THE ANNIHILATION OF SUPERDISLOCATIONS IN NI3AL DURING DEFORMATION AT ROOM-TEMPERATURE

Transmission electron microscopy evidence is given of mechanisms of an nihilation that take place in the course of the room-temperature plast ic deformation of Ni3Al. Under a load orientation that favours the ope ration of a single-slip system, the short dipoles that are present in foils sectioned parallel to the slip plane are identified as elongated closed superdislocation loops instead of dipoles terminating at free surfaces. The fact that dipoles are often aligned in rows such that on e extremity of a given dipole corresponds with the closest extremity o f the next dipole in the screw orientation is explained in terms of th e cross-slip properties of Ni3Al-based alloys. The presence of two dis tinct categories of dipole rows is interpreted in terms of two differe nt approach mechanisms. The formation of antiphase-boundary tubes by d irect annihilation of screw segments is questioned.