（1. China Academy of Launch Vehicle Technology, Beijing 100076, China） (2. Powder Metallurgy Institute, Central South University, Changsha 410083, China）
Carbon/carbon composites modified by HfC-SiC and HfC-ZrC-SiC were fabricated by reactive melt infiltration. A comparative study of their microstructure, ablation behavior and infiltration mechanism was conducted by SEM, EDS and XRD. Results indicated that the increase of Si content was beneficial to the infiltration effect, but excess Si reduced composites-ablation performance. When the silicon mass fraction of infiltration mixture reached 40%, fine grains of ZrHfC solid solutions evenly distributed in the C/CHfCZrCSiC composites, which significantly improved its ablation resistance. A dense and continuous oxide layer formed on the ablated surface of C/C-HfC-ZrCSiC composites, while for the C/CHfCSiC， the oxide scales were porous. C/C-HfC-ZrC-SiC exhibited better anti-ablation resistance, and the mass ablation rate and linear ablation rate of the composite(infiltrated with the mixture in which Hf, Zr and Si mass fraction ratio is 30∶30∶40) were 0.08 mg·cm-2·s-1 and -3.30 μm·s-1, respectively. Compared with C/C-HfC-SiC(infiltrated with the mixture in which Hf and Si mass fraction ratio is 60∶40), the mass ablation rate of C/C-HfC-ZrC-SiC decreased by 46.7%.