A phase-field model coupled with a thermodynamic database Original Research Article

A phase-field model for the solidification of multi-component alloys, capable of being integrated with thermodynamic databases, has been developed. The solid–liquid interface is modelled as a mixture of solid and liquid phases. The solute concentration of the solid phase depends only on the local temperature while the solute concentration of the liquid phase is affected by solute rejection (or absorption) from the solid being formed together with the extent of any chemical diffusion in the liquid. The governing equations for the phase-field model have been derived in a thermodynamically consistent way such that the parameters in these equations are fully determined. By linking directly with the thermodynamic database MTDATA, the model is capable of simulating the microstructural evolution of real alloys. Numerical calculations for aluminium–silicon alloys show that the phase-field driving force changes in a similar manner to the thermodynamic driving force, although the phase-field driving force changes more quickly than the thermodynamic driving force when the system approaches equilibrium. The phase-field mobility is shown not to be a trivial function of constitutional undercooling. With the new phase-field model, the width of the liquid–solid interface region is allowed a much large value with the continuity of all parameters in the phase-field model and properties of interface maintained, and hence the model is suitable for simulating large-scale systems.