EARLY-STAGE DECOMPOSITION KINETICS IN Ni-Al ALLOYS-II. CLUSTERDYNAMIC MODELLING OF FORMER EXPERIMENTAL RESULTS

摘要

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℃ 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-l2 at. Al at 500℃ and Ni-l4 at. Al at 550℃, 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-l2 at. Al at 500℃ 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-l4 at. Al at 550℃ 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 clas- sical nucleation to pure coarsening with increasing initial supersaturations is quantified by additional CDM calculations.