Assessment of phase equilibria and thermodynamic properties in the Fe-RE (RE = rare earth metals) binary systems

This study focuses on investigating phase equilibria and thermodynamic stability of intermetallic compounds made of the transition metal Fe and rare earth (RE) elements. By using the CALPHAD method and reliable experimental information from the literature, the binary systems of Fe-Y, Fe-Er, and Fe-Lu were reassessed. To improve our previous calculations of Fe-RE (RE = Tb and Dy) binary systems, the Gibbs energy expressions of intermetallic compounds Fe2Tb and Fe2Dy were modified to avoid artificial breaks in their heat capacity curves. Thermodynamic parameters obtained are self-consistent, and the Gibbs energies of the Fe-RE (RE = Tb, Dy, Er, Lu, and Y) phases were accurately expressed to reappear available both thermodynamic data and phase equilibria. This work was further combined with the previous calculations of the Fe-RE (RE = La, Ce, Pr, Nd, Sm, Gd, Ho, and Tm) systems to discuss thermodynamic characteristics and phase equilibria of Fe-RE binary systems in detail. A trend was noticed for the change of thermodynamic properties and phase equilibria of the Fe-RE binary systems with RE atomic number. Generally, as the RE atomic number increases, the formation temperatures of the Fe-RE intermetallic compounds increase gradually, and the enthalpy of mixing of liquid Fe-RE (apart from Fe-Y and Fe-Ce) alloys and the enthalpy of formation of the Fe-RE (apart from Fe-Y, Fe-Ce, Fe-Gd, and Fe-Dy) intermetallic compounds become increasingly negative. The results provide a thorough set of thermodynamic parameters of thirteen Fe-RE binary systems, which could serve as a sound basis for developing a thermodynamic database of Fe-RE-based alloy systems.