A strategy to improve the anti-ablation performance of C/C composites under cyclic oxyacetylene flame: SiC/HfB₂ multi-layer alternating coatings prepared by CVD

A SiC/HfB₂ multi-layer alternating coating was developed on carbon/carbon (C/C) composites using a chemical vapor deposition (CVD) process to improve the ablation resistance of C/C composites under cyclic ablation conditions. The microstructure, phase composition, and ablation behavior of the multi-layer coatings were systematically investigated. Specifically, the CVD process allowed for control over the coating thickness and uniformity, thus enabling the preparation of coatings with different numbers of sublayers. Compared with the SiC/HfB₂ and (SiC/HfB₂)₆ coating, the (SiC/HfB₂)₄ coating showed better performance due to low thermal stress and the synergistic effect of SiC and HfB₂ layers. After cyclic ablation for 30 s × 3, the (SiC/HfB₂)₄ coating demonstrated significantly low linear and mass ablation rates of −0.26 μm/s and 0.14 mg/s, respectively. Additionally, the introduction of a (SiC/HfB₂)₅-SiC coating with an outermost SiC layer further enhanced ablation resistance. The outermost SiC layer effectively reduces thermal stress and prevents flaking, while the multi-layer alternating structure prevents stress concentration, enhancing overall stability. This study highlights the effectiveness of multi-layer coatings in enhancing ablation resistance, providing a viable approach for protecting C/C composites in cyclic ablation environments.