On the mechanisms of nucleation and subsequent development of the PLC bands in an AlMg alloy

Abstract

The nucleation and subsequent development of the Portevin-Le Chatelier bands during tensile deformation in a binary AlMg alloy was investigated by the digital image correlation technique. The following states of the material were employed for the current investigation: coarse-grained (CG), fine-grained (FG) after equal channel angular pressing (ECAP), severely strained (SS) after ECAP followed by cold rolling. Special attention was paid to the nucleation of an embryo band by maximizing the contrast of the deformation images. Particular spatiotemporal patterns of the alloy in three different conditions, testifying to the initiation of an embryo band having a wedge shape on the lateral surface of the specimen, were obtained at high and intermediate strain rates. The evaluation of the serration amplitude and the band velocity showed that the dependence of these values on strain consists of two stages (the linear growth-up/drop stage and the steady-state stage) for CG materials and only one stage (the linear growth-up/drop stage) for FG materials. The nucleation of deformation bands always occurs according to a mixed mechanism, in which the thickening of the embryo slows down with a decrease in the strain rate.

Characterization of the spatiotemporal behavior of the PLC bands in austenitic steel during deformation at elevated temperature

“…The kinetic characteristics of the deformation bands were determined from the local strain rate maps. The velocity of PLC bands is determined as the speed of the displacement of the areas corresponding to the maximum local strain rate within the band [5]. Fig.…”

“…Local strain rate values were determined by numerically, differentiating strain data with respect to time. More details about the DIC method are described in previous works [5,8].…”

“…the dynamic process of dislocations pinning by solute atoms during their blocking on obstacles [4]. The macroscopic manifestation of this phenomenon is observed as serrated flow stress related to strain localizations in the form of shear macro bands [5] which leads to surface roughness as a result of their propagation [6].…”

Nonlinear dynamics of an individual Portevin--Le Chatelier deformation bands

“…For comparison with the date from literature, it is worth noting, that the embryo bands as the earliest stages of PLC bands generation were observed in Al−Mg system alloys using video recording with a rate of more than 500 fps [17][18][19][20][21][24][25][26][27]. In early study [4], on the basis of 25 fps video recording of bands, three hypothetical scenarios for the transversal growth of an embryo band in a flat sample were proposed: a) band nucleates at a lateral sample surface with its width unchanged while growing until outlet to the opposite lateral surface; b) band with a thickness of a few atomic planes " shoots through" the cross-section, and then expands in the direction of the expanding stresses; c) wedge-shaped embryo band crosses the cross-section in the direction of maximum tangential stresses.…”

Room-Temperature Strengthening, Portevin-Le Chatelier Effect, High-Temperature Tensile Deformation Behavior, and Constitutive Modeling in a Lightweight Mg-Gd-Al-Zn Alloy

“…Research on the strengthening mechanism is developing towards the quantification of individual strengthening mechanisms and elucidation from atomic mechanisms. On the other hand, the Portevin-Le Chatelier (PLC) effect, a serrated flow phenomenon, has attracted widespread attention in Al-Mg system alloys [ 21 , 22 ], nickel superalloys [ 23 ], steel [ 24 ], and magnesium-lithium alloys [ 25 ] and is developing towards the application of digital-imaging correlation techniques and the elucidation of the underlying mechanism. The aim is to lessen and remove the bad influence of the PLC band on the surface quality of the worked piece.…”