On the origin of work softening of Ni3Al deformed along [001] above the peak temperature

Single crystalline specimens of Ni3Al were compressed along [001] at three different temperatures (600, 835 and 920 °C). Above the peak temperature (TP=800 °C), the stress–strain curves show a yield drop caused by work softening. Transmission electron microscopy (TEM) methods were used to analyse the structures of the superlattice dislocations formed at different deformation temperatures showing that the Burgers vector and glide plane do not change (±a〈110〉{111}). Below TP, screws and screw dipoles consisting of Kear–Wilsdorf (KW) locks are dominating. Above TP, screw dipoles are not observed indicating their dynamic recovery. Above TP, dislocations of all characters contain antiphase boundary (APB) faults that lie inclined to their glide plane. It is proposed that their motion occurs by APB fault dragging. Calculations were carried out to model the work-softening behaviour observed above TP. It is concluded that both the yield stress and yield drop are governed by the value of the mobile dislocation density and its evolution with strain.