Microstructure evolution and phase interface characterization in anti-ablation (Hf_1/4Zr_1/4Ta_1/4Ti_1/4)C-coated C/C composites

Ta and Ti elements are often used as modified components to densify the loose oxide film for HfC/ZrC coatings after long-term ablation, while the synergistic effect among their multi-phase oxides on the ablation resistance of the coatings for C/C composites is still being explored. In this work, a (Hf_1/4Zr_1/4Ta_1/4Ti_1/4)C high-entropy carbide ceramic was proposed as an advanced anti-ablation coating for C/C composites and the multicomponent synergistic effect on the ablative behavior was investigated. At the initial ablation, the O atoms first reacted with Hf and Zr elements to form m-(Hf, Zr)O₂. The TiO₂ was prone to decompose into TiO and then evaporated from the coating during ablation, slowing down the volatilization of Ta₂O₅. The remaining TiO₂ and Ta₂O₅ diffused to m-(Hf, Zr)O₂ and produced a phase transition from Ta/Ti-doped m-(Hf, Zr)O₂ to o-(Hf, Zr)₆Ta₂O₁₇/o-(Hf, Zr)TiO₄. The formation of nanotwin between (Hf, Zr)₆Ta₂O₁₇ and (Hf, Zr)TiO₄ enhanced the toughness of the oxide film. Although excessive Ta₂O₅ broke the stability of the oxide film, the Hf-Zr-rich oxide skeleton (Ta/Ti-doped (Hf, Zr)O₂, (Hf, Zr)₆Ta₂O₁₇ and (Hf, Zr)TiO₄)) ensured that C/C substrates were intact after ablation for 180 s, showing superior ablation resistance.