It was noted that a simulation of dislocation dynamics in L12 alloys had furnished new insights into the problem of the strength anomalies which were observed in such materials. The results of this simulation were compared with those of previous analytical models. Some interesting consequences were deduced, with regard to strain-rate sensitivity and work-hardening rate, by combining results from these models. It appeared that the simulation entirely confirmed the 2 main assumptions of the extended-locking-unzipping model. The stress anomaly could be reproduced by the simulation only in the case where Kear-Wilsdorf locks were very difficult to unlock, and where mobility was controlled by a drag force on jogs. The simulation also suggested that some unlocking of Kear-Wilsdorf barriers, which was a basic assumption of the locking-unlocking model, was likely to occur at higher temperatures. It was shown that the extended-locking-unzipping model provided a framework in which a gradual transition between the 2 extreme situations, of locking-unzipping on the one hand, and locking-unlocking on the other hand, could be easily described in terms of a balance between exhaustion and multiplication in the former case, which was gradually replaced by a balance between exhaustion and unlocking in the latter case. A flow stress anomaly and a high work-hardening rate were easily deduced from the extended-locking-unzipping model in the pure locking-unzipping situation. The introduction of some degree of unlocking at higher temperatures, as suggested by the simulation, resulted in a decrease in the work-hardening rate; as observed experimentally. The persistence of a flow stress anomaly in this higher temperature-range required that the relative increase in the unlocking rate, with increasing temperature, should be smaller than the increase in the exhaustion rate; as intuitively expected.

Comment on a Simulation of Dislocation Dynamics and the Flow Stress Anomaly in L12 Alloys. F.Louchet: Philosophical Magazine A, 1998, 77[3], 761-8