A novel Hf_0.75Zr_0.25N solid solution coating with high mechanical strength: Ablation protection application above 2200°C

Obtaining coatings with excellent ablation resistance is a longstanding challenge for the ablation protection of carbon/carbon (C/C) composites. In this work, a single phase Hf_0.75Zr_0.25N solid solution ultra-high temperature ceramic (UHTC) coating was proposed, and prepared on the surface of C/C composites by chemical vapor deposition (CVD) for the first time. The results revealed that the hardness and Young's modulus of Hf_0.75Zr_0.25N coating are higher than those of HfN and ZrN coatings, reaching 33.35 GPa and 316.42 GPa, respectively. After ablation for 180 s under oxygen acetylene flame with a temperature exceeding 2200 °C, the Hf_0.75Zr_0.25N coating retained its structural integrity and exhibited lower ablation (R_m: 0.26 mg/s; R_h: 0.32 μm/s). This is mainly attributed to the formation of the dense Hf-Zr-O oxide scale promoted by the oxidation sintering reaction during ablation. The above results indicate the nitride solid solution UHTC has great potential as ablation resistance coating at ultra-high temperatures.