Deformation stability transition of notched metallic glasses

Abstract

Systematical experiments, simulations and microscopic characterizations on double edge notched samples manifested a transition from brittle instability to steady plasticity. Effects of ligament length, geometrical notch parameters as well as thickness were studied. It was found that ligament length is essentially the space provider for intersection of shear bands. With a narrow ligament, it is unlikely to form V-shaped double shear bands because of the limited region between notch tips. Meanwhile, the plastic deformation ability is determined by stress triaxiality. With a wider ligament, V-shaped double shear bands become predominant in controlling deformation stability, accompanying with much higher plasticity than previous investigations because of large-regions of shear band entanglements. Such plasticity enhancement is proven to have weak linkage with the restriction of crosshead of machines, and it is the resultant response of notch configuration. Besides, thickness is less influential to global plasticity. On another hand, by means of hydrostatic stress embedded free volume model, shear banding process is simulated by FEM model, by which the shear band evolution patterns in tests could be well understood and explained. The current findings could further enrich the plastic stability mechanism of metallic glasses under complex stress states. As well, those parameters on notch configurations could provide the state-of-the-art parameters used for fabrication of porous metallic glasses.