Single crystalline specimens of Ni3Al were compressed along [001] at three different temperatures (600, 835 and 920C). Above the peak temperature (Tp = 800C), the stress-strain curves exhibited a yield drop caused by work softening. Transmission electron microscopy methods were used to analyse the structures of the superlattice dislocations formed at various deformation temperatures, showing that the Burgers vector and glide plane did not change (±a<110>111). Below Tp, screws and screw dipoles consisting of Kear-Wilsdorf locks were predominant. Above Tp, screw dipoles were not observed; indicating their dynamic recovery. Above Tp, dislocations of all characters contained antiphase boundary faults that were inclined with respect to their glide plane. It was proposed that their motion occurred by antiphase boundary fault-dragging. Calculations were carried out in order to model the work-softening behaviour observed above Tp. It was concluded that both the yield stress and yield drop were governed by the value of the mobile dislocation density and its evolution with strain.

On the Origin of Work Softening of Ni3Al Deformed along [001] above the Peak Temperature. Rentenberger, C., Karnthaler, H.P.: Materials Science and Engineering A, 2001, 319-321, 347-51