Ablation-resistant Y₂O₃-modified (Hf_0.2Ta_0.2Zr_0.2Ti_0.2Nb_0.2)C high entropy ceramics in oxyacetylene flame above 2100 °C

This study investigates the ablation behavior of Y₂O₃-modified (Hf_0.2Ta_0.2Zr_0.2Ti_0.2Nb_0.2)C high-entropy ceramics (HECs) under oxyacetylene flame at temperatures above 2100 °C. The Y₂O₃ content is systematically varied (5–20 vol%), and it is found that the optimal 15 vol% Y₂O₃ content facilitates the in-situ formation of a dense gradient oxide layer. This layer integrates refractory (Nb, Ta)₂O₅ and (Hf, Zr, Me)O_x skeletons with a Y-rich molten matrix, effectively suppressing oxygen penetration and reducing the volatilization of low-melting-point oxides. The sample exhibits superior ablation resistance, with linear and mass ablation rates of −12.8 ± 0.7 × 10⁻³ mm/s and 2.5 ± 0.2 × 10⁻³ g/s, respectively, outperforming unmodified HECs and other Y₂O₃-modified ceramics. Thermodynamic simulations reveal that Y₂O₃ stabilizes the oxide layer through the formation of Y-containing compounds, achieving a good balance between liquid-phase filling and refractory skeleton integrity. These findings will advance the design of rare-earth-modified HECs for ultrahigh-temperature thermal protection systems in aerospace applications.