Size-effects in tensile fracture of rejuvenated and annealed metallic glass

Abstract

Hundreds of Pt-based metallic glass samples with diameters ranging from sub-100 nm to 100 µm are subjected to cryogenic rejuvenation and annealing above glass transition temperature before tensile loading at room temperature. Shear-localized failure with no ductility is observed in large samples whereas the smaller diameter specimens show ductile necking irrespective of the structural state of metallic glass. With decreasing sample diameter, the fracture surface changes from vein pattern to featureless in the shear-localized samples and the ductility increases in the necked samples. Despite similar size-dependent trends, the changes in deformation mode and fracture morphology occur at different diameters in as-cast, rejuvenated, and annealed samples. The critical diameters for transitions from shear localization to necking and from vein pattern to smooth fracture surface shift to larger values in cryogenically rejuvenated samples whereas annealing has the opposite effect. Rejuvenation promotes homogeneous-like flow and suppresses catastrophic tensile failure in nanoscale metallic glasses.