Room: 315B
Session Chairperson: TBA
1:30 pm
ELECTRODEPOSITED Ni-Al PARTICLE COMPOSITE COATINGS: D.F. Susan, K. Barmak, A.R. Marder, Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015-3195
Electrodeposited metal matrix/metal particle composite coatings (EMMC's) were deposited, heat treated, and characterized. Nickel matrix/aluminum particulate coatings deposited on a nickel substrate was chosen as a model system. The microstructure of the as-plated and heat treated coatings was characterized using light optical microscopy (LOOM), SEM, quantitative image analysis (QIA), and EPMA. A schematic model is presented for coating morphological development during codeposition of small, electrically conducting particles. The heat treated coatings consist of a two phase mixture of y solid solution and Ni3Al (gamma-prime) with small Kirkendall voids also present. The hardness of the heat treated coatings increased with increasing Ni3Al content and remained constant with extended heat treatment time. Oxidation tests were performed isothermally in air at 800, 900, and 1000°C for up to 900 hrs. and the depth of the oxidation attack was determined. Throughout the investigation, the Ni-Al coatings were compared to conventional pure Ni coatings deposited under similar conditions.
1:50 pm
FORMATION OF THIN COLORED FILM ON STAINLESS STEEL: G.S.Gupta, Dept. of Mining, Minerals and Materials Engineering, The University of Queensland, St.Lucia, Queensland - 4072, Australia
Formation of colored film on type 304 stainless steel has been studied using chromic acid and potassium dichromate solutions. Permanent colors have been obtained using immersion and electrolytic (potentiostatic) methods. The effect of different parameters on the coloring process including temperature, coloring methods, solution composition, stirring, surfactant etc., have been noted. Moderate temperature of the solution, electrolytic method, use of surfactant and stirring of the solution were found to enhance the coloring process. A coloring solution which is strongly oxidized and acidic in nature is recommended. It is advisable that after the extended use of the coloring solution, fresh solution should be used.
2:10 pm
TRICATIONIC PHOSPHATE COATING ON GALVANNEALED STEEL SHEET: Carlos Nelson Elias, Mila Marques Justo, Escola de Engenharia Metaurgica de Volta Redonda, Av dos Trabalhadores 420, 27260 740 Volta Redonda, RJ - Brazil
The galvannealed compared to galvanized steel sheet has excellent paint adhesion, weldability and corrosion resistance after painting. However, the coating tends to cause exfoliation when undergoing severe deformation. This coating is used in the automobile industry. Since the mass loss is very large, it accumulates on the metal mold and results in severe damage to the surface quality of the formed panel affecting press workability and damaging the tool. Nevertheless, phosphating is the most widely used pretreatment, since it serves as an excellent paint base, increases corrosion resistance to metal paints, aids in cold forming of steel and increases the lubricant power of oil applied to the pieces subjected to friction and wear. The influence of galvannealed morphology on the phosphate crystal feature is not well understood. In this work, a tricationic phosphate coating was applied to a surface of a low carbon steel and an interstitial free steel with galvannealed coating. Our paper will discuss the structural and mechanical properties resulting from this treatment.
2:30 pm
PROGRESS TOWARD THE DEVELOPMENT OF DENDRIMER-BASED PROTECTIVE COATING: Larry A. Milco, Donald A Tomalia, Michigan Molecular Institute, 1910 W. St. Andrews Road, Midland, MI 48640-2696
There is a considerable demand for thin film coatings to which other substances will not stick. Coatings are required to protect surfaces from soils, stains, ice, graffiti, insects, oils, corrosion and chemical and biological contaminants. Moreover, as legislative pressures to remove volatile organic solvents from coating formulations persist, the demand for alternative water-borne systems continues to increase. The incorporation of dendritic polymers in non-stick coating formulation is a highly viable approach to overcoming the limitations associated with conventional polymer systems. Non-stick coatings were prepared by crosslinking dendrimers with linear polymers. The high advancing and receding contact angles and low contact angle hysteresis of water and hexadecane on the coatings are indicative of the non-stick (low adhesion) properties of these surfaces.
3:05 pm
PULSED LASER DEPOSITION OF COLLAGEN AND APATITE/COLLAGEN COMPOSITE BIOCOMPATIBLE THIN FILMS: J.A. Conklin, C.M. Cotell, Surface Modification Branch, Code 6671, U.S. Naval Research Laboratory, Washington, D.C. 20375
Thin films comprising either collagen or a composite of hydroxyapatite (HA) and collagen were deposited by pulsed laser deposition (PLD) on various substrates. Films were deposited using either a KrF (248nm) or ArF (193nm) excimer laser and the substrates were maintained at room temperature. Collagen films were characterized by SEM, Fourier transform infrared (FT-IR) spectroscopy and gel electrophoresis. The functional groups on the collagen molecule remained intact through the laser ablation process, but there was evidence for some loss of secondary structure. In addition, the surface morphology was a function of the laser fluence and the gas environment during PLD. Less denaturation of the molecule was observed when the ablation was at 193nm than at 248nm. For the composite films, the target material consisted of a 70/30 (by weight) mixture of apatite/collagen, the same ratio found in bone. The resulting composite films were a homogenous mixture of amorphous collagen and highly crystalline apatite.
3:40 pm BREAK
4:00 pm
PROTEINS FROM OYSTER SHELL AS MODELS FOR BIODEGRADABLE COMMERCIAL POLYMERS: A.P. Wheeler, Department of Biological Sciences, Clemson University, Clemson, SC 29634
Virtually all minerals formed by organisms are composites, containing an organic phase (matrix) which enhances the mechanical properties of the inorganic phase and which presumably controls mineral growth. The matrix of the CaCO3 shell of oysters contains soluble, highly anionic proteins which in vitro adsorb to mineral and in so doing alter mineral growth. Based on the surface reactive properties of these proteins, synthetic analogs have been made which have properties that make them candidates as inhibitors for mineral scale and corrosion and as dispersants. Synthesis of a simple matrix protein analog, polyaspartic acid, is possible on a significant scale using dry thermal polymerization and aspartic acid as the only reactant. Thermal polyaspartic acid is highly biodegradable when compared to polymers currently used for commercial surface reactive applications.
4:20 pm
THE APPLICATION AND SUBSEQUENT CROSS-LINKING OF A BIOLOGICAL POLYMER ON ALUMINUM METAL: Douglas C. Hansen, Naval Research Laboratory, Washington, D.C. 20375-5343
Biological polymers that are used by organisms in the formation of structural materials and protective coatings are widespread in nature. An example of such a polymer is the protein utilized by the blue mussel Mytilus edulis as a varnish coating on its byssal threads. This protein is of high molecular weight (>100,000) and is unique in containing the catecholic amino acid L-dopa. This protein exhibits high affinity for metals and acts as a substrate for the enzyme catechol oxidase, which catalyzes the two electron oxidation of catechol to o-quinone. This reaction is essential in the formation of a two component sclerotized resin. The adsorption of this protein onto pure aluminum (99.99999%) and subsequent cross-linking of the adsorbed protein results in a significant shift in the critical pitting potential and polarization resistance of the treated aluminum. Atomic Force Microscopy (AFM) measurements clearly show that treatment of the protein adsorbed onto Highly Ordered Pyrolytic Graphite (HOPG) with catechol oxidase results in a stable, varnish-like coating.
4:40 pm
ADSORPTION OF ADHESIVE PROTEINS FROM THE MARINE MUSSEL, MYTILUS EDULIS, ON POLYMER FILMS IN THE HYDRATED STATE USING ANGLE DEPENDENT XPS AND AFM: A.M. Baty, P.K. Leavitt, C.A. Siedlecki, B. J.Tyler, P.A.Suci, R.E. Marchant, G.G.Geesey. Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717-0398
The adsorption of Mussel Adhesive Protein (MAP) from the marine mussel Mytilus edulis has been investigated on polystyrene (PS) and poly (octadecyl methacrylate) (POMA) surfaces using angle dependent XPS and AFM. XPS analysis was performed at LN temperatures without dehydrating the samples and at room temperature following dehydration. The analyses indicate that adsorbed MAP is stabilized on the surface of the PS through specific interactions preventing the protein from losing lateral spatial distribution across the surface upon dehydration. The adsorbed MAP on the POMA surface is representative of a loosely bound protein layer that is adsorbed through non-specific types of interactions allowing the protein to lose much of its lateral distribution when dehydrated. These data demonstrate that the surface chemistry of the polymer films influences protein-protein and protein-surface interactions, and that hydration plays a significant role in structuring protein-surface interactions.
Room: 340B
Session Chairpersons: Prof. Enrique J. Lavernia, Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA 92717; Dr. Benji Maruyama, Wright Laboratory/NIST, 2230 10th ST STE 1, WPAFB, OH 45433
2:00 pm INVITED
PRESSURE INFILTRATION TECHNIQUE FOR SYNTHESIS OF ALUMINUM-FLY ASH PARTICULATE COMPOSITES: P.K. Rohatgi, R Q. Guo, H. Iksan, R. Asthana, Materials Department, University of Wisconsin, Milwaukee, WI 53201
Aluminum - fly ash composite was prepared by pressure infiltration technique. Loosely packed beds of cenosphere fly ash (above 55 vol% in the composite) can be successfully infiltrated by molten aluminum under pressure in the range of 0.3-0.7 MPa, and the density of the composite is 1.4 g /cm3 compared to the density 2.68g/cm3 for aluminum. Cenosphere fly ash particles are very light materials (density: 0.4 - 0.6 g/cm3). The microstructure of composite showed that there was uniform distribution of fly ash particles in the aluminum matrix. The mechanism of pressure infiltration and the reaction between aluminum and fly ash during infiltration and solidification will be discussed. Selected properties including hardness, microhardness, and compressive strength of aluminum - fly ash composites were determined and the results are presented in this paper.
2:30 pm
WETTABILITY OF NICKEL COATED GRAPHITE BY ALUMINUM: S. W. Ip, R. Sridhar, J.M. Toguri, Department of Metallurgy and Materials Science, University of Toronto, Toronto, ONT, Canada M5S 3E4; T. Stephenson, INCO Limited, J. Roy Gordon Research Laboratory, 2060 Flavelle Boulevard, Mississauga, ONT, Canada L5K 1Z9
Graphite is a very attractive candidate for aluminum MMC's. However, aluminum does not wet graphite. Thus the production of aluminum-graphite composite is difficult. Nickel is a material known to be wetted by aluminum. INCO Limited recently has developed a novel technique for coating graphite fibres with nickel. It was found that such coating promotes aluminum wetting on the fibres. To determine the wettability of aluminum on nickel coated graphite, the sessile drop technique along with a high temperature x-ray setup was used. Samples of graphite, electrolytic nickel, and nickel coated graphite were examined. Contact angles determined for these samples showed that graphite is non-wetting while the nickel coated graphite provided better wetting than electrolytic nickel. The nickel-aluminum interface of the samples were examined microscopically using SEM.
2:55 pm
MICROSTRUCTURAL INVESTIGATION OF INERT GAS ATOMIZED SiC/Al-Li-Cu-Mg-Zr ALLOY BASED MMC POWDERS: S. Özbilen, Gazi University, Faculty of Technical Education, Department of Metals Education, Teknikokullar, Arkara, Turkey
Variable amount SiC short fibres hardened & Al-Li-Cu-Mg-Zr alloy based MMC powders were produced by inert gas atomization under Ar, in a pilot plant down-draught atomizer with a Mannessman type nozzle. Melt temperature was 875°C and gas pressure was 1.85 MPa. Powder based alloy matrix CM was sieved dry. SEM and TEM investigation was used for microstructural characterization. Emphasis was given to the effect of PM processing route on the nature of bonding between matrix and second phase fiber particles.
3:20 pm
IN SITU PROCESSING OF TiB2/Cu-ALLOY COMPOSITES BY REACTIVE PRESSURELESS INFILTRATION (RPI): V. Shtessel, M. Koczak (deceased), Department of Materials Engineering; R. Mutharasan, Department of Chemical Engineering, Drexel University, Philadelphia, PA 19104
The process of Reactive Pressureless Infiltration (RPI) for in situ synthesis of Cu-Mn/TiB2 composites from elemental powders has been investigated. Primary factors, which alter phase composition and microstructure of the MMCs are enthalpy and relative free energy of reinforcement formation, initial powder size, processing temperatures and matrix wettability of the reinforcement. The Cu-Mn/TiB2 composite material was synthesized by matrix assisted displacement reactions, where the desired reinforcement forms gradually as a result of liquid infiltration and reaction. A weak boride former, e.g. Mn, is mixed with B in the bottom layer and infiltrated with Cu-Ti alloys. The process involves two consecutive steps: (1) formation of weak boride, e.g. Mn + 2B -> MnB2; (2) displacement reactions, e.g. MnB2 + Ti-Cu -> TiB2 + Cu-Mn. This route is advantageous due to improved wettability of Mn compounds by copper. Composites with 5, 7 10, 15, 20 and 30v/o of TiB2 have been produced and their microstructures and mechanical properties are being evaluated. Typical microstructures illustrate an even distribution of 0.5 - 5 micron particulates of TiB2. Possible mechanisms of the microstructure development during the process of reactive infiltration were analyzed. The study demonstrates that TiB2 forms by interfacial reaction: Ti + MnB2 = TiB2 + Mn. A kinetic model of the process has been proposed. The model enables us to determine the infiltration rate, the thickness of reacted layer as a function of time, the rate of reaction of TiB2 formation, the concentration profile of each component in the reactive layer. The model shows good agreement with experimental results. The RPI process is a promising technique for in situ, net-shape manufacturing of Cu-based MMCs. This research is supported by Office of Naval Research.
3:45 pm BREAK
3:55 pm INVITED
BREAKTHROUGH OF CONTINUOUS FIBRES REINFORCED CERAMIC COMPOSITES FOR INDUSTRIAL APPLICATIONS: M. H. van de Voorde, European Union, Joint Research Center, Institute for Advanced Materials, 1755 ZG Petten, The Netherlands
Long fibre Ceramic Composite Materials form the materials for the technology of the 21st century; this will be demonstrated on the hand of a number of industrial applications. A resume will be given of the ceramic composites used in space applications. An overview of the "inorganic fibres" and "continuous fibres ceramic composite materials" is planned with indications of their advantages and problem areas. This data base generation, and engineering properties as joining, machining and NDE. Developments will be highlighted to made cost competitive ceramic composites with high temperature stability, corrosion resistant and good mechanical properties for long duration. The breakthrough of mew technologies with CFCC's use will be sketched. The needs for Research, Development and Technology on CFCC are pinpointed and indications for a European programme given. The market trends are also resumed.
4:25 pm
PROCESSING OF DAMAGE-TOLERANT, ENVIRONMENTALLY-STABLE, ALL-OXIDE CERAMIC COMPOSITES: C.G. Levi, J.Y. Yang, B.J. Dalgleish, Materials Department, University of California, Santa Barbara, CA 93106
Ceramic composite systems based on all-oxide constituents are of interest for high temperature applications owing to their inherent oxidative stability but must also be designed to exhibit damage tolerance. One microstructural design concept relies on crack deflection through a porous matrix rather than at fiber/matrix interfaces, which is the more conventional approach to toughening in CMC's. The requisite matrix must have an optimum combination of toughness and strength which can be achieved by incorporating a minimum amount of fine, well distributed porosity, and must also be chemically and microstructurally stable at high temperatures. Composites based on this concept have been synthesized using vacuum infiltration of aqueous mullite-alumina slurries into woven polycrystalline alumina fiber preforms, followed by precursor impregnation and sintering. Initial evaluation of these materials shows promising behavior under tension and potential for notch insensitivity and thermal stress tolerance. Current understanding of the underlying mechanisms as well as microstructural design and processing issues relevant to the attainment of this behavior will be discussed. Research sponsored by DARPA under URI Grant N00014-92-J-1808.
4:50 pm
DENSE IN-SITU TiB2/TiN AND TiB2/TiC CMCS: REACTIVE SYNTHESIS AND PROPERTIES: I. Gotman, F. Olevsky, E.Y. Gurmanas, Department of Materials Engineering, Technion-Israel Institute of Technology, Technion City, Haifa 32000, Israel
In-Situ TiB2/TiN and TiB2/TiC CMCs were fabricated from fully dense BN-Ti and B4C-Ti powder blends with and without the addition of Ni powder. Three different methods were used: pressureless and pressure-assisted displacement reaction synthesis and thermal explosion under pressure. Application of a moderate external pressure (¾ 200 MPa) was shown to be sufficient to ensure full density of TiB2/TiN/Ni and TiB2/TiC/Ni composites. The addition of Ni powder allowed to significantly reduce the ignition temperature of thermal explosion due to the formation of the low temperature Ti-Ni eutectic phase. Thus, the preheating temperature or thermal explosion, as well as the processing temperatures of displacement reaction synthesis (¾ 1200°C) were considerably lower than those typical of current methods used for the processing/consolidation of CMCs. Microstructure and composition of materials obtained were characterized by x-ray diffraction and scanning and transmission electron microscopy (SEM and TEM). Mechanical properties were evaluated by measuring microhardness, fracture toughness and three-point bending strength. High fracture toughness of TiB2/TiN/Ni and TiB2/TiC/Ni CMCs was obtained indicating that fine Ni dispersions are effective in dissipating the energy of propagating cracks.
5:10 pm
FIBER FRAGMENTATION DURING PROCESSING OF METALLIC MATRIX COMPOSITES: Nicole M. Gorey, Donald A. Koss, John R. Hellman, Department of Materials Science and Engineering, Penn State University, University Park, PA 16802
Room: 230D
Session Chairman: D.J. Donaldson, Consultant, 18160 Cottonwood Road #158, Sunriver, OR 97707
2:00 pm
LAYERED DOUBLE HYDROXIDES FOR TREATMENT OF BAYER PROCESS LAKE WATER: A.J. Perrotta, Alcoa Technical Center, Alcoa Center, PA 15069-0001, F.S. Williams, Alcoa Alumina & Chemicals, L.L.C., Point Comfort, TX 77978-0101, L. Stonehouse, Alcoa of Australia, Kwinana R & D, Western Australia
Layered double hydroxides (LDHs) or the so-called anionic clays are the analog of the extensively studied family of cationic smectite clay minerals. The successful treatment of Bayer lake waters requires the removal of anions, both inorganic and organic; thus, the utilization of these anionic clays are ideally suited for this process. Insitu crystallization of layered double hydroxides have resulted in the removal of anions from Bayer lake water at two different refineries. Data on the removal of anions and their selectivity for intercalation in the layered double hydroxide indicates that the order of removal is CO3, C2O4, SO4. The monovalent chloride ion is least preferred but also can be extracted at significant levels at the higher level of treatment. The total organic carbon (TOC) is also lowered significantly. Measurements on succinate and malonate, both diacids, show a significant reduction at the higher levels of treatment. Successful regeneration of hydrocalumite show the thermal products of mayenite and calcium oxide which can then be recrystallized in lake water with concomitant further reduction in anion content. Additional experiments using ultrasonic radiation show an enhanced carbonate removal through increased calcite formation.
2:25 pm
TECHNICAL PECULIARITIES AND VIABILITY OF HYDROTHERMAL TREATMENT OF RED MUD: Károly Solymár, Janos Steiner, József Zõldi, ALTAK Consulting Ltd. H-1125 Budapest, Zsolna u.31-33. Hungary
The regeneration of the chemically bound caustic soda and alumina from red mud was studied in laboratory and pilot plant scale between 260 and 320°C as a function of caustic soda concentration and final A/C ratio of the liquor, lime dosage and retention time. The pilot plant tests have been carried out in a tube digester facility of 3.0 m3/h designed by HUNGALU ALUTERV-FKI Ltd. and the test work was performed in cooperation with the team from the Almásfuzitó Alumina Refinery. At 260-320°C iron-rich iron-aluminium-hydrogarnets (Ca-Al-Fe-hydrosilicates) were formed allowing 90-95% Na2O and 20-70% Al2O3 content of red mud to be recovered as a function of the final A/C ratio with a specific lime consumption of 2.5-3.0 kg CaO/kg regenerated NaOH. The tube digester was found as an adequate equipment. The viability of the process highly depends on the price ratio of the caustic soda and burnt lime. The latest development in red mud separation also increased the viability of the hydrothermal treatment of red mud.
2:50 pm
EXPLOITING THE RHEOLOGY OF BAUXITE RESIDUE IN TAILINGS DISPOSAL STRATEGIES: N. Pashias, D.V. Boger, Advanced Mineral Products Research Center and Department of Chemical Engineering, The University of Melbourne, Parkville, Victoria 3052, Australia
This paper demonstrates how an understanding of the complex rheological properties of bauxite residue suspensions can be exploited in the implementation of a dry disposal strategy. Comparative data are presented for bauxite residue generated from three refineries in Australia and from refineries in Jamaica, Suriname, and Brazil. The necessary properties for optimum handling of the residue at high concentrations and for dry stacking and/or slope deposition are established.
3:15 pm BREAK
3:35 pm
MOBILITY ON MUD: Danys Morin, Société d'électrolyse et de Chimie Alcan Ltée, Vaudreuil Works, Jonquiére, Québec
The Vaudreuil Alumina plants use deep thickeners to prepare their red mud for disposal in a 60 ft. high wet stack. Management of this stack requires four-seasons access to the pipework and occasional dust suppression procedures. From peak to foothills the stack can display all the phases of fluidity present in the mud. Vaudreuil has developed a family of vehicles to provide the required access from a 25 tonne amphibian to spread gypsum on the mud to control dusting, to a 1.5 tonne tractor-trailer for personnel transport. This paper describes the units in detail and explains how the characteristics of the mud can be used to give a good load-bearing capacity.
4:00 pm
OPTIMIZATION OF GRINDING OF ALUMINAS IN THE ROTARY-VIBRATION MILL AND THEIR EFFECT ON PHYSICAL PROPERTIES OF MOULDERS: Mariusz A. Wojcik, Tomasz Gajda, University of Mining and Metallurgy, Faculty of Materials Science and Ceramics, av. Mickiewicza 30,A-3, 30-059 Cracow, Poland; Ansgar Luttermann, Fachhochschule Munster, Fachbereich Chemieingenieurwesen Stegerwaldstrasse 39,d-48565 Steinfurt, Germany
The properties of high alumina ceramics are strongly influenced by the properties of the starting raw materials such as the grain size distribution and their morphology. Due to this, the grinding operation is an important step in the process of ceramic mass production. The investigations presented show that compared to other mills, the use of a rotary vibration mill will reduce time of grinding, the energy consumption and yield finer powders. The aim of these investigations was to obtain alumina powders with d50 approximately 3 um and d90 close to 10 um. Two different starting materials were tested. The process of grinding was performed according to various parameters such as filling ratio, amount of grinding media, alumina and water, ball set and frequency. The influence of ratios between the grinding media, alumina and water are shown. The influence of ball size, time and frequencies on the kinetics of grinding are shown. Finally the effect of alumina grinding on the physical properties such as green and fired density and shrinkage are shown and discussed in this paper.
4:25 pm
RESULTS OF TESTS OF THE FINE GRINDING OF ALUMINA IN THE ROTARY-VIBRATION MILL WITH LOW FREQUENCY OF VIBRATION: Jan Sidor, Mariusz A. Wojcik, University of Mining and Metallurgy, Faculty of Materials Science and Ceramics, av. Micklewicza 30, a-3, 30-059 Cracow, Poland
Results of the investigations of the fine grinding of alumina (below 0.5-2µm) were presented in this paper. Tests were carried out in the laboratory rotary-vibration mill with a low frequency of vibration below 16 Hz at two sets of work. In the first set, the mill chamber had both rotary and vibration movements, while in the second one, the mill chamber made only the vibration movement such as in the case of a classic vibration mill. Results show that it is possible to obtain a high purity alumina with low energy consumption in both sets.
Room: 230A
Session Chairperson: Dave Belitskus, Alcoa Technical Center, Alcoa Center, PA 15069
2:00 pm
IMPROVEMENT OF THE ALUMINIUM CELL LINING BEHAVIOUR BY USING SiC: M.M. Ali, A.A. Mostafa, R&D Management, The Aluminium Company of Egypt, Naga Hamadi, Egypt
Now, the finite element analysis techniques (FEA) are widely used in the aluminium reduction cells. For example, to select new lining materials or to better understanding of the aluminium cell behaviour, through the use of modelling concepts. One of the important studies is the thermal model of the aluminium reduction cells. A 2-D FEA model has been established, tested and verified to study the thermal balance of the cell. This paper presents a study for using a new lining material. The effect of this material on the ledge profile and thermal distribution were discussed.
2:25 pm
PROPERTIES OF A COLLOIDAL ALUMINA-BONDED TiB2-COATING ON CATHODE CARBON MATERIALS: H.A. Øye, Institute of Inorganic Chemistry, The Norwegian University of Science and Technology, 7034 Trondheim, Norway; V. de Nora, J.-J. Duruz, G. Johnston, MOLTECH S.A., 9 Route de Troinex, 1227 Carouge, Geneva, Switzerland
Laboratory studies of colloidal alumina-bonded TiB2 have been carried out. The following properties have been demonstrated: Thermal expansion somewhat higher than carbon materials, electrical conductivity of the same order as graphite, porosity of coating 
30%, resistance to sodium is high if the coating is protected by infiltrated aluminium, strong adherence of the coating to carbon materials even after thermal cycling, high abrasion resistance of the coating, wettability of the coating by liquid aluminium, the coating's action as a barrier to sodium penetration. The barrier action to sodium is the ability to form a stable liquid aluminium layer in the pores of the coating which will slow down the reaction: Al(l)+3 NaF(in electrolyte)=3 Na(in C cathode)+ AlF3 (in electrolyte) as the sodium stabilizing C is no longer in close contact with the bath.
2:50 pm
PENETRATION FORCE OF BATH COMPONENTS INTO POT LININGS DESCRIBED BY NONEQUILlBRIUM THERMODYNAMICS: Stig F. Johansson, Skamol a/s, Østergade 58-60, DK-7900 Nykøbing Mors, Denmark; Signe Kjelstrup, The Norwegian University of Science and Technology, Department of Physical Chemistry, N-7034 Trondheim, Norway
From principles of irreversible thermodynamics, a simple expression is developed for the driving force for transport of bath constituents across a non-isothermal matrix into the refractory lining in aluminium electrolysis furnaces. The expression shows that the transport outwards of aggressive substances is favoured by the temperature gradient. Possible applications are demonstrated for 3 penetrating gases with a variety of applied and proposed refractory materials. Common to all results is a possible reduction of the rate of penetration into barriers by a smaller temperature gradient due to the entropies of reaction. This can be accomplished by proper heat insulation below. A set of conclusions regarding the resistance of chemical barriers to penetration by bath components completes the paper.
3:15 pm BREAK
3:35 pm
FLUORIDE ATTACK ON ALUMINO-SILICATE REFRACTORIES IN ALUMINIUM ELECTROLYSIS CELLS: Jørn Rutlin, Tor Grande, Department of Inorganic Chemistry, Norwegian University of Science and Technology, N-7034 Trondheim, Norway
The phase relations in the system sodium fluoride - mullite are relevant to chemical reactions that take place in fireclay based refractory materials used in the bottom lining of aluminium electrolysis cells. The solid-liquid phase relations have been investigated by means of differential thermal analysis, powder X-ray diffraction analysis and microscopy. At sub solidus temperatures the four compounds sodium fluoride, cryolite, nepheline and 
-alumina have been found at excess amount of sodium fluoride. At lower concentration of sodium fluoride, corundum is formed at the expense of -alumina. The solidus temperature was observed at 857±5°C which corresponds well with results in systems with higher aluminium fluoride content. An apparent eutectic was observed at 12±0.5 mole% mullite. Nepheline and cryolite are the two main components of the melt crystallizing at the solidus temperature. The liquidus temperature at the solubility limit was observed at 943°C and at 7.5±0.5 mole% mullite. The present results are discussed in relation to the deterioration mechanism of alumino-silicate refractories.
