Portevin–Le Chatelier effect

The Portevin–Le Chatelier effect (PLC) describes a serrated stress-strain curve or jerky flow, which some materials exhibit as they undergo plastic deformation, specifically inhomogeneous deformation. This effect has been long associated with dynamic strain aging or the competition between diffusing solutes pinning dislocations and dislocation breaking free of this stoppage.

The onset of the PLC effect appears when the strain rate sensitivity becomes negative and inhomogeneous deformation starts. This effect also can appear on the specimens surface and bands of plastic deformation. This process starts at a so-called critical strain, which is the minimum strain needed for the onset of the serrations in the stress-strain curve. The critical strain is both temperature and strain rate dependent. The existence of some critical stain are attributed to better solute diffusivity due to the deformation created vacancies and increased mobile dislocation density. Both of which contribute to the instability in the substitutional alloys, while interstitial alloys are only effect by the increase in mobile dislocation densities.

Temperature affects both the speed of band propagation through the material and the critical strain. The speed of band propagation is proportional to the temperature (lower temp lower speeds, higher temp higher speeds). Often time the critical stain will first decrease due to temperature. The temperature effect on PLC regime is causes by the increased ability of the solutes to diffuse to the dislocations with increasing temperature. Although the mechanism of diffusion is not entirely defined, it is believed that solute atoms diffuse by either volume (high temperatures), diffusion in stacking fault ribbon between partial dislocations (intermediate) or pipe diffusion(low temperature).

While temperature related to rate of diffusion, strain rate determines the time that the dislocations take to overcome these obstacles and have a dramatic effect on the conditions of the PLC effect. So generally the critical stress will decrease with imposed strain rate. Also the higher stress rate the lower the band speed

Often found in Al alloys (especially of the Mg variety) precipitates complicate the PLC effect.

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