Single crystals that were well-annealed, and oriented along [001] in order to suppress <100> dislocations, were used to study the onset of slip. Under a constant stress, slip initiated abruptly with increasing temperature. The slip vector was identified, as being <011>, by means of slip-line and transmission electron microscopic observations. There was a rate-independent slip initiation temperature that decreased approximately linearly with stress. The transmission electron microscopic observations showed that <011> slip was blocked by dislocation locking along both of the two <111> directions in the {011} glide plane. This locking was attributed to non-planar splitting of the screw component along the 3-fold line directions. The blocking of <011> slip by dislocation-locking long 2 line directions contrasted with <111> dislocations in NiAl that were locked only along the screw orientation, and to <100> dislocations that were not locked at all. This explained why <011> slip was more difficult than <111> or <001> slip, the general absence of <011> dislocations from annealed crystals and the need for these dislocations to be nucleated in [001]-oriented NiAl.

The Onset and Blocking of <011> Slip in NiAl. Y.Q.Sun, N.Yang: Acta Materialia, 2003, 51[18], 5601-12