Selective Laser Melting of Partially Anisotropic Rare Earth-based Permanent Magnets

Abstract

Additive manufacturing based on selective laser melting (SLM) promises versatile new opportunities for hard magnetic materials as key materials for electrification. However, SLM technology is challenging, especially for today’s strongest permanent magnets based one rare earth (RE) metals. It requires special processing chambers to handle the powders sensitive to oxidation. SLM of RE-based permanent magnet material so far was mainly performed on nanocrystalline Fe-Nd-B powder with overstoichiometric Fe content (e.g. MQP-S from Magnequench). Recently, it has been shown, that due to rapid solidification in SLM, a nanocrystalline microstructure with hard magnetic properties develops in the bulk [1]. In addition, the development of very fine Fe-Nd-B microstructures with directed crystal growth and finely dispersed Nd-rich phase is possible [2].Material systems such as Co-Sm or Fe-Pr-Cu-B can offer advantages for SLM processing. Due to their solidification process and phase equilibria, they form magnetically advantageous microstructures. Permanent magnet properties can be obtained by annealing, without the need of subsequent powder metallurgical processing or rapid quenching. By a proper choice of processing parameters and post-annealing conditions good permanent magnet properties and partial magnetic anisotropy can be realized for printed parts of both materials. In the case of (CoCuFeZr)17Sm2 a coercivity of 2.77 T, remanence of 0.78 T and maximum energy density of 109 kJ/m3 have been achieved (Fig. 1). Due to texture of the printed parts the remanence is 24 % higher than for a comparable isotropic sintered magnet. In the case of FePrCuB a coercivity of 0.67 T, remanence of 0.67 T and maximum energy density of 69.8 kJ/m3 have been obtained (Fig. 2). Due to higher degree of texturing, the printed parts so far exhibit a 26 % higher remanence compared to identically annealed cast material of the same composition. The paper highlights the correlation between microstructure and related magnetic properties for the processing parameter-sets used.  Fig. 1: Microstructural and magnetic properties of (CoCuFeZr)17Sm2 SLM-printed component.  Fig. 2: Microstructural and magnetic properties of FePrCuB SLM-printed component.