Ablation behavior of high-entropy carbides ceramics (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C upon exposition to an oxyacetylene torch at 2000?C

The ablation performance of a high-entropy ceramic carbide, (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C, was performed by oxyacetylene ablation flame, simulating the extreme service environment at 2000 degrees C. Phase and microstructure characterization at multi-length scales was carried out. During ablation, a compositionally and microstructurally complex oxidation layer formed on the ablation surface, which consisted of a combination of (ZrxHf1_x)6(Nby-Ta1_y)2O17, Ti(NbxTa1_x)2O7, and Tix(ZraHfbNbcTa1_ a-b-c)1_xO2. Based on the microstructure information, the ablation mechanisms were proposed considering the oxidation thermodynamics and kinetics. Comparable rates of O inward diffusion and Ti outward diffusion are suggested, and a particular innermost dense layer composed of isolated (ZrxHf1_x)6(NbyTa1_ y)2O17 grains embedded in a continuous Ti(NbxTa1_x)2O7 matrix is considered to be beneficial for a better ablation resistance.