Effects of the second phase on the microstructure and ablation resistance of HfC coating on C/C composites

To improve the ablation resistance of HfC coating on carbon/carbon composites prepared by supersonic atmospheric plasma spraying, SiC, TaC and ZrC ceramics were added into HfC coating as the second phase. Effects of the second phase on the microstructure, interface bonding strength and ablation resistance of HfC coating were researched. The structure of HfC-SiC coating was denser and smoother than that of HfC-TaC and HfC-ZrC coatings. The dense structure, high interface bonding strength and formation of continuous Hf-Si-O glassy film resulted in the better ablation resistance of HfC-SiC coating. During ablation, the HfC-TaC coating was oxidized to a stable Hf6Ta2O17 glassy film, which could restrain the oxygen penetration. A porous HfO2-ZrO2 layer was generated on the HfC-ZrC coating after ablation, some HfO2 and ZrO2 particles may be flown away by the high-speed flame. So, the ablation resistance of HfC-ZrC coating was worse than the other two coatings.