Superior synergistic oxidation resistance of medium-entropy carbide ceramic powders rather than multi-phase carbide ceramic powders

To date, some questions about medium-entropy carbide ceramics and the corresponding multi-phase carbide ceramics with the same cations and proportions remain unclear. Regarding oxidation behavior, do both have synergistic oxidation abilities and what role does entropy stabilization play in medium-entropy carbides? In this work, the oxidation behaviors of HfC–ZrC–TiC multi-phase carbide (HZT-MPC) and (Hf_1/3Zr_1/3Ti_1/3)C medium-entropy carbide (HZT-MEC) powders were investigated. After thermogravimetry (TG) oxidation, the TG curve of HZT-MPC had a bimodal distribution. The “preferential oxidation” of HfC/ZrC occurred within HZT-MPC, followed by the formation of multi-phase oxides (HfO₂, ZrO₂, and TiO₂). The uneven compositional distribution slowed their solid solution reactions to form Ti-doped (Hf,Zr)O₂ and (Hf,Zr)TiO₄. The TG curve of HZT-MEC had a single peak. A uniform compositional distribution at the atomic scale promoted the rapid interdiffusion of oxides, forming Ti-doped (Hf,Zr)O₂ and (Hf,Zr)TiO₄ without ZrO₂, HfO₂, and TiO₂ after TG oxidation. Additionally, HZT-MEC had a higher onset oxidation temperature (T_o; 470 °C) than did HZT-MPC (430 °C), and the TG single peak of HZT-MEC was between the TG bimodal peaks of HZT-MPC. Therefore, HZT-MEC showed superior oxidation resistance compared to HZT-MPC, which was attributed to the entropy stabilization effect of HZT-MEC suppressing the “preferential oxidation” of HfC/ZrC and the “delayed oxidation” of TiC, promoting the synergistic oxidation ability of multiple principal elements.