HIGH-TEMPERATURE INTERFACIAL REACTIONS OF SIC WITH METALS

Interfacial reactions of SiC with selected high temperature metals have been studied at temperatures between 1000 and 1200-degrees-C for various times. The metals include Nb, a strong carbide former, Ni, Co, and stainless steel. Reactions of the metals with SiC in this temperature range were extensive; various metal silicides, metal carbides, ternary metal-silicon-carbides, and unreacted carbon were formed as layered reaction products in the reaction zones. In some systems, massive or localized interfacial melting was observed as a result of metal-silicide formation. The occurrence of interfacial melting resulted in the formation of nonplanar interfaces and fracture beneath the SiC interface, while planar interfaces were generated in the absence of interfacial melting. Reactions of SiC with Ni, Co, and stainless steel resulted in the formation of clustered carbon precipitates with modulated or randomly scattered characters. The nature of the C precipitation behavior depends upon the specific metal system and is a function of distance from the reaction interfaces. In contrast, no unreacted carbon was found in the SiC/Nb system. In all cases, the decomposition of SiC was sluggish. The rate limiting step for the metal/SiC reactions is discussed. Discontinuous decomposition of SiC is proposed to explain the modulation of C precipitates. The effect of interfacial melting on the mechanical properties of metal/SiC composites is addressed.