Tailoring ablation resistance of (Hf,Zr,Ta)C coatings above 2000 °C: Critical role of Ta content

Multicomponent (Hf,Zr,Ta)C ceramics are promising candidates for ablation-resistant coating materials applied in ultrahigh-temperature environments. However, the influence of compositional variations on their ablation behavior remains insufficiently understood. In this study, the effect of Ta content on the ablation resistance of (Hf,Zr,Ta)C coatings was systematically investigated. Moderate Ta addition promotes the densification of oxide scales, whereas excessive Ta reduces the thermochemical stability of the oxide scale, leading to increased ablation damage. The optimized composition, the T15 coating, exhibits superior ablation resistance, maintaining structural integrity for 300 s under an ~2160 °C oxyacetylene flame. This enhancement is attributed to the co-formation of the (Hf,Zr,Ta)O₂ and (Hf,Zr)₆Ta₂O₁₇ phases. Ta⁵⁺ partially dissolves into (Hf,Zr)O₂ (~5 at%), reducing the oxygen vacancy concentration and improving the oxidation resistance. Additionally, the Ta-rich liquid phase generated from the decomposition of (Hf,Zr)₆Ta₂O₁₇ enhances oxide scale densification and contributes to structural stability during cooling through peritectic transformation. These results demonstrate that non-equimolar multicomponent carbides offer a feasible strategy for improving the ablation resistance of ultrahigh-temperature coatings.