Tailoring the Hf/(Ti+Ta) ratio to achieve synergistic oxide-induced ablation resistance in C/C-(Hf, Ti, Ta)C-SiC composites

Despite the improved ablation resistance offered by Hf-based ultra-high temperature ceramics (UHTCs) in carbon/carbon (C/C) composites, the porous oxide scales formed during ablation limits their long-term thermal stability, hindering advanced application. Herein, this work proposed the incorporation of Hf/Ti+Ta with varying molar ratios into C/C composites via reactive melt infiltration, and the resulting multi-component oxides after ablation promoted the formation of a dense oxide layer, thereby improving long-term ablation performance. The finding reveals that all samples were relatively dense and exhibited an identical layered structure around carbon fibers. Notably, the composites with a Hf/Ti/Ta molar ratio of 8:2:1 (8-HTT) exhibited superior ablation resistance, owing to the formation of a dense, adherent surface oxide layer, consisting of (Hf, Ti, Ta)O₂ and HfTiO₄. As the ablation duration increased to 240 s, the linear ablation rate for 8-HTT decreased to 0.7 μm/s, which was attributed to the self-healing effect enabled by low-melting-point oxide Hf₆Ta₂O₁₇. This work establishes a theoretical foundation and optimization strategy for designing high-performance ablation-resistant C/C composites for extreme thermal environments.