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

Multi-component (Hf,Zr,Ta)C ceramics are promising candidates for ablation-resistant coating materials applied in ultra-high 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, while 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 the ~2160 °C oxyacetylene flame. This enhancement is attributed to the co-formation of (Hf,Zr,Ta)O₂ and (Hf,Zr)₆Ta₂O₁₇ phases. Ta⁵⁺ partially dissolves into (Hf,Zr)O₂ (~5 at.%), reducing oxygen vacancy concentration and improving oxidation resistance. Additionally, the Ta-rich liquid phase generated from (Hf,Zr)₆Ta₂O₁₇ decomposition enhances oxide scale densification and contributes to structural stability during cooling via peritectic transformation. These results demonstrate that non-equimolar multi-component carbides offer a feasible strategy for improving the ablation resistance of ultra-high temperature coatings.