LOW-ENERGY DISLOCATION-STRUCTURES IN CYCLICALLY DEFORMED NI3AL SINGLE-CRYSTALS

Low-energy dislocation structures in Ni3Al single crystals (oriented f or single slip) fatigued at room temperature were studied using transm ission electron microscopy. In general, dislocation structures in fati gued Ni3Al were composed of primary superdislocations, edge superdislo cation bundles (mutually trapped edge superdislocations), primary edge superdislocation dipoles (line vector parallel-to [121BAR]), and faul ted superdislocation dipoles (line vector parallel-to [110BAR] or para llel-to [011BAR]). No wall or cell structure was observed. Paired prim ary superdislocations, as they glided in the (111) slip plane during c yclic deformation, were energetically unstable because of the fluctuat ion of the separation between two superpartial dislocations (b = +/- 1 /2[101BAR]). The fluctuation led to an increase in the line energy of the primary superdislocations, and resulted in the onset of several di slocation reactions. Since the resulting dislocations of these reactio ns were all sessile, their line energy remained unchanged during cycli c deformation. Accordingly, they were considered to be energetically m ore stable than primary superdislocations.