The structural heterogeneity response and the STZ evolution in Zr-based metallic glass during nanoindentation creep

In this paper, the rheological behavior of the bulk metallic glass Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be₂₂ (Zr-BMG) was investigated by nanoindentation. Firstly, nanoindentation tests were conducted on Zr-BMG at different loading rates. Then the Maxwell-Voigt model was employed to model the creep behavior, the viscoelastic and viscoplastic deformations during the creep were separated to analyze, and the delay spectrum during the creep process was calculated. It was found that structural heterogeneity evolves dynamically at the nanoscale during nanoindentation creep. Finally, the size of the shear transition zone (STZ) during creep was calculated by the strain rate sensitivity (SRS) method. The results show that at higher loading rates, the viscoelastic units cannot fully relax, leading to transition into viscoplastic deformation. Zr-BMG has stronger deformation resistance at higher strain rates, which usually leads to a smaller STZ. Furthermore, STZ is more easily activated and evolves into a response of structural heterogeneity to external stimuli, and the material exhibits more obvious creep fluidity. The indentation creep mechanism is due to the deformation of the micro-shear domains in Zr-BMG, leading to the activation and expansion of defects, which ultimately irreversibly merge into larger defects, revealing the process of local atomic rearrangement and diffusion.