Abstract:The grain boundaries as a fast diffusion path for solutes play an important role in multi-component diffusion-controlled phase transformations. In order to study the phase transformations in consideration of the grain boundary diffusion, the diffusion along grain boundary is incorporated in the quantitative phase field model coupled with the Kim-Kim-Suzuki (KKS). An integration method was used to calculate the equivalent grain boundary diffusion in the phase field method. The thermodynamic and mobility data was obtained from Thermo-Calc and DICTRA software respectively. The effect of the number of grain boundaries, the spatial distribution and size distribution (PSD) of α phase on the α phase dissolution was researched in the paper. The results show that grain boundaries are a faster element diffusive path. The number of grain boundaries is larger, the kinetics of α phase dissolution is faster. Namely, the kinetics of α phase dissolution is fastest when phase located at triple junctions; However, the dissolution kinetics is little difference when α phase is on the grain boundary and distribute uniformly in the matrix. Compared to the phase dissolution rate in two-dimensional condition, the effect of the grain boundary diffusion on dissolution kinetics is more obvious in three-dimensional condition. When phase transformation is dominated by bulk diffusion of solute, the spatial distribution of α phase is a main factor affecting the α phase dissolution. But when phase transformation is dominated by grain boundary diffusion of solute, the effects of other size distributions on the dissolution of alpha phase are not obvious except for uniform PSD.