Glissile non-coplanar superdislocations, and mechanisms of faulted-dipole formation in γ-TiAl

Abstract

〈101] and ½〈2] non-coplanar C-type and S-type dislocation core structures, where partial dislocations lie on two parallel {111} slip planes, are proposed. Such cores involve three parallel partial dislocations, one of which is delocalized on two {111} planes, delineating two regions of stacking fault. The distinction is made between glissile and sessile C-type and S-type superdislocation cores. Glissile cores can enable 〈101] and ½〈112] superdislocations to glide in low-energy complexes with small Burgers vector components and no high-energy antiphase boundary, whilst sessile cores can give rise to dipole formation. The mechanisms of faulted dipole formation and destruction are proposed which involve the glissile ⌆ sessile transformation of C-and S-type superdislocation cores. The glissile ⌆ sessile transition simply requires the rearrangement of the core of the partial dislocation which is delocalized over two parallel {111} planes. Such a transition cannot be detected by weak-beam (WB) transmission electron microscopy (TEM). The possibilities of erroneous interpretation of WB TEM experimental data are discussed.