Portevin–Le Chatelier effect

The Portevin–Le Chatelier effect describes a serrated stress-strain curve, which some materials exhibit as they undergo plastic deformation. This effect occurs, when solute atoms (e.g C in steels) have sufficient mobility and thus can segregate at a dislocation core. Because these positions are energetically favorable, these atoms lock the dislocation. A larger force (and therefore stress) is necessary to move the dislocation, as a cloud of solute atoms accompany the dislocation. Eventually, the dislocation breaks loose from the solute atoms, i.e the drag stress for dislocation movement is reduced. When a freed dislocation runs through the crystal it disturbs other locked dislocations, and may cause an avalanche-like freeing of dislocations. Materials that undergo the PLC effect obey a nonmonotonic stress-strainrate-behavior. Since this process can happen several times, it leads to serrations in the curve. Moreover, the softening behavior leads to localized deformations. Due to the localized deformations some materials, e.g., aluminum-magnesium alloys, develop a rough surface during deformation processes, rendering them useless for autobody or casing applications.