A tool for modelling of microsegregation: An approximation method for partition coefficients in experimentally determined multicomponent phase diagrams

A complete set of partition coefficients of all alloying elements in multic omponent systems is an essential input for solidification models. An approx imation method for partition coefficients in experimentally determined phas e diagrams has been developed. The equilibria of the binary boundary system s and the eutectic valleys are used as a basis for the approximation in ter nary systems. The method has been verified by a comparison of approximated and known (calculated by the CALPHAD method) partition coefficients in the Al-Cu-Si system. The ratio of the end points of calculated tie-lines is in excellent agreement with approximated partition coefficients. In the empiri cal Al-Cu-Si phase diagram, the approximated partition coefficients yield s olid concentrations that are close to the measured solidus surface.