Molecular dynamics simulations for nanoindentation response of nanotwinned FeNiCrCoCu high entropy alloy

Twin boundary (TB) plays an important role on the plastic deformation of high entropy alloy (HEA). The strong effects of TB on the deformation response of HEA are revealed from atomic level based on the defect structure, shear strain and surface morphology, by comparing the nanoindentation behavior of nanotwinned FeNiCrCoCu HEA (nt-HEA) and single-crystal FeNiCrCoCu HEA (single-HEA). The plastic deformation of nt-HEA is mainly dominated by the dislocations slip confined by first twinning layer, the TB migration, the dislocation nucleation at TB and the stacking fault tetrahedron (SFT) formation, while the dislocation loop emission is the main plastic deformation feature of single-HEA. Compared to the case for single-HEA, the nanoindentation induces more dislocations in nt-HEA. The shear strain in nt-HEA mainly distributes in the first twinning layer, due to the obstacle effect of TB. The shear zone is larger in nt-HEA, and the distribution of shear strain on the nt-HEA surface is more symmetric. The nanoindentation generates fewer steps on the nt-HEA surface, and then brings about a relatively smooth surface for nt-HEA. These findings provide an insight into the TB effect on the nanoindentation response of FeNiCrCoCu HEA, and develop the application of nanotwinned HEA systems.