Ablation resistance of (Hf, Ta)B2-(Hf, Ta)C-SiC ceramics: boride and carbide phase contents significantly affecting the ablation behaviour

In order to elucidate the synergistic mechanism of boride and carbide phase in ultrahigh-temperature ceramics (UHTCs) under ablation condition, in this work, the ablation behaviour of (Hf, Ta)B 2 -(Hf, Ta)C-SiC ceramics with different (Hf, Ta)B 2 to (Hf, Ta)C molar ratios was systematically investigated by oxygen-acetylene test under a heat flux of 3.2 MW/m 2 . It was found that the oxides generated from (Hf, Ta)B 2 and (Hf, Ta)C enhanced the matching capacity of oxides with different melting points, being formed a dense ablation layer. When the molar ratio of (Hf, Ta)B 2 to (Hf, Ta)C was 2:1, the ceramic achieved a near-zero ablation rate (0.042 μm/s), which was 1.62 times lower than that of (Hf, Ta)C-SiC ceramics. The mechanism for the enhanced ablation resistance was attributed to the Hf 6 Ta 2 O 17 generated during the ablation reaction, which reduced the viscosity of the ablation products and infiltrated into the pores of ceramics. The formation of such ablation layer could inhibit the impregnation of oxygen and the depletion of easily volatile oxides, including SiO 2 and B 2 O 3 , being formed a multi-element composite ablation layer with self-healing ability, which was helpful for the protection of the substrate from continuous oxidation damage.