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 characterized 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 using 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 previously unknown paradigm of criticality in the localization of deformation.
Highlights
Complexity in materials deformation is important for engineering and involves fundamental nonequilibrium physics
The Portevin–Le Chatelier (PLC) effect implies the creation of deformation bands in a sample (Fig. 1) when it is loaded beyond the yield point: Such bands nucleate and may or may not propagate depending on the class of PLC instability present [7, 8]
The PLC effect is attributed to dynamic strain aging (DSA) [11,12,13], and the crucial physics is in the interaction of the dislocations as the fundamental carriers of plastic deformation with the solute atoms in the alloy [14,15,16]
Summary
Complexity in materials deformation is important for engineering and involves fundamental nonequilibrium physics. The deformation bands are accompanied by material instabilities; in the case of tensile tests, stress drops, which produce serrated stress-strain curves (Fig. 1B). Theories of increasing complexity have been proposed such that they would account for the necessary dislocation physics: elementary classes of immobile and “aging,” solute bound dislocations, and mobile ones producing plastic deformation. Such models and a multitude of experiments have been recently introduced to explore the physics of the PLC effect: phases in the band nucleation [17,18,19,20] and dynamics including
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