Early-stage decomposition kinetics in Ni–Al Alloys—I. Small and wide-angle neutron scattering investigation on Ni–13 at.% Al and clusterdynamic modelling Original Research Article

The early stages of the formation of ordered γ′-precipitates in Ni–13 at.% Al have been investigated at aging temperatures of 450, 500, and 550°C. Cluster size distributions with radii down to 0.3 nm have been determined by means of small and wide-angle neutron scattering. The observed decomposition kinetics have been analysed in terms of a clusterdynamic decomposition model that accounts for the low nucleation energy for the formation of ordered precipitates in this alloy. The results of the clusterdynamic modelling of the experimental data reveal that the character of the decomposition reaction depends strongly on the initial supersaturation. A nucleation reaction takes place only at rather low initial supersaturations (ξ0<1.16). With increasing initial supersaturations, the influence of nucleation diminishes. At higher initial supersaturations (ξ0>1.35), decomposition proceeds solely by coarsening of an initial distribution of small clusters.