Correlation versus randomization of jerky flow in an AlMgScZr alloy using acoustic emission

International audienceJerky flow in solids results from collective dynamics of dislocations which gives rise to serrated deformation curves and a complex evolution of the strain heterogeneity. A rich example of this phenomenon is the Portevin-Le Chatelier effect in alloys. The corresponding spatiotemporal patterns showed some universal features which provided a basis for a well-known phenomenological classification. Recent studies revealed peculiar features in both the stress serration sequences and the kinematics of deformation bands in Al-based alloys containing fine microstructure elements, such as nanosize precipitates and/or submicron grains. In the present work, jerky flow of an AlMgScZr alloy is studied using statistical analysis of stress serrations and the accompanying acoustic emission. As in the case of coarse-grained binary AlMg alloys, the amplitude distributions of acoustic events obey a power-law scaling which is usually considered as evidence of avalanchelike dynamics. However, the scaling exponents display specific dependences on the strain and strain rate for the investigated materials. The observed effects bear evidence to a competition between the phenomena of synchronization and randomization of dislocation avalanches, which may shed light on the mechanisms leading to a high variety of jerky flow patterns observed in applied alloys

Breakdown of antiferromagnet order in polycrystalline NiFe/NiO bilayers probed with acoustic emission

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Unusual behavior of the Portevin - Le Chatelier effect in an AlMg alloy containing precipitates

Stress serration patterns and kinematics of deformation bands associated with the Portevin - Le Chatelier effect in an Al-Mg alloy were investigated by analyzing the evolution of the applied stress and axial strain distribution. In contrast to usually observed strain localization behaviors, referring to propagating and static deformation bands at high and low strain rates, respectively, the propagation mode was found to persist in a wide strain-rate rang

Dislocation transport and intermittency in the plasticity of crystalline solids

International audienceWhen envisioned at the relevant length scale, plasticity of crystalline solids consists in the transport of dislocations through the lattice. In this paper, transport of dislocations is evidenced by experimental data gathered from high-resolution extensometry carried out on copper single crystals in tension. Spatiotemporal kinematic fields display spatial correlation through characteristic lines intermittently covered by plastic activity. Intermittency shows temporal correlation and power-law distribution of avalanche size. Interpretation of this phenomenon is proposed within the framework of a field dislocation theory attacking the combined problem of dislocation transport and long-range internal stress field development. Intermittency and transport properties show remarkable independence from sample size, aspect ratio, loading rate, and strain-rate sensitivity of the flow stress

Peculiar spatiotemporal behavior of unstable plastic flow in an AlMgMnScZr alloy with coarse and ultrafine grains

The work addresses the effects of nanosize particles and grain refinement on the patterns of stress serrations and kinematics of deformation bands associated with the Portevin–Le Chatelier instability of plastic flow. The results are discussed from the viewpoint of competition between various dynamical modes of plastic deformation associated with collective dynamics of dislocation

Relationship between relaxation mechanisms and strain aging in an austenitic FeMnC steel

International audienceBasic relaxation experiments confirm that dislocation gliding in a V-microalloyed Fe-22 wt.% Mn-0.6 wt.% C steel is thermally activated at room temperature. This impediment to gliding is believed to be a necessary condition for the occurrence of mechanical twinning inducing the twinning induced plasticity effect in the considered family of high manganese austenitic steels. The relaxation experiments also induce a static strain aging phenomenon enhanced by applied stress and systematically trigger the dynamic strain aging mechanism and observable serrations on further tensile loading

Intermittency and Deformation Band Propagation in an Austenitic FeMnC TWIP Steel

Plastic deformation of austenitic FeMnC TWIP steels exhibits complex spatiotemporal patterns associated with the occurrence of deformation bands and the concomitant fluctuations of the deforming stress. Although the plastic instability is a generic property of these steels and is usually attributed to interaction of dislocations with solutes (the Portevin-Le Chatelier effect), both the kinematics of the deformation bands and the characteristic shape of stress serrations observed in the carbon-containing TWIP steel at room temperature manifest unusual features. The nature of these peculiarities and the mechanism of jerky flow in such steels are unclear. In the present work, an attempt is made to get an insight into the jerky flow in the Fe22Mn0.6C steel by studying the time series characterizing the evolution of plastic deformation at various scales: stress-time curves, local strain field, and acoustic emission accompanying the deformation processes. Stress and strain fluctuations related to two distinct scale ranges are detected and characterized

Domain Structure and Magnetization Reversal Micromechanisms in Quasi-Two-Dimensional Exchange-Biased Nanomagnetics

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Effect of microstructure on continuous propagation of the Portevin–Le Chatelier deformation bands

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