Dependence of ductile-brittle transition related with serrated flow on viscosity dominated by glass forming ability in ZrxTi65-xBe27.5Cu7.5 metallic glasses

The transition in deformation mode from ductile to brittle related with glass forming ability (GFA) was systematically investigated via uniaxial compression tests in ZrxTi65-xBe27.5Cu7.5 metallic glasses (MGs). As the GFA increases, both the number and amplitude of serrated flow decrease gradually in stress-strain curves. There are two main reasons for the reduction in viscosity during shear deformation. First, the larger elastic energy is mainly dissipated in the form of heat and the temperature rises within shear bands beyond the melting points. Second, the MGs with better GFA contain larger excess quenched-in free volume due to rapid solidification. Based on the Cohen-Grest model, large free volume can effectively decrease the atomic packing density and reinforce the mobility of atoms, greatly reducing the viscosity during shear deformation. Hence, for the reduction of the viscosity during deformation, the coupling effect of temperature and free volume matters. Multiple shear bands are activated by applied stress and interact strongly with each other, significantly improving the plasticity. The initiation of multiple shear bands is an indicative of much serrated events in stress-strain curves. Thus, the change in viscosity associated with GFA dominates the occurrence of serrated flow, facilitating the transition between ductile and brittle deformation.