4:00 pm
PYROHYDROLYSIS OF SPENT POTLINING: Vladimir Blinov, Tor Grande, Harald A. Øye, Department of Inorganic Chemistry, Norwegian University of Science and Technology, N-7034 Trondheim, Norway
Due to the toxic nature of spent potlining (SPL) this is becoming one of the major environmental concerns for the aluminium industry today. SPL also represents a major recovery potential because of its fluoride and energy content. The Elkem SPL recycling process is one of several technically feasible alternatives for treatment and recycling of SPL. In this process the fluorides can potentially be recovered by a pyrohydrolysis of the oxyfluoride silicate slag from the Elkem process. The thermodynamic aspects of this pyrohydrolysis are discussed in the present work. Chemical activity of fluorides in actual oxyfluoride silicate melts has been determined by means of high temperature mass spectroscopy and the Knudsen effusion method. Only sodium fluoride was observed as volatile species for dry melts. The chemical activity of sodium fluoride in several melts could therefore be determined by the Knudsen effusion method. Together with data on the activity of sodium oxide, the present activity data of sodium fluoride enable a calculation of the equilibrium pressure of HF during pyrohydrolysis of SPL.
4:25 pm
IDENTIFICATION OF NONLINEAR SWELLING PRESSURE DISTRIBUTION OF ALUMINUM REDUCTION CELL: H.S. Sayed, Structural Eng. Dept., Cairo University, Egypt; M.M. Megahed, Mechanical Eng. and Prod. Dept., Cairo University, Egypt; F. Dawi, S. Abdella, R&E Dept., EgyptAlum Co, Nagi Hammadi, Egypt
The swelling pressure has the most significant effect on determining the cathode life among other loads applied on the steel casing of the aluminium reduction cell. In previous research, an identification technique is applied to determine the average swelling pressure value that is exerted on the side wall of the cell. The identification technique made use of the measured deformation of the cathode steel casing at different elapsed times (after 88 and 615 days) on an existing cathode that belongs to EgyptAlum. A new set of measurements has been conducted at different elapsed time (after 1055 days). This new set of measurements has been conducted at different elapsed times (after 1055 days). This new set of measurements gives a unique opportunity to reassess the identified swelling parameters. On the other hand, the distribution of the swelling pressure along the cathode interface with the vertical steel walls of the cell, has a significant effect on the performance of the steel casing. In this paper, the distribution of the swelling pressure, the interface of the carbon blocks and the steel casing, are identified. A nonlinear elasto-plastic model for the steel casing using combination of shell and beam elements is developed. The carbon blocks are modeled using solid and truss elements. The model utilizes Dewing model that describes the swelling pressure as a function of the elapsed time and confined swelling strain rate to determine the swelling pressure distribution. The swelling pressure is initiated using a predetermined free and confined swelling rate. As a nonlinear analysis progress with item, the confined swelling rate of the previous time step is used to assess the swelling pressure at the interface for the subsequent steps. The swelling pressure distribution is then determined at any elapsed time.
4:50 pm
MODELLING OF DYNAMIC LEDGE HEAT TRANSFER: Chuck C. Wei, John J.J. Chen, Barry J. Welch, The University of Auckland, Chemical & Materials Engineering Dept., Auckland, New Zealand; Vaughan R. Voller, University of Minnesota, Dept. of Civil & Mineral Engineering, Minneapolis, USA; M.P. Taylor, New Zealand Aluminium Smelters Company Ltd., Invercargill, New Zealand
Cell disturbances such as anode effect and process operations such as feeding, anode changing and metal-tapping often cause variations in the heat balance of a reduction cell, resulting in deviations from the optimum operating conditions. A dynamic ledge heat transfer model built on an earlier one-dimensional dynamic simulation by the authors and based on the finite difference method was used to solve the transient heat conduction with phase change in the sidewall/ledge region. Fixed-grid and deforming-grid spacings were respectively superimposed on the sidewall and ledge region in order to track the moving front. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were considered.
Room: 232A
Session Chairs: J.C. Malas, Wright-Patterson AFB, OH 45433-6533; V.L. Acoff, Dept. of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487
2:30 pm
ELECTRONIC PROTOTYPING: TOWARDS VIRTUAL MATERIALS RESEARCH: S.R. LeClair, Wright Laboratory, Materials Directorate, Wright-Patterson AFB, OH 45433-7746; S.L. Thaler, PanAptics, Inc., 12906 Autumn View Dr., St. Louis, MO 63146-4331
The most significant first step toward electronic prototyping (EP) in the research community has been the pursuit of intelligent processing (i.e., closed-loop process control), effectively using in situ sensors to monitor both process parameters (energy input), material behavior (changes in bulk structure, temperature, etc.), and characterize materials at the atomic scale, wherein material properties such as strength, residual stresses, composition, phase, compressibility, modulus, etc., are monitored and controlled in real-time. Of interest are the identity of interrelationships between sensed variables which enable fault detection - discover and monitor, in real-time, an evolving taxonomy (a set of linear and other meaningful relationships) which can be classified as "faults"; process stability analysis - establish a measure of stability, in real-time, by assessing process response/noise in the context of energy input, apparatus actuation, and the control algorithm requisite variety; and response time - establish a measure of performance, in real-time, of "sensor-actuator" limits to affect specific processing requirements. Yet these capabilities are merely near-term - the more interesting, longer term capability is the pursuit of process discovery, i.e., how these relationships and measures might provide insight into explaining phenomena of interest and/or enable the development of a material or process model in situ.
2:55 pm
ACCURATE, RELIABLE CONTROL OF PROCESS GASES BY MASS FLOW CONTROLLERS: J. Hardy, T. McKnight, Instruments and Controls Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6003
The thermal mass flow controller, or MFC, has become an instrument of choice for the monitoring and controlling of process gas flow throughout the materials processing industry. MFCs are used on CVD processes, etching tools, and furnaces and in the semiconductor industry are used on 70% of the processing tools. Reliability and accuracy are major concerns for the users of MFCs. Calibration and characterization technologies have been developed and implemented for mass flow devices. A test facility is available to industry and universities to test and develop gas flow sensors and controllers and evaluate their performance related to environmental effects, reliability, reproducibility, and accuracy. Additional work has been conducted in the area of accuracy. A gravimetric calibrator was invented that allows flow sensors to be calibrated in corrosive, reactive gases to an accuracy of 0.3% of reading. This paper will present possible sources of error in MFC process gas flow monitoring and control, and will present an overview of corrective measures which may be implemented with MFC use to significantly reduce these sources of error.
3:20 pm
MONOLITHIC MICRO-SPECTROMETER FOR LOW-COST LIQUID AND GASEOUS CONSTITUENT PROCESS MONITORING: S. Rajic, C.M. Egert, Engineering Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-8039
A monolithic miniature spectrometer suitable for a variety of sensing applications including industrial process monitoring has been developed. The device consists of a solid structure with a volume less than 6 cubic centimeters. All optical components of the spectrometer including two aspheric mirrors, a diffration grating, and entrance and exit surfaces are fabricated onto the surface of the structure. All light paths are internally contained within the structure. The result is a small, rugged spectroscopic sensor ideally suited for use as a process monitor. Due to its monolithic nature, the device requires no post-fabrication alignment; nor can it be knocked out of alignment during use. The prototype device discussed here was produced in PMMA by precision diamond turning; however, lower cost manufacturing approaches involving injection molding (using diamond turned molds) are under development to produce an affordable sensor. Due to its rugged monolithic design, small footprint, and low cost, the monolithic micro-spectrometer is ideally suited for distributed process monitoring applications often required for industrial processes. It is expected that specific sensor designs will be required for specific applications so as to maximize the performance and resolution over the operating range. The performance of this device as well as the design tradeoffs necessary to optimize performance for given applications will be discussed in the report.
3:45 pm
AN ULTRASONIC SENSOR FOR HIGH TEMPERATURE MATERIALS PROCESSING: Rollie E. Dutton, Materials Directorate, Wright Lab., WL/MLLM, Bldg 655 Ste 1, Wright-Patterson AFB, OH 45433-7817; David A. Stubbs, University of Dayton Research Institute Structural Integrity Division, 300 College Park, Dayton, OH 45469-0120
A sensor has been developed and tested that is capable of emitting and receiving ultrasonic energy at temperatures exceeding 900°C (1652 f) and pressures above 150 MPa (22,500 psi). The sensor works with standard ultrasonic pulser-receivers and has a demonstrated capability of measuring workpiece deformation during hot isostatic pressing (HIP). Details of the sensor design, performance, and the coupling of ultrasonic to the workpiece are described. Ultrasonic data acquired by the sensor, in situ, during HIP runs are presented.
4:10 pm BREAK
4:20 pm
TWO METHODS FOR EMBEDDING OPTICAL FIBERS IN METAL COMPONENTS: L.J. Talarico*, S.W. Allison1, C.A. Blue**, H.M. Meyer III***, L. Riester**; *Engineering Technology Division, Oak Ridge National Laboratory; **Metals and Ceramics Division, Oak Ridge National Laboratory; ***Development Operations, Y-12 Plant; Oak Ridge, TN 37831
Manufacturing or embedding optical fiber sensors in composite materials such as graphite-epoxy, cementitious, plastic or ceramic components is of growing importance to a variety of smart materials and structures applications. A variety of fiber optic sensors can measure strain, pressure, and temperature by observing changes in an output signal fluorescence spectrum or a shift in output signal peak wavelength. The ability to measure these parameters on the surface of, as well as within, a part could provide experimental data for evaluating models, perhaps identifying some inferior parts on-line, and monitoring operating behavior. Some examples are monitoring cure and assessing thermal damage in polymer matrix composites by measuring changes in the epoxy fluorescence spectrum and monitoring densification during powder pressing. Other potential applications include engine diagnostics, condition based maintenance of aircraft and vehicle components, and monitoring and control in the metal forming and materials processing industries.
4:45 pm
EXAMINATION ON THE USE OF ACOUSTIC EMISSION FOR MONITORING METAL FORGING PROCESS: A STUDY USING SIMULATION TECHNIQUE: W.M. Mullins, TMC, Inc., WL/MLIM, WPAFB, OH 45433-7746; R.D. Irwin, Dept of Electrical Engineering and Computer Science, Ohio University, Athens, OH; J.C. Malas III, S. Venugopal, Materials Process Design, Materials Directorate, Wright Laboratory, WPAFB, OH 45433-7746
Physical models for acoustic emission (AE) are introduced and expressions are derived to predict AE activity from such parameters as applied stress, strain, and strain rate. These models are then incorporated into a visco-plastic finite-element simulation program, and the acoustic emission event rate generated during metal-forming operations are predicted. Simulation results are presented for upsetting operations on a typical C-Mn type steel for various friction and die geometry conditions. The AE model predictions compare well with the available experimental results reported in the literature and demonstrate that AE signatures can be reliably simulated. The signatures predicted for metal forging are fairly insensitive to changes in certain processing parameters. This suggests that AE event rate monitoring may not be well suited for monitoring changes in microstructure and friction during forging operations. Some very preliminary studies of event spectral analysis have been performed which show that AE spectral features may be sufficiently dependent on structure and loading to warrant further examination for application to monitoring metal-forging processes.
5:10 pm
SHEAR MODE EMAT AS A SENSOR FOR COMPOSITE LAMINATE FABRICATION: David K. Hsu, Center for Nondestructive Evaluation, Iowa State University, Ames, IA 50011
The polarization direction of shear mode ultrasound interacts strongly with the fiber direction in a composite laminate. Using conventional piezoelectric ultrasonic transducers, we have shown that cross-polarized shear waves were effective for sensing ply orientation errors and ply sequence anomalies. In this paper, we extend the technique to use electromagnetic acoustic transducers (EMAT), particularly for green (uncured) graphite epoxy composite laminates. Preliminary results will be shown and potential applications for quality control will be discussed.
Room: 231A
Session Chairperson: A. Kasaaian, Elkem Metals Co., P.O. Box 299, Marietta, OH 45750
2:30 pm
RECOVERY OF BISMUTH AND ANTIMONY FROM THE ELECTROLYTE IN COPPER ELECTROREFINING TANKHOUSE: Kouji Ando, Naoyuki Tsuchida, Sumitomo Metal Mining Co., Ltd., Niihama Research Laboratories, Hydrometallurgical Research Center, 3-5-3, Nishibara, Niihama, Ehime 792, Japan
An ion-exchange process for recovery of antimony and bismuth from the copper electrorefining process has been studied on both a bench scale test and a pilot test. Recently, the ion exchange technique for the removal of antimony and bismuth from the electrolyte has been in a practice. In the existing technology, the metals recovered are required to process further. The separation of antimony and bismuth is sometime difficult and costly. Sumitomo Metal Mining has developed a noble process to recover antimony and bismuth metals directly from the eluent by an electrowinning. Furthermore, antimony and bismuth were successfully separated. The content of bismuth in antimony metal was less than 0.2%, while the content of antimony in bismuth metal was less than 0.4%.
2:55 pm
THE USE OF POLYMER CONCRETE IN ACID CONTAINMENT EQUIPMENT FOR ELECTROMETALLURGICAL PLANT PRACTICE: G.J. Karcas, Corrosion Technology International, Gent, Belgium
Various non-ferrous Metals such as Copper, Nickel, Lead, Zinc and Precious Metals are produced via electrorefining and electrowinning processes. Apart from controlling electro-chemical conditions for the production of these metals, there has always existed the challenge of controlling the severely deleterious effect of the aqueous environment which serves as the medium for the production of these metals. The practice of acid containment in electrometallurgical operations has entered the world of high technology with the advent of advanced acid resistant materials such as Vinyl Ester Resin which is either combined with concrete to form Polymer Concrete or used to coat or line various acid containing vessels and surfaces. The North and South American copper industry has indulged quite heavily in the use of polymer concrete cells, electrolyte storage tanks, and the use of Vinyl Ester Resin for corrosion protective systems. Electrolytic cell and electrolyte storage tank construction has undergone a transformation from a multiple part configuration to a single piece unit. The combination of a wood, steel, or concrete frame with a lining made of lead, asphalt, rubber or plastic has been historically successful in providing protection from chemical and mechanical attack in electrolytic cells and electrolyte storage tanks all over the world. These combinations have now entered the world of obsolescence as materials such as polymer concrete have proven to provide exceptional corrosion and mechanical protection with greatly reduced maintenance requirements. Polymer concrete cells and electrolyte storage tanks fall into the category of modern tankhouse equipment which includes anode preparation machines and stainless steel cathodes, all of which play a vital role in improving quality and productivity while lowering operating costs. Polymer Concrete Cells, and other modern equipment, are succeeding in the difficult, yet important, task of driving electrometallurgical plants into the next millennium.
3:20 pm
POSSIBILITIES TO LOWER ENERGY USE IN ELECTROWINNING BY MODIFICATIONS OF LEAD ANODES: O. Forsén , J. Aromaa, Helsinki University of Technology, Laboratory of Corrosion and Material Chemistry, Vuorimiehentie 2, FIN-02150, Espoo, Finland
Lead alloys are most common anodes in metal electrowinning processes from acid solutions, even though their oxygen overpotential is very high. New inventions like mixed metal oxide anodes are not widely used, the main reasons being possibly doubts on the anode operation and large capital investments on the existing lead anodes. The main reaction on lead anodes in sulphate solutions is oxygen evolution, and on the lead dioxide film it has a high overpotential. In this paper we have studied possibilities to decrease the energy consumption in metal electrowinning by lowering the anode overpotential. Samples from currently used anode material were coated with different lead alloys using plasma spraying and detonation coating. Also modifications on the anode microstructure by melting and controlled cooling and additions of certain ions to the electrolyte were studied. Most of the studied procedures were able to lower the anode potential about 100 - 150 mV at the operating current density of 500 A/m2. Rapid cooling during the anode casting was found to be the simplest and thus also the least expensive way to lower the anode potential.
3:45 pm
STUDIES RELATING TO THE DEVELOPMENT OF AN ANODE FOR LEAD ELECTROWINNING: D.J. Robinson, Dremco Inc., Phoenix, AZ; T.J. O'Keefe, University of Missouri, Rolla, MO; C. Bemelmans, Hazen Research, Golden, Colorado; R. George, South Coast Air Quality, Diamond Bar, California
The pyrometallurgical method of recycling car batteries suffers from a potential for air pollution violations, which prompts the desire for a viable hydrometallurgical alternative. Several Processes have been proposed, including leach-electrowinning routes using HBF4 and/or H2SiF6 based electrolytes, along with anodes of PbO2 on inert substrates. A study has been carried out to evaluate the proposed systems, with the intention of demonstrating a six month life of an electrolyte-anode combination. The work, which focused on the use of H2SiF6, has indicated that there was no acceptable anode, and has lead to the development of a technique to produce smooth, glassy, adherent coatings on graphite, and to the development of an anode composed of a series of copper cored graphite rods. The paper will present results on leaching and electrowinning experiments, as well as the description of a flowsheet for a pilot plant that will be used to produce one tone per day of refined lead from spent battery paste.
4:10 pm
APPLICATION OF ELECTROCHEMICAL MEMBRANE METHODS IN HYDROMETALLURGY OF COPPER: A.S. Mustafinova, A.A. Zharmenov, Chemical-Metallurgical Institute, Karaganda, Republic of Kazakstan
Production of electrolytic copper is characterized by large volumes of acidic spent solutions the utilization of which requires considerable expenditures of neutralizing agents. At present, an economically substantiated technology does not exist for treatment of sulfuric acid rinse solutions and spent copper electrolyte which will allow for repeated use of the acid and the metal salts. Therefore, for this aim the most advantageous is the use of electromembrane methods. In the paper there is stated the essence of developed technologies which are distinguished by low waste and provide the extraction from the solutions of metallic copper, nickel and sulphuric acid. There are also considered methods of copper electrolyte processing allowing to regulate its composition by that or another component (H2SO4, Cu, Ni, As). On the base of the detailed study of the behaviour of various types of ion- exchanger membranes in copper-, nickel-, zinc-, arsenic- bearing sulphate solutions there is realized the selection of the most suitable membranes (MK-401, MA-411, MB-2 and MKL-1/MAL-2). Some variants of electromembrane processing of spent solutions of the hydrometallurgy process have passed productions tests on a number of copper-electrolyte enterprises of the countries of CIS (cooperation of Independent States). These tests showed high efficiency of developed methods.
4:30 pm
ELECTROMETALLURGY, PAST, PRESENT, AND FUTURE: F. Habashi, Laval University, Department of Mining and Metallurgy, Quebec City, Quebec, G1K 7P4, Canada
While pyrometallurgy is an ancient art and hydrometallurgy can be traced to the Middle Ages, electrometallurgy is the most recent technology since it started only after the discovery of electric current in the ninteenth century. Davy, Faraday, and Bunsen laid the foundation of this technology which had a great impact on other areas of metallurgy, e.g., the liberation of aluminum for the first time from its salts. Once aluminum was available, it was used to liberate other metals from their oxides. Electrometallurgical processes, however, are capital intensive. Improvement of the present technology should be intensely investigated.
4:55 pm
FACTORS AFFECTING CO-DEPOSITION OF COBALT AND NICKEL: R. Luo, R.V. Kumar, Department of Mining and Mineral Engineering, University of Leeds, Leeds, LS2 9JT, UK; D.J. Fray, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, UK
Room: 230C
Session Chairperson: Jaffar G. Ameeri, Aluminium Bahrain, P.O. Box 570, Manama, Baharain
2:00 pm
TRACKING THE CARBONISATION PATHWAY OF DIFFERENT PITCHES AND PITCH COKE MIXTURES BY CRYSTALLITE HEIGHT (Lc) MEASUREMENT: N.R. Turner, Bitmac Limited, Scunthorpe Works, Dawes Lane, Scunthorpe, North Lincolnshire, DN15 6UR, UK
Pitches with a range of properties, e.g. Q.I. content, were carbonised to a final temperature of 1080°C. The same pitches were co-carbonised with finely divided petroleum coke. Lc has been measured at the end of the carbonisation cycles and at intermediate points to track the status of carbonisation for different pitches and pitch/filler coke combinations. The original pitch Q.I. content and pitch aromaticity appear to influence the carbonisation pathway of the pitch and the pitch-coke mixtures according to Lc data. The properties of the filler coke also appear to influence the ultimate size of the crystallites formed in the binder matrix at the end of the carbonisation cycle. It appears that there is a variable degree of interaction between the filler coke and the pitch, with extent of the interaction depending on the properties of the two components. The results so far reinforce the importance of consistency in raw materials preparation and in the baking process if uniform anodes are to be produced.
2:25 pm
ABSORPTION OF OXYGEN FROM AIR INTO COAL TAR PITCH: Jaromir Cibulec, Daniel Kostal, DEZA Corporation, P.O. Box 28, 757 28 Valasske Mezirici, Czech Republic
Changes in the properties of coal tar pitch during contact with atmospheric oxygen were studied. There were found to be changes in the content of toluene insolubles and the melting point. These changes are dependent on the quantity of the absorbed oxygen and on the temperature of the pitch during absorption. As the reaction of the air with the pitch is very rapid, reaction speed is controlled by the speed of absorption of oxygen into the pitch. When surface of the pitch is motionless, the rate determining step of the reaction is controlled by the rate of absorption of the oxygen into the pitch which is dependent on the diffusion coefficient of molecular oxygen in air. When the surface of the pitch is agitated, the reaction rate is controlled by the rate of reaction of the oxygen with the pitch. The mechanism of the reaction is described and a practical application is discussed.
2:50 pm
X-RAY AND MICROSCOPY INVESTIGATIONS ON THE CATALYST-CARBONIZED STRUCTURE OF COAL TAR PITCH--PETROLEUM COKE PILOT ANODES: Jilai Xue and Harald A. Oye, Institute of Inorganic Chemistry, the Norwegian University of Science and Technology, N-7034 Trondheim, Norway
The carbonization has important impacts on the energy consumption and the productivity in anode baking. It was found that the coke yield of the coal tar pitch binder in its mixtures with petroleum coke increased with addition of catalysts, such as S, AlF3, and FeCp2 (CO)4. Then the structures of the samples taken from the carbon pilot anodes with and without above additions were further investigated using X-ray diffraction and microscopic techniques. The remained S, Al and Fe in the carbons after heat treatments were also analysed. The coke yield, Lc value, and porosity will be presented against various heat treatment temperatures for different additions. The possibility of obtaining the carbon anodes by lower baking temperatures with the required structure will be discussed based on above results.
3:15 pm BREAK
3:35 pm
COAL-TAR/PETRO INDUSTRIAL PITCHES: E.R. McHenry, Koppers Industries, 1005 Wm. Pitt Way, Pittsburgh, PA 15238
Throughout the 20th Century coal tar has been the dominant raw material for producing industrial pitches in North America. However, the coal tar supply in North America has been decreasing due to closure of metallurgical and foundry coke-oven batteries. Because of lower carbon yield, petroleum-based pitches have only limited usage. To increase the raw material base and provide more flexibility in characteristics, coal tar/petro pitches are being developed. The evaluation of the coal-tar/petro industrial pitches is reported.
4:00 pm
PETROLEUM PITCH, A REAL ALTERNATIVE TO COAL TAR PITCH AS BINDER MATERIAL FOR ANODE PRODUCTION: Roger Marzin, Carola Acuna, Intevep S.A., Departamento de Refinacion, Apdo. 76343, Caracas 1070 A, Venezuela; Maria de Oteyza, Maraven, S.A., Nuevos Desarrollos, PO Box 829, Caracas 1010A, Venezuela; Raymond C. Perruchoud, R&D Center, Le Chable, P.O. Box 157, CH-3960 Sierre, Switzerland
A petroleum pitch, specially developed for aluminum anodes was produced, at commercial scale, as a real alternative to coal tar pitch. Using a highly aromatic refinery stream and well designed process conditions, it is possible to produce the right chemical composition needed for a high quality binder material for anodes. Through a Dynamic Process Optimization study, the paste formulation and parameters were adjusted to produce full size anodes with 100 % petroleum pitch. The performance of baked anodes were similar to coal tar pitch anodes, with the advantage of a much lower content of cancerogenic Polycyclic Aromatic Hydrocarbons (PAH). Comparative green and baked anode properties, PAH emissions and storage stability test for molten pitch are presented.
4:25 pm
REDUCTION OF POLYCYCLIC AROMATIC HYDROCARBONS (PAH) IN ANODES BY USING PETROLEUM PITCH AS BINDER MATERIAL: A COMPARAISON OF ANODE PROPERTIES AND ANODE BEHAVIOR OF PETROLEUM AND COAL TAR PITCH ANODES: Dr. Ulrich Mannweiler R&D Carbon Ltd. Winterthurerstrasse 92, CH-8006 Zürich, Switzerland; Raymond C. Perruchoud, R & D Carbon Ltd., Le Chable, P.O. Box 157, CH-3960 Sierre, Switzerland; Roger Marzin, Intevep S.A., Departamento de Refinacion, Apdo. 76343, Caracas 1070 A, Venezuela
Petroleum pitch as binder material of anodes has the great advantage, that the content of cancerogenic Polycyclic Aromatic Hydrocarbons (PAH) compared to coal tar pitch is practically inexistent. In applying the correct content of pitch and through optimization of all process parameters during anode manufacturing, full size anodes with coal tar pitch (CTP) and petroleum pitch (PP) have been prepared in an anode plant. While baked anode properties for coal tar and petroleum pitch anodes are very similar, the PAH content can be reduced by 98 %. In this paper the behavior of representative lots of coal tar and petroleum pitch anodes in 100 kA electrolysis cells and the properties of the resulting anode butts will be described.
4:50 pm
TESTS OF PITCH PRODUCED FROM THE MIXTURE OF COAL RESIN AND REMAINDERS AFTER OIL PYROLYSIS: M.L. Itskov, E.A. Yanko, Russian National Aluminium-Magnésium Institute (VAMI), 199026 St. Petersburg, Russia; V.V. Krukov, Central Investigations Laboratory, 101000, Moscow, Russia
Actually the main type of binding materials, used in the anode paste production is a coal tar pitch. This binder provides the necessary quality of anode, but its using is related to increased emissions of cancerogenous matters, especially, benzapyrene, into the anode paste and aluminium reduction plants. The cancerogenous danger could be considerably reduced if using, as a binding material in the anode paste production, pitch produced at the distillation of the mixture of coal resin and remainders after oil pyrolysis, called "modified pitch". This report gives the results of laboratory investigations and industrial tests of anode paste, produced with using above mentioned binder, in the aluminium reduction. The laboratory investigations and industrial tests on Soderberg pots have shown, that by using the modified pitch we succeeded to produce anode paste of satisfactory quality. In this case we achieve a considerable reducing of the emissions of cancerogenous matters, namely benzapyrene, from the surface of anode.
Room: 230B
Session Chairperson: Julian V. Copenhaver, NSA - A Division of Southwire, P.O. Box 500, Hawesville, KY 42348
2:00 pm
ON THE EFFICIENCY OF IN-LINE DEVICES TO CLEAN THE MELT: P. Pouly, E. Wuilloud, Alusuisse Technology and Management Ltd., Technology Center Chippis, 3965 Chippis, Switzerland
Rotating impellers for injecting gas into aluminium melt are an often used in-line device to remove impurities. However, the treatment efficiency is seldom investigated, as the precise effect of flotation is not well understood. Moreover, the interpretation of the results obtained by measuring the inclusion content is not always obvious. For these reasons, it is sometimes observed that rotors work in an erroneous way. This paper illustrates how the variation of some parameters can affect, either in a good or a bad way, the efficiency of rotating impellers. The problematic of measurement techniques with some of their limitations will also be exposed. A special emphasis will be laid on inclusion removal.
2:20 pm
THE FLUID MECHANICS IN THE HI10 HYCAST REACTOR: Bodil Hop, Frede Frisvold, Stein Tore Johansen, SINTEF Materials Technology, N-7034 Trondheim, Norway; Bjørn Rasch, Hydro Aluminium a.s R&D Centre, N-6600 Sunndalsøra, Norway
The flowfield in the HI10 HYCAST reactor is investigated both theoretically and experimentally. The paper demonstrates how fluid flow calculations can be used to interpolate between experimental velocities. The experiments are performed by a two component Laser Doppler-technique in a reactor which has one single baffle. In the 3-dimensional computation a rotating grid for the rotor is imposed on the stationary grid for the reactor body. The flow effects caused by the baffle are discussed in relation to metallurgical performance. The turbulent dissipation rate is translated into bubble sizes and the result is compared to experimental bubble sizes. The paper discusses the reasons for deviations between predicted and experimental velocities.
