Effect of mechanically induced structural rejuvenation on the deformation behaviour of CuZr based bulk metallic glass

Abstract

Severe plastic deformation of bulk metallic glasses leads to rejuvenation of the amorphous structure. Here we present results demonstrating an improved plasticity for a Cu45Zr45Al5Ag5 bulk metallic glass alloy rejuvenated by severe plastic deformation via high-pressure torsion (HPT). Nanoindentation as well as atomic force microscopy measurements performed on the cross-section of HPT samples provide evidence for the enhancement in plasticity. A robust algorithm developed to reliably detect and quantify the discontinuities (pop-ins) in the nanoindentation load–displacement curves is applied to a large dataset. The results related to the rejuvenated structure demonstrate (i) a reduction of the number of detectable pop-ins as well as (ii) a reduction of their displacement offset. Furthermore, (iii) a pronounced increase in the total creep value is observed and correlates with a plasticity criterion as well as a reduced hardness and Young’s modulus that are heterogeneously distributed across the samples due to localized strain softening during HPT. Finally, (iv) atomic force microscopy topographies obtained from selected indents support the findings, showing less pronounced steps in the plastic pile-up. The experimental results indicate that rejuvenation by HPT processing leads to structural and dynamical heterogeneities, increased atomic mobility and an improved plastic deformation response.