The effect of Hf₆Ta₂O₁₇ self-sintering on the cyclic ablation and mechanical performances of C/Hf-Ta-Si-C composites with a PyC-SiC bilayer interphase

As the primary barrier of ultra-high temperature ceramic based composites against high-speed flame ablation, oxidized skins significantly influence ablation resistance and mechanical properties. To enhance the cyclic ablation performance of C/Hf-Si-C composites, Ta was introduced into the matrix through polymer infiltration and pyrolysis method with a Hf:Ta ratio of 3:1, aimed at promoting the self-sintering of the oxidized skin. Cyclic ablation, falling impact and bending performances of C/Hf-Ta-Si-C composites were investigated. The introduction of Ta markedly improved the compactness, cohesion and bonding strength of the oxidized skin on ablated C/Hf-Ta-Si-C composites. As a result of these enhancements, the ablation resistance, impact tolerance and residual flexural strength of the cyclic ablated C/Hf-Ta-Si-C composites significantly increased. After 3 × 60s ablation cycles, the residual flexural strength of the ablated C/Hf-Ta-Si-C composites was about 195.9 ± 20.7 MPa, which was notably higher than that of the 3rd ablated C/Hf-Si-C composites (89.9 ± 12.6 MPa). Interestingly, after the introduction of Ta, the stress decline trend in the ablated composites changed from continuous downward decline to ladder like decline. This was attributed to that the self-sintering of the Hf₆Ta₂O₁₇ optimized the compactness of the ablated matrix during ablation process and increased the compressive stress on C_f during cooling.