Plasticity in cyclic indentation of a Cu-Zr-based bulk metallic glass after tensile loading: An experimental and molecular dynamics simulation study

In this study, we combined experiments and molecular dynamics simulations to investigate the deformation of metallic glasses subjected to previous tensile deformation. The experimental investigations were conducted on a Zr67Cu10.6Ni9.8Ti8.8Be3.8 (wt%) sample and the molecular dynamics simulations were performed on a Cu64.5Zr35.5 sample. Initially, plasticity was induced in the specimens by tensile deformation through the formation of shear bands, and we studied the further evolution of plasticity using cyclic indentation. We found that the macroscopic properties measured in experiments, such as hardness and hysteresis width, qualitatively agree with simulations. We use the molecular dynamics simulations to analyze the microscopic properties resulting from cyclic indentation and determine the polyhedral packing structures ('motifs') after tensile deformation in regions outside and around the shear bands. We then followed their evolution after each indentation cycle. Our findings indicate that areas outside the shear bands experience higher shear strain during cyclic indentation and that all motifs increased in fraction but evolved differently inside and outside the shear bands. The first indentation leads to the strongest change in microstructure, affecting both the material within and outside of shear bands. Repeated indentation mostly acts on the shear bands. These changes lead to a stabilization of the material in the sense that motifs with high coordination number and hence bond formation are established.