Effects of alloying on deformation twinning in high entropy alloys

In the current work, molecular dynamics (MD) simulations were employed to model the compressive property of FCC (face centered cubic) Al0.25CoFeNiCu0.75 high entropy alloy (HEA) nanopillars. For comparison the binary, ternary and quaternary derivatives based on Ni-Cu-Fe-Co-Al system along with pure Ni were investigated. The twin nucleation and migration stress, atomic strain and stress and generalized planar faults energy (GPFE) of the compositions were calculated. The simulation results suggest that plastic deformation of all nanopillars is mediated by deformation twinning, but both the yield strength and flow stress decrease with the increase in the number of alloying elements, implying the decrease in the twin nucleation and migration stresses, respectively. The atomic strain and stress, increasing with the addition of alloying elements, provide direct evidences at atomic scale for the severe lattice distortion resulting in the decrease in stacking fault energy (SFE) and twin boundary energy as shown in the GPFE curves. The SFE of Al0.25CoFeNiCu0.75 HEA is 16mJ/m(2). The twinnability of the studied compositions also increases with the addition of alloying elements, so twinning deformation dominates in the current nanocrystals.