Distinguishing superdislocation dissociation mechanisms in L1₂ crystal structures Examples with Al₆₇Mn₈Ti₂₅

Abstract

The nature of dissociated superlattice dislocations in Mn-modified Al₃Ti deformed at 673 K has been studied with transmission electron microscopy weak-beam imaging assisted with computer simulations. The observed images of dissociated a〈110〉 superdislocations under a variety of diffraction conditions have been matched successfully with simulated images formed by assuming dissociation into two a/2〈110〉 partials separated by an antiphase boundary. The simulations show that both fringe contrast from stacking faults and single dislocation images should be observed with certain diffraction conditions for a superlattice-intrinsic stacking fault-dissociated superdislocation. These differences make it possible to select a series of imaging conditions beforehand to identify the dissociation mechanism even if the partials are very closely spaced. Evaluation of the g·b criteria often used in attempting to identify partial dislocations has shown that these criteria must be used with caution, especially when the spacing of the partials is small.