Formation and dilatation of shear bands in a Cu-Zr metallic glass: A free volume perspective

We study the tensile deformation behaviour of metallic glass Cu$_{50}$Zr$_{50}$ as a function of quenching rate using molecular dynamics simulations. The atomic scale shearing is found to be independent on atomic free volume, and the macroscopic correlation between the yield strength and the density (or average free volume) is a coincidence that the samples with large free volume also have a low density of shear-resistant local five-fold symmetry. In the relatively slowly quenched ($\leq 10^{10}$ K/s) samples, shear bands have a dilatation about 0.5\%, which compares well with recent experiment results. In contrast, although more active local shearing occurs in the rapidly quenched samples, shear bands are not observed. This is because the strain energy disperses into local atomic shearing at the macroscopically elastic stage and, hence, is not sufficient for shear band activation, resulting in homogeneous deformation and appreciable plasticity.