DISLOCATION CORE STRUCTURES IN THE ORDERED INTERMETALLIC ALLOY TIAL

Evidence for the locking of both ''ordinary'' (b=(a/2)[110]) and ''super'' (b=a[101]) dislocations has been reported in the literature, and possible models for the locking processes have been proposed. In the present study, high resolution transmission electron microscopy (HREM) and calculated image simulations were combined to provide atomic level observations of these dislocation core structures. The results of this study suggest that the core of ordinary dislocations is compact and that the motion of these dislocations is inhibited by intrinsic lattice friction and not by dislocation core dissociations. In contrast, the core of screw superdislocations was observed to be dissociated in a non-planar configuration. The results suggest that the leading super partial dislocation cross-slipped from one {111} plane to a cube plane and then redissociated on another {111} plane. The end result of this process is a sessile configuration that contains an intrinsic stacking fault on the (111BAR) plane, an extrinsic stacking fault on the (111) plane, and an antiphase boundary on the (010) plane in between.