In situ SEM study of formation and growth of shear bands and microcracks in bulk metallic glasses

Formation and growth of shear bands and microcracks in bulk metallic glasses of Zr57Cu15.4Ni12.6Al10Nb5 and Zr41.2Cu12.5Ni10Ti13.8Be22.5 have been investigated through in situ tensile tests in scanning electron microscope using a single-edge notched specimen. Atom force microscope was used to study the three-dimension pattern of fine shear bands. The results show that besides shear stress, normal stress plays also an important role in forming and growing of shear bands, which appear first during loading. Mode II shear microcrack will initiate and propagate first in the shear planes along shear bands. The mode II cracks will open and become a shallow I+II complex crack because there is a component of normal stress. As soon as the complex crack (or cracks) becomes a mode I crack penetrating the thickness through propagating from the surface (or surfaces) toward the centre, the specimen will fracture immediately.