Tunable Tensile Ductility of Metallic Glasses with Partially Rejuvenated Amorphous Structures

We report that the tensile ductility of metallic glass (MGs) is tunable by introducing gradient rejuvenated amorphous structures (GRASs) using large-scale atomistic simulations. The results revealed that the introduced GRASs promote spatial strain fluctuation in MGs upon yielding, acting as heterogeneous sources for triggering multiple shear bands in the interior unrejuvenated region, thus resulting in a more dispersed plastic shearing throughout the sample. It is also demonstrated that increasing both the volume fraction and the structural disordering degree of GRASs can improve the tensile ductility of MGs and lead to a ductile-to-brittle transition, although at the expense of some strength. Moreover, the critical volume fraction of GRASs required for switching the transition was found to depend on the specific structural disordering degree. The observed structural state-dependent transition of the deformation mode was further understood from a mechanical perspective by considering the competition between the macroscopic yield strength and the critical stress of the material required for shear delocalization, based on which a criterion was developed to predict the critical transition boundary in MGs with GRASs across a wide range of structural states. The findings provide a detailed atomistic understanding of the relationship between the structural state and mechanical properties in MGs with spatially distributed structural heterogeneities, which may offer some insights for designing and processing MGs with a sought-after combination of ductility and strength.