Direct Observation of Antiphase Boundaries in the Fe3Al Superlattice

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Abstract
Antiphase boundaries have been observed in thin foils of a Fe3Al superlattice prepared from the bulk material, using transmission electron microscopy techniques. This particular alloy forms two distinct types of superlattice; the first is a high temperature modification based on an imperfect B2‐type lattice, while the second is a lower temperature modification based on the more perfect DO3‐type lattice. A distinct type of antiphase boundary has been found to be associated with each ordered configuration, and their geometry and energy have been analyzed in detail. The critical conditions necessary to reveal these antiphase boundaries by transmission electron microscopy have been treated. In particular, it is found that antiphase boundary contrast is obtained only when the foil is critically oriented for diffraction from a strong superlattice reflection. Furthermore, the detailed dynamical theory of electron diffraction has been applied successfully to the present observations. Finally, some contrast effects associated with intersecting antiphase boundaries have been observed and interpreted using the kinematical theory of electron diffraction.