Additive manufacturing based on selective laser melting (SLM) promises new opportunities for hard magnetic materials as key materials for electrification. However, SLM technology is challenging, especially for today’s strongest permanent magnet materials such as Fe-Nd-B. Special processing chambers are required for processing the oxidation-sensitive powder. Further, powders with a suitable morphology are needed to ensure good quality of the printed structures. Finally, only quite specific microstructures enable good permanent magnet properties such as high coercivity Hc, high remanence Jr and high maximum energy density (BH)max. In the case of Fe-Nd-B such microstructures consist of small hard magnetic grains in the µm or nm scale. Traditionally, these are realized by conventional powder metallurgical processes or rapid solidification (melt-spinning). SLM of FeNdB based permanent magnet material has been mainly performed on nanocrystalline Fe-Nd-B powder with overstoichiometric Fe content (e.g. MQP-S from Magnequench). In the present contribution it is demonstrated, that due to rapid solidification in SLM, nanocrystalline microstructures with hard magnetic properties develop in the bulk. Depending on the composition different nanostructures can be realized. Coercivities of up to 1.16 T and remanences of up to 0.7 T have been achieved so far [1]. A special inert gas process chamber for SLM was used to fabricate the samples. Rapid solidification during SLM is enabled by the formation of a shallow melt pool during laser melting. Melt pool depths as low as 20 to 40 µm have been achieved.

[1] D. Goll, F. Trauter, T. Bernthaler, J. Schanz, H. Riegel, G. Schneider, Micromachines 12 (2021) 538