Thermomechanical characterization of Portevin–Le Châtelier bands in AlMg3 (AA5754) and modeling based on a modified Estrin–McCormick approach

Lebedkina

Mogucheva

et al. 2017

Metals

Abstract: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. Ultra-fine-grained microstructure was obtained using equal-channel angular pressing of the initial coarse-grained alloy. Tensile tests were carried out on flat specimens at strain rates in the range from 3 × 10 −5 to 1.4 × 10 −2 s −1 . Using local extensometry techniques, it was found that the presence of nanoscale precipitates promotes quasi-continuous propagation of deformation bands in the entire strain-rate range. The grain refinement leads to a transition to relay-race propagation at high strain rates and static strain localization at low rates. The results are discussed from the viewpoint of competition between various dynamical modes of plastic deformation associated with collective dynamics of dislocations.

Section: Plc Bands Patternssupporting

confidence: 60%

Peculiar Spatiotemporal Behavior of Unstable Plastic Flow in an AlMgMnScZr Alloy with Coarse and Ultrafine Grains

Lebedkina

Mogucheva

et al. 2017

Metals

“…A convenient way to visualize evolution of the deformation bands during the entire test is to construct local strain-rate maps by collecting loc  data from the DIC along the vertical centerline of the specimen and plotting them as a function of time and position (cf. (Klusemann et al, 2015) for temperature maps). Fig.…”

Section: Analysis Of the Considère Strainmentioning

confidence: 99%

Interrelation between the Portevin Le-Chatelier effect and necking in AlMg alloys

Zhemchuzhnikova

International Journal of Plasticity

Yuzbekova

et al. 2018

Plastic flow instability caused by the Portevin Le-Chatelier (PLC) effect and its influence on the necking instability were studied in a binary and a precipitation-strengthened AlMg alloy using the digital image correlation (DIC) technique. Coarse-grained structure and two different fine-grained states distinctly distinguished by dislocation density were produced in both alloys using similar routes of thermomechanical processing. The patterns of stress serrations and strain localization observed at different strain rates include virtually all common types of behavior of the PLC effect. Besides, particular spatiotemporal patterns testifying to a concurrency between the propagation and localization of deformation bands are detected at low strain rates. Despite this diversity, the analysis of deformation curves with smoothened-out serrations bears evidence that the onset of necking always corresponds to the geometric Considère condition. Nevertheless, visualization of the evolution of the local strain-rate field using DIC indicates that the two mechanisms of plastic instability are closely interrelated and modify each other's behavior. The neck formation is associated with a progressive immobilization of the PLC bands, ending by the ultimate strain localization. The coexistence of two kinds of instability during necking gives rise to specific spatiotemporal patterns including oscillatory strain localization.

“…Similar behavior was observed at all strain rates for both orientations. This result allows to invalidate an alternative mechanism of low strain hardening at the stage A [8], based on the suggestion of propagation of a Lüders-like deformation band and requiring conditions favorable for aging of dislocations by solute atoms [28]. Besides the overall pattern, Figure 1c reveals loc  fluctuations both in space and time.…”

Section: Three-stage Work-hardening Behaviormentioning

confidence: 94%

Complexity and Anisotropy of Plastic Flow of α-Ti Probed by Acoustic Emission and Local Extensometry

Amouzou

Lebedkina

et al. 2018

Preprint

Current progress in the prediction of mechanical behavior of solids requires understanding of spatiotemporal complexity of plastic flow caused by self-organization of crystal defects. It may be particularly important in hexagonal materials because of their strong anisotropy and combination of different mechanisms of plasticity, such as dislocation glide and twinning. These materials often display complex behavior even on the macroscopic scale of deformation curves, e.g., a peculiar three-stage elastoplastic transition, the origin of which is a matter of debates. The present work is devoted to a multiscale study of plastic flow in α-Ti, based on simultaneous recording of deformation curves, 1D local strain field, and acoustic emission (AE). It is found that the average AE activity also reveals three-stage behavior, but in a qualitatively different way depending on the crystallographic orientation of the sample axis. On the finer scale, the statistical analysis of AE events and local strain rates testifies to an avalanche-like character of dislocation processes, reflected in power-law probability distribution functions. The results are discussed from the viewpoint of collective dislocation dynamics and are confronted to predictions of a recent micromechanical model of Ti strain hardening.