Rapid heat treatment to improve the thermal shock resistance of ZrO2 coating for SiC coated carbon/carbon composites

ZrO2 coating was prepared on the surface of SiC coated C/C composites by supersonic plasma spraying. Some defects, such as voids and micro-cracks, were observed on the surface of ZrO2 coating after plasma spraying. A novel heat treatment method conducted by oxyacetylene torch was proposed. Through adjusting the gas fluxes of O2 and C2H2, heat treatment temperature can be attained to the melting point of ZrO2 (about 2700 °C) rapidly, which was expected to eliminate the defects formed in the plasma spraying. Surface roughnesses of the ZrO2 coating before and after heat treatment were 23.14 and 14.39 μm, respectively. Heat treatment smoothed the rough surface of the as-sprayed ZrO2 coating and eliminated the defects (voids and micro-cracks) efficiently. After 8 thermal cycles from 2000 °C to room temperature under oxyacetylene torch, the ZrO2 coating without heat treatment was peeled off with the exposure of needle-like carbon fibers. In contrast, the ZrO2 coating with heat treatment was uniform and the coating thickness remaining unchanged.