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High entropy alloys (HEAs) are promising candidates for high-temperature structural material applications. Oxidation is a major factor that must be accounted for when designing such materials and it is thus important to study the oxidation behavior of HEAs to enable the optimum design of next generation materials. In this study, the thermodynamic behavior of interstitial oxygen in a Mo-Nb-Ta-W high entropy alloy was explored beyond the dilute limit. This was accomplished by sampling configurations of the HEA and HEA-oxygen systems from an isothermal–isobaric ensemble using a series of first-principle-based Monte Carlo simulations. It was found that the interstitial oxygen had comparable stability at tetrahedral (T) sites and octahedral (O) sites. The stability of the interstitial oxygen was correlated with the composition of the surrounding local metallic environment. The O-site interstitial oxygen was further found to arrange in ordered clusters and was associated with enhanced mechanical properties as demonstrated by an increase in the bulk modulus with increasing oxygen content. Finally, the solubility of the interstitial oxygen in the alloy was found to decrease with temperature.


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Journal of Applied Physics