Multiphase-field model for multicomponent alloys coupled to thermodynamic databases

The solidification microstructure of Ni-baae superalloys consists basically of primary γ dendrites and secondary precipitations in the interdendritic regions (γ′, laves, carbides etc.). Information about the amount and spatial distribution of these precipitations and also about microsegregation is of great importance for further treatment of cast parts and for the development of new alloys. In order to simulate microstructure formation and microsegregation in directionally solidified samples, a multiphase multicomponent phase field model is used. Multicomponent phase equilibria are obtained online through thermodynamic calculations from thermodynamic databases following the CALPHAD approach. These are coupled to the phase field calculations, which take into account primary solidification as well as secondary phase formation. The microstructure formation of solidification and subsequent homogenisation is simulated using this approach. The calculated element distribution maps are compared to measured ones, which have been obtained from directionally solidified samples.