Medium-entropy ceramics surfaces with organic tethers: A route to rapid densification and improvement anti-ablation performance for C/SiBCN-(Hf_1/2Zr_1/3Ti_1/6) C composites

Ultra-high temperature ceramics-based composites exhibit immense promise for thermal protection systems; however, challenges of sintering difficulty, prolonged densification periods remain critical obstacles to their broader application. In this work, a (Hf_1/2Zr_1/3Ti_1/6) C medium entropy ceramic (MEC) powder was grafted with active groups (-OH and -vinyl) through surface micro-oxidation and dechlorination reactions. Owing to VinMEC's high sintering activity and enhanced crosslinking of precursors, densification was accomplished in just two PIP cycles when this vinyl-grafted MEC (VinMEC) powder was doped in a vinyl-SiBCN precursor to prepare a C/SiBCN-VinMEC composite. Under the ablation of a 7 MW/m² oxyacetylene flame, C/SiBCN-VinMEC exhibited a LAR of 1.99 μm/s. This exceptional anti-ablation performance is primarily attributed to the formation of high melting point (Hf, Zr, Ti) O₂ oxide skeleton, along with high viscosity liquid phase of (Hf, Zr) TiO₄. Furthermore, the C/SiBCN-VinMEC demonstrates remarkably low costs attributed to its short densification cycle (2 PIP cycles), mild processing conditions (pressureless, <1400 °C), and minimal raw material expenses (2D carbon fiber cloth and high precursor utilization). This rapid fabrication method offers a cost-effective and high-performance route for the production of ultra-high temperature thermal protection composites.