Ablation behavior of C/SiC-ZrB₂ composites prepared via polymer precursor impregnation and pyrolysis in high-enthalpy plasma flows

This study investigates the ablation behavior of polymer precursor impregnation and pyrolysis-derived C/SiC–ZrB₂ composites under high-enthalpy plasma flows. Composites with 60 vol% ZrB₂ and 40 vol% SiC exhibit stable surface temperatures (1760–1815 °C) and low ablation rates R_l from −6.67 × 10⁻⁵ to −9.67 × 10⁻⁴ mm/s, which is attributed to the formation of a cohesive ZrO₂–SiO₂ oxide layer that mitigates oxygen diffusion and erosion. By contrast, composites with 80 vol% ZrB₂ and 20 vol% SiC are subjected to drastic temperature increases (>2800 °C) under extreme conditions (3.5 MW/m²). Such high ZrB₂ content leads to the formation of numerous ZrO₂ columnar crystals on the surface, which accelerates surface catalytic reactions, thereby increasing the surface temperature. Thermodynamic simulation results reveal that SiC in ZrB₂–SiC composites is subjected to thermochemical instabilities and atomic oxygen oxidation. These exothermic processes ultimately promote SiC decomposition, ZrO₂ skeleton collapse, and C fiber combustion, leading to the overall composite failure. Achieving the optimal ablation resistance requires a careful balance of ZrB₂/SiC volume ratio to stabilize the oxide layer while minimizing catalytic effects. These findings contribute to the design of advanced hypersonic thermal protection systems.