Wet oxidation behavior of C/SiC–SiHf(B)CN composites at high temperature

To further improve the oxidation resistance of C/SiC–SiBCN at temperatures over 1200 °C, C/SiC–SiHfCN and C/SiC–SiHfBCN composites were prepared by a new method called chemical vapor infiltration (CVI) combined with polymer infiltration and on-line pyrolysis (PIOP) process. The weight change behavior, mechanical properties, and microstructure of C/SiC–SiHf(B)CN before and after oxidation in wet oxygen were studied in detail. Through the replacement of B by Hf, the weight loss of the composite in high-temperature wet oxygen environment has been significantly reduced. The strength retention of C/SiC–SiHfBCN is up to 75% after oxidation in wet oxygen at 1400 °C and the strength retention of C/SiC–SiHfBCN can reach 85% after oxidation in an atmosphere with high oxygen and water vapor content at 1300 °C. In addition, microscopic analysis showed that after oxidation at 1400 °C, only the fibers in the near-surface matrix were oxidized to some extent and hafnium has been enriched at the composite surface. Our work provides a reference for the study of the oxidation resistance of C/SiC composites in harsh environments.