Investigating the Portevin-Le Chatelier effect by the acoustic emission and laser extensometry techniques

The Portevin-Le ChAtelier (PLC) effect is a spectacular effect of dynamic strain aging in many alloys deformed in certain intervals of strain rates and temperatures. The main feature of the PLC effect is a negative strain rate sensitivity of stress, which is linked with stress fluctuations, a macroscopic spatio-temporal localization of plastic deformation (nucleation and propagation of deformation bands) and an intense acoustic emission. Recent theoretical studies have pointed out that cooperative dislocation motion is a necessary condition for plastic instabilities to occur under conditions of negative strain rate sensitivity. In this work the potential of acoustic emission and laser extensometry to monitor in situ cooperative dislocation motion due to PLC effect is reviewed and examined experimentally in an Al-1.5 wt.% Mg alloy. At the conditions of testing, the alloy exhibits a Luders phenomenon followed by the C- and/or B-type of the PLC effect. The results indicate that different dislocation processes are responsible for the Luders phenomenon, the nucleation of PLC bands and the propagation of PLC bands. (C) 2002 Elsevier Science B.V. All rights reserved.