Phase equilibria and thermodynamic properties in the RE-Co (RE=rare earth metals) binary systems

In this work, seven Co-RE (RE=Pr, Nd, Tb, Dy, Ho, Er and Tm) binary systems were re-assessed by using the CALPHAD method based on reliable experimental information from the literature. The Gibbs energies of the solution phases and the RE-Co intermetallic compounds in these seven RE-Co binary systems were accurately expressed according to the experimental results including the crystal structure and heat capacity. The available thermodynamic parameters of these seven RE-Co binary systems were obtained, which can be used to reproduce well the experimental phase diagram and thermodynamic data. Furthermore, the present work was combined with the previous calculations of five RE-Co (RE=Y, La, Ce, Sm and Gd) binary systems to discuss thermodynamic characteristics and phase equilibria of twelve RE-Co (RE=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Y) binary systems. A trend was found for the change of phase equilibria and thermodynamic properties of the RE-Co binary systems with RE atomic number. In general, the formation temperatures of the RE-Co intermetallic compounds increase with increasing of the RE atomic number, and the enthalpy of mixing of liquid RE-Co (apart from Y-Co, Ce-Co and Nd-Co) alloys and the enthalpy of formation of the RE-Co (apart from Y-Co, Ce-Co and Gd-Co) intermetallic compounds become increasingly negative. Finally, the complete and self-consistent thermodynamic parameters of the RE-Co binary systems was established, which would provide a significant basis for developing a thermodynamic database of the multi-component RE-Co-based magnetic alloys.