Diffusion coefficients of multi-principal element alloys from first principles

TL;DR

This paper introduces a first-principles computational method to accurately predict diffusion coefficients in multi-principal element alloys, revealing key factors controlling atomic mobility and enabling targeted alloy design.

Contribution

We develop the embedded local cluster expansion (eLCE) method to connect electronic structure calculations with kinetic Monte Carlo simulations for multicomponent diffusion.

Findings

Local kinetic barriers dominate diffusion control.

Diffusion behavior depends on vacancy migration barriers and percolation pathways.

Identified alloy compositions with anti-sluggish diffusion.

Abstract

Vacancy-mediated diffusion in multi-principal element alloys (MPEAs) remains poorly understood. Existing computational methods face challenges in connecting electronic structure to macroscopic transport coefficients due to the large number of chemical elements. To address this, we introduce the embedded local cluster expansion (eLCE), which bridges first-principles calculations with kinetic Monte Carlo simulations to compute the matrix of multicomponent diffusion coefficients. Applying this approach to refractory MPEAs in the V-Cr-Nb-Mo-Ta-W system, we evaluate the complete mobility and diffusion tensors of a six-component alloy at finite temperatures. We find that local kinetic barriers, rather than thermodynamics or vacancy correlation factors, primarily control diffusion in these materials. Whether diffusion is sluggish or anti-sluggish depends on the mean vacancy migration barrier relative to the rule-of-mixtures estimate and on the availability of percolating pathways of fast-diffusing species. We use this insight to screen the senary composition space and identify compositions with anti-sluggish diffusion. This study presents a predictive, first-principles approach for computing non-dilute transport coefficients and designing MPEAs with targeted transport properties.