The faulted dipoles which were associated with the low-temperature deformation of the -phase were characterized by using conventional, high-resolution and  in situ  heating transmission electron microscopy. The results indicated that the formation of these faulted dipoles involved the localized pinning of a super-dislocation, bypassing of the pinning-point, and the drawing-out of a dipole whose energy was then reduced by the passage of partial dislocations and the formation of an extrinsic stacking fault. The extrinsic nature of the stacking fault was detected by comparison with computer-generated image simulations, and was confirmed by atomic-resolution lattice images. These faults were bounded by single or double Shockley partial dislocations, but the latter occurrence was rare. The low-temperature stability of this defect was attributed to the ordered structure of TiAl, and the high-temperature instability of the faulted dipoles was attributed to a localized reordering of the crystal structure via diffusive processes.

B.Viguier, K.J.Hemker: Philosophical Magazine A, 1996, 73[3], 575-99