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

Abstract

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.

Scaling in the Local Strain-Rate Field during Jerky Flow in an Al-3%Mg Alloy

“…Finally, although the present paper was devoted to a statistical analysis of the intermittence of plastic flow in the conditions of plastic instability, a qualitatively different phenomenon arising from these experiments is worth noting. Similar to several other materials for which similar data have been reported [44][45][46], the scale of observation provided by the local extensometry reveals both intermittent and wavy patterns of local strain heterogeneities beyond the PLC bands (see Figure 1). Therewith, the intermittence manifests itself as localized bright spots corresponding to .…”

“…ε a plastic flow of alloys prone to the PLC effect is characterized by power-law statistical distributions on multiple scales. Whereas for materials non-subject to plastic instability, avalanche-like intermittent behavior is only visible on fine scales revealed by the AE [25][26][27] or the local extensometry technique [44][45][46]; it engrosses deformation curves in the DSA conditions, giving rise to a macroscopically unstable deformation. At the same time, there is no consensus in the literature on the PLC effect as to which of the observed serrations should be taken into consideration in the analysis of jerky flow.…”

“…It occurs that they reveal another ubiquitous feature of the macroscopically smooth flow, namely, wavy patterns in the time evolution of the spatial repartition of plastic strain [39][40][41][42][43]. Moreover, a few recent works reported on a duality in the sense that the strain-rate bursts obey scaling distributions and, at the same time, are organized in wavy structures in the spatiotemporal maps [44][45][46].…”

Phenomenological approach towards modelling the acoustic emission due to plastic deformation in metals

“…This will be further unfolded in the upcoming full-length publication where the effects of loading conditions and metallurgical factors will be incorporated explicitly in the proposed model framework within a time-proven dislocation kinetics approach. The important challenges, which have yet to be addressed in modelling include the effects of texture, impurities and plastic instabilities, which strongly affect the AE behaviour in structural materials [36][37][38]. With the appropriate calibration, this offers a robust and consistent interpretation of the AE data, equipping materials scientists with the new functionality of the modern AE technology, and enabling in-situ monitoring and the analysis of dislocation kinetics in materials.…”

Effect of Cold Swaging on the Bulk Gradient Structure Formation and Mechanical Properties of a 316-Type Austenitic Stainless Steel

“…During swaging, competition between dislocation slide and twinning occurred. Furthermore, it might also be associated with competition between different glide systems [ 25 ]. However, according to Ref.…”