The activation energy for the octahedral cross-slip of super-dislocations, from a (111) glide plane onto a (1¯11) cross-slip plane, in L12 ordered alloys was calculated by using a 3-dimensional treatment. By approximating bow-outs, in the 2 super-partials, by using piece-wise straight segments, the problem could be analyzed in 4-dimensional phase space. At sufficiently low or high stresses, the activation path could be directly identified. In the case of intermediate stresses, a more sophisticated treatment was necessary. Material parameters for Ni3Al were used in numerical evaluations. It was found that the saddle-point energy was far beyond the regime of homogeneous thermal activation. It was concluded that (111) cross-slip during plastic deformation could be nucleated only heterogeneously; as when a forest dislocation intersected the glide plane. With regard to the  in situ  transmission electron microscopic observation of flipping between different planes, cross-slip could nucleate at the foil surface and occurred by intermittently flipping onto the (010) plane; where it formed a Kear-Wilsdorf lock. From this configuration, the flips into (111) and (1¯11) were symmetrical and were expected to be equally likely. But because the (111) and (1¯11) configurations had higher energies than that of the Kear-Wilsdorf lock, this transition could occur only when the mobility in the (010) plane was high but the resolved shear stress on the (010) plane vanished.

G.Schoeck, W.Püschl: Philosophical Magazine A, 1997, 75[3], 823-31