Molecular Dynamics Simulations of Micromechanical Behaviours for AlCoCrFeNi2.1 High Entropy Alloy during Nanoindentation

Eutectic high entropy alloys are noted for their excellent castability and comprehensive mechanical properties. The excellent mechanical properties are closely related to the activation and evolution of deformation mechanisms at the atomic scale. In this work, AlCoCrFeNi2.1 alloy is taken as the research object. The mechanical behaviors and deformation mechanisms of the FCC and B2 single crystals with different orientations and the FCC/B2 composites with K-S orientation relationship during nanoindentation processes are systematically studied by molecular dynamics simulations. The results show that the mechanical behaviors of FCC single crystals are significantly orientation-dependent, meanwhile, the indentation force of [110] single crystal is the lowest at the elastic-plastic transition point, and that for [100] single crystal is the lowest in plastic deformation stage. Compared with FCC, the stress for B2 single crystals at the elastic-plastic transition point is higher. However, more deformation systems such as stacking faults, twins and dislocation loops are activated in FCC single crystal during the plastic deformation process, resulting in higher indentation force. For composites, the flow stress increases with the increase of B2 phase thickness during the initial stage of deformation. When indenter penetrates heterogeneous interface, the significantly increased deformation system in FCC phase leads to a significant increase in indentation force. The mechanical behaviors and deformation mechanisms depend on the component single crystal. When the thickness of the component layer is less than 15 nm, the heterogeneous interfaces fail to prevent the dislocation slip and improve the indentation force. The results will enrich the plastic deformation mechanisms of multi-principal eutectic alloys and provide guidance for the design of nanocrystalline metallic materials.