Thermodynamic Assessment Of Fe-Bi-Ce And Sn-Cu-Ce Systems

Rare earth elements were used in metal material to improve the microstructure, physical properties and mechanical properties of materials. Phase relations of and Fe-Bi-Ce and Sn-Cu-Ce systems are important in understanding metallurgical role of Ce in cast iron and Sn-Cu based lead-free solder alloys.1. By using a CALPHAD approach, the Ce-Bi binary system was assessed on the basis of reported thermodynamic and phase-equilibrium data and then extrapolated to Fe-Bi-Ce ternary system combined with the Fe-Ce and Fe-Bi binary systems assessed in literatures.2. The interfacial reaction between Bi and Fe-45at.%Ce alloy at773K was investigated to verify the reliability of thermodynamic calculations. The reaction path is liquid (Bi)/CeBi2+Fe/Fe-45at.%Ce in this couple. It was found that only one intermetallic compound, CeBi2, was formed at the interface in this couple. The experimental results were reasonably explained using a recently reported model by adopting the thermodynamics assessed herein.3. Thermodynamic assessment of Sn-Cu-Ce ternary system has been thermodynamically assessed based on experimental data about phase equilibria and thermodynamic properties by using CALPHAD approach combined with first-principle calculations of formation enthalpy of key compounds. The solution phases (liquid, Fcc_Al, Bcc_A2and Bct_A5) were treated as substitutional, of which the excess Gibbs energies were modeled by Redlich-Kister polynomial. Considering its crystal structure and solid solubility range, intermetallic compound, Ce11Sn10, was described with a three-sublattice model (Ce)0.429(Sn)0.429(Ce,Cu,Sn)0.142. Other binary and ternary intermetallic compounds were described as stoichiometric phases because of their limited homogeneity ranges. During optimization, Ce-Sn binary system was first assessed, and then phase relations in Sn-Cu-Ce ternary system were modeled by combining with the optimized Ce-Cu and Cu-Sn binary systems in literatures. A set of thermodynamic parameters for all knew phases were obtained, which can reproduce most experimental data.20figures,13tables,97references.