The use of computational thermodynamics for the determination of surface tension and Gibbs–Thomson coefficient of multicomponent alloys

Abstract

The simulation of casting processes demands accurate information on the thermophysical properties of the alloy; however, such information is scarce in the literature for multicomponent alloys. Generally, metallic alloys applied in industry have more than three solute components. In the present study, a general solution of Butler’s formulation for surface tension is presented for multicomponent alloys and is applied in quaternary Al–Cu–Si–Fe alloys, thus permitting the Gibbs–Thomson coefficient to be determined. Such coefficient is a determining factor to the reliability of predictions furnished by microstructure growth models and by numerical computations of solidification thermal parameters, which will depend on the thermophysical properties assumed in the calculations. The Gibbs–Thomson coefficient for ternary and quaternary alloys is seldom reported in the literature. A numerical model based on Powell’s hybrid algorithm and a finite difference Jacobian approximation has been coupled to a Thermo-Calc TCAPI interface to assess the excess Gibbs energy of the liquid phase, permitting liquidus temperature, latent heat, alloy density, surface tension and Gibbs–Thomson coefficient for Al–Cu–Si–Fe hypoeutectic alloys to be calculated, as an example of calculation capabilities for multicomponent alloys of the proposed method. The computed results are compared with thermophysical properties of binary Al–Cu and ternary Al–Cu–Si alloys found in the literature and presented as a function of the Cu solute composition.