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 reveal that the ductile GRASs promote the formation and propagation of new shear bands in the interior unrejuvenated region by suppressing the catastrophic propagation of individual shear bands across the GRASs, thus resulting in a more dispersed plastic shearing throughout the sample. It is also demonstrated that increasing both the volume fraction and degree of structural disordering of GRASs can improve the tensile ductility of MGs and lead to a brittle-to-ductile transition of the deformation mode, although at the expense of some strength. Moreover, the critical volume fraction of GRASs required for switching the transition is found to depend on the specific degree of structural disordering. The observed structural state-dependent transition of the deformation mode is 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 is 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 partially rejuvenated amorphous structures, which may offer useful insights for designing and processing MGs with a sought-after combination of ductility and strength. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.