Thermodynamic assessment of the RE-B (RE=Ho, Er, Tm) binary systems

Abstract

To develop novel Nd-Fe-B-based permanent magnets with rare earth (RE) metals, phase equilibria and thermodynamic information of multi-component RE-Fe-B-based alloy systems is indispensable. In this work, thermodynamic assessment of the RE-B (RE=Ho, Er, Tm) binary systems as the important binary systems in the RE-Fe-B-based alloy systems were carried out using the CALPHAD (Calculation of Phase Diagram) method. The solution phases including liquid, hcp(α-Ho, α-Er and α-Tm) and rhombohedral(β-B) in the RE-B (RE=Ho, Er, Tm) binary systems are modeled by the substitutional solution model. The intermetallic compounds, HoB2, HoB4, HoB6, HoB12, HoB66, ErB2, ErB4, ErB12, ErB66, TmB2, TmB4, TmB12 and TmB66, are treated as the stoichiometric compounds. Self-consistent thermodynamic parameters to describe Gibbs energies of phases in the RE-B (RE=Ho, Er, Tm) binary systems were obtained finally. The calculated results agree well with the reported data.