Phase-field modeling of bimodal microstructures in nickel-based superalloys

The phase-field approach is used to study the formation and ageing of bimodal microstructures in a model Ni-based superalloy. Particular attention is paid to the definition of interfacial energies in the presence of elastic strain fields and to the incorporation of these energies in the phase-field formalism. During a two-step annealing procedure, our model predicts the formation of large anisotropic gamma' precipitates (called secondary precipitates) and small, almost isotropic gamma' precipitates (called tertiary precipitates). Finally, the phase-field model is used to characterize the ageing of tertiary precipitates. In agreement with experiments, we show that the mean size of the tertiary precipitates first grows as t(1,3) and finally reaches a plateau. This peculiar behavior is explained using phase-field simulations with prescribed geometries and with the development of a simple analytic model. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.