Effect of carbon interlayer on oxidation behavior of C/SiC composites with a coating from room temperature to 1500°C

Two C/SiC composites were prepared by AP-CVI and LP-CVI method. Oxidation tests of the C/SiC composites and a C/C composite with a coating were conducted in dry air from room temperature to 1500°C for 5 h. A continuous series of empirical functions relating weight change after 5 h oxidation to temperature was found to fit the test results of the three composites quite well. Oxidation behavior of the three composites could be described by a continuous function over the full temperature range. The SiC matrix made the coating cracking temperature of the AP-CVI C/SiC being 100°C lower than that of the C/C, and the PyC interlayer with a different thickness made the coating cracking temperature and matrix cracking temperature of the LP-CVI C/SiC being 100°C lower than those of the AP-CVI C/SiC. There was an optimum thickness of the PyC interlayer for improving the oxidation resistance of C/SiC composites. The thicker the PyC interlayer, the lower the transition temperature, the higher the mechanical properties, but the larger the maximum weight loss. Below the transition temperatures, the activation energies of reaction for the C/C and C/SiC composites varied little. Above the coating temperatures, the Si–W layer had higher activation energy for diffusion than the Si–Zr layer.