CVD HfC-based solid solution coatings for the ultra-high temperature ablation protection of SiC-coated C/C composites

To mitigate the formation of a porous oxide layer in a single HfC coating during long-term ablation, this work employed chemical vapor deposition to fabricate solid-solution Hf_xZr_1−xC coatings on SiC-coated C/C composites. The microstructure, thermal properties, and ablation behavior of these coatings were investigated through experimental and first-principles calculations. Results indicated that all coatings exhibit a single-phase NaCl-type solid solution structure with uniform elemental distribution. As the Zr content increases, the coefficient of thermal expansion of the Hf_xZr_1−xC coating increases, while the enhanced lattice distortion leads to reduced thermal conductivity. After proportional regulation, the mass and linear ablation rates of the Hf_0.5Zr_0.5C coating are reduced by 40.98 % and 46.15 %, respectively, after ablation for 180 s at 2300 °C. The formation of a dense and uniform Hf_0.5Zr_0.5O₂ solid-solution oxide layer enhances the ablation resistance, which is attributed to its compositional homogeneity and the fusion of grain boundaries during ablation, thereby effectively suppressing oxygen diffusion and promoting more cooperative oxygen transport. This study indicates that solid-solution structure ceramic coatings hold promising prospects for application in the field of ultra-high-temperature thermal protection.