Temperature, Strain and Strain Rate Dependence of Serrated Flow in Bulk Metallic Glasses

Abstract

New findings on the inhomogeneous plastic deformation of bulk metallic glasses (BMGs) have shown a disappearance of serrated flow below a critical temperature or above a critical strain rate. This correlates with a change in the strain rate sensitivity (SRS) from negative to positive values, suggesting a change in the deformation mechanism. In addition, a change in the SRS correlating with the increase in the stress drop magnitude is observed with increasing strain. Results on the serration and flow dependence for the binary BMG Cu₅₀Zr₅₀ show close phenomenological similarities with the Portevin - Le Châtelier or dynamic strain aging effect known for crystalline solids. An alternative model for the appearance and disappearance of serrated flow based on the structural relaxation of the atomic configuration of shear transformation zones is described.