The boundaries were studied, by means of transmission electron microscopy, in a D03 long-range ordered single crystal. Two types of antiphase boundary contrast were observed. The normal p-type antiphase boundary contrast was imaged using superlattice reflections. This type of contrast was caused by a basic displacement of ¼<111> or ½<111> across the antiphase boundary. On the other hand, the anomalous a-type antiphase boundary contrast was imaged using fundamental reflections. The latter contrast was weak, asymmetrical in dark-field and discontinuous along a closed antiphase boundary loop. It was demonstrated that the anomalous a-type contrast was caused by a small non-crystallographic displacement of atoms near to the antiphase boundary. Detailed examination of anomalous antiphase boundary contrast indicated that the fault vector depended upon the basic displacement as well as upon on the antiphase boundary orientation. The main component of the fault vector was found to be perpendicular to the antiphase boundaries, with a basic displacement magnitude of ¼<111>. The additional displacement was explained in terms of mechanical and chemical relaxations of the antiphase boundaries and with reference to the anomalous plastic behavior of Fe3Al.

TEM Investigation of Non-Crystallographic Displacements near Antiphase Domain Boundaries in D03 Ordered Fe3Al. W.Liu, A.Gemperle, J.Gemperlova, V.Paidar, E.Nembach: Acta Materialia, 1998, 46[17], 6173-82