Ablation resistance of Hf/Zr-based multiphase coating/matrix-modified C/C composites at ultrahigh temperatures

Different Hf/Zr-based multiphase coating/matrix-modified C/C composites are fabricated through a reactive melt infiltration (RMI) process adopting ZrSi₂ and HfSi₂-ZrSi₂ hybrid alloys with three molar ratios (i.e., 3:1, 1:1, and 1:3). The in-situ coatings with reticular silicide alloy as skeleton are generally continuous and integrated with the matrix. The microstructure evolution of the composites before and after ablation and ablation mechanisms are then methodically examined. The introduction of Hf into Zr-based coatings could improve the ablation resistance. With increasing oxygen partial pressure, (Zr, Hf)Si₂ is first oxidized to form dense Zr-rich (Hf, Zr)O₂ as the oxidized coating skeleton. Thereafter, the escape of gaseous products with high partial pressure leads to the formation of voids and gaps in the coating. Elevated Hf content promotes the sintering of the oxidized layer, and enhances the composite's ablation resistance. The results provide some insights into anti-ablation design and the combination of multiple techniques.