The mechanism of nano-scale shear banding in metallic glass

Shear banding features the deformation of metallic glass (MG) at low temperature. Understanding how a shear band forms is of primary importance for the toughening of MG and for the widening of their applications. This study used the molecular dynamics method to reveal the shear banding mechanisms in MG under different loading conditions. The MG used for the analysis was the binary glass Zr50Cu50. It was found that the underlying mechanism of plastic deformation, which is reflected by the rearrangement of atoms, is characterised by the sudden increase of kinetic energy of local atomic clusters, and that shear banding is a stress-driven coalescence of these localized atomic rearrangements. Under the simple shear loading, a shear band forms at the region of the maximum shear stress. However, under a uniaxial compression, a shear band may not form since there is no particular band of maximum shear stress and the randomly occurred local rearrangements do not necessarily align with the maximum shear direction. As such, the formation of a shear band depends on whether the mismatch strain caused by a local rearrangement is large enough to cause an event in the neighbourhood. The ratio of the local strain rate to the applied strain rate can be used as a severity measure of the local atomic rearrangement. Reducing the applied strain rate can eventually facilitate the shear banding.