An area-tailored (Hf, Ta)B₂-SiC coating for ultra-high thermal protection: Design and evolution of microstructure

In the service environments of advanced aircrafts, thermal and aerodynamic loads on different areas of carbon/carbon composites thermal-structural components exhibit significant variation, often leading to cracking or failure of the protective coatings due to mismatched thermal expansion and stress accumulation. To address the problem, an innovative area-tailored protective coating strategy is proposed in this paper. An area-tailored (Hf, Ta)B₂-SiC coating was designed and prepared, featuring enriched (Hf, Ta)B₂ in the central area and SiC in the edge area, and was evaluated under oxyacetylene flame. After ablation, the area-tailored coating showed good cyclic ablation resistance due to the alleviated thermal stress mismatch across different coating regions, whose thickness and mass loss rates decreased by 104 % and 103 % after ablation for 30 s, respectively, compared to the uniform (Hf, Ta)B₂-SiC coating. The ablation resistance is manifested in the thermostability of Hf-based oxides, sintering densification, and grain boundary pinning, which reduce oxygen diffusion and improve the stability of the oxide layer. This work provides a new strategy and inspiration for the design and preparation of coatings for thermal structural components.