Improved oxidation and ablation resistance of SiC_f/SiC-HfB₂ composites: Role of oxygen-blocking scale and protection mechanism

To improve the oxidation and ablation resistance of SiC_f/SiC composites, the as-synthesized ultrafine HfB₂ powder was used as the modification phase to fabricate SiC_f/SiC-HfB₂ composites, and their oxidation and ablation behaviors were investigated. Compared with the unmodified SiC_f/SiC composites, the oxidation resistance at 800–1500 °C and the ultra-high temperature ablation resistance of SiC_f/SiC-HfB₂ composites were significantly improved. After oxidation, a compact compound glass scale consisting of HfO₂, HfSiO₄ and Si-Hf-O glass was formed, providing the effective oxidation protection. A dual-phase oxide scale composed of HfO₂ skeleton and Si-Hf-O glass was formed after ablation, exhibiting the high viscosity, the significant oxygen-blocking effect and resistance to gas flow scouring. The improved oxidation and ablation resistance of SiC_f/SiC-HfB₂ composites could be attributed to the effective protective role of oxygen-blocking scales formed during the oxidation and ablation processes.