2:40 pm
IN-LINE FLUXING WITH HIGH SPEED MULTIPLE DISPERSER ROTORS: D.C. Chesonis, H. Yu, Aluminum Company of America, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069; M. Scherbak, Aluminum Company of America, Ingot Technology Group, 900 South Gay Street, Knoxville, TN 37902
The impurity removal efficiency of in-line fluxing equipment depends strongly on the interfacial area between the gas bubbles and the molten metal. High interfacial areas can be generated by direct shearing of the gas bubbles using rotating dispersers. Placing multiple dispersers on a single rotor shaft and injecting gas into the metal at each disperser increases this direct shearing, improving the efficiency of the in-line fluxing unit. Small dispersers can operate at high gas loading and high speed without vortexing. Small dispersers also allow smaller metal treatment units, reducing floor space requirements and metal holdup. This paper will summarize the theory behind the direct shearing approach and will present data illustrating the difference in trace element removal for single, double, and triple disperser rotors. Comparisons with other in-line fluxing equipment will also be presented.
3:00 pm
EVOLUTION OF THE ALPUR® ROTOR TOWARDS IMPROVED PERFORMANCE
REPLACEMENT Panel Discussion on Hydrogen Levels
3:20 pm
QUANTIFIED QUALITY AND EFFICIENCY IMPROVEMENTS AT SAPA, LTD.: Stephen J. Rose, SAPA Ltd., Saw Pit Lane, Tibshelf Derbyshire DE55 5NH, England; David W. Busch, Foseco Inc., 777 Old Saw Mill River Road, Tarrytown, NY 10591-6729
SAPA, Ltd. is a 3 press aluminium extrusion operation specializing in quality flat and hollow product with a small remelt facility for in house generated scrap. In 1994 a decision was made to improve the overall quality of the in plant remelt facility. The first capital improvement was the installation of a SNIF Sheer P-60U two nozzle degassing system with immersion heaters. This unit was started up in December of 1994. A new melter with an exhaust collection system was brought on line in September of 1995. This paper will describe how improved melt treatment produced measurable economic benefits downstream.
3:40 pm BREAK
3:50 pm
CHLORINATION OF TiB2 GRAIN REFINED ALUMINIUM: T. Gudmundsson, G. Saevarsdottir, T.I. Sigfusson, Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik, Iceland; D.G. McCartney, Department of Materials Engineering & Materials Design, University of Nottingham, United Kingdom
The effects of fluxing grain refined molten aluminium with Ar/Cl2 gas mixtures have been studied both in the laboratory and during experimental casthouse trials. Samples taken during gas fluxing were subjected to chemical analysis and examined in the scanning electron microscope (SEM). Detailed chemical analysis of agglomerates was undertaken in the SEM using energy dispersive X-ray analysis and the elements Na, K and F were found to be associated with TiB2 clusters. Results will be presented in detail and discussed in the context of previously published work on grain refiner characterization and wettability of TiB2 in liquid Al/salt mixtures.
4:10 pm
COALESCENCE BEHAVIOUR OF ALUMINUM DROPLETS UNDER A MOLTEN SALT FLUX COVER: K.J. Friesen, T.A .Utigard, Department of Metallurgy and Materials Science, University of Toronto, 184 College Street, Toronto, Ontario, Canada M5S 1A4; C. Dupuis, J.P .Martin, Arvida Laboratories and Development Centre, Alcan International Ltd., 1955 Mellon Blvd., Jonquière, Québec, Canada G7S 4K8
The formation of a suspension of aluminum droplets in salt fluxes used during the refining and recycling of aluminum, leads to decreased aluminum recovery. To enhance the coalescence and recovery, it is required to remove the oxide layer formed on the surface of these small aluminum drops. Coalescence behaviour of aluminum droplets under a molten salt flux cover was investigated using a hot stage microscope at a temperature of 740°C. Two salt systems were studied: i) an equal weight mixture of NaCl-KCl with chloride and fluoride additives and ii) the MgCl2-KCl system with fluoride additives. Chloride salts did nothing to enhance coalescence but fluoride additions to both salt systems removed the oxide film from the metal. NaF, KF and Na3AlF6 additives were the most effective salts at stripping away the oxide layer and promoting coalescence. As the concentration of MgCl2 increased, the ability of the droplets to coalesce decreased significantly.
4:30 pm
KINETICS OF MAGNESIUM REMOVAL FROM ALUMINUM ALLOYS BY CHLORINE FLUXING: Qian Fu, J.W .Evans, Dept. of Materials Science and Mineral Engineering, University of California, Berkeley CA 94720
Chlorine fluxing (sparging chlorine-argon mixtures into the melt) is a standard procedure for eliminating magnesium from Al-Mg alloys. The kinetics of the reactions/mass transport involved have not been extensively studied in the past. The paper describes an ongoing investigation of those kinetics. Much of the work to date has been using laboratory-scale melts with magnesium removal measured by analysis of samples. Techniques have been developed to measure both bubble frequency and bubble residence time in the melt, enabling estimation of the total interfacial area and, consequently, the intrinsic kinetics of the phenomena involved. It is observed that, above the melting point of MgCl2, there exists a "critical Mg concentration". Above this critical concentration the reactions are sufficiently fast that all entering chlorine is converted to MgCl2 and there are negligible chlorine emissions. Below this concentration, Mg mass transport in the alloy appears to be rate-controlling. The results are interpreted in terms of a mathematical model for fluxing. The paper also describes the preliminary results of experiments on a larger scale (few tens kg alloy) in which bubble probes are used to detect the dispersion of gas injected into the melt and measure the interfacial area.
4:50 pm
INTERFACIAL TENSION BETWEEN ALUMINUM AND CHLORIDE-FLUORIDE MELTS: A. Silny, Institute of Inorganic Chemistry, Slovak Academy of Sciences, SK-84236 Bratislava, Slovakia; T.A. Utigard, Department of Metallurgy and Materials Science, University of Toronto, M5S 3E4 Toronto, Canada
A technique was developed for the measurement of the interfacial tension between liquid metals and molten salts at elevated temperatures. The technique is based on the measurement of the capillary depression ocurring when a capillary, which is moved vertically down through the molten salt layer, passes through the salt/metal interface. The depression is measured by simultaneous video recording of the immersion height of the alumina capillary and the position of a liquid meniscus in a horizontal tube connected to the alumina capillary. The interfacial tension was measured in the following systems: aluminium and an equimolar melt of NaCl and KCl with several salt additions at 1000 K, aluminium and NaCl-NaF at 1123 K, and aluminium and NaCl-KF at 1123 K and aluminium and equimolar melt of NaCl-KCl with additions of NaF, KF, LiF, BaF2, SrF2, CaF2, Na3AlF6, MgF2 and AlF3. It was found that the interfacial tension decreases with increasing NaF, KF, LiF, CaF2, BaF2 and SrF2 additions, remains unchanged with AlF3 additions and slightly decreases with MgF2 and Na3AlF6 additions. Aluminium and equimolar melt of NaCl-KCl with additions of LiCl, AlCl3, BaCl2, CaCl2, MgCl2. All above chlorides slightly increase the interfacial tension in the system. Obtained data are compared with the ones found in literature and some conclusions for the aluminium refining and recycling were derived.
5:10 pm
A COMPARATIVE STUDY ON THE EFFICIENCIES OF Na2SiF6 AND AlF3 FOR DEMAGGING MOLTEN ALUMINUM BY SUBMERGED POWDER INJECTION: A. Flores-Valdéz, M.A. Hinojosa-SanMiguel, A.H. Castillejos-Escobar, E. Macias-Avila, F.A. Acosta-González, Centro de Investigación y de Estudios Avanzados del IPN, Unidad Saltillo, P.O. Box 663, 25000 Saltillo, Coahuila, México
A comparative study on the efficiencies of Na2SiF6 and AlF3 for demagging molten aluminum by submerged powder injection is reported. Experimental trials carried out at a scale of 250 Kg molten metal furnace capacity showed that the higher efficiencies, ~ 70%, were attained by the use of the Na2SiF6 powder. The basic parameter to establish the comparison between the two demagging agents was the powder size, maintaining constant the other important parameters, e.g., initial magnesium content, carrier gas flow-to-powder flow ratio, pressure of the carrier gas, temperature of the bath, the dimensions of the reactor and the shape and dimensions of the injection lance. The removal efficiency was monitored analyzing the magnesium content in both the metal and the slag. The fumes produced were also analyzed, having found that the Na2SiF6 powders have the inconvenience of giving place to the generation of highly toxic SiF4 fumes.
Room: 330C
Session Chairperson: En Ma, Louisiana State Univ., Dept. of Mechanical Eng., Baton Rouge, LA 70803
2:00 pm INVITED
COMBUSTION FLAME SYNTHESIS OF NANOPHASE MATERIALS: B.H. Kear*, G. Skandan***, N. Glumac**, and Y. Che*, *Ceramics, **Mechanical & Aerospace Engineering, Rutgers University, NJ, ***Nanopowder Enterprises, Inc. Piscataway, NJ
Non-agglomerated nanopowders are becoming increasingly important for a number of commercial applications including UV-scattering, chemical mechanical polishing (CMP), displays and catalysis, among others. We have developed a continuous nanopowder production process, called Chemical Vapor Condensation (CVC), which involves precursor pyrolysis and condensation in a reduced pressure environment. We have introduced a flat-flame combustor unit, operable at low pressures, as a heat source in place of the original hot wall reactor. The temperature profile is uniform across the entire face of the burner, therefore, the reactants experience the same processing history and the powder has a uniform particle size distribution. The modified process, called Combustion Flame-Chemical Vapor Condensation (CF-CVC), has been used to produce a range of non-agglomerated nanoparticles (3-50 nm average particle size) of single phase, multiphase, and multicomponent materials. Examples include Al2O3, SiO2, TiO2, Al2O3/SiO2 and Eu:Y2O3. The as-synthesized powder is fully pyrolyzed (characterized by TGA), has a high surface area (SiO2 > 300 m2/g; TiO2 > 80 m2/g), and is non-agglomerated (TEM and BET pore size distribution). In addition, when the superheated particles leaving the combustion flame impinge on a heated substrate, in situ sintering can occur. Nanoporous or dense films or multilayered thin film structures can be synthesized. We have demonstrated the scalability of the process by increasing the burner diameter. Design consideration, processing parameters, powder characteristics and the commercial potential for the powders will be discussed. This work is supported in part by the Office of Naval Research contract #N00014-95-C-0283.
2:30 pm
EVIDENCE OF SURFACE ROUGHNESS IN NANOSTRUCTURES: M. José Yacamán, Institute de Física, Universidad Nacional Autóma de México, Apdo, Postal 20-364, 01000 México, D.F., México
Nanostructured Materials present very unique properties which has allow several technological applications. In the case of chemical reactions nanostructured materials have been used as catalyst. It is know that reduction of the particle size to a few nanometers produce an increased catalytic activity. The origin of this activity has been attributed to the increase surface area. We will show in this paper that nanoparticles present an increased surface roughness. This roughness increases the number of kink which provide an excellent site for promoting chemical reactions. In order to characterized the roughness we have used a new technique which combines High Resolution Electron Microscopy with computer length, It will be also shown that in several cases, the particle size in the image do Dot correspond with the true particle size. A method to correct this problem will be discussed.
3:00 pm INVITED
NANOSTRUCTURED MATERIALS VIA CHEMICAL ROUTES: Kenneth E. Gonsalves, Department of Chemistry & Institute of Materials Science, University of Connecticut, Storrs, CT 06269
This talk will focus on the chemical synthesis and processing of nanostructured materials. The precursor chemistry for the synthesis of nanostructured metals, ceramics, polymers, biomaterials, semiconductors and nanocomposites will be outlined and selected examples presented. Issues such as material purity, homogeneity, agglomeration and scale-up will be addressed.
3:30 pm BREAK
3:45 pm
TEM AND HRTEM OF NANOSTRUCTURED M50 TYPE STEEL PREPARED BY HOT PRESSING OF CHEMICALLY SYNTHESIZED POWDERS: G. M. Chow1, C.R. Feng2, Naval Research Laboratory, Washington, DC 20375; S.P. Rangarajan, X. Chen, K.E. Gonsalves, Institute of Materials Science, University of Connecticut, Storrs, CT 06269; C.C. Law, Pratt & Whitney, United Technologies Corporation, East Hartford, CT 06108. 1Laboratory for Molecular Interfacial Interactions, 2Materials Science Division
Nanostructured M50 type steel materials were prepared by hot pressing the precursor powders chemically synthesized using two different techniques, namely, thermal decomposition and co-reduction. During the hot press process, the precursor powders were transformed to nanocrystalline phases with the precipitation of carbides. Simultaneously the crystalline powders were densified. The densified samples were studied using both conventional and high resolution transmission electron microscopy. The effects of hot pressing temperature, time and pressure on the evolution of nanostructures, grain growth and defects formation are discussed.
4:05 pm
SYNTHESIS OF NANOSTRUCTURE W/Cu/Co ALLOY BY THERMOCHEMICAL METHOD: Gil-Geun Lee, Gook-Hyun Ha, Dong-Won Lee, Byoung-Kee Kim, Korea Institute of Machinery & Materials, 66 Sangnam-Dong, Changwon, Kyungnam 641-010, Korea
Nanostructure W/Cu/Co alloy was developed by thermochemical processing method using metallic salt precursors as the starting material for improving thermal, electrical and mechanical properties. Nanostructure W/Cu/Co powder have loosely agglomerated homogeneous clusters of nanoscale size W( 50 nm), Cu. and Co particles. The density and microhardness of the sintered nanostructure W/Cu/Co increased with increasing of Co content from 0.1 to 0.7wt.%, but electrical conductivity drastically decreased with addition of Co. Full density for nanostructure W/Cu/Co was achieved when sintered at 1473K for 20 minutes in H2 atmosphere with addition of 0.5wt.%Co. It was proved that optimum Co content is under 0.5wt.% when based on the relations between electrical conductivity and density. It is shown that nanostructure W/Cu/Co have higher sinterability and better electrical conductivity than conventional W/Cu/Co.
4:25 pm
MÖSSBAUER EFFECT STUDY OF MECHANICALLY ALLOYED 
-Fe3Zn10 and 1-Fe5Zn21 CUBIC INTERMEDIATE PHASES: Oswald N.C. Uwakweh, Zhentong Liu, Materials Science & Engineering, University of Cincinnati, Cincinnati, OH 45221-0012
The Mössbauer effect measurements of as-ball milled mechanically alloyed Fe-Zn intermediate phases of 
-Fe3Zn10 and -Fe5Zn21 compositions exhibit characteristic spectra consisting of triplets. Each is characterized with an Fe-site with a high quadrupole splitting measuring 0.94 mm/s, together with three other doublets. In the aged states, both compositions show spectra free of the Fe-site with the large quadrupole splitting. This suggests that both have similar metastable states, while their separate transformation paths to stable equilibrium states yield distinct crystal structures as found in the literature.
4:45 pm
NEUTRON DIFFRACTION & PHASE EVOLUTION OF MECHANICALLY ALLOYED 
-FeZn13 INTERMETALLIC: Oswald N.C. Uwakweh, Zhentong Liu, Materials Science & Engineering, University of Cincinnati, Cincinnati, OH 45221-0012; Brian Chakoumakos, Stephen Spooner, Oak Ridge National Laboratory, Solid State Division, Oak Ridge, TN 37831-6393
High Energy Ball -Milling is used to synthesize 
-FeZn13 intermetallic. The mechanically alloyed phase in the as-millet state is determined to be metastable, while the characteristic stages associated with the stable equilibrium transformation are identified based on DSC measurements. The as-milled material is described in terms of mechanical mixture of the elemental constituents, while the equilibrium state is confirmed to have a C2/m space group, with lattice parameters of a=13.40995 Å, b=7.60586 Å, c=5.07629 Å, and =127° 18'. The atomic positions of Fe and Zn are compared with reported values.
Room: 340D
Session Chairperson: Martin Crimp, Dept. of Materials Science and Mechanics, Michigan State University, East Lansing, MI 48824
2:00 pm INVITED
TITLE TBA: James C. Williams, General Electric Aircraft Engines, 1201 Edison Drive, Cincinnati, OH 45216
2:30 pm
THE STRUCTURE OF MATERIALS ENGINEERING; A NEW MODEL FOR MATERIALS ENGINEERING CURRICULA: Blair London, Linda S. Vanasupa, Robert H. Heidersbach, Materials Engineering Department, California Polytechnic State University, San Luis Obispo, CA 93407
We have developed a new model for the materials engineering curriculum designed around a structure that must be carefully "built" during our program. The model clarifies the materials engineering curriculum, representing a new organizational structure that incorporates the broad concepts yet allows room for technological changes. We used four guiding principles: (1) the curriculum must impart certain core competencies to the students, (2) the courses are either four or five units (quarter system), many with a strong laboratory emphasis, (3) the sequence of courses is logical and can be clearly communicated, and (4) it must be accredited. The model can be summarized by the major physical features of the building. The foundation includes an introduction to materials engineering and a course on the structure of solids. The pillars represent the four basic parts of materials engineering (thermodynamics, kinetics, mechanical properties, electronic properties) that are common to, and "hold up", all other aspects of the field. The roof consists of basic courses in metals, ceramics, polymers, and composites along with several technical electives. Finally, the building shows the capstone Senior Project as the culmination of their undergraduate education.
2:55 pm
MATERIALS SCIENCE CURRICULUM: HOW WE SHOULD BE CHANGING IT: David Laughlin, Dept. Materials Science & Engineering, Carnegie Mellon Univ., Pittsburgh, PA 15213
The Materials Science curriculum in many Universities is a direct descendant of their Metallurgy or Metallurgical Engineering curriculum. As such, they often have in them "relics" of the past that seem to some to be outdated. One of the theses of this presentation is that some of the "relics" are indeed "holy relics" which if they are discarded by "reforming zealots" may lead to a crisis in the curriculum. A second thesis, is that indeed some of the elements of the curriculum must be changed in order to better prepare our students for the changing directions of the field. In this presentation the important elements which should remain are discussed as are some new themes that currently are not universally present in our curricula. Suggestions on how these "old" and "new" themes are to be integrated into the overall curricula will close out the presentation.
3:20 pm
UNDERGRADUATE ENGINEERING AND MSE EDUCATION AT THE UNIVERSITY OF MICHIGAN: J.W. Jones, R. Gibala, Dept. of Materials Sci. and Engineering, Univ. of Michigan, Ann Arbor, MI 48109-2136
The College of Engineering at the University of Michigan has begun an ambitious program to restructure its undergraduate curriculum. The new curriculum will increase freshman year participation in engineering and provide an active program for each student to learn communication skills throughout the curriculum, while increasing flexibility within all discipline-specific curricula. Furthermore the new approach calls for the restructuring of courses into 4 credit-hour units, thereby enabling students to complete their studies in 4 years by selecting 4 courses of 4 credit hours in each of 8 semesters for a total of 128 credit hours. The impact of this new curriculum template on Materials Science and Engineering education at Michigan will be described. Emphasis will be placed on proposed changes in laboratory and design courses to accommodate a strong and professionally administered engineering communications segment. The approaches used to provide breadth and depth in the MSE curriculum will also be described. Finally, the impact of these college-wide changes on MSE's role in providing an introductory materials education to non-MSE majors will be described.
3:45 pm INVITED
TITLE TBA: Harold Weinstock, Air Force Office of Scientific Research, 110 Duncan Avenue, Bolling AFB DC 20332-0001
4:15 pm
PANEL DISCUSSION: Participants to be announced. A summary of the symposium as completed by the Panel Discussion is planned to be submitted for publication in the JOM.
Room: 332
Session Chairpersons: Paul T. Vianco, Sandia National Laboratories, Department 1831, Mail Stop 0340, P.O. Box 5800, Albuquerque, NM 87185; James A. Warren, Metallurgy Division, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899
2:00 pm INVITED
THE NIST SOLDER INTERCONNECT DESIGN TEAM PROGRAM: James A. Warren, Carol A. Handwerker, Metallurgy Division, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899
The NIST Solder Interconnect Design Team has been found to address several pressing issues in the design and fabrication of circuit board. Having met frequently over the past three years, in partnership with academic and industrial researchers, the Team has established an agenda for solving solder joint shape, and the consequential thermal/mechanical properties of the formed joint. Our ultimate goal is to provide the industrial community with a suite of useful software tools for solder interconnect design, and to provide solved test problems (available electronically on the World Wide Web), that can be modified to suit the needs of the particular user. With this in mind we are actively supporting the development of software which will interface the public domain program Surface Evolver, which has been shown to be quite capable at computing equilibrium meniscus shapes. A discussion of the outstanding problems, as well as the software tools under development will be presented.
2:20 pm INVITED
MODELING NON-ISOTHERMAL INTERMETALLIC LAYER GROWTH IN THE 63Sn-37Pb SYSTEM: Paul T. Vianco, P.L. Hopkins, K.L. Erickson, D.R. Frear, R. Davidson, Department 1831, Mail Stop 0340, P.O. Box 5800, Sandia National Laboratories, Albuquerque, NM 87185
The reliability of mechanical and electronic systems can be acutely dependent on the integrity of the soldered joints used in their assembly. During product manufacture, intermetallic layers from in reaction zones between the dissimilar materials of solder joints. Thermal cycling during service can cause further growth of the intermetallic layer, which may jeopardize the mechanical integrity of the joint as well as its capacity for rework or repair later on. Models describing service-related changes to solder joint microstructure are essential to understanding and predicting the long-term mechanical reliability and serviceability of these interconnects. In previously published work (J. Electronic Materials, v. 23, No. 8, 1994, pp. 721-729) a model describing the diffusion-controlled growth of multiple intermetallic layers and the displacement of the interfaces between layers was developed and implemented in a one-dimensional computer code based on the method-of-lines. The model can accommodate cases involving: (1) finite initial layer thickness, (2) rate-limiting interfacial reactions, (3) multiple and variable diffusion coefficients, and (4) finite material boundaries. Additionally, the effects of nucleation can be modeled empirically. A transformation of spatial coordinate circumvented the need to remesh the growing and (or) shrinking layers. Results from the one-dimensional code were verified by comparing the numerical output with analytical solutions for simple systems involving two, three, and five layers. The computer code was then applied for analysis of intermetallic layer growth from solder aging experiments performed with 100Sn and 63Sn-37Pb solders. The analysis indicated that intermetallic layer growth was consistent with bulk diffusion mechanism involving Cu and (or) Sn and variable diffusion coefficients that reflect some enhanced diffusion during early growth. In this work, non-isothermal solder-aging experiments were done with the 63Sn-37Pb/Cu system using two temperature histories: a low frequency history consisting of 4 cycles per day between -50 and 170°C, and a high frequency history consisting of 72 cycles per day and the same limits. Thicknesses of both the Cu3Sn and Cu6Sn5 intermetallic layers were determined as a function of time for both temperature histories. An enhanced version of the previously developed model was used to predict the non-isothermal intermetallic layer growth for both temperature histories. Arrhenius expressions for diffusion coefficients in both the Cu3Sn and Cu6Sn5 layers were determined using experimental data from previous isothermal studies. This paper describes the non-isothermal experiments and a comparison of calculated and observed layer growth as a function of time. This work was performed at Sandia National Laboratories and supported by the U.S. Department of Energy under contract DE-AC04-94AL8500.
2:50 pm INVITED
SOLDER JOINT FORMATION, SIMULATION AND RELIABILITY PREDICTION: Xiaohua Wu, Kai Hu, Xinyu Dou, Gary Mui, Chao-pin Yeh, and Karl Wyatt, Applied Simulation and Modeling Research (ASMR), Corporate Software Center (CSC), Motorola Inc., 1303 E. Algonquin Road, Mail Stop: IL01/ANX2, Schaumburg, IL 60196
The fatigue-induced solder joint failure of surface mounted electronic devices has become one of the most critical reliability issues in electronic packaging industry. Solder joint reliability performance has been found to be highly dependent on the solder joint configuration, which, in turn, is governed by bond pad size, component weight, alloy material, and leadframe structure, as well as solder reflow characteristics. The objective of this work is to develop numerical models: 1) to simulate the solder joint formation during the reflow process; 2) to determine the stress/strain distribution within the joint; and 3) further predict the reliability (fatigue life) of the solder joints. The solder joint formation process during solidification stage can be simulated using the Surface Evolver software tool developed by University of Minnesota. The thermomechanical stress-strain analysis can then be carried out using ANSYS to study selected critical design/manufacturing parameters such as leadframe geometry, pad size and dimensions, solder paste volume, leadframe placement misalignment, etc. This effort also involves the development of interface linking Surface Evolver and ANSYS.
3:15 pm BREAK
3:25 pm INVITED
COMPUTATIONAL CONTINUUM MODELING OF SOLDER JOINT INTERCONNECTS: Steve Burchett, M.K. Neilsen, D.R. Frear, J.J. Stephens, Department 9117, Mail Stop 0443, P.O. Box 5800, Sandia National Laboratories, Albuquerque, NM 87185
The most commonly used solder for electrical interconnects in electronic packages is the near eutectic 60Sn-40Pb alloy. This alloy has a number of processing advantages (suitable melting point of 183°C and good wetting behavior). However, under conditions of cyclic strain and temperature (thermomechanical fatigue) the microstructure of this alloy undergoes a heterogeneous coarsening and failure process that makes prediction of solder joint lifetime complex. A visco-plastic, microstructural dependent, constitutive model for solder has been developed and implemented into a finite element code. With this computational capability, the thermomechanical response of solder interconnects, including microstructural evolution, can be predicted. This capability was applied to predict the thermomechanical response of various solder interconnects to determine the effects of variations in geometry and loading. In this paper, the constitutive model will be briefly discussed and response predicted by the constitutive model will be compared to material test results. Finally, the results of computational studies to determine the effect of geometry and loading variations will be presented. This work was performed at Sandia National Laboratories, and supported by the U. S. Department of Energy under Contract No. DE-AC04-94AL8500.
3:50 pm INVITED
AN ELASTOPLASTIC BEAM MODEL FOR COLUMN-GRID-ARRAY (CGA) SOLDER INTERCONNECTS: Steven M. Heinrich*, J.A. Swanson*, and P.S. Lee**; *Rockwell Automation, Allen-Bradley Co., Milwaukee, WI 53233; **Department of Civil and Environmental Engineering, Marquette University, Milwaukee, WI 53233
A semi-analytical model is developed and implemented to analyze the deformation of solder columns in column-grid-array (CGA) assemblies. Each solder column is modeled as a prismatic beam of circular cross-section, subjected to end shearing deflections caused by thermal mismatch between the module and the circuit board. The solder is idealized as an elastic-perfectly plastic material whose yielding is governed by the Von Mises criterion. Since the columns are relatively short, transverse shear deformation has been incorporated into the beam model. The results generated with the model indicate the following: (a) yielding is governed by bending for slenderness ratios (height-to-diameter) of h/d
1/
3; (b) the nonlinear stiffness relationship for a sheared column, presented in dimensionless form, reduces to a single curve which is valid for arbitrary values of slenderness ratio (1/3) and material parameters; (c) the dimensionless relationship between maximum shear strain (in the Tresca sense) and the relative end deflection depends on Poisson's ratio but is independent of the other material parameters and the slenderness ratio. The nonlinear stiffness results presented in the paper may be used to create more efficient finite element models of entire assemblies by replacing each column with a single nonlinear spring element. When used in conjunction with an appropriate Coffin-Manson relationship, the maximum shear strain curves presented herein may be utilized to estimate column fatigue life.
4:15 pm INVITED
EFFECT OF ASSEMBLY STIFFNESS AND TEMPERATURE CYCLE PARAMETERS ON THERMOMECHANICAL RESPONSE OF SOLDER JOINTS: Ahmer Syed, Delco Electronics Corporation, M/S T100-26, 700 East Firman Drive, Kokomo, IN 46904
Grain boundary sliding and matrix creep are recognized as the main contributors to creep behavior of eutectic Sn/Pb solder joints in thermomechanical loading. The relative contribution and dominance of these mechanisms in the total response is governed by the external (temperature, assembly stiffness, CTE mismatch) as well as the internal shape (shape, size and thickness of the solder joint) factors. This paper examines the effect of external factors on the grain boundary and matrix creep response of solder joints. Experimental as well as numerical techniques are employed to compare which mechanism dominates under several different assembly stiffness and temperature profile conditions. A fatigue life prediction model which accounts for different mechanisms is used to determine the impact of grain boundary sliding and matrix creep on solder joint fatigue life.
