A molecular dynamics study of the influence of nucleation conditions on the phase selection in Fe50Mn30Cr10Co10 high entropy alloy

Abstract

Non-equiatomic high entropy alloys with single or multiphase microstructures offer opportunities to optimize the mechanical properties through compositional variation. The Fe-Mn-Cr-Co alloys have shown the potential to activate nanotwinning at large strains even at room temperatures, thereby enhancing both ductility and strength. This paper presents a molecular dynamics study of phase formation during solidification of Fe50Mn30Cr10Co10 using a modified embedded atom method potential. The evolution of the phases has been investigated using adaptive common neighbour analysis, composition analysis, and radial distribution function. In contrast to the reported microstructures containing FCC and HCP phases, a BCC phase with the average composition of the alloy has resulted under homogeneous conditions. On the other hand, heterogeneous nucleation from an initial FCC seed resulted in a dual-phase microstructure of FCC and HCP at 300 K in agreement with the experiments. Interestingly, annealing at 900 K did not alter the phase fractions in samples from both nucleation conditions. Analysis based on the empirical thermodynamic parameter suggested by Ye et al. [Materials Today (2016), Vol19, p349–362] and valence electron concentration (VEC) supports the formation of both types of microstructures observed here. Hence, biasing the nucleation process is believed to strongly influence the type of phases formed in this alloy.