Modelling Multicomponent Alloys Across Length Scales: Insights from an Interdisciplinary Approach

Contributed talk at the 2024 CoSeC Conference.

CoSeC is the Computational Science Centre for Research Communities, and is administered by the Scientific Computing Department (SCD) of the UK Science and Technology Facilities Council.

Abstract

So-called ‘high-entropy alloys’ (HEAs)—those alloys containing four or more elements combined in near-equal ratios—are of interest for a range of next-generation engineering applications. Moreover, from a fundamental science perspective, they represent a fascinating but challenging class of materials to study. ‘Fascinating’ because the large ‘entropy of mixing’ in such systems stabilises single-phase solid solutions containing combinations of elements which do not readily form binary alloys. ‘Challenging’ because the size of the phase space grows combinatorially with the number of chemical species considered, and because inclusion of elements at arbitrary concentrations frequently necessitates the use of comparatively large, computationally expensive, supercells in theoretical studies. Such challenges necessitate interdisciplinary development of modelling approaches which span length scales.

Here, I will present results demonstrating that an old idea—the Coherent Potential Approximation (CPA)—combined with a new, perturbative approach developed for analysing the energetic cost of chemical fluctuations in multicomponent alloys, can provide a computationally inexpensive and physically insightful method for examining the phase stability of these complex systems. I will present results from case studies on a range of prototypical high-entropy alloys demonstrating that the approach successfully captures the phase behaviour of these systems, as well as providing fundamental physical insight into the electronic (and occasionally magnetic) origins of atomic ordering tendencies. The emphasis will be on how a combination of electronic structure calculations, atomistic models, and enhanced sampling techniques can be combined to provide insight into the phase behaviour and physical properties of these materials.