Fabrication of a Functionally Gradient Material of TiC-SiC System by Chemical Vapor Deposition

Abstract

Oxidation-resistant coating using chemical vapor deposition on continuous fiber reinforced ceramics having lower thermal expansion coefficient (α) than the coated layer (SiC) was studied. A SiC-fiber reinforced TiC matrix composite (SiC/TiC composite, α=5.6×10^-6K^-1) was used as a substrate and the TiC-SiC system was chosen as a coating. The CVD was carried out in TiCl₄-SiCl₄-CH₄-H₂ system at deposition temperature of 1350°C and total gas pressure of 60 Torr. Compositionally gradient TiC-SiC layers were formed by stepwise change of the Ti/(Ti+Si) ratio in the feed gas. Peeling occurred along the edges of the coating in the case of SiC coating, but it did not occur at all in a TiC-SiC coating with an optimum gradient composition. These results agreed with the thermal stress analysis using F. E. M.