Oxidation Behavior of C/SiC Composite with CVD SiC-B4C Coating in a Wet Oxygen Environment

A two-layered self healing coating with a B4C internal layer and a SiC external layer is prepared on C/SiC composite by chemical vapor deposition (CVD). Microstructure and component of the coating was analyzed by SEM, EDS, and XRD. Oxidation behavior of SiC-B4C coated C/SiC composite was compared with SiC-SiC coated C/SiC in an environment of P-H2O/P-O2/P-Ar 14/8/78 at 700 degrees C, 1,000 degrees C and 1,200 degrees C for 100 h, respectively. It is demonstrated that the SiC-B4C coating is more efficient to protect the composite from oxidation than SiC-SiC coating below 1,000 degrees C due to the self healing behavior. After oxidized at 700 degrees C for 100 h, the residual flexural strength of SiC-B4C coated C/SiC is about 86%, and that of SiC-SiC coated is about 64%. While after oxidized at 1,200 degrees C, the former is about 86% and the later is about 89%. This is due to the enhanced evaporation of B2O3 at higher temperature.