Oxidation and Thermal Shock Resistance of SiC Compositionally Graded Carbon Fiber-Reinforced Carbon Composite Materials

Abstract

SiC compositionally graded carbon fiber-reinforced carbon composite(CFC) materials, which were composed of CVD SiC, SiC/CFC layer and CFC substrate, were fabricated, and their oxidation and thermal shock resistance were studied by weight loss method. It was found that both CVD SiC and SiC/CFC layer were effective to increase the oxidation resistance, and so did the SiC/C layer to the thermal shock resistance. The oxidation resistance of CFCs with CVD SiC increased with increasing the ratio of thermal expansion coefficient(CTE) of substrate to that of CVD SiC, and the effect of SiC/CFC layer on improvement of thermal shock resistance became maximum when the difference in CTE was minimal. It was also observed that the direction of surface cracks in CVD SiC was mostly normal to the direction of the smallest CTE on each substrate. These results can be explained in terms of tensile or compressive stresses in CVD SiC at a cooling period of a thermal shock test or that of fabrication.