Shear localization and its dependence on microstructural length scales in metallic glass composites

Abstract

Extrinsic approaches for the pursuit of ductility in metallic glasses have involved the introduction of a ductile crystalline phase to inhibit the propagation of a dominant shear front through the amorphous matrix material. Using nanoindentation, we explore the role of crystalline inclusions in metallic glass matrix composites with a focus on the onset of shear banding in the amorphous matrix and the nature of shear band propagation using the propensity for localization and its dependence on indentation strain rate. When indentation length scales are favorable to distribute strain to both the crystalline dendrites and amorphous matrix, we reveal a reduction in the number of detectable displacement bursts and an accompanying decrease in the magnitude of individual depth excursions from shear banding. A decrease in the stress at the onset of shear banding is also correlated with shear band trajectories interacting with the amorphous-crystalline interfaces (ACIs). Our results thus demonstrate that ACIs reducing the activation barrier for shear banding combined with dendrites arresting propagating shear fronts act to enhance the nucleation rate and in turn, promote a more homogeneous plastic response.