Effect of thick SiC interphase layers on microstructure, mechanical and thermal properties of reaction-bonded SiC/SiC composites Original Research Article

Two types of thick (∼3 μm) SiC interphase layers with new concept between fiber and matrix were prepared; the porous SiC interphase by polymer impregnation and pyrolysis (PIP) treatment, and the two-ply interphase consisting of carbon and β-SiC by chemical vapor deposition (CVD) treatment. The SiC/SiC composites with these new interphase layers were fabricated by reaction bonding (RB) process. The effect of these interphase layers on microstructure, mechanical and thermal properties of SiC/SiC composites was investigated. The densities of SiC/SiC composites in this study attained to relative densities of 92%. The microstructural observation revealed that the two-ply interphase by CVD treatment prevented the fibers from reacting with the melting Si during RB process. This effect leads to the fiber pull-out phenomenon in the specimen with the two-ply interphase, and therefore this specimen exhibited non-catastrophic failure behavior and high bending strength. The thermal conductivities of specimens in this study were much higher than those of the composites by conventional process. The relative density and thermal conductivity of SiC/SiC composites in this study are high enough to attain the assumed design criteria for fusion reactors.