Oxidation Resistant Coating of TiC-SiC System on C/C Composite by Chemical Vapor Deposition

Oxidation resistance and oxidation mechanism of a carbon/carbon composite (C/C composite), on which inner layer of TiC and outer of SiC were coated by chemical vapor deposition, were investigated. The CVD conditions used were, TiCl4-CH4-H2 or SiCl2-CH4-H2 system, deposition temperatures ranging from 1050° to 1350°C and total gas pressures ranging from 40 to 100 Torr. TiC coating was 7-50μm thick and SiC coating was 70-270μm thick. The oxidation resistance of the coated C/C composite was estimated from room temperature to 1300°C in air using several heating programs. In two layers-coating, the number of thermal cracks which generated on the surface of the coated layer decreased and the oxidation resistance improved depending on the thickness ratio of TiC to SiC coating as compared with SiC monolayer-coating. It is recognized that large compressive stress generated in the outer layer of SiC and TiO2 (rutile) formed along the thermal cracks in the coated layers after the oxidation.