Size distribution of shear transformation zones and their evolution towards the formation of shear bands in metallic glasses

• S-atoms prefer to initialize in low-packing, liquid-like areas.
• The size and distribution of STZs with strain are investigated.
• Formation of SB is linked with super-sized STZs.

The room temperature tensile deformation behavior of two metallic glasses (MGs), Cu64Zr36 and Cu40Zr60, was investigated, by employing molecular dynamics simulations, with a view to examine the evolution of plastic deformation at the atomistic scale. It was found that after reaching the maximum stress, atoms in areas with lower packing efficiency, which have liquid-like polyhedral atomic configurations, exhibit larger displacement. On further deformation, the atoms in rigidly packed regions, which have solid-like polyhedral atomic configurations, also start partaking in the plastic deformation, especially within the shear band region. The average shear transformation zone (STZ) size, defined by the coordination neighborhood of highly strained atoms, was found to increase from 17 ± 3 to 106 ± 6 atoms within the strain range of 7–12%, which spans the shear band initiation to mature formation, in both MGs examined. A detailed examination of the distributions of the number and the size of STZs as a function of strain reveals that the formation of the shear band is linked with the occurrence of a few super-sized STZs.