CLIMB AND GLIDE OF A 3[111] DISLOCATIONS IN AN ALUMINUM SIGMA=3 BOUNDARY/

High-resolution transmission electron microscopy observations are pres ented of the motion of grain-boundary dislocations within an aluminium Sigma = 3[0 (0) over bar 1] bicrystal. The observations show the glid e of dissociated a/3[111] grain-boundary dislocations on the incoheren t Sigma = 3(2<(11)over bar>) boundary. These dislocations are subseque ntly incorporated into a growing coherent two lamella where further mo tion occurs by climb. Analysis of the tip of the advancing twin sugges ts that nucleation of coherent twin segments may be initiated by the a bsorption of a lattice dislocation in the boundary with the subsequent dissociation to form a/3[111] and a/6[(2) over bar 11] grain-boundary dislocations.