Investigation of the softening behavior in severely deformed micromachined sub-surface of Zr-based bulk metallic glass via nanoindentation

Abstract

In this study, the orthogonal micromachining of a Zr-based bulk metallic glass (BMG) was carried out at different cutting speeds and undeformed chip thicknesses. The work softening behavior of the micromachined sub-surface was characterized via nanoindentation. It was observed that the serrated flow in the load-displacement curves during nanoindentation depends on the previous machining conditions. The softening in the machined subsurface was studied up to a depth of 300 µm and the minimum and the maximum reductions in nanohardness with respect to unmachined region were 13% and 37%, respectively. Furthermore, the shear transformation zone volume of the machined surface was determined and its correlation with the cutting force coefficients Kc and Kt was observed. Differential scanning calorimetry (DSC) reveals an increase in the free volume due to micromachining of BMG. This work presents a nanoindentation-based framework and insight into the changes occurring in the sub-surface due to severe plastic deformation in BMG.