Metastable disordered polymorphs of the L12-type intermetallic were prepared by means of heavy deformation or rapid solidification. In order to study reordering during annealing, transmission electron microscopic images were obtained of reordering during the in situ annealing of largely disordered melt-spun material which contained Fe and which was slightly off-stoichiometric, with excess Ni. The results indicated that the grain boundaries in such alloys were incapable of nucleating chemical long-range order, and appeared to maintain a disordered face-centered cubic nature. Reordering began via the 1-dimensional growth of lamellar structures from pre-existing nanoscopic ordered nuclei behind moving grain boundaries. This was consistent with the emigration of excess Ni; firstly to antiphase domain boundaries, and then to grain boundaries. This explanation was confirmed by a kinetic analysis of magnetic variations during reordering.

Evidence for Disordered Character of Grain Boundaries in a Ni3Al-Based Alloy during Reordering. Lay, S., Yavari, A.R.: Acta Materialia, 1996, 44[1], 35-41