Phase-field simulation of γʹ coarsening behavior in cobalt-based superalloy

Abstract

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