precipi tates, and a uniformity in phase, precipitate and grain size distribution are often beneficial for improving the strength and ductility as well as the resistance in fatigue and creep failures. The control of microstructure is accomplished by modifications in alloy chemistry and processing conditions. Several examples of microstructural control in lead-free solder systems will be discussed. More forward-looking approaches for further control of microstructure in solder alloys and composites, e.g., by distribution of nano-scale dispersoid particles will also be discussed.
9:20 am INVITED
LEAD-FREE SOLDERS FOR ELECTRONIC ASSEMBLY: Fay Hua, Judy Glazer, Hewlett-Packard Co., Electronic Assembly Development Center, Mail Stop 4U-3, 1501 Page Mill Road, Palo Alto, CA 94304
This paper gives an up dated literature review on the metallurgy of lead-free solders for electronic assembly. The review includes newly reported technical data on existing binary Sn-based eutectic alloys: Sn-Ag, Sn-Bi, Sn-Cu and Sn-In. It also reviews the newly developed multi-component solder alloys in following systems: Sn-Zn-In, Sn-Zn-Bi, Sn-Zn-Sb, Sn-Ag-Zn, Sn-Ag-Cu(-Sb), Sn-Ag-Bi, Sn-Ag-In(-Sb), Sn-Bi-In, and Sn-Bi-Sb. The characteristics of these alloys described are chemical composition, physical properties, microstructure, and mechanical properties. The manufacturability issues and applications of these lead-free solders in electronic assembly will be presented.
9:45 am INVITED
SUMMARY OF RECENT STUDIES OF THE EFFECT OF PROCESSING ON MICROSTRUCTURE OF SOME SOLDER ALLOYS: James Clum, E. Cotts, N. Jiang, Mechanical Engineering, Physics Department, State University of New York at Binghamton, Binghamton, NY 13902
A variety of solder alloys selected from the Sn-based, and In-based systems, have been examined to test for the interaction of composition with processing conditions in controlling alloy microstructure. Rate of solidification, amount of compressive strain, annealing temperature and time were the independent variable studied. Grain size, phase fraction and microhardness have been monitored as measures of microstructural changes. A simple factorially designed experimental plan has been used to conduct and interpret the tests. A major effect of solidification rate and a secondary effect of the interaction between deformation and annealing was observed for most alloys. The effect of alloy composition is reflected primarily in terms of the role of Tambient/Tm on microstructural stability. Some other processing related characteristics of these solder alloys will also be discussed such as creep and stress relaxation behavior. The role of microstructure in behaviors such as grain boundary sliding will be illustrated.
10:10 am
EVALUATION OF ALTERNATIVES TO LEAD SOLDERS FOR PRINTED WIRING APPLICATIONS: James F. Maguire, Boeing Co., P. O. Box 3999, Defense & Space Systems Group, Mail Stop 3W-97, Seattle, WA 98124
This paper describes the first phase of a three year program undertaken by Boeing to evaluate "no lead" materials as a potential replacement for solder in printed wiring assembly applications. This program is looking at a number of different potential replacements including both conductive adhesives and "no lead" solder materials. In addition, the impact of other environmentally driven process changes such as "no clean" soldering and lead free PWB finishes are being tested for compatibility with "no lead" attachment materials. The phases of this program are: Phase I: Initial materials evaluations, processability, stability of electrical performance in environmental exposure, sequential exposure to temperature/humidity cycling and thermal shock environments, compatibility with "standard" finishes (reflowed solder and "de-oxidized" copper), down Selection for Phase II testing; Phase II: detailed material performance testing, stability of contact and bulk resistance during environmental exposure, compatibility with high speed/RF applications, * Compatibility with existing PWA processes such as - pre-conformal coat cleaning, rework/repair, down selection for Phase III testing; Phase III: Development of design allowables and manufacturing processes. This paper will discuss the results of Phase I of this program which evaluated a total of 21 conductive adhesives and 8 commercially available solder alloys with control samples fabricated with Sn63 solder.
10:30 am
CREEP AND MECHANICAL PROPERTIES OF Sn-5%Sb SOLDER: Rao K. Mahidhara, K. Linga Murty and Fahmy M. Haggag, Tessera Inc., 3099 Orchard Drive, San Jose, CA 95134; North Carolina State University, Raleigh, NC 27695; Advanced Technology Corporation, Oak Ridge, TN 37830
A knowledge of the mechanical and creep properties of solder materials is required both for alloy development and life-prediction. We report here tensile and creep properties of Sn-5%Sb which is one of the candidate materials for replacing lead-based solders in electronic packaging. The temperature and stress dependencies of the strain-rate are evaluated using both the tensile and creep tests. In addition, the recently developed Stress-Strain Microprobe (SSM) is used to evaluate the strain-rate dependence of stress through automated ball indentation (ABI) tests at ambient. An excellent correlation is noted between creep and ABI data. While creep tests covered low stresses, ABI corresponded to high stresses which revealed breakdown of the Norton-law noted at lower stresses. While creep tests took 5 months time, the ABI tests were completed in a matter of hours although they covered 3 orders of magnitude strain-rates. The utility of ABI technique in solder joints is clearly pointed out and such tests are planned on real joints. ABI tests at elevated temperatures were not performed to-date. Such a facility is now under development and future plans include testing at elevated temperatures on bulk as well as solder joints.
10:50 am BREAK
11:00 am
CHARACTERIZATION OF 58Bi-42Sn SOLDERED ON Sn-Pb COATED SURFACE: Zequn Mei, Fay Hua, Judy Glazer, Hewlett-Packard Co., Electronic Assembly Development Center, Mail Stop 4U-3, 1501 Page Mill Road, Palo Alto, CA 94304
As reported in our previous work, solder joints of 58Bi-Sn on 80Sn-20Pb coated surface failed prematurely in thermal cycles between -40°C to 100°C. The failure mechanism was identified to be the dissolving of Pb atoms into the 58Bi-Sn solder joint during soldering, which caused formation of the ternary eutectic 52Bi-30Pb-18Sn with melting point of 95°C. In this paper, study of three types of solder joints will be reported: (1) 58Bi-42Sn soldered on Cu surface, (2) 58Bi-42Sn solder on 80Sn-20Pb coated surface, and (3) 57.5Bi-41.5Sn-1Pb soldered on Cu surface. These solder joints were aged at 80°C and 110°C. The evolution of the grain or phase sizes and the degradation of mechanical properties will be characterized as function of aging time. Early results indicate that the grains grew much faster in the solder joints containing Pb atoms (types 2 and 3 above), which reduced mechanical strength and ductility, than the solder joints without Pb atoms (type 1). Detailed results will be reported in the meeting.
11:20 am
MICROSTRUCTURAL STABILITY AND MECHANICAL PROPERTIES OF TIN-SILVER-COPPER SOLDER JOINTS: Iver E. Anderson, Ozer Unal, Ames Laboratory, Iowa State University, 122 Metals Development Bldg., Ames, IA 50011
The properties of a Pb-free ternary eutectic solder alloy, Sn-4.7Ag-1.7Cu (wt.%), which was discovered in our laboratory have been evaluated. This patented alloy has a melting point of 217°C, a fine 3-phase eutectic microstructure, and a very good solderability. The primary goal of this investigation has been to enhance its microstructural stability for high temperature environments, greater than 125°C, and to improve its overall mechanical properties, especially for extended service. Thus, minor modifications were made in the base eutectic alloy to control microstructural aging without degrading solderability. Alloying effects on solder/Cu joints in the as-soldered and aged conditions were studied. Tensile strength and shear strength measurements were made using butt and lap shear joint configurations, respectively, under various loading conditions. The results will be presented and their implications will be discussed. Support from the DOE-BES-DMS under Contract No. W-7405-Eng-82 is gratefully acknowledged.
11:40 am
THERMAL AGING AND IN-BOARD PEEL TESTING OF PB-FREE SOLDERS FOR UNDERHOOD APPLICATIONS: Martin W. Weiser, Julie A. Kern, Celeste A. Drewien, Frederick G. Yost, Johnson Matthey Electronics, Spokane Assembly Products Group, 15128 E. Euclid Avenue, Spokane, WA 99216; University of New Mexico, Mechanical Engineering Department, Albuquerque, NM 87131; Sandia National Laboratories, Materials and Process Sciences Center, Albuquerque, NM 87185
The thermal aging and post aging joint strength of four Pb-free solder alloys on a Ag-Pt thick film metalization were studied as the last part of a larger evaluation of solder/flux/metalization systems for use in high temperature under hood automotive application. The solders were the Sn-Ag and Sn-Ag-Cu eutectics and a Bi modified version of each. Solder pastes were reflowed on metalized alumina in a commercial inert atmosphere belt furnace. Aging of both sessile drops and in-board peel test samples was conducted at 134 to 190°C for up to 1000 hours. Addition of Bi and/or Cu increased the intermetallic growth rate and decreased the in-board peel strength.
12:00 am
RATE-CONTROLLING MECHANISM DURING PLASTIC DEFORMATION OF 95.5Sn4Cu0.5Ag SOLDER JOINTS AT HIGH HOMOLOGOUS TEMPERATURES: Hans Conrad, Z. Guo and Y. H. Pao, Materials Science and Engineering Department, North Carolina State University, Raleigh, NC 27695; Ford Scientific Research Laboratory, Materials Systems and Reliability Department, 20000 Rotunda Drive, Dearborn, MI 48121
The effects of stress and temperature on the creep rate of 95.5Sn4Cu0.5Ag solder joints at 22°C to 168°C were investigated employing stress-change and temperature-change tests. The resulting plastic deformation kinetics are in accord with those obtained previously in constant strain rate tests. They are better described by an obstacle-controlled dislocation glide kinetics equation than the usual Dorn equation for diffusion-controlled mechanism. The Helmholtz free energy for overcoming the obstacles is 0.28µb3, where µ is the shear modulus and b the Burgers vector. The activation volume is of the order of 1000 b3. The plastic deformation kinetics are in reasonable accord with the intersection of dislocations as the rate-controlling mechanism. However, alternative mechanisms are not ruled out.
12:20 pm
ALLOY DESIGN OF Sn-Zn-X (X=In, Bi) SOLDER SYSTEM THROUGH PHASE EQUILIBRIA CALCULATIONS: Sueng Wook Yoon, Jeong Ryong Soh, Byeong-Joo Lee, Hyuck Mo Lee, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Kusung-Dong 373-1, Yusung-Gu, Taejon, Korea 305-701; Materials Evaluation Center, Korea Research Institute of Standards and Science, P.O. Box 3, Taedok Science Town, Taejon, Korea 305-606
Thermodynamic studies of the Sn-Zn-X (X=In, Bi) system have been carried out in terms of phase equilibria to design Pb-free solder alloys which are drop-in replacement for Sn-37Pb alloy. Based on the result of phase equilibria calculations, several selected alloys were chosen and analyzed by DSC, XRD and EPMA techniques. Microstructures of as-cast and heat-treated alloys were examined as well as the interface between solder joint and Cu substrate by optical microscopy and SEM. Spreading area test and preliminary mechanical test were performed to investigate the possibility as an alternative of eutectic Pb-Sn-solder.
12:40 pm
ALLOY DESIGN OF Sn-Ag-In-Bi-Sb SOLDER SYSTEM USING THERMODYNAMIC CALCULATIONS: Byeong-Joo Lee and Hyuck Mo Lee, Materials Evaluation Center, Korea Research Institute of Standards and Science, Yusong P.O. Box 102, Taejon 305-600, Korea; Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Kusong-Dong 373-1, Yusong-gu, Taejon 307-701, Korea
Room: 340C
Session Chairs: J.E. Sanchez, Jr., University of Michigan, Ann Arbor, MI 48109; C.V. Thompson, Dept. of Materials Science and Engineering, M.I.T., Cambridge MA 02139
8:30 am INVITED
GRAIN GROWTH IN POLYCRYSTALLINE THIN FILMS: C.V. Thompson, Dept. of Materials Science and Engineering, M.I.T., Cambridge MA 02139
Polycrystalline thin films are used in a wide variety of applications, especially in electronic and magnetic devices and systems. In these applications, the properties, performance and reliability of polycrystalline films are strongly affected by the average grain size, grain shapes, the way in which grain sizes are distributed and the distribution of grain orientations. These vary with deposition technique and with deposition conditions, and can also be modified through post-deposition processing. The factors which affect the structure and crystallographic texture of polycrystalline films will reviewed and categorized. Approaches for process development for application-specific optimized structures will be outlined.
9:10 am
NEW MICROSTRUCTURAL CHARACTERISTICS OF POLYCRYSTALLINE GOLD THIN FILMS: Alexander H. King, Varun Singh, Department of Materials Science & Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794-2275
We have made detailed observations of unsupported gold thin films, using transmission electron microscopy. These films embody a strong [111] fiber texture, as found in many FCC metal thin films. Rotations of individual grains about the [111] surface normal are observed and we present a simple model that mimics this behavior, providing a reasonable explanation for it. We will also present an analysis of the triple junctions in the films showing that symmetry is the most significant factor in determining the energy associated with a triple junction. We will show that supposed "U-lines" do not embody the disclinations that are expected on the basis of Bollmann's analysis. Acknowledgment: This work is supported by the National Science Foundation, under grant number DMR-9530314.
9:30 am
MODELING OF GRAIN GROWTH IN THIN FILMS WITH TEXTURE: Harold J. Frost, Johan Grape, Thayer School of Engineering, Dartmouth College, Hanover, NH
We have developed our two-dimensional simulation of grain growth to include several effects which apply for the case of large-grained polycrystalline thin films in which the grains completely traverse the film thickness and the grain boundaries are all nearly perpendicular to the plane of the film. To properly include the effects of texture we must include the following factors which differ among individual grains based on crystallographic orientation: surface energies for the film-substrate and film-covering interface; elastic compliances, and the related strain-energy densities when elastic strains are imposed; yield stresses, which limit the elastic strains and strain-energy densities. In this paper we will expand on previous treatments by explicitly allowing for variations in grain boundary energy and mobility, based on the relative misorientation of neighboring grains. In this case, the grain growth evolution favors pairs of grains separated by low angle (low energy) grain boundaries. Such low energy boundaries generally separate grains of the same texture component. Other effects, such as pinning by surface grooving, pinning by precipitate particles or holes in the film, and solute drag may also be included in the simulations.
9:50 am
POST-PATTERNING MICROSTRUCTURE EVOLUTION OF Al-Cu INTERCONNECT LINES: D. P. Field, TexSEM Laboratories, Inc., 226 W. 2230 N., Provo, UT 84604
Optimization of microstructural features in interconnect lines for integrated circuits is becoming increasingly important for device reliability as the minimum feature size continues to shrink. Recent efforts have clearly demonstrated that not only grain size and precipitate morphologies are affected by the patterning and subsequent anneal, but also the crystallographic texture and grain boundary structure evolve during this process. For narrow lines, the (111) fiber texture sharpens and the near-bamboo grain structure is controlled by interface area minimization and grain boundary energy minimization. The current work describes the competing energetics associated with the process. Experimental results using orientation imaging microscopy as the analysis technique on Al-1% Cu interconnect lines are shown to support the analyses.
10:10 am BREAK
10:30 am INVITED
CRYSTALLOGRAPHIC TEXTURE EVOLUTION DURING FILM FORMATION AND ANNEALING IN SPUTTERED Al ALLOY/Ti AND Al ALLOY/TiN/Ti LAYERS: J.E. Sanchez, Jr., University of Michigan, Ann Arbor, MI 48109; P.R. Besser, J. Williams, Advanced Micro Devices, Sunnyvale, CA 94088; D.K. Knorr, Rennselaer Polytechnic Institute, Troy, NY 15128
Ti, TiN and Al alloy thin films comprise the basis for patterned metallization interconnects in advanced integrated circuit devices. Ti in particular has been shown to provide increased reliability of the primary Al conductor against electromigration-induced failures. A proposed mechanism is for this improvement is increased Al (111) film fiber texture due to the presence of the Ti underlayer. A review of extensive Al texture characterization by x-ray diffraction methods will be presented for various Ti, TiN, and Al layering schemes and sputter deposition conditions. Factors such as substrate surface energy, substrate roughness, Al grain growth, and "texture inheritance" between layers will be discussed. Deposition and processing schemes for improved Al (111) texture and improved interconnect reliability will be provided.
11:10 am
THE EFFECT OF MICROSTRUCTURE AND LOCAL MICROSTRUCTURE VARIATIONS ON ELECTROMIGRATION FAILURE DISTRIBUTIONS: Dirk D. Brown, AMD, Sunnyvale, CA 94088; John E., Sanchez, Jr., University of Michigan, Ann Arbor, MI 48109; Matt A. Korhonen, Che-Yu Li, Cornell University, Ithaca, NY 14850
In narrow metal lines used for chip level interconnects, the electromigration reliability is affected by variations in the microstructure. Electromigration failure distributions were obtained experimentally for six different Al-Cu interconnect widths, ranging from 1mm to 8mm. Or each of these line widths, the microstructure was characterized (using TEM) and the initial stress distribution was calculated. This information was used, with a flux divergence model, to simulate the entire failure distribution for each line width. These simulations, when compared to the experimental failure distributions, were used to quantify important material parameters, such as atomic diffusivities and failure criteria. This information, in turn, can be used to accurately extrapolate electromigration data. A detailed failure analysis was carried out on the simulated lines to study the effect of microstructure variations on electromigration failure.
11:30 am
LOCAL GRAIN BOUNDARY STRUCTURE CHARACTERIZATION IN VOIDED COPPER INTERCONNECTS: R.R. Keller, National Institute of Standards and Technology, Materials Reliability Division, 325 Broadway, Boulder, CO 80303; J.A. Nucci, Cornell University, School of Electrical Engineering, Phillips Hall, Ithaca, NY 14853; D.P. Field, TexSEM Laboratories, Inc., 226 West 2230 North #120, Provo, UT 84604
We have characterized grain boundary structures and local textures in oxide passivated copper lines which had undergone thermal stress-induced voiding. Grain boundary misorientations and the crystallographic character of boundary planes were determined for individual grain boundaries using electron backscatter diffraction in the scanning electron microscope as well as focussed ion beam images. We have summarized the data for a number of boundaries immediately adjacent to voids and made direct comparisons to boundaries from regions which remained intact. These data were acquired from the same lines, and so represent measurements from material with identical thermal histories. The results suggest that significant variations in local structure exist in narrow lines, and that those local regions associated with more favorable kinetics are more susceptible to void formation and growth.
Room: 330E
Session Chairpersons: James C. Williams, GE Aircraft Engines, 1 Neumann Way, Evendale, OH 45215; Young-Won Kim, UES, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432
8:25 am OPENING REMARKS
8:30 am INVITED
PROCESSING-PROPERTY-MICROSTRUCTURE RELATIONSHIPS IN TiAl-BASED ALLOYS: M H. Loretto, D. Hu, A. Godfrey, T.T. Cheng, I.P. Jones, P.A. Blenkinsop, IRC in Materials for High Performance Applications, The University of Birmingham, Edgbaston B15 2TT, UK
A range of TiAl-based alloys has been produced by plasma melting either small buttons (1kg samples) or ingots (up to 50kg). These alloys have been subsequently processed using isothermal forging, extrusion and/or HIPping. Some problems associated with the melting and subsequent processing of these alloys will be discussed and the ways found to overcome these problems outlined. Microstructural data obtained from some of these alloys will be presented which show the relationship between processing route and microstructure, and these observations will be correlated with mechanical properties. It will be shown that the microstructure can be closely controlled by appropriate processing and further that for a range of alloy compositions the properties can be controlled more by processing than by composition. For other alloys the composition is more important.
9:00 am
DEFORMATION OF NANOCRYSTALLINE Ti-48Al: L.S. Kim, T. Klassen, C.J. Altstetter, R.S. Averback, Materials Science and Engineering Department, University of Illinois, 1304 W. Green St., Urbana, IL 61801
When the grain size is a few tens of nanometers, TiAl is ductile at moderately elevated temperatures. Such grain sizes were produced by ball milling of titanium and aluminum powders, which must be consolidated without excessive grain growth. Green compacts (80% dense) were sinterforged at temperatures near 650°C, achieving relative densities of 99%. The final grain size was roughly 60 nm. The deformation temperature is several hundred degrees below those used for sintering microcrystalline powders. Pore elimination is promoted during sinterforging by the deviatoric stress components due to the absence of die- wall constraints. The resultant shear deformation is undoubtedly enhanced by grain boundary deformation modes in nanocrystalline material. Hardness measurements at moderately elevated temperatures are used to develop the constitutive relation for deformation of TiAl. Densification and deformation have been studied as a function of temperature, load and grain size.
