Superior synergistic oxidation resistance of medium-entropy carbide ceramic powders rather than multi-phase carbide ceramic powders
Jiachen Li, Fanyu Lu, Tao Li, Yanqin Fu, Junhao Zhao, Junshuai Lv, Yulei Zhang
Abstract
Until now, some questions about medium-entropy carbide<strong> </strong>ceramic and the corresponding multi-phase carbide<strong> </strong>ceramic with the same cation and proportion remain unclear. Regarding oxidation behavior, do both have a synergistic oxidation ability 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<sub>1/3</sub>Zr<sub>1/3</sub>Ti<sub>1/3</sub>)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 (HfO<sub>2</sub>, ZrO<sub>2</sub> and TiO<sub>2</sub>). Uneven compositional distribution slowed down their solid solution reactions to form Ti-doped (Hf, Zr)O<sub>2</sub> and (Hf, Zr)TiO<sub>4</sub>. While the TG curve of HZT-MEC had a single-peak characteristic. Uniform compositional distribution at the atomic scale promoted the rapid interdiffusion of oxides, forming Ti-doped (Hf, Zr)O<sub>2</sub> and (Hf, Zr)TiO<sub>4</sub> without ZrO<sub>2</sub>, HfO<sub>2 </sub>and<sub> </sub>TiO<sub>2 </sub>after TG oxidation. Additionally, HZT-MEC had a higher onset oxidation temperature (470 °C) compared to 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 suppressed the “preferential oxidation” of HfC/ZrC and the “delayed oxidation” of TiC, promoting the synergistic oxidation ability of multi-principal elements.