Three L12 long-range ordered intermetallic compounds were studied using transmission electron microscopic methods. The superlattice glide dislocations could dissociate according to two schemes: antiphase boundary coupled unit dislocations or superlattice intrinsic stacking fault coupled super Shockley partials; both of them were analysed by weak-beam transmission electron microscopic methods. The nanostructures resulting from severe plastic deformation carried out by high pressure torsion were strongly affected by the different dissociation schemes of the dislocations. Antiphase boundary-dissociated superlattice dislocations and especially the antiphase boundary tubes they form lead to the destruction of the long-range order by high pressure torsion-deformation as observed in Cu3Au and Ni3Al, whereas in Zr3Al heavily deformed (about 100000% shear strain) at low temperatures the order was not destroyed since the deformation occurred by superlattice intrinsic stacking fault-dissociated dislocations. In addition to the effects on the long-range order the different dissociation schemes of the dislocations have a strong impact on the refinement and destruction of the crystalline structure by severe plastic deformation. They seem to be decisive for the dynamic recovery considered as the limiting factor for the final grain sizes and the possibility of reaching amorphisation. Finally, the correlation between the reduction of the long-range order and the structural refinement occurring during severe plastic deformation was different in the three different alloys: In Cu3Au, the long-range order was already strongly reduced before the structural refinement reaches saturation, in Ni3Al both were occurring simultaneously, whereas in Zr3Al, the formation of the nanograins does not seem to be connected with disordering.

Electron Microscopy of Severely Deformed L12 Intermetallics. D.Geist, C.Gammer, C.Mangler, C.Rentenberger, H.P.Karnthaler: Philosophical Magazine, 2010, 90[35-36], 4635-45