Atomic-scale oxidation mechanism of high-entropy carbides via density functional theory and ab initio molecular dynamics

High-entropy carbides (HECs) are increasingly recognized as promising materials for high-temperature applications, thanks to their remarkable mechanical properties and resistance to oxidation. This study investigates the initial oxidation mechanisms of HEC (Zr₀.₂₅Hf₀.₂₅Nb₀.₂₅Ta₀.₂₅)C through density functional theory and ab initio molecular dynamics simulations. Our results indicate that the (100) surface exhibits the highest stability, where oxygen molecules dissociate into atoms that preferentially adsorb at the threefold hollow site. Further analysis shows that oxygen atoms preferentially bond with Zr and Hf atoms, leading to the formation of oxides. The interaction between oxygen and the surface exhibits mixed ionic–covalent characteristics. Furthermore, oxygen atoms diffuse from the surface to subsurface octahedral sites via tetrahedral interstitial sites, with a migration barrier slightly above that of corresponding binary carbides. This research enhances our understanding of the oxidation resistance in HECs.