Temperature dependence of the oxidation resistance of SiC coated carbon/carbon composite

Abstract

The oxidation of SiC coated carbon/carbon composite (C/C) is studied and correlated to the surface stress conditions. Based on the calculation, the thermal stress induced from the difference in coefficient of thermal expansion (CTE) between the C/C substrate and the SiC coating is as large as a few hundred MPa when the variation of processing temperature is more than 1200 °C, which is enough for the occurrence of microcracks in the SiC coating layer. The analysis of stress distribution reveals that a lower reaction sintering temperature and a thicker SiC coating layer are preferred to avoid the occurrence of microcracks. But cracking seems inevitable if the reaction sintering of the SiC layer is processed above 1400 °C to produce a SiC coating followed by cooling to room temperature. An in situ measurement of the oxidation weight loss of coated C/C demonstrates that the abnormal variation of oxidation rate with respect to the test temperature is consistent with the prediction of closure of the stress-induced microcracks in the SiC coatings.