Superlattice intrinsic stacking faults were observed in Ni3Al polycrystals deformed in compression between room temperature and 800C. A detailed weak-beam analysis indicated that the superlattice intrinsic stacking faults originated at a screw partial with a Burgers vector of ½<110>. Starting from the stable dissociation into two partials with collinear Burgers vectors and with an antiphase boundary stabilized on {001}, one of the two ½<110>  partials could split, under the effect of a high local stress, into an edge Shockley and a partial with a Burgers vector of ½<112>. The latter produced a superlattice intrinsic stacking faults as it escaped from its initial position in a {111} plane. Calculations of the total energy of the threefold dissociation revealed the presence of a secondary minimum when the 1/3<112> partial lay between 25 and 50nm from the Shockley partial, in good agreement with the weak-beam observations. However, the superlattice intrinsic stacking faults exhibited large deviations from this equilibrium distance when they resulted from deformation at low temperatures and, in any case, they exhibited a strong tendency to serration, with segmentation of the 1/3<112> partial along <110> directions. These features attested to a high Peierls force acting on the 1/3<112> partials. The equilibrium shape of a superlattice intrinsic stacking fault was described in terms of a thermally aided process: the higher the temperature, the larger the probability of recombination. Deformation or annealing at an intermediate temperature was expected to favour the presence of elongated superlattice intrinsic stacking faults of almost homogeneous width. Steps on superlattice intrinsic stacking faults had been revealed in weak-beam experiments. They resulted from the intersection of the superlattice intrinsic stacking faults with superdislocations. It was shown that such events affected the equilibrium shape of the outer 1/3<112> partial. Surface energies were measured for several split configurations. The energies of the antiphase boundaries on {100} and {111} were 140 and 180mJ/m2, respectively. The superlattice intrinsic stacking fault energy was expected to lie between 5 and 15mJ/m2.

On the Presence of Super Lattice Intrinsic Stacking Faults in Plastically Deformed Ni3Al. P.Veyssiere, J.Douin, P.Beauchamp: Philosophical Magazine A, 1985, 51[3], 469-83