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Session Chairpersons: Prof. Leon L. Shaw, Dept. of Metallurgy and Materials Engineering, University of Connecticut, Storrs, CT 06269; Dr. David E. Alman, U.S. Department of Energy, Albany Research Center, Albany, Oregon 97321
8:30 am INVITED
COMMERCIAL PROCESSING OF METAL MATRIX COMPOSITES: W.C. Harrigan, Jr., Alyn Corporation, P.O. Box 16249, Irvine, CA 92623
Discontinuously reinforced metal matrix composites are a class of materials that exhibit a blending of properties of the reinforcement and the matrix. The reinforcement can be ultrahigh strength whiskers, short or chopped fibers or particles. Each of the reinforcements have property or cost attributes which dictates use in a given situation. Commercial producers have concentrated on composites with particles because of cost issues. These composites have been made by a number of manufacturing techniques. These include powder metallurgy, casting and spray deposition. The technique that has consistently produced high property composites has been powder metallurgy. Recent work in this area has been on refining techniques that offer lower cost manufacturing. Scale-up of facilities to produce vacuum hot pressed composite billets has been completed with the help of DOD funds through a Defense Procurement Act Title 3 program. Several companies have been working with a CIP-Sinter process to produce lower cost billet stock. This talk will review the recent cost reduction programs and the implications of these programs on the commercialization of these composites.
SYNTHESIS AND MICROSTRUCTURAL CHARACTERIZATION OF NiAl-Al2O3 FUNCTIONALLY GRADIENT COMPOSITE: D. Padmavardhani, A. Gomez, R. Abbaschian
Reactive Hot Compaction of Ni and Al powders in which one or both of the powders were preoxidized was carried out to fabricate functionally gradient composite (FGC) of NiAl with in-situ Al2O3 reinforcement. The FGC consisted of five layers with a variation of alumina content from less than 4% on one side to about 52% on the other. The gradient in the composition was obtained by stacking different powder mixtures of desired compositions. The alumina formed a continuous network around the NiAl during the compaction process. The effects of powder oxidation and heating rate on the formation of NiAl, Al3Ni and Al3Ni2 will be discussed on the basis of the DTA and microstructural studies.
POWDER METAL-MATRIX COMPOSITES: SELECTION AND PROCESSING: M.J. Tan and Zhang Xi, School of Mech. & Prod. Eng., Nanyang Technological University, Nanyang Avenue, Singapore 2263
There has been growing interest in the last decade in the development of metal-matrix composites (MMCs) for the aerospace industries because of their attractive physical and mechanical properties, and enhanced elevated temperature capabilities. However, some of the fabrication techniques (e.g. using powder metallurgy) for this new class of MMCs are hampered by (i) the poor distribution of the reinforcements, and (ii) the limited room temperature ductility of the composites and hence formability. This presentation reports work done to address the above two problems by (i) an analysis based on size difference of matrix and reinforcement particles, taking into account the processing parameters, and (ii) introducing an innovative way of extruding brittle composites to increase its formability. By mainly considering the size difference effect of matrix powder and reinforcement particle, a critical value of reinforcement size is proposed to predict whether a uniform distribution of reinforcement is possible in powder metallurgy of particulate reinforced metal matrix composites. A uniform distribution of reinforcement could be expected only when the reinforcement size dT is not less than a critical value dC which is a function of reinforcement size dr and volume fraction Vf and reduction ratio of secondary processing, R. In extrusion, a Front Pad Extrusion Method was used to avoid fir-tree cracking on the surfaces of extrudates, especially the brittle metal composites. By this method, the MMCs were successfully extruded without any surface cracking, and all the extrudates were found to be covered by a thin layer of the pad material. This was illustrated using a schematic flow pattern of the extrudate and pad material in the dead metal zone during extrusion. Furthermore, decreased pressure requirements were necessary for extrusions using the front pad extrusion method.
CHARACTERIZATION OF Cu/Cu2O COMPOSITES PRODUCED BY ELECTROCHEMICAL DEPOSITION: F.S. Miller, D.C. Van Aken, Dept. of Metallurgical Engineering, E.W. Bohannan and J.A. Switzer, Dept. of Chemistry, The University of Missouri, Rolla, MO 65409
Nanocrystalline composites of copper metal and cuprous oxide were produced at room temperature by electrodeposition from an alkaline copper lactate solution. The phase composition can be continuously changed by controlling the cathode current density. At current densities below 0.1 mA/cm2 nearly pure cuprous oxide is produced and at 2.5 mA/cm2 nearly pure copper is produced. At intermediate current densities composite structures are formed. These thin films show unique optical properties that are related to the 10 to 20 nm grain diameter of Cu2O produced by electrodeposition. During deposition of the composite material the electrode potential oscillates spontaneously at fixed current density. Microstructural information obtained by TEM indicates the formation of a metastable compound that may be related to the electrode potential oscillations. This work has been funded in part by the National Science Foundation under contract DMR-92-02872.
