A two-dimensional microsegregation model for the description of microstructure formation during solidification in multicomponent alloys: Formulation and behaviour of the model

A new two-dimensional model for the simulation of microstructure formation and microsegregation during solidification of multicomponent alloys is presented. The model combines a direct simulation of the primary phase formation based on a previously published pseudo-front tracking method [Jacot A, Rappaz M. Acta Mater 2002;50:1909; Acta Mater 2002;50:3971] and a mixture approach for the description of the formation of secondary phases. A general formalism is proposed to describe the influence of back diffusion on the evolution of the type, amount and composition of the interdendritic phases. The model is coupled to the phase diagram software Thermo-Calc to obtain the phase equilibrium in the mixture and the concentrations to be prescribed at the primary phase/mixture interface. The model incorporates a parameter that permits distinguishing between coupled and divorced growth modes of eutectics. The difficulty of bridging grains that have different crystallographic orientations due to the grain boundary energy being larger than twice the solid/liquid interface energy is modelled phenomenologically by introducing a coalescence undercooling. The model is used to investigate the influence of the primary phase morphology on microsegregation and is compared with simpler onedimensional approaches. The influence of impingement, coalescence, coarsening and grain size distribution is discussed.