Microstructure and anti-ablation performance of HfC-TaC and HfC-ZrC coatings synthesized by CVD on C/C composites

HfC-TaC and HfC-ZrC biphase coatings were synthesized on C/C composites through CVD technique with the aim of elevating the anti-ablation performance of the HfC monophase coating. The phase composition, microstructure and anti-ablation performance of the biphase coatings were researched, as well as the ablation mechanism of the coated C/C samples. Results manifested that both the HfC-TaC and HfC-ZrC coatings exhibited a compact and particle-stacked structure and combined well with the C/C substrate. Incorporating TaC is capable of enhancing the anti-ablation performance of the HfC coating by reason of forming the stable Hf₆Ta₂O₁₇ phase during ablation. The evaporation and mechanical denudation of the Hf-Ta-O glassy film leaded to the HfC-TaC coating exfoliation. In comparison to the HfC and HfC-TaC coatings, the HfC-ZrC coating exhibited superior anti-ablation performance on account of the solid solution sintering between the HfO₂ and ZrO₂ particles and the good anti-scour performance of the oxide layer. After exposure to oxyacetylene torch for 120 s, the mass and linear ablation rates of the HfC-ZrC-coated C/C sample were only 0.63 mg/s and 0.21 μm/s, respectively.