Deformation-induced medium-range order changes in bulk metallic glasses

Bulk metallic glasses (BMGs) naturally have excellent strength and elasticity while structural rejuvenation into higher energy glassy states is often required to improve ductility. However, our understanding of the detailed atomic ordering changes that occur during rejuvenation processes, such as plastic deformation, remains limited. This study utilizes nanobeam electron diffraction in a transmission electron microscope as an effective method to reveal the structural changes that occur after deformation in two Zr-based BMGs. Our findings indicate that heavy deformation from indentation or fracture causes an increase in the size of fcc-like medium-range order (MRO) clusters in a harder icosahedral dominated matrix, which corresponds to local softening of the BMGs. By examining the structure evolution at different points in the fracture process, we reveal that the mechanism of growth of MRO clusters is likely driven by enhanced diffusion from local temperature rise and/or free volume generation rather than deformation-induced nucleation and growth of new MRO sites.