Cold versus hot shear banding in bulk metallic glass

We present an analysis of the shear-banding dynamics in a bulk metallic glass (BMG), including the temperature rise in the band, the sliding speed of the band, and the time elapsed as well as the step size of the shear offset growth in a stop-and-go cycle. This model analysis quantitatively demonstrates that the major shear band can remain cold and slide in a stick-slip manner. We predict that the shear step (distance covered by a stop-and-go cycle) scales with the sample size and machine stiffness. We also illustrate the conditions when such serrated shear is unsustainable and a hot shear band directly develops in a runaway instability (catastrophe). These findings provide physical insight into the shear-instability processes and offer useful information for improving the plasticity of BMGs. The calculation results are used to explain several intriguing recent experimental observations, including the stick slip of the dominant shear-band and the sample-size effects on the plastic-flow behavior of BMGs.