Oxidation behavior of C-SiC composites with a Si-W coating from room temperature to 1500 degrees C

Oxidation tests of carbon fiber reinforced silicon carbide composites with a Si-W coating were conducted in dry air from room temperature to 1500 degr eesC for 5 h. A continuous series of empirical functions relating weight ch ange to temperature after 5 h oxidation was found to fit the test results q uite well over the whole temperature range. This approach was used to inter pret the different oxidation mechanisms. There were two cracking temperatur es of the matrix and the coating for the C-SIC composite. Oxidation behavio r of the C-SIC composite was nearly the same as that of the coated C-C comp osite above the coatings cracking temperature, but weight loss of the C-SiC composite was half an order lower than that of the coated C-C composite be low the cracking temperature. As an inhibitor, the SiC matrix increased the oxidation resistance of C-SiC composites by decreasing active sites availa ble for oxidation. As an interfacial layer, pyrolytic carbon decreased the activation energy below 700 degreesC. From 800 degreesC to 1030 degreesC, u niform oxidation took place for the C-SiC composite, but non-uniform oxidat ion took place for the coated C-C composite in the same temperature range. The Knudsen diffusion coefficient could be used to explain the relationship between weight loss and temperature below the coating cracking temperature and the matrix cracking temperature. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.