4:40 pm INVITED
BEHAVIOR OF SOLDER JOINTS UNDER COMPLEX DISPLACEMENT LOADING: Matthew G. Bevan, Manfred Wutting, The John Hopkins University, Applied Physics Laboratory, John Hopkins Road, Laurel, MD 20723
In many applications, solder is exposed to a complex fatigue spectrum composed of thermal effects, shock and vibration. In the laboratory; however, solder is usually tested using simple wave forms generated by mechanical testers or by thermal cycling. In order to apply laboratory results to predict the real world fatigue, several crucial steps are necessary. One of these steps is understanding how to combine the effects of simple displacement (or stress) waves to predict the effects of complex waves. One method of combining waves is to use a linear damage accumulation model employing rainflow analysis. Briefly, rainflow analysis establishes an envelope to strain (or stress) range of the waveform, and then measures the reversals within the range. Damage from the envelope is added to the damage from the individual reversals within the envelope to calculate the damage of the whole cycle. The linear damage accumulation model is not valid for all loading conditions. Damage is accumulated in a linear fashion, assuming there is no wave-to-wave interaction. For Mode I (tensile) loading, this assumption is known to be false. Six mechanisms for-wave-to-wave interaction are known. The wave-to-wave interaction can significantly accelerate or delay fatigue crack propagation. In contrast, Mode III (tearing) loading has shown no wave-to-wave interaction. Very little research has been done to investigate damage accumulation in solder. The paper looks at single solder joints in shear. First the fatigue behavior of the solder joints is characterized using sine waves under displacement control. Then by looking at sums of waves with a constant displacement envelope, the damage from minor waves may be separated from damage from the major, envelope wave. The results show that the linear damage accumulation model (using rainflow analysis) is accurate as long as the minor waves remain in the elastic range. Once the minor waves begin to generate plastic deformation, the damage accumulates more rapidly than predicted.
5:05 pm INVITED
THERMOMECHNICAL FATIGUE TESTING OF SOLDER ALLOYS: Mark A. Palmer, P.E. Redmond, R.W. Messler, Jr., Materials Science and Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12180
Thermomechanical fatigue (TMF) is one of the most common sources of failure in solder joints. TMF occurs due to thermal cycling, as a cyclic stress is induced on the solder joint due to thermal expansion mismatch. Due to the complicated nature of thermomechanical fatigue, directly testing a material's resistance to TMF is not straight forward. A novel test apparatus has been developed which allows the direct measurement of stress due to thermal cycling. The TMF behavior of three alloys, eutectic Sn-Bi, Sn-Pb, and Sn-Ag as examined by this apparatus will be presented. The data will be compared with that generated by other test methods.
5:25 pm INVITED
EVALUATION OF INTERMETALLIC PHASE FORMATION AND CONCURRENT DISSOLUTION OF INTERMETALLIC DURING REFLOW SOLDERING: M. Schaefer, W. Laub, R.A. Fournelle and J. Liang, Materials Science Program, Marquette University, 1515 W. Wisconsin Ave., Milwaukee, WI 53201-1881; Allen-Bradley Company, 1201 S. Second St., Milwaukee, WI, 53204
Room: 340C
Session Chairs: J.P. Sullivan, J.A. Floro, Sandia National Labs, Albuquerque, NM 87185
2:00 pm INVITED
EVOLUTION OF GRAIN STRUCTURE IN THIN FILM REACTIONS: K. Barmak, Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015
The granular nature of polycrystalline thin films is playing an increasingly important role in their performance as the dimensions of the grains and those structures in which the thin films are used become comparable. Consequently, greater attention is being paid to the factors that affect the grain structure of thin films and its evolution. This paper will address the evolution of grain structure during the reaction of polycrystalline thin films. Experimental evidence from calorimetry, x-ray diffraction and transmission electron microscopy studies of a number of thin film systems will be reviewed and the role of reactant phase microstructure in these reactions will be highlighted. Theoretical models that combine nucleation and growth processes in the formation of the product phase will be presented and the impact of heterogeneous boundary nucleation on the evolution of grain structure in thin film reactions will be discussed.
2:40 pm
THE MICROSTRUCTURAL DEVELOPMENT OF THIN FILM COPPER GOLD ORDERED INTERMETALLIC COMPOUNDS: Jonathan Gorrell, Paul Holloway, Dept. of Material Science and Engineering, University of Florida, Gainesville, FL 32611-6400; Hal Jerman, EG&G IC Sensors, 1701 McCarthy Blvd., Milpitas, CA 95035
Recent developments in microelectromechanical systems (MEMS) have created a need for stronger metal thin films that are resistant to stress relaxation. Intermetallic compounds are noted for their strength and resistant to creep, but these properties have rarely been studied in thin films of intermetallics. We have sputter deposited layered structures of copper and gold so that the intermetallic compounds Cu3Au, CuAu and CuAu3 would form. The samples were initial heated to 475°C to allow intermixing of the copper and gold layers and the evolution of the intrinsic and extrinsic stresses were characterized during the process. The samples were then annealed at temperatures where the intermetallic phases would form. The intermetallic phases were tested for strength and stress relaxation using a Tencor Flexus 2320. The microstructure and composition were examined with TEM, EDX, Electron Microprobe, and X-Ray diffraction. This data allows us to relate strength and resistance to stress relaxation to microstructure and the heat of formation of the various copper gold intermetallic compounds.
3:00 pm
CHARACTERIZATION OF GRAIN BOUNDARIES IN Al INTERCONNECTS BY ORIENTATION IMAGING MICROSCOPY: C. Wu, C.L. Bauer, B.L. Adams, W.W. Mullins, Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA
Characterization of microstructure (grain orientation, grain-boundary inclination, microtexture, etc.) in thin-film interconnects is especially important because grain size usually approximates film thickness, thereby enhancing short-circuit diffusion induced by electric fields (electromigration), mechanical stress (stress voiding), temperature gradients (thermomigration), and capillarity (grain-boundary grooving). In this research, grain boundaries in polycrystalline Al interconnects have been characterized by orientation imaging microscopy and analyzed in terms of the interconnectivity of triple junctions. In general, results indicate that a variety of thermodynamic and kinetic properties can be extracted by rapid acquisition and processing of large data sets and correlated with the (five) degrees of crystallographic freedom of individual grain boundaries. Research supported, in part, by the National Science Foundation under Grant DMR-9319896.
3:20 pm
REAL-TIME MEASUREMENTS OF MICROSTRUCTURAL EVOLUTION IN Ag THIN FILMS ON SiO2: Eric Chason, Jerry Floro, Sandia National Laboratories, Albuquerque, NM 87185-1415; Steven C. Seel, Carl Thompson, Massachusetts Institute of Technology, Cambridge, MA
Understanding and controlling the microstructure in thin metal films used for IC interconnects is essential for maintaining high reliability. Although the microstructure of Al films has been heavily studied, the switch to Cu for interconnects in the future will lead to different microstructural evolution than in current technology. In order to study the kinetics of grain growth and texture evolution, we have developed an in situ X-ray system that can measure the concurrent evolution of (111) and (100) textured crystallites during annealing. We present results from the annealing of Ag films, which have similar elastic properties to Cu. This work was supported by the U.S. Department of Energy under contract DE-AC04.
3:40 pm BREAK
4:00 pm INVITED
STRESS RELAXATION AND THERMAL EVOLUTION OF FILM PROPERTIES IN AMORPHOUS CARBON: J.P. Sullivan, Sandia National Labs, Albuquerque, NM 87185
Large stress relaxation is observed in amorphous carbon films deposited by pulsed-laser deposition which are subsequently thermally annealed. In the as-deposited state, the films exhibit very high compressive stress, > 6 GPa, which has been thought to be either necessary or unavoidable in order to form a high percentage of 4-fold coordinated (diamond-like) carbon bonds and which can also hamper important electronic applications of these films. Stress measurements performed in situ and ex situ following thermal annealing up to 600°C indicate the stress may be reduced nearly two orders of magnitude. The stress relaxation is not dominated by interfacial relaxation nor is it accompanied by large scale changes within the film (e.g. graphitization) as indicated by in situ and ex situ electrical measurements, ex situ X-ray reflectivity, Raman spectroscopy, and experiments using different substrates. The bonding structure and mechanisms of thin film evolution in these unique amorphous films will be discussed. Work at Sandia was supported by an LDRD through the U.S. DOEunder contract no. DE-AC04-94AL85000 and by a CRADA.
4:40 pm
MICROSTRUCTURE AND TEXTURE DEVELOPMENT IN CUBIC BORON NITRIDE THIN FILMS: D.L. Medlin, P.B. Mirkarimi, G.F. Cardinale, K.F. McCarty, Sandia National Laboratories, Livermore CA 94551
Cubic boron nitride (cBN) is an sp3-bonded material with many properties and applications that are similar to diamond. Although cBN can be synthesized in bulk form at high temperature and pressure, synthesis in thin film form requires the simultaneous bombardment of the growing film with a high flux of energetic ions. cBN films grow with a unique, layered microstructure in which sp2-bonded graphitic boron nitride initially forms near the substrate interface, and nucleation and growth of the sp3-bonded cubic phase occurs further up in the film. Both the graphitic and cubic layers exhibit strong preferential crystallographic orientations: the graphitic layer possesses a strong in-plane [0002] orientation, whereas the cBN possesses an in-plane [111] orientation. This preferential orientation is consistent with an alignment between the cBN {111} planes and the basal planes of the layer of highly oriented graphitic boron nitride that forms in the initial stages of film growth. This relationship provides insight into the mechanisms controlling the initial nucleation of cBN and subsequent microstructural evolution of the films. This work is supported by the U. S. Department of Energy under contract DE-AC04-94AL85000 and in part by OBES-DMS.
5:00 pm
CHARACTERIZATION OF SrRuO3 THIN FILMS: MICROSTRUCTURE/PROPERTY RELATIONSHIP: F. Chu, Q.X. Jia, C. Adams, T.E. Mitchell, Materials Science and Technology Division, Mail Stop K 765, Los Alamos National Laboratory, Los Alamos, NM 87545; Q. Zhu, Physics Department, Brookhaven National Laboratory, Upton, NY 11973
Metallic oxide SrRuO3 thin films have been grown using pulsed laser deposition on LaAlO3 substrates at different substrate temperatures. The surface morphology and microstructural properties of the SrRuO3/LaAlO3 system have been studied using high resolution synchrotron x-ray diffraction, conventional x-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Electrical properties of SrRuO3 thin films with different microstructures have been measured. It is found that films deposited at 250°C are amorphous, and show semiconductor-like temperature dependence of electrical conductivity. Films deposited at 425°C are crystalline with very fine grain size (100~200Å), and show both metallic and semiconductor-like temperature dependence of the electrical conductivity in different temperature regions. Synchrotron x-ray diffraction and transmission electron microscopy unambiguously indicate that epitaxial [001] and [110] growth of the orthorhombic films takes place for deposition temperature above 650°C, where the [001] texture is dominant. Films deposited at 775°C show a resistivity of 280 mW-cm at room temperature. Microstructures of epitaxially grown films and possibilities for improving the thin film growth are discussed, based on geometric considerations for both film and substrate. The optimized deposition conditions to grow SrRuO3 thin films on LaAlO3 substrates have been found. Possible engineering applications of SrRuO3 thin films with different microstructures are discussed.
Room: 330E
Session Chairpersons: Chain T. Liu, Oak Ridge National Laboratory, Metals & Ceramics Div., PO Box 2008, Oak Ridge, TN 37831-6115; G.T. (Rusty) Gray, III, Los Alamos National Laboratory, Los Alamos, NM 87545
1:55 pm OPENING REMARKS
2:00 pm INVITED
THE ROLE OF GRAIN SIZE AND SELECTED MICROSTRUCTURAL PARAMETERS IN STRENGTHENING FULLY-LAMELLAR TiAl ALLOYS: D.M. Dimiduk, Wright Laboratories Materials Directorate, WL/MLLM, WPAFB, Dayton, OH 45433; P.M. Hazzledine, T.A. Parthasarathy, UES, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432; S. Seshagiri, SYSTRAN, Inc., 4126 Linden Ave., Dayton, OH 45432
More than five years ago wrought processing was first used to produce fully-lamellar microstructures in TiAl alloys having grain sizes less than ~400mm. These alloys exhibit an improvement in overall balance of properties, especially at high temperatures. More recently, such microstructural forms led to exceptional yield strengths (>1000Mpa at low temperatures), while maintaining attractive high-temperature properties. The improvements appeared to be attained principally through an unusually high apparent sensitivity of strength on grain size. Studies reported an apparent value for the slope of the "Hall-Petch plot" approaching 5 Mpa
for fully lamellar gamma alloys, while that for single phase or duplex microstructures is near unity. The present investigations examine the slope of the Hall-Petch plot for fully lamellar microstructures, paying particular attention to the lamellar microstructural variables. Results show that 
2-lamella thickness and spacing, and 
-lamella thickness can vary over more than two orders-of-magnitude. These in turn influence the value of 
o in the Hall Petch plot, and often change concomitantly with grain size in processing. Nonetheless, the corrected value of the Hall-Petch constant exceeds a magnitude of 2 Mpa; and it is strain dependent. The investigations also examine dislocation activity, flow behavior, glide barriers and slip multiplicity for polysynthetically twinned or PST crystals (single-grain analogue of fully lamellar material), then map this behavior into an explanation of the yield behavior of high strength fully lamellar gamma alloys.
2:30 pm INVITED
BULK, DEFECT, AND INTERFACIAL PROPERTIES OF TiAl and Ti3Al: M.H. Yoo, C.L. Fu, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
Available theoretical and experimental data on the elastic constants, point defect properties, shear fault energies, and ideal cleavage energies of TiAl and Ti3Al are reviewed, including the recently calculated / and 2/ interfacial energies. Enhanced slip by ordinary dislocations along pseudo-twin and rotational / and the 2/ interfaces is a contributing factor to the strong plastic anisotropy of a fully lamellar microstructure. According to the calculated interfacial fracture energies, cleavage cracking is to occur on 2/ boundaries and the least likely on true-twin boundaries. The roles of misfit dislocations, kinetics of dislocation-interface interactions, and hydrogen embrittlement in deformation and fracture of two-phase TiAl alloys are discussed. This research was sponsored by the Division of Materials Sciences, U.S. Department of Energy, under contract number DE-AC05- 96OR22464 with Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corporation.
3:00 pm
INTERNAL STRESSES IN LAMELLAR TiAl: P.M. Hazzledine, UES, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432; M.A. Grinfeld, Department of Mechanical and Aerospace Engineering, Rutgers University, P.O. Box 909, Piscataway, NJ 08855; D.M. Dimiduk, Wright Laboratories Materials Directorate, WL/MLLM, WPAFB, Dayton, OH 45433
Internal stresses necessarily develop in multilayered coherent materials with mismatched lattice parameters as the individual layers adjust to their neighbors. In Ti-Al the layers consist of 2 plates and six orientation variants of gamma plates which occur in an apparently random sequence. The internal stresses in any one layer are affected by the orientations of all its neighbors. We have calculated, in closed form, the stresses present in one layer of a stack of gamma layers in which the sequence of variants is in any order and of any length and in which the thicknesses of each layer may take any value. In addition we have calculated the stresses in a stack of alternating 2 and layers of arbitrary thicknesses. The results are applicable directly to an idealized form of PST TiAl in which the domain size is large and the lamellae thickness is small. The relaxation of internal stresses which occurs in thick lamellae and by the formation of domains is discussed. The consequences of both these relaxations to the plastic strength of PST TiAl are examined.
3:20 pm
RELATIONSHIPS BETWEEN MICROSTRUCTURE/COMPOSITION AND MECHANICAL PROPERTIES OF GAMMA TITANIUM ALUMINIDES: W.O. Soboyejo, Y. Ni, C. Mercer, Dept. of Materials Science and Engineering, Ohio State University, 2041 College Road, Columbus, OH 43210; A.B.O. Soboyejo. Dept. of Aerospace Engineering, Applied Mechanics and Aviation, Ohio State University, 155 W. Woodruff Ave., Columbus, OH 43210; R. Armstrong, Dept. of Mechanical Engineering, University of Maryland, College Park, MD 20742
Quantitative relationships will be presented for the prediction of basic mechanical properties (yield/ultimate tensile strength, fracture toughness and plastic elongation to failure) at room- and elevated- temperature. These include Hall-Petch relationships between basic mechanical properties and the average equiaxed grain size/lamellar packet size. Multiple linear regression expressions are also presented for the prediction of the effects of grain/packet size, lamellar volume fraction and composition. The observed grain size dependence of mechanical properties is shown to be consistent with Hall-Petch exponents predicted for dislocation/dislocation and dislocation/grain boundary interactions in duplex 2 + alloys. The implications of the empirical relationships are assessed for the engineering of balanced mechanical properties in gamma titanium aluminides.
3:40 pm BREAK
3:50 pm INVITED
TEMPERATURE DEPENDENT DEFORMATION IN GAMMA TITANIUM ALUMINIDES: S.H. Whang, Z.M. Wang, Q. Feng, C. Wei, Polytechnic University, Six Metrotech Center, Brooklyn, NY 11201
Deformation of gamma titanium aluminides may be best described by the lack of sufficient ductility at RT as well as intermediate temperatures, and the anomalous yielding at high temperatures. Such deformation behavior is mainly attributed to unusual behavior of two independent slip systems: superdislocation slip and ordinary dislocation slip, both of which simultaneously operate over the entire temperature range in the polycrystalline alloys. For this reason, the study on the role of individual slip system is required to carry out deformation experiments with single crystals of a -TiAl alloy. In -Ti-56Al, the yield stress curves of superdislocation slip show positive temperature dependence over two distinct temperature regimes while those for ordinary dislocation slip exhibit a single temperature range. These distinct temperature regimes can be explained with the characteristic features of the dislocation structures which were obtained from the postmortem examinations of the deformed specimens conducted by TEM. The thermodynamic aspects of both cross-slip configurations of superdislocations will be presented based on anisotropy strain energy calculations. Finally, the CRSS values depend on deformation orientation in superdislocation slip, in consistent with the cross-slip models. The details of the orientation dependence will be discussed.
4:20 pm
PLASTIC INSTABILITIES IN 
-TiAl AND THEIR RELATION TO WORK HARDENING AND TOUGHNESS: François Louchet, Groupe Physique du Metal, LTPCM- UMR.CNRS/INPG/UJF, B.P. 75, Domaine Universitaire, 38402 - St Martin d'H'eres, France
Flow stress anomaly in -TiAl is associated, as in many other intermetallics, to a strain rate sensitivity (SRS) close to zero, to plastic instabilities, and to a high work hardening rate (WHR). In situ TEM observations also show a jerky motion of groups of cusped ordinary screw dislocations (1), in agreement with macroscopic instabilities. The present paper investigates these instabilities in the framework of the Local Pinning Unzipping (LPU) model (2), in which the flow stress anomaly and the low value of the SRS are predicted as a consequence of a balance between dislocation exhaustion and multiplication rates. This balance is applied here to groups of N dislocations, and results in a non linear equation in N, from which the minimum stress required to deform the material at a given strain rate can be determined. The corresponding average value of N is obtained as a function of temperature. The consequences of the temperature dependence of N on both WHR and toughness are discussed. Possible consequences on the particular dramatic brittleness of PST materials loaded perpendicular to lamellar boundaries (3), in which slip in -TiAl takes place across lamellae, can also be contemplated as a function of these instabilities, and particularly in terms of the variations with temperature of the number N of dislocations in pile-ups.
(1). S. Farenc and A. Couret, Mat. Res. Soc. Symp., 1993, vol.288, p.465.
(2). F. Louchet et B. Viguier, Phil. Mag. A , 1995, vol.71, p.1313.
(3). M. Yamagushi, H. Inui, K. Kishida, M. Matsumoro and Y. Shirai, Mat. Res. Soc. Symp., 1995, vol.364, p.163.
4:30 pm
MORPHOLOGICAL ASPECTS OF 1/2<110] UNIT DISLOCATIONS IN AND (
2 +) TiAl ALLOYS: Sriram Seshagiri, SYSTRAN Corporation, 4126, Linden Ave., Dayton, OH 45432; Dennis M. Dimiduk, Materials Directorate, WL/MLLM, WPAFB, OH 45433; Vijay K. Vasudevan, Dept. of Materials Sci. & Eng., Univ. of Cincinnati, Cincinnati, OH 45221
The b=1/2<110] unit dislocations are a dominant part of the deformation substructure in both single phase () and two-phase (2+) TiAl alloys, at ambient temperatures and above. These dislocations have been characterized in a coarse-grained (~300 mm) single-phase binary TiAl alloy. The results show that these dislocations undergo double cross-slip, resulting in numerous pinning points (jogs) and mixed character dislocation segments bowed about these pinning points, giving rise to a cusped morphology. The linear pinning-point density in single-phase alloys increases with deformation temperature from ~2-5 mm-1 at RT, to ~10 mm-1 at higher temperatures, with an attendant increase in the yield strength of the alloy. In two-phase (2+) fully-lamellar polycrystals and PST crystals the, lamellae thicknesses are typically ~1mm, which is approximately the same order as the free-segment length of the unit dislocations in the single-phase alloys. Hence, the morphological evolution of 1/2<110] unit dislocations in the fully lamellar material, wherein deformation propagation is constrained by the lamellae dimensions, is of particular interest. Transmission electron microscopy observations pertaining to these aspects, and their implications on strength and plasticity, will be discussed in the presentation.
4:50 pm
TENSILE/COMPRESSIVE PROPERTIES OF SINGLE CRYSTAL GAMMA Ti-55.5%Al ALLOY: Marc Zupan, Kevin J. Hemker, Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD 21218
Understanding of the deformation mechanisms that lead to the flow strength anomaly of Ni3Al has been greatly enhanced by the measurement of the orientation dependence of flow stress and tension/compression asymmetry. To date, lack of high quality single crystals sufficiently large to facilitate mechanical testing have precluded such studies of TiAl. High quality single crystals of -Ti(55.5%)Al have been grown using an optical float zone furnace, which provides a containerless growing environment. These crystals have been oriented and cut into microsample tension/compression specimens with a gage area of 250 mm x 250 mm and effective gage length of 300 mm. These specimens have been deformed using a microsample testing machine which applies loads on the order of 1 lb. and strain using an interferometric strain gage. Stress-strain curves will be reported for a variety of orientations, temperatures and as a function of the sense of applied load. Experimental results will be discussed within the current context of current dislocation theories.
Room: 231C
Session Chairpersons: R.R. Beebe, Consultant, Tucson, AZ; C.H. Bucknam, Senior Coordinator, Newmont Metallurgical Services, Salt Lake City UT
2:30 pm KEYNOTE
COMMUNITY ASSISTANCE--AN INTEGRAL PART OF DOING BUSINESS IN THE MINING INDUSTRY: Leonard Harris, Consultant and Former General Manager, Minera Yanacocha, Peru; and Rosa H. Harris, President for Life of the Ladies Association of Minera Yanacocha (ADAMINYA), Lone Tree, CO 8O124
It is becoming increasingly obvious to mining and exploration companies, when operating overseas, that their activities should not conflict with the interests of the surrounding communities. The world's largest heap leach operation, Minera Yanacocha, has installed community assistance programs in Peru, concerned with health, education, electrification, agricultural assistance and road improvements. The programs are conducted with joint venture government and non government organizations and a ladies association composed of the employees' wives and female staff.
3:10 pm
WINTER HEAP LEACHING AT PEGASUS GOLD'S BEAL MOUNTAIN MINE:J.E. Micheletti, T.J. Weitz, Beal Mountain Mining, Inc., Anaconda, MT 59711
Pegasus Gold's Beal Mountain Mine is located near the Continental Divide, SW Montana. Conventional surface mining utilizes crushing, heap leaching, carbon absorption/desorption, electrowinning and refining to produce approximately 60,000 oz gold annually. A leach pad sits at 2,300 meters (7,500 ft) elevation. Winters are long and cold with average snow accumulations of 1-2 meters; temperatures fall below minus 40°C and wind chill temperatures below 70°C. The Beal Mountain staff has developed special tools and procedures for burying drip emitter lines, and managing the heap and process solutions to allow for uninterrupted gold recovery during the winter season. Management of water balance and spring runoff is critical to the operations' success, due to mountainous terrain, high precipitation and proximity to a fishery and elk herd. The mine has an extensive network of land application disposal (LAD) and stormwater control systems to assure environmental protection and regulatory compliance.
3:35 pm
OVERCOMING CLIMATOLOGY LIMITATIONS ON HEAP LEACHING: J.J. Komadina, Executive Vice President, Pikes Peak Mining Company, Victor, CO; R.R. Beebe, Consultant, Tucson, AZ 85751-2O48
Heap leaching of gold ores has enjoyed wide acceptance in the arid and semi-arid regions of the western U.S., Australia and South America. There are areas, however, where cold weather or excessive precipitation can limit the usefulness of heap leaching. Even in Nevada, difficulties can be encountered which call for special operating procedures. This paper discusses general climatological limitations and some of the techniques used to extend heap leaching into colder conditions. A case history of the Pikes Peak operation in Colorado examines "Valley-fill" technology as an ideal cold-climate solutions, where topographical conditions permit.
4:10 pm
CYANIDE SOLUTION DETOXIFICATION JAR TESTS: C.H. Bucknam, Senior Coordinator, Newmont Metallurgical Services, Salt Lake City, UT 841O8
Environmental regulatory requirements for discharge of solutions and closure of operations for the gold mineral processing industry have been moving towards meeting USEPA inorganic drinking water standards. Use of jar tests for water treatment process development is suitable for preliminary scoping work, conducted in a research laboratory for optimization studies, and at the site of the water treatment. Experimental methods utilize standard jar test equipment in effort to produce solutions that meet standards for USEPA inorganic drinking water, after chemical treatment of cyanide solutions. The materials tested included gold-bearing pregnant solutions from heap leach operations, gold plant barren solutions from Merrill-Crowe zinc cementation gold recovery process and final gold heap-leach wash solutions after carbon-in-column recovery. Experiments include cyanide destruction with sodium hypochlorite, and arsenic co-precipitation coupled with mercury precipitation.
4:35 pm
GREENSTONE RESOURCES LTD.--SANTA ROSA PROJECT: Randy Martin, Chief Operating Officer and Executive Vice President, Greenstone Resources Ltd., Toronto, Ontario, Canada M5E 1S2
Greenstone Resources Ltd. constructed and operates the Santa Rosa open pit, heap leach gold mine in Veraguas, Panama. The project was commissioned in 1995 at a designed capacity of 1.8 million tons per year. The ore exhibits a long leach up to three years, and requires three stage crushing to minus 3/8 inch to achieve on average a 74% gold recovery. The crushing plant is required to handle high volumes of clay and the circuit includes a Barmac Crusher. Panama receives over 3 meters of rain annually and Greenstone is using innovative means to control the project's water balance. Greenstone has developed a successful approach to operating a low grade (1.5 gm Au/T) deposit under difficult operation conditions.
5:00 pm
THE PLASTIC INFLUENCE AND ITS APPLICATION IN LEACHING PROCESSES FAVORING COST AND ENVIRONMENTAL IMPACTS: Juan B. Cabezas, J.B.C. (Minermat Inc.) Consultorks, Santiago, Chile
The favorable characteristics and workability of plastics as a replacement of wood, lead, stainless steel, asphalt and other materials are described. Various types of plastics have proven to be the most favorable choice for handling a variety of acidic, alkaline and organic solutions, as well as pulps, chemical wastes, slurries or tailings for impoundments. The material origin of various plastics, methods of manufacturing and specifications applied to leaching solutions are discussed, including availability and costs. Examples of select plastics are considered for use as alternatives of other materials under severe environmental requirements.
