Vacancy formation energies and migration barriers in multi-principal element alloys

TL;DR

This study uses density-functional theory to analyze vacancy stability and diffusion barriers in a refractory-based multi-principal element alloy, revealing how local lattice distortion influences atomic migration and material durability under irradiation.

Contribution

It provides the first detailed computational analysis of vacancy behavior in refractory MPEAs, linking local lattice distortion to diffusion barriers and irradiation response.

Findings

Lattice distortion correlates with migration barriers in the alloy.

Ti and Zr atoms have lower diffusion barriers than Mo and W.

Vacancy diffusion likelihood varies with alloy composition under irradiation.

Abstract

Multi-principal element alloys (MPEAs) continue to garner interest as structural and plasma-facing materials due to their structure stability and increased resistance to radiation damage. Despite sensitivity of mechanical behavior to irradiation and point-defect formation, there has been scant attention on understanding vacancy stability and diffusion in refractory-based MPEAs. Using density-functional theory, we examine vacancy stability and diffusion barriers in body-centered cubic (Mo0.95W0.05)0.85Ta0.10(TiZr)0.05. The results in this MPEA show strong dependence on environment, originating from local lattice distortion associated with charge-transfer between neighboring atoms that vary with different chemical environments. We find a correlation between degree of lattice distortion and migration barrier: (Ti, Zr) with less distortion have lower barriers, while (Mo, W) with larger distortion have higher barriers, depending up local environments. Under irradiation, our findings suggest that (Ti, Zr) are significantly more likely to diffuse than (Mo, W) while Ta shows intermediate effect. As such, material degradation caused by vacancy diffusion can be controlled by tuning composition of alloying elements to enhance creep strength at extreme operating temperatures and harsh conditions.