Effects of pre-strain on the nanoindentation behaviors of metallic glass studied by molecular dynamics simulations

[Display omitted] •Pre-tensile stress has a “weaken” mechanism on MG indentations.•Pre-compressive stress has a “harden” to “weaken” effects transition.•Brittle shear banding occurs on MGs with high pre-stress.•The plastic-brittle transition is mainly attributed to the potential energy state of MG. Nanoindentation simulations have been performed on pre-compressed and pre-stretched Cu64Zr36 metallic glasses (MGs) samples via molecular dynamics methods, to investigate the effects of pre-stress on the mechanical behavior, deformation performance and shear bands forming morphologies of the MG material. The results have shown that pre-tensile stress has a more intuitive “weaken” impact on the mechanical performance of the MG. While for pre-compressive cases, with increasing compressive strain, the pre-stress has a “harden” to “weaken” effects transition. Based on Hertz’s contact, the analysis of simulation results indicated both the stress state of the material and the structural change induced by applied stress contribute to the “harden/weaken” effects. Besides, the shear bands morphologies under indentations are also found to be influenced by the sign and magnitude of the pre-stress. And if the pre-stress is large enough, the shear banding would propagate spontaneously and rapidly, which may result in brittle deforming mode happened in the indentation process. Furthermore, By using the energy analysis method, this plastic to brittle transition is inferred to be connected with the stress state and potential energy stored in the material. If the stored potential energy exceeds the essential forming energy of shear bands, the fracture would happen once local area is triggered by external stress.