Anelasticity and plasticity in metallic glasses from an atomistic perspective

The relationship between the structure of metallic glasses and their mechanical behaviour is currently poorly understood. The most widely accepted theory for the atomic-scale deformation mechanisms of metallic glasses is related to the activation of shear transformation zones (STZs). The anelastic behaviour of metallic glasses under load is related to local STZ activation, while plastic deformation and shear banding are related to the percolation of STZs. Here we derive an atomistic description of the relationship between the deformation behaviour of metallic glasses and their intrinsic properties. The removal of thermal noise by simulating athermal quasi-static shear processes allows even small strain variations and elastic excitations to be identified and analysed. Analogous to Eshelby's description of an inclusion, the long-range effect of the quadrupolar elastic field induced by the STZ in the surrounding material causes a vortex-like motion of the surrounding atoms between the four wings of the quadrupolar stress field. The two-unit STZ-vortex mechanism has the potential to be crucial in understanding anelasticity and the transition to plastic deformation via STZ percolation and shear band formation. A number of fundamental insights into shear band formation, shear band branching and multiplication or the transition from shear banding to cracking are revealed. Some of these results are corroborated for the first time by experimental observations at the nanoscale, obtained using precession nanodiffraction mapping in the transmission electron microscope.