Ablation behavior of C/C-(Hf_0.2Ta_0.2Nb_0.2Zr_0.2Ti_0.2)C composites under oxyacetylene and plasma flame at different temperatures

To investigate the ablation behavior of C/C-(Hf_0.2Ta_0.2Nb_0.2Zr_0.2Ti_0.2)C composites under different environments, the composites were produced by the precursor infiltration and pyrolysis (PIP) process. Their ablation behavior and mechanisms under oxyacetylene flame and plasma flame at different temperatures for 60 s were systematically studied. The results showed a clear difference between mass and linear ablation rates. Under the oxyacetylene flame at 2510 °C, the composite had a high mass ablation rate of 5.84 mg/s because the oxide layer peeled off, although the linear rate was 46.2 μm/s. In contrast, under the plasma flame at 2479 °C, the mass ablation rate dropped significantly to 2.84 mg/s, while the linear rate remained similar at 39.23 μm/s. Microstructural analysis showed that the protective mechanism relies on a solid oxide skeleton embedded in a liquid healing phase. Under plasma conditions, sputtered oxides reacted to form stable HfTiO₄ and ZrTiO₄ at the edge region. This healed the defects and made the layer dense, effectively reducing the total mass loss. However, when the ablation temperature exceeded 2500 °C, the rapid volatilization of liquid-phase oxides compromised the integrity of the protective layer, leading to a marked reduction in the composite's ablation resistance.