Tuesday , PM Room: 315A
Session Chairpersons: K. Togano, National Research Institute for Metals, Tsukuba, Japan; R.D. Blaugher, National Renewable Energy Laboratory, Golden, CO
2:00 pm INVITED
THE EFFECT OF PROCESSING ON THE MICROSTRUCTURE OF Bi2Sr2CaCu2Ox/Ag SUPERCONDUCTOR: K. Togano, H. Kumakura, H. Kitaguchi, H. Fujii, National Research Institute for Metals, Tsukuba 305, Japan; T. Hasegawa, Y. Hikichi, Showa Electric Wire and Cable Co., Ltd., Kawasaki 210, Japan
The Bi2Sr2CaCu2Ox/Ag(2212) conductors with high Jc can be fabricated by applying partial melting process, in which the 2212 phase melts incongruently. However, the presence of nonsuperconducting solid phases in the liquid makes it very difficult to achieve an ideal grain alignment of 2212 phase on cooling. In this paper, we report detailed studies on the distribution of nonsuperconducting phases and its effect on the nucleation and growth behavior of 2212 crystals. As one of the methods to control the distribution, we applied centrifugal gravity fields of up to ~100 g to the samples during melting process. Gravity effect was more significant for thick 2212 conductor, for which interface effect was less dominant. The improvement of grain alignment for the multilayered Ag/2212 conductors and the results of Jc measurement will be presented.
2:20 pm
REACT-WIND-AND-SINTER TECHNIQUE FOR THE MANUFACTURE OF POWDER-IN-TUBE Bi2Sr2CaCu2Ox COILS: J. Schwartz, S. Boutemy, National High Magnetic Field Laboratory, 1800 E. Dirac Dr., Tallahassee, FL 32310
Heat treating powder-in-tube Bi2Sr2CaCu2Ox coils such that short sample properties are obtained in large quantities is an important challenge. The wind-and-react technique suffers from poor temperature control due to the coil thermal mass and the sensitivity of the superconductor to the peak temperature and cooling rates. With the react-and-wind approach, however, optimum conductor performance is not obtained since it is degraded by strain during winding. A new technique is being developed at the NHMFL: the react-wind-and-sinter technique. Long lengths of powder-in-tube conductor are reacted by pulling the tape through a furnace with a controlled atmosphere. The temperature profile is controlled to emulate the partial-melt step of the conventional heat treatment. This method allows a more uniform reaction in long lengths of conductor. The tape is then insulated and wound into the desired coil shape and sintered isothermally. This repairs the cracks and achieves high phase purity and grain alignment. Here we report progress on this approach for HTS coils.
2:40 pm INVITED
DEVELOPMENT OF LONG LENGTH Bi-2212 SUPERCONDUCTORS: R. Wesche, EPFL, Centre de Recherches en Physique des Plasmas, CH-5232 Villigen PSI, Switzerland
Superconducting AgNiMg and Ag/Bi-2212 multicore wires of up to 40 m length have been fabricated by the powder-in-tube method. The optimum heat treatment conditions and the critical temperature have been found to depend on the wire diameter and the matrix material. In addition, the cooling rates are of importance for the achievable Tc values. Generally, the AgNiMg-sheathed wires behave like thinner Ag/Bi-2212 wires. Maximum Tc values of 92K have been achieved for both matrix materials. These observations suggest very rapid grain-boundary assisted diffusion of oxygen through the AgNiMg matrix. Short sample jc values (1 mV/cm) of up to 80,000 A/cm2 (4.2 K, B=0) and 3000 A/cm2 (77 K, B=0) have been achieved in Ag/Bi-2212 multicore wires of 1 mm diameter. For AgNiMg/Bi-2212 multicore wires of 1.5 mm diameter maximum zero field jc values of 55,000 and 2000 A/cm2 have been reached at 4.2 and 77K, respectively. First results for the jc values in Bi-2212 wires of long lengths will be presented.
3:00 pm INVITED
HOT-DEFORMATION TREATMENTS OF Y123 AND Bi2223 MATERIALS: Q.Y. Hu, D. Yu, H.K. Liu, T. Chandra, S.X. Dou, Centre for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2500, Australia
Y123 and Bi2223 bulks were hot compressed isothermally in a temperature range of 780-850°C under constant stresses of 15-50 MPa for 60 min. It was found that the mass density of the bulk Y123 and Bi2223 superconductors has been increased. This was achieved by reducing the enclosed voids in the materials under the pressure at high temperature. In addition of high mass density, texture structure in the superconductors has also been improved by hot compressing which in turn increased critical current of both materials. Ag-sheathed Bi2223 wires were hot-rolled into thin tapes at about 800°C at a four-high laboratory rolling machine with attachment of a tube furnace. It was found that hot-rolled tapes had higher core mass density but sausaging was severer than cold-rolled samples. Apart from the hot rolling, the Bi2223 tapes were also hot compressed under the condition of uniaxial loading and it was found that the treatment enhanced the core density, resulting in the improvement of the critical current of the samples.
3:20 pm INVITED
EFFECT OF pO2, C, AND Ag ON THE DECOMPOSITION PATHWAYS IN THE Bi-Sr-Ca-Cu-O: R.W. McCallum, L. Margulies, K.W. Dennis, M.J. Kramer, Ames Laboratory, Iowa State University, Ames, IA 50011
The promise of usable forms of high temperature superconducting wires and tapes rests on developing techniques for processing highly textured materials. Understanding the effect of Ag and pO2 on the chain of peritectic reactions initiated during melting is necessary in order to optimize the processing parameters of Bi-Ca-Sr-Cu-O-Ag composites. Previously, work on the solubility of Ag in the Bi2212 melt revealed a large liquid immiscibility gap and a eutectic on each side of this gap. In addition, the sub-liquidus phase reactions in this system were examined in greater detail for 0.01, 0.2, and 1.0 bar pO2. This work showed that the peritectic reactions varied as a function of pO2. The role of Ag was shown only to depress the peritectic decomposition temperatures. C was shown to have only a very minor effect for near stoichiometric materials. This work is currently being extended to the Bi2221 + Ag system. Supported by U.S. Department of Energy, under Contract No. W-7405-Eng-82.
3:40 pm BREAK
3:50 pm INVITED
THICK-FILM PROCESSING FOR TL-OXIDE WIRE AND TAPE: R.D. Blaugher, R.N. Bhattacharya, D. Ginley, P. Parilla, D. Schulz, National Renewable Energy Laboratory, Golden, CO 80401
Thick-film processing using techniques such as dip coating, ink spraying and electrodeposition represent promising approaches for fabricating HTS wire or tape for the Tl-oxide superconductors. The wire and tape processing for long lengths of the Tl-oxides, in contrast to the Bi-materials, is not as well advanced due primarily to a lower level of effort. The Tl-oxides, moreover, offer the potential for operation at 77K in practical magnetic fields of 3-5 T, which is supported by measurements on the irrreversibility behavior of the Tl-1223 single layer compound with Pb and Sr substitution. Thick-film processing methods such as electrodeposition and ink spraying present a viable approach for producing a cost effective HTS wire or tape with technologically acceptable transport properties. This paper will review the progress in the Tl-oxide wire and tape processing for thick-film techniques. The relative merits of conventional mixed-oxide and highly reactive sub-micron precursor as prepared by electrodeposition will be discussed. The prospects and predicted cost for a "long length" thick-film process using electrodeposition and ink spraying will also be presented.
4:10 pm
THE EFFECTS OF CARBON ON TlBa2Ca2Cu3Ox PHASE FORMATION IN THE Tl(F)-Ba-Ca-Cu-O SYSTEM: Y.S. Sung, X.F. Zhang, P.J. Kostic, D.J. Miller, Materials Science Division and Science and Technology Center for Superconductivity, Argonne National Laboratory, Argonne, IL 60439
The effects of carbon on TlBa2Ca2Cu3Ox phase formation in the Tl(F)-Ba2Ca2Cu3Oz system have been investigated. Samples of varying carbon content were prepared by controlling the carbon content in the Ba2Ca2Cu3Oz precursor powders that were mixed with TlF and reacted to form the superconducting phase. The samples were characterized by x-ray diffraction, scanning and transmission electron microscopy, and DC magnetization. It was found that carbon induced the formation of the Tl2Ba2Ca2Cu3Oy phase. While TlBa2Ca2Cu3Ox was the primary phase at low carbon contents, Tl2Ba2Ca2Cu3Oy became the dominant phase at high carbon contents, in spite of a 1:2:2:3 (Tl:Ba:Ca:Cu) starting composition. For intermediate carbon levels, there was a strong tendency to form superlattices as a result of intergrowth between TlBa2Ca2Cu3Ox and Tl2Ba2Ca2Cu3Oy. This work was partially supported by the U.S. Department of Energy, Basic Energy Sciences-Materials Sciences, under Contract No. W-31-109-ENG-38 and by the National Science Foundation through the Science and Technology Center for Superconductivity under Contract No. DMR 91-20000.
4:30 pm INVITED
USE OF PARTIAL MELTING IN Tl-1223 COIL PRODUCTION: J.C. Moore, S. Fox, M.J. Naylor, S.K. Wivell, C.R.M. Grovenor, University of Oxford, Dept. of Materials, Parks Road, Oxford OX1 3PH, UK
We have investigated a number of practical aspects in the manufacture of demonstrator coils from Tl-1223 PIT tape. Coils have been fabricated using a wind and react method from 5 m tapes with an insulating MgO coating, giving engineering Jc values of 2500 Acm-2. However, the performance of these sintered tapes in external magnetic field is at present poor. Previous work has suggested that only improved grain alignment can overcome this weak link problem and we have chosen to investigate a melt processing route in order to achieve this. A considerable effort has been put into correlating the effects of process variables (melt T, heating and cooling rates) on the microstructure in PIT samples. We will discuss the choice of precursor powder, composition of 1223 and heating schedule which gives the best properties in small coils.
4:50 pm INVITED
MODIFICATION OF Bi-2223 PRECURSORS BY POWDER ENGINEERING METHODS: O.A. Shlyakhtin, A.L. Vinokurov, V.V. Ischenko, N.N. Oleinikov, Dept. of Chemistry, Moscow State University, 119899 Moscow, Russia
Reactivity of Bi-2223 precursors is rather sensitive to the microstructure of the last ones, i.e., to the size of 2212 particles and spatial distribution of minor phases. The primary way to change precursor microstructure is connected with the change of precursor synthesis technique. Relying on our studies of particle size evolution during synthesis and thermal treatment of oxide powders, we propose a method of fine and directed modification of precursor microstructure in frames of the same synthesis technique. This method is based on the mechanical and ultrasonic treatment of precursor powders at the intermediate stages of their synthesis by chemical methods.
5:10 pm
RECENT ADVANCES IN POLYCRYSTALLINE OXIDE SUPERCONDUCTORS: PROCESSING, PROPERTIES, AND APPLICATIONS: M. Sisodia, A. Gupta, R.K. Yadava, Dept. of Metallurgical Engineering, Malaviya Regional Engineering College, Jaipur 302 017, India
This talk will review some of the processing techniques adaptable to high-Tc superconductor fabrication with much emphasis on desirable geometries, improved properties, microstructure control, and its associated practical problems that result in its good performance in magnetic fields. It has been observed that the improvement and optimization of Jc is hindered by the formation of jospehson weak links at grain boundaries, flux creep/flux flow effects, and anisotropic properties in polycrystalline high-Tc superconducting materials. Although the oxide superconductors in polycrystalline form have very poor in-field Jc, it can be improved by studying the current flow. The inhomo geneous current flow in these materials is discussed with the help of results for laser slicing and magnetooptic imaging experiments. Lastly, the advanced applications of each are discussed.
Room: 330B
Session Chair: F. Sommer, Max-Planck-Institut für Metallforschung, Institut für Werkstoffwissenschaft, Seestr. 75, D-70174 Stuttgart, Germany
2:00 pm INVITED
RECENT ADVANCES IN THE THERMOCHEMICAL INVESTIGATION OF SELECTED Al-Ni-R (R=RARE EARTH METALS) ALLOYS: G. Borzone, N. Parodi, R. Ferro, Dipartimento di Chimica e Chimica Industriale, Divisione di Chimica Inorganica e Metallurgia, Università di Genova, I-16146 Genova, Italy
The aluminum-based intermetallic compounds are the subject of growing interest for their combination of properties such as low density, good resistance to corrosion and heat, etc. For the Al-transition metal alloys, we may mention that the addition of rare earths to Al-rich alloys can bring about a significant modification of macro- and microstructure resulting in improvement in strength, thermal stability, etc. Several applications of selected Al-M-R (M-transition metal) alloys for their typical characteristics such as magnetic properties and hydrogen storage capability may be worthy of note. The knowledge of their thermodynamic properties may therefore be useful in gaining information on stable and metastable phases of these systems. To this end, we have begun a systematic study on the reactivity of the Al-R and Al-Ni-R alloys using calorimetric techniques, x-ray diffraction and microscopy analyses. The results so far obtained for selected Al-Ni-R alloy compositions will be illustrated and discussed.
2:30 pm
THERMODYNAMIC MODELLING AND APPLICATIONS OF THE Ti-Al-N PHASE DIAGRAM: K. Zeng and R. Schmid-Fetzer, Techn. Universitaet Clausthal, AG Elektronische Materialien, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld, Germany
The Ti-Al-N phase diagram has been assessed and a consistent set of thermodynamic functions has been developed. Three ternary line compounds, 
1-Ti3AlN0.56, 2-Ti2AlN082, 3-Ti3Al2N2, and the interaction parameters of the ternary solution phases Ti and Ti have been modelled. The experimental phase equilibria at 1573K can be well reproduced. Inconsistencies are detected at lower temperatures, which are also related to the observed melting behavior of the ternary phases. These inconsistencies and the current approach to determine the Gibbs energies of the ternary phases are discussed in detail. Applications of the proposed thermodynamic model include the diffusion path of the Ti/AlN contact system at 1473 K, the reactions of Al+TiN powder mixtures in Al-matrix composites and Al/TiN interface reaction.
3:00 pm
APPLICATION OF EVALUATED THERMODYNAMIC DATA FOR LIGHT METAL ALLOY SYSTEMS TO CASTING AND HEAT-TREATMENT PROCESSES: P. Spencer, B. Meurer, I. Hurtado, T. Buhler, S. Fries, Lehrstuhl für Theoretische Hüttenkunde, Rheinisch-Westfälisch-Techniche Hochschule Aachen - RWTH, D-52056 Aachen
The critical thermodynamic evaluation of alloys formed from the components Al, Cu, Mg, Si, Zn to produce technologically important constitution information will be described. Isothermal sections and isopleths relevant to phase formation in commercial alloys will be presented. The use of the evaluated data to investigate phase formation sequences and enthalpy effects during solidification under equilibrium and non-equilibrium conditions will be discussed and simulations of heat-treatment processes taking into account the influence of diffusion rates on the development of phase constitution will be described.
3:30 pm BREAK
3:45 pm
UNIFIED SOLUTION MODEL FOR BINARY, TERNARY AND HIGHER ORDER METALLIC, CERAMIC SYSTEMS, AQUEOUS SOLUTIONS, POLYMER BLENDS AND FOR PHASE DIAGRAM CALCULATIONS: M. Hoch, Dept. of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH 45221
The Hoch-Arsphofen model has been applied to binary, ternary and higher order metallic, ceramic systems, aqueous solutions, polymer blends and used for phase diagram calculations. The model is an expansion of the regular solution model: it assumes that in a binary system the A-B bond properties depend on the surroundings. The model was derived from ternary and quaternary systems, and no ternary or higher order interaction parameters are needed. An equation for Cp(L-s) has been developed, based on Tg, the theoretical glass transition temperature, where, below the melting point, the entropy of the liquid equals that of the solid, and the Gibbs energy difference G(L-s) is a maximum. Examples of all four types of systems are presented.
4:15 pm
INTERACTIONS BETWEEN INTERSTITIAL ATOMS AND VACANCIES IN METALS: Rex B. McLellan, Department of Mechanical Engineering and Materials Science, Rice University, PO Box 1892, Houston, TX 77251-1892
The statistical mechanics of interactions between dissolved interstitial atoms and lattice vacancies in metals is discussed. Interstitial atoms occupy sites nearest-neighbor to a monovacancy creating "decorated" vacancies. The effect of such clusters on the thermodynamic properties of the solid solution and the kinetics of the migration of both lattice atoms and interstitial solutes is considered. Specific calculations will include C - austenite and systems involving hydrogen in palladium-based binary matrixes.
4:45 pm
ENERGETICS OF ALLOY FORMATION WITHIN STATISTICAL THERMODYNAMICS AND ELECTRON THEORY: R.N. Singh, Department of Physics, Sultan Qaboos University, PO Box 36 Al-Khod, Postal Code 123, Oman
The deviations of the thermo-physical functions from the additive rule of mixing as a function of concentration, temperature and pressure is a key to the understanding of the energetics of alloy formation. Within the framework of statistical thermodynamic model, a suitable link is established between the bulk observable properties and the nature of atomic interactions in strongly and weakly correlated systems. It helps to analyze the role of enthalpic and entropic effects on alloy formation. The implications of basic interactions (i.e. electron-electron, ion-ion and electron-ion) on formation energy are also discussed from electronic theory. Pairwise interactions calculated from the first principle theory are found to have a direct correspondence to the order energy which occurs as a free parameter in various thermodynamic models.
Room: Salon 6
Location: Clarion Plaza Hotel
Session Chairs: Beverly Aikin, CWRU-NASA LeRC, 21000 Brookpark Road, MS 106-5, Cleveland, OH 44135; Thomas Battle, DuPont White Pigments and Mineral Products, Edge Moor Plant, Edge Moor, DE 19809
2:30 pm
SYNTHESIS AND PROPERTIES OF POTASSIUM HEXATITANATE WHISKERS: Zuomei Jin, Lisheng Wang, Jifen Huang, Dept. of Metal Materials, Chengdu University of Science and Technology, Chengdu, P.O. Box 610065, Sichuan China
The optimum conditions for synthesizing potassium hexatitanate whiskers (hereinafter called as PHW) were systematically examined using fast-cooling melt method. The intermediate and final products were determined by x-ray diffraction analysis, SEM and differential thermal analysis. A synthetic mechanism of PHW by melt method was proposed. The physical properties of obtained PHW were measured. A ratio of whisker length to whisker diameter is preferably 50 to 200. A PVC resinous composition containing 10-30% of obtained PHW is believed to show that the mechanical properties, heat resistance and abrasion resistance are much improved. For example, the tensile strength is 1.9 times larger than that of PVC resinous matrix and thermal deforming temperature is raised from 84°C to 120°C.
2:55 pm
SYNTHESIS OF TI(N1-xCx) WHISKERS: Niklas Ahlen, Mats Johnsson and Mats Nygren, Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
A route for synthesis of Ti(N1-xCx) whiskers (0 ¾ x ¾ 1), in a yield of 70-90 vol% has been established. The whiskers are ¾ 1 µm in diameter and 10-30 µm in length. They are straight and have smooth surfaces. The Ti(N1-xCx) whiskers have been synthesized carbothermally via a Vapour-Liquid-Solid (VLS) growth mechanism in the temperature region 1200-1600°C. The starting materials consisted of TiO2, C, an Ni-catalyst, and NaCl used as precursor for Cl. The synthesis of TiC whiskers are made in an Ar (g) atmosphere while the Ti(N1-xCx) whiskers are prepared in N2 (g) which besides preventing oxidation also acts as nitrogen source for the whiskers. The main impurities in the whisker product are minor amounts of unreacted carbon, oxygen and remnants of the Ni-catalyst. The VLS-mechanism is complex and involve formation of gaseous TiClx species, which are transported to the catalyst. However, the overall reaction is a straightforward carbothermal reduction/nitridation reaction.
3:20 pm
RECEPTION OF CERAMIC FIBERS FROM JOINTLY PRECIPITATED HYDROXIDES: Maximilian N. Kopylovich, Alexey K. Baev, and Alexander A. Chernik. Department of Analytical Chemistry, Byelorussian State Technological University, 13a Sverdlov Street, Minsk, 220630 Republic of Belarus
The coprecipitation method is perspective for reception of ceramic fibers. The essence of the method consists of a joint precipitation of hydroxides or salts with the subsequent branch, washing, drying and heating of a precipitate. The joint precipitation of hydroxides has a number of features. The hydroxides of metals can interact at the moment of a joint precipitation that results in occurrence of solid solutions. It was proven that in many systems containing by 2 and more hydrolyzed metal ions under certain conditions the formation of heteronuclear hydroxocomplexes occurs in solutions. The further interaction of specified hydroxopolymers causes formation of complex polynuclear structures reach the size of colloidal particles. The latters are X-ray amorphous and they are a prestructure of the future material. Such prestructure can be transformed into a final crystal product at lower temperature and smaller duration of heat treatment in comparison with oxide technology accepted in manufacture of ceramic fibers at present. It will allow to expand a palette of ceramic fibers and to lower their cost price.
3:45 pm
MEASUREMENT AND MONITORING OF AIRBORNE PARTICLES--TECHNIQUES AND REGULATIONS: Martin Harper, PhD, SKC, Inc., 863 Valley View Road, Eighty Four, PA 15330
Measurement of the nature and number of suspended particles in breathing air is used in health effect studies and to demonstrate compliance with government (OSHA, MSHA, EPA) regulations. The characteristics of the aerosol (e.g. fibrous, biological, metaliferous) and the requirements of the regulations govern the choice of technique. Three health-based size distributions are recognized (inhalable, thoracic, and respirable), but the definition of the fractions has varied over time. Current size separation and sampling equipment for aerosols includes impingers, elutriators, filters, impactors, cyclones, and various direct-reading instruments based on, for example, light scattering, or particle motions. Factors which influence the choice include sensitivity, accuracy, portability and ease of use, calibration requirements, cost, and government regulations. Some instruments are well matched to the health-based size fractions, and others less so. The history and current state of regulations will be reviewed, and the types of instruments will be described.
4:10 pm
DUST EXPLOSIBILITY PARAMETERS FOR METAL POWDERS: C. James Dahn, Safety Consulting Engineers, Inc., 2131 Hammond Drive, Schaumburg, IL 60173
The processing, manufacture and handling of powdered metals can employ widely varying process conditions which affect the potential for ignition, the explosion output and resultant collateral damages. This paper presents an overview of the factors (i.e., particle size distribution, particle cloud density, degree of turbulence, oxygen content and ambient temperature) which impact the minimum ignition energy requirement and explosive output of metallic powders. Processing conditions which strongly affect the output of an explosion, as measured in terms of maximum pressure achieved and maximum rate of pressure rise, are presented. Parameters influencing the energy requirements for ignition of an explosion will be emphasized. Dust cloud characterization under controlled conditions can be utilized to predict and, when necessary, to minimize powdered metal processing hazards.
4:35 pm
CONTROL OF BERYLLIUM POWDER AT A DOE FACILITY: Gerald C. Langner, K.L. Creek, R.G. Castro, Industrial Hygiene Section, Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545
Although only a small percentage of the general population and work force will face exposure to airborne beryllium, the effects of this exposure to the individual can be permanent and devastating. One effect, chronic beryllium disease (CBD), a granuloma and fibrotic lung disease with latency, can be developed after inhalation exposures to beryllium. In this study, the principal investigators conducted a hazard characterization of the beryllium powder plasma spray operation at Los Alamos National Laboratory using side-by-side, laser-induced breakdown spectroscopy (LIBS) sampling with conventional industrial hygiene techniques. We used results of the sampling data to reevaluate work practices and engineering controls associated with the plasma spray operation. As a consequence, work practices have changed, and new engineering controls and facility design changes will be implemented. These revised engineering controls include modifications to the beryllium spray chamber and design of auxiliary equipment used during routine spray chamber maintenance.
Room: 232C
Session Chairpersons: Jan-C. Carlén, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036; Dr. R.H. Tuffias, Ultramet, 12173 Montague St., Pacoima, CA 91331
2:00 pm
JOINING AND FABRICATING RHENIUM USING EXPLOSIVE METAL WORKING TECHNIQUES: Donald J. Butler, Sr. Project Engineer, Northwest Technical Industries, Inc., 2249 Diamond Point Road, Sequim, WA 98382
Rhenium has many unique and interesting properties, but some of those same properties make Rhenium difficult to fabricate and weld. Explosive metal working also has some interesting capabilities. Northwest Technical Industries, under contract from the NASA Lewis Research Center, has been successful using the explosive welding technique to join Rhenium to metals such as Tantalum, Molybdenum, TZM Molybdenum, Vanadium and C 103 Niobium. This paper will describe the explosive welding process and present the results of the work that has been completed with Rhenium. Also, this paper will describe how explosives can be used to form metal parts and explore the potential of using explosive metal forming techniques with Rhenium.
2:20 pm
STATE OF THE ART FABRICATION PROCESSES FOR IRIDIUM/RHENIUM THRUST CHAMBERS: R. Tuffias, Ultramet, 12173 Montague St., Pacoima, CA 91331
Chemical vapor deposition (CVD) has been used to fabricate rhenium liquid rocket combustion chambers since 1977. CVD iridium was first applied to rhenium chambers for high temperature oxidation protection in 1984. Since that time, CVD iridium/rhenium (Ir/Re) chambers have been successfully hot-fire tested at various facilities in both nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) and oxygen/hydrogen (O2/H2) bipropellants, at mixture ratios ranging from 4 to 17, for a total of nearly 200 hours. An alternate processing method is to form the rhenium by powder metallurgy and apply the iridium by electroplating. Hot-fire testing of this processing method to date includes 43 seconds in NTO/MMH and approximately 11 hours in O2/H2 at a mixture ratio of about 3, an oxidizing potential that may actually be benign to unprotected rhenium. This paper will discuss alternate processing methods and their relationship to fabricating Ir/Re combustion chambers, as well as test methods for evaluating their efficacy.
2:40 pm
DEVELOPMENT OF BONDED RHENIUM/Nb-1%Zr TUBING FOR THE SP-100 SPACE NUCLEAR REACTOR: Michael Kangilaski, Advanced Methods and Materials, 1798 Technology Drive, #251, San Jose, CA 95110; E.D. Sayre (retired); D.C. Wadekamper, T.J. Ruffo, General Electric Company, San Jose, CA
The SP-100 Space Nuclear Reactor design required a rhenium barrier between the uranium nitride nuclear fuel and the niobium alloy cladding. For higher strength and thermal performance it was deemed desirable to metallurgically bond the rhenium tube to the Nb-1%Zr tube. The bonding was achieved by brazing both ends of the rhenium and Nb-1%Zr tubes with a special braze adapter and then hot isostatically pressing (HIP) the brazed assembly. A considerable amount of effort went into developing a two stage HIP cycle for the bonding. A relatively low pressure was chosen in the first stage to assure that the weaker Nb-1%Zr tube collapsed uniformly onto the rhenium tube without any deformation occurring in the stronger rhenium tube. Avoidance of deformation in the rhenium was necessary because rhenium has low ductility at the HIP'ing temperature of 1350°C. In the second stage the temperature and pressure were increased to assure metallurgical bonding of the rhenium and Nb-1%Zr tube.
3:00 pm
A HISTORY OF RHENIUM IN HIGH-PERFORMANCE BIPROPELLANT ROCKET ENGINES: R.H. Tuffias, R.B. Kaplan, Ultramet, 12173 Montague St., Pacoima, CA 91331; M.A. Appel, Jet Propulsion Laboratory (retired), California Institute of Technology, Pasadena, CA
In the late 1 970s, the Jet Propulsion Laboratory (JPL) contracted Ultramet to provide oxidation protection for a carbon composite rocket engine thrust chamber using the liquid bipropellant fluorine/hydrazine, an application for which rhenium was selected. In the late 1990s, the first rhenium thrust chamber will fly in space. This paper will discuss the period between these two milestones and those that made it possible.
