Atomistic simulations of tensile responses in polycrystalline HCP CoCrFeMnNi high-entropy alloys

Abstract Molecular dynamics simulations are conducted to study the grain size, temperature, and strain rate dependences of the tensile properties and deformation mechanisms in polycrystalline hexagonal close-packed (HCP) CoCrFeMnNi HEAs. Our computations reveal that the plastic deformation mechanism of polycrystalline HCP CoCrFeMnNi HEA is predominantly mediated by grain boundary motion and stacking fault generation, while dislocation nucleation and propagation play a minor role. With increasing average grain size from 3.06 to 14.20 nm, the yield strength of polycrystalline HCP HEA shows a monotonic increase, consistent with the inverse Hall-Petch relationship. The damage behavior of polycrystalline HCP HEA exhibits a distinct grain size dependence, in which smaller grains lead to uniformly distributed damage throughout the specimen but larger grains result in severe local destruction. It is revealed that the polycrystalline HCP HEA exhibits significant thermal softening at elevated temperatures and remarkable strain rate hardening at higher strain rates. Furthermore, the dependences of deformation mechanisms on the temperature and strain rate are also analyzed in detail. These findings provide fundamental insights into the mechanical properties and deformation mechanisms of the polycrystalline HCP HEAs, offering important guidance for their rational design and engineering applications.