Published online by Cambridge University Press: 22 February 2011
Recent work has shown that antiphase domains are observed in alloys based around TiAl if they are quenched from the alpha field. The present work has shown that the anti phase domain boundaries (APDBs) are in fact not simple APDBs but are composed of very thin (about 2 nm) 90° domains. Although the contrast is dominated by the fact there is a 1/2<101> displacement between the domains either side of this thin 90° domain, there is somewhat more complex contrast associated with the APDBs than the hard sphere model would predict. Annealing studies of the complex APDBs in a Ti49Al alloy have shown that the originally irregular APDBs in the quenched material facet on {111} planes. The significance of these observations is discussed in terms of mechanisms by which the APDBs are formed in TiAl and in terms of the planar fault energies in the Llo structure.