Low-energy dislocation structures in Ni3Al single crystals (oriented for single slip) fatigued at room temperature were studied using transmission electron microscopy. In general, dislocation structures in fatigued Ni3Al were composed of primary superdislocations, edge superdislocation bundles (mutually trapped edge superdislocations), primary edge superdislocation dipoles (line vector ∥ ), and faulted superdislocation dipoles (line vector ∥  or ∥ ). No wall or cell structure was observed. Paired primary superdislocations, as they glided in the (111) slip plane during cyclic deformation, were energetically unstable because of the fluctuation of the separation between two superpartial dislocations (b = ± 1 2). The fluctuation led to an increase in the line energy of the primary superdislocations, and resulted in the onset of several dislocation reactions. Since the resulting dislocations of these reactions were all sessile, their line energy remained unchanged during cyclic deformation. Accordingly, they were considered to be energetically more stable than primary superdislocations. © 1994.
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