Solidification Modeling of Microsegregation

Abstract: A phase transformation from liquid to solid phase takes place when the material solidifies. Limited diffusion during this phase transition causes microsegregation, which is aphenomenon during solidification that leads to the formation of secondary phases andconcentration gradients. This affects the properties of the material and how it is to be treatedin further processing steps. Due to the complexity of the solidification process, a modelingapproach has been used for investigation of microsegregation. The Scheil-Gulliver model assumes negligible diffusion in the solid phase but an exchange ofsolute during back-diffusion can have an important influence on solidification. While the Brody-Flemings model considers this, it is questionable in its assumptions. A new proposedmodel by John Ågren that considers multicomponent diffusion effects have been implementedusing the Matlab-Toolbox for Thermo-Calc. The model is used to perform solidification simulations for the binary Al-2.1Cu and theternary Al-2.1Cu-1Si system (at%) and the results are compared to the Scheil-Gulliver modeland DICTRA simulations. The Ågren model gives excellent results for the binary system athigh cooling rates. It does however show deviations from the DICTRA results at lowercooling rates and for the ternary system.