High-entropy alloys (HEAs) are becoming increasingly important in advanced manufacturing applications due to their exceptional material properties, including oxidation resistance at and within extreme conditions. In this study, a combined experimental and theoretical approach is used to elucidate surface/near-surface details of structural, energetic, and chemical/electronic properties of CoCrFeNi, a quaternary fcc HEA, upon exposure to oxygen. Employing Density functional theory (DFT) calculation and DFT-driven Molecular Dynamics (DFT-MD), as well as photoelectron spectroscopy, we show strong evidence that, at the oxygen coverages used, oxidation is limited to the near-surface region of this random HEA and that the propensity of oxidation of Cr >> Fe approximate to Co >> Ni atoms, identified by an enhanced hybridization of the O 2p with the Cr 3d, and lesser extent to Fe and Co. Moreover, comparing to the O interaction strength in pure metal surfaces, there is weakening of Cr-O binding due to the presence of Co and Ni while Co-O binding is stronger. Ni-O does not seem to be affected, but being this the weakest interaction, O binds to Cr, Fe, and Co and little is left to bind with Ni.
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