Mesoscopic simulations of dislocation motion in dynamic strain ageing alloys

A mesoscopic 2D computer model is introduced to investigate the thermally activated motion of dislocations within a random array of obstacles. The simulations are performed with regard to the collective dislocation effects underlying the plastic instabilities associated with the Portevin–Le Chatelier effect (strain-rate softening instability). To this end, dynamic strain ageing (DSA) by solute diffusion towards glide dislocations, which are temporarily arrested at obstacles, are taken into account in addition to the long-range interactions between the dislocations. It is shown that strain-rate softening arises as a result of the interplay between DSA and long-range dislocation interactions, while neither of the effects alone induces instability. Results of simulations at constant stress rate are presented, and the respective statistics of dislocation activation is discussed.