Morphological evolution of γ' and γ'' precipitation in a model superalloy: Insights from 3D phase-field simulations

This study explores the role of nucleation conditions of γ'' and γ' strengthening phases in determining the microstructural characteristics of Ni-based superalloys. A 3D phase-field model is employed to investigate the competitive growth behavior of these phases under aging conditions at 850 K. The analysis reveals that the initial nucleation conditions significantly affect the equilibrium phase morphology, including size dispersion and spatial distribution, while the final equilibrium volume fractions remain constant. Equal initial nucleation densities of γ'' and γ' phases promote a more uniform spatial distribution, reduced size dispersion, and decreased von Mises stress, leading to improved precipitation strengthening. This is particularly important, as both precipitate phases show an opposite sign of the misfit compared to the matrix. This leads to a minimum state of elastic energy for an even distribution of precipitates in an alternating setting and allows for tuning of the equilibrium fraction, constrained by elastic interaction. These findings highlight the importance of optimizing preferential nucleation to enhance the microstructure and properties of Ni-based superalloys.