Formation of MoSi2-SiC composite coatings by chemical vapor deposition of Si on the surface of Mo2C layer formed by carburizing of Mo substrate

The formation process of MoSi2/*b-SiC composite coating by chemical vapor deposition of Si on the Mo2C layer formed in advance on a Mo substrate by a carburizing process was investigated using optical microscopy, field-emission scanning electron microscopy cross-sectional transmission electron microscopy and X-ray diffraction. The composite coating was composed of equiaxed MoSi2 grains with average size of 300 nm and the *b-SiC particles with average size of 92 nm, which were mostly located at the grain boundaries of MoSi2. The morphology of *b-SiC particles was oblate-spheroidal shape and volume percentage was approximately 19.3%. The number of cracks in the composite coating was smaller than that for the monolithic MoSi2 coating by the reduced mismatch of thermal expansion coefficient with the Mo substrate. The formation mechanism of MoSi2/*b-SiC composite coating was suggested on the basis of microstructure observation.