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, HfB₂-SiC composites were synthesized by integrating self-made single-crystal HfB₂ 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 HfB₂ microrods into the HfB₂-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.% HfB₂ microrods exhibited a minimal weight gain (0.018 mg/cm³). 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced><mml:mrow><mml:mn>10</mml:mn> <mml:mover><mml:mn>1</mml:mn> <mml:mo>¯</mml:mo></mml:mover> <mml:mn>0</mml:mn></mml:mrow> </mml:mfenced> </mml:math> crystal planes present on HfB₂ 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 HfB₂ microrods and provides a promising design concept for HfB₂ composites, which lays both theoretical and material groundwork for the development of a new generation of hypersonic vehicles.