Evolution of free volume and shear band intersections and its effect on hardness of deformed Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass

Introduction of shear bands in metallic glasses is usually regarded as being responsible for softening metallic glasses. Here we present that hardness of deformed Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass (BMG) exhibits an initial decrease and a subsequent increase with plastic strain. This extraordinary variation of hardness was studied by investigating evolution of shear band intersections and free volume with plastic strain. As plastic strain increases from 6% to 83%, the density of shear bands increases from 0.04 to 0.92 mu m(-1). Meanwhile, the distribution width of shear band spacings gradually narrows, and the number of intersections between shear bands increases. When plastic strain is larger than 47%, the number of intersections increases faster. Free volume in the deformed BMG at room temperature increases with plastic strain increasing from 6% to 83%. Both free volume induced softening and shear band interaction induced hardening may affect the hardness of the deformed BMG. In the plastic strain range of 0%-47%, free volume induced softening mainly contributes to the initial decrease in hardness with plastic strain. In the plastic strain range of 47%-83%, shear band interaction induced hardening may lead to the increase in hardness with plastic strain, after counteracting free volume induced softening. (C) 2016 Elsevier B. V. All rights reserved.