Novel high-entropy ultra-high temperature ceramics with enhanced ablation resistance

Ultra-high temperature ceramics (UHTCs) offer great potential for applications in extreme service environments, such as hypersonic vehicles, rockets and re-entry spacecraft. However, the severe ablation caused by high-speed heat flow scouring and high-temperature oxidation limits the engineering application of UHTCs. In this work, we report a novel high-entropy UHTC (Ti_0.2Zr_0.2V_0.2Nb_0.2Cr_0.2)(C_0.5N_0.5), which exhibits superior ablation resistance and light weight compared with traditional UHTCs. Specifically, at a temperature of 2650 K, the mass ablation rate of the material was measured as 1.025 × 10⁻² g·s⁻¹, and the density was calculated to be 6.7 g·cm⁻³. The impressive ablation resistance of (Ti_0.2Zr_0.2V_0.2Nb_0.2Cr_0.2)(C_0.5N_0.5) is attributed to the incorporation of a self-healing mechanism, which is associated with the in-situ formation of a medium-entropy oxide (TiVCr)O₂ during the ablation process. The medium-entropy oxide can seal pores and cracks to retard oxygen diffusion and prevent the material from fragmentation, thereby resulting in outstanding ablation resistance.