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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
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