Thermal Effects in the Shear-Transformation-Zone Theory of Amorphous Plasticity: Comparisons to Metallic Glass Data

TL;DR

This paper extends the shear-transformation-zone theory of amorphous plasticity to include thermal effects, successfully explaining metallic glass behavior, creep, and superplasticity, and highlighting limitations of conventional theories.

Contribution

It introduces a generalized STZ theory incorporating thermal effects, providing a unified framework for understanding metallic glass deformation and flow behavior.

Findings

Accounts for strain-rate dependence of metallic glass viscosity

Captures transient stress-strain behavior during loading

Explains superplasticity onset as a transition between creep and flow

Abstract

We extend our earlier shear-transformation-zone (STZ) theory of amorphous plasticity to include the effects of thermally assisted molecular rearrangements. This version of our theory is a substantial revision and generalization of conventional theories of flow in noncrystalline solids. As in our earlier work, it predicts a dynamic transition between jammed and flowing states at a yield stress. Below that yield stress, it now describes thermally assisted creep. We show that this theory accounts for the experimentally observed strain-rate dependence of the viscosity of metallic glasses, and that it also captures many of the details of the transient stress-strain behavior of those materials during loading. In particular, it explains the apparent onset of superplasticity at sufficiently high stress as a transition between creep at low stresses and plastic flow near the yield stress. We also argue that there are internal inconsistencies in the conventional theories of these deformation processes, and suggest ways in which further experimentation as well as theoretical analysis may lead to better understanding of a broad range of nonequilibrium phenomena.