Effect of carbon interlayer on oxidation behavior of C/SiC composites witha coating from room temperature to 1500 degrees C

Two C/SiC composites were prepared by AP-CVI and LP-CVI method. Oxidation t ests of the C/SiC composites and a CIC composite with a coating were conduc ted in dry air from room temperature to 1500 degreesC for 5 h. A continuous series of empirical functions relating weight change after 5 h oxidation t o temperature was found to fit the test results of the three composites qui te well. Oxidation behavior of the three composites could be described by a continuous function over the full temperature range. The SiC matrix made t he coating cracking temperature of the AP-CVI C/SiC being 100 degreesC lowe r than that of the C/C, and the PyC interlayer with a different thickness m ade the coating cracking temperature and matrix cracking temperature of the LP-CVI C/SiC being 100 degreesC lower than those of the AP-CVI C/SiC. Ther e was an optimum thickness of the PyC interlayer for improving the oxidatio n 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 acti vation energies of reaction for the C/C and C/SiC composites varied little. Above the coating temperatures. the Si-W layer had higher activation energ y for diffusion than the Si-Zr layer. (C) 2001 Elsevier Science B.V. All ri ghts reserved.