Ablation behavior of C/C–Zr_1-xHf_xC-SiC composites under an oxyacetylene flame at above 2500 °C

In order to enhance ablation resistance of C/C composites, Zr_1-xHf_xC and SiC were introduced into C/C composites, and ablation behavior of the composites was studied. In the composites (CHZS), HfC and ZrC produced a solid solution, and solid solubility of HfC in ZrC was 0.4, which indicated that the solid solution was defined to be Zr_0.6Hf_0.4C. Compared with C/C–ZrC–SiC composites (CZS), CHZS possessed a better ablation resistance. During ablation of CHZS, Zr_0.6Hf_0.4C is oxidized to produce HfO₂ and ZrO₂, and HfO₂ particles played a pinning effect, which fixed molten oxide coating. Moreover, due to low CTE of HfO₂ and decreasing content of ZrO₂, there was a smaller thermal stress and its distribution area on CHZS ablation surface, thus thermal stress corrosion was weakened to strengthen integrity of oxide coating. In this case, a complete and continuous HfO₂-ZrO₂ coating was formed on CHZS surface, which could resist oxygen diffusion and reduce oxidation rate of the composites.