EARLY-STAGE DECOMPOSITION KINETICS IN Ni-Al ALLOYS-I. SMALL AND WIDE-ANGLE NEUTRON SCATTERING INVESTIGATION ON Ni-13 at. Al AND CLUSTERDYNAMIC MODELLING

摘要

The early stages of the formation of ordered γ'-precipitates in Ni-l3 at. Al have been investi- gated at aging temperatures of 450, 500, and 550℃. 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 super- saturations (ζo < 1.16). With increasing initial supersaturations, the influence of nucleation diminishes. At higher initial supersaturations (ζo > 1.35), decomposition proceeds solely by coarsening of an initial distri- bution of small clusters.