Aspect ratio-dependent nanoindentation behavior of Cu64Zr36 metallic glass nanopillars investigated by molecular dynamics simulations

In this paper, we study nanoindentation in Cu64Zr36 metallic glass (MG) nanopillars with different aspect ratios by molecular dynamics simulations. The activation of shear transformation zones (STZs) and the deformation behavior of MG pillars are discussed during nanoindentation loading and unloading processes. Buckling and serrated flow are the two types of deformation behaviors observed during nanoindentation. For large aspect ratio pillars, a sudden stress drop in the load–displacement curve is found that relates to the buckling process, while smaller aspect ratio pillars exhibit large stress fluctuations. The serrated flow is associated with STZ activation. STZs are locally activated, and their number gradually increases with increasing indentation depth during loading, whereas their number decreases during unloading. For pillars with a large aspect ratio, no new STZs are activated and their number decreases rapidly once the indenter has left the sample because of the buckling deformation. In contrast, new STZs are activated for pillars with smaller aspect ratio during the unloading process. Analysis of STZ activation and shear localization reveals an inhomogeneous deformation process and an increase in the degree of structural heterogeneity as the aspect ratio of the pillars increases for both loading and unloading stages. The present work provides an insight into the atomic-scale plastic deformation behavior of MG nanopillars during nanoindentation loading and unloading processes