9:20 am
ROLE OF MICROSTRUCTURE ON SUPERPLASTICITY IN 
-TiAl ALLOYS: R.S. Mishra, A.K. Mukherjee, Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616
A number of 
-TiAl alloys exhibit superplasticity. The optimum superplastic temperature is strongly dependent on the grain size. For materials with grain sizes >10 µm, the superplastic temperatures are above 2 transition temperature. On the other hand, superplastic temperatures for materials with grain sizes <5 µm is below 1373K. Surprisingly, however, the state of second phase, i.e., ordered 2 or disordered a does not influence the kinetics of superplastic deformation and the parametric dependencies remain similar. These observations suggest that the slip accommodation and dislocation climb in g phase as the rate controlling mechanism. Some new results on nanocrystalline TiAl are presented, which shows the possibility of low temperature superplasticity. The flow stresses in submicrocrystalline and nanocrystalline -TiAl alloys are consistent with a slip accommodation model.
9:40 am
MICROSTRUCTURE AND TENSILE PROPERTIES OF ROLLED GAMMA TITANIUM ALUMINIDE: Gopal Das, Pratt and Whitney, P.O. Box 109600, West Palm Beach, FL 33410-9600; Helmut Clemens, Plansee AG, Technology Center, A-6600 Reutte, Austria
Gamma titanium aluminide (Ti-47Al-2Cr-2Nb-0.2B, Ti-47Al-2Cr-0.2Si at. %) sheets were produced by near-isothermal rolling of forged material. The microstructures resulting from annealing of the rolled sheets below and above the eutectoid temperatures were studied by a combination of optical, X-ray, SEM, and TEM methods. Transition temperatures including the alpha transus temperature were determined by DTA and annealing experiments. Textures were studied on as-rolled and annealed sheets. Tensile properties of annealed specimens were determined at RT-800°C. Deformation microstructure was analyzed by TEM and fractographs were studied by SEM. In the case of Ti-47Al-2Cr-0.2Si at. % the influence of strain rate on the ductile-to-brittle transition temperature was studied for different microstructures. Additionally, the superplastic behavior was investigated for Ti-47Al-2Cr-0.2Si (at. %) sheet in the temperature range of 1000-1100°C. The results will be presented and the underlying deformation mechanisms discussed. The Ti-47Al-2Cr-2Nb-0.2B sheet material was provided by McDonnell Douglas and AFWL/MLLM and the portion of the work based on Ti-47Al-2Cr-2Nb-0.2B sheet material was supported by NASA LeRC, Cleveland, OH, under Contract No. NAS3-26385.
10:00 am BREAK
10:20 am
EFFECT OF EXTRUSION TEMPERATURE ON THE MICROSTRUCTURE OF A POWDER METALLURGY TiAl-BASED ALLOY: L.M. Hsiung, T.G. Nieh, Lawrence Livermore National Laboratory, P. O. Box 808, L-370, Livermore, CA 94551-9900; D.R. Clemens, Advanced Engineering Operations, Pratt & Whitney, West Palm Beach, FL 33410-9600
The microstructure of a P/M Ti-47Al-2Cr-1Nb-1Ta (at.%) alloy powder-extruded at different temperatures has been studied. Three different temperatures: one near to the eutectoid temperature (T1), one within the (+) two phase field (T2), and one at a phase field (T3), were employed for the extrusion. The as-prepared powder consists of mainly phase and small amount of supercooled 
/B2 grains and a fine-grained (+2) duplex structure. The observation of stacking faults coexisted with thin plates within the 2 grains reveals that stacking faults are intimately related to the formation of the plates within the 2 phase. A nearly fully lamellar (FL) structure composed of alternating and 2 lamellae is developed for the alloy extruded at T3. Both lamellar grain size and lamellar interface spacing are finer than those in conventionally processed FL TiAl alloys.
10:40 am
SUPER TRANSUS PROCESSING OF Ti-48Al-2Nb-2Cr ALLOYS: G.E. Fuchs, Lockheed Martin Company, P.O. Box 1072, Schnectady, NY 12301-1072
Fine grained lamellar microstructures would be expected to exhibit high strength, high creep strength, high fracture toughness and moderate ductility. This presentation discusses the use of high temperature extrusion to produce fine grained lamellar microstructures in both ingot and powder metallurgy Ti-48Al-2Nb-2Cr alloys. The effect of processing parameters, such as extrusion temperature and cooling rate, on the microstructure and properties are examined. In addition, the thermal stability of the fine grained microstructures was examined by subsequent heat treatments. The results of this study indicate that fine grained lamellar microstructures can be generated in both ingot and powder metallurgy materials. However, the selection of the appropriate processing parameters is required to optimize the microstructure and properties.
11:00 am
DENSE IN SITU TIAL IMCS VIA PRESSURE-ASSISTED THERMAL EXPLOSION: I. Gotman, C. Zakine, E.Y. Gutmanas, Department of Materials Engineering, Technion, Haifa 32000, Israel
Dense -TiAl and in-situ TiAl based IMCs were fabricated via pressure-assisted thermal explosion. Fine Ti-Al powder blends with and without the addition of BN or NiB were used as the starting reagents. Rapid heating to the ignition temperature of thermal explosion was realized via resistive heating or by placing the reagent compacts into a preheated pressure die. The presence of an additional low temperature phase in the composition with NiB greatly assisted the process of consolidation. The application of a moderate external pressure (¾ 200 MPa) during processing was shown to be enough to accommodate negative volume changes associated with reactive synthesis and, thereby, to ensure full density of the final product. Microstructure and phase composition of the materials obtained were characterized employing x-ray diffraction and scanning and transmission electron microscopy (SEM and TEM) with energy dispersive analysis (EDS). The entire procedure of thermal explosion under pressure could be performed in open air without noticeable oxidation damage to the final product. Rapid cooling due to heat transfer into the pressure die allowed to prevent the coarsening of microstructure in the materials synthesized. The formation of a finely distributed reinforcing phase resulted in high mechanical properties of the in-situ TiAl matrix composites.
11:20 am
PROCESSING AND PROPERTIES OF INVESTMENT CAST, NEAR-BINARY TIAL ENGINE EXHAUST VALVES: Steven G. Dettloff, Wesley R. Thayer, Walter W. Milligan, Department of Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931
Near binary gamma TiAl engine valves were investment cast by the Hitchener process. Effects of HIP temperature, pressure and time on mechanical properties and microstructure were investigated, and the HIP process was optimized for ductility. A HIP + heat treat study was able to separate the beneficial contributions of porosity closure and microstructural development. Effects of iron additions on the optimum aluminum content were noted and will be discussed. We gratefully acknowledge the support of GM Powertrain, Ron Cafferty and Paul Mikkola, who provided the valves and financial support, as well as the National Science Foundation, under grant DMR-92-57465, which is monitored by Dr. Bruce MacDonald.
11:40 AM
AUTOGENOUS GAS TUNGSTEN ARC WELDABILITY OF CAST ALLOY Ti-48Al-2Cr- 2Nb VERSUS EXTRUDED ALLOY Ti-46Al-2Cr-2Nb-0.9Mo: V.L. Acoff, D. Bharani, Department of Metallurgical and Materials Engineering, Box 870202, The University of Alabama, Tuscaloosa, AL 35487-0202
In the majority of the engineering applications for which gamma based titanium aluminide alloys are being considered, fusion welding is the primary form of joining. Sound (crack and void free) welds using the gas tungsten arc welding (GTAW) process with matching, or near matching, filler metal have been accomplished. However, procedures for consistently producing crack-free autogenous (without filler metal) GTA welds have not been achieved. This paper will discuss the autogenous gas tungsten arc weldability of cast alloy Ti-48Al-2Cr-2Nb (at.%) and of extruded alloy Ti-46Al-2Cr-2Nb-0.9Mo (at.%) and will compare their resultant fusion zone microstructure and properties. Samples were spot welded without any preheat. Microstructural characterization has been performed using optical microscopy and scanning and transmission electron microscopy equipped with an energy dispersive X-ray spectroscopy (EDS) system. Mechanical properties of the fusion zone will be discussed in terms of Vickers microhardness numbers and tensile testing.
Room: 231C
Session Chairpersons: William Petruk, Consultant, Former Chief Mineralogist, CANMET, Ottawa; S.K. Chryssoulis, AMTEL, London, Ontario, Canada
8:30 am KEYNOTE
TEXTURES OF GOLD MINERAL PHASES RELATED TO HEAP LEACHING: William Petruk, Consultant, Former Chief Mineralogist, CANMET, Ottawa, Canada K1A OG1
Native gold and electrum are the main gold minerals recovered by heap leaching. Recovery depends on ore textures that influence exposure during crushing and grinding in preparation for heap leaching. Textures include gold-bearing veinlets along fractures and microfractures, and gold occurrences along grain boundaries. Small encapsulated gold grains in quartz, pyrite and arsenopyrite are not likely exposed, and generally non-recoverable. Similar submicroscopic forms of gold are not recoverable by heap leaching. Detailed studies have shown that many so-called encapsulated gold grains may occur either along weakly bonded grain boundaries or microfracture in minerals, which become exposed by fine grinding. Ore textures in various ores will be reviewed. Ore types include gold in arsenopyrite-pyrite-quartz veins, gold-chalcopyrite deposits, disseminated gold in sediments, Carlin-type gold ores, gold-pyrite associations, and gold in volcanogenic ores, etc.
9:05 am
MINERALOGIC EVALUATION OF UNLEACHED GOLD IN BIOOXIDIZED LEACH RESIDUES: S.K. Chryssoulis, AMTEL, London, Ontario, Canada N6G 4X6; Rong Yu Wan, Newmont Metallurgical Services, Salt Lake City, UT 841O8
Gold associations were established in a biooxidized, chlorinated CIL residue assaying 0.02 oz Au/t and in a biooxidized thiosulfate leach residue assaying 0.01 oz Au/t. Detailed Mineralogic study involved: assays of screened fractions; light microscopy; ion probe microanalysis to quantify 'invisible' gold in sulfide minerals; proton probe microanalysis to detect submicroscopic gold in chert; and laser microprobe analysis to detect and quantify preg-robbed gold. In the CIL residue most of the gold is preg-robbed (71%). In the thiosulfate leach residue, gold occurs mainly as submicroscopic disseminations in microcrystalline quartz (chert). In both residues the 'invisible' gold in pyrite accounts for a minor fraction of the gold assay. Quantitative determination of the gold occurrence in the two residue samples established conclusively that gold adsorption on carbonaceous matter in the thiosulfate leach is of minor importance.
9:30 am
PROCESSING OPTIONS FOR HEAP LEACHING CARBONACEOUS SULFIDIC GOLD ORES: G. Ramadorai, President, EnMet Associates, Inc., 11225 E. Quick Draw Place, Tucson, AZ 85749-9551
This paper addresses processing options for recovering gold from carbonaceous sulfidic gold ores. These include, but not limited to, the following methods: (1) Hypochlorite pretreatment followed by cyanidization; (2) Chemical blanking agents pretreatment followed by cyanidization; (3) Non-cyanide heap leaching techniques; (4)Biological pretreatment followed by cyanidization; (5) Biological pretreatment followed by non cyanide heap leaching. Issues of costs, economics, recoveries, testing methods, state of advancement etc., will be discussed in the paper.
10:00 am BREAK
10:10 am
GEOLOGY AND CHARACTERISTICS OF GOLD MINERALIZATION IN FOUR SIBERIAN GOLD DEPOSITS, RUSSIA: A.D. Genkin, N.S. Bortnikov, Y.G. Safonov, IGEM, Russian Acad. of Sciences, Moscow, Russia; L.J. Cabri and G. McMahon, CANMET, 555 Booth St., Ottawa, Canada K1A OT1; C.J. Stanley, Natural History Museum, London, U.K.; F.E. Wagner, D.J. Friedl, Physik-Dept., Technische Univ., Munchen, Germany
A multidisciplinary investigation (SIMS, EPMA, Mossbauer) was used to characterize gold in four Siberian mesothermal sulfide gold deposits: Olympiadnenskoe and Veduginskoe within the Enisei Mountain Range and Nezhdaninskoe and Sentachan in the Verchoyansk-Kolyma area. It was found that some of the mineralization is refractory in all four deposits, occurring in large part as "invisible" gold in arsenopyrite and a lesser amount in pyrite. The gold concentration and distribution vary considerably, both within and between grains of arsenopyrite, with implications for processing options, such as heap leaching.
10:35 am
AUGMENT X4 TECHNOLOGY FROM THE LAB TO FEASIBILITY; A CASE STUDY: K.M. Schall, K.A. Brunk, G.R. Maxwell, Augment Technologies, Denver, CO 80235
Gold ores containing oxide copper incur significant cost penalties when leached with cyanide, because 4-5 moles of cyanide are consumed for each mole of leached copper. This equates to ~4 lbs of NaCN per lb of leached Cu. Total cost of excess NaCN consumption plus CN destruction can exceed $4.00 per ton of ore. AuGMENT Technologies has developed and demonstrated a new process that can: 1) economically recover 70-80% of cyanide fed to a mill; 2) produce salable copper cathodes; and 3) reduce the need for cyanide destruction facility. Standard resin processing and electrowinning equipment are used to recover the cyanide and produce copper cathodes. Steps have been taken to determine: 1) how to develop resin kinetics; 2) how the AuGMENT Process can be scaled up; 3) how much savings is incurred at mill site; and 4) how the novel 'electro-elution' circuit achieves efficient operation.
11:00 am
COPPER RECOVERY AND CYANIDE REGENERATION FROM CYANIDE SOLUTIONS: H. Soto and F. Nava, Dept. Mines and Metallurgy, Laval University, Quebec City, Quebec G1K 7P4
A method has been developed to recover cyanide and copper from heap leach cyanide solutions containing copper complexes and thiocyanate. Copper is precipitated as copper thiocyanate or copper cyanide, depending on pH and concentrations of thiocyanate and cyanide in effluents. Precipitates assaying over 50% Cu show good dewatering qualities and separate readily from effluents by filtration. Solutions containing bulk of cyanide are oxidized with ozone to transform remaining thiocyanate to cyanide, resulting in purified cyanide solution that can be recycled. The pH of the effluent is lowered to optimize precipitation and oxidation, and then raised to regenerate the cyanide. Recoveries are in excess of 96% of Cu and CN. Efficiencies of oxidation are 85-90%. Economic evaluation indicates a profitable process for solutions containing more than about 250 ppm copper. A bleed of barren solutions from cyanocidic gold/copper ores could be treated economically by heap leaching, since CN consumed by Cu could be regenerated at no cost.
Room: 315A
Session Chairpersons: P.J. McGinn, University of Notre Dame, Notre Dame, IN; J.L. MacManus-Driscoll, Imperial College of Science, Technology and Medicine, London, UK
8:30 am INVITED
EFFECT OF COMPOSITION ON GROWTH MECHANISM IN SEEDED-MELT PROCESSED YBa2Cu3Ox: D. Shi, K. Lahiri, S. Sagar, Dept. of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH 45221-0012
Single- and multiple-domain levitators of YBa2Cu3Ox have been processed using the seeded melt texturing method. It has been found that the growth rate has varied depending upon the undercooling, the temperature gradient, and composition. A systematic study has been carried out to establish the relationship between the growth front velocity and composition, in particular the 211 concentration. For a given undercooling and temperature gradient, the growth rate of the domain can be strongly affected by the 211 density in the matrix. Evidences will be provided to show the important contributions of compositions and 211 morphology to the growth rates of center domain during the seeded melt texturing.
8:50 am INVITED
EFFECTS OF Ce-BASED ADDITIONS ON THE MICROSTRUC-TURE AND MAGNETIC PROPERTIES OF MELT TEXTURED YBa2Cu3O7-
: P.J. McGinn, A. Banerjee, T. Meignan, Dept. of Chemical Engr., Univ. of Notre Dame, Notre Dame, IN 46556
The effects of CeO2 and BaCeO3 additions on the microstructure and magnetic properties of melt textured YBa2Cu3O7-
(Y-123) have been investigated. Both types of additions are effective in reducing the coarsening of Y2BaCuO5 particles in the melt during texturing. Both additions also lead to improvements in the magnetic properties of Y-123 compared to samples without Ce-based additions. The Ce-based additions are found to produce a "peak effect" in the magnetic hysteresis loop. The dependence of microstructure and magnetic flux pinning properties on the amount of Ce-based addition will be discussed.
9:10 am
GROWTH KINETICS OF MELT TEXTURED YBCO SUPERCONDUCTOR: V Selvamanickam, R.S. Sokolowski, Intermagnetics General Corporation, Latham, NY 12110; C.E. Oberly, Wright Patterson Air Force Base, Dayton, OH 45433; K. Salama, Y. Zhang, S. Salib, Texas Center for Superconductivity, Houston, TX 77204
The growth kinetics of YBCO superconductor have been studied by quench experiments during seeded isothermal melt-texturing. An undercooling of 15°C is found to be necessary to initiate nucleation of YBa2Cu3Ox following peritectic decomposition. A smooth transition is observed in the growth anisotropy with increasing undercooling, with the growth being faster along the c-axis at low undercoolings (15 to 25°C) and faster along the a-b plane at high undercoolings (>25°C). Based on these findings, a modified melt-texturing process was developed, where, instead of slow cooling following melting, an isothermal hold was employed in the temperature range where the growth is isotropic. By this modification, the time required to texture 1" diameter disks was reduced to 15 hours which is about 4 to 5 times faster than a typical slow cooling melt-texturing process. Correspondingly, the same magnitude of levitation force was achieved in a much shorter time in samples quenched during the modified process. Further, this process modification enabled a single do main growth over the entire sample thickness of 0.5", which could not be achieved by the slow cooling process. This research was sponsored by the Air Force Office of Scientific Research.
9:30 am INVITED
HIGH CRITICAL CURRENTS IN HIGH-ANGLE GRAIN BOUNDARIES IN YBCO SUPERCONDUCTOR: K. Salama, S. Sathyamurthy, A.S. Parikh, Texas Center for Superconductivity, 3201 Cullen Blvd., University of Houston, Houston, TX 77204-5769
A serious limitation to applications of YBCO superconductors is the presence of weak links in the form of grain boundaries. The high resistivity of YBCO grain boundaries is mainly attributed to the presence of solidified liquid phase and cracks at these boundaries. Using the liquid phase removal method, YBCO melt textured bars, over 10 cm in length and 0.5 cm2 in cross-section, are processed with "clean" grain boundaries free of secondary phases and cracks. Bars processed by this method are found to consist of several large domains separated by clean grain boundaries. The bars are polycrystalline in nature with an average of 5 grain boundaries for every one cm in length. Using transport current measurements, the bars are found to carry currents in excess of 1000 Amps (current limit of source available) at 77 K and self field with very small voltage drop (20 to 50 µV). Also, the same effect persists in the presence of external magnetic field up to 1.5 T at 77K. Contrary to previous findings, the misorientation angles of grain boundaries in these samples are found to be significantly high, ranging between 30° and 80°. These results indicate that the high angle grain boundaries in these bars are capable of sustaining very large currents and therefore make them suitable for applications such as current leads and current limiters.
9:50 am INVITED
SEARCH FOR NEW SUPERCONDUCTING SYSTEMS RELATED TO THE INFINITE LAYER FAMILY COMPOUNDS: NORMAL PRESSURE SYNTHESIS AND THE ROLE OF DOPING: R. Cloots, S.U.P.R.A.S., University of Liège, Chemical Institute B6, Sart-Tilman, B-4000 Liège, Belgium; H. Bougrine and M. Ausloos, S.U.P.R.A.S., University of Liège, Physics Institute B5, Sart-Tilman, B-4000 Liège, Belgium
The aim of this paper is to report on investigations on the influence of alkali and rare-earth ions doping in Ca1-xSrxCuO2 and Ba2Cu3O4Cl2 (and related compounds), in particular on their synthesis conditions and crystallographic structures. We concentrate the attention on the possibility to induce a charge transfer mechanism between constitutive layers by impurity doping, leading to a possible insulating-metal (superconductor) transition. Electrical resistivity and thermoelectric power measurements are presented in order to verify a possible superconducting behavior.
10:10 am BREAK
10:20 am
INVESTIGATIONS OF THE CHEMICAL COMPATIBILITY OF SUBSTRATES FOR 123 MELT-TEXTURED CERAMICS: F. Auguste, R. Cloots, S.U.P.R.A.S., University of Liège, Chemical Institute B6, Sart-Tilman, B-4000 Liège, Belgium; G. Moortgat, Centre de Recherche de l'Industrie Belge des Céramiques, Avenue Gouverneur Cornez 4, B-7000 Mons, Belgium; H. Bougrine, P. Clippe, M. Ausloos, S.U.P.R.A.S., University of Liège, Physics Institute B5, Sart-Tilman, B-4000 Liège, Belgium
The production of dense superconducting ceramics is affected by the thermal processing and parameters like the oxygenation process and the texture development. One of the serious problems which prevents the formation of useful REBa2Cu3O7-x-like bulk ceramics (RE = rare earth) for practical applications is the existence of weak links at the grain boundaries. Another annoying feature is that all usual containers or substrates for the growth react with the melt leading to a strong contamination of the "in situ" produced materials. The choice of the substrate is also very relevant for film growth. The cases of SrTiO3, MgO, Al2O3, and BaZrO3 crucibles for solution growth of single crystals of REBa2Cu3O7 has been investigated for the production of long length fibers or other complicated shapes of bulk Y or RE-123 materials. The chemical compatibility of the "substrate" towards the Y or RE-123 mixture is reported at various melt-texturing growth stages. For comparison, we looked at three different materials: BaZrO3, SrTiO3, and MgO.