3:20 pm BREAK
3:40 pm
DIRECTED LIGHT FABRICATION OF RHENIUM COMPONENTS: John O. Milewski, Dan J. Thoma, Gary K. Lewis, Materials Science and Technology Division, Los Alamos National Laboratory, P.O. Box 1663, MS G770, Los Alamos, NM 87545
Directed Light Fabrication (DLF) is a direct metal deposition process that fuses powder, delivered by gas into the focal zone of a high powered laser beam to form fully dense nearnet shaped components. This is accomplished in one step without the use of molds, dies, forming, pressing, sintering or forging equipment. DLF is performed in a high purity inert environment free from the contaminants associated with conventional processing such as oxide and carbon pickup, lubricants, binding agents, cooling or cleaning agents. Applications using rhenium have historically been limited in part by its workability and cost. This study demonstrates the ability to fuse rhenium metal powder, using a DLF machine, into free standing rods and describes the associated parameter study. Microstructural comparisons between DLF deposited rhenium and commercial rhenium sheet product is performed. This research combined with existing DLF technology demonstrates the feasibility of forming complex rhenium metal shapes directly from powder.
4:00 pm
THE IMPACT OF THE MECHANICAL PROPERTIES OF RHENIUM ON STRUCTURAL DESIGN: A.J. Sherman, A.J. Fortini, B.E. Williams, R. Tuffias, Ultramet, 12173 Montague St., Pacoima, CA 91331
Pushed by extreme aerospace requirements, exotic materials with unusual properties are being pressed into service. One such material is rhenium. With a density of 21 g/cm3, it is an unlikely material for structural applications, but with an ultimate strength of 20,000 psi at 2000°C, it is the strongest metal at this temperature and comparable in strength to carbon composites up to 2500°C. In order to design structural parts, it is necessary to be able to model their load/ deflection relationship. Such analysis typically assumes that the material is elastic and conforms to Hooke's Law (stress being linearly proportional to strain). When the material becomes inelastic or plastic, failure is assumed to occur, since a permanent deformation takes place This limit is referred to as the yield strength. Typical yield strengths for engineering materials such as steel are roughly 60-80% of the material's ultimate strength. For these materials, then, a linear analysis permits a design range up to 60-80% of the ultimate capability of the material. As long as the material is operated in this range, the relationship between stress and strain remains constant. Rhenium, on the other hand exhibits a "classical yield strength" that can be as low as 10% of its ultimate strength, and its stress-strain relationship varies based on its previous stress history. If a structural design is based on this classical yield strength, 90% of the capability of the material is effectively discarded. Room temperature yield strength data for CVD (chemically vapor deposited) rhenium have included values as high as 45,000 psi and as low as 8,000 psi. Rocket engine designers are currently in a quandary as to the meaning of this data and how to use it to design components. This paper will discuss some of the strength data and present alternatives.
4:20 pm
MATERIALS PROPERTY TEST RESULTS OF RHENIUM: Melvin L. Chazen, TRW Space & Technology Division, One Space Park, Bldg. 01-1050, Redondo Beach, CA 90278
The use of rhenium as a material of construction for high performance liquid apogee/ perigee or delta-V engine applications is very beneficial as the engine performance is less limited by operating wall temperatures due to the performance. Rhenium has a very high melting point (>5700F) but does require protection from oxidation from the products of combustion. Iridium has been demonstrated as a successful high temperature protective coating (melting point >4400P). There are two methods of producing rhenium thrust chambers for high performance engines which have been successfully demonstrated which are chemical vapor deposition of iridium lined rhenium and powder metallurgy rhenium coated with iridium. An investigation was conducted to determine the material properties of both CVD and PM rhenium which was sponsored by NASA-LeRC on the SSRT program. Material property tests consisted of tensile, ultimate, modulus and low cycle fatigue at room temperature, 1500F and 25OOF with a minimum number of tensile tests at 2700-3500F and high temperature creep at 3000F This paper presents these results which indicate that both CVD and FM rhenium are usable for flight engines. In addition a summary of the results of engine tests with experimental PM rhenium will be presented.
4:40 pm
JOINING OF RHENIUM AND ITS ALLOYS: Sunder S. Rajan, Hughes Aircraft Company, Electron Dynamics Division, 3100 West Lomita Blvd., Torrance, CA 90509-2999
The processing parameters used to join rhenium and selected alloys containing rhenium are described. Resistance and laser welding as well as brazing processes as applied to these materials are reviewed. The metallurgical factors governing the choice of the process parameters and their influence on structural integrity are illustrated. The influence of alloy selection, use of proper filler materials and the factors governing their selection are reviewed. Experience has shown that pure rhenium, MolyRhenium and Tungsten/Rhenium alloys can be successfully joined by either welding or brazing processes.
Room: 330A
Session Chairperson: N.J. Kim, Center for Advanced Aerospace Materials, POSTECH, Pohang, 790-784, Korea
2:00 pm
CREEP BEHAVIOR OF ALUMINUM STRENGHENING WITH VERY HIGH VOLUME FRACTIONS OF SUBMICRON ALUMINA PARTICLES: C. Verdon, D.C. Dunand, Department of Materials Sciences and Engineering, Room- 8-328, Massachusetts Institute of Technology, Cambridge, MA 02139
High-temperature mechanical properties of dispersion strengthened cast aluminum containing 0.3 µm alumina particles were investigated. Compression creep tests were performed on samples containing three different volume fractions of oxide dispersoids, i.e. 25%, 33% and 43%, in the temperature range between 450°C and 600°C. Both as-cast materials, whose grain size in the range of centimeter, and extruded materials, which exhibit submicron grains, were tested. In the coarse-grained materials, the deformation is controlled by dislocation creep, whereas the deformation of the finegrained materials is controlled either by diffusional creep or by dislocation creep, depending on temperature and stress. The high values of the apparent stress exponents and of the apparent activation energy indicate a threshold stress for both creep regimes. Experimental results are discussed with respect to existing dispersion strengthening models.
2:25 pm
STRUCTURE AND PROPERTIES OF Si PARTICULATE REINFORCED ALUMINUM MATRIX COMPOSITES: S.J. Song, D.H. Kim, Dept. of Metallurgical Engineering, Yonsei University, 134 Shinchondong, Seodaemunku, Seoul, 120749, Korea; J.S. Kim, Materials Engineering & Test Dept., Hyundai Motors Company, 700 Yangchungdong, Jungku, Ulsan, 681791, Korea
To obtain a homogeneous distribution of fine Si particles in aluminum matrix, Si particulate reinforced aluminum matrix composites have been processed by using P/M method. 20-40µm size Si particulates and Al alloy powders were mixed, degassed and extruded at 350°C for pure Al matrix composites and at 400°C for 2024 and 6061 matrix composites. Wear properties of the composites have been discussed in terms of the observed microstructural characteristics and physical properties such as tensile properties and thermal expansion coefficients.
2:50 pm
THE DEVELOPMENT OF LIGHT COMPOSITE MATERIALS WITH LOW COEFFICIENT OF THERMAL EXPANSION: M. Smagorinslci, S. Grenier, P.G. Tsantrizos, PERMA, 1744 William, Montreal, Quebec, Canada, H3J IR4
The aerospace industry uses several types of Al-based composite materials. The main criteria for their application are light weight, high strength and hardness, low CTE, and high dimensional stability (capability to keep dimensions unchanged under thermal load). Theoretical formulas were developed to calculate the CTE of binary composites, as well as the ideal diameter of the strengthening particles for composites working under stringent physical engineering conditions. The calculations which were performed permitted to select the volume fraction and the dimension of the reinforcing particles which offer the most potential. Based on these calculations, composites containing 40% of reinforcing particles were selected and produced using the Vacuum Plasma Spraying (VPS) method. The VPS netshape forming of composites was shown to possess distinct advantages over conventional manufacturing processes. The VPS technique can be used to fabricate advanced composites with complex shapes, high density (9798% of the theoretical density) and, uniform particles distribution of various ceramic materials (size and composition). Plastic deformation and heat treatment result in further density improvement, which in turn significantly improves the mechanical properties of the composites.
3:15 pm
MICROSTRUCTURES AND MECHANICAL PROPERTIES OF DIE CAST SiCp/Al COMPOSITES: Tae-Won Lee, Jun-Ho Seo, Chi-Hwan Lee, Department of Metallurgical Engineering, Inha University, Inchon, Korea
This study was focused to investigate the effect of die casting parameters on the microstructure and mechanical properties of SiCp (10 and 20 vol%)/Al composites. Die casting was performed using the mold preheated at 130°C under the pressure of 916 kg/m3 and pouring temperature of 650~700°C. In this work, twostage injection system, which was composed of slow and high speed injections, was used to prevent the input of air during injection. The speeds of slow and high speed injections were 0.3~0.6 and 1.4 m/s, respectively. It was found that the SiC particles were homogeneously distributed in refined Al matrix. This results from the rapid mixing of Al and SiC particles during injection and the low segregation due to fast solidification rate. These microstructures provided good roomtemperature mechanical properties.
3:40 pm
FABRICATION AND TENSILE PROPERTIES OF SiCP/AZ91 Mg COMPOSITES BY HOT EXTRUSION: Doo-Myun Lee, Chi-Hwan Lee, Department of Metallurgical Engineering, Inha University, Inchon, Korea
The tensile properties and microstructural evolution of hot-extruded SiCp/AZ91 Mg matrix composites have been investigated as functions of extrusion parameters and SiC particulate size. Also, the effect of SiC particulates on. the grain size of matrix in the composites was studied. The AZ91 Mg alloy powders prepared by wet attrition milling from Mg machined chips were hotpressed with and without SiC particulates, hot-extruded and then solutiontreated. The microstructural observation revealed that both the composites and Mg alloy have equiaxed grains due to the dynamic recrystallization during hot extrusion. The tensile strength of the both alloys increased with increasing extrusion ratio, and the strength of the composites were higher than that of the Mg alloy without reinforcement. It was found that the tensile strength of the both materials decreased after solutiontreatment; the decrease in tensile strength of the composites was considerably smaller than that of the Mg alloy. The grain growth of the matrix in the composites was inhibited by the introduction of the SiC particulates, resulting in the improvement in the yield strength of the composites.
4:05 pm
IMPROVED HIGH CYCLE FATIGUE PROPERTIES OF TITANIUM-BASED PARTICULATES COMPOSITES: I. Hagiwara, S. Emura, Y. Kawabe, National Research Institute for Metals 1-2-1 Sengen, Tsuluba 305, Japan
The titaniumbased particulates composites are known to exhibit superior physical and mechanical properties compared to the unreinforced alloy. In cases where TiB or TiC is used as the reinforcing particulates, it has been reported that the fatigue fracture originates neither from the interior of particulate nor from the particulate/matrix interface, put rather from the matrix. Therefore it is suggested that the high cycle fatigue strength of the composite is strongly dependent on the matrix microstructure. In the present work, the effect of the matrix microstructure on the high cycle fatigue strength was studied for blended elemental P/M Ti6Al2Sn4Zr2Mo/lOTiB and Ti6Al1.7feO.lSi/10 TiB composites. It was found that the composites with a fine acicular - two-phase microstructure showed an improved high cycle fatigue strength over those for conventionally processed composites with colony matrix microstructure.
4:30 pm
INFLUENCE OF FIBRE STRENGTH DISTRIBUTION ON THE FATIGUE BEHAVIOUR OF A TiB2 Is/SCS-6 COMPOSITE: J. Liu, J.G. Pursell, P. Bowen, IRC for High Performance Materials/School of Metallurgy and Materials, The University of Birmingham, Edgbaston, Birmingham B 15 2TT, UK
The fatigue behaviour of silicon carbide fibre reinforced titanium matrix composites (TMCs) has been the subject of numerous studies. Bridging is found to he the dominant mechanism leading to the decrease in the crack growth rate us the fatigue crack grows. However, once the bridging fibres fail, the benefit of bridging will diminish. The influence of statistical fibre strength distribution on matrix cracking in fibre composites has been modeled by assuming the strength of the fibres falls in a twoparameter Weibull distribution. However, recent studies have shown that the fibre strength in TMCs is bimodal. The aim of this paper is to study the effects of fibre strength, and especially of those fibres with lower Weibull modulus. on the fatigue behaviour of a Ti,321s/SCS6 composite. First, single fibre tensile tests were conducted to evaluate the fibre strength distribution in both asreceived uncl fatigued specimens. The fracture surfaces of the fibres showing different strengths were examined using a SEM to distinguish lowstrength fibres fractographically. Fatigue tests were also conducted on single edge notched specimens. Different maximum loads and notch sizes were employed so that different fibre stresses were obtained. Acoustic emission, and direct current potential drop techniques were used to detect fibre failure and to monitor the crack growth. respectively. After the fatigue tests, the percentage of lowstrength fibres in the specimens was again estimated fractographically. The influence of fibre distribution was also modeled by characterizing the fibre strengths using two twoparameter Weibull distributions. The results show that the percentage of the lowstrength fibres plays an important role in determining the fatigue behaviour of the composite. Under identical loading condition, specimens with more lowstrength fibres are. of cause, more likely to fail. and this has been quantified.
Room: 314B
Session Chairpersons: O.W. Holland, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
2:00 pm INVITED
RECENT ADVANCES INTO UNDERSTANDING THE ROLE EXTENDED DEFECTS PLAY DURING TED: K. Jones, University of Florida, P.O. Box 116400, Gainesville, FL 32611
2:30 pm INVITED
DEFECT-ENGINEERED SHALLOW JUNCTIONS: Elaine G. Roth, O.W. Holland, Oak Ridge National Laboratory, Oak Ridge, TN 37831
3:00 pm INVITED
LOW ENERGY IMPLANTATION: A. Agarwal, Bell Laboratories, 600 Mountain Ave, Murray Hills, NJ 07974
3:30 pm BREAK
Session Chairperson: C.R. Abernathy, University of Florida, PO Box 116400, Gainesville, FL 32611
3:45 pm
EFFECT ON ION DAMAGE ON THE ELECTRICAL AND OPTICAL BEHAVIOR OF p-TYPE GaAs AND InGaP: K.N. Lee, J. Lee, J. Hong, S.J. Pearton, C.R. Abernathy, W.S. Hobson*, University of Florida, PO Box 116400, Gainesville, FL 32611; *Bell Laboratories, 600 Mountain Ave., Rm. 7-B-207, Murray Hill, NJ 07974
4:00 pm INVITED
PLASMA ASSISTED PHYSICAL VAPOR DEPOSITION OF METAL NITRIDE THIN FILMS: W.J. Meng, General Motors Research and Development Center, 30500 Mound Rd., Warren, MI 48090
4:30 pm
THE ROLE OF ION ENERGY IN DETERMINING THE STRUCTURAL AND ELECTRICAL QUALITY OF InN GROWN BY ECR AND RF-MOMBE: S.M. Donovan, J.D. Mackenzie, C.R. Abernathy, S.J. Pearton, P.C. Chow1, J. Van Hove*, University of Florida, PO Box 116400, Gainesville, FL 32611; *SVT Associates, 7620 Executive Dr., Eden Prairie, MN 55344
4:45 pm
EFFECT OF ION ENERGY ON THE OPTICAL PROPERTIES OF RARE EARTH DOPED III-NITRIDES GROWN BY RF-MOMBE: J.D. Mackenzie, S.M. Donovan, D. Salgado, L. Abbaschian, C.R. Abernathy, S.J. Pearton, U. Hommerich*, P.C. Chow**, J. Van Hove**, J. Zavada***, University of Florida, PO Box 116400, Gainesville, FL 32611; *Hampton University, **SVT Associates, 7620 Executive Dr., Eden Prairie, MN 55344; ***US Army Research Office
Room: Salon 3
Location: Clarion Plaza Hotel
Session Chairperson: W.S. Walston, GE Aircraft Engines, 1 Neumann Way, M85, Cincinnati, OH 45215
2:00 pm INVITED
STATUS, ISSUES AND CHALLENGES IN LIFE ASSESSMENT METHODOLOGY OF HOT SECTION COMPONENTS OF INDUSTRIAL TURBINES: K.G. Kubarych, Solar Turbines, 2200 Pacific Highway, P.O. Box 85376, San Diego, CA 92186
Abstract not available.
2:50 pm
LIFE PREDICTION BASED ON CRACK GROWTH BEHAVIOR FOR GAS TURBINE NOZZLES: N. Isobe, S. Sakurai Mechanical Engineering Research Laboratory, Hitachi Ltd., Japan; K. Kumada, Hitachi Works, Hitachi Ltd., Japan
Life prediction method for gas turbine nozzles was discussed. In gas turbine nozzles, crackings due to cyclic thermal strain generating with start-up and shut-down of turbines limit the life of components. This thermal strain is usually compression and holded during steady operation time. Therefore, it will be necessary to consider the effect of compressive creep or relaxation to the evaluation of crack growth behavior in nozzles. We conducted crack growth tests at 900°C using a strain wave form including compressive strain hold. Test results showed that crack growth rate in compressive strain hold tests were faster than that in no strain hold tests. A fracture mechanics approach was carried out to evaluate this compression hold effects. By using creep J-integral, a good correlation for crack growth data was obtained. A crack growth analysis considering stress gradient in the component was also carried out and we discussed about its accuracy using inspection data for 25MW class gas turbine nozzles.
3:10 pm
RELIABLE TBC'S FOR THE INDUSTRIAL GAS TURBINE DESIGN: W. Beele, W. Stamm, SIEMENS/KWU, Wiesenstr. 35, D-45473 Mulheim/Ruhr, Germany
This paper reviews the TBC-design as meanwhile established in aircraft technology and highlights the reasons why a reliable industrial gas turbine TBC-design has to differ in various material system properties. The development steps for Industrial Gas Turbine-(IGT-)TBC-systems will be presented as well as fundamental research activities like cyclic oxidation tests with enlarged high temperature aging periods, and first design results will be given in some real components examples. The actual use of TBC's in existing gas turbine designs is characterized by: TBC's were developed and approved by SIEMENS in a large test program including several types of cyclic and static high temperature oxidation and corrosion testing, the investigation of the mechanical properties for modeling issues and the review of the P&W-development steps and results for the aircraft application.
3:30 pm BREAK
3:50 pm
NON-DESTRUCTIVE EVALUATION OF HIGH TEMPERATURE OXIDATION DAMAGE USING ELECTROCHEMICAL TECHNIQUES: D.C. Tamboli, A.K. Rawat, V. Desai, Mechanical Materials and Aerospace Engineering Department, University of Central Florida, Orlando, FL 32816
Electrochemical techniques have been widely used as life prediction tools in corroding structures and coatings for aqueous corrosion. However, there has not been much attention given to the applicability of these techniques in assessing high temperature oxidation damage. In the high temperature oxidation, the metallic substrate is covered with an oxide film which has semiconducting properties. Electrochemical techniques such as electrochemical polarization and electrochemical impedance spectroscopy reveal vital information about the electronic transport properties of this oxide film by monitoring the response of the system to applied D. C. and A. C. potentials respectively. The protective properties of an oxide are largely dependent on the electronic and ionic transport through the oxide layer. In the ex-situ studies, the oxidized specimens are immersed in a highly reversible redox electrolyte. The parameters such as polarization resistance, open circuit potential changes and the oxide band gap potential obtained using these techniques showed good qualitative corroboration with the observed oxidation damage in the alloys studied.
4:10 pm
PREDICTIONS OF MICROSTRUCTURE CHANGES IN COATED TURBINE BLADES DURING SERVICE: X. Qiao, J.E. Morral, Department of Metallurgy and Materials Engineering, University of Connecticut, Storrs, CT 06269-3136
With DICTRA software, it is possible to predict microstructural changes in coated turbine blades during service. In the present work, this technique is illustrated by calculating the microstructures that will form between a nickel base +1 alloy and MCrALY type + alloys. It is shown that a number of different microstructures can form initially, depending on the coating composition. As the average composition of the coating varies during service, the microstructure may change several times. These variations can be illustrated on an "Interdiffusion Microstructure Map."
4:30 pm
EFFECTS OF SUBSTRATE CURVATURE AND ROUGHNESS ON RESIDUAL STRESSES IN OXIDE FILMS: J.K. Wright, R.L. Williamson, Idaho National Engineering Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2218
Finite element simulations are used to examine residual thermal stresses and strains in protective Al2O3 scales on Fe3Al specimens, both during cooling from oxide formation temperatures and during subsequent thermal cycling. Geometrically, the simulations focus on regions of local curvature, either due to corners or substrate surface roughness. A variety of substrate corner radii and film thicknesses are considered. The effects of substrate material behavior are investigated by not only considering the actual elastic-plastic response of the aluminide substrate, but also the limiting cases of purely elastic and perfectly plastic material behavior. When plasticity is permitted, the substrate is able to deform to accommodate stresses at the corner, and the film is in tension along the outside surface and compression near the interface. These tensile stresses are of concern for coating integrity, since corners are observed experimentally to be sites of oxide cracks and spallation.
4:50 pm
REPAIR WELDING OF 1.0CR-1MO-0.25V BAINITIC TURBINE ROTOR: YoungKun Oh, Kia Motors Corporation, Production Engineering R/D Department, J.E. Indacochea, GwangSoo Kim
Weld repair of ASTM A-470 class 8 high pressure steam turbine rotor steel has been performed to extend the service life of older fossil units. Multipass SAW, MIG and TIG welding have been employed. Microhardness of the base metal was VHN 253, however it dropped to VHN 227 at the heat affected zone close to unaffected base metal for SAW. This area of hardness drop is called "softening zone" and has a width of 0.5~0.6mm. During creep rupture test, failure occurred around the softening zone and rupture time was 772.4hr at 19ksi and 593°C. At ruptured area, spherical types of coarsened carbides, which were revealed molybdenum rich M6C were observed. Based on creep rupture life, SAW and/or high heat input TIG process provide the best creep rupture life and it could operate about 8-10 years.
5:10 pm
MATHEMATICAL MODELLING OF ELECTRON BEAM EVAPORATION: Adam Powell, Gerardo Trapaga, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; Paul Minson, Intel Corporation, Rio Rancho, NM 87114
Mathematical models of vapor and melt pool transport phenomena in electron beam evaporation are used to design an optimal beam scanning pattern to achieve a desired evaporant flux distribution at the substrate. The vapor transport model uses the Direct Simulation Monte Carlo method to calculate evaporant flux distribution at the substrate from the temperature distribution at the source, the activities of source species, background gases and system geometry. The source temperature distribution is adjusted manually in order to produce the desired flux distribution at the substrate. The melt pool model then calculates the heat flux distribution which the scanning electron beam must impart to the molten source surface in order to produce the desired temperature distribution, accounting for thermal losses to radiation and evaporation. Finally, a surface heat transfer model is used to calculate minimum beam local heating by the scanning beam.
Room: Salon 4
Location: Clarion Plaza Hotel
Session Chairperson: L.K. Mansur, Oak Ridge National Laboratory
2:00 pm
LIQUID METAL COMPATIBILITY OF STRUCTURAL MATERIALS WITH LIQUID LEAD-BISMUTH AND MERCURY: J.R. Weeks, Brookhaven National Laboratory, Upton, NY 11973-5000
Both liquid mercury and liquid lead-bismuth eutectic have been proposed as possible target materials for spallation neutron sources. During the 1950's and 1960's a substantial program existed at Brookhaven National Laboratory as part of the Liquid Metal Fuel Reactor program on the compatibility of bismuth, lead, and their alloys with structural materials. Subsequently, compatibility investigations of mercury with structural materials were performed in support of the development of Rankine-cycle mercury turbines for nuclear applications. The present talk will review our understanding of the corrosion/mass-transfer reactions of structural materials with these liquid-metal coolants. Topics to be discussed include the basic solubility relationships of iron, chromium, nickel, and refractory metals in these liquid metals, the results of inhibition studies, the role of oxygen on the corrosion processes, and specialized topics such as cavitation corrosion and liquid-metal embrittlement. Emphasis will be placed on utilizing the understanding gained in this earlier work in the development of heavy-liquid-metal targets for spallation neutron sources.
2:30 pm
MODELING AND OPTICAL STUDIES OF THE WATER-METAL INTERFACE IN SPALLATION NEUTRON SOURCE TARGETS: L.L. Daemen, G.J. Kanner, R.S. Lillard, D.P. Butt, T.O. Brun, W.F. Sommer, Los Alamos National Laboratory, Los Alamos, NM 87545
In spallation neutron sources neutrons are produced when a beam of high-energy particles (e.g., 1 GeV protons) collides with a (water-cooled) heavy metal target such as tungsten. The resulting spallation reactions produce a complex radiation environment (which differs from typical conditions at fission and fusion reactors) leading to the radiolysis of water molecules. Most water radiolysis products are short-lived but extremely reactive. When formed in the vicinity of the target surface they can react with metal atoms, thereby contributing to target corrosion. We will describe the results of calculations and experiments performed at Los Alamos to determine the impact on target corrosion of water radiolysis in the spallation radiation environment. Our computational methodology relies on the use of the Los Alamos radiation transport code, LAHET, to determine the radiation environment, and the AEA code, FACSIMILE, to model reaction-diffusion processes. The experiments make use of ultra-fast Raman spectroscopic techniques. Laser Raman spectroscopy enables us to identify the chemical species formed in water and at a metal surface during irradiation, as well as to observe the growth of corrosion products at the water-metal interface.
3:00 pm
IN SITU STUDIES OF AQUEOUS CORROSION OF TARGET AND STRUCTURAL MATERIALS IN WATER IRRADIATED BY AN 800 MEV PROTON BEAM: D.P. Butt, G.S. Kanner, L.L. Daemen, R.S. Lillard, Los Alamos National Laboratory, Los Alamos, NM 87545
Radiation enhanced, aqueous corrosion of solid spallation-neutron-source targets, such as tungsten, or target cladding or structural materials, such as superalloys and stainless steels, is a significant concern in accelerator-driven transmutation technologies. In this paper we describe methods for control and in situ monitoring of corrosion in accelerator cooling water loops. Using electrochemical impedance spectroscopy, we have measured the corrosion rates of aluminum 6061, copper, Inconel 718, and 304L stainless steel in the flow loop of a water target irradiated by a milliamp, 800 MeV proton beam. We also briefly describe our second generation experiments, scheduled to begin in early 1997. In these experiments we will measure the corrosion rates of tungsten, tantalum, Inconel 718, aluminum 5053, and 316L, 304L, and HT-9 stainless steel. We also discuss our laser diagnostic techniques for directly observing the production of corrosive radiolysis products as well as corrosion products near the surface of target materials.
3:30 pm BREAK
3:50 pm
STATIC CORROSION OF MARTENSITE/FERRITE AND AUSTENITIC STEELS IN MERCURY AT 300°C: Y. Dai, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
Mercury corrosion will be one of the critical problems for a spallation neutron source using Hg as target material. Preliminary results of static corrosion tests on 316L austenitic steel and on MANET and F82H martensitic/ferritic steels will be presented. Smooth and notched C-ring-shaped specimens were prestressed before putting them into Hg. The tests were performed at 300C and interrupted after different durations. After cooling down to room temperature, the change of morphology of specimen surfaces was examined. For 316L specimens after 160 hrs of corrosion, Hg covered all surfaces. However, for F82H and MANET, there was almost no Hg on surfaces after 500 hrs, but surfaces were covered with Hg after an additional 500 hrs. F82H had the thickest oxide layer (about 0.5 µm thick after 1000 hours), MANET was next, and 316L had the thinnest oxide layer. The mechanisms for wetting and oxidation will be discussed.
4:20 pm
SURFACE OXIDES AND THE BEHAVIOR OF ALUMINUM COMPONENTS IN THE APT TARGET/BLANKET SYSTEM: M.R. Louthan, Jr., Savannah River Technology Center, Aiken, SC 29808
The mechanical properties of the aluminum alloys in the accelerator production of tritium (APT) target/blanket system are sensitive to exposure and processing history. Several of the APT applications require exposure to flowing, hot water under heat transfer conditions. The thermal conductivity of the protective film is low and limits the temperature drop across the aluminum. This reduction in heat transfer will raise metal-oxide interface temperature and play a major role in the corrosion processes. Under heat transfer conditions, the oxide-metal interface temperature will increase both oxide thicknesses and service temperatures for aluminum. Interrelationships among service, oxide development and water chemistry are similar to those for reactor service and this paper relates anticipated performance in the APT system to reactor experience.
