Phase-field modeling of bimodal particle size distributions during continuous cooling

Abstract Microstructures in Nickel-base alloys typically contain a two-phase mixture of γ/γ′. The microstructure having a bimodal size distribution of γ′ is of particular interest because it has important property consequences [1] . In this paper, the phase-field method with an explicit nucleation algorithm is employed to investigate the microstructural development during a continuous cooling with various cooling rates. It is demonstrated that bimodal particle size distributions can be achieved at an intermediate cooling rate due to a coupling between diffusion and undercooling, in which the system experiences two peaks of well-isolated nucleation events. It is suggested that this is caused by soft impingement, followed by a renewal of driving force for nucleation, followed by a subsequent soft impingement. Under very high cooling rates, the microstructure becomes unimodal, because undercooling always outruns diffusion and the microstructure never reaches soft impingement.