Characterization of plasticity in model metallic glasses by a detailed analysis of the plastic events

Plastic deformation in metallic glasses is governed by discrete, highly localized atomic rearrangements known as Shear Transformations. However, a universally accepted criterion and robust methodology for characterizing these fundamental plastic events, especially as a function of the internal structure of the glass, remains elusive. In this work, we use Molecular Dynamics simulations to systematically characterize the plastic behavior of Cu$_{64}$Zr$_{36}$ metallic glasses as a function of the quenching rate used during preparation. We employ a detection method based on an energetic criterion to identify and fully characterize the elementary plastic events in terms of their number, plastic intensity, and size. We then model these localized rearrangements as Eshelby's inclusions to reconstruct the macroscopic stress-strain curves obtained from quasi-static athermal shear tests.
Our results show that lower quenching rates yield more relaxed glasses with higher stiffness and strength and a stronger tendency toward abrupt strain localization and shear band formation, reflected in a small number of plastic events that abruptly increase at the yield point and that tend to align in the shear band direction. Conversely, higher quenching rates result in less relaxed glasses where plastic deformation proceeds through a larger number of spatially dispersed events, promoting a more homogeneous flow. The spatial distribution of the plastic events shows an evident anticorrelation between the plastic events and the full icosahedra. The Eshelby's inclusion framework successfully and accurately reconstructs the macroscopic stress-strain curves, validating that the overall plastic response is mainly governed by the distribution of these discrete microscopic rearrangements.
This study provides a robust methodology for characterizing and interpreting plasticity in metallic glasses, demonstrating that the complex, heterogeneous nature of amorphous plasticity can be effectively modeled as localized plastic cores within an elastic matrix, and for proposing a microscopic framework for modeling and designing ductile metallic glasses.