J. Liu 1, L. Schäfer 1, H. Merschroth 2, J. Harbig 2, Y. Yang 3, M. Weigold 2, S. Barcikowski 3, O. Gutfleisch 1 and K. Skokov 1

1 Functional Materials, Department of Material Science, Technical University of Darmstadt, Alarich-Weiss-Str. 16, 64287, Darmstadt, Germany

2 Institute of Production Management, Technology and Machine Tools, Department of Mechanical Engineering, Technical University of Darmstadt, Otto-Berndt-Straße 2, 64287, Darmstadt, Germany

3 Faculty of Chemistry, Technical Chemistry I and

Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Universitaetsstr. 7, 45141 Essen, Germany

Additive Manufacturing (AM) of permanent magnets, is an upcoming and challenging task in material science and engineering. The reasons are twofold: (a) functionality depends on interface, structure, defect and chemistry control on the nanoscale in the printed parts, and (b) the availability of adequate powder precursors for functional printing. The binder-free AM technique like Laser Powder Bed Fusion (L-PBF) allows for the fabrication of fully-dense and functionalized components with complex geometry. However, a microstructure necessary for high coercivity is difficult to obtain by L-PBF due to its high cooling rate. The well-known Nd-Fe-B system consists of magnetically decoupled 3-10 µm grains of the hard magnetic RE2Fe14B (RE = Rare earth element) phase, isolated from each other by a finely distributed RE-rich phase, leading to the highest performance of all magnets around room temperature. L-PBF is normally annihilating this specific microstructure. In order to achieve the desired microstructure and hard magnetic properties after printing, we propose here Pr-Fe-Cu-B based alloy as a useful alloy system [1] and compare this with its Nd-based counterpart. Pr-Fe-Cu-B is known for its high coercivity in bulk state and the formation of, besides others, the uncommon intermetallic Pr6Fe13Cu grain boundary phase. We show here a novel microstructure stable for additive manufacturing with high coercivity.

Our studies describe the Pr-Fe-Cu-B alloys and their post heat treatment optimization for L-PBF. A wide compositional region in the Pr-Fe-Cu-B system was characterized and qualified regarding the magnetic properties throughout the process chain. In order to achieve an improved flowability and refined microstructure, the grain boundary engineering with nanoparticles (NPs) shows a great potential. The nanoparticle functionalized Pr-Fe-Cu-B powder was validated as precursor for AM. During L-PBF, the hypothesis of heterogeneous nucleation induced by NP inoculums during resolidification is explored with the goal of suppressing grain coarsening and realizing more uniaxial growth.

We acknowledge the support of the Collaborative Research Centre/Transregio 270 HoMMage.

[1] L. Schäfer, K. Skokov, J. Liu, M. Maccari, T. Braun, S. Riegg, I. Radulov, J. Gassmann, H. Merschroth, J. Harbig, M. Weigold, O. Gutfleisch, Design and Qualification of Pr-Fe-Cu-B Alloys for the Additive Manufacturing of Permanent Magnets, Advanced Functional Materials: 2102148.