Shear localization-induced amorphization in nanocrystals during high strain rate deformation

Abstract

Shear localization is the predominant form of failure of metals at high strain rates where amorphization often occurs. However, the mechanism and role of amorphization in shear localization are not yet clearly understood. In this work, a series of shear deformations of nanocrystals with different grain sizes at high strain rates are investigated using molecular dynamics simulations. The results show that amorphization is not the result of thermal melting, but a new plastic deformation mechanism in the process of shear localization, which serves as a complement to dislocation and grain boundary to support plastic deformation at a high strain rate. The critical shear strain at which shear localization and amorphization occur is greater for small-grained specimens than for large-grained specimens. This can be attributed to the fact that small-grained specimens have more defects and slip systems that can be activated, which cause amorphization to occur later. The strain rate has a significant influence on shear localization and amorphization. The processes of shear localization and amorphization become more complicated at extremely high strain rates than at relatively low strain rates.