Effect of microstructure on continuous propagation of the Portevin–Le Chatelier deformation bands
Résumé
Influence of severe plastic deformation (SPD) on plastic instability associated with the Portevin-Le Chatelier (PLC) effect was investigated in an AlMg alloy in a high strain-rate range corresponding to the well-known phenomenon of continuous propagation of PLC bands. Comparison with the model coarse-grained alloy reveals numerous unusual features of spatiotemporal behavior observed after different kinds of SPD processing that gives rise to an extreme grain refinement and an increase in the lattice dislocation density. Whereas SPD strongly alters the deformation curves, leading to either suppression of stress serrations or occurrence of serration types usually associated with static deformation bands, the band propagation persists in all material states. Surprisingly, smooth plastic deformation of the mostly work-hardened alloy neither corresponds to a uniform plastic flow but is related to propagation of a deformation band. The effect of the microstructure parameters on jerky flow can be explained through their influence on the propagation velocity and degree of localization of plastic deformation in the PLC bands. In particular, the loss of the PLC band mobility is discussed in relation with the conditions for the onset of necking and the formation of the localized shear band leading to fracture.
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