Portevin–Le Chatelier effect
[2] The onset of the PLC effect occurs when the strain rate sensitivity becomes negative and inhomogeneous deformation starts.
[2] The existence of a critical strain is attributed to better solute diffusivity due to the deformation created vacancies and increased mobile dislocation density.
Félix Savart made the discovery when he observed non-homogeneous deformation during a tensile test of copper strips.
[5] Much of the underlying physics of the Portevin-Le Chatelier effect lies in a specific case of solute drag creep.
As soon as the solute atom catches up, the stress on the dislocation significantly increases, causing the process to repeat.
[6] The cyclic changes described above produce serrations in the plastic region of the stress strain diagram of a tensile test that is undergoing the Portevin-Le Chatelier effect.
The variation in stress also causes non-homogeneous deformation to occur throughout the sample which can be visible to the naked eye through observation of a rough finish.
Apparently a rougher surface provides more nucleation points for high stress, which help initiate deformation bands.
It was found that if a material is pre-strained to a value ½ of that required to initiate jerky flow, and then rested at the test temperature or annealed to remove vacancies (but low enough that the dislocation structure is not affected), then the total critical strain is only slightly decreased as well as the types of serrations that do occur.
The serrations are more irregular with smaller amplitudes than type C.[3] C bands are often seen at low applied strain rate or high temperatures.
[11] These are identified with random nucleated static bands with large characteristic stress drops the serration.
Currently there are no models that can capture the change in band types [3] Portevin-Le Chatelier (PLC) effect is a proof of non-uniform deformation of CuNi25 commercial alloys at intermediate temperature.
The PLC effect is known to induce blue brittleness in steel; additionally, the loss of ductility may cause rough surfaces to develop during deformation (Al-Mg alloys are especially susceptible to this), rendering them useless for autobody or casting applications.
