Ductile to brittle transition of fracture of a Zr-based bulk metallic glass: Strain rate effect

• The quasi-static and Split Hopkinson Tensile experiments were performed on a typical Zr-based metallic glass.
• A significant ductile-to-brittle transition was discovered due to the increase of the applied strain rate.
• The underlying mechanism of DBT behavior was revealed by the Mohr-Coulomb criterion and the critical STZ volume.

Quasi-static and dynamic tensile experiments were conducted on a Zr-based bulk metallic glass at room temperature. A significant ductile-to-brittle transition was identified with increasing strain rate, based on the changes in the macroscopic fracture mode from shear to normal tension and in the microscopic fracture feature from vein patterns to fine dimples and/or nanoscale periodic corrugations. According to the Mohr-Coulomb criterion, it is revealed that such a transition is due to the competition between the intrinsic critical shear and tensile strengths at different strain rates. Microscopically, the strain-rate-induced transition is attributed to the change in the motion of local atomic groups from shear transformation zone to tension transformation zone, in which the characteristic volume of shear transformation zone is a key parameter.

For crystalline metals and alloys, in particular body centered cubic (BCC) metallic and alloys, the temperature, microstructure and strain rate are the main factors that affect the ductile-to-brittle transition (DBT) behavior. The free volume for metallic glasses is analogous to microstructure for crystalline materials, and both them can be tuned by heat-treatment. Then it is reasonable to expect that the three factors can also affect the DBT behavior on the metallic glasses. The former two factors (temperature and free volume) have been confirmed by uniaxial loading experiments, while the third one (strain rate) has been rarely shed light on. The present work is dedicated to investigate the effect of strain rate on the DBT behavior of a typical Zr-based bulk metallic glass, which is revealed by the critical value of shear transformation zone volume within the framework of the cooperative shear model.Figure optionsDownload as PowerPoint slide