Analytical model and molecular dynamics simulations of the size dependence of flow stress in amorphous intermetallic nanowires at temperatures near the glass transition

Abstract

Molecular dynamics (MD) simulations are used to compute the flow stress of amorphous metallic nanowires that are deformed at temperatures near the glass transition. The simulations predict a strong size dependence of flow stress and predict the existence of a critical wire radius that minimizes the flow stress. Examination of the cross sections of the wires shows evidence of significant free-volume nucleation and diffusion during straining. The MD results are interpreted using a simple analytical model that assumes that the wire deforms by a combination of viscous flow, together with a diffusional deformation process in which free volume is continuously nucleated in the interior of the wire, and subsequently diffuses to the surface. The predictions of the model are in good qualitative agreement with simulation results. The analytical model is used to estimate the critical wire dimensions where this diffusional mechanism is likely to replace viscous creep at time scales that are inaccessible using MD simulations.