Ablation behavior and mechanism of C/C-HfC-ZrC-SiC composites in hypersonic oxygen-enriched environment

To reveal the ablation behavior and mechanism of multiple ceramic matrix modified C/C composites in hypersonic environment, C/C-HfC-ZrC-SiC composites were prepared by precursor infiltration and pyrolysis technique with a mixed precursor of hafnium-zirconium-polycarbosilane (PHC:PZC:PCS, 35:35:30 wt.%) and the ablation resistance of the composites was characterized by hypersonic oxygen-enriched ablation test with varying ablation distance and time. After 60 s ablation with the decrease of ablation distance from 80 mm to 50 mm, the linear and mass ablation rates of the composites increased from 16.1 ± 0.5 μm/s and 5.41 ± 0.48 mg/s to 27.5 ± 2.7 μm/s and 9.07 ± 0.57 mg/s, respectively. Under the ablation distance of 50 mm, the linear and mass ablation rates increased from 15.5 ± 1.9 μm/s and 6.81 ± 0.86 mg/s to 27.5 ± 2.7 μm/s and 9.07 ± 0.57 mg/s, respectively, corresponding that the ablation time increases from 20 s to 60 s. The results showed that the ablation performance of C/C-HfC-ZrC-SiC composites in hypersonic environment were controlled mainly by thermochemical reaction and mechanical erosion depended on the ablation distance and time. The formation of glassy SiO₂embedded with (Hf_xZr_1-x)O₂particles provides a protective barrier to relieve the oxidation of the inner composites, which is benefit to enhance the composites’ ablation resistance through withstanding the strong shear force generated by the hypersonic airflow.