Microstructure and Ablation Behavior of C/C-SiC-(Zr(x)Hf(1−x))C Composites Prepared by Reactive Melt Infiltration Method

C/C-SiC-(Zr(x)Hf(1−x))C composites were prepared by the reactive melt infiltration method. The microstructure of the porous C/C skeleton and the C/C-SiC-(Zr(x)Hf(1−x))C composites, as well as the structural evolution and ablation behavior of the C/C-SiC-(Zr(x)Hf(1−x))C composites, were systematically investigated. The results show that the C/C-SiC-(Zr(x)Hf(1−x))C composites were mainly composed of carbon fiber, carbon matrix, SiC ceramic, (Zr(x)Hf(1−x))C and (Zr(x)Hf(1−x))Si(2) solid solutions. The refinement of the pore structure is beneficial to promote the formation of (Zr(x)Hf(1−x))C ceramic. The C/C-SiC-(Zr(x)Hf(1−x))C composites exhibited outstanding ablation resistance under an air–plasma environment at around 2000 °C. After ablation for 60 s, CMC-1 appeared to possess the minimum mass and linear ablation rates of only 2.696 mg/s and −0.814 µm/s, respectively, which are lower than those of CMC-2 and CMC-3. During the ablation process, a Bi-liquid phase and a liquid–solid two-phase structure were formed on the ablation surface which could act as an oxygen diffusion barrier to retard further ablation, which is responsible for the excellent ablation resistance of the C/C-SiC-(Zr(x)Hf(1−x))C composites.