10:40 am
MACROSEGREGATION OF 211 PARTICLES DURING ZONE MELT TEXTURING OF Y123: H. Balwada, P.J. McGinn, Dept. of Chemical Engr., Univ. of Notre Dame, Notre Dame, IN 46556
The phenomenon of 211 particle pushing by the solidification front during zone melt texturing has been studied. In the presence of second phase additions of PtO2 and BaCeO3, 211 particle refinement occurs. This refinement results in macroscopic segregation of 211 particles to the periphery of the sample rod. This phenomenon has been observed in samples textured with additions of PtO2 (.2 wt% and .5 wt%) and BaCeO3 (2 wt%) at speeds of 0.5 mm/hr and 1mm/hr. Without additions to refine the 211, this phenomenon is not observed. It was also found that higher texturization speeds lead to multiple grain nucleation at the solid/liquid interface. Particle pushing continues to take place under these circumstances, as long as the growth mechanism does not become dendritic, in which case this phenomenon is not observed. Effects of various solidification parameters on the extent of 211 particle segregation will be discussed.
11:00 am INVITED
MELT PROCESSING OF SCREEN-PRINTED ReBCO ON SILVER AT REDUCED TEMPERATURES AND OXYGEN PARTIAL PRESSURES: J.L. MacManus-Driscoll, N. Zafar, Centre for High Temperature Superconductivity and Dept. of Materials, Imperial College of Science, Technology and Medicine, Prince Consort Road, London, SW7 2BP, UK
A thermodynamic approach has been applied to the processing of rare earth barium cuprate superconductors (ReBCO). Studies were made on various ReBCO thick films which had been screen-printed onto Ag substrates. Using a coulometric titration technique, thermodynamic studies and reduced temperature and pressure (RTP) processing methods were carried out the thick film samples of ReBCO/Ag. The parameters governing the melt processing of ReBCO/Ag were optimised with a knowledge of phase stabilities and phase relations with respect to both temperature and oxygen partial pressure. Furthermore, accurate control of the oxygen partial pressure enabled the determination of the phase chemistry and the crystal growth rates during processing.
11:20 am
THE FABRICATION AND ANALYSIS OF BULK YBCO FOR USE IN AN INDUCTIVE FAULT CURRENT LIMITER: J.P.G. Price,* S. A. L. Foulds,* T.C. Shields,* D. J. Moule, P. D. Evans, J. S. Abell,* *School of Metallurgy and Materials, School of Electrical Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
Fault current limiters (FCL) have the potential of becoming one of the first major applications for high temperature superconductors. To improve commercial confidence in high temperature superconductivity, it is imperative that superconductors are produced and tested in certain applications. In this work, melt processed YBCO rings have been produced for use in an inductive fault current limiter. Various dopants and thermal treatments are utilized to improve the mechanical, electrical, and magnetic properties of the material. Using the FCL, critical current density (Jc) measurements can be made. Several different arrangements of the components of the FCL and the limiting performance are outlined. Characterization of the material is performed using polarized light microscopy, scanning electron microscopy, and pulsed Jc measurements. The final aim of this work is to determine whether bulk YBCO is suitable for use in inductive fault current limiters.
11:40 am
ADVANCES IN THE PROCESSING AND APPLICATIONS OF HIGH TEMPERATURE SUPERCONDUCTING FILMS: A. Gupta, M. Sisodia, R.K. Yadava, Dept. of Metallurgical Engineering, Malaviya Regional Engineering College, Jaipur 302 017, India
High critical temperature (high-Tc) superconductors have captured the interest of engineers and scientists world wide. For its commercial utilization in the field of microelectronics and electronic systems, they must be fabricated into desirable configurations - thin and thick films. During studies, it has been observed that these superconducting thin films operating at liquid N2 temperature offer great possibilities for faster, more sensitive and precise electronics devices. Present paper reviews the fabrication techniques of high-Tc superconducting thin films which primarily includes pulsed laser deposition, molecular ion beam epitaxy, chemical vapor deposition (CVD) by using epitaxial growth on single crystal substrates (YSZ, MgO, Si, etc.) with excellent microstructural control and properties relationship. In addition to it, thick film fabrication is also discussed with major techniques like screen printing and plasma spraying along with associated processing parameters. Furthermore, advanced applications of each are enumerated at length.
Room: 330B
Session Chairs: R. Schmid-Fetzer Technical Universitaet Clausthal, AG Elektronische Materialien, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld, Germany
8:30 am
THE SHORT- AND MEDIUM-RANGE STRUCTURE CHARACTERISTIC OF AMORPHOUS ALLOYS: K. Suzuki, K. Shibata, T. Otomo* and H. Mizuseki, Institute for Materials Research, Tohoku University, Sendai, Japan, *National Laboratory for High Energy Physics, Tsukuba, Japan
Atoms in amorphous alloys are combined into a configuration of minimizing the local energy in the short-range structure instead of relaxing the total energy minimum of a system. The short-range order of amorphous alloys often shows similarity to that of their crystalline counterparts. The survival of the local coordination in amorphous alloys is also confirmed by the vibrational density-of-states. However, the medium-range structure of amorphous alloys has an quite unique nature in contrast to the crystalline alloys. The low-energy excitation in amorphous alloys appearing in the energy range of 1 to 3 meV, which is usually observed as an excess specific heat in addition to the Debye-type harmonic vibration, is contributed from the locally collective motion characterized spatially by the medium-range structure fluctuations. The experimental results mentioned above for Pd-Si, Pd-Ge, Pd-Ni-P and V-Ni amorphous alloys were observed by pulsed neutron scattering based on accelerators, which is a powerful tool for characterizing the structure of amorphous alloys, because a very wide dynamic range of energy- and momentum-transfer can be surveyed.
9:00 am INVITED
NEUTRON DIFFRACTION STUDIES OF LIQUID ZINTL-ALLOYS UP TO 2000: K.R. Winter, University of Dortmund, Department of Chemistry, Physical Chemistry I, D-44227 Dortmund, Germany
Neutron diffraction measurements have been carried out on equiatomic liquid Zntl-alloys, such as KPb, CsPb, and NaSn, over a wide temperature interval, ranging from 800 to 2000 K, and at pressures up to 150 bar. In the crystalline state, these are semiconducting compounds containing tetrahedrally coordinated polyanions. The diffraction results indicate the survival of polyanions in the expanded liquid alloys even up to high temperatures, as indicated by the persistence of the peak of S(Q) at Q
1Å-1, which is indicative of intermediate-range order. The position of this peak shifts towards lower Q-values, its height decreases, and its width drastically increases with increasing temperature and correspondingly decreasing density. The experimental results and the corresponding real-space information are compared with the crystal structures in the solid state and with the results of recent ab-initio molecular dynamics calculations and computer modelling studies. In addition, we present neutron diffraction data on the effect of pressure on the structure factor of solid CsPb in the rotator phase.
9:30 am INVITED
TRANSFORMATION OF THE AMORPHOUS TO THE NANO-CRYSTALLINE STATE: R. Luck, K. Lu*, Max-Planck-Institut fur Metallforschung, SteebstraBe 75, D-70174 Stuttgart, Germany, *also with National Laboratory for RSA, Institute of Metal Research, Academia Sinica, Shenyang 110015, China
The crystallization of amorphous materials has been studied extensively during the last two decades. However, the formation of nanocrystals - that is a crystalline morphology with an average grain size of 5 to 50 nm - from t he amorphous state has been detected few years ago. Since that time it is used more and more. This procedure is performed isothermally below the crystallization temperature. We present data of the kinetics of this process. The transformation has been monitored by the measurement of several physical properties; we have applied especially the measurement of magnetic susceptibility. Magnetic measurements are able to detect the onset of the transformation of amorphous Ni-P alloys much earlier than was possible with differential scanning calorimetry. The transformation kinetics can be analyzed by means of the Avrami plot based on the Johnson-Mehl-Avrami equation. The kinetics of further solid state reactions in the nanostructured material can be investigated similarly.
10:00 am BREAK
10:15 am INVITED
THE EFFECT OF ORDER-DISORDER PHASE TRANSFORMATION ON VOLUME INTERDIFFUSION: E. Rabkin, B. Straumal, W. Gust, Institute fur Metallkunde and Max-Planck-Institut fur Metallforschung, Seestr. 75, D-70174 Stuttgart, Germany
The volume interdiffusion has been studied in Fe-Si single crystals in the vicinity of A2-B2 ordering and in Cu-Au single crystals in the vicinity of Al-L12 ordering. Decreased interdiffusivity rates were found, as expected, in the ordered Fe-Si alloys. In the Cu-Au alloys, however, the interdiffusivity in the ordered region is higher than it could be expected by extrapolation of the diffusivities in the disordered phase. Different approaches were used to calculate the thermodynamic factor for interdiffusion, and the results obtained are in qualitative agreement with the experimental data. The influence of the variation of the partial molar volumes of the components during the phase transition on the calculated interdiffusivities is discussed.
10:45 am INVITED
THE METASTABLE STATE OF AMORPHOUS ALLOYS: R. Bormann, Institute for Materials Research, GKSS Research Center, D-21494 Geesthacht, Germany
In the past, the thermodynamic state of amorphous phases has been of great concern. Due to highly non-equilibrium preparation processes involving rapid quenching and condensation techniques it has been assumed that these alloys are frozen-in liquids where a thermodynamic description cannot be applied. Recently however, the existence of a metastable state in single-phase and phase-separated amorphous alloys has been confirmed unambiguously by electromotive force (EMF) measurements and characterized by calorimetric and structural investigations. EMF measurements also allow the direct determination of the chemical potentials of the least noble component and thereby (for binary systems) the Gibbs energy of the amorphous phase. By means of thermodynamic modeling, e.g. by the CALPHAD method, phase diagrams of metastable phases can be calculated for the amorphous phase. These can predict the amorphous phase formation during rapid quenching of the melt and during solid-state reactions. The results demonstrate that the formation of amorphous alloys is strongly determined by the thermodynamics of the undercooled liquid and the amorphous phase.
11:15 am INVITED
THERMODYNAMIC CONSIDERATIONS IN THE RATIONALIZATION OF SOLID-STATE AMORPHIZATION BETWEEN METALS AND III-V SEMICONDUCTORS: Y.A. Chang, Department of Materials Science and Engineering, University of Wisconsin, Madison, WI 53706; F.-Y. Shiau, Trace Storage Technology Corp., Hsinchu, Taiwan, China; S.-L. Chen, CompuTherm LLC, Middleton, WI 53562; S. Mohney, Department of Materials Science and Engineering, Penn State University, University Park, PA 16802
In addition to binary metal/metal systems, solid-state amorphization reactions have been reported to occur in numerous ternary III-V semiconductor/metal systems such as GaAs/Ni, GaAs/Co, InP/Ni, InP/Pd, InP/Co and InP/Pt. In this presentation a thermodynamic argument will be presented first to rationalize the occurrence of an amorphous phase in a model binary system. This argument will be used next to rationalize solid-state amorphization in III-V semiconductor/metal systems focusing on the GaAs/Co case. In this system, sufficient thermodynamic information is available.
Room: Salon 6
Location: Clarion Plaza Hotel
Session Chairs: John Moore, Dept. of Met and Matls, Colorado School of Mines, Golden, CO 80401-1887; Iver Anderson, Ames Laboratory, Iowa State University, 122 Metals Development Bldg, Ames, IA 50011-3020
8:30 am
CHEMICAL SYNTHESIS AND PROCESSING OF NANOSTRUCTURED ALUMINUM NITRIDE POWDERS: G.M. Chow, L.K. Kurihara, R. Rayne, L.S. Choi, P.E. Schoen, Naval Research Laboratory, Washington, DC 20375; M.I. Baraton, Laboratory for Ceramics and Surface Treatment, University of Limoges, France; Laboratory for Moelcular Interfacial Interactions, Code 6930/Center for Bio/Molecular Science and Engineering, also at Department of Biochemistry, Georgetown University, Washington, DC; Materials Science Division; Chemistry Division
Nanostructured ceramic AlN materials are fabricated using chemical routes. The precursor powders of aluminum hydroxide are synthesized by hydrolysis of aluminum tri sec butoxide. These precursor powders are calcined and subsequently transformed to nanoscale AlN powders by nitriding in an ammonia environment furnace at temperatures to 1100°C. The AlN powders are consolidated to green bodies by cold isostatic pressing. The green bodies are sintered in a nitrogen furnace for densification. Characterization techniques include XRD, TEM, HRTEM, DSC, and surface FTIR. The effects of solvent, pH on the control of particle size, particle size distribution and agglomeration are addressed.
8:55 am
FREEZE DRYING SYNTHESIS OF OXIDE POWDERS: A STEP TO POWDER ENGINEERING: O.A. Shlyakhtin, V.V. Ischenko, O.A. Brylev, N.N. Oleinikov, Department of Chemistry, Moscow State University, 119899 Moscow, Russia
Spray freezing of multicomponent aqueous solutions followed by freeze drying leads to formation of homogeneous salt powders with stable and extensive porous structure. The influence of specific microstructure on the properties of fine powders obtained by thermal decomposition of these precursors remains underestimated. Indeed the decomposition of the native freeze dried salt precursor resulted in the formation of single phase LiCoO2 at T=300°C while breaking the aggregates before decomposition led to multiphase product. In the other case carefully controlled influence on the microstructure of the intermediates allowed us to accelerate 3-5 times the rate of grain growth during annealing of Fe2O3 and BaZrO3 fine powders.
9:20 am
FRONTIERS IN PREPARATION OF Si3N4 POWDER BY RFPCVD: Rioyu Hong, Guoliang Zheng, Hongzhong Li, and Jianmin Ding, Inst. of Chem. Metallurgy, Chinese Academy of Sciences, Beijing 100080, China; Energy Research Corp., Great Pasture Road, Danbury, CT 06813
Radio frequency plasma chemical vapor deposition (RFPCVD) method is used to prepare ultrafine Si3N4 powder on a large scale. The characteristics of the RFPCVD method are given. It is pointed out that there are three kinds of mathematical models for the RF plasma generator and RFPCVD reactor: thermodynamic, hydrodynamic, and aerosol dynamic models with respective features. Research work on theoretical and technical studies for the preparation of ultrafine Si3N4 powder are given in detail. At last, the existing problems of the RFPCVD technology are given: (1) The thermodynamic, hydrodynamic and technical studies should be combined together. (2) Hydrodynamic modeling should be made for the RF plasma generator and CVD reactor simultaneously. (3) The improvements for preparing the Si3N4 powder should be combined with the aftertreatment of the product and also should be related to its sintered properties. (4) The improvements of the Si3N4 ceramic should be combined with the preparation of composite ceramics or surface modification of Si3N4 particles.
9:45 am BREAK
10:00 am
PREPARATION OF COMPOSITE PARTICLES BY RAW MATERIAL SOLUTION INJECTION: Hiroyuki Nakamura*, Yun-Fa Chen+, Kunio Kimura*, Hiroshi Tateyama*, Hideharu Hirosue*, Kyushu National Industrial Institute Japan , +Institute of Chemical Metallurgy, China
Composite particles, which are expected as raw materials for composite, are often prepared by alkoxide method or homogeneous precipitation method. However, using these methods, it seems to be rather difficult to control structure of the coating layer (ex. multi-layered, homogeneously mixed, graduated layered). From this point of view, the presenters tried to prepare composite particles by injecting raw material solution into a dispersion of core particles (diameter: micro meter order). The presenters believe that this method will make it easier to control the structure of coating layer. In this presentation, preparation of alumina-hydrate coated SiC whiskers is investigated. We used SiC whiskers as core particles and aluminum salt (nitrate, chloride, sulfate) solution as raw material solution, relationships between preparation conditions (injection speed, concentration of core particles etc.) and morphology of coated particles were explored. Moreover, application of this method for preparation of double-layer coated particles will be presented.
10:25 am
REACTIVE SYNTHESIS OF CERAMIC POWDERS: John J. Moore, Dennis W. Readey, Dept. of Met. and Matls Engr., Colorado School of Mines, Golden, CO 80401-1887
Reactive synthesis has been used to synthesize a number of different ceramic powders, such as TiB2, SiC, Si3N4. This paper will discuss the effect of reaction parameters, e.g., type of synthesis reaction, exothermicity of reaction, reactant particle size, reaction temperature and time, on the control of the size of the product powder, product yield, chemistry and purity.
10:50 am
SYNTHESIS OF ALUMINUM NITRIDE POWDERS USING DC-PLASMA PROCESSING: Paul Prichard, Matthew Besser, Daniel Sordelet, Iver Anderson, Ames Laboratory (USDOE), Iowa State University, Ames, IA 50011-3020
Experiments were performed to synthesize AlN powders by reacting Al with N using a conventional dc-plasma as a heat source. Attempts to form AlN powders by feeding Al powder into a nitrogen-rich plasma open to the atmosphere produced mainly aluminum oxide. Subsequent experiments were run inside a chamber which was backfilled with nitrogen. The nitrogen environment suppressed the formation of aluminum oxide, but little AlN was formed by using Al powder as the feedstock material. A furnace and crucible assembly was designed to feed molten Al directly into a convergent nozzle positioned directly at the face of the dc-plasma gun. Powders formed using this arrangement show a significant increase in the level of AlN formation. The presence of AlN was verified by chemical analysis and X-ray diffraction. Results were dependent upon chamber pressure, plasma velocity and molten liquid feed rate. The experimental parameters, equipment design and results will be reported in detail, and a suggested reaction mechanism will be discussed.
11:15 am
MECHANOCHEMICAL SYNTHESIS OF ULTRAFINE CERAMIC POWDERS: J. Ding, T. Tsuzuki, P.G. McCormick, Research Centre for Advanced Mineral and Materials Processing, The University of Western Australia, Nedlands, Perth, WA 6907, Australia
The synthesis of ultrafine alumina and zirconia powders by mechanochemical reaction has been investigated using x-ray diffraction, TEM and DSC measurements. Mechanical milling of AlCl3 or ZrCl4 with CaO resulted in nanoscale mixtures of the starting phases, with no evidence of the occurrence of any reaction during milling. The formation of separated 10-20 nm particles of g-Al2O3 within a CaCl2 matrix occurred after heat treating the as-milled AlCl3/CaO mixture above 350°C. Cubic ZrO2, particles 5-10 nm in diameter, were formed after heat treatment above 300°C. With both reactions, removal of the CaCl2 by-product phase was carried out using an appropriate solvent. Measurements of the effect of heat treatment temperature on crystal structure and particle size will be reported.
Room: 232C
Session Chairperson: Prof. Dr. D.V. Drobot, Moscow State Academy of Fine Chemical Technologies, Pr. Vernadskogo 86, 117571 Moscow, Russia
8:30 am
PREPARATION OF NANOSIZED RHENIUM OXIDE AND RHENIUM BASED METAL PARTICLES BY THERMAL DECOMPOSITION OF ORGANIC PRECURSORS: G.A. Seisenbaeva, D.V. Drobot, Moscow State Academy of Fine Chemical Technologies, Pr. Vernadskogo 86, 117571 Moscow, Russia; V.G. Kessler, Moscow State University; Moscow, Russia; M. Sundberg and M. Nygren, Arrhenius Laboratory, University of Stockholm, Sweden
The thermal decomposition of the organic derivatives of rhenium (Re4O2(OMe)16 (I), ReMoO2(OMe)7 (II), Re4-xWxO2 (OMe)16 (III), Re2O5(acac)2 (IV)) in air at temperatures below 400°C leads in case of I, III and IV to the oxide powders containing fine particles (40-60 Å) with ReO3 type structure included into amorphous matrix, while in case of II a mixture of ReO3 and MoO3 phases was obtained. In an inert atmosphere (N2, Ar) at 300-400°C. I also gives a ReO3 phase, II and III give a pseudocubic phase with Re1-xMxO2 composition (M=Mo, x ¾ 0.25), while IV provides spherical amorphous particles (~1 µm size) of rhenium metal. The reduction of I-III in hydrogen atmosphere leads to formation of single-phase metal product (with the 
-phase alloy structure) at the temperature about 300-400°C.
8:50 am
SOFT CHEMISTRY ROUTE TO RHENIUM-BASED MATERIALS: V.G. Kessler, Moscow State University; Moscow, Russia; G.A. Seisenbaeva, D.V. Drobot, Moscow State Academy of Fine Chemical Technologies, Pr. Vernadskogo 86, 117571 Moscow, Russia
The so called soft chemistry approach is usually based on hydrolytic or pyrolytic decomposition of the complexes of metals with organic ligands. The methoxides of rhenium (I), rhenium and molybdenum (II) and rhenium and tungsten (III) were prepared by anodic oxidation of rhenium metal in methanol in the presence of LiCl as electrolyte and methoxides of countermetals. Acetylacetonate, Re2O5(acac)2 (IV) was obtained by interaction of re2O7 and Hacac in toluene. I and III are insoluble in common organic solvents and air stable in contrast to highly soluble and air and moisture sensitive II. IV is insoluble in hydrocarbons and dissolves in ethers with decomposition. All these compounds are volatile at reduced pressure and decompose in inert atmosphere into mixed low-valent oxides or, in case of IV, into rhenium metal.
