Single-Crystal HfB 2 Nanorod-Induced Synergy in HfB 2 –SiC Ultrahigh-Temperature Ceramics: Enhancement of Mechanical and Ablation Resistance

Achieving a synergistic improvement in the toughness and oxidation resistance of boride ultrahigh-temperature ceramic composites remains a challenge for advancing new-generation hypersonic vehicles. In this study, HfB 2 –SiC composites were synthesized by integrating self-made single-crystal HfB 2 microrods with commercial powders via spark plasma sintering, which exhibited enhancement of mechanical and ablation resistance. Compared to the sample without addition, the incorporation of 6 wt.% single-crystal HfB 2 microrods into the HfB 2 –SiC composites resulted in a 4.1% increase in hardness and a 37.6% improvement in fracture toughness, reaching 15.45 ± 0.89 GPa and 7.58 ± 0.66 MPa·m 1/2 , respectively. After static oxidation at 1,500 °C in air for 300 min, the ceramic block supplemented with 3 wt.% HfB 2 microrods exhibited a minimal weight gain (0.018 mg/cm 3 ). Upon exposure to a plasma flame at 2,000 °C for a period of 60 s, the material demonstrated a mass ablation rate of −0.013 mg/s and a linear ablation rate of 0.25 μm/s. Based on the experimental results, the excellent oxidation and ablation resistance might be related to the naturally low reactivity of the exposed 10 1 ¯ 0 crystal planes present on HfB 2 microrods, which aligns with the findings from first-principles calculations. This approach improves the comprehensive performance of the material by leveraging the inherent strengths of single-crystal HfB 2 microrods and provides a promising design concept for HfB 2 composites, which lays both theoretical and material groundwork for the development of a new generation of hypersonic vehicles.