Research Progress in Oxidation-Resistant and Ablation-Resistant Ultrahigh-Temperature Ceramic Coatings

With the rapid development of hypersonic flight vehicles and advanced aerospace propulsion systems，key hot-end components such as nose cones，wing leading edges，and nozzle throat liners are subjected to long-term extremely coupled environments involving ultrahigh temperatures，severe oxidation，and high-velocity gas flow impingement during service.These conditions impose exceptionally stringent requirements on the oxidation and ablation resistance of protective materials.Ultrahigh-temperature ceramic (UHTC) coatings，featuring ultrahigh melting points，excellent chemical stability at elevated temperatures，and strong ablation resistance，are regarded as one of the most promising material systems for next-generation thermal protection.The research progress on oxidation-resistant and ablation-resistant UHTC coatings was systematically reviewed in this paper，and the fabrication processes，oxidation-resistant and ablation-resistant behavior，and underlying mechanisms of carbide-based and boride-based UHTC coatings were summarized and analyzed.For carbide-based UHTC coatings，the failure characteristics of coatings such as ZrC，HfC，and TaC under high-temperature oxidation and ablation environments were critically evaluated，and the key roles of second-phase incorporation，solid-solution strengthening，and gradient and multilayer structural designs in suppressing crack propagation，alleviating thermal stress mismatch，and stabilizing oxide product layers were reviewed.For boride-based UHTC coatings，the oxidation-resistant and ablation-resistant mechanisms of coatings such as ZrB2，HfB2，and TaB2 were systematically analyzed，and the self-healing behavior of B2O3 and borosilicate glass phases，the structural support provided by high-melting-point oxide skeletons，and their temperaturedependent protective characteristics were summarized.Meanwhile，fabrication processes for UHTC coatings，including atmospheric plasma spraying，chemical vapor deposition/infiltration，reactive melt infiltration，pack cementation，and precursor impregnation and sintering，were reviewed.The relationships among coating microstructure，interfacial bonding state，and in-service performance under different processing conditions were analyzed，and key bottlenecks currently encountered by UHTC coatings under high-enthalpy gas flows and long-duration service，such as oxide-layer volatilization，interfacial degradation，and brittle damage，were identified and summarized.Finally，future directions involving multicomponent and multiphase composite design，interface engineering and regulation，and intelligent materials design were outlined，and useful references were provided for the optimized design and engineering application of oxidation-resistant and ablation-resistant UHTC coating systems.