Controllable growth of (Hf, Zr)B₂ solid solution coating via CVD for ultra-high temperature ablation of C/C composites

In this paper, we have successfully addressed the challenges of cracking and spalling in HfB₂ coatings during ablation through the novel synthesis of (Hf, Zr)B₂ solid solution coatings using the chemical vapor deposition (CVD) method. The ablation resistance of the coating exhibited an initially improving trend followed by a subsequently deterioration as the Zr content increased. When the Hf/Zr molar ratio in the (Hf, Zr)B₂ solid solution coating was 1:1, a thicker Hf-Zr-O amorphous oxide layer was formed during ablation, which acted as a barrier, preventing the inward diffusion of oxygen. As a result, the (Hf_0.5Zr_0.5)B₂ solid solution coating exhibited superior ablation resistance with a mass ablation rate of only −0.216 mg/s and a linear rate of −0.089 µm/s. These findings underscore the enormous potential of boride solid solution UHTC as exceptional candidates for ultra-high temperature ablation resistant applications.