DISLOCATION CORE STRUCTURES IN THE ORDERED INTERMETALLIC ALLOY TIAL

Evidence for the locking of both ''ordinary'' (b=(a/2)[110]) and ''sup er'' (b=a[101]) dislocations has been reported in the literature, and possible models for the locking processes have been proposed. In the p resent 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 thi s study suggest that the core of ordinary dislocations is compact and that the motion of these dislocations is inhibited by intrinsic lattic e friction and not by dislocation core dissociations. In contrast, the core of screw superdislocations was observed to be dissociated in a n on-planar configuration. The results suggest that the leading super pa rtial dislocation cross-slipped from one {111} plane to a cube plane a nd then redissociated on another {111} plane. The end result of this p rocess 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.