Thermodynamic re-assessment of the Fe-Tm and Fe-Ho binary systems

Thermodynamic re-assessment of the Fe-Tm and Fe-Ho binary systems were carried out with the help of the CALPHAD method based on the previous optimizations and the critical review of the available experimental information in the published literature. The substitutional solution model was used to describe liquid phase and fcc-Fe, bcc-Fe, hcp-Tm, bcc-Ho and hcp-Ho solid solution phases and their excess terms of Gibbs energies were expressed with the Redlich-Kister polynomial. The intermetallic compounds, Fe17Tm2, Fe23Tm6, Fe3Tm, Fe2Tm, Fe17Ho2, Fe23Ho6, Fe3Ho and Fe2Ho, were treated as stoichiometric compounds considering the experimental heat capacity of two intermetallic compounds (Fe2Tm and Fe2Ho) in the low temperature range. Self-consistent thermodynamic parameters to describe the Gibbs energies of various phases in the Fe-Tm and Fe-Ho binary systems were obtained finally. The calculated results in this work are in good agreement with available phase equilibira data and thermodynamic data.