The Effect of Grain Boundary Mobility on the Formation of Second Phases in Nanostructured Binary Alloys

On the basis of the phase field theory, the features of the formation of second-phase precipitates in polycrystalline binary alloys are studied, taking into account the grain boundary mobility, anisotropic impurity diffusion near the boundaries, and thermal fluctuations. The difference in the interaction parameters at the grain boundaries and in their volume, as well as accelerated grain boundary diffusion, can lead to the heterogeneous formation of second phases, the distribution of which can correspond to nonwetting or complete or partial wetting of the boundaries. The presence of the grain boundary mobility leads to an increase in the volume fraction of the second phases. In the case of complete or partial wetting, the resulting second phase can move along with the grain boundary. In the case of nonwetting, the second phase is formed near the grain boundaries and is practically immobile, while precipitates grow mainly along the direction of motion of the boundary. In the case of nonwetting, separation of precipitates from the boundary is also observed.