At high temperatures, oxidation is generally regarded as an unavoidable degradation process for ceramic protective coatings. Here, oxidation is shown to drive dynamic glass evolution and form a robust self-sealing barrier under extreme thermal conditions. An in situ alloyed boride–silicide composite coating is constructed, and the controlled incorporation of HfSi₂ is found to change oxide-scale development by providing additional Hf and Si sources during oxidation and promoting the early formation and continuous reconstruction of a highly sealing Hf–Si–O glassy layer. The optimized coating exhibits exceptional oxidation resistance at 1700 °C, with the oxygen permeability and carbon loss rate reduced by 61.67% and 75.26%, respectively, corresponding to an average protection efficiency of 99.94%. Mechanistically, oxidation-driven glass evolution seals pores and microcracks and slows inward oxygen diffusion, whereas appropriate HfSi₂ incorporation helps compact and stabilize the glassy layer, while excessive glass stiffening reduces high-temperature fluidity and weakens scale integrity. These findings provide a general design method for improving self-sealing oxidation protection at high temperatures.

Carbon-based composites are widely utilized in aerospace engines, thermal protection systems of hypersonic vehicles, and ultrahigh-temperature structural components, due to their lightweight nature, high strength, excellent mechanical properties, and thermal stability. However, the inherent susceptibility of carbon-based composites to high-temperature oxidation significantly limits their service life, highlighting the urgent need for the development of efficient oxidation-resistant barriers to enhance the long-term operational stability. In recent years, ultra-high temperature ceramic (UHTC) coatings have attracted considerable attention owing to their outstanding oxidation resistance. Nevertheless, such protective coatings still face critical challenges to hinder practical applications, including crack propagation, dynamic consumption instability of oxidation glass films, generation of oxidation holes and interfacial damage, which remain prevalent. In this work, a comprehensive overview of the research progress in UHTC coatings for carbon-based composites is provided, with particular emphasis on examining the influence of hierarchical structural design on oxidation resistance. Specifically, the role of advanced manufacturing techniques in optimizing microstructural stability and interfacial bonding strength is thoroughly discussed. Furthermore, the high-temperature oxidation protection mechanisms of UHTC coatings are examined, including strategies to optimize the composition of the oxidation glass film, stabilize the self-generated glass phase, and enhance densification of coating. In addition, various characterization methods are discussed for evaluating the oxidation resistance of the coatings, along with a systematic evaluation of stability under different service conditions. Finally, analysis of current technical challenges and unresolved issues, especially challenges and technical prospects regarding the field of oxidation-resistant coatings for carbon-based composites are discussed, while offering perspectives on future developments.

To achieve high oxygen blocking structure of the ZrB₂-MoSi₂ coating applied on carbon structural material, ZrB₂-MoSi₂ coating was prepared by spark plasma sintering (SPS) method utilizing ZrB₂-MoSi₂ composite powders synthesized by self-propagating high-temperature synthesis (SHS) technique as raw materials. The oxygen blocking mechanism of the ZrB₂-MoSi₂ coatings at 1973 K was investigated. Compared with commercial powders, the coatings prepared by SHS powders exhibited superior density and inferior oxidation activity, which significantly heightened the structural oxygen blocking ability of the coatings in the active oxidation stage, thus characterizing higher oxidation protection efficiency. The rise of MoSi₂ content facilitated the dispersion of transition metal oxide nanocrystals (5-20 nm) in the SiO₂ glass layer and conduced to the increasing viscosity, thus strengthening the inerting impact of the compound glass layer in the inert oxidation stage. Nevertheless, the ZrB₂-40 vol%MoSi₂ coating sample prepared by SHS powders presented the lowest oxygen permeability of 0.3% and carbon loss rate of 0.29×10^-6 g·cm^-2·s^-1. Owing to the gradient oxygen partial pressure inside the coatings, the Si-depleted layer was developed under the compound glass layer, which brought about acute oxygen erosion.

TaB₂-SiC coating modified by different content of MoSi₂ was fabricated on graphite substrate with SiC inner coating by liquid phase sintering to elevate the anti-oxidation capability of the TaB₂-SiC coatings. As compared to the sample with the TaB₂-40wt%SiC coating, the coating sample modified with MoSi₂ exhibited a weight gain trend at lower temperatures, the fastest weight loss rate went down by 76%, and the relative oxygen permeability value reduced from about 1% to near 0. More importantly, the large amount of SiO₂ glass phase produced over the coating during oxidation was in contact with the modification of MoSi₂, which was proved to be beneficial to the dispersion of Ta-oxides. A concomitantly formed continuous Ta-Si-O-B compound glass layer showed excellent capacity to prevent oxygen penetration. However, when the TaB₂ content was sacrificed to increase the MoSi₂ content, the relative oxygen permeability of the coating increased instead of decreased. Thus, on the basis of ample TaB₂ content, increasing the MoSi₂ content of the coating is conducive to reducing the relative oxygen permeability of the coatings in a broad temperature region.