Frank–Read source mechanism, mobile dislocation density exhaustion and flow stress anomaly in L12 alloys: a dislocation dynamics study

Abstract

We present a dislocation dynamics simulation study on the effect of Kear–Wilsdorf locks formation on the Frank–Read mechanism at temperatures below the peak temperature of the flow stress in some L12 alloys. The simulation developed in this paper differs from previous ones by taking into account the detailed structure of the connection of the Kear–Wilsdorf lock with the glissile part of the dislocation, as well as by allowing glide in the cube plane. Assuming that the plastic strain is carried out by the motion and development of the kinks connecting the Kear–Wilsdorf locks, we analyse their behaviour under the effect of an applied stress at temperatures below the peak temperature. We show that the area swept by an expanding dislocation loop in the octahedral plane, starting from an edge dislocation segment, is the result of the competition between the locking rate and the velocity of its screw part, whatever the length of the initial segment. When the applied stress is smaller than a critical stress τc/ d , the length of a moving edge segment decreases until it eventually stops. For a stress larger than τc/ d , the length of the segment increases and Frank–Read sources may develop. The first case is referred to as convergence, the second as divergence. The simulation results are applied to the analysis of the micro- and macro-yield behaviour of these alloys as well as to some of their specific properties.