In-situ TEM observations of dislocations motion in stoichiometric NiAl single crystals

In an attempt to understand the relationship between dislocation mobility and the observed changes in ductility with heat treatment and alloy purity, in-situ straining TEM experiments have been carried out. Single crystals of high and commercial purity, with different orientations and thermal histories, were used in the present investigation. In all the samples dislocation motion was readily observed. The pre-existing dislocations were sessile while the newly generated dislocations glide in slip bands. Dislocations were generated both from the foil edge and the foil interior. Cross-slip was noticed in [110] and [001] oriented single crystals. These orientations also exhibited loop and debris formation after limited deformation. Dislocation motion occurred by rapid jumps in the high purity materials whereas the dislocations moved in a slow, regular manner in the commercially pure materials.