Transition from softening to hardening related with strain rate in Zr-based metallic glasses

The dynamic deformation and fracture behavior of Zr-based metallic glasses related with strain rate were systematically investigated by dynamic uniaxial compressive tests over a wide range of strain rate . The dynamic fracture strength with the increase of the strain rate shows two stages, i.e., the transition from strain-rate softening to strain-rate hardening. In the first stage, the temperature rise within the shear bands gradually increases due to increasing strain rate. The viscosity in the shear bands greatly reduces and the free volume keeps increasing, which results in the occurrence of strain-rate softening and significantly promotes the propagation of shear bands of Zr-based MGs. However, in the second stage, the increasing temperature in the shear band results in the occurrence of localized crystallization of Zr-based MGs. The shear bands are difficult to extend due the strong interaction between multiple shear bands and dendritic crystal, leading the occurrence of strain-rate hardening.