Fabrication and ablation behavior of ZrB₂-SiC/ZrB₂-TiB₂-SiC gradient coating on carbon/carbon composites

ZrB₂-SiC coatings show promise for thermal protection systems (TPS) in carbon/carbon (C/C) composites but are limited by thermal expansion mismatch. Here, a ZrB₂-TiB₂-SiC transition layer was fabricated via pack cementation to enhance the compatibility of an atmospheric plasma sprayed (APS) ZrB₂-SiC coating. The ZrB₂-SiC/ZrB₂-TiB₂-SiC coating demonstrated superior cyclic ablation resistance at 2670 ℃ compared to conventional Zr-based coatings, attributed to (i) Rapid densification of ZrO₂ in the outer layer, combined with the self-healing capability of SiO₂. (ii) The graded ceramic distribution in the transition layer alleviates the mismatch in coefficient of thermal expansion both externally and internally. (iii) The novel Zr-Ti-Si-O glass scale, characterized by low oxygen diffusivity and reduced vapor pressure, reduces gas generation within the transition layer, mitigating internal stress and impact on the outer layer. These findings provide fundamental insights and highlight the potential of ZrB₂-SiC/ZrB₂-TiB₂-SiC coating for C/C composites in extreme environments.