First principles exploration of near-equiatomic NiFeCrCo high entropy alloys

Abstract

High entropy alloy NiFeCrCo was systematically studied in the range of near-equal atomic concentrations, i.e., 10–40 at.%, by first-principles tools and high throughput calculations. Enthalpy of mixing, lattice parameter (a0), bulk modulus (B), and shear modulus (G) were calculated by the exact muffin-tin orbital method combined with coherent potential approximation (EMTO-CPA) for over 2700 compositions of the NiFeCrCo alloy as a single-phase solid solution in paramagnetic state. It was found that certain elements have the most significant influence on each property, namely, Cr on enthalpy of mixing, Co on a0, Fe on B, Co on G, and Cr on the ratio of B/G. An equation to predict the enthalpy of mixing by use of binary enthalpy data was evaluated and was found to have a good accuracy with a root-mean-square deviation (RMSD) of 42 meV per formula unit in the prediction. A similar equation to predict bulk modulus with weighted contribution from first–shell interaction is proposed and tested on all alloys. This equation was also found to be accurate with a RMSD of 6 GPa. Finally, it was found that shear moduli of all tested alloys are largely dependent on C44, while the concentration of Co has a noticeable control on C44. Spin polarized calculations were performed for a select group of alloys with both EMTO-CPA and the Vienna ab-initio Simulation Package (VASP) with special quasi-random structure models for comparison. Good agreement was found between these methods.