Using the Coherent Potential Approximation and DFT to Examine the Phase Behaviour of High-Entropy Alloys: Case Study of Al_xCrFeCoNi.

Contributed talk at the 2024 CCP5 AGM. CCP5 is the Collaborative Community Project (CCP) for simulation of condensed phases.

Abstract

High-entropy alloys—those alloys containing four or more elements combined in near-equal ratios—represent a fascinating but challenging class of physical systems 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.

Here, I will present results demonstrating that an old idea—the Coherent Potential Approximation (CPA)—and a new, perturbative approach developed for multicomponent alloys [1-4], can provide a computationally efficient and physically insightful method for examining the phase behaviour of these complex systems. A direct analysis based on density functional theory (DFT) calculations enables inferral of phase transitions directly, while also facilitating extraction of atom-atom effective pair interactions suitable for further exploration of the phase space via lattice-based atomistic simulations using both conventional and enhanced sampling techniques. The case study will be the Al_xCrFeCoNi alloy, where we were recently able to demonstrate that the outlined methodology correctly predicts the transition from fcc to bcc lattice type with increasing $x$, as well as the emergence of intermetallic phases, in alignment with the experimentally observed phase behaviour [5].

References

[1] C. D. Woodgate, J. B. Staunton, Phys. Rev. B 105, 115124 (2022).

[2] C. D. Woodgate, J. B. Staunton, Phys. Rev. Materials 7, 013801 (2023).

[3] C. D. Woodgate, D. Hedlund, L. H. Lewis, J. B. Staunton, Phys. Rev. Materials 7, 053801 (2023).

[4] C. D. Woodgate, J. B. Staunton, J. Appl. Phys. 135, 135106 (2024).

[5] C. D. Woodgate, G. A. Marchant, L. B. Pártay, J. B. Staunton, arXiv:2404.13173.