9:10 am
REDUCTION OF AMMONIUM PERRHENAT TO METAL RHENIUM: V.P. Seleznev, D. Mendeleev, University of Chemical Technology of Russia, Miusskaya Sq. 9, Moscow 125047, Russia
9:10 am
BINUCLEAR RHENIUM CLUSTERS AS A BASIS FOR METAL COATINGS AND NEW FUNCTIONAL MATERIALS: A.V. Shtemenko, Ukrainian State University of Chemical Technology, Gagarin Av. 8, Dniepropetrovsk 320005, Ukrainia
Thermal behaviour of binuclear halogenated and halogencarboxylated Re26+ clusters, synthesized according to elaborated procedures, is studied. It is shown, that the last stage of thermal distribution of the substances in vacuum or inert atmosphere is formation of metal rhenium with content of contaminants 0,001-0,01%. Method of obtaining of composite material of "metal-oxide" type is elaborated, providing the best combination of thermophysical and mechanical properties in wide temperature intervals. Density of rhenium framework of the material approaches to that of theoretical and microhardness of 250-260 kg/mm2.
9:30 am
THE CATALYTIC PROPERTIES OF SUPPORTED RHENIUM AND RHENIUM HEPTASULFIDE: Margarita A. Ryashentseva, Zelinski Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow, Leninsky prospect 47, Russian
The catalytic properties of supported rhenium were widely investigated in the reactions of de, hydrogenation, hydrogenation of hydrocarbons and reforming of petrol fractions. Lowpercentage bimetallic supported catalysts containing rhenium and palladium have been developed. A world first publication of these results were in 1960's - a little bit earlier than known Pt - Re reforming catalysts. An effective catalyst, rhenium heptasulfide has been found in the chemical synthesis of S - and N - containing heterocycles compounds. It is a specific selective catalyst for the hydrogenation of the pyridine ring without affecting the benzene ring in aryl-substituted pyridines, including those containing silicon, isoquinolines, annelated pyridine and condensed aromatic compounds. The process of hydrogenation in the presence of alcohols is going on along with N - alkylation on rhenium heptasulfide. Selective hydrogenation of various number of physiologically active substances, containing a pyridine ring could afford some alkaloids and their analogs.
9:50 am BREAK
10:10 am
CHEMISTRY OF BINUCLEAR RHENIUM CLUSTERS: A.V. Shtemenko, B.A. Bovykin, Ukrainian State University of Chemical Technology, Gagarin Av. 8, Dniepropetrovsk 320005, Ukrainia
Binuclear rhenium clusters are the first examples of inorganic substances, which contain multiple metal-metal bond, that is the reason of some special (unique) properties of these compounds. Mechanism of formation of Re3+ clusters is thoroughly studied by us that became the base of elaboration of new technological methods of synthesis of different types of binuclear Re26+ clusters. On the base of accomplished investigations the perspective of binuclear rhenium clusters application is shown as precursors for obtaining of rhenium and new inorganic materials on it's basis, catalysis and promotors of catalytic systems among them.
10:30 am
SOLID STATE CHEMISTRY OF RHENIUM HALOGENIDE AND OXIDES: D.V. Drobot, Moscow State Academy of Fine Chemical Technologies, Pr. Vernadskogo 86, 117571 Moscow, Russia; M.B. Varfolomeev, Institute of the Chemical Problems of Microelectric, Pr. Vernadskogo 86, 117571 Moscow, Russia
Results of the investigations of the phase equilibriums in the systems Re-O-Hal (Hal = C1, Br, I) individual phases M(ReO4)3 (M = metals of the III group) in systems Re-O-M and corresponded crystallohydrates M(ReO4)3nH20 (n = 3; 4; 4,5 and 8) are discussed. By experimental dates P-T-x diagrams of binary systems are obtained and it is shown that oxohalides Re204Cl5 (Hal = Cl, Br) can be obtained. By means of vapour pressure measurements thermodynamic dates for sublimation and vaporisation processes of individual phases are obtained. Thermostability of ReI3-x and lower rhenium iodides is investigated. The processes of chlorination of Re(IV) and Re(VI) oxides are investigated. Total results are the importance for CVD processes and technology of Re compounds purification. The methods of controlled synthesis ReO3, ReHalx, ReOyHalx, M(ReO4)3 and M(ReO4)3 nH20 are described. Crystall structure and thermal stability of M(ReO4)3 and M(ReO4)3 nH20 are investigated. It is shown that crystal! structure of M(ReO4)3 nH20 depends on the size of ri for M3+.
10:50 am
USAGE OF ELECTRODIALYSIS METHOD FOR PREPARING HIGH-PURITY RHENIUM CHEMICAL COMPOUNDS: A.V. Elutin, M.V. Istrashkina, Z.A. Peredereeva, State Research Centre-State Institute of Rare Metals-GIREDMET, 5 B. Tolmachevsky Per., Moscow 109017, Russia
This report presents the results of studies the process of electrodialysis of rhenium-containing solutions. It contains experimental data obtained by studying transport of rhenium and impurity elements through different membranes and selection of optimal electromembrane system, electrode materials and ion-exchange membranes. The received data have allowed to develop methods of electrodialysis conversion of potassium perrhenate to superpure ammonium perrhenate and preparation of highpurity concentrated perrhenic acid by treatment of contaminated salts. It is found that the method of electrodialysis is very efficient for recovery of rhenium from complicated sulphuric-acid solutions containing molybdenum, iron, zinc, lead and other elements. The described methods are successfully used at Russian enterprises.
11:10 am
PROGRESS IN ANALYTICAL CHEMISTRY OF RHENIUM: Ludmilla V. Borisova, V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 117975 Moscow, Kosygin Str. 19, Russia
Rhenium speciations in various solutions, which are important for process and analytical chemistry have been studied for many years. Model systems, containing Rhenium, different ligands and reductors, equilibrium diagrams of Rhenium compounds were studied. Analytical forms of Rhenium compounds and their properties (oxidative-reductive, complexability, catalytical and etc.), their composition, structure, mechanism and reaction kinetics with the used of WMS, IR, ESR, NMR and kinetic spectroscopy methods were revelated. Effective analytical systems were discovered on the basis of these investigations. Perspective methods of optical and potentiometrical sensors, catalytic methods for cone. of alkaline and acid medias with detection limit down to 0.001 µgRe/ml, coulometric method for mg Re determination, ICPAES, luminescence, thermochromatographical, spectrophotometric, ESR and other methods were developed. Some of them are in use as FIA detectors. New sorbents, watersoluable polymers with membrane filtration, electrodialysis and electromigration appeared to be the base for effective isolation and preconcentration of Rhenium. Express-testing methods, based on the catalytic properties of "unusual" state of oxidation Rhenium - Re (VI), were created and applied for analytical control on several manufactures (limit of detection up to 0.001 µg/ml). The developed methods comprise the basis of analytical control during the reworking of Rhenium-containing ores, technological rests, waste Re-Pt catalysators, volcanic products from Kurila Islands, being used in field conditions, and also for geochronology by Re/Os isotop ratio.
11:20 am
RHENIUM (I)-CARBONYL COMPOUNDS OF DI-2-PYRIDYL KETONE: ELECTROCHEMICAL SENSORS FOR ELECTROPHILES AND METAL IONS: Mohammed Bakir, Department of Chemistry, The University of the West Indies, Mona Campus, Kingston 7, Jamaica, W.I.
Room: 330A
Session Chairperson: J.E. Benci, Wayne State University, Dept. of Materials Science and Engineering, Detroit, MI 48202
8:30 am
DEFORMATION BEHAVIOUR OF 7075AL/ SICP COMPOSITE DURING MULTIPASS DEFORMATION AT HIGH TEMPERATURES: A. Razaghian, D. Yu, T. Chandra, Department of Materials Engineering, Wollongong University, Wollongong, NSW, 2522, Australia
Hot deformation behaviour of 7075 aluminium alloy containing 15 vol% of SiC particles (average size of 14 am) and the monolithic alloy was studied at 300 and 400°C at constant strain rate of ls-1 under condition of uniaxial compression. The effect of delay between two consecutive passes on the high temperature mechanical strength and microstructural development was examined. The results showed that the fractional softening (%FS) increased in both reinforced and monolithic alloys when the deformation temperature increased from 300 to 400°C, but monolithic alloy showed a slightly higher FS compared to composite under identical deformation conditions. TEM examination revealed that the monolithic alloy and composite contained almost similar substructures after either single or double pass deformation at a given temperature irrespective of interpass hold time. However, some subgrain growth was observed in these materials during holding after deformation at 400°C, but this was not the case at 300°C. The absence of subgrain growth at lower temperature can be attributed to pinning effect by fine dispersions present in the matrix. The structural study also showed that static recrystallization did not occur in these materials during hold time between passes, and the fractional softening occurs mainly due to static recovery.
8:55 am
WEAR PROPERTIES OF PARTICULATE REINFORCED ALUMINUM ALLOYS: Yeong-gi Cho, Su-young Kim, Ikmin Park, Kyungmox Cho, Dept. of Metallurgical Eng. Pusan National University, Pusan 609735, Korea
Wear properties of cast AlSiCp composites were characterized under dry and lubricated conditions. Wear tests were performed employing blockonroller type and pinondisk type machines. Test conditions including applied load, sliding speed and sliding distance were changed for wear tests. Wear behavior was investigated by analyzing worn surfaces and debris, mainly as a function of the sliding speed. Results show that there exist transition speeds at which the minimum wear rate occurs for both dry and lubricated conditions. However the appearance of wear transition is not well defined for the lubricated wear. It was found that SiCp reinforcement affects wear at the low sliding speeds and the softening of Al matrix dominates wear at the high sliding speeds. Main wear mechanism is abrasive wear although some amounts of adhesive wear are observed especially at the high sliding speeds.
9:20 am
FATIGUE CRACK GROWTH BEHAVIOR OF DIECAST AND CAST SiC PARTICULATES REINFORCED ALUMINUM COMPOSITES: Song-Hee Kim, Iee-Jeoung Kim, Department of Materials Engineering, Kangwon National University, Chunchon, Kangwondo, Korea, 200701
The fatigue crack growth rate (FCGR) of SiC particulates reinforced aluminum matrix composites containing 10vol.% and 20vol.% of SiC fabricated by the casting and the die-casting processes have been studied over a wide range of stress intensity factor for various load ratios. The effect of volume fraction of SiC on FCGR was also investigated for the diecast and cast composites. Fracture toughness was found to affect the fatigue crack growth behavior at the higher level of stress intensity factor range; however, at lower level, fatigue crack roughness related with the volume fraction of SiC reinforcement was more responsible for the fatigue crack growth. Diecast composite with 20vol.% of SiC showed the superior fatigue crack propagation resistance at the lower level of AK, but the inferior resistance at the higher level of AK due to the decreased ductility and fracture toughness.
9:45 am
HIGH STRAIN RATE SUPERPLASTICITY OF DISCONTINUOUS FIBER REINFORCED PUR ALUMINUM COMPOSITES: Tsunemichi Imai, Sumito Kojima, Isao Tochigi, Gilles L'Esperance, Bande Hong, Daming Jiang; National Industrial Research Institute of Nagoya, Hirate-cho, Kita-ku, Nagoya 462, Japan; Nagoy Minucipal Industrial Research Institute, 4-3-4 Rokuban-cho, Atsuta-ku, Nagoya 456, Japan; Ecole Polytechnique de Montreal, PO Box 6079, Station A, Montreal (Quebec) Canada; Harbin Institute of Technology, Harbin 150001, China
High Strain Rate Superplasticity (HSRS) of metal matrix composite has a great potential to apply to components and structures in automobile and aerospace industries and even semi-conductor packings since the composites exhibits excellent mechanical, physical and thermal properties. IN90 pure aluminum (Al) alone and AlN/1N90 pure Al composite made by PM method, and -Si3N4w/99.99% pure Al composite fabricated by squeeze casting were hot-rolled after extrusion and the superplastic characteristics were investigated to clarify the deformation mechanism. IN90 Al alone hot-rolled about 773K could produce the m value of more than 0.3 and 300~450% at the strain rate of about 0.01s-1 and at 913~923K and also has threshold stress in the strain rate less than 0.01s-1. -Si3N4w/99.9% pure Al composite exhibits the m value of 0.47 and the total elongation of about 200% at the strain rate of 0.5s-1 and at 903K. The results indicate that the HSRS could occur by grain boundary sliding without interfacial sliding at liquid phase, because the optimum temperature to produce the HSRS is just below incipient melting temperature.
10:10 am
FRACTURE BEHAVIOR OF COBALT COATED Al203 SHORT FIBER REINFORCED 2024 Al COMPOSITE: K.H. Baik*, E.S. Lee, and S. Ahn, Advanced Materials Division, Research Institute of Industrial Science and Technology, San 32, Hyojadong, Pohang, Kyungbuk 790330, Korea; *Dept. of Materials Science, Oxford University, UK
The effect of chemical reaction at coating/fiber interface on the fracture behavior of 2024 Al alloy reinforced with Co coated Al2O3 fibers were investigated. Al2O3 fibers were coated with metallic Co by solgel process using Co acetate compound. The coated fibers were annealed at temperatures ranging from 300 to 1000°C in vacuum to generate interfacial reaction between the Co coating and the Al2O3 fiber. Regardless of the annealing temperatures, a fair amount of solute Co was detected near the Al2O3 fiber surface ensuring the good bonding between the coating and the fiber. AlgCO2 and Co203 phases were formed at high annealing temperatures. SEM fractography of the composite showed the change of fracture behavior as a result of the interfacial reaction. Fiber debonding was frequently observed in the composite rein forced with fibers annealed at low temperatures. On the other hand, the composite with fibers annealed at higher temperatures had improved tensile strength, and showed much smaller dimples around the fibers and relatively less fiber pull-out. In-situ SEM fracture study was performed to understand the micro fractureprocess of the composite.
10:35 am
THE INFLUENCE OF SOLUTIONIZING TIME AND TEMPERATURE ON THE BONDING CHARACTERISTICS AND MICROSTRUCTURES BETWEEN THE PARTICLES AND MATRIX IN COMPOSITES WITH 6061 AND 2014 ALLOYS REINFORCED WITH ALUMINA PARTICLES: Daniel Salas, Javier Ponce, Erica Corral, S.K. Varma, Department of Metallurgical and Materials Engineering, The University of Texas at El Paso, El Paso, TX 79968-0520
The influence of solutionizing time and temperature on the microstructural development and bonding characteristics between the matrix and the particles will be characterized in composites with 6061 and 2014 aluminum alloys reinforced with 0.10, 0.15 and 0.20 volume fractions of Ai2O 3 particles (VFAP) solutionized at 520, 530, and 540°C for different times up to 20 hours to produce various grain sizes after quenching. The different heat treated samples after solutionizing v,/ill be subjected to room temperature tensile fracture at various strain rates (attainable in an Instron tensile testing machine) and the fracture surfaces will be characterized by SEM and related to the UTS. The samples deformed to various true strains will be analyzed in the TEM to determine the influence of solutionizing time on the microstructural development during the deformation. The results on the composites will be compared with similar treatments performed on the alloys in their monolithic forms in order to determine the deformation mechanisms in the composites. This research has been supported by the National Science Foundation through the grant number HRD9353547.
11:00 am
HOT DEFORMATION BEHAVIOR OF (SiCw+SiCp)/AA2124 COMPOSITES: Yeon-Chul Yoo, ByungChul Ko, and Joon Park, Department of Metallurgical Engineering, Inha University, Inchon 402751, Korea
The hot deformation behavior of 15 vol.% (SiCw + SiCP.) reinforced AA2124 composites was investigated by hot torsion tests. The AA2124 Al based composites with different volume fractions of SiCw and SiCP reinforcements were fabricated by the powder metallurgy. Detailed analyses of flow curves and deformed microstructures were made to identify the hot restoration mechanism, such as dynamic recrystallization or dynamic recovery. Also, the dependence of flow stress and ductility on temperature and strain rate was studied. From the flow curves and microstructures of the hot deformed composites, it has been found that dynamic recrystallization was responsible for the hot restoration of the composites. The flow stress of the hybrid composites was higher than that of the monolithic AA2124 alloy. The flow stress and ductility of the hybrid composites were investigated with respect to the ratio of SiCw and SiCP, reinforcements.
11:25 am
ANALYSIS OF RESIDUAL STRESSED IN Ti-ALLOY, SCS-x MMC's BY NANOINDENTATION: K.L. Kendig, R. Gibala, D.B. Miracle, B.S. Majumdar; Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI; Materials Directorate, Wright Laboratory, Wright-Patterson Air Force Base, OH; UES Inc., Dayton, OH
Knowledge of variation of residual stresses aids in prediction of composite deformation and failure. Hardness measurements with high spatial resolution using extremely low load indentations, such as by nanoindentation techniques, may be an indicator of such variation of residual stresses. In this work, nanoindentation was used to determine hardness as a function of radial position from a fiber for a Ti6Al-4V, SCS-6 SiC fiber composite and a Ti-15V-3Al-3Cr-3Sn, SCS-0 SiC fiber composite, each in the as-consolidated condition. Residual stress predictions from a finite element model were compared to the hardness distributions obtained by nanoindentation. A small difference in nanoindentation hardness was found between the two phases of the Ti-6Al-4V matrix in the Ti-6Al-4V, SCS-6 composite, which likely masked any effects of residual stress on hardness. The Ti-15V-3Al-3Cr-3Sn, SCS-0 system was chosen to avoid this complication and to allow more direct correlation between predicted residual stress and nanoindentation hardness.
Room: 314B
Session Chairperson: Rajiv K. Singh, University of Florida, 317 MAE, PO Box 116400, Gainesville, FL 32611-6400
8:30 am INVITED
ATOMIC VERSUS MOLECULAR BEAMS FOR DOPING OF III-V MATERIALS DURING GROWTH IN ULTRAHIGH VACUUM: C.R. Abernathy, University of Florida, PO Box 116400, Gainesville, FL 32611
9:00 am INVITED
RECENT ADVANCES IN CARBON NITRIDE AND RELATED HARD COATING MATERIALS: Y.P. Chung, North Western University, 2145 Sheridan Rd., Evanston, IL 60208
9:30 am INVITED
MEASUREMENTS AND SIMULATION OF BEAM-ENHANCED EPITAXIAL GROWTH PROCESSES: E.H. Chason, Sandia National Laboratory, Albuquerque, NM 87185
10:00 am BREAK
Session Chairperson: Roy Clarke, Department of Applied Physics, University of Michigan, Ann Arbor, MI 48109-1120
10:15 am INVITED
MICROSTRUCTURAL EVOLUTION IN LOW ENERGY BEAM PROCESSING OF THIN FILMS: Krishna Rajan, Rensselaer Polytechnique Institute, Dept. of Materials Science & Eng., MRC-110, Troy, NY 12180-3590
10:45 am INVITED
UHV SPUTTER-DEPOSITION OF ULTRATHIN MAGNETIC FILMS AND MULTILAYERS: J.R. Childress, University of Florida, PO Box 116400, Gainesville, FL 32611
11:15 am
DEPOSITION OF DIAMOND FROM ALCOHOL PRECURSORS IN AN ELECTRON CYCLOTRON RESONANCE PLASMA: Donald R. Gilbert, Rajiv K. Singh, University of Florida, PO Box 116400, Gainesville, FL 32611
11:30 am INVITED
SPUTTER DEPOSITION OF PHOSPHORS FOR ELECTROLUMINESCENT FLAT PANEL DISPLAY: Mark R. Davidson, Paul H. Holloway, Balu Pathangey, University of Florida, University of Florida, PO Box 116400, Gainesville, FL 32611
Room: Salon 3
Location: Clarion Plaza Hotel
Session Chairperson: Dr. K. Dannemann, GE Power Generation Engineering, One River Road, Schenectady, NY 12345
8:30 am
THE EFFECT OF THICKNESS AND TOTAL SULFUR CONTENT ON PWA1480 OXIDATION: A SCALE ADHESION MAP: J.L. Smialek, NASA Lewis Research Center, Cleveland, OH 44135
The cyclic oxidation resistance of advanced superalloys is dramatically improved when the typical sulfur impurity levels are reduced from about 3-10 ppmw to below 1 ppmw. Optimum scale adhesion can be obtained when the sulfur content is reduced below a discreet critical level. To demonstrate this phenomenon, coupons of PWA1480 were desulfurized by a hydrogen annealing process. The degree of desulfurization was controlled by sample thickness and annealing time and temperature, but did not strictly follow a Dt/L2 diffusion parameter dependency. From an initial sulfur value of 6 ppmw, 15 different sulfur levels were produced ranging from 0.05 to 4 ppmw. Cyclic oxidation resistance in 1100°C tests improved directly with the degree of desulfurization, reaching an optimum below about 0.2 ppmw. Furthermore, at equivalent sulfur levels, thick samples were prone to greater weight loss than thin samples. The results are discussed in terms of an adhesion map based on the equivalent number of interfacially segregated monolayers of sulfur.
