Stress-state-dependent deformation behavior in Ni-Nb metallic glassy film

The transition in deformation mode from highly localized to non-localized deformation was investigated in Ni60Nb40 glassy film by monitoring the reduction in thickness during film/substrate co-bending. It is revealed that in addition to the film thickness, the mode of plastic deformation depends on the stress state. With the reduction in thickness of thin film, tensile stress can efficiently suppress the change in deformation mode from highly localized to non-localized deformation in comparison with compressive stress. A mechanism for the stress-state-dependent deformation mode change in glassy alloys is discussed on the basis of the pressure/stress effect of plastic deformation and Griffith's crack-propagation criterion. This study provides distinct evidence of the deformation mode change in metallic glassy film via the variation in stress state, and also sheds light on the deformation mechanism of glassy alloys.