Ultra-High-Temperature Ceramic HfB2-SiC Coating for Oxidation Protection of SiC-Coated Carbon/Carbon Composites

To protect the carbon/carbon (C/C) composites from oxidation, an outer ultra-high-temperature ceramics (UHTCs) HfB2-SiC coating was prepared on SiC-coated C/C composites by in situ reaction method. The outer HfB2-SiC coating consists of HfB2 and SiC, which are synchronously obtained. During the heat treatment process, the formed fluid silicon melt is responsible for the preparation of the outer HfB2-SiC coating. The HfB2-SiC/SiC coating could protect the C/C from oxidation for 265h with only 0.41x10(-2)g/cm(2) weight loss at 1773K in air. During the oxidation process, SiO2 glass and HfO2 are generated. SiO2 glass has a self-sealing ability, which can cover the defects in the coating, thus blocking the penetration of oxygen and providing an effective protection for the C/C substrate. In addition, SiO2 glass can react with the formed HfO2, thus forming the HfSiO4 phase. Owing to the pinning effect of HfSiO4 phase, crack deflecting and crack termination are occurred, which will prevent the spread of cracks and effectively improve the oxidation resistance of the coating.