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

: Schäfer, Lukas; Skokov, Konstantin; Liu, Jianing; Maccari, Fernando; Braun, Tobias; Riegg, Stefan; Radulov, Iliya; Gassmann, Jürgen; Merschroth, Holger; Harbig, Jana; Weigold, Matthias; Gutfleisch, Oliver

Fulltext ()

Advanced Functional Materials 31 (2021), No.33, Art. 2102148, 8 pp.
ISSN: 1616-301X
ISSN: 1616-3028
Journal Article, Electronic Publication
Fraunhofer IWKS ()

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 Pr21Fe73.5Cu2B3.5 and Nd21Fe73.5Cu2B3.5 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)2Fe14B grains embedded in a matrix of intermetallic (Nd,Pr)6Fe13Cu phase. Furthermore, it is demonstrated that Pr21Fe73.5Cu2B3.5 exhibits a higher coercivity than Nd21Fe73.5Cu2B3.5 because of a finer and more homogeneous grain size distribution of the Pr2Fe14B phase. The final L-PBF printed Pr21Fe73.5Cu2B3.5 samples provide a coercivity of 0.75 T.