10:15 am BREAK
SPATIALLY VARIED INTERFACES AS A PROBE OF INTERFACE FAILURE MECHANISMS IN Ti-MATRIX COMPOSITES: Benji Maruyama, Wright Laboratory/NIST, 2230 10th ST STE 1, WPAFB, OH 45433; Douglas B. Gundel, Systran Co., Inc., 4126 Linden Ave., Dayton, OH 45432; Sunil Warrier, Universal Energy Systems, 4401 Dayton-Xenia Rd., Dayton, OH 45432
Spatially Varied Interfaces is a design concept for composite synthesis whereby the interface mechanical response is tailored to the composite needs by varying the interface properties in patterns of weak and strong areas. In the SiCf/Ti-alloy system, random patterns have been fabricated, along with bands, longitudinal stripes and helices. To be presented are results of transverse tensile and longitudinal fatigue crack growth experiments where selected regions of the interface are systematically strengthened or weakened, and the perturbation of the failure process is measured to gain a better understanding of the stress states and interface failure mechanisms. This work was conducted in the Metals & Ceramics Division of the Materials Directorate at Wright Laboratory.
THE PROPERTIES AND MICROSTRUCTURE OF Al-BASED COMPOSITES REINFORCED WITH CERAMIC PARTICLES: M. Samgorinski, S. Grenier, A. Cavasin, T. Brzezinski, G. Kim, P.G. Tsantrizos, PERMA, 1744 William, Montreal, Quebec, Canada H3J 1R4
Al-based composite materials which were produced by Powder Metallurgy (PM) and Vacuum Plasma Spraying (VPS) are presented in this article. The objective was to produce materials with low coefficients of thermal expansion (CTE), tailored to approach that of steel (13x10-6 K-1), and to improve the mechanical properties of the matrix. Composite materials based on Al are used in different fields where weight and thermal stability are key requirements, such as aerospace components, electronic packaging, high precision instrumentation, and automobile engine components. The nature, size and the relative quantities of the different reinforcing phases were considered in calculations involving the optimization of the main characteristics of the composites. Fine dispersed powders (5-20 µm) of Si3N4, AlN, TiB2, Al2O3, 2Al2O3·2SiO2, B4C and SiC were used as the strengthening phases, while pure Al, 6061 and Al-Si alloy were used as the matrix. The dimensional and relaxation stability were investigated for several composites. The influence of plastic deformation and heat treatment on the structure and properties of VPS deposited composites were also investigated. It was found that a combination of plastic deformation and heat treatment (annealing or quenching with aging) increased the mechanical properties, on average, by a factor of 1.5 to 2.
EFFECT OF MICROSTRUCTURAL ARRANGEMENT ON THE MECHANICAL PROPERTIES OF Ni/a-Al2O3 METAL-CERAMIC COMPOSITES: E.D. Rodeghiero, E.P. Giannelis, Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853-1501
The degree to which a ductile metallic phase can be used to toughen brittle ceramic materials is highly dependent on the microstructural dispersion of the metallic constituent, the metal's aspect ratio and characteristic size, and the amount of constraint imposed on the metal by the ceramic matrix. This talk will focus on the effect of these parameters on the mechanical properties, and in particular the fracture toughness, of Ni/a-Al2O3 composites prepared through both in-situ and conventional approaches. The composites discussed will vary from particulate toughened cermets prepared from chemical and/or powder approaches to complex, anisotropic materials containing Ni foils or fibers. Through evaluation of the experimental evidence and theoretical models, the optimum microstructural arrangement of the Ni phase in the a-Al2O3 matrix will be presented.
FRACTURE TOUGHNESS OF SILICON CARBIDE PARTICULATE REINFORCED ALUMINUM ALLOY COMPOSITES: A.B. Pandey, Materials Directorate Wright Laboratory, WL/MLLM, Wright-Patterson AFB, OH 45433 and Systran Corporation, 4126 Linden Avenue, Dayton, OH 45432; B.S. Majumdar, UES, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432; D.B. Miracle, Materials Directorate Wright Laboratory, WL/MLLM, Wright-Patterson AFB, OH 45433
This study is part of an overall effort to optimize the strength toughness combination in discontinuously reinforced aluminum (DRA) composites for application in aerospace structures. Two different matrix alloys were considered, namely Al-2009 and Al-7091, to represent intermediate and high strength matrices, respectively, and they were reinforced with SiC particles of 4.9 and 10.4 mm. The powders were consolidated directly via blind-die extrusion, thus reducing processing time significantly from conventional vacuum hot pressing techniques. Fracture toughness tests were performed with precracked bend bars, and the J-resistance curves were determined. Damage modes were evaluated in both tensile and fracture toughness samples, in an attempt to understand the factors that may provide intrinsic toughness improvement without significant loss of strength. The mechanical properties and damage modes were compared with control samples of unreinforced materials fabricated using an identical processing route as the composites. Data from these control materials provided an added insight that has often lacked in past fracture toughness studies. This work was performed at Materials Directorate Wright Laboratory, Wright-Patterson AFB, OH.
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