8:50 am
ENVIRONMENTAL DEGRADATION OF GAS TURBINE MATERIALS IN STEAM: Y. Patel, D.C. Tamboli, V. Desai, Mechanical Materials and Aerospace Engineering Department, University of Central Florida, Orlando, FL 32816; N.S. Cheruvu, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228
Steam has been proposed as an efficient cooling medium for the hot section components in the advanced gas turbines as an option for more efficient cooling allowing them to operate at higher efficiency. However, the effects of steam and its impurities such as NaCl and Na2SO4 on the environmental degradation of gas turbine superalloys is little known. Three common gas turbine superalloys; X-45, IN-738 and Inconel-617 were exposed to steam at higher temperature. Cylindrical specimens with central bore were kept at elevated temperature and exposed to three steam environments flowing through the bore. The three environments are (a) steam generated from deionized water, (b) steam generated from deionized water with 5ppm each of NaCl and Na2SO4 and (c) steam generated from deionized water with 50ppm each of NaCl and Na2SO4. The respective exposure times were 1450, 2950 and 3900 hours. IN-738 showed severe internal oxidation in steam without contaminants. In contaminated steam the hot corrosion damage was maximum in Inconel-617. X-45 showed less oxidation damage than IN-738 and less hot corrosion than Inconel-617.
9:10 am
THE OXIDE LAYER PHASE STRUCTURE OF MCRALY-COATINGS: N. Czech, W. Stamm, Siemens AG Power Generation Group, and B. Kolarik, Fraunhofer-Institute for Chemical Technology
During service blades and vanes of stationary gas turbines are subjected to high temperatures. The increase in surface temperatures causes a more severe attack on the MCrAlY-coatings. These coatings are taken for bond coats for thermal barrier coatings as well. The production of a homogeneous oxide layer during service is necessary for a good oxidation protection and for a good adhesion to the ceramic. We will present in-situ X-ray measurements on 8% and 12% Al containing MCrAlY-coatings with and without Re at three different temperatures versus time. At lower temperatures mainly a two phase mixture of Cr2O3 and Al2O3 is detectable with different size distributions for the coatings with 8% and 12% Al. On microsections the -phase depletion is analyzed. At 1050°C a pure Al2O3 oxide layer is established. No Re can be found in the top layer.
9:30 am
THE EFFECT OF RHODIUM WEIGHT PERCENT ON THE OXIDATION RESISTANCE OF PLATINUM RHODIUM MODIFIED ALUMINIDE COATINGS ON MAR M-509 AND FSX-414 COBALT BASE ALLOYS: J. Kimmel, Z. Mutasim, Solar Turbines, Inc., 2200 Pacific Highway, San Diego, CA 92186-5376
Cobalt based alloys such as Mar-M 509 and FSX-414 are coated with a precious metal aluminide (platinum-rhodium-aluminide) to provide enhanced oxidation and hot corrosion resistance in gas turbine applications. The role of rhodium in the aluminide coating is not well understood. There is limited data suggesting that it provides added oxide adherence and reduced refractory element diffusion from the base alloy too the coating interface, thus reducing the tendency of spallation during high temperature exposure. However, too high of a rhodium content decreases the ductility of the coating and, after cyclic oxidation, may result in coating cracking and spallation. The objective of this study is to evaluate platinum-rhodium-aluminide optimum rhodium weight percentage on Mar-M 509 and FSX-414 cobalt based alloys. Metallurgical evaluation was performed on platinum rhodium aluminide coatings with varying rhodium weight variation between 0% and 10%. Oxidation tests were performed at 2000°F/1000 hours, 2100°F/1000 hours (100 hour cycles). Characteristics such as coating thickness, composition, microstructure, and weight changes were evaluated for the as-coated and oxidized specimens using SEM and EDX analysis.
9:50 am BREAK
10:20 am
HIGH TEMPERATURE OXIDATION OF NICKEL BASED SUPERALLOYS IN STEAM: V. Desai, D.C. Tamboli, Mechanical Materials and Aerospace Engineering Dept., University of Central Florida, Orlando, FL 32816; N.S. Cheruvu, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228
An improvement in the cooling of hot gas path components of the has turbines has been sought by replacing air with steam as a cooling medium. However the materials problems associated with steam at high temperature are unknown for gas turbine superalloys. This information is very crucial for the reliability and life prediction of the gas turbine components. In this study, oxidation in steam has been studied for four nickel based superalloys commonly used in the gas turbines, IN738, Inconel 617 and CMSX-4. The study was carried out at four different test temperatures within the range of 800°C to 950°C for times up to 1400 hours. The oxidation tests were also carried out in air to provide a comparison between the oxidation in steam and air. The results indicated higher internal oxidation in IN738 compared to other two alloys. The oxidation attack observed in IN738 was higher in steam compared to air, whereas in other alloys reverse was the case.
10:40 am
NITRADATION AND MECHANICAL DEGRADATION OF COATINGS IN GAS TURBINE BLADES: J. Kameda, T.E. Bloomer; Ames Laboratory & CATD, Iowa State University, Ames, IA 50011; S. Sakurai, Mechanical Engineering Research Laboratory, Hitachi Ltd., 3-1-1, Saiwai Hitachi 317, Japan
In-service environmental attack and mechanical degradation of CoNiCrAlY coatings in gas turbine blades have been investigated using a scanning Auger microprobe (SAM) analysis and small punch (SP) testing technique. Coating degradation was found to strongly depend on the location of blades operated for 21000h under liquefied natural gas. SAM analyses revealed extensive formation of AlN and Ni enriched in inner (concave) coatings but not in outer (convex) ones. The oxidation and carbonization also occurred more substantially in near surface regions of the inner coating. SP specimens were prepared from the inner and outer coatings in order that the specimen surface could be located near surface or interface coatings. SP tests demonstrated that the oxidation and nitridation in the inner coating produce significant mechanical degradation. Brittle cracking in the inner coating occurred at low strains (<3%) up to 950°C though near interface coatings showed a little higher ductility. The outer coatings near the surface and interface showed higher RT ductility (>6%) than the substrate and a rapid increase in the ductility above 800°C. The coating degradation mechanism is discussed in light of the distribution of operating temperatures.
11:00 am
DIFFUSION AND OXIDATION BEHAVIOR OF ELECTRODEPOSITED NI-AL PARTICLE COMPOSITE COATINGS: D.F. Susan, K. Barmak, A.R. Marder, Lehigh University, Department of Material Science and Engineering, Bethlehem, PA 18015
The high temperature diffusion and oxidation behavior of electro-deposited Ni matrix/Al particle coatings was studied to determine the relationships between coating microstructure and high temperature behavior. The coatings, containing up to approximately 20 vol. % Al particles, were deposited on nickel substrates and heat treated at 635, 800, and 1000°C for up to 100 hours. Upon heat treatment at 635 and 800°C, a two phase structure of Ni3Al (1) and solid solution develops with small Kirkendall voids also present. At 1000°C, the coating contains only a solid solution in agreement with the Ni-Al phase diagram. The microhardness of the coating was found to increase with increasing Nail content. Both as-plated and heat treated coatings were oxidation tested in air at 800, 900, and 1000°C for up to 900 hours. Results indicate that the Al content is sufficient to form a protective Al2O3 scale on the coatings during isothermal exposure at these temperatures.
11:20 am
HIGH TEMPERATURE OXIDATION BEHAVIOR OF NIOBIUM ALUMINIDE INTERMETALLICS WITH MOLYBDENUM SILICIDE AND NICKEL ALUMINIDE PROTECTIVE COATINGS: Y. Li, W.O. Soboyejo, R.A. Rapp, Ohio State University, Department of Material Science and Engineering, Columbus, OH 43210
Niobium aluminide intermetallics can exhibit attractive combination of high-temperature strength retention and room-temperature ductility/damage tolerance. Preliminary studies have also shown that niobium aluminides have moderate oxidation resistance at temperatures up to ~750°C in the uncoated condition. However, their oxidation kinetics are not fully understood. In this study, the high-temperature oxidation resistance of niobium aluminide intermetallics (Nb-15Al-10Ti, Nb-15Al-25Ti, Nb-15Al-40Ti and Nv-12.5Al-41Ti-1.5Mo) was studied using uncoated and coated alloys. Protective coatings were formed via in-situ chemical reactions designed to promote the siliciding an aluminizing of Mo and Ni substrate layers, respectively. The isothermal and cyclic oxidation behavior of coated and uncoated materials in air were then studied in the temperature range between 650 and 850°C. The oxide scales and internal layers were analyzed using XRD, SEM and EDX. The implications of the results are assessed for potential high-temperature applications of niobium aluminide intermetallics.
11:40 am
ELECTRO-SPARK ALLOYED HEAT RESISTANT COATINGS ON THE WC-CO BASE: A.D. Verkhoturov, S.V. Nikolenko, N.V. Lebukhova, Institute of Materials of Russian Academy of Sciences, Khabarovsk, Russia
Electro-spark alloying of the metallic surfaces is one of the most perspective coating technologies, among the many other current coating processes. The main advantages of this method include the possibility of depositing any current conducting materials on the surface; high adhesive strength of the layer, and the simplicity of the process. Electro-spark coatings usually have a relatively low continuity of 60-90%; defects (pores, microfractures), heterophase structure. In spite of that, it is possible to achieve, by using refractory alloys as electrodes, a stable effect of increasing heat-resistance. The research conducted by the Institute of Material Science of the Russian Academy of Sciences (Khabarovsk, Russia) showed that electrode materials which examine increasing heat-resistance, can be put in the following order (based on the main component): boride-carbide-nitride. The highest hardness (20-24 GPa) and wear resistance among coatings on steel, is achieved with a hard alloy with tungsten carbide-cobalt base (WC-92%, Co-8%). For increasing Wc-Co alloy electro-spark coatings', deposited on the parts working in high temperature and wear conditions, resistance to high-temperature oxidizing, we propose including self-fluxing materials or heat-resistant intermetallics in the alloy. The research in new materials, that include additives of Ni-Cr-B-Si and Ni3Al (0, 5-25%) to the Wc-Co alloy, was also conducted. We have studied the characteristics of macro- and microstructure of materials and coatings, as well as their chemical compositions, electrode material transfer kinetics, and the optimal conditions of alloying the surfaces. Kinetics of high-temperature oxidizing and phase composition of the interaction products, were examined using a differential thermal analysis in non-isothermal conditions method.
Room: Salon 4
Location: Clarion Plaza Hotel
Session Chairperson: W.F. Sommer, Los Alamos National Laboratory, Los Alamos, NM 87545
8:30 am
RESISTIVITY CHANGES IN SUPERCONDUCTING-CAVITY-GRADE Nb FOLLOWING HIGH-ENERGY PROTON IRRADIATION: C.L. Snead, A. Hanson, G.A. Greene, C.J. Czajkowski, Brookhaven National Laboratory, Upton, NY 11973-5000; K.C. Chan, Los Alamos National Laboratory, Los Alamos, NM 87545; H. Safa, DSM/DAPNIA/SEA--C.E. SACLAY, 91191 Gif sur Yvette, France
Niobium superconducting rf cavities are proposed for use in the proton LINAC for spallation neutron applications. Because of accidental beam loss and continual halo losses along the acceleration path, the concern of the degradation of the superconducting properties with accumulated irradiation arises. Residual-resistivity-ratio (RRR) specimens of Nb, with a range of initial RRR's, were irradiated at room temperature at energies from 200 MeV to 2000 MeV. Four-probe resistance measurements were made at room temperature and at 4.2 K both prior and after irradiations. Proton fluences ranged from 5 x 1014 to about 5 x 1016 p/cm2. These room-temperature results simulate the resistance changes to be expected in LINAC operation for the cavities having been exposed to the radiation and then cycled through an anneal to room temperature. The defect structures produced have been characterized using both scanning and transmission microscopy. Implications of the results to proposed cavity operation and recent results on cavity irradiations will be presented.
9:00 am
POST-IRRADIATION TESTING OF TARGET COMPONENTS AFTER SERVICE IN LAMPF: F. Carsughi, H. Derz, G. Pott, W.F. Sommer, H. Ullmaier, M. Zaslawsky; Institut für Festkörperforschung, D-52425 Jülich, Germany; Heissen Zellen des Forschungszentrum Jülich, D-52425 Jülich, Germany; Los Alamos National Laboratory, Los Alamos, NM 87545
Radiation damage is considered to be the most critical load for the lifetime of components in or close to the proton beam penetrating the target of high power spallation sources. Specimens irradiated in operating medium-power spallation devices are at present the only source of direct information on the behavior of materials in a spallation environment. Within an international cooperation, the following specimens will be investigated in the hot cells at KFA Jülich: (1) A hemispherical LAMPF window made of INCONEL 718, (2) A spherical LAMPF water degrader made of INCONEL 718 and 316 SS, (3) Two curved PSI windows made of DIN 1.4926 SS and irradiated in LAMPF, and (4) A complete target from ISIS consisting of Ta plates in a 304 SS housing. After cutting and preparation of different types of miniaturized specimens the following tests will be performed: 3 point bending tests, ball punch tests, microhardness measurements, scanning (and possibly transmission) electron microscopy, and tensile tests (only for ISIS specimens where ample material is available). First results for specimens obtained from (1) and (2) will be reported.
9:30 am
SIMULATION IRRADIATIONS OF TARGET AND STRUCTURE COMPONENTS FOR SPALLATION NEUTRON SOURCES: E. Camus, N. Wanderka, H. Wollenberger, Hahn-Meitner-Institut, D-14109 Berlin, Germany
Beside damage levels up to 10 dpa per month, the spallation reaction induces high levels of transmutation products, mainly hydrogen (up to 0.5 at.% per month) and helium (up to 0.1 at.% per month). Dual-beam irradiations with heavy ions, protons, and/or helium ions with energies up to 300 keV make it possible to introduce such damage levels and high hydrogen or helium contents within hours. We present experimental results on the microstructure evolution and on mechanical properties of simulation irradiated steels and tantalum. The cavity microstructure is investigated by means of transmission electron microscopy (TEM). Field-ion microscopy with atom probe (FIM-AP) shows fine scale radiation-induced segregation. Hardness measurements on specimens implanted at low temperature with heavy ions, protons, and/or helium have been performed and reveal a drastic increase of hardness. Both the displacement rate and the hydrogen or helium implantation rate used in simulation irradiations are orders of magnitude higher than those produced in spallation environments. Data correlation, with special emphasis on the influence of the hydrogen or helium implantation rate, is discussed.
10:00 am BREAK
10:20 am
TRIPLE ION-BEAM STUDIES OF RADIATION DAMAGE EFFECTS IN A HIGH POWER SPALLATION NEUTRON SOURCE ENVIRONMENT: L.K. Mansur, K. Farrell, E.H. Lee, G.R. Rao, J.D. Hunn, P.M. Rice, M.B. Lewis, S.W. Cook, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6376
The unique Triple Ion-Beam Facility (TIF) at ORNL allows researchers to mimic significant features of the NSNS irradiation environment by producing displacement damage and injecting He and H simultaneously. In this work, therefore, austenitic EC316LN and ferritic 9Cr2WVTa alloys were irradiated using the TIF to investigate radiation damage effects. Irradiations were carried out using 4 MeV Fe++, 400 keV He+, and 200 keV H+ simultaneously to accumulate 50 dpa, 10,000 appm He, and 50,000 appm H, respectively. Irradiations were carried out at temperatures from 50 to 200°C. The specific ion energies were chosen to maximize the damage and the gas accumulation at the same depth of ~1 µm. Microstructure and surface hardness of irradiated specimens were evaluated by TEM and the Nanoindenter, respectively. This report summarizes damage microstructure as a function of irradiation depth from cross-sectioned TEM specimens and hardness variation of the bombarded surfaces.
10:50 am
IRRADIATION DAMAGE OF FERRITIC/MARTENSITIC STEELS: FUSION PROGRAM DATA APPLIED TO THE SPALLATION NEUTRON SOURCE APPLICATION: R.L. Klueh, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6376
Ferritic/martensitic steels in the target structure of a spallation neutron source will experience many of the extreme conditions expected in a fusion power plant (i.e., high-energy neutrons that produce large amounts of displacement damage and transmutation helium). Thus, studies of the steels for fusion are relevant for the spallation neutron source application. The ferritic/martensitic steels are candidates for fusion because of superior swelling resistance, better liquid-metal compatibility, higher thermal conductivity, and lower thermal expansion than austenitic steels. The major problem with ferritic/martensitic steels involves the effect of irradiation on fracture, as determined by a Charpy impact test. Fast reactor irradiation produces an increase in the ductile-brittle transition temperature and decrease in the upper-shelf energy. The effect saturates with fluence for fast-reactor irradiation, but the saturation values observed for irradiation in a fast reactor do not apply for irradiation in a mixed-spectrum reactor under conditions where transmutation helium is generated simultaneously with displacement damage. This helium effect is one of the critical issues that needs to be understood, since high helium concentrations will be generated in conjunction with the displacement damage in a fusion reactorand in the target of a spallation neutron source, should a ferritic/martensitic steel be chosen for that application.
11:20 am
ACTIVATION OF MATERIALS PROPOSED FOR USE IN SUPERCONDUCTING LINAC APPLICATIONS: A. Hanson, C.L. Snead, G.A. Greene, C.J. Czajkowski, K.C. Chan, H. Safa; Brookhaven National Laboratory, Upton, NY 11973-5000; Los Alamos National Laboratory, Los Alamos, NM 87545; DSM/DAPNIA/SEA, C.E. SACLAY, 91191 Gif sur Yvette, France
Linacs are proposed for spallation neutron sources which are capable of relatively high beam currents. Associated with the transport of these high currents will be relatively high beam losses to the linac structures from the beam halo and occasional mis-steering. A series of irradiations have been conducted at the Saturne, France, accelerator in which specimens of steel, copper, NbTi, aluminum, and niobium were exposed to protons with energies from 400 to 2000 MeV. Gamma activation measurements were made for various times subsequent to the end of the beam. Absolute and relative activity levels have been achieved on which estimates of the exposure levels to maintenance personnel can be made. Particular attention was given to Nb because of its prominence in scenarios that call for superconducting rf-cavity linacs. For Nb the activation products for the various irradiations were determined and compared with code predictions.
Room: 231B
Session Chairpersons: M.E. Schlesinger, Department of Metallurgical Engineering, University of Missouri-Rolla, 1870 Miner Circle, Rolla, MO 65409-0340; Dr. S. Wang, ASARCO Inc., Technical Services Center, 3422 South 700 West, Salt Lake City, UT 84119
8:30 am
SULFIDE CAPACITY OF FeO-BASED SLAGS: R.G. Reddy, W. Zhao, Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487
Sulfide capacities of FeO-based silicate slags were calculated a priori using the Reddy-Blander model. Experiments were done using encapsulation method for several slag systems as a function of compositions and temperatures. The experimental results agree with the predicted data very well. The predicted sulfide capacity data was used in calculation of the sulfur distribution ratio in the slags and metal.
8:55 am
SULFIDE CAPACITY OF SLAGS: R. Sridhar, S. Simeonov, J.M. Toguri, Department of Metallurgy and Materials Science, University of Toronto, Toronto, Ontario, Canada, M5S 3E4
During the experimental studies on sulfide capacities of non-ferrous metallurgical slags it was found that the choice of the thermodynamic data base is important for calculating the sulfur potential in such measurement. It was also found that some of the earlier sulfide capacity measurements required recalculation. The available sulfide capacity for different slag systems were reviewed after recalculations. This analysis suggested high sulfur solubility in halide melts which were confirmed by experiments reported in another paper. The reviewed data on sulfide capacities are presented together with calculations of sulfur partition achievable with different slags.
9:20 am
SULFUR SOLUBILITY IN CaCl2-CaF2 and BaF2-BaCl2 MELTS: S. Simeonov, R. Sridhar, J.M. Toguri, Department of Metallurgy and Materials Science, University of Toronto, Toronto, Ontario, Canada M5S 3E4.
CaF2 additions are made to oxide based slags used for steel desulfurization to aid in sulfur removal. It is commonly held that CaF2 by itself does not possess sulfur removal capability but enhances fluidity of CaO based slags which helps desulfurization. Recently BaF2 additions to CaO and BaO based slags have been studied to improve their sulfide capacity. To better understand the sulfur removal mechanism, sulfur solubility measurements were carried out on CaCl2-CaF2 and BaCl2-BaF2 melts. Results showed that contrary to earlier expectation they have high sulfur solubility and higher than that for sodium silicate slags which are used for desulfurization. The conventional sulfide capacity definition based on exchange of oxygen and sulfur ions in slag used for defining desulfurization power of slags do not apply to such melts as there are no oxygen ions present and no oxygen ion transfer takes place.
