Shear shuffling governs plastic flow in nanocrystalline metals: An analysis of thermal activation parameters

TL;DR

This study reveals that shear shuffling at grain boundaries governs plastic deformation in nanocrystalline metals, with universal scaling behavior linking energy barriers to residual load, similar to metallic glasses.

Contribution

It demonstrates that grain boundary shear shuffling dominates plasticity in nanocrystalline metals and introduces a universal scaling law for activation energy barriers.

Findings

Shear activation volume is 6b^3.

Strain rate sensitivity is 0.03.

Activation energy scales as ΔG ∝ Δτ^{3/2}.

Abstract

From strain rate- and temperature-dependent deformation studies on nanocrystalline PdAu alloys with grain sizes $\leq$ 10nm, the shear activation volume $6b^3$, strain rate sensitivity 0.03 as well as the Helmholtz 0.9eV and Gibbs free energy of activation 0.2eV have been extracted. The close similarity to values found for metallic glasses indicates that grain boundary mediated shear shuffling dominates plasticity at the low end of the nanoscale. More fundamentally, we find that the energy barrier height exhibits universal scaling behavior $\Delta G \propto \Delta\tau^{3/2}$, where $\Delta\tau$ is a residual load, giving rise to a generalization of the Johnson-Samwer $T^{2/3}$ scaling law of yielding in metallic glasses.