Observation of shear bands in the Vitreloy metallic glass subjected to HPT processing

Abstract

The parameters of shear band evolution with deformation were examined in the Vit105 bulk metallic glass. For this purpose, two halves of disks of the bulk metallic glass were joined together and processed by high-pressure torsion for various strains: from compression without rotation, to rotation for 5 revolutions. The discrepancy between the experimentally observed and predicted shear strains was detected. The actual strain is significantly smaller than the predicted one. The SEM examination of the internal surfaces of two joint halves of an HPT-processed disk allowed to study the formation and accumulation of shear bands under an increased imposed strain. The maximum density of the shear bands is observed at the edges of the HPT samples and in areas adjacent to the upper anvils. An increase in strain leads to an increase in the shear bands density. The observed minimum shear band spacing is equal to 0.5 μm after HPT processing for 5 revolutions. According to the structural changes recorded by XRD (an increase in the free volume content by about 1.3%) and formation of a high density of shear bands, HPT leads to a significant structural transformation of the amorphous structure of the BMG.