Abstract
Recent observations using transmission electron microscopy have shown that defects which show contrast similar to that expected from antiphase domain boundaries (APDBs) are commonly observed within the gamma phase in quenched samples of alloys based on TiAl. Detailed examination has been carried out on several alloys and it has been found that the contrast is complex. It has been argued previously that the complexity is associated both with dynamical interactions and with a supplementary displacement across the APDB. In the present paper it is shown that the situation is more complex than either of these suggestions, and that all of the defects which give contrast characteristic of APDBs in TiAl-based alloys are in fact made up of two closely spaced 90° domain boundaries. The reasons for this and the relation between this conclusion and earlier work on APDBs in similar structures, such as CuAu, are discussed.