SOLID-STATE REACTIONS OF SIC WITH CO, NI, AND PT

Solid state reactions between SiC ceramics and Co, Ni, and Pt metals have been studied at temperatures between 800 and 1200-degrees-C for various times under He or vacuum conditions. Reactions between the metals and SiC were extensive above 900-degrees-C. Various metal silicides and carbon precipitates were formed in layered reaction zones. Interfacial melting was also observed at certain temperatures; teardrop-shaped reaction zones, porosity, and dendritic microstructure resulting from melting/solidification were evident. The metal/ceramic interfaces exhibited either planar or nonplanar morphologies, depending upon the nature of the metal/ceramic reactions. Concave interfacial contours were observed when interfacial melting occurred. By contrast, planar interfaces were observed in the absence of interfacial melting. In all cases, the decomposition of SiC was sluggish and may serve as a rate limiting step for metal/ceramic reactions. Free unreacted carbon precipitates were formed in all the reaction zones and the precipitation behavior was dependent upon the metal system as well as the location with respect to the SiC reaction interface. Modulated carbon bands, randomly scattered carbon precipitates, and/or carbon-denuded bands were formed in many of the reaction zones, and the carbon existed in a mixed state containing both amorphous and graphitic forms.