Design and Qualification of Pr–Fe–Cu–B Alloys for the Additive Manufacturing of Permanent Magnets

Abstract The direct use of an advanced binder‐free additive manufacturing technique, namely laser powder bed fusion (L‐PBF), does not easily allow obtaining variously shaped, fully dense Nd–Fe–B magnets with high coercivity. The process inherently leads to the re‐melting of the powder and appearance/disappearance of undesired/desired microstructural features responsible for low and large coercivity. In this work, the development of a useful microstructure responsible for high coercivity in Pr 21 Fe 73.5 Cu 2 B 3.5 and Nd 21 Fe 73.5 Cu 2 B 3.5 alloys and a possible way to produce fully dense permanent magnets via additive manufacturing processes is demonstrated using: (i) suction casting technique, which provides a high cooling rate and thus similar microstructures as in L‐PBF but requires only very small amounts of powder; (ii) conventional L‐PBF processing using kg of powder, and (iii) a subsequent annealing treatment that is similar to a conventional sintering treatment. The subsequent heat treatment is necessary to develop high coercivity by forming a novel microstructure: hard magnetic (Nd,Pr) 2 Fe 14 B grains embedded in a matrix of intermetallic (Nd,Pr) 6 Fe 13 Cu phase. Furthermore, it is demonstrated that Pr 21 Fe 73.5 Cu 2 B 3.5 exhibits a higher coercivity than Nd 21 Fe 73.5 Cu 2 B 3.5 because of a finer and more homogeneous grain size distribution of the Pr 2 Fe 14 B phase. The final L‐PBF printed Pr 21 Fe 73.5 Cu 2 B 3.5 samples provide a coercivity of 0.75 T.