Abstract: To mitigate the degradation of mechanical properties caused by high-temperature melt erosion and reactions during the reactive melt infiltration process for fabricating carbon fiber reinforced ultra-high-temperature ceramic matrix composites, this work proposes an in-situ protection strategy that utilizes chemical vapor infiltration to uniformly fabricate a PyC/SiC/ZrC multi-layer interface layer on carbon fibers, thereby avoiding damage to carbon fibers. The results showed that the introduction of a PyC/SiC/ZrC interface layer significantly increased the flexural strength of the prepared composites by 133.3% in comparison to composites with a single PyC interface layer. Besides, after ablation under oxygen acetylene flame for 240 s, the mass and linear ablation rates show significant reductions of 69.6% and 90.1%, respectively. The tailored PyC/SiC/ZrC multi-layer interface delivered dual functionality: (i) synergistically introducing multiple pathways for energy dissipation while shielding fibers from Zr-Si melt erosion through the multi-layer interface, thus enhancing mechanical properties; (ii) in-situ generating a protective ZrO₂/SiO₂ oxide barrier layer on fibers during ablation to improve ablation resistance. This work provides new insights and valuable references for the efficient preparation of ceramic matrix composites with excellent ablation protection and mechanical properties.

Key words: PyC/SiC/ZrC multi-layer interface, In-situ C_f protection, C_f/ZrC-SiC composites, Ablation resistance, Mechanical properties, CVI