Interfacial compositions of solid and liquid in a phase-field model with finite interface thickness for isothermal solidification in binary alloys

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We show that a finite interface thickness in an isothermal phase-field model for alloy solidification introduces a chemical potential gradient in the interfacial region and the solute trapping effect, and the relationships between material properties and parameters in the phase-field equation can be determined at a low interface velocity limit condition. Also we show that there are upper bounds on the interface thickness and the interface kinetics coefficient, which vary with thermophysical properties of alloys. The predicted compositions of solid and liquid at the interface with this model are in good agreement with those obtained by numerical simulation of one-dimensional isothermal solidification of an Al--2-mole-%-Si alloy at 870 K.