Wide-temperature range oxidation-ablation resistance of vacuum hot-pressed NbC-modified HfC ultra-high temperature ceramics

The static-oxidation behaviour at 1700 °C and ablation resistance under an oxyacetylene flame of vacuum hot-pressed NbC-modified HfC (Hf_1-xNb_xC) ultra-high temperature ceramics were investigated. Additionally, the phase compositions of HfO₂[sbnd]Nb₂O₅ ceramics heat-treated in Ar were analysed to systematically explain the oxidation-ablation mechanism of Hf_1-xNb_xC. The results indicated that the stable phases of HfO₂-50 mol% NbO_2.5 ceramics heat-treated at 1700[sbnd]1900 °C were Nb₂Hf₆O₁₇ and NbO₂. The antioxidant temperature limit for Hf_1-xNb_xC was ≥ 1700 °C. At 1700 °C for 30 h, Hf_0.8Nb_0.2C formed a dense oxide film comprising bulky HfO₂ bonded by lathy Nb₂Hf₈O₂₁, which exhibited the best anti-oxidation property. Furthermore, Hf_0.9Nb_0.1C developed a dense “free-standing” single-phase HfO₂ film under an oxyacetylene flame at 4.2 MW/m² for 40 s × 3, demonstrating excellent high-temperature ablation resistance. The formation-decomposition mechanism of Nb₂Hf₆O₁₇ and the effects of NbC on the morphology and size of HfO₂ grains under an oxyacetylene flame at 2.4 MW/m² were examined.