9:45 am
ASPECTS OF SLAG OPTIMIZATION IN SMELTING OF Cu-Ni SULFIDE CONCENTRATES: A.A. Hejja, R.H. Eric, School of Process and Materials Engineering, University of the Witwatersrand, Johannesburg, Private Bag 3, WITS 2050, South Africa
The first part of this study deals with the importance of surface tension of slags produced in the smelting of sulfide concentrates. Theoretically the method of determining the surface tension of slags was laid down by Boni and Derge. The values obtained experimentally for a series of main oxide components were grouped into a useful correlation incorporating experimental constants for the relevant oxides present in the slag, some of these giving the surface tension value for the particular slag. These estimated values were coupled with or incorporated into the slag viscosity plots to show the correlation between the two factors. This is also important from a refractory attack point of view in the furnace operation. In the second part an attempt is made toward the optimization of slag composition relevant both for electric and reverberatory smelting processes. Using the knowledge of the viscosity and electrical conductivity of the slags at the temperature of furnace operation, the mode of optimization is based on Besselt function correlations which utilize the trend of the mostly parabolic plots of viscosities and conductivities. The results obtained by this method agree well with the optimum slag compositions being used in established operations derived from years of practical experience for various slags used in the furnaces. However, due to extensive turbulence in suspension and gas injected bath smelting processes, the outlined methods cannot be used for these processes. Also great caution should be exercised in their application for three electrode circular furnaces with separate slag cleaning.
10:10 am BREAK
10:20 am
SOLUBILITY OF BISMUTH AND LEAD IN IRON AND IRON-CARBON ALLOYS: Lewen Chang, Sandeep Malhotra, Mark E. Schlesinger, Department of Metallurgical Engineering, University of Missouri-Rolla, 1870 Miner Circle, Rolla, MO 65409-0340
The thermodynamic properties of Fe-C-Bi and Fe-C-Pb alloys are of interest for a variety of reasons related to steel production and recycling; however, experimental data on phase equilibria in these systems are scarcer. Experimental procedures will be described for an ongoing research program measuring the activities of Bi and Pb in solid and liquid Fe and Fe-C alloys. Preliminary results will be presented, with the primary goal of using measured solubilities to derive model parameters for calculating bismuth and lead activities as a function of temperature and alloy composition.
10:45 am
THERMODYNAMICAL INVESTIGATIONS OF METALLURGICAL AND MATERIALS PROCESSES AND PHENOMENA: Vladimir Mindin, AFP, 111 East Shore Road, Manhasset, NY 11030; Yakov Mindin, Polytechnic University, Six MetroTech Center, Brooklyn, NY 11201
The report presents results of thermodynamical investigation of wide range of complex systems, including carbo thermal reduction of silica, silicon carbide obtaining from different precursors, anode processes during molten salts electrolysis, tin atomization in AAS, interaction in copper-, manganese- and sulfur- containing systems. Special attention is paid to thermodynamical approach to investigation and estimation of multi component multi element compositions stability. Environmental topic in the report is presented by discussion of two important issues: (a) problem of radioactive wastes interaction -with environment, and (b) investigation on thermodynamic stability of exhaust from different sources. Also are discussed very important problems of informational support (thermodynamics data accuracy) of complex systems thermodynamics simulation.
11:10 am
OXYSULPHIDE IN METALLURGY OF NICKEL AND COBALT: I.D. Reznik, A.V. Tarasov, T.A. Kharlakova, State Research Institute of Non-Ferrous Metals, Acad. Korolyov Street, 13, Moscow, Russia, 129515; E.N. Selivanov, Institute of Metallurgy of the Ural's Branch of the Russian Academy of Sciences, 101 Amundsen Street, Ekaterinburg, Russia, 620147
On blowing nickel matte in a converter without quarts, first the oxidation of metallic iron and a part of FeS occurs without evolving sulfur dioxide, the formed FeO dissolves in a sulfide smelt and form a homogeneous Oxysulphide smelt. On further increasing the FeO content, the Oxysulphide separates into 2 layers. Based on the laboratory investigation of FeO-(FeS+Feo) - (Ni3S2+Nio) ternary phase we have identified the separation region at 1250°C. The boundaries of the separation region have the form of an arc and the composition of the separated Oxysulphide layers is defined by the canodes. In the nickel or copper-nickel matte - calcium oxidesilica slag system at 1250°C three layers, namely sulfide, Oxysulphide, and slag may be formed. A high slag basicity due to the presence of CaO can serve to enhance the activity of FeO; a low nickel content in the matte corresponds to a high concentration of FeS therein; FeO from slag and FeS from the matte form a homogeneous FeO-FeS solution, i.e. an Oxysulphide layer. The investigation on the "Camebakes" apparatus and by the nuclear gamma-ray resonance spectroscopy method of the phase composition in a slowly cooled Oxysulphide layer has shown the presence of four phases. wustite, troilite, ferronickel grains, and calcium oxide-silica inclusions. Knowledge of regulaties in the oxysulphides formation makes it possible to use them in pyrometallurgy of nickel and cobalt or preventing their formation.
Room: 232B
Session Chairperson: P.K. Liaw, Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996-2200
8:30 am INVITED
RELIABILITY OF FERROELECTRIC CERAMIC MULTILAYER DEVICES: Z. Suo, X. Gong, Mechanical and Environmental Engineering Department, Materials Department, University of California, Santa Barbara, CA 93106
In a multilayer actuator, each internal electrode terminates an edge inside the active ceramic. Around the edge, the nonuniform electric field generates an incompatible strain field, which, in its turn, generates stresses and may cause the ceramic to crack, leading to device failure. The industry has been exploring alternative electrode configurations to alleviate the stress concentration. The effort has been empirical and benefited little from numerical simulations. An inherent difficulty is that the actuator ceramics have nonlinear electro-mechanical interactions, of which no unified mathematical description is now available. This talk describes the basic phenomena, and a crack nucleation model that includes essential features of this nonlinearity. The model shows that, everything else being fixed, a critical layer thickness exists, below which a multilayer actuator will not crack around its internal electrode edges.
9:00 am
NON-LINEAR FRACTURE PROCESSES IN LAMINATED METAL COMPOSITES: Don Lesuer, Bob Riddle, Chol Syn, L-342, Lawrence Livermore National Laboratory, Livermore, CA 94551
Numerous fracture processes exist in layered materials. These processes, which include crack bridging, crack deflection, stress redistribution and local plane stress deformation, will, in general, increase the fracture toughness of layered materials over that observed for non-layered materials. However, their specific influence on toughness (namely their influence on initiation toughness, growth toughness and R-curve behavior) is a function of the specific fracture mechanism active during crack growth. Many of these mechanisms compete with one another. The active mechanism(s) are strongly dependent on the material properties of the component layers, laminate architecture (such as volume fraction of the component materials and layer thickness), and interface properties. This paper will discuss the various fracture mechanisms in laminated metal composites (LMCs) containing alternating layers of ductile and brittle materials. The layers between these component materials have sharp interfaces. Specific systems include LMCs of an aluminum matrix composite and a monolithic aluminum alloy as well as ultrahigh-carbon steel and brass. Simulations of crack growth in these materials have been done using finite element analysis to study the non-linear fracture processes involved. The influence of component material properties, interface properties and laminate architecture on these processes will be described.
9:30 am
A QUANTIFICATION OF THE FABRIC STACKING SEQUENCE EFFECT ON THE MECHANICAL PROPERTIES OF A 2-D WOVEN NICALON FIBER FABRIC REINFORCED SiC COMPOSITE: Wei Zhao, Peter K. Liaw, Dept. of Materials Sciences and Engineering, The University of Tennessee, Knoxville, TN 37996-2200; Nianni Yu, Dept. of Engineering Sciences of Mechanics, The University of Tennessee, Knoxville, TN 37996-2200; Elizabeth R. Kupp, David P. Stinton, The Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
The mechanical behaviour of continuous fiber reinforced ceramic matrix composites is affected by several factors, such as: the type and thickness of fiber/matrix interface, the fiber strength statistical distribution and degradation after processing, the fabric stacking sequence of the laminate etc. For a 2-D plain woven Nicalon fiber cloth reinforced silicon carbide (SiC) with a SiC interfacial coating, little attention has been paid to the stacking sequence effect. In this paper, the fabric stacking sequence effects on the stress-strain distribution in flexural laminate bars, and the elastic properties of the laminate are calculated. A theoretical calculation model is established based on a combination of the classical laminated plate theory and an undulation model depicting fiber continuity and undulation shape, which is first developed by Chou et al. A closed-form FORTRAN program is compiled. Different combination of fiber lamina orientation and their stacking sequence are studied.
10:00 am BREAK
10:30 am INVITED
TOUGHENING AND FATIGUE PERFORMANCE OF BRITTLE AND SEMI-BRITTLE STRUCTURAL MATERIALS: John J. Lewandowski, Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106
Significant efforts are being devoted to the cost effective processing of advanced structural materials with unique combinations of stiffness, strength, toughness, and fatigue resistance. Such efforts are necessarily multi-disciplinary and often combine the skills of academic investigators in Materials Science and Engineering, Mechanical Engineering, and Civil Engineering, as well as other related disciplines with those from both the materials producer and user community. Recent work at CWRU in conjunction with a variety of collaborators has begun to investigate the factors controlling the magnitude of performance enhancement possible in brittle and semi-brittle systems where a variety of approaches to toughening are being explored. The presentation will overview recent research by the P.I. and his collaborators on a number of different materials systems where toughening is being accomplished via the incorporation of ductile/tough reinforcements. The presentation will follow with documenting the fatigue performance of such systems.
11:00 am
INTERFACIAL INTERLOCKING FROM POROUS OXIDES: Z. Zhang, Z. Xing, J.K. Shang, Department of Materials Science and Engineering, University of Illinois, Urbana, IL 61801
Surface oxides on metals are often highly porous and the pore structure depends on oxidant and kinetics of oxidation. In this work, the oxide structure on aluminum-alloy surface was modified by chemical and electrochemical processes to produce different pore sizes and morphology. Interfacial bonds were then formed from these porous oxides and the crack growth resistance of the interfaces measured in air and corrosive environments. Significant differences were found among interfaces with different oxide microstructures. Micromechanical models were developed to determine the interlocking resistance from porous oxides. Based on the model, the role of interfacial interlocking in interfacial crack growth is discussed.
11:30 am
NOTCHED TENSILE PROPERTIES OF CERAMIC MATRIX COMPOSITES: F.W. Zok, High Performance Composites Center, Materials Department, University of California, Santa Barbara, CA 93106-5050
Fiber-reinforced ceramic matrix composites (CMCs) are being developed for a variety of high temperature components for gas turbine engines. Many of these components are complex in shape and will be subjected to local stress concentration under normal service conditions. The presentation will focus on the effects of stress concentrating features such as sharp slits and circular holes on the tensile properties of CMCs. Modeling and experimental efforts aimed at improving our understanding of the relationship between the mechanisms of inelastic deformation and their effects on notched strength will be reviewed. Results on MAS/Nicalon and woven SiC/SiC systems indicate that the conditions for fracture in the regions around holes are stochastic in nature and depend on the volume under stress. An approach for implementing weakest link statistics for predicting notched properties will be outlined. Recent work has revealed that inelastic deformation is also attainable in all-oxide CMCs with strong interfaces and porous matrices. The notched properties of these materials will be presented and their behavior compared with that of systems with weak interfaces. Research sponsored by ARPA-URI, Grant N00014-92-J-1808.
Room: Salon 8
Location: Clarion Plaza Hotel
Session Chairpersons: KNona C. Liddell, Department of Chemical Engineering, Washington State University, Pullman, WA 99164; Garry W. Warren, Department of Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, AL 35487
8:30 am
RECENT DEVELOPMENTS IN RARE-EARTH-BASED ADVANCED PERMANENT MAGNET MATERIALS: FACTORS AFFECTING ACQUISITION AND STABILITY OF COERCIVITY: L.H. Lewis, Materials Science Division, Department of Applied Science, Bldg. 480, Brookhaven National Laboratory, Upton, NY 11973-5000, C.H. Sellers, Idaho National Engineering Laboratory, Lockheed Idaho Technologies Co., Idaho Falls, ID 83415-2211, V. Panchanathan, Magnequench International, Inc., 6435 Scatterfield Road, Anderson, IN 46013
The basic relationships that link the microstructural properties of advanced permanent magnet materials to the magnetic hysteretic properties such as the magnetic hysteretic properties such as the coercivity are subtle and often difficult to quantify. These difficulties are magnified when the magnetic materials are fabricated by methods such as rapid solidification, which has the potential to produce non-equilibrium phases and structures in a nano-scaled matrix.
9:00 am
Nd-Fe-B POWDERS FOR BONDED MAGNETS--AN OVERVIEW: V. Panchanathan, Magnequench International, Inc., 6435 Scatterfield Road, Anderson, IN 46013
The rapidly solidified Nd-Fe-B powders form the entire basis of the bonded magnet industry. At present the rapid solidification is carried out exclusively by melt spinning, a technique in which a stream of molten alloy is directed onto the outer surface of a rapidly spinning wheel, producing flake like particles having highly stable and magnetically hard microstructure. These particles are comminuted into powder before being processed into bonded magnets. These powders are magnetically isotropic. These powders are magnetically isotropic. The bonded magnets made using these powders range in energy product of 5 MGOe for injection molded magnets to about 12 MGOe for compression molded varieties.
9:30 am
MAGNETISATION MECHANISMS IN EXCHANGE COUPLED MAGNETS: R. Street, Research Centre for Advanced Mineral and Materials Processing, The University of Western Australia, Nedlands, WA 6907, Australia
Nanocrystalline composites containing grains of hard (typically RE/TM alloys) and soft (typically 
-Fe) magnetic materials exhibit the commercial useful property of remanence enhancement. The modelling of remanence enhancement in terms of inter- and intra- grain magnetic exchange coupling will be explained. The results of measurements of the magnetic properties of Nanocrystalline remanence enhanced magnets prepared by mechanochemical and melt quenching processes will be described.
10:00 am BREAK
10:30 am
RARE EARTH-BASED GIANT MAGNETOSTRICTIVE MATERIALS: S.F. Cheng, Naval Surface Warfare Center, Silver Spring, MD 20903; A.E. Clark, Clark Associates, Adelphi, MD 20783
Among the many extraordinary features of the rare earths are their magnetic and magnetoelastic properties. The rare earths, e.g., Tb, Dy, Nd, Sm, are known worldwide for their large magnetocrystalline anisotropy and magnetization, which has led to the importance of magnetic rare earths as vital ingredients of modern permanent magnets. In this paper, we focus on the strain dependence of these giant effects which gives rise to huge magnetostrictions, magnetomechanical couplings, and E effects. Magnetostrictions greater than 10-3 have been measured at temperatures as high as 250°C. At low temperatures Magnetostrictions reaches ~10. No other solid state material can match these values.
11:00 am
AQUEOUS CORROSION STUDY OF RAPIDLY SOLIDIFIED NdFeB PERMANENT MAGNETS WITH TiC ADDITIONS: M. Arenas, G.W. Warren, Department of Metallurgical & Materials Engineering, University of Alabama, Tuscaloosa, AL 35487, C.P. Li, K.W. Dennis, and R.W. McCallum, Dept. of Materials Sci. & Engineering, Iowa State Univ., Ames Laboratory, Ames, IA 50011
A corrosion study of a bonded NdFeB permanent magnet material alloyed with titanium carbide additions has been undertaken. Bonded magnets produced by rapid solidification of the alloy and consolidation in a polymer matrix are
attractive due to lower cost, greater durability, and useful shape-forming ability. Melt spinning is used to produce ribbons of the desired composition. The ribbons are formed by the ejection of molten alloy onto the surface of a rotating wheel. The samples tested were ribbons of different composition and wheel speed. Commercial epoxy was used as a bonding medium.
Room: 314A
Session Chairpersons: Dr. Wilbur C. Simmons, Research Office, P.O. 12211, Research Triangle Park, NC 27709; Dr. A.B. Geltmacher, Naval Research Laboratory, Code 6380, 4555 Overlook Drive SW, Washington, DC 20375
8:30 am INVITED
DUCTILE FRACTURE IN STEELS AND ALUMINIUM ALLOYS: John F. Knott, School of Metallugy and Materials, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
Ductile fracture mechanisms in these alloys, of such importance to modern civilization, are set in the context of the main applications for which they are used. Thin-sheet applications encompass two main aspects: prevention of localized shear fracture in sheet-forming, promotion of reproducible shear fractures in the "ripping" of "ring-pulls" on beverage cans or in the stamping-out of milk-bottle tops from oil. Both aspects relate to the generation of through-thickness shear fractures. In thick-section applications, it is necessary to address local fracture mechanisms in the combination of steep strain-gradient and high hydrostatic tension ahead of a notch or pre-crack. The prime micro-mechanisms are microvoid coalescence and "fast (in-plane) shear" linkage resulting from a (plane-strain) localization of flow. Behaviour in steels and high-strength aluminum alloys is contrasted and recent findings on "mixed-mode" shear fracture criteria are discussed. Attention is drawn to a number of applications for which "plane-stress" and "plain-strain" methodologies must be combined.
8:55 am INVITED
MODELLING LARGE DEFORMATION AND FAILURE IN MANUFACTURING PROCESSES USING INTERNAL STATE VARIABLES: Doug Bammann, Mechanics and Simulation of Manufacturing Processes Department, Mail Stop 9405, Sandia National Laboratories, Livermore, CA 94551
A state variable model for describing the fine-deformation behavior of metals is described. A multiplicative decomposition of the deformation gradient into elastic, volumetric plastic (damage), and deviatoric plastic parts is considered. With respect to the natural or stress-free configuration defined by this decomposition, the thermodynamics of the state variable theory is investigated. This model incorporates strain rate and temperature sensitivity, as well as damage, through a yield surface approach in which the state variables follow a hardening minus-recovery format. The microstructural underpinnings of the model are presented along with a detailed description of the effects which each model parameter has on the predicted response. Issues associated with the implementation of this model into finite element codes are also discussed. A range of problems involving damage at various loading rates are presented including hydroforming, prediction of forming limit diagrams from limiting dome height studies and cracking during welding processes. In each case, experiments are well described by predictions based on this model.
9:20 am INVITED
THE EFFECT OF HYDROSTATIC PRESSURE ON THE ROOM TEMPERATURE FORMABILITY OF METAL SHEETS: Henry Piehler, Consortium for the Advancement of Deformation Processing Research, Department of Materials Science and Engineering, Carnegie Mellon University, Wean Hall 2323, Pittsburgh, PA 15213
The effect of pressure on the room temperature formability of 6111 T4 aluminum and ß 21 S titanium sheets was evaluated in stretching, drawing, as well as plane strain. The sheet formability tests were performed using the patented Carnegie Mellon hot triaxial deformation system in conjunction with a specially developed 2 in diameter hemispherical punch and forming fixture. The strain state was varied by using different sample widths and lubrication conditions. Tests were conducted at ambient pressure and constant pressures of up to 70 MPa (10 ksi). Increasing all pressures used in forming increased the formability of the al sheets along all forming paths. The largest pressure-formability increase in the Al sheets occurred in plane strain. Biaxial stretching tests on the ß 21 S sheets revealed that the formability actually decreased under a pressure of 10 ksi compared to the formability at ambient pressure. This pressure-induced formability decrease was accompanied by a change in fracture path and its mechanism is currently being investigated.
9:45 am INVITED
MICROSTRUCTURAL EFFECTS ON CAVITATION AND FRACTURE IN SUPERPLASTIC METALS: Amit K. Ghosh, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109
Cavitation leads to flow localization and fracture during superplastic forming process. In this paper, several approaches on the micromechanical aspects of cavitation are critically examined. With plasticity effects present, constrained diffusional and plasticity-induced growth of cavities have been proposed in the dislocation creep regime. In the superplastic regime, however, cavitation behavior is considerably complicated by the predominance of grain boundary sliding and grain rotation effects. Consequently the amount of grain boundary sliding strain has a major effect on the degree of cavitation through cavity initiation, growth and coalescence. Dynamics of cavitation and its effect on strain localization leading to fracture has been examined. Also detailed quantitative aspects of cavity initiation on cavity growth have been carefully documented to separate the phenomenon of continuous nucleation of new voids from the cavity growth process. It appears that dynamic grain growth which influences grain boundary sliding in a major way, also influences cavitation. Thus flow localization and fracture are critically affected by microstructural evolution effects such as dynamic recrystallization and dynamic grain growth. Illustrative examples will be given from various metallic system.
10:10 am INVITED
MECHANISMS OF DUCTILE FRACTURE IN CRACK-TIP FRACTURE PROCESS ZONES: Peter F. Thomason*, Department of Metallurgy and Materials Science, University of Cambridge, Cambridge CB2 3QZ; *on leave from University of Salford
The strength and toughness of engineering alloys, under conditions where general yielding and subcritical crack growth precede catastrophic fracture, are critically depend on nucleation, growth and coalescence of microvoids in fracture process zones that are generally subject to high mean-normal stresses. It is shown that, at these high mean-normal stress levels, microvoid nucleation and coalescence can become the controlling process of ductile fracture in crack-tip plastic zones, with negligible dilatational void-growth prior to microvoid coalescence on the fracture surface. This effect is direct result of high mean-normal stresses promoting the microvoid coalescence process when the microvoids are still relatively small and widely spaced; thus virtually all dilational void-growth is confined to the final void-coalescence fracture surface, and the result of plastic limit-load failure (or internal microscopic necking) between adjacent microvoid nuclei.