Room: 231B
Session Chairpersons: R.G. Bautista, Mackay School of Mines, University of Nevada, Reno, NV 89557: G. Ramadorai, EnMet Associates Inc., 11225 E. Quick Draw Place, Tucson, AZ 85749
2:30 pm
PRODUCTION OF THERMAL SPRAY-QUALITY METAL AND ALLOY POWDERS BY PLASMA PROCESSING: P.V. Ananthapadmanabhan, K.P. Sreekumar, N. Venkatramani, Laser & Plasma Technology Division, Bhabha Atomic Research Centre, Bombay-400 085, India; Patrick R. Taylor, Department of Mining & Metallurgical Engineering, University of Idaho, Moscow, ID 83844
Feedstock powders of metals, alloys and ceramics for thermal spray applications have to meet several specifications. Particle shape, size and distribution, powder flow characteristics and density are the important factors that need to be controlled, in order to ensure high spray efficiency and better coating properties. Thermal plasma technology can be effectively utilized to produce metal, alloy and ceramic powders for spray applications. The present paper describes plasma spheroidisation of commercially available aluminum powder and nickel-aluminum powder blend in a plasma reactor. Results show that the processed powder particles bear spherical morphology with excellent flow characteristics, ideal for thermal spray applications.
2:55 pm
NON-ELECTROLYTIC DEPOSITION OF SILVER ON TO TUNGSTEN-POWDER PARTICLES: Jae-Ho Lee, Hong lk University, Department of Metallurgy and Materials Engineering, 721 Sangsu dong, Mapo-gu, Seoul 121-791, Korea; G.P. Martins, Colorado School of Mines, Department of Metallurgical and Materials Engineering, Golden, CO 80401
For some electronic applications where a dispersed electrically-conductive particulate phase is employed, the conductivity of the surface (or near-surface region) of the particles provides for the primary mechanism which determines its electrical conductivity. Particles of a less expensive material, which may have desirable thermal-expansion properties, when coated with silver offer a means of also obtaining desirable electrical properties at a lower cost. The research conducted was focused primarily on the development of silver-coated tungsten particles for thick-film polymeric conductors. The ammoniacal electrolyte was formulated from silver-nitrate, glycine inhibitor and formaldehyde reductant. The reduction, and subsequent deposition, of silver occurred selectively on the surface of the tungsten particles. Coated particles were assessed by SEM imaging. The thickness of the silver coating was estimated to be approximately 100nm on the basis of a mass account and the coating being uniform. The electrical conductivity of a silver-coated tungsten-powder pellet was found to be similar to that of a silver-powder pellet, of identical geometry.
3:20 pm
VISCOSITY MODELING OF TERNARY ALUMINOSILICATE MELTS: Z. Zhang, R.G. Reddy, The Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487-0202
Viscosity of CaO-aluminosilicate ternary melts were estimated using a structure based model. The model considers depolymerization effects and related breakdown of the silicate network structure on the addition of metal oxides to the melts. The predicted values are in good agreement with the experimental values over the whole temperature and composition range.
3:45 pm
COPPER DEOXIDIZATION BY BUBBLING HYDROGEN/NITROGEN MIXTURES THROUGH THE MELT: Claudio Parra De Lazzari, Jose Deodoro Trani Capocchi, Department of Metallurgical and Materials Engineering, Escola Politecnica de Universidade de Sao Paulo, Sao Paulo SP-Brazil
The determination of the governing step of the deoxidization rate and the effects of the hydrogen content of the mixtures (C), the diameter of the delivery orifice (
) and the Reynolds number of the orifice (Roe) on the product Av keg was investigated. Av is the total surface area of the interface between the bubbles and the melt keg, is the mass transfer coefficient in the gas phase. The design of the experiments was based on a two levels statistic fractionated factorial planning Oxygen in the melt was measured as a function of time. In the prevailing experimental conditions it was found that the governing step of the deoxidization rate was the transport of hydrogen in the gaseous phase and that Av kejg increases with C, and Reo.
4:10 pm BREAK
4:20 pm
CHEMICAL WEAR OF REFRACTORIES IN THE SLAG LINE OF VOD LADLES FOR THE PRODUCTION OF STAINLESS STEELS: B. Blanpain, P. Wollants, Department of Metallurgy and Materials Engineering, K.U. Leuven, de Croylaan 2, B-3001 Leuven, Belgium, and B. Hallemans, ALZ, Genk-Zuid zone 6A, B-3600 Genk, Belgium
The slag line in vacuum oxygen decarburization (VOD) ladles is a severe environment for refractory materials during the refining of stainless, steels. Magnesia-chrome bricks are currently the refractory materials of choice for this application. The actual performance of a fixed quality of magnesia-chrome bricks is however largely dependent on the conditions during the VOD process cycle. This presentation addresses the aspects of chemical interaction between the slag phase and the magnesia-chrome refractory materials. As-delivered and postmortem bricks have been analyzed by optical microscopy, x-ray diffraction and scanning electron microscopy. Different phenomena were observed such as slag penetration and oxide reduction. These experimental observations are the basis for a modeling of the slag/magnesia-chrome reaction. The aim is to investigate alternate, viable VOD processing routes which are less demanding on the refractory materials.
4:45 pm
PHASE EQUILIBRIA IN THE OXIDE-SATURATED Ca-Mg-O SYSTEM: Xiaoping Xu, Mark E. Schlesinger, Department of Metallurgical Engineering, University of Missouri-Rolla, 1870 Miner Circle, Rolla, MO 65409-0340
Recent research results have claimed that previously accepted Gibbs energies of formation of CaO and MgO are in error, and that MgO is actually more stable than CaO at lower temperatures. The potential impact of this on the existing thermodynamic database and on calculations using 
G0f values for these oxides is considerable. However, the newly calculated values remain controversial. Equilibration of pure CaO and MgO with a metal phase at temperatures between 1100°C and 1200°C allows the new G0f values to be "tested," using a previously derived thermodynamic model for liquid CaMg alloys to calculate activities in the metal phase. The fit between actual and predicted alloy compositions determines the likelihood that the new thermodynamic values are valid.
5:10 pm
REDUCTION OF MnO PELLETS BY CARBON-SATURATED LIQUID IRON: Jose Roberto de Oliveira, Marcelo Breda Mourdo, Paulo dos Santos Assis and Jorge Alberto Soares Tenorio, Dept. of Metallurgical and Materials Engineering, University of Sao Paulo, 05508-900, Sao Paulo, Brazil
The goal of this study was to investigate the reduction of MnO pellets by carbon saturated liquid iron. The effects of the initial Mn and Si content in the bath were explored. The tests were performed in laboratory apparatus, where MnO pellets reacted with a saturated liquid iron bath. The reduction time was taken by measurement of the CO pressure variation with the time. The results showed the effect of initial Mn, C and Si content in the bath. The Kinetics of MnO reduction increases with the decrease in the initial MnO content in the bath. Si in the bath increases the reduction rate of the MnO pellets.
Room: 232B
Session Chairperson: S.X. Mao, Department of Mechanical Engineering, University of Calgary, Calgary, Alberta, Canada, T2N 1N4
2:00 pm INVITED
CREEP DEFORMATION AND RUPTURE OF Al2O3 UNDER STATIC AND CYCLIC LOADING: Darrell Socie, Department of Mechanical Engineering, University of Illinois, Urbana, IL 61801
Results of the tension and torsion tests on a commercial grade of vitreous bonded, 99.8% Al2O3, show that creep deformation is enhanced significantly under shear stress. Microstructural observations show that extensive grain boundary sliding occurs in the torsion specimens and gives rise to a large initial creep deformation. Evidence of cavity formation is found throughout the specimen. Little evidence of grain boundary sliding or cavitation was found in the tensile specimen even though the tensile stress was four times larger. The combined action of one tensile stress 1 and one compressive stress, -3, doubles the grain boundary shear stresses to 2. This results in more grain boundary sliding and early cavity formation under shear loading. In addition the compressive stress will cause a wedging action on individual grains that will result in a grain facet stress of n. This stress will be added to the tensile stress, 1 , to enhance cavity coalescence and microcrack growth.
2:30 pm
AN INVESTIGATION OF FIBER/MATRIX INTERFACE OF A NICALON FIBER REINFORCED SILICON CARBIDE COMPOSITE WITH A SILICON CARBIDE INTERFACIAL COATING: Wei Zhao , Peter K. Liaw, David C. Joy, Dept. of Materials Sciences and Engineering, 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 properties of ceramic matrix composites (CMCs) can be controlled by tailoring the fiber/matrix interface, especially the type of interfacial materials and their thickness. A new Nicalon/SiC composite with SiC as an interfacial coating processed by a forced-flow chemical vapor infiltration (FCVI) method at the Oak Ridge National Laboratory demonstrates improved high-temperature oxidation resistance than that with a carbon interfacial coating. However, it is difficult to differentiate the SiC interface from the matrix using scanning electron micrographs, because of nearly identical microstructures and similar chemical compositions of the fiber, the matrix, and the interfacial coating. In this paper, the line-scan chemical analysis technique in scanning electron microscopy (SEM) is used to investigate the SiC interfacial coating. As-received and oxidized specimens are studied. The existence of elements, such as Si, C, O, and Cl, and their distributions along the fiber/matrix interface, are detected. The profile of interface chemical composition can be used to identify interface structure as well as thickness. The effect of interface composition on mechanical properties is also studied.
3:00 pm
CRACK NUCLEATION ON ELASTIC POLYCRYSTAL SURFACE IN CORROSIVE ENVIRONMENT: Z. Suo, H. Yu, Mechanical and Environmental Engineering Department, Materials Department, University of California, Santa Barbara, CA 93106
This paper analyzes a process of crack nucleation on the surface of a ceramic subject to a stress parallel to the surface, in an environment where the ceramic evaporates slowly and deforms elastically. Both grain boundary tension and elastic stress concentration cause the surface to groove along its intersections with the grain boundaries. Two behaviors are identified. If the applied stress is small, the grooves approach an invariant shape, and the ceramic erodes by gross mass loss. If the applied stress is large, the grooves sharpen into crack fronts, and the ceramic breaks by decohesion. The models relate crack nucleation threshold and time to the applied stress, surface and grain boundary tensions, chemical free energy, grain size, and kinetic parameters. Surface self-diffusion is also included in the analysis.
3:30 pm BREAK
4:00 pm
ROLE OF GRAIN BOUNDARY PHASE DURING HIGH-TEMPERATURE FATIGUE-CRACK GROWTH IN CERAMICS: J. K. Shang, D. Yao, C. Huang, Department of Materials Science and Engineering, University of Illinois, Urbana, IL 61801
Role of grain boundary phase on high-temperature fatigue-crack growth were examined in a TiB2/SiC composite and polycrystalline aluminas of different purities at 800-1100°C. The low-purity alumina and the composite contained a continuous film of glassy phase on the grain boundary while the high-purity aluminas contained either little or no continuous grain boundary phase. In the low-purity alumina and the composite, fatigue crack growth rate increased drastically as the cyclic frequency was decreased. The cyclic crack growth rate was slower that the creep crack growth rate at the same maximum stress intensity. In contrast, fatigue crack growth in the high-purity alumina was relatively insensitive to cyclic frequency and the fatigue crack growth rate was faster than the creep crack growth rate for the same maximum stress intensity. The difference in the fatigue crack growth behavior is explained in terms of the different fatigue crack growth mechanisms in these ceramics.
4:30 pm
THE MECHANICAL BEHAVIOR OF CONTINUOUS FIBER REINFORCED CERAMIC COMPOSITES (CFCCs): N. Miriyala, P.K. Liaw, C.J. McHargue, The University of Tennessee, Knoxville, TN 37996; L.L. Snead, Oak Ridge National Laboratory, Oak Ridge, TN 37831
The mechanical behavior of two Nicalon fabric reinforced ceramic matrix composites, with alumina and silicon carbide as the matrix materials, respectively, were investigated. Four point-bend tests were conducted at ambient and elevated temperatures to study the monotonic and cyclic fatigue behavior. The stress-strain curves were non-linear for both composites, at ambient as well as elevated temperatures. During cyclic loading, the modulus of the composite was monitored to serve as a measure of the loss in load bearing capacity of the composites due to cyclic fatigue loading. Progressive damage in the composites was monitored by optical and electron microscopy techniques. The differences in the composite monotonic and cyclic fatigue behavior, depending on the orientation of the fabric plies to the loading direction, and the micromechanisms responsible for the differences, will be the focus of the paper.
5:00 pm
MECHANICAL PROPERTIES OF SILICON NITRIDE CERAMICS WITH ANISOTROPIC MICROSTRUCTURE: Hisayaki Imamura, Pine Ceramics Research Association, Synergy Ceramics Laboratory, Nagoya, Japan; Kiyoshi Hirao, Manual E. Brito, Motochiro Toriyama and Shuzo Karzaki, National Industrial Research Institute of Nagoya, Nagoya, Japan
Room: Salon 8
Location: Clarion Plaza Hotel
Session Chairpersons: Timothy W. Ellis, Kulicke and Soffa Industries, Inc., 2101 Blair Mill Road, Willow Grove, PA 19090; Ramana G. Reddy, Dept. of Metallurgical Eng., University of Alabama, Tuscalossa, AL 35487
2:00 pm
ANODE EFFECT IN NEODYMIUM OXIDE ELECTROLYSIS: Rudolf Keller, Kirk T. Larimer, EMEC Consultants 4221 Roundtop Road, Export, PA 15632
In the electrolysis of neodymium oxide from a molten fluoride electrolyte, anode effects may occur at the carbon anodes, interfering with smooth cell operation. In laboratory experiments, we attempted to circumvent this problem selecting electrolytes with a high oxide concentration, possibly at relatively low rare earth content, but cathodic deposition was not satisfactory. A regime at higher cell voltage was discovered to yield good cell performance, but evolution of considerable amounts of fluorocarbon compounds suggested that a reactive treatment of the off-gases would be necessary for environmental acceptability. Subsequent experimentation at low cell voltage revealed conditions for satisfactory operation without occurrence of anode effects and without any formation of CF4 and C2F6.
2:30 pm
THERMODYNAMIC MODELING OF CALCIOTHERMIC REDUCTION OF NdF3: P.T. Velu, R.G. Reddy, Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487
Production of neodymium metal by reduction of NdF3 with calcium in the presence of calcium chloride is studied. The thermodynamic calculations of the reduction process was carried out using method of minimization of Gibbs energy. Yield of neodymium metal was calculated as a function of temperature and salt composition. Nd increased with increase in temperature and also increase in CaCl2. Impurity content of the alloy decreased with increase in CaCl2. The calculated data is an excellent agreement with the large scale experimental data.
3:00 pm BREAK
3:30 pm
IMPROVEMENT OF MAGNETIC PROPERTIES OF NANOCOMPOSITE NdFeB MELT SPUN RIBBONS BY ELEMENT SUBSTITUTION: W. C. Chang, S. H. Wu, Department of Physics, National Chung Cheng University, Ming-Hsiung, Chia-Yi, Taiwan, China; B.M. Ma, C. O. Bounds, Rhone-Poulenc, Rhone-Poulenc Rare Earths and Gallium, CN 7500, Cranbury, NJ 08512
The magnetic properties of the nanocomposite NdFeB melt spun ribbons are strongly determined by the remanence, coercivity and the squareness of its demagnetization curve. In this paper, three approaches in improving the magnetic properties of 
-FE/Nd2Fe14B type nanocomposite melt spun ribbons will be addressed: (1) the effect of Co substitution for Fe on the remanence enhancement (2) the effect of La substitution for Nd on the improvement of remanence and the squareness of the demagnetization curve and (3) the effect of Cr substitution for Fe on the enhancement of the coercivity and the squareness of the demagnetization curve.
4:00 pm
THE MAGNETIC PROPERTIES AND CRYSTALLIZATION PHENOMENA OF MELT EXTRACTED Nd9.8Fe90.2-XBX (X=6 through 11) FILAMENTS: Q. Chen, B. M. Ma, C.O. Bounds, Rhône-Poulenc, Rare Earths and Gallium, CN 7500, New Jersey
Recently, Nd-lean and/or boron-rich melt spun materials have attracted attention as potential materials for bonded magnet applications. Since the alloys can deviate significantly from the stoichiometric Nd2Fe14B composition, additional phases are usually present in the products. The size and volume fraction of these phases play important roles in determining the strength of exchange coupling interaction between phases and, consequently, the magnetic properties obtained. It is of interest to know how the Nd and/or boron contents impact the crystallization behavior and the magnetic properties of these materials. An alloy series of Nd9.8Fe90.2-xBx, where x=6 through 11 was prepared by a newly developed melt extraction technique at various wheel speeds.
Room: 314A
Session Chairpersons: Professor John W. Hancock, Department of Mechanical Engineering, University of Glasgow, Scotland G12 8QQ, UK; Dr. Peter Matic, Naval Research Laboratory, Code 6380, 4555 Overlook Drive SW, Washington DC 20375
2:00 pm INVITED
MODELING OF DUCTILE FRACTURE: Alan Needleman, Division of Engineering, Brown University, Providence, RI 02912
Analyses of fracture are discussed where the initial-boundary value problem formulation allows for the possibility of a complete loss of stress carrying capacity, with the associated creation of new free surface. Hence, fracture arises as a natural outcome of the deformation process without any ad hoc failure criterion being employed. The failure mechanisms modeled are plastic void growth and coalescence, and cleavage cracking (so that the ductile-brittle transition can be analyzed). The role of porosity induced weakening in precipitating shear band failures will be illustrated. However, the main emphasis will be on recent predictions of crack growth, including ductile-brittle transitions and three dimensional effects such as shear-lips.
2:25 pm INVITED
NON-LOCAL EFFECTS IN DUCTILE FRACTURE PREDICTIONS: Viggo Tvergaard, Department of Solid Mechanics, Technical University of Denmark, DK-2800 Lyngby, Denmark
Continuum studies of ductile fracture have been based on local constitutive relations, which do not represent a material length scale. The resulting numerical predictions show inherent mesh sensitivity, since the softening material behaviour near final failure will tend to give localized damage in regions as narrow as possible within the mesh resolution. Nonlocal constitutive relations, with the delocalization related to the damage mechanism, have been proposed for ductile fracture where damage involves the nucleation and growth of voids to coalescence. The effect of using this nonlocal material model will be illustrated by a number of analyses, including studies of shear band failure, ductile matrix failure in metal matrix composites, and failure involving two size - scales of voids. Based on recent comparisons with cell - model predictions of localization in a void - sheet the relevant material length scale for a ductile fracture model are discussed.
2:50 pm INVITED
NUMERICAL SIMULATION OF DUCTILE RUPTURE: ANALYSIS OF EXPERIMENTAL SCATTER AND SIZE EFFECT: Jacques Besson, A. Pineau, Ecole des Mines de Paris, Centre des Matériaux, CNRS URA 866, 91003, BP 87 Evry Cedex, France
Ductile rupture behavior is usually characterized with specimens of various types including smooth and notched bars, compact tension specimens, bending bars. In addition, similar specimens geometries of different sizes are also used. Using different specimen geometries allows to investigate the effect of mechanical parameters such as stress triaxility and amount of plastic deformation on ductile rupture. Changing specimen sizes allows to evaluate experimental dispersion and size effects. Considering these effects is of primary importance for the transferability of laboratory tests carried out on relatively small samples to assess the resistance of relatively large industrial components. Both dispersion and size effect are caused by material heterogeneities which have to be accounted for by modeling. This work presents both experimental data and numerical simulation relative to dispersion and size effects on two very different materials. The first one is a plane carbon steel containing MnS inclusions which easily debond from the matrix so that rupture is essentially controlled by void growth. The second material is a cast ferrite - austenite duplex stainless stainless steel. Microcracks are continuously nucleated in the embrittled ferrite so that final rupture is essentially controlled by void nucleation. Both materials were tested using axisymmetric smooth and notched bars and Charpy specimens of different sizes. In order to obtain microstructural data, relevant to modeling, both materials were carefully examined. In the first case, initial local void densities (MnS inclusion content) were measured using image analysis. In the second case, local crack nucleation rates were determined by carrying out interrupted tensile tests and determining crack locations. These examinations are needed to get physically based data to be used in the modeling thus reducing the number of "fitting parameters". Modeling of rupture, dispersion and size effects can be done using two different approaches both based on finite element analysis. The first one (uncoupled) consists in carrying out simulations of the mechanical response of structures assuming that the material is undamaged. Subsequently, a local rupture criterion is applied to the structure to determine that the material remains unchanged. Subsequently, a local rupture criterion is applied to the structure to determine its failure probability. It is therefore assumed that damage is small enough not to affect the stress strain distribution in the part. In addition the material is supposed to break according to the weakest link theory. The second approach (coupled) is based on continuum damage mechanics using models for ductile metals such as those proposed by Gurson and Rousselier. In this case, the effect of damage evolution on stress distribution in the parts can be fully accounted for. In addition the effect of defect spatial distribution can also be investigated. No specific assumption has to be made on the onset of rupture. Finite element calculations were carried out for both materials using the Gurson-Tvergaard/Rousslier constitutive equations. Initial void volume fractions (first material) or microcrack nucleation rates (second material) were randomly distributed in the structures. Dispersion can be modeled by carrying a Monte Carlo type simulation using the same mesh and different random drawings. Size effect is modeled by keeping the element size constant, thus increasing the number of elements for larger structures. The uncoupled approach was also used for the first approach. Results show that size effect and dispersion can be successfully modeled using both approaches. The fully coupled approach, although more time consuming, is thought to be the most promising since: (1) it is based on fewer assumptions, (2) it can be applied to any geometry (e.g. cracked components); in particular it gives much better results on smooth tensile specimens, (3) it can model the interaction between neighboring heterogeneities clusters.
3:15 pm BREAK
3:25 pm INVITED
MICROSTRUCTURE MECHANICS DESCRIPTION OF DUCTILE FRACTURING IN POLYCRYSTALS: Ronald W. Armstrong, C.C. Chen, G.R. Irwin, M.E. Natishan, F.J. Zerilli*, X.J. Zhang, Department of Mechanical Engineering, University of Maryland, College Park, MD 20742; *Permanent address: Research and Technology Depth Naval Surface Warfare Center, Silver Spring, MD 20903-5000
Evidence is reviewed of particle size aspects of hole formation and growth, texture effects and grain size influences, for example, as revealed in stereosection fractographs of titanium and steel alloy ductile failure surfaces, in the latter case, near to the condition of cleavage fracturing. The results are related to model considerations of particle debonding and local region strain rate enhancement and plastic instability properties (see e.g. J.P. Gudas, G.R. Irwin et al., in "Defect Assessment in Components - Fundamentals and Applications", Mechanical Engineering Publications Ltd. London, 1991, pp. 549-568), as well as to constitutive equation aspects of plasticity and fracturing.
3:40 pm INVITED
MACROCRACK NUCLEATION IN DUCTILE MATERIALS: Owen Richmond, Aluminum Company of America, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069
In ductile materials, it is typical of many microcracks and pores to nucleate and grow before some of these coalesce to form dominant macrocrack which leads to ultimate failure. This paper is concerned with quantitative identification of the microstructural regions in which this macrocrack nucleation occurs, and the development of constitutive relations for these regions. These microstructure-based constitutive relations can then be used in macromechanical analyses to evaluate potential improvement in macroscopic behavior due to alterations in microstructure.
4:05 pm INVITED
MICROSTRUCTURAL EFFECTS IN DUCTILE FRACTURE: Anthony W. Thompson, Lawrence Berkeley National Laboratory, MS 62-203, One Cyclotron Road, Berkeley, CA 94720
Microvoid coalescence or MVC fracture depends strongly on microstructure. This applies to each of the constituent processes of MVC, namely nucleation, growth and coalescence of voids, and is true for both transgranular and intergranular MVC. Experimental as well as analytical evidence on this point reveals both needs for further experiments, and gaps in analytical understanding. Methods to vary the behavior of MVC processes, such as variations in temperature, or introduction of hydrogen, convey further information (provided MVC fracture is maintained) and have proven valuable in understanding these processes; of particular value are the notch bend tests, in which stress state can readily be varied to identify control of stress, strain, or a combination of the two.
4:30 pm
A MODEL FOR CRACK INITIATION AND CRACK GROWTH IN DUCTILE MATERIALS: Xi Zhang and Yiu-Wing Mai, University of Sidney, Centre for Advanced Materials Technology, Department of Mechanical and Mechatronic Engineering, Sydney, New South Wales 2006, Australia
A refined mathematical model is presented in this paper to account for the effects of void nucleation, growth and coalescence on fracture initiation and subsequent quasi-static, slow and little crack growth in ductile materials under plane strain and mode I condition. A chain of larger voids uniformly-distributed ahead of the crack tip is used to model the discontinuous fracture process and discontinuous nucleation of small voids at second-phase particles is the main cause for crack initiation in high strength and ductility steels. A cumulative damage criterion, which is the ratio of uncracked length between the crack tip and the first large void to characterize size, is employed. Effects of crack-tip constraint and material parameters on ductile fracture are discussed in terms of the gradient of the variation of crack-tip constraint within the damage zone. Estimation of upper-bound fracture toughness is established and numerical results show that, with the exception of crack growth there is no obvious constraint effect on ductile crack initiation.
4:50 pm
DUCTILE CAVITY GROWTH IN NORMALLY BRITTLE MATERIALS: Donald R. Curran, R.E. Tokheim, and T. Cooper, SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025
The term "ductile fracture" can be interpreted in a number of ways, but to a materials scientist who focuses on microscopic mechanisms the meaning is clear: "ductile fracture" means that failure occurs by the nucleation, growth, and coalescence of approximately ellipsoidal microscopic voids in plastically deforming material. To be sure, extremely ductile materials stretched under plane or uniaxial stress conditions may fail in the absence of voids by simple plastic necking. Nonetheless, in most practical engineering applications of failure in ductile materials, microscopic "ductile fracture" play a central role in the failure process. Frank McClintock was one of the pioneers in this area (as well as many others), and his 1968 paper [J. Appl. Mech., 35, p.363], along with papers by C.A. Berg [Proc. Fourth U.S. National Congress Appl. Mech. 2 (1962) 885], J.R. Rice and D.M. Tracy [J. Mech. & Phys. Solids, 17 (1969) 202], A.L. Gurson [Trans. ASME, J. Eng. Mater. & Technol. (1977) 2], and M.Y. He and J.W. Hutchinson [J. Appl. Mech. 48 (1981) 830], stimulated much further work. The above papers discussed the conditions for cavity growth in a viscous or plastically deforming material under tension and shear. In the present paper, we take a similar approach, but consider cases in which the cavity growth is driven not only by the externally applied stresses, but also by internal cavity pressure. Such conditions arise when a material is exposed to penetrating radiation from lasers or x-ray sources of sufficient fluence to cause local heterogeneities to vaporize while leaving the matrix material relatively cool. Under such loading conditions, microscopic cavity pressures of several tens of GPa may be produced, sufficient to cause the surrounding matrix material to flow plastically, even when the matrix material is a normally brittle material like a ceramic. Under some boundary conditions, the expanding cavities may drive the matrix material into tension, producing brittle tensile fractures between cavities. We present a computer model of the above processes, and illustrate the model with several example calculations.
5:10 pm INVITED
HYDROGEN EFFECTS ON THE DUCTILE FRACTURE ON IRON-BASED SUPERALLOYS: Neville R. Moody*, I. Baskes*, J.E. Angelo,* and T. Tsuji**; *Sandia National Laboratories, P.O. Box 969, Mail Stop 9403, Livermore, CA 94551; **Hizuoka University, Hamamatsu, Japan
Austenitic superalloys can exhibit dramatic reductions in ductility and crack growth resistance when hydrogen triggers a change in failure mode. All failures begin by void growth at fractured matrix carbides. However, void growth is prematurely terminated terminated in hydrogen by second generation void formation at slip band intersections and separation of interconnecting slip band segments. As a first approximation to understanding hydrogen effects on the fracture process, we have combined the Embedded Atom Method with Monte Carlo simulations to model the segregation of hydrogen to dislocation in slip bands and slip band intersections. We will present these results and draw a direct correlation between the segregation of hydrogen to slip band intersections, void formation, and crack growth susceptibility.
