Phase equilibria and solubility limits in the B-Ce-Fe-Nd system

International audience; Nd-based (Nd-Fe-B) permanent magnets are widely used in the field of new energies. However, the worldwide pressure on their supply is pushing manufacturers to develop new magnets with reduced Nd content, replaced by other less critical rare earths (RE), typically Ce and La. The complexity induced by the multitude of elements involved in the production of this new set of magnets requires a numerical approach. The overall objective of this study is to better predict the manufacturing conditions of these substituted magnets of global composition (Nd,RE)$_2$Fe$_{14}$B.This work focuses on the effect of the addition of Ce to the Nd-Fe-B base system, which may lead to the formation of the CeFe$_2$ intermetallic with poor magnetic properties. This phase may dissolve a significant amount of Nd and has an impact on the efficiency of the magnets.In parallel to the experimental approach on the interactions between rare earths within the (RE)$_2$Fe$_{14}$B composition, a thermodynamic database related to these new magnets is being developed with the CALPHAD method. Experimental results on this quaternary system and thermodynamic properties reinforced by ab-initio calculations on some constitutive phases will be presented. Some application calculations will also illustrate the usefulness of the CALPHAD approach to improve the control of the compositions and microstructures of magnets during the manufacturing processes of such complex materials.