Microstructure and ablation resistance of C/C-HfC-SiC composites prepared by RMI with different powder particle sizes

To improve the ablation and scouring resistance of C/C composites, powder with particle sizes of 0.5–1 μm, 1–3 μm and 10–20 μm were used as infiltration powder to prepare C/C-HfC-SiC composites, named HSV-0.5-1, HSV-1-3 and HSV-10-20, respectively. Results show that the agglomeration of the powder makes it difficult to form a uniform and dense ceramic layer on the sample surface. The content of HfC ceramics increases with the particle size of the initial powder. In addition, the grain size of HfC first increases and then becomes irregularly spherical as the initial powder particle size increases. After ablation for 40s, HSV-1-3 shows the best resistance to ablation due to the mixed crystal form of flakes and spheres that form a denser oxide film in the center of the ablation. In three subsequent room-temperature airflow scour tests, the oxide film of HSV-1-3 and HSV-10-20 were damaged in the sample surface. After following ablation for 40 s, HSV-10-20 showed good ablation resistance with the linear ablation of −0.75 μm/s. The reason is the high HfC content and dense ceramic layer contribute to the formation of a continuous and complete oxide layer that prevents oxygen diffusion during ablation. This work provides guidance on the use of particle size in the RMI.