Molecular simulation of microstructure evolution and plastic deformation of nanocrystalline CoCrFeMnNi high-entropy alloy under tension and compression

Highlights:• A microstructure analysis of the correlation between stress and microstructural changes during the plastic deformation of nanocrystalline CoCrFeMnNi HEA under tension and compression.• An obvious phase transformation (FCC→BCC→HCP) and parallel twin-behavior due to the interaction of intrinsic SFs are obtained for single-crystal CoCrFeMnNi HEA under tension and compression.• Grain refinement appeares in some regions of materials during the compressive loading.• It shows that homogeneous dislocation nucleation and SF growth are appeared for polycrystalline CoCrFeMnNi HEA. Meanwhile, the growth rates of intrinsic SFs released from different grain boundaries are almost equal. -- Abstract: High-entropy alloys (HEAs) composed of equal numbers of five or more elements exhibit excellent mechanical properties. The unique nanostructures for the materials may have novel plastic deformation. By using molecular dynamics simulations, the plastic deformation of single-crystal and polycrystalline CoCrFeMnNi high-entropy alloys was analyzed under tension and compression. The simulation results suggested that the FCC→HCP phase transformation occurred during the plastic deformation of the HEA material. Meanwhile, for the compressive loading, grain refinement occurred due to the interaction of intrinsic stacking faults (SFs) with different direction, and cause the discrepancy of crystal orientation, which efficiently improve the strength of the material. As the strain increased, some parallel twins appeared in HCP phase regions, generating the stress fluctuation behavior shown in the stress-strain curves. The atomic snapshots of polycrystalline CoCrFeMnNi high-entropy alloy show homogeneous dislocations nucleation, and that the distance of different intrinsic SFs with the same direction of movement was equal to eight layers of atoms. The results are qualitatively consistent with experiments and provide a fundamental understanding of plastic deformation in FCC CoCrFeMnNi HEA.