10:35 am BREAK
10:45 am INVITED
IMPROVED PROPERTIES OF HSLA AND DUAL-PHASE STEELS: Gareth Thomas, Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 97420-1760 and National Center for Electron Microscopy, Lawrence Berkeley Laboratory, Berkeley, CA 94720
The utilization of controlled rolling and quenching from the finish roll allows the design of composite microstructures, whereby the advantages of the second phase are optimized while the less desirable features of this phase are simultaneously mitigated by the presence of the other constituent phase. The size, morphology, distribution, shape and volume fracture of the second phase critically control the mechanical properties, especially fracture and fatigue of the dual phase systems. As a consequence, these structures offer a degree of metallurgical flexibility that is absent in single phase structures or in many precipitation strengthened systems, for attaining optimum sets of mechanical properties. Examples are presented here of martensite/austenite (~2 - 5%) mixtures designed for optimum combinations of high strength, toughness, and wear properties in medium carbon steels, e.g., for mining and agricultural applications; low carbon martensite/ferrite (~80%) structures for high strength, cold formability, improved low temperature ductility, and attractive improved corrosion resistance in concrete. In all cases these steels can be produced on line in a hot mill by controlled rolling and direct quenching.
11:10 am
EXPERIMENTAL AND THEORETICAL ANALYSIS OF THE CAVITATION AND FAILURE BEHAVIOR OF A SUPERPLASTICALLY DEFORMED NEAR-GAMMA TITANIUM ALUMINIDE ALLOY: Carl M. Lombard, Perikles D. Nicolaou, Amit K. Ghosh, S. Lee Semiatin, US Air Force Wright Laboratory, WL/MLLM, Room 101, Building 665, Wright Patterson Air Force Base, OH 45433; UES, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432; Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109
The uniaxial hot tension behavior of a near-gamma titanium aluminide alloy sheet (Ti-45.5Al-2Cr-2Nb) was determined in the as-rolled condition (initial grain size ~3 to 5 µm) and a rolled-and-heat treated (1177°C/4 hours) condition (initial grain size ~10 to 12 µm). Microstructure evolution, cavitation rates, and failure modes were established via constant strain rate tests at 10-4 to 10-2 sec-1 and test temperatures between 900 and 1200°C. For both initial microstructural conditions, the failure mode was established as predominantly cavitation/fracture controlled. Cavity growth rates was greatest at lower temperatures and in the heat treated specimens; the higher cavitation rates in the heat treated specimens led to elongations only approximately one-half those of the as-rolled material. Experimental results were then compared with a 'force equilibrium approach' theoretical analysis of the isothermal hot tension test under cavitating conditions. Model results delineated the competition between failure controlled by localized necking versus fracture, the latter being defined by a critical volume fraction of cavities. The validity of the modeling approach was confirmed through the analysis of the experimental results and data from the literature.
11:30 am
THE EFFECT OF HYDROSTATIC AND SHEAR STRESSES ON THE HOT WORKING BEHAVIOR OF BULK METALS: Henry Piehler, Consortium for the Advancement of Deformation Processing Research, Department of Materials Science and Engineering, Carnegie Mellon University, Wean Hall 2323, Pittsburgh, PA 15213
The effect of pressure on the hot workability of a Ti-49.5Al-2.5Nb-1.1Mn (a/o) titanium aluminide was evaluated using both isothermal compression and isothermal hydrostatic upsetting tests. Tests were conducted at 1050°C to strains of the order of one with and without pressure of 260 MPa to evaluate the effect of pressure on flow stress response, fracture retardation, and hot worked microstructure. The samples deformed without pressure exhibited noticeable cracks on the bulged free surface as well as internal deformation-induced voids; the superimposition of pressure suppressed both these types of deformation damage. Pressure was observed to have a neglible effect on the flow stress response, which could be adequately described by the von Mises criterion in all cases. Similarly, pressure had a negligible effect on dynamic recrystallization and microstructure under the conditions investigated. Preliminary results on pore closure in Osprey processed IN 718 subsequently deformed by isothermal hydrostatic upsetting are also presented.
11:50 am
THE EFFECT OF MATERIALS PROCESSING ON FRACTURE OF METALS: Clyde L. Briant, Division of Engineering, Brown University, Providence, RI 02912
Thermomechanical processing of metals is often used to improve the fracture properties of materials. When materials are processed at room temperature, one can often achieve good control over resulting properties because one can avoid dynamic recovery and recrystallization. However, when processing is carried out at elevated temperature, dynamic changes can occur and make control difficult. In this paper we report on work in which refractory metals were processed at elevated temperatures try to achieve optimum fracture strength as measured in four point bending. The results will show that there is an optimum processing range to achieve fracture resistance. If the material is processed at too low a temperature internal cracks that occurred during processing will cause failures. If the processing temperature is too high, recrystallization occurs and the material will fail by low energy brittle fracture.
12:10 pm
THE INFLUENCE OF INCLUSIONS ON THE FRACTURE TOUGHNESS OF AerMet 100: J.W. Morris, Jr., J. Chan and K. Sato, Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 97420-1760 and, Center for Advanced Materials, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
AerMet 100 is an ultra-high strength alloy recently that was recently commercialized by Carpenter Technology. The alloy is a secondary hardening, Fe-Ni-Co-Cr-Mo alloy that is age-hardenable to yield strength above 250 ksi, and fractures in a ductile mode at ambient temperature even after hardening to peak strength. The alloy is currently under investigation for potential use in aircraft landing gear. As expected from its ductile fracture mode, the fracture toughness of AirMet 100 is strongly dependent on the density of inclusions with sizes greater than about 2 µm. As the inclusion spacing increases from ~0.2 to ~0.8 mm, the fracture toughness rises by roughly 70%, from ~110 ksiin. Metallurgical analysis shows that the large inclusions in these alloys are primarily rare earth (La, Ce, Nd) oxysulfides. The rare earth elements are present in the low concentration in the alloy, and, presumably, represent intentional additions to getter metalloid impurities such as sulfur. Research has shown that substantial improvements in toughness can be obtained by filtration before solidification. The toughness of AerMet 100 can be further improved by modifying, the alloy heat treatment the alloy heat treatment to alter the distribution of hardening precipitates. A brief pre-age at 510°C prior to the standard aging at 485°C significantly increases the fracture toughness, particularly in the case of the low-toughness sample.
12:30 pm
STEREO-SECTION FRACTOGRAPHIC STUDY OF FRACTURE BEHAVIOR OF A Ti6Al4V ALLOY: Xian J. Zhang and R.L. Tregoning, Department of Mechanical Engineering, University of Maryland, College Park, MD 20742; Fracture and Fatigue Branch, Naval Surface Warfare Center, 3A Leggett Circle, Annapolis, MD 21402
The stereo-section fractography (SSF) technique has been employed to study the relationship of surface microfractographic features and internal microstructures. In this way, a direct correspondence is established between various fracture modes and microstructural details beneath the fracture surface of fracture toughness and fatigue specimens of an () Ti6Al4V alloy. The measurements show a one to one relation between surface and internal features. It was found that ductile holes formed along grain boundaries and also, cleavage facets cut through grains. It was evident that the microscopic texture formed in the solidification process affects the fracture mechanisms and hence, the fracture toughness of the alloy. Thus, the SSF technique is demonstrated as a very useful tool for the study of fracture behavior of materials.
Room: Salon 7
Location: Clarion Plaza Hotel
Session Chairpersons: Dr. Jeffrey Waldman, Dept. of Materials Engineering, Drexel University, Philadelphia, PA 19104; Dr. William E. Frazier, Naval Air Warfare Center Aircraft Division, Patuxent River, MD 20657
8:00 am
P/M APPLICATIONS IN THE AUTOMOTIVE INDUSTRY: Alan Lawley, Dept. of Materials Engineering, Drexel University, Philadelphia, PA 19104
The North American automotive industry is now a major user of P/M products. In the last sixteen years the weight of P/M parts in a family vehicle has increased from 7.7 to 13.7 kg. and this trend is expected to continue. The results of a recent Delphi Study predict substantial growth over the next decade in power train applications (camshaft lobes, conrods, bearing caps, transmission gears, valve seat inserts, and valve guidelines). In this presentation, three P/M automotive case studies are examined in terms of the technical and economical factors that resulted in commercial viability: (i) the pressed and sintered main bearing cap, (ii) the warm formed turbine hub, and (iii) the powder forged connecting rod. Potential new P/M automotive applications are also discussed.
8:30 am
HIPPING OF P/M PRODUCTS: James H. Hahn, Pressure Technology Inc., Warminster, PA 18974
Abstract not available.
8:55 am
NET SHAPE PROCESSING OF NAVY AIRCRAFT MATERIALS: William E. Frazier, Naval Air Warfare Center Aircraft Division, Patuxent River, MD 20657
New and emerging Navy aircraft systems must satisfy the demanding performance requirements of the 21st Century, and yet, be affordable. This paper examines how advanced, net-shape technology is being implemented and how it can be used to reduce the cost and enhance the performance Navy aircraft.
9:20 am
PRESSURE CYCLING ENHANCED DENSIFICATION IN SEVERAL COMPOSITE COMPACT SYSTEMS: Ching-Yao Huang, G.S. Daehn, Dept. of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210
Recently, it has been observed that pressure cycling can significantly enhance densification of composite powder compacts in the constrained uniaxial consolidation. The simple explanation for this is that differential compressibility in the constituents of composites drives plasticity in the deformable phrase and the net compressive stress biases the resulting strain to fill porosity in compacts. In the present paper, several composites powder systems including Pb, Zn, Al matrices and Al2O3p, TiO2p, SiCw, reinforcements have been studied in room temperature consolidation in static and cyclic loading. Effects of pressure cycle maximum stress, amplitude, and period on the densification of composite powder compacts are observed and analyzed in terms of matrix strength as well as reinforcement properties including size, shape, and agglomeration. Some simple ideas are able to explain the observed results.
9:45 am
HIGH-NITROGEN AUSTENITIC STAINLESS STEEL POWDERS PORDUCED BY GAS ATOMIZATION: G.O. Rhodes, W.B. Eisen, Crucible Research Center, 6003 Campbells Run Rd., Pittsburgh, PA 15205
Nitrogen is increasingly being utilized as an interstitial alloying element in stainless steels due to the intrinsic benefits imparted on the strength and corrosion resistance properties. Using an alloy design model, austenitic stainless steel powders consisting of about 6-12% manganese, 22% nickel, 25-28% chromium, 4-8% molybdenum and having 0.6 to 1.25% nitrogen have been produced using nitrogen gas atomization. The nitrogen contents attained are substantially higher than predicted at a temperature of 1600°C and nitrogen partial pressure of 100kPa using current thermodynamic models. The powders are subsequently consolidated to full density by hot isostatic pressing (HIP), and in the solution annealed condition the materials exhibit tensile yield strengths of up to 700 MPa with good tensile ductility and excellent corrosion resistance. The development and evaluations of the new steel are described in comparison to other established super austenitic stainless steels and nickel base corrosion resistant alloys.
10:10 am
SELF SINTERING AND BONDING USING ELECTROEXPLODED NANOSIZE ALUMINUM POWDERS: Henry R. Piehler, Gennady V. Ivanov, Frederick Tepper, Dept. of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213; Institute of Petroleum Chemistry, Academy of Sciences, Tomsk, Russia; Argonide Corp., Gateway Towers, Pittsburgh, PA 15222
Aluminum powders approximately 100 nanometers in diameter, made by the process of electroexplosion of wire in argon, have stored surface and strain energy that is released at threshold temperatures well below the melting point. This energy release and accompanying temperature increase allows self sintering and bonding to occur at relatively low temperatures. We studied the self sintering of nanosize aluminum powders made by electroexplosion by heating cold compacted pellets to 450C, at which point they exothermed with the generation of light and sufficient heat to partially melt the pellets. Preliminary results are also reported for bonding conventional aluminum powders and sheets using the energy release and temperature increase from exotherming nanosize electroexploded aluminum powders.
10:35 am
FREE FROM FABRICATION OF HIGH STRENGTH METAL COMPONENTS & DIES: C.C. Bampton, K. Newell, S. Fowser, Rockwell Science Center, Thousand Oaks, CA 91358; Rocketdyne, DeSoto Avenue, CA 91303
A two-staged method has been developed for free form fabrication of nickel and iron based alloy parts directly from alloy powders without the need for tooling or machining. The method provides shape and property control equal or superior to investment castings in the same base alloys. A major advantage of the approach is the ability to utilize commercially available selective laser sintering systems with virtually no modification from their standard configurations as intended for plastic model generation direct from CAD data bases. We have demonstrated the feasibility of shape, dimension and property control for complex, low production volume rocket engine components and for tools and dies intended for higher volume commercial production applications in fully hard commercial steels and superalloys. A new finite element model has been developed specifically to aid in control of sinter densification without distortion or cracking.
11:00 am
DEVELOPMENT OF A MANUFACTURING PROCESS FOR AFFORDABLE, COMPLEX NET SHAPE P/M COMPONENTS: Ellen W. Robare, Clifford M. Bugle, Tony E. Zahrah, Phillip A. Parrish, Dynamet, Inc. Washington, PA 15301; MATSYS, Inc., Arlington, VA 22209
This paper describes the background and progress of a research and development effort called Rapid Net Shape Forming. This effort involves the development and reduction to practice of a process, known as the MetalShell process, for manufacturing complex net shape powder metal components. The process involves the use of electroformed nickel to create a net shape HIP canister. One of the outstanding features of the process is that it can be used to make hollow parts with thin walls. Potential applications for this technology include titanium and beryllium components including fan blades, inlet guide vanes, nozzle hardware, prosthetic devices, and intermetallic and composite components. This effort uses recent advances in process modeling and in-process sensing technologies to reduce the lead time and number of iterations required to make a net shape component. This is turn will make components more cost effective. The areas being exploited include rapid prototyping from CAD files to generate patterns and molds, numerical simulation of the electroforming process to optimize shield design and uniformity of canister thickness, and numerical simulation of HIP consolidation to predict final component dimensions.
11:25 am
ENHANCEMENT OF SINTERING KINETICS IN NANOCRYSTALLINE ALUMINA POWDERS BY ELECTRIC PULSING: R.S. Mishra, A.K. Mukherjee, Dept. of Chemical Engineering and Material Sciences, University of California, Davis, CA 95616
Plasma activated sintering (PAS) involves application of electric pulsing before the sintering cycle. A comparative study has been carried out on nanocrystalline alumina powders with y and a starting phases. The results obtained with and without electric pulsing clearly establish the enhanced sintering kinetics due to prior electric pulsing. These results are explained on the basis of dielectric properties of the powders. In addition the present results show that the powder with a-phase sinters better. High densities (>98%) can be obtained in less than 10 minutes at 1573 K. The time and temperature are significantly lower as compared to the conventional sintering parameter of 1773 K and 3 h. The reason for slower sinterability of powder with y-phase is linked to formation of vermicular structuring during transformation to a-phase. Examples of obtaining sintered products with simple shape in one step using PAS would be shown.
Room: 340A
Session Chairperson: Prof. John H. Perepezko, Department of Materials Science and Engineering, University of Wisconsin, Madison, WI 53706
8:30 am INVITED
COMPUTER SIMULATIONS OF THE STRUCTURAL, DYNAMIC, ELECTRONIC AND MAGNETIC PROPERTIES OF AMORPHOUS ALLOYS: J. Hafner, Institut für Theoretische Physik, Technische Universität Wien, Wiedner Haupstrasse 8-10/136, A-1040 Wien, Austria
There is hardly any area in materials science where the necessity to supplement the experimental information acquired in the laboratory by the results of computer experiments is felt as urgently than for liquid and amorphous materials. The classical example is the structure: whereas laboratory experiments describe a one-dimensional projection of the three-dimensional structure, the computer-simulation delivers the full set of the atomic coordinates. During the last years, a wide variety of computational tools have been developed. These techniques can essentially be classified in three groups: (a) Ab initio local-density functional techniques in the spirit of the Car-Parrinello method. While in this approach no further assumption beyond the reduction of the many-electron Hamiltonian to an effective one-electron form is required, the massive computational effort restricts the application to models with at most a few hundred inequivalent atomic sites. (b) A variety of tight-binding (TB) based techniques (ranging from TB molecular dynamics (MD) and Monte Carlo (MC) to tight-binding-bond approaches to many-atom forces) allow to treat larger systems, albeit at lower accuracy. (c) Classical MD and MC based on effective interatomic pair and volume forces derived via effective-medium approximations, pseudo-potential theory, TB-moment expansions...etc. In this talk I shall attempt to review the state-of-the-art of the computer-modeling of the structural, dynamic, electronic and magnetic properties of amorphous alloys. This work has been supported by the Bundesministerium für Wissenschaft, Forschung und Kunst through the Center for Computational Materials Science.
9:10 am INVITED
AB INITIO STUDIES OF THE ELECTRONIC STRUCTURE AND ENERGETICS OF BULK AMORPHOUS ALLOYS: G.M. Stocks, D.M.C. Nicholson, Y. Wang, X.-D. Wang, C.L. Fu, W.A. Shelton, Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008-6114, Oak Ridge, TN 37831-6114; J.C. Swihart, Physics Department, Indiana University, Bloomington, IN 47405
We present results of first-principles LDA calculations of the electronic structure and energetics of Ni40Pd40P20 and Zr60Al15Ni25 bulk amorphous alloys based on large unit cell (about 300 atoms) structural models of the amorphous state. The calculations are made tractable by the order-N locally self-consistent multiple scattering (LSMS) method implemented on massively parallel computers. For the Zr2Ni-based system, we have also studied the energetics and bonding of some competing stable and metastable ordered phases into which the amorphous state decomposes. The implications of these calculations for understanding the unusual stability of bulk amorphous alloys will be stressed. Work sponsored by ORNL Laboratory Directors Research and Development fund, BES-DMS and OCTR-MICS USDOE, under contract DE-AC05-96OR22464 with Lockheed-Martin Energy Research Corporation.
9:50 am INVITED
ELECTRONIC STRUCTURE AND RELATED PROPERTIES OF METALLIC GLASSES: LINEAR MUFFIN-TIN ORBITALS CALCULATIONS: S.K. Bose, Physics Department, Brock University, St. Catharines, Ontario L2S 3A1, Canada
We describe various aspects of electronic structure calculation for metallic glasses using the Linear Muffin-Tin Orbitals (LMTO) scheme. A method of calculating the electronic transport properties based on the LMTO-recursion method and the Kubo-Greenwood formula is discussed. The practical limitations of the method and the ways to overcome them are presented. We discuss calculations of the magnetic properties within the framework of multiple scattering formalism assuming collinear magnetic structure and using the Linear Muffin-Tin Orbitals Green's Function (LMTO-GF) method. Results for the effective exchange coupling parameters and local magnetic moments for amorphous Fe and Co are discussed with special emphasis on the dependence of these quantities on the local and global features of the structure. A simple interpolation scheme, based on the electronic properties of the pure components, is proposed for estimating the spin fluctuation effects in transition metal glasses.
10:30 am BREAK
10:50 am INVITED
REAL-SPACE ELECTRONIC STRUCTURE APPROACH TO CHEMICAL ORDER IN AMORPHOUS ALLOYS: P.E.A. Turchi, Lawrence Livermore National Laboratory (L-268), P.O. Box 808, Livermore CA 94551; D. MAYOU, LEPES-CNRS, 25 Avenue des Martyrs, BP 166, F-38042 Grenoble Cedex 9, France
A recently developed real-space approach for studying the electronic structure properties of materials which exhibit both chemical and topological disorders is presented, within the tight-binding framework. For a chemically random alloy, we show that the Coherent Potential Approximation (CPA) equations can be solved self-consistently in real-space with the same accuracy as is currently done in reciprocal space, in the case of homogeneous and inhomogeneous systems. Based on the orbital peeling technique, effective on-site and many-body interactions which build up the configurational part of the total energy are computed. With this energetics, Monte Carlo simulations based on the Kawasaki spin-exchange dynamics are performed to predict chemical short-range order in amorphous alloys. The relaxation of the lattice is performed with TB-molecular dynamics simulations, and the overall scheme can be reiterated to self-consistency. Advantages of this global scheme are discussed and application to Zr-Ni alloys are presented. Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48. Partial support from NATO under contract CRG 941028 is gratefully acknowledged.
11:30 am INVITED
FREE VOLUME, PERCOLATION, AND GLASS TRANSITIONS: Mo Li, W.M. Keck Laboratory of Engineering Materials 138-78, California Institute of Technology, Pasadena, CA 91125
Free volume model is examined systematically and quantitatively in a model binary liquid using molecular dynamics simulations. It is found that at the glass transition, the liquid-like cells undergo a percolation transition. However, further analysis shows that free volumes do not exhibit any cooperative behavior at the percolation threshold. The continuous change in thermodynamic and transport properties suggests that the glass transition is kinetic in nature. Implication of the percolating properties of the free volumes in transport properties of undercooled liquids will also be discussed.
