Micro-alloying and the Toughness of Glasses: Modeling with Pinned Particles

TL;DR

This paper models how adding pinned particles to glasses enhances their toughness by increasing shear modulus and yield stress, using a scaling theory to unify the results.

Contribution

It introduces a zero-temperature, quasi-static model with pinned particles to explain toughness improvements in glasses, including a universal scaling law.

Findings

Pinned particles significantly increase toughness.

Shear modulus and yield stress both rise with pinned particle density.

A universal scaling curve describes the data across different conditions.

Abstract

The usefulness of glasses, and particularly of metallic glasses, in technological applications is often limited by their toughness, which is defined as the area under the stress vs. strain curve before plastic yielding. Recently toughness was found to increase significantly by the addition of small concentrations of foreign atoms that act as pinning centers. We model this phenomenon at zero temperature and quasi-static straining with randomly positioned particles that participate in the elastic deformation but are pinned in the non-affine return to mechanical equilibrium. We find a very strong effect on toughness via the increase of both the shear modulus and the yield stress as a function of the density of pinned particles. Understanding the results calls for analyzing separately the elastic, or "Born term" and the contributions of the "excess modes" that result from glassy disorder. Finally we present a scaling theory that collapses the data on one universal curve as a function of rescaled variables.