Microstructure evolution of Zr60Al15Ni25 bulk metallic glass subjected to rolling at room temperature

The microstructure evolution of Zr60Al15Ni25 bulk metallic glass during rolling at room temperature has been investigated by differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM). The released heat due to the structural relaxation before glass transition in the DSC curves indicates a two-state characteristic of atomic movement during rolling of the metallic glass, as modeled in the free volume model and shear-transformation-zone theory. The HRTEM images show that nanocrystallization preferentially occurs in the transition regions between the shear bands and the undeformed amorphous matrix. The gradient content distribution of excess free volume along the width of a shear band is conceived, based on which the variation of viscosity within a shear band is analyzed. Then the mechanism of deformation-induced crystallization is discussed within the frame of viscous flow.