The influence of shearable and nonshearable precipitates on the Portevin-Le Chatelier behavior in precipitation hardening AlMgScZr alloys

Abstract

The well-known mechanisms of interaction between precipitates and dislocations are shearing (for shearable precipitates) and bypassing mechanisms (for nonshearable precipitates). The transition from shearable to nonshearable precipitates in precipitation hardening alloys leads to changes of dislocation motion mode and dislocation multiplication behavior, which inevitably causes different PLC behaviors.In this study, we systematically investigate the influence of shearable and nonshearable Al3(Sc, Zr) precipitates on PLC behaviors by experimental characterization for precipitation hardening AlMgScZr alloys. We analyze the onset strain, critical strain-rate range, serration amplitude, and propagation behavior of PLC bands in detail for AlMgScZr alloys with shearable and nonshearable precipitates, respectively. We find that the transition from shearable to nonshearable precipitates changes the PLC band propagation behavior, decreases the magnitude of serration amplitude, expands the strain-rate range as well as decreases the critical strain rate between normal behavior (the critical strain increases with the increase of strain rate) and inverse behavior (the critical strain decreases with the increase of strain rate) regimes due to the different dislocation-precipitate interactions. Besides, the transition from shearable to nonshearable precipitates increases the onset strain at normal behavior while decreases the onset strain at inverse behavior depending on the different roles of precipitates in the solute-dislocation interaction. Finally, we reveal the nature of influence of different dislocation-precipitate interactions on PLC behavior considering different strengthening mechanisms based on quantitative characterization on precipitates and dislocation density.

Flow behaviour and microstructural stability in an Al–3Mg-0.2Sc alloy processed by high-pressure torsion at different temperatures

“…It should be noted that, although σ 𝑦 appears to decrease with increasing grain sizes for annealing at T ≥ 673 K, it is unlikely that grain boundary strengthening becomes again predominant because the mean free path is consistently determined by the precipitate interspacing. There may also occur a gradual change in the deformation mechanism from precipitate shearing to Orowan looping due to the increasing presence of nonshearable particles as reported for other Al-Sc alloys [59,61]. This is consistent with the occurrence of considerable work-hardening in the HPT-processed alloy deformed at RT after annealing at T ≥ 673 K. It also explains the increased elongations attained during tensile testing [38,62].…”

A Molecular Dynamics Study on the Dislocation-Precipitate Interaction in a Nickel Based Superalloy during the Tensile Deformation

“…In the classical dislocation-precipitate interaction theory, the dislocation prefers to shear the precipitate if the precipitate size is small enough, otherwise, dislocation tends to bypass it with the so-called Orowan loop (see e.g., [37,38]) generated. The classic theory fits well to the cases with spherical precipitates [39,40]. To quantify the interaction mechanisms in the alloys containing non-spherical precipitates, the mean radius of the precipitate has been used [8,11].…”

Research on strain aging behavior of ultra-high strength dual-phase steel

“…Dynamic strain aging may appear at a sufficiently higher temperature or low strain rate of some materials. It is caused by repeated locking and unlocking of dislocation during deformation, leading to serrations on the tensile curve, known as the Portevin-Le Chatelier effect [ 1 ]. Because of the dislocation locking in steel by interstitial atoms, there will be a static strain aging phenomenon where the stress-strain curve after reloading does not follow the original curve before reloading [ 2 , 3 ].…”