Early-stage decomposition kinetics in Ni–Al alloys—II. Clusterdynamic modelling of former experimental results

Abstract

In Part I it was shown that the early stages of the formation of γ′-precipitates in a Ni–13 at.% Al alloy aged at 450, 500 and 550°C can be interpreted in the frame of a clusterdynamic decomposition model (CDM) that accounts for the generally low nucleation energies in this alloy. In this part CDM is used for modelling decomposition reactions in Ni–12 at.% Al at 500°C and Ni–14 at.% Al at 550°C, and the results are compared with experimental data from literature. All experimental results presented in Part I and II are well described by CDM with a consistent set of model parameters. The CDM calculations reveal that in Ni–12 at.% Al at 500°C with a small initial supersaturation, a classical nucleation reaction takes place, confirming the former interpretation of the experimental data. On the other hand, in Ni–14 at.% Al at 550°C with a higher initial supersaturation CDM predicts a pure coarsening reaction without any nucleation, which is in contradiction to the former interpretation of the data. The transition from classical nucleation to pure coarsening with increasing initial supersaturations is quantified by additional CDM calculations.