Fracture Toughness of Metallic Glasses: Ductile-to-Brittle Transition?

TL;DR

This paper presents a model that predicts the fracture toughness of metallic glasses and identifies a ductile-to-brittle transition driven by structural relaxation, aligning with experimental findings.

Contribution

It introduces a coupled plastic deformation and free boundary problem model to quantitatively analyze fracture toughness and ductile-brittle transitions in metallic glasses.

Findings

Existence of an elasto-plastic crack tip instability in relaxed glasses

Marked decrease in toughness with increased structural relaxation

Model aligns with experimental ductile-to-brittle transition observations

Abstract

Quantitative understanding of the fracture toughness of metallic glasses, including the associated ductile-to-brittle transitions, is not yet available. Here we use a simple model of plastic deformation in glasses, coupled to an advanced Eulerian level set formulation for solving complex free boundary problems, to calculate the fracture toughness of metallic glasses as a function of the degree of structural relaxation corresponding to different annealing times near the glass temperature. Our main result indicates the existence of an elasto-plastic crack tip instability for sufficiently relaxed glasses, resulting in a marked drop in the toughness, which we interpret as a ductile-to-brittle transition similar to experimental observations.