Propagating bands of plastic deformation in a metal alloy as critical avalanches

TL;DR

This study reveals that propagating bands of plastic deformation in a metal alloy behave like critical avalanches, with velocity fluctuations and statistical properties consistent with avalanche dynamics, providing new insights into deformation localization.

Contribution

It demonstrates that the velocity fluctuations of propagating deformation bands follow critical avalanche statistics, linking plastic instability to critical phenomena.

Findings

Band velocities exhibit large fluctuations similar to crackling noise.

Velocity burst statistics match mean-field avalanche models.

Deformation localization shows signs of criticality.

Abstract

The plastic deformation of metal alloys localizes in the Portevin--Le Chatelier effect in bands of different types, including propagating, or type 'A' bands, usually characterised by their width and a typical propagation velocity. This plastic instability arises from collective dynamics of dislocations interacting with mobile solute atoms but the resulting sensitivity to the strain-rate lacks fundamental understanding. Here we show, by employing high-resolution imaging in tensile deformation experiments of an aluminum alloy, that the band velocities exhibit large fluctuations. Each band produces a velocity signal reminiscent of crackling noise bursts observed in numerous driven avalanching systems from propagating cracks in fracture to the Barkhausen effect in ferromagnets. The statistical features of these velocity bursts including their average shapes and size distributions obey predictions of a simple mean-field model of critical avalanche dynamics. Our results thus reveal a novel paradigm of criticality in the localization of deformation.