The structure of boundaries between antiphase regions in TiAl-based alloys

High-resolution transmission electron microscopy has been used to examine the detailed structure of antiphase boundaries in the tetragonal γ-phase in TiAl-based alloys. In agreement with earlier work using diffraction contrast images and microdiffraction it has been shown that, associated with each antiphase domain boundary separating domains where the c axes are parallel, there is a thin (2 nm) layer in which the c axis is at right angles to the c axis of the domains either side. The reasons why such a complex defect is found in TiAl alloys but is not found in other L1 0 phases which have been examined, are briefly discussed