On the adsorption of oxygen to high entropy alloy surfaces up to 2ML coverage using Density Functional Theory and Monte Carlo calculations

TL;DR

This study uses density functional theory and Monte Carlo simulations to investigate oxygen adsorption and diffusion on high-entropy alloy surfaces, revealing key factors affecting oxidation resistance and surface reactivity.

Contribution

It provides a detailed computational analysis of oxygen interactions with a specific high-entropy alloy, highlighting the roles of Ti, Zr, Nb, Al, and Ta in oxidation behavior.

Findings

High reactivity of the alloy surface to oxygen with up to 2 monolayers coverage.

Ti and Zr increase surface reactivity, while Nb, Al, and Ta enhance resistance.

Oxygen diffusion is favored in Zr-rich regions and slowed by Ti and Al.

Abstract

To enhance our understanding of oxidation in high-entropy alloys, the early stages of oxidation on the surface of Al10Nb15Ta5Ti30Zr40 were studied using density functional theory and thermodynamic modeling. Surface slabs were generated from bulk configurations sampled from equilibrium using a multicell Monte Carlo method for phase prediction. The bulk structure was found to be a single BCC phase in good agreement with experimental observations. The oxygen adsorbed with a strong preference for sites with Ti and Zr and avoided sites with Nb-Al and Nb-Ta. The surface was shown to be highly reactive to oxygen, yielding a dominating oxygen coverage of two monolayers over the temperature range of 100 to 2600 K and an oxygen pressure range of 10-30 to 105 bar. Inward oxygen diffusion at low coverage was preferred in regions rich with Zr but slowed with the addition of Ti and Al. Diffusion rates drastically decreased at 1 ML, especially in the region rich with Ti and Zr, where strong metal-oxygen bonds were reported. Our results indicated that a high content of Ti and Zr increased the reactivity of the HEA surface to oxygen. The presence of Nb also enhanced the resistance to oxygen adsorption, especially when partnered with Al and Ta. Inward oxygen diffusion was likely to occur at low coverage in regions rich with Zr but could be protected against with the addition of Al and Ti. The limitations of the present work are discussed. This study may provide insights that assist with devising short- and long-term mitigation strategies against material degradation related to high-temperature oxidation.