Phase-field simulation of γ′ coarsening behavior in cobalt-based superalloy

Because the microstructure characteristics of gamma' strengthened cobalt-based superalloys are critical for anticipated next generation superalloys, the morphological evolution and coarsening behavior of gamma' precipitates during isothermal aging in Co-Al-W ternary alloys are investigated using the phase-field method. Accurate gamma' evolution over the entire aging process is simulated through coupling with the antiphase domain and the elastic energy. With a change in gamma' volume fraction from 38% to 66%, the coarsening rate of gamma' precipitates shows an approximately linear increase, primarily due to the increased diffusion potential difference between the gamma matrix and gamma' precipitate. The coalescence between adjacent precipitates is promoted in the high gamma' volume fraction, resulting in polyhedral precipitates and particle size distribution (PSD), which agrees with MLSW theory. The morphology transition mechanism of gamma' is showed through the evolutions of interfacial energy and elastic energy, and the effects of microstructure features on the coarsening rate and coarsening mode are discussed. Results of this study provide guidance for the development of Co-based superalloys with optimized microstructures.