PLC: Portevin-Le Chatelier effect
Definition:A plastic instability observed in many dilute alloys when deformed at certain ranges of strain rate and temperature [1].
Explanation:The PLC effect is attributed to dynamic interactions between mobile solute atoms and dislocations, termed dynamic strain aging (→DSA). The effect occurs in many alloys deformed in certain intervals of strain rates and temperature. 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 [2]. In general, PLC band can be classified into three types based on the type of serrations that appear in the stress-strain curve of polycrystalline materials during constant strain rate tensile tests. The appearance of the serrations changes from type A to type B and then to type C, either with decreasing strain rate or increasing temperature. Type A serrations are associated with repetitive continuous propagation of deformation bands along the gauge length of the sample and are often nucleated at one end of gauge length. Type B serrations correspond to a hopping propagation of localized bands in the axial tensile direction of the specimen. Type C serrations are characterized by random nucleation of localized deformation bands accompanied by large stress drops [3].
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Fig. 1 PLC band classification by the serration morphology in tensile curves [3].
SFB-Link:Due to the PLC effect, the strength of steel may increase; however, the plasticity and ductility decrease drastically. The PLC effect is known to induce blue brittleness in steel.
References:[1] A Chatterjee, P Mukherjee, N Gayathri, On statistical behavior of stress drops in Portevin–Le Chatelier effect. Mater. Sci., Vol. 34, No. 5, August 2011, pp. 1113–1117
[2] Neuhäuser H, Klose F B , Hagemann F, On the PLC effect in strain-rate and stress-rate controlled tests–studies by laser scanning extensometer. Journal of Alloys and Compounds vol. 378 issue 1-2 September 22, 2004.
[3] P Rodriguez, Serrated plastic flow, Mater. Sc., Vol.6, No.4, September 1984, pp. 653-663