Plastic deformation of metallic glasses: Size of shear transformation zones from molecular dynamics simulations

Plastic deformation in metallic glasses well below their glass transition temperatures T-g occurs spatially heterogeneously within highly localized regions, termed shear transformation zones (STZs). Yet, their size and the number of atoms involved in a local shear event, remains greatly unclear. With the help of classical molecular dynamics (MD) computer simulations on plastic deformation of the model glass CuTi during pure shearing, we address this issue by evaluating correlations in atomic-scale plastic displacements, viz. the displacement correlation function. From the correlation length, a universal diameter of about 15 angstrom, or, equivalently, approximately 120 atoms is derived for a variety of conditions, such as variable strains, strain rates, temperatures, and boundary conditions. Our findings are consistent with a recent model proposed by Johnson and Samwer.