5:30 pm INVITED
NEAR-TIP FRACTURE PROCESSES IN DUCTILE MATERIALS: Kwai S. Chan, Southwest Research Institute, San Antonio, TX 78238
Ductile fracture is generally considered to occur via void nucleation, growth, and coalescence mechanisms that result in a dimpled fracture appearance. For many materials, void initiation and growth take place at hard particles or inclusions. However, ductile fracture involving void formation has been observed in materials that contain neither hard particles nor inclusions. In this paper, the near-tip fracture processes in several structural alloys, including Al-, Ti-, and Nb-base alloys, that exhibit ductile fracture in a variety of microstructures with and without hard particles are summarized. Possible mecha nisms for the formation of dimpled fracture in these materials are identified. These fracture mechanisms are correlated with the microstructures and the fracture resistance curve to provide a basic understanding of the role of microstructure in the crack-tip fracture process, the transition from ductile to brittle fracture, and the source of fracture resistance.
Room: Salon 7
Location: Clarion Plaza Hotel
Session Chairperson: Prof. Henry R. Piehler, Dept. of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
2:00 pm
MECHANICAL PROPERTIES OF LASER FORMED P/M INCONNEL AND STAINLESS STEEL: J.W. Sears, Lockheed Martin KALP, Inc., Schenectady, NY
Abstract not available.
2:30 pm
POWDER INJECTION MOLDING (PIM) OF INCONEL 718 AEROSPACE COMPONENTS: Robert M. Schmees*, Joe Spirko**, Juan Valencia**, *Pratt & Whitney, West Palm Beach, FL; **Concurrent Technologies Corp., Johnstown, PA
The feasibility and cost benefit of using PIM for the manufacture of aerospace components was investigated. An optimized thermal processing cycle was developed for hydrogen sintering, vacuum sintering, and HIPing the PIM Inconel 718 parts. The parts were subsequently solution and precipitation heat treatment. A tensile, creep, stress rupture, low cycle fatigue, and high cycle fatigue data base was generated. Tensile properties exceeded AMS 5663 minimum specification requirements. The associated cost reduction was greater than 50%. Both J52-P-409 Bushings and F119 Aircraft Mounted Nozzle Sidewall Saddle Supports were fabricated out of PIM Inconel 718.
3:00 pm
ADVANCES IN CUBIC PHASE (Al2Cr)3Ti ALLOY COATING TECHNOLOGY: D.K. Dewald*, D.E. Mikkola**, *Waubik, Inc., Hancock, MI 49930; **Dept. of Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931
Cubic phase alloys of (Al2Cr)3Ti are being developed as high temperature, oxidation resistant coatings for Ti-based materials. High quality powders of these alloys have been made by high pressure gas atomization (HPGA) and are now available from a commercial powder manufacture. The powders have been applied to Ti-6Al-4V, Ti-6242, and Ti-47Al2Cr-2Nb alloy sample pieces using low pressure plasma spray (LPPS) to form coatings 100-150µm thick. Coupons cut from the samples have been subjected to high temperature cyclic oxidation tests. The as applied and oxidation tested coatings have been analyzed for structure and integrity. The results of these tests and analysis, related advancements in coating development, and powder processing will be discussed.
3:30 pm
MICROSTRUCTURAL ANALYSIS OF MECHANICALLY ALLOYED AND POWDER METALLURGY PROCESSED W-HfC AND W-Ir-HfC PENETRATOR RODS: Christine Kennedy, L.E. Murr, S. Pappu, D. Kapoor*, Dept. of Metallurgical and Materials Engineering, The University of Texas at El Paso, El Paso, TX 79968; *Army Research Development and Engineering Center, Picatinny, NJ 07806
Tungsten heavy alloys (WHA) as well as depleted uranium (DU) alloys (U-0.75% (Ti) for example) have been the primary materials employed in large caliber, U.S. tank ammunition or kinetic energy (KE) penetrators. Since the deformation behaviors and resulting ballistic performance of these alloys are different, there has been considerable effort to develop alternative and more effective penetrator materials. This study involves the mechanical alloying (MA) and PM processing of tungsten-hafnium carbide (1, 2, and 5 weight percent) and W-HfC containing 0.1% lr as a novel approach to WHA development. Slugs of W-1HfC, W-5HfC, and W-2HfC-0.5 lr and W-5HfC-0.5 lr processed from MA powder corresponding to high-speed attritor milling times ranging from 8 to 40 h, have been examined by light metallography and transmission electron microscopy (TEM). These products are remarkably free of disclocations and average (bulk) hardness range from 700 VHN for W-1HfC to 1200 VHN for W-5HfC precursor powders milled 16 h. The corresponding W-5HfC-0.5 lr hardness was 1250 VHN, and there were some interesting metallographic differences between the W-5HfC and W-5HfC-0.5 lr. HfC particle size and size distribution measurements have also been made in the TEM, and the effects of attritor milling time on residual hardness and microstructure have been examined.
4:00 pm
IN SITU METAL MATRIX COMPOSITES UTILIZING INTERMETALLIC MATRIX COMPOSITE (IMC) REINFORCEMENT: S.L Kampe*, J.S. Marte*, L. Christodoulou**, T. Zarrah**, *Virginia Polytechnic Institute and State University, Blacksburg, VA 24061; **MATSYS, Inc., Arlington, VA 22209
A new processing methodology is described whereby metal matrices are reinforced in situ by deformation-processing of metal/IMC blends. The IMC "reinforcement" is exemplified by its high strength, attributable to high loadings of dispersed ceramic (e.g. 30-50 v%) within its intermetallic matrix. Processability of the metal/IMC composite is governed by the thermodynamic compatibility of the metal and the intermetallic, and the relative high temperature flow behavior of the metal and the IMC. The methodology will be illustrated through its application to a titanium metal matrix composite, produced by hot extrusion of prealloyed Ti-6Al-4V and IMC (Al3Ti + 40 v% TiB2) powders. Microstructures and preliminary mechanical behavior will be presented for composites produced over a range of deformation processing conditions and with varying percentages of IMC reinforcement.
4:30 pm
RHEOLOGY OF POWDER INJECTION MOULDED PARTS: Sedat Özbïlen, Gazi University, Faculty Technical Education, Metal Dept., Ankara, Turkey
The determination of the variation of pressure against time for PIN feedstocks during their stay in the mould has gained importance in PIM technology, a hot research area of recent years. The possibility of this will case the control of properties of the parts that will be produced with this technology, such that the conditions to increase the productivity of the process can be realized. In the present work, the rheology of 3I6L stainless steel powder-variable binder mixes were therefore studies. Results of this investigation will be presented.
Room: 340A
Session Chairperson: Patrice E.A. Turchi, Chemistry and Materials Science Department (L-268), Lawrence Livermore National Laboratory, PO Box 808, Livermore, CA 94551
2:00 pm INVITED
MOLECULAR DYNAMICS SIMULATION OF MECHANICAL PROPERTIES OF AMORPHOUS ALLOYS: Tomoyasu Aihara Jr., Tsuyoshi Masumoto, and Yoshiyuki Kawazoe, Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-77, Japan
Macroscopic mechanical properties of materials arise from cooperative dynamics of atoms. However, it is difficult to detect the atomistic dynamical behavior by in situ experiment. We performed a large scale molecular dynamics simulation to study the deformation and fracture processes in Zr-Ni amorphous alloy. Finnis-Sinclair type pair functional potentials is used. Uni-axial strain is applied for a nano-size rod with constant strain rate at various temperatures. Tensile processes are traced by checking the internal energy and by the snapshots for atom configuration. The discrete atomic model reproduces the behavior of the continuum matter. The correlation between the inhomogeneous atom configuration and atomic level stress is analyzed.
2:40 pm INVITED
METASTABILITY AND PROPERTIES OF METALLIC BULK GLASS FORMING ALLOYS: Hans J. Fecht, Institute of Metallic Materials, Technical University Berlin, Hardenbergstrasse 36, PN 2-3, D-10623 Berlin, Germany
The absence of crystallization over a wide time/temperature window can be utilized to produce bulk metallic glass by relatively slow cooling of the melt. For a number of alloys including the multicomponent Pd-Ni-P, Au-Pb-Sb, Zr-Cu-Ni-Al, and Zr-Ti-Ni-Cu-Be alloys the relevant thermodynamic and thermomechanical properties of the metastable glassy and undercooled liquid states have been measured below and above the glass transition temperature. These measurements include specific heat, viscosity, density and elastic properties as functions of temperature. As a result it becomes obvious that the maximum undercooling for these alloys is given by an isentropic condition before an enthalpic or isochoric instability is reached. Alternatively, these glasses can also be produced by mechanical alloying, thus replacing the thermal disorder by static disorder and resulting in the same thermodynamic glass state. For the "weaker" glasses the isentropic instability also coincides with a divergence of the viscosity. During heating through the undercooled liquid a nanoscale phase separation occurs for most glasses as a precursor of crystallization. Further measurements of the mechanical and tribological wear properties point to the unique engineering applications of this new class of advanced materials.
3:20 pm BREAK
3:40 pm INVITED
ENVIRONMENTAL EFFECT IN BULK AMORPHOUS ALLOYS: C.T. Liu, L. Heatherly, D.S. Easton, Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6115; C.H. Chen, Health Science Research Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, Akihisa Inoue, Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-77, Japan
Recent studies indicate that moisture-induced hydrogen embrittlement is a major cause of low ductility and brittle fracture of many intermetallic alloys in moist air at ambient temperature. This embrittlement involves the reaction of reactive elements in intermetallic alloys with the moisture in air and the generation of atomic hydrogen which penetrates into crack tip and causes loss of tensile ductility. In the current study, bulk amorphous alloys based on Zr-Al-Ti-Cu-Ni were tested in tension at room temperature in various environments. Preliminary results indicate that the tensile fracture strength of about 1400 MPa is not strongly affected by test environments. These results alone do not rule out the possibility that these amorphous alloys may react with moisture during tensile testing. Additional work involving laser desorption spectroscopy will be conducted in order to detect this reaction. Research sponsored by the Laboratory Directed Research and Development Program of the Oak Ridge National Laboratory, U.S. Department of Energy, under contract number DE-AC05-96OR22464 with Lockheed-Martin Energy Research Corporation.
4:20 pm INVITED
SEEBECK PHENOMENON ON AMORPHOUS-CRYSTALLINE INTERFACE AND AMORPHOUS-CRYSTALLINE THERMOCOUPLE: Mikhail V. Finkel, DAATH-Scientific Center, 9926 Haldeman Avenue #36A, Philadelphia, PA 19115; Jim S.-J. Chen, Mechanical Engineering Department, Temple University, 12th & Norris Street, Philadelphia, PA 19122
Thermo-electric Seebeck phenomenon on amorphous-crystalline interface in several alloys is studied. The thermocouples, consisting of amorphous and crystalline parts of the same alloy are proposed and investigated. The amorphous-crystalline transition zone formed by heating of amorphous alloys in heterogeneous temperature field serves as a hot junction. It is shown that this zone could be made as narrow as 10-100 mm. Thermo-Electric Moving Force (TEMF) for thermocouples made from Fe-B, Ni-Fe-Si-B, and Co-Fe-Si-B alloys was measured. TEMF of thermocouple made from Co-Fe-Si-B alloy in its as-cast condition can achieve 8.1 µV/K, and it is constant in the range 293K to 593K. It is shown that relaxation of the amorphous structure affects the TEMF of amorphous-crystalline thermocouple. (Patent is applied)
Room: 330G
Session Chairperson: David J. Srolovitz, Dept. of Materials Science & Engineering, University of Michigan, Ann Arbor, MI 48109-2136
1:30 pm INVITED
INFLUENCE OF THE CRYSTALLOGRAPHIC PARAMETERS OF GRAIN BOUNDARIES ON THEIR ENERGETIC, KINETIC AND CHEMICAL PROPERTIES: E. Rabkin, Wolfgang Gust, Max-Planck-Institut für Metallforschung and Institut für Metallkunde, Seestr. 75, D-70174 Stuttgart, Germany
We review the recent experimental data about the dependence of the grain boundary (GB) energy on the misorientation of adjacent grains and on the inclination of the GB plane. The relationship between inclination dependence of the GB energy and the morphology of faccted twin Gbs in Cu and Ag is demonstrated. The kinetics of development of the faccted morphology at the originally flat twin GB in Cu is studied experimentally. The strong influence of small additions of Bi on the chemical compositions of Gbs in Cu is shown. The effect of atomic ordering on the GB energy is considered. The discontinuous ordering reaction in Fe-50 at.% Co alloy in combination with the analysis of the electron backscattered Kikuchi patterns is used to study the atomic mobility in Gbs in the ordered B2 alloy. It is shown that the low energy special Gbs exhibit also the decreased atomic mobility.
2:10 pm
THE EFFECTS OF GRAIN BOUNDARY MISORIENTATION ON M23C6 PRECIPITATION AND SENSITIZATION IN 304 STAINLESS STEEL: Elizabeth Trillo, L.E. Murr, Department of Metallurgical and Materials Engineering, The University of Texas at El Paso, El Paso, TX 79968
The correlation between grain boundary misorientation and energy has been the subject of study even before Stickler and Vinckier (in 1963) demonstrated that sensitization behavior is related to the energy of different types of individual boundaries in the sensitizing temperature range of 500-850°C. This research goes beyond these types of studies by attempting to uncover the role of grain boundary misorientation on M23C6 precipitation behavior in 304 stainless steel. The four materials utilizaed in this study having differing carbon contents (0.01, 0.025, 0.05, 0.07%C) and were heat treated at 670°C for 10 and 50 hours. In addition, the 10 hour samples were deformed (0, 10, and 20% true strain) to observe simultaneous strain effects. Electrochemical Potentiostatic Reactivation (EPR) tests were performed to characterize the sensitization behavior, and the precipitation behavior was observed through the transmission electron microscope (TEM) at 200kV. A "critical nucleation energy" was found to be in the range of 16 mJ/m2 to 265 mJ/m2 which corresponds to the energies of special boundaries, no precipitation was observed on coherent twin boundaries (#16 mJ/m2). This research supported in part by the Patricia Roberts Harris Fellowship.
2:30 pm
GRAIN BOUNDARY SEGREGATION AND PRECIPITATION EFFECTS ON ENVIRONMENT-INDUCED CRACKING: S.M. Bruemmer, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA
Environment-induced cracking at internal interfaces has long been explained due to local chemistry differences. Widespread use of high resolution analytical techniques (analytical transmission electron microscopy and scanning Auger microscopy) has recently "quantified" this effect by direct correlation's between grain boundary composition and intergranular failure. Examples of this quantification will be presented and critical interfacial compositions identified for various metallic alloys. material susceptibility can often be minimized by controlling segregation and precipitation characteristics at grain boundaries. Compositional anisotropy among internal interfaces, and its effect on cracking, will also be demonstrated and discussed. Work supported by the Office of Basic Energy Sciences, Division of Materials Sciences, U.S. Department of Energy under contract DE-AC06-76 RLO 1830.
2:50 pm
SELECTIVE PRECIPITATION ON GRAIN BOUNDARY: J. Jang, Y.B. Lee*, I.H. Kuk, K.A.E.R.I., P.O. Box 105 Yusong, Taejon, KOREA; *Korea Univ. I Anam-dong, Sungbuk-gu, Seoul, KOREA
Ni-Cr-Fe Alloy (UNS N06690) is being widely used as corrosion resistant tubing material in nuclear power plants and believed beneficial to stress corrosion resistance to have intergranular chromium carbide precipitates (semi-continuously or continuously). Alloys were prepared through VIM and ESR and tubular products were fabricated by pilgering process. Several solution heat treatments were conducted at a relatively rapid heating and cooling rate. Selective precipitation of chromium carbide along grain boundary was observed in this alloy. Even along a single grain boundary carbide precipitates were revealed as very discretely distributed in association with twins. Distribution and orientation relationship of precipitates with grain boundary in association with twins were analyzed through electron microscopy and explained with CSL model.
3:10 pm BREAK
3:30 pm INVITED
ATOMISTIC STUDIES OF SOLUTE-ATOM SEGREGATION AT GRAIN BOUNDARIES IN METALS: SIMULATION AND EXPERIMENTS: David N. Seidman, Northwestern University, Department of Materials Science and Engineering, Evanston, IL 60208-3108
I review our studies of the relationship between the atomic structure of grain boundaries (GB) and solute-segregation in binary metallic alloys. The principal experimental tool utilized to measure segregation is atom-probe microscopy. This is used in conjunction with Monte Carlo techniques (Metropolis algorithm and overlapping distributions MC) to explore the multidimensional GB phase space. Experimentally we determine the five macroscopic degrees of a GB employing transmission electron microscopy and then determine the Gibbsian interfacial excess of solute of the same GB employing atom-probe microscopy. The simulational approach uses lattice statics calculations to determine initially the lowest energy GB structures and then MC simulations to calculate their Gibbsian excesses. The effects of both the macroscopic and microscopic degrees of freedom are studied. It is demonstrated that the Gibbsian excess is a complicated function of both the macroscopic and microscopic degrees of freedom. Also a GB's atomic structure determines the partition between segregation at dislocation's cores and in the elastic stress fields of GB dislocations. It is concluded that none of the geometric criteria discussed in the literature is capable of predicting the propensity for GB segregation. This research is supported by the National Science Foundation, Division of Materials Research.
4:10 pm
INTERFACE ENGINEERING FOR SINTERING CORDIERITE GLASS-CERAMIC COATINGS ON MOLYBDENUM: Thomas A. Kuhr, Guo-Quan Lu, Dept. of MSE, VPI & SU, Blacksburg, VA 24061
An economical technology for laying down thick ceramic coatings on a metal substrate is to tape-cast a ceramic slurry on the metal surface followed by binder burn-out and sintering. We used the technology to produce cordierite coatings on molybdenum for use as electrostatic wafer chucks. A critical issue in the production was adhesion between the two materials after the coatings were sintered at temperatures ranging from 900°C to 1000°C. To solve the problem, thin metallic interlayers were deposited by electroplating on Mo surface before tape-casting. We will discuss the selection and processing of several interlayer materials that significantly enhanced adhesion between the ceramic coating and metal substrate.
4:30 pm
ADVANCE IN STUDY OF NON-EQUILIBRIUM SEGREGATION ON INTERFACE: Xinlai He, Huaiyang Cui, Department of Materials Physics, University of Science and Technology Beijing, 100083, Beijing, China
Equilibrium segregation of solute on interface has been recognized quite a long time. In recent years, there are more interests in non-equilibrium segregation, for example, the boron non-equilibrium segregation on grain boundaries during cooling, annealing and pre-strained treatment has been studied systematically. In 1991, by means of Particle Tracking Autoradiograph (PTA) technique, it was found that boron non-equilibrium segregates on moving boundaries during recrystallization in low carbon steels (X.L.He). In Fe-3%Si alloy with b.c.c. structure, it was observed that no detectable boron segregation on boundaries during continuous cooling and annealing but a stronger boron segregation on moving boundaries during recrystallization (S.H.Zhang, 1992). Recently, in Fe-30%Ni with f.c.c. structure, a significant segregation of boron was shown on recrystallizing boundaries while segregation of boron was hardly observed on primary grain boundaries during recrystallization at high temperature (H.Y.Cui, 1995). These investigations indicate that three characteristics relate with the moving boundary segregation: (1)the segregation accompanied with motion of boundary (2)the degree of the segregation was higher than that at thermodynamical equilibrium (3)the velocity of moving boundary and addition of alloy elements influenced on the segregation process. In order to explain the phenomenon, based on the interaction between dislocations and the moving boundaries during recrystallization, a dislocation relaxation and widening grain boundary mechanism of solute segregation on moving boundaries was proposed.
4:50 pm
MOLECULAR-DYNAMICS SIMULATION OF GRAIN BOUNDARY MIGRATION: B. Schonfelder, S.R. Phillpot, D. Wolf, Materials Science Division, Argonne National Laboratory, Argonne, IL 60439; G. Gottstein, Institute fur Metallkunde und Metallphysik, RWTH Aachen, D-52056 Aachen
Molecular-dynamics simulations are used to induce the migration of a flat (001) twist grain boundary (GB) by anistropically straining a bicrystal of Cu at high temperatures. The observed migration process has the following three characteristic features: (1) the motion of the GB is viscous and continuous; (2) the observed drift velocity is proportional to the applied driving force and thermally activated; (3) the activation energy for migration is significantly lower than either that for GB diffusion or that for self-diffusion in molten Cu. The atomic-level mechanism of grain-boundary migration is discussed. *Work supported by the US Department of energy, BES-Materials Science under Contract No. W-31-109-Eng-38.
Room: 330F
Session Chairpersons: P. Grant, University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH, UK; M.A. Iman, US Navy Naval Research Lab, Materials Science & Technology Div., Washington, DC 20375
2:00 pm
FABRICATION OF TiNi INTERMETALLIC COMPOUNDS BY SELFPROPAGATION HIGH-TEMPERATURE SYNTHESIS PROCESS (SHS): Suk-Kwon Ko, Joong-Chai Jung, Jong-Hyeon Lee, Chang-Whan Won, Rapidly Solidified Materials Research Center(RASOM), Chungnam National University, Yuseong, Taejon, 305-764 Korea
TiNi intermetallic compounds were manufactured by the self-propagating high-temperature synthesis process. The effects of chemical composition(Ni/Ti=0.5 ~2.0 molar ratio), compaction pressure and preheating temperature on the reaction were investigated. As the molar ratio of Ni, compacting pressure and preheating temperature were increased, the combustion temperature and its velocity were increased. In the every mole ratio of M, without preheating, secondary phases such as Ti2Ni, TiNi3, Ti3Ni4 as TiNi were found in the products according to the XRD analysis. At the same condition, the products prepared by of 200 were TiNi single phases by perfect reaction. Hence, the reasons to form the different phases during the reaction and the forming mechanism of TiNi for combustion reaction were discussed.
2:20 pm
RAPID SYNTHESIS OF NANOSTRUCTURAL INTERMETALLICS AND THEIR BULK MECHANICAL PROPERTIES: S.M. Pickard, A.K. Ghosh, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2136
A PVD process has been developed to produce bulk intermetallics at high rate by direct vacuum evaporation. Independent elemental sources are directly heated using 5kW electron beams and the evaporate is deposited as a nanolaminated (layered) structure at a rate of 1-mm/minute on a rotating substrate. Insitu reaction occurs on the heated substrate to produce a homogenous nanograined bulk intermetallic deposit. The deposit can be further thermomechanically processed to produce optimum mechanical properties. TIA1, NiA1 binary and ternary alloy systems has been chosen for initial evaluation of potential mechanical property and processing advantages of bulk PVD. Both relatively thin 9140-180mm) and relatively thick (2.3) mm) layers of intermetallic alloys, have been formed. Hardness characterisation of the -deposited film shows a Vickers hardness value which is 2-3 times higher than the expected value for an as cast alloy. An initial flow stress of 700-800 MPa has been observed for the T1A1, which is higher than that of conventional cast material, with delimitation failure of the layered material. Tests on the bulk material using 3-Point banding indicate and rupture strength of 450-500MPa for Ti-30a% A1, with linear-elastic loading response to failure, indicative of extrinsic defect controlled strength. Elevated temperature tensile tests are being conducted on the intermetallics to determine rate sensitivity.
2:40 pm
DEVELOPMENT OF Nb3Al Mo and Nb3Al TiCr BASED ALLOYS: E. Passa, G. Shao, P. Tsakiropoulos, Dept. of Materials Science and Engineering, University of Surrey, GU2 5XH, UK
Abstract not available.
3:00 pm
COMPRESSIVE STRENGTH AND FATIGUE PROPERTIES OF BE-A1 ALOYS: R. Schneeberger, B. Bavarian, School of Engineering and Computer Science, California State University at Northridge, Northridge, CA 91330; R. Hayes, Metals Technology, Inc. 19080 Nordhoff St, Northridge, CA 91330
Both 40 and 62 wt% beryllium compositions were evaluated for ambient and elevated temperature compressive strength at low and high strain rates. Data indicated a strong influence of beryllium percentage along with an increase of yield point for fast strain rates of 0.5-3 in/in/minute. Fatigue properties of a ternary Be-A1-Ag cast and extruded material were determined for full reversal and standard tension fatigue conditions. Typical S-N curve behaviour including endurance limit was observed.
3:20 pm
CREEP BEHAVIOUR OF TWO BERYLLIUM-ALUMINIUM ALLOYS: R. Schneeberger, B. Bavarian, School of Engineering and Computer Science, California State University, Northridge, 18111 Nordhoff St, Northbridge, CA 91330; R. Hayes, Metals Technology, Inc 19080 Nordhoff St, Northridge, CA 91330.
Creep testing performed on 40 and 62 wt% beryllium compositions of a power metallurgy composite alloy at several elevated temperatures indicated a dependence of steady state creep rates and times to rupture on beryllium content, test direction, stress, and test temperature. A stress exponent of 8.5 for 40% beryllium and 10 for 62% beryllium was obtained form tests at 550 degrees F 630 degrees F. Activation energies for creep were somewhat higher than for self-diffusion in either pure metal, and exhibited significant anisotropy.
3:40 pm BREAK
4:00 pm
BERYLLIUM ALUMINUM ALLOY DEVELOPMENT FOR INVESTMENT CASTING: Nancy F. Levoy, Brian J. Smith, Nuclear Metals Inc., 2229 Main St., Concord, MA 01742
Be-Al alloys are unique, light weight, composite alloys that combine high specific stiffness and substantial strength with good ductility and toughness. This combination of properties makes these alloys attractive for many high performance aerospace applications. Due to the inherent problems associated with casting Be-Al alloys, processing of these alloys has previously been restricted to rolling or extrusion of prealloyed powder compacts. Beralcast(363 is a new cast in-situ composite alloy containing 65 wt% Be that is formed by the controlled solidification processing of a higher-order Be-Al alloy. This paper will describe the development of the Beralcast( family of alloys specifically for production of near net shape components via investment casting.
4:20 pm
OXIDATION BEHAVIOUR OF Nb3A1-xMo ALLOYS: E. Passa, G. Shao, P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, England, UK
Phase selection and microstructural refinement in Nb-17A1-xMo (x=20,30,40) alloys can be controlled via alloy design and solidification processing route. The formation of ordered (B2) or disordered (A2) phases in the as cast microstructures of cold hearth processed ingots and cold hearth melt overflow processed ribbons will be briefly reviewed. DSC and TG studies of the ingots and ribbons will be discussed with emphasis on the oxidation behaviour of the alloys. It will be shown that additions of Mo can improve the oxidation behaviour of Nb3A1.
4:40 pm
GRAIN SIZE CONTROL AND PROPERTIES OF TiAl-BASED ALLOYS: S. Davey, P. Gouma, A. Godfrey, D. Hu, P.A. Blenkinsop, M.H. Loretto, IRC in Material for High Performance Applications, The University of Birmingham, Edgbaston B15 2TT, UK
The production of TiA1-based alloys with small grain sizes has been approached in two distinct ways. Firstly, by addition of B-containing compounds to the melt and secondly via atomisation and subsequent processing. These route coupled with hot extrusion, allow control of the microstructure of these alloys so that a wide range of properties can be obtained. Results for several different alloys will be presented and the influence of composition on control of microstructure and hence of properties will be illustrated.
5:00 pm
MICROSTRUCTURE AND MECHANICAL PROPERTIES OF GAMMA TITANIUM ALUMINIDE STRIP: Gopal Das, Pratt & Whitney, P.O. Box 109600, West Palm Beach, FL-33410-9600
Thin gamma titanium aluminide (Ti-45A1-2Cr-2Nb at.%) series, 20 mils thick, were produced by the melt overflow rapid solidification technology (MORST) process. The microstructure resulting from heat treatments was studied by a combination of optical, X-ray, SEM and TEM methods. Transition temperatures including the alpha transits temperature were determined by DTA. Textures of gamma TiA1 strips were studied on as-cast and heat treated specimens. The microhardness was measured for specimens subjected to different heat treatments. Tensile properties of heat treated specimens were determined at RT-760°C along the strip growth direction and perpendicular to it. The material failed in a brittle manner at RT for both orientations. It started to yield at 650°C and at 760°C, it failed in a ductile manner. The strain-to-failure along the direction perpendicular to strip growth direction was poor. Deformation microstructure was analysed by TEM and fractographs were studied. Results will be compared with those of investment cast and wrought gamma titanium aluminised. This work was supported by NASA LeRC, Cleveland, OH under Contract No. NAS3-26385.
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