Microscopic Calculation of Flow Stress in Cu-Mg Metallic Glass

TL;DR

This study uses shear-deformation simulations on amorphous Mg-Cu systems to analyze flow stress, revealing size-dependent behaviors and characterizing localized plastic events with distributions of slip volumes and critical stresses.

Contribution

It introduces a microscopic approach to calculate flow stress in metallic glasses and characterizes localized plastic events through their slip volumes and critical stresses.

Findings

Flow stress in large systems is well-defined and smooth.

Small systems exhibit discontinuous stress-strain behavior due to localized events.

Critical stresses for plastic events range from 200 MPa to 500 MPa, averaging 316 MPa.

Abstract

We have carried out shear-deformation simulations on amorphous Mg-Cu systems at zero temperature and pressure, containing 2048-131072 atoms. At the largest size a smooth stress-strain curve is obtained with a well-defined flow stress. In the smallest system there are severe discontinuities in the stress-strain curve caused by localized plastic events. We show that the events can be characterized by a slip volume and a critical stress and we determine the distribution of these quantities from the ensemble of all events occurring in the small system. The distribution of critical stresses at which the enthalpy barriers for the individual events vanish is spread between 200 MPa and 500 MPa with a mean of 316 MPa, close to the flow stress observed in the largest system.