Thermodynamic–kinetic model for the simulation of solidification in binary copper alloys and calculation of thermophysical properties

Abstract

An earlier developed thermodynamic–kinetic solidification model for binary copper alloys is extended to take into account the formation of the bcc phase via the peritectic transformation and the formation of binary compounds from the fcc phase. Also the eutectic and eutectoid transformations are simulated but only approximately, by modeling the movement of the fcc/eutectic and fcc/eutectoid interfaces due to the diffusion kinetics of the fcc phase only. The new model can handle binary copper alloys containing solutes Ag, Al, Cr, Fe, Mg, Mn, Ni, P, Si, Sn, Te, Ti, Zn and Zr. Depending on the alloy composition, cooling rate and dendrite arm spacing, the model determines the fractions and compositions of the phases (liquid, fcc, bcc, compounds) and calculates thermophysical material properties (enthalpy, specific heat, thermal conductivity, density and liquid viscosity), needed in heat transfer models, from the liquid state down to room temperature. The model is applied to Cu–Sn and Cu–Zn alloys but also to some other binary alloys to show the effect of cooling on the phases formed. Depending on the alloy system, the solidification structures obtained after real cooling processes are shown to be quite different from those estimated from phase diagrams.