Strain rate sensitivity of a Cu60Zr40 metallic and nanoglass

Abstract

The strain rate sensitivity, m, of a binary Cu60 Zr40 nanoglass (NG) and metallic glass (MG) are investigated using nanoindentation. Indentations were performed at different loading rates in the range of 0.26–8 mN/s, which gives equivalent indentation strain rates over three decades. The load vs. displacement curves of MG exhibited noticeable displacement bursts at low loading rates, which gradually decreased with increasing loading rate suggesting a transition from more to less severe heterogeneous plastic flow. While in the case of NG, no noticeable displacement bursts are present at any of the loading rates suggesting a near homogeneous plastic flow. In both NG and MG, the hardness decreases with increasing loading rate, resulting in negative strain rate sensitivity, m. The m for NG is higher than the MG, indicating a more homogeneous flow underneath the indentation. Interface indentation experiments and subsequent analysis of the deformation zone showed a larger number of fine secondary shear bands (SSBs) in NG as compared to the primary shear bands (PSBs), while the plastic flow in MG is accommodated mostly by the PSBs. The findings of the current study will help improve the understanding of the plastic deformation behavior of NGs and provide insights for designing the novel microstructural architecture of amorphous alloys with improved ductility.