Ductile fracture in notched bulk metallic glasses

Abstract

The deformation of bulk metallic glasses (BMGs) is generally driven by highly localized shear. Due to such inhomogeneous flow, failure occurs in a catastrophic brittle manner through rapid shear banding, often associated with very limited plastic strain macroscopically. Here, we demonstrate metal-like ductile fracture in Zr-based BMGs under tension, a completely opposite situation, by suppressing shear banding. In the absence of shear bands, nucleation of cavies/voids and subsequent void growth and coalescence dominate the initial plastic failure process, enabling BMGs to display the essential characteristics of ductile fracture, with deep dimples and cup-and-cone morphology. This ductile fracture only occurs in amorphous alloys, but not in the fully crystallized counterpart. Furthermore, the characteristic decohesion strength of the ductile fracture in Zr-based BMGs was found to be 1.75 GPa, one of the highest among engineering metals and alloys. These present findings reveal the previously hidden ductile behavior of BMGs, suggesting an alternative method to enhance the ductility of BMGs by removing shear banding.