A unified model of grain-boundary segregation kinetics was established, which could simulate the equilibrium and non-equilibrium grain-boundary segregation kinetics during isothermal ageing. The results of model fittings/predictions were in a good consistence with those of the experiments. Values of several important parameters, such as vacancy formation energy, vacancy migration energy, and complex migration energy derived by model fittings, showed a reasonably good agreement with those in the references. Relationship between the equilibrium and non-equilibrium grain-boundary segregation mechanisms was discussed in detail. The segregation peak/depletion trough observed in the non-equilibrium segregation kinetics may be ascribed to the vacancy flux. The equilibrium segregation kinetics was considered as a special case in non-equilibrium segregation kinetics with the zero vacancy flux. Both the equilibrium and non-equilibrium segregation kinetics were believed to be dominated by vacancy-solute complex flux. The proposed unified model could be a significant progress in grain-boundary segregation theory, with applications in guiding the design of materials.

A Unified Model of Grain-Boundary Segregation Kinetics. J.Wu, S.Song: Journal of Applied Physics, 2011, 110[6], 063531