Shear band evolution and hardness change in cold-rolled bulk metallic glasses

Abstract

A systematic investigation of the shear band evolution and hardness change with deformation was performed on cold-rolled Zr 64.13Cu 15.75Ni 10.12Al 10 and Zr 46.5Cu 45Al 7Ti 1.5 bulk metallic glasses. It was found that primary shear bands reach saturation after 7% in thickness reduction and only primary shear bands exist below 20% in thickness reduction, based on statistical analyses of primary shear band spacing, angle and offset. Rolling creates more free volume, and deformation-induced residual stress distribution in a heavily rolled specimen relative to the as-cast specimen has been determined. Larger tensile residual stresses are generated on the side surface as compared with those on the top surface, while compressive residual stresses in the middle are induced. Such residual stresses strongly influence the hardness measured. It is also revealed that after stress relief, the hardness does not decrease considerably in heavily rolled/annealed specimens here as compared to as-cast/annealed specimens, probably due to low shear band density.