Room: 330G
Session Chairperson: David N. Seidman, Northwestern University, Materials Science and Engineering Dept./MLSB, 2225 North Campus Drive, Evanston, IL 60208-3108
8:30 am INVITED
TEMPERATURE AND CONCENTRATION DEPENDENCE OF GRAIN BOUNDARY-DIFFUSION OF 63Ni IN PURE AND BORON-DOPED Ni3Al: Stefan Frank, Jörg Rüsing and Christian Herzig, Institut für Metallforschung, Universität Münster, Germany, now: Hahn-Meitner-Institut, Berlin, Germany
Knowledge about the diffusion behaviour in the grain boundaries of pure and of boron-doped Ni3Al is of basic importance to improve our understanding of the boron-effect and the mechanical properties of polycrystalline Ni3Al. We report on a first study of grain boundary diffusion in pure and doped Ni-rich Ni3Al polycrystals. Diffusion penetration profiles were determined by a serial sectioning technique using a precision parallel grinding device. The low energy -decays of the 63Ni tracer were detected by liquid scintillation counting. The high efficiency allowed to significantly increase the detectable concentration range of the measured profiles and provided the basis for investigating grain boundary self-diffusion in Ni3Al in a meaningful way. For comparison grain boundary self-diffusion in pure Ni was re-investigated in true type R-kinetic. It is known that the temperature dependence of the grain boundary diffusion parameter P=Dgb of 63Ni in pure Ni and in both Ni3Al materials is of the Arrhenius type. The absolute values of P follow the sequence P Ni>P Ni3Al>P Ni3Al+B. The remarkably higher activation enthalpy Qgb (Ni3Al) in comparison with Qgh (Ni) can be attributed to the grain boundary structure of the strongly ordered Ni3Al compound. Ni-diffusivity in the doped alloy is about 2-3 times lower than in pure Ni3Al. A prospective reason for the decreased diffusivity is the segregation of B and the thereby enhanced cosegregation of Ni in the grain boundaries. The strong segregation of boron leads to a certain blocking of diffusion paths of the Ni atoms. High angle grain boundary energies in pure and R-doped Ni3Al are derived from the diffusion data applying the Borisov et al.relation. The effect of stoichiometry on grain boundary self-diffusion in Ni3Al was investigated for compositions between 73 and 78 at% Ni. A V-shaped concentration dependence of P with a minimum at near 75 at% Ni was observed which becomes very distinct at lower temperatures. At e.g. 1066 K P increases by about one order of magnitude from stoichiometric to Ni-rich Ni3Al. This behaviour is related to the change in composition and state of order of grain boundaries in non stoichiometric Ni3Al.
9:10 am
CALCULATIONS OF DIFFUSION AND SEGREGATION IN Al-Cu GRAIN-BOUNDARIES: X.Y. Liu, J.B. Adams, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 105 South Goodwin Avenue, Urbana, IL 61801; Wei Xu, Lawrence Livermore National Laboratory, University of California, Livermore, CA 94551
We have studied the atomistic mechanisms of electromigration in Al-Cu, in specific, the diffusion of atoms and segregation of Cu atoms in the Al grain-boundaries with a newly developed EAM interatomic potential constructed by the Force-Matching Method. The potential parameters are fitted to available experimental data plus ab initio force database. The energetic and structural properties of Cu segregation and the effect in atomic diffusion path and activation barriers are studied. The grain-boundary calculations, in agreement with ab initio results, show that the Cu segregation is dominated by size effects in the Al-Cu system, i.e., Cu atoms segregate to sites which are locally compressed. In the case of a 
11 tilt boundary, this predicts that the Cu will segregate to sites away from the symmetric center of the boundary.
9:30 am
ATOMISTIC SIMULATION OF GRAIN BOUNDARY STRUCTURE AND DIFFUSION IN B2 NiAl: Yuri Mishin, Diana Farkas, Virginia Polytechnic Institute and State University, Materials Science and Engineering Department, Blacksburg, VA 24061
We modify the existing embedded-atom potentials for NiAl by fitting them to self-diffusion data for pure Ni and Al and to the triple-defect model for this compound. Using the modified potentials and molecular statics we calculate the structure, excess energy and cohesive energy of [001] tilt grain boundaries in NiAl. The calculations are performed for 25 orientations with $\Sigma$ values from 5 to 185. For each orientation the lowest-energy stoichiometric boundary structure is established. Low-$\Sigma$ orientations are associated with minima of the boundary energy and maxima of the cohesive energy. The boundary structures obtained are analyzed in terms of the structural unit model. For two lowest-energy boundaries, $\Sigma=5$ (210) and $\Sigma=13$ (230), we simulate tracer self-diffusion in the boundary core both parallel and normal to the tilt axis. We assume the vacancy mechanism and calculate the vacancy formation and migration energies in the boundary core. To calculate the boundary diffusion coefficients we use the technique proposed recently by one of us [Phil. Mag. A 72, 1589 (1995)]. This technique combines the matrix method with Monte Carlo simulations of individual vacancy-tracer encounters. The effective activation energy is calculated in a wide temperature range and compared with the spectrum of individual jump energies in the boundary. The results are discussed in terms of the grain boundary mass transport and its effect on high temperature properties of NiA.
9:50 am
THE IVANTSOV GROWTH EQUATION AND INTERFACIAL KINETICS: Zi-Kui Liu, Y. Austin Chang, Department of Materials Science and Engineering, 1509 University Avenue, University of Wisconsin-Madison, Madison, WI 53706
The growth equation of parabloid was first derived by Ivantsov1 and later modified by Trivedi2 to take into account the interfacial energy and finite interfacial mobility (interfacial kinetics). The modification was done by first considering the effects of the interfacial kinetics and the interfacial energy and curvature, and then solving the diffusion equations on the composition at the interface. Though the modification was necessary, the growth equation was much more complicated that the original Ivantsov equation. In a recent publication by us, the advantage of the modern development of computational thermodynamics was taken and the Ivantsov equation was then used directly with the actual composition after taking into account the interfacial energy and the finite interfacial mobility. It was pointed out by a reviewer that this approach was not self evident if it is identical to Trivedi's modification. In the present report, we will formulate a consistent framework to describe the phenomena.
10:10 am
MICROSTRUCTURAL CHARACTERIZATION OF TiAl3 PRODUCT LAYERS IN AlCuSi/Ti AND AlCu/Ti REACTION COUPLES: C. Wauchope, J.E. Sanchez, Jr., University of Michigan, Ann Arbor, MI 48109; P.R. Besser, R. Alvis, Advanced Micro Devices, Sunnyvale, CA 94088
Metallization interconnects in advanced integrated circuits are typically fabricated from Al alloy (500-1000nm)/Ti (20-50nm) multilayer thin films. The Ti provides several effects in the Al layer; improved reliability against electromigration-induced failure, reduced Al grain size, increased Al (111) fiber texture, and reduced Al thickness due to Ti+Al reaction to form TiAl3. The TiAl3 reaction occurs during thermal processing and device fabrication, and leads to increased line resistance as the Al thickness is reduced. We present detailed cross-section transmission electron microscopic analysis of TiAl3 layers formed in AlCuSi/Ti and AlCu/Ti reaction couples. Results show that the Al alloy/TiAl3 and TiAl3/Ti interfaces are "clean" and free of intermediate phase layers. In addition local energy dispersive x-ray spectroscopy (EDS) analyses show Si partitioning in the TiAl3 region in AlCuSi/Ti samples. The TiAl3 grain size is roughly independent of Al alloy type, and depends primarily on total TiAl3 thickness. These results are described in terms of models which describe the effects of Cu and Si alloying additions on the TiAl3 formation kinetics, in particular to the Ti+Al reaction rate dependence on the Ti/AlCuSi thickness ratio.
10:30 am BREAK
10:50 am INVITED
STRUCTURE, COMPOSITION AND THERMAL STABILITY OF METAL/CERAMIC INTERFACES: Manfred Rühle, Max-Planck-Institut für Metallforschung, Seestr. 92, D-70174 Stuttgart, Germany
Metal/ceramic interfaces play a crucial role in different areas of materials science such as metallic interconnects in semiconductors, adhesion of oxide scales on metal substrates, thermal barrier coating, composites and bonding between bulk parts of metals and ceramics. It is of great interest to correlate the microstructure of those interfaces to their properties. The possibilities of getting information on the structure and composition of metal/ceramic interfaces will be discussed for several systems. The focus will be mainly on model systems (Cu/Al2O3, Ni/Al2O3, Nb/Al2O3) but also applications for real materials will be discussed. Segregation of impurities may lead either to an increase or decrease of the adhesion. Therefore, it is crucial to determine those impurities as accurately as possible. Metal/ceramic interfaces are often exposed to high temperatures at different atmospheres. Therefore, the thermal stability under service conditions is of great interest. The paper will describe recent advances and possibilities of determining the structure, composition and chemical reactions at those interfaces by conventional transmission electron microscopy, high-resolution transmission electron microscopy and analytical electron microscopy. The results of experimental studies will be compared to results of ab-initio first principles calculations and to experimental studies on the adhesion of metal films on ceramic substrates.
11:30 am
THE Al/Ni AND Al/Cu INTERFACIAL REACTIONS UNDER THE INFLUENCE OF ELECTRIC CURRENT: Wen-Chyuarn Liu, Sinn-wen Chen, Department of Chemical Engineering, National Tsing-Hua University, Hsin-Chu, Taiwan 30043, China
Electromigration has been observed and quite extensively investigated in the integrated circuit devices with the electric current density higher than 105 A/cm2. The electric current density in the electronic packaging was usually lower and the effect of electromigration has not been discussed. This study investigated the effect of weaker electric current, up to 103 A/cm2, upon the chemically-driven interfacial reactions in the Al/Ni and Al/Cu systems by analyzing their reaction couples. The reaction couples would be heated by the passing-through electric current. The temperatures of the reaction couples increased with the increasing electric density. Annealed at the same temperatures, similar results were found for the reaction couples with and without the passing-through electric current. Same intermetallics, such as Al3Ni and Al3Ni2, were formed at the interfaces, and the thickness of the reaction layers was the same. It was concluded that the electric current density up to 103 A/cm2 has little effect upon the interfacial reactions in the Al/Ni and Al/Cu systems.
Room: 330F
Session Chairpersons: D. Tsakiropoulos., Dept. of Materials Science and Engineering, University of Surrey, Guildford, Surrey, GuZ 5XH, UK; D. Upadhyaya, University of Idaho, Institute for Materials and Advanced Processes, Mines Bldg 204, Moscow, ID 83844-3026
8:30 am
THERMODYNAMICS OF VACUUMTHERMIC REDUCTION OF LIGHTWEIGHT MAGNESIUM-LITHIUM ALLOY: Dajian Wang, Department of Metallurgy, Kunming University of Science and Technology, Kunming, Yunnan 650093, China
The principles of preparation of light weight alloy of Mg-Li alloy with a low-density less than 1g/Cm3 with vacuumthermic reduction are described according to the preliminary laboratory-scale results. The process involves the use of ferrosilicon and aluminium to reduce magnesia and lithium oxide concurrently in a vacuum furnace to mixing gas of metallic magnesium and lithium due to the higher pressures for both magnesium and lithium. The metallic vapours are cooled at the lower temperature part of the furnace. Thermodynamic analysis of related reactions and their equilibrium constants revealed the probabilities of reactions and preferable reductants of ferrosilicon or aluminium. The alloying effects at low pressure of reduced magnesium and lithium and their evaporation may significantly dominate the progress of the process. Based on the calculation determination of activity coefficients of components in Mg-Li binary, the thermodynamic aspects for both reduction process and vaporisation process are systematically analysed in the paper.
8:50 am
STRESS RELIEVING METHODS FOR THICK ALUMINIUM ALLOY PLATE: EVALUATION BY X-RAY DIFFRACTION RESIDUAL STRESS MEASUREMENT: Bernt Jaensson, CSM Materialteknik AB, Box 13200, S-58013 Linköping, Sweden; Alfred Heinz, Hoogovens Aluminium Walzprodukte GmbH, Postbox 920, D-56009 Koblenz
In the design of metallic structural parts for aircraft there are, basically, two approaches that can be taken: either the part is built up from a number of individually formed elements which are joined by riveting or adhesive bonding, or the part is sculptured from a single forging or piece of plate. In this situation, designers of small aircraft tend to use the first approach, while integrally machine parts are dominant in the structure of large aircraft. However, the balance between the two options is also changing with time, in that present-day aircraft engineers are increasingly favouring the sculpturing method. Contributing to this trend is the availability of numerically controlled high-speed milling machines, as well as forgings and plate with low levels of residual stress. The choice between a hand forging/die forging or plate is often dictated by the height of the final part. Since plate can be more efficiently stress relieved - by stretching - it is the preferred choice whenever the thickest available plate can accommodate the part. In the last couple of years, plate producers have strived to raise the upper limit of the thickness range from, say, 150 mm to 250 - 300 mm. In so doing, might exceed the capacity of existing stretching presses, which necessitates the use of an alternative stress-relieving method e.g. stepwise cold compression. With respect to the resulting residual stress level, one could ask the question to which extent the relative advantage of plate over forging is preserved in this case. An earlier investigation of the relationship between stress-relieving of die forgings, residual stresses and distortion during machining is recapitulated to give a background to the present work, which involves measurement of through-thickness stress variations in 100 and 150 mm thick plate, stress relieved by stretching, and in cold compressed plate of 200 mm thickness.
9:10 am
TEXTURE CONTROL OF ALUMINUM ALLOY SHEETS: C.-H. Choi, K.-H. Kim, D.N. Lee, School of Materials Science and Engineering and Center for Advanced Materials Research, Seoul National University, Shinrimdong, Kwanak-ku, Seoul 151-742, Korea
In order to achieve good deep drawability it is imperative to obtain well developed {111}texture which gives rise to the higher plastic strain ratio. It is difficult to obtain the texture from conventional rolling and annealing processes. Therefore an unconventional rolling process which causes shear deformation has been introduced in addition to the conventional rolling process. Various combinations of the conventional and unconventional rolling processes and the annealing process have been theoretically and experimentally studied to obtain the well developed {111}texture which in turn gave rise to a substantial increase in the plastic strain ratio.
9:30 am
THERMO-MECHANICAL BEHAVIORS OF Al-Ni-Mm AMORPHOUS ALLOYS: S.J. Hong, H.S. Kim, C.W. Won, S.S. Cho, B.S. Chun; Department of Metallurgical Engineering and RASOM, Chungnam National University Kung-dong, Yuseong-gu, Tacjeon 304-750, KOREA; P.Warren, B. Cantor, OCAMAC, Department of Materials University of Oxford Parks Road, Oxford, OX1 3PH, UK
The Al-M-Mm (Mm=misch metal) alloys have been produced by a gas atomization, a sing roll melt spinning and a twin roll spinning methods. These alloys have amorphous structure, finely mixed structure consisting of aluminium phase, intermetallic compounds homogeneously embedded in the ultrafine "rained aluminium matrix and intermetallic compounds in the large "rained aluminium matrix depending on the process variables. The alloy powders and ribbons have been warm compacted to various relative densities at various temperatures. The cylindrical and ring shapes compacts have been upsetted at various temperatures and the plastic deformation behaviours have been investigated using TEM, DSC and XRD. The density distribution, load, deformed geometry, friction coefficient, interparticle bonding behavior have been compared with the theoretically calculated ones. The forming limit diagrams have obtained from the ring compression tests.
9:50 am
MICROSTRUCTURES AND MECHANICAL PROPERTIES OF AZ91 AND AM60 MG ALLOYS BY TWIN ROLL PROCESS: S.S. Cho, B.S. Chun, C.W. Won, B.S. Lee, H. Baek, K.H. Yim, Department of Metallurgical Engineering and RASOM, Chungnam National University Kung-Dong, Yusong-gu, Taejon 304-750, KOREA F.H. Froes, Institute for Materials and Advanced Process, University of Idaho, Mines Building, Room 321 Moscow, Idaho 83844-3026
It is well known that Mg alloys are quite attractive for structural use in aerospace and automotive industry due to the light weight. The properties of RS AZ91 and AM60 Mg alloys by twin roll cast will be compared with commercial ingot metallurgy alloys. The process including flake production, degassing, cold compaction and hot consolidation will be discussed. The Corrosion behavior will be also discussed.
10:10 am BREAK
10:30 am
MECHANICAL PROPERTIES OF Mo-Al ALLOYS BY TWIN ROLL PROCESS: S.S. Cho, B.S. Chun, C.W. Won, S.D. Kim, B.S. Lee, H. Baek, Department of metallurgical Engineering and RASOM, Chungnam National University Kung-Dong, Yusong-gu, Taejon 304-750, Korea; F.H. Froes, Institute for Materials and Advanced Process, University of Idaho, Mines Building, Room 321 Moscow, Idaho 83844-3026
Rapid solidification processing(RSP) has been exploited to improve mechanical properties of materials. This study will focus on the process including the production of flake by twin roll cast, degassing, cold compaction and hot extrusion. The properties of experimental Mg-AI alloys are compared with ingot metallurgy alloys. The corrosion and wear behavior will be discussed.
10:50 am
NUMERICAL ANALYSIS OF MICROSEGREGATION IN AL ALLOY WELD METALS: C.H. Lee, E.P. Yoon; RASOM, Dept. of Met. Eng., The Hanyang University, Seoul, Korea, 133-791
During solidification of alloys under rapid thermal excursion of welds, the solute redistribution brings out microsegregation. The microsegregation causes the formation of non-equilibrium second phases, shrinkage and porosity degrading properties and forming solidification crack. Therefore, it has been required to predict microsegregation quantitatively. To predict the degree of microsegregation, more exact and appropriate computer simulation technique has been being actively used during last two decades. In this study, an advanced two dimensional model was suggested on the basis of the previous one and two dimensional models. In the new model, both primary and secondary arm regions were defined for the analysis region. Before calculation of microsegregation, the analysis region was determined by the theoretical equation for the primary and secondary arm spacing. The growth in the primary arm region was assumed to be a planar for effective calculation. Especially, for the growth of a secondary arm, a simple and effective mathematical function was established to show the growing pattern(polynomial interface). The solute diffusion in the solid phase was calculated by finite difference method (FDM). The solid-liquid interface movement was considered to be in local equilibrium state indicated by the phase diagram.
11:10 am
PHASE STABILITY OF Ab66Mn9(Ti, Zr)25-DISPERSION-STRENGTHENED Al ALLOY: Seung-Zeon Han, Seong I. Park, Seon-Jin Kim, Hyuck-Mo Lee, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Kusung-Dong 373-1, Yusung-Gu, Taejon, Korea 305-701; Department of Materials Engineering, College of Engineering, Hanyang University, Hacngdang-Dong 17, Seongdong-Gu, Seoul, Korea 133-791
The addition of Mn to the tetragonal Al3(Ti1-xZrx) phase produced cubic Ll2-type Al66Mn9(TiZr)25 phase with a small amount of second phases such as Al8Mn5 and Al2Zr, still existing in the as-cast state. Second phases disappeared when intermetallic compounds were homogenized at 1000°C for 24 hours. After homogenization, intermetallic compounds were mixed with pure A1 in the form of powder by attritor mill and then vacuum hot pressed. IDS (intermetallic-dispersion-strengthened) Al alloys prepared in this way were analyzed in terms of phase stabilities and microstructures through XRD, SEM and TEM methods.
11:30 am
EFFECTS OF MICROALLOYING WITH Ce, Ni AND Si ON THE BEHAVIOUR OF INGOT ALUMINIUM ALLOY: C912 (A1-Zn-mg-Cu): Y.L. Wu, G.G. Li, F.H. Froes and J. Liu, BIAM, PO Box 81, Beijing 100095, China; IMAP, University of Idaho, Moscow, Idaho 83844-3026; Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069-0001
The present paper will discuss the effects of microalloying with Ce, Ni and Si on the behaviour of the ingot aluminium alloy C912 (A1-9Zn-2Cu-2Mg). The relationship between the chemistry, processing, microstructure and mechanical behaviour will be present for direct chill cast ingots which were subsequently extruded. Preliminary results show that this alloy class can exhibit attractive combination of strength and corrosion resistance.
11:50 am
SOLIDIFICATION PROCESSING FOR THE PRODUCTION OF FINE GRAIN ALUMINUM ALLOY MATERIALS: Akira Sato, Garo Aragane, Yoshiaki Osawa, and Susumu Takamori; National Research Institute Far Metals, Tsukuba, Ibaraki 306 Japan
It is well-known that metallic materials having fine grain crystal structures possess high mechanical properties, ie., high strength and at the same time high toughness. A new process named "Rapid solidification with vigomus agitation" is developed to produce large ingots having fine grain and homogeneous structures. The molten alloys are rapidly solidified with watercooled copper molds and at the same time stirred vigorously by graphite rods during falling down of the melt through the gap between the mold and the rod. The results obtained using Al-Si alloys are as follows. The mean grain size of primary crystals in slurry become smaller with increasing the intensity of cooling and the rotation speed of stirring rod. Primary and eutectic Si grains are not only small but also globular when the agitation is strong enough.
| Search | Technical Program Contents | 1997 Annual Meeting Page | TMS Meetings Page | TMS OnLine |
|---|