Tension–compression asymmetry of HCP CoCrFeMnNi high entropy alloy nanowires

The tension–compression asymmetry is commonly observed in conventional hexagonal close-packed (HCP) metals and its alloys, however, such a mechanical asymmetry still remains unclear in HCP high-entropy alloys (HEAs). In this study, we adopt molecular dynamics simulation to investigate the mechanical properties and deformation mechanisms of the HCP CoCrFeMnNi HEA nanowires under uniaxial tension and compression along the [0001] orientation. The results show that the HCP HEA nanowire exhibits an obvious tension–compression asymmetry at both the linear elastic and plastic deformation stages. Similar to the conventional HCP metals, the HCP CoCrFeMnNi HEA nanowire also shows elastic softening during tension while elastic hardening during compression. Such an elastic tension–compression asymmetry originates from the disparity in interatomic friction between the adjacent slip planes at the linear elastic regime under tensile and compressive loadings. In the plastic deformation stage, the yield and flow stresses of the HCP HEA nanowire in compression are both remarkably higher than the counterparts in tension, which can be ascribed to the completely different deformation mechanisms in tension and compression. Under the tensile loading, dislocation slip, phase transition, and deformation twinning are the dominant plastic deformation mechanisms and weakens the HCP HEA nanowire. During compression, dislocation slip and atomic amorphization dominates the plastic deformation and thus facilitates the strengthening. This work provides mechanistic insights into the deformation mechanism and mechanical response of the HCP HEAs, which is of importance for their rational design and device applications.