Thermal-activation model for freezing and the elastic robustness of bulk metallic glasses

Despite significant atomic-scale heterogeneity, bulk metallic glasses well below their glass transition temperature exhibit a surprisingly robust elastic regime and a sharp elastic-to-plastic transition. Here it is shown that, when the number of available structural transformations scales exponentially with system size, a simple thermal-activation model is able to describe these features, where yield corresponds to a change from a barrier energy dominated to a barrier entropy dominated regime of shear transformation activity, allowing the system to macroscopically exit its frozen state. A yield criterion is then developed, which describes well the existing experimental data and motivates future dedicated deformation experiments to validate the model.