Unraveling structural relaxation induced ductile-to-brittle transition from perspective of shear band nucleation kinetics in metallic glass

Abstract

Structural relaxation induced ductile to brittle transition seriously hampers the practical applications in metallic glasses. Although there have been many researches focusing on the hidden physical mechanism of ductile to brittle transition, the correlation between ductile to brittle transition and shear band nucleation kinetics is still unclear. In this work, by applying for one new studying strategy based on the nanoindentation, the evolution of the thermodynamic property, the macroscopic mechanical behavior and the corresponding shear band nucleation kinetics including the nucleation site type, the nucleation site density and the nucleation rate with annealing time at one Sub-glass transition temperature, were systematically investigated. We found that there appears one critical annealing state corresponding to the ductile to brittle transition and then the ductile-to-brittle transition induced by structural relaxation is the comprehensive result of the transition of the shear band nucleation mode, the nucleation site density and the nucleation rate. These results provide new enlightenment for the structural relaxation effect on the shear band nucleation and the macroscopic deformation behaviors, and for developing new metallic glasses with improved mechanical properties.