High-temperature interactions of refractory metal matrices with selected ceramic reinforcements
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I.
INTRODUCTION
MANY proposed
aerospace systems require low-density materials with substantially improved high-temperature mechanical properties and oxidation resistance. Composite materials based upon metal matrices with ceramic reinforcements offer such potential. In order to understand the interaction of metallic matrices with ceramic reinforcements, it is necessary to focus on the metal/ ceramic interface. From a structural viewpoint, this interface controls the transfer of load between a metallic matrix and its ceramic reinforcement. The particular type of bonding at the interface will determine the shear strength and will thereby influence the mechanical properties of a composite. Ideally, such an interface should be a mechanical continuum, i.e., one that has atomic bonding across the interface, but one which is also a chemical discontinuum, implying no possible interdiffusion between the matrix and the reinforcement. In most practical situations, however, a chemical continuum exists across this interface, resulting in compound formation at the interface and some loss in mechanical strength, tll The design of heterogeneous, composite metal/ ceramic materials is limited by the lack of understanding of fundamental interaction mechanisms between metal matrices and ceramic reinforcements, as well as by a paucity of useful compatibility data. In particular, a thorough understanding of the mechanisms and the nature of interactions between metallic matrices and ceramic re-
A. JOSHI, Senior Staff Scientist, Research and Development Division, H.S. HU, Staff Scientist, Research and Development Division, L. JESION, Senior Associate Materials Engineer, Missile Systems Division, and J. WADSWORTH, Manager, Metallurgy Department, Research and Development Division, are with Lockheed Missiles & Space Company, Palo Alto, CA 94304. J.J. STEPHENS, formerly with Lockheed Research and Development Division, is Senior Member of Technical Staff, Sandia National Laboratories, Albuquerque, NM 87185. Manuscript submitted January 2, 1990. METALLURGICALTRANSACTIONSA
inforcements at high homologous temperatures is needed in order to be able to establish a scientific basis for the future selection of metal/ceramic systems. Matrix/reinforcement systems may be separatedt21 into three different classes. The first, "class I," is that in which the reinforcement and matrix are mutually nonreactive and insoluble at either processing or service temperatures. These systems include classic dispersionstrengthened metals such as Ni-ThO2 or Cu-AI203; in such systems, the ceramic reinforcement is usually incoherent with respect to the metallic matrix, resulting in relatively poor bonding across the interface. The second, "class 11,~ is that in which the reinforcement and matrix are mutually nonreactive but have mutual solubility. Typically, these systems include eutectics, i.e., systems in which the matrix and the reinforcement are soluble as liquids above the eutectic temperature but are reasonably nonreactive as solids below the eutectic temperatu
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