Shear deformation and plasticity of metallic glass under multiaxial loading

The evolution of multiple shear bands in a Zr-based metallic glass under multiaxial loading was systematically investigated by the small punch test. Unlike the fast propagation of the individual shear band and catastrophic failure of the metallic glass under uniaxial tensile or compressive loading, the metallic glass can be controlled to create regularly arrayed fine multiple shear bands under multiaxial loading. The distribution of the shear bands displayed a cobweb-like pattern along radial and circumferential directions. A large equivalent plastic strain (19.6%) was achieved in the metallic glass under multiaxial loading, which was far higher than that gained under uniaxial compressive loading. The multiaxial loading method was also applied to evaluate the mechanical properties of the annealed Zr-based metallic glass. Three types of failure modes were observed in the as-cast or annealed specimens: circumferential and radial shear failure, and radial normal (cleavage) failure. In contrast with uniaxial tension and compression, the multiaxial loading by small punch test was found to be very suitable for the evaluation of the mechanical properties of metallic glasses and, further, to distinguish the transition from ductility to brittleness more accurately. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.