Predesigned Carbon Vacancies Unlock Superior Oxidation Resistance of High‐Entropy Carbides by Stabilizing a Protective M–C–O Interphase

Abstract

ABSTRACT The initial oxidation stage of high‐entropy carbides (HECs) is a decisive yet poorly understood “black box” that governs their ultimate performance for ultra‐high‐temperature applications. Here, we unveil a powerful strategy—predesigning carbon vacancies—to fundamentally enhance HECs oxidation resistance. By integrating in situ x‐ray diffraction (XRD) and in situ transmission electron microscopy coupled with electron energy loss spectroscopy (TEM‐EELS), we provide the first direct, atomic‐scale visualization of oxygen atoms preferentially occupying these predesigned vacancies during the incipient oxidation stage, leading to the dynamic formation of a metastable metal–carbon–oxygen (M–C–O) interfacial layer. Our combined experimental and theoretical analyses reveal a dual enhancement mechanism: kinetically, M–C–O suppresses both oxygen adsorption on the (111) surface and its subsequent inward diffusion; thermodynamically, they stabilize the HEC lattice at elevated temperatures, thereby increasing the energy barrier for M─C bond cleavage. This work not only deciphers the atomistic origin of enhanced oxidation resistance but also establishes a simple, general, and efficient design principle for next‐generation ultra‐high‐temperature ceramics.