Characterization of superdislocation dissociations in Al₆₆Ti₂₅Cr₉ with transmission electron microscopy observations and image simulations

Abstract

The nature of dissociated superlattice dislocation cores in Al₆₆Ti₂₅Cr₉, deformed at room temperature, has been characterized by weak-beam transmission electron microscopy (TEM) and comparison of experimental images with computer-simulated images. The displacement fields associated with narrowly dissociated APB- and SISF-dissociated ‹110› superdislocations were calculated to account for the asymmetry in dislocation contrast and led to a better understanding of the formation of images. Such calculations are a powerful aid, when coupled with image simulations, in distinguishing the “real” intensity peaks from the supplementary peaks that can be generated under experimental imaging conditions. While both APB- and SISF-dissociated superdislocations were identified, the vast majority of superdislocations were determined to be APB-dissociated. Corrected values of the fault energies (γ^APB and γ^SISF ) have been measured for this alloy. These energies and the observed dissociations are shown to be self-consistent.