A simulation of dislocation dynamics and of the flow stress anomaly in L1(2) alloys

This work examines the flow stress anomaly of L1(2) alloys by means of a mesoscopic two-dimensional simulation of dislocation dynamics. The basic properties modelled are slip in the octahedral plane, the conditions at which screw dislocation segments are locked by formation of Kear-Wilsdorf locks and subsequently unlocked, and the mobility of jogs in the cube plane. The range of temperatures investigated varies between 200 and 600 K, scaling with the domain of anomaly of Ni3Al-based alloys. The simulations indicate that strain is mostly provided by the sliding of kinks. Two conditions are simultaneously required in order to reproduce the flow stress anomaly: firstly kink mobility should be hindered via the dragging of jogs and secondly, irrespective of the probability of locking, locks should not be destroyed easily. The simulations suggest, in addition, that two different flow stress regimes take place in the temperature domain of the stress anomaly. At the onset of the anomaly, the flow stress is determined by kink motion, itself a function of kink height, whereas in the high-temperature regime the flow stress is governed by the unlocking of the weakest incomplete Kear-Wilsdorf lock of the microstructure. The results of the present computer model are discussed in relation to experimental observations and existing theoretical models.