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

To improve the oxidation and ablation resistance of SiCf/SiC composites, the as-synthesized ultrafine HfB2 powder was used as the modification phase to fabricate SiCf/SiC-HfB2 composites, and their oxidation and ablation behaviors were investigated. Compared with the unmodified SiCf/SiC composites, the oxidation resistance at 800-1500 oC and the ultra-high temperature ablation resistance of SiCf/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 SiCf/SiC-HfB2 composites could be attributed to the effective protective role of oxygen-blocking scales formed during the oxidation and ablation processes.