Collective Dislocation Behaviour in Dilute Alloys and the Portevin—Le Chatelier Effect

Abstract

The Portevin-Le Chatelier effect is discussed in terms of a model based on behaviour of crystal lattice defects. The model integrates two aspects of this behaviour: dynamic strain ageing associated with solute diffusion to dislocations and evolution of the densities of mobile and forest dislocations. The association of the PLC effect with the condition that the strain rate sensitivity of the flow stress be negative is demonstrated by linear stability analysis. It is further shown that plastic strain rate at a given specimen site undergoes relaxation oscillations in time keeping the average at the value prescribed by the imposed deformation (or loading) conditions. All characteristics of temporal behaviour can be found from the model. It is shown that this behaviour gives rise to a spatial pattern whose features can be investigated numerically provided the band propagation velocity is known. The importance of studying this quantity is emphasized.