The weak-beam method of electron microscopy was used to study dissociation and fault energies in disordered and ordered Ni3Fe. For the ordered structure, this was of particular interest because the plastic behaviour was then determined by the dissociation mode of the superlattice dislocations. Single crystals of Ni3Fe were quenched in order to suppress the formation of the long-range ordered phase, and strained at room temperature. From the dissociation of the Shockley partials, the stacking-fault energy, γ, of the disordered face-centered cubic phase was deduced to be 95mJ/m2. A section of the disordered and deformed crystal was subsequently fully ordered (Ll2 superlattice structure) and additionally deformed. A complex stacking fault energy, γCSF, of 123mJ/m2 was deduced from dissociated unit dislocations which were sessile since they had been introduced before ordering. Deformation of the ordered crystal proceeded via the formation of superlattice dislocations. These dislocations exhibited four-fold dissociation, and measurements of the antiphase boundary energy yielded a value, γAPB, of 133mJ/m2; which was in good agreement with calculated values. The dissociation could be used to explain the observed dislocation structure.

Fault Energies in Ordered and Disordered Ni3Fe. A.Kornera, H.P.Karnthaler: Philosophical Magazine A, 1985, 52[1], 29-38