Size dependent hidden serration behaviors of shear banding in metallic glass thin films

Serration usually observed in metallic glass (MG) is attributed to the shear band propagation and reflects the heterogeneous deformation in a large-length scale. However, the knowledge concerned small length scale heterogeneous deformation intrinsically related to shear transformation zones (STZ) in metallic glass is inadequate, for the difficulty to probe the variable in deformation process on small spatial scales. In this study, we investigated the small length scale hidden serration upon nanoindentation on metallic glass film. The hidden serration was attributed to STZs evolution, instead of shear band propagation. More heterogeneous structure which contains more STZs with larger volume, getting more possibilities to be activated and percolated, result in small-scale serration in the slope curve of load-displacement. The hidden serration patterns established a correlation between load-displacement curve and shear banding process down to microscopic level. It offers a deep understanding of heterogeneous structures dependent plasticity in metallic glasses.