THE STRUCTURE OF BOUNDARIES BETWEEN ANTIPHASE REGIONS IN TIAL-BASED ALLOYS

High-resolution transmission electron microscopy has been used to exam ine the detailed structure of antiphase boundaries in the tetragonal g amma-phase in TiAl-based alloys. In agreement with earlier work using diffraction contrast images and microdiffraction it has been shown tha t, associated with each antiphase domain boundary separating domains w here the c axes are parallel, there is a thin (2 nm) layer in which th e 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 n ot found in other Ll(0) phases which have been examined, are briefly d iscussed.