Optimizing the Particle Size Distribution in Permanent Magnet Composites to Extrude Flexible Filaments for Additive Manufacturing

Abstract

Additive manufacturing (AM) of composites is attracting much interest in high-tech sectors for fabricating complex high-performance objects with tailored properties [1]. For permanent magnets (PMs), the challenge is to develop magnets by AM with no geometrical restrictions, high filling factor (FF), and non-deteriorated PM properties [2], together with finding alternatives (e.g., improved ferrites and promising MnAlC-based alloys) to rare earth-based magnets [3].Composites (PM particles/polymer) were synthesized by solution casting, followed by extrusion of filaments for 3D-printing, being reported for the very first time (Fig. 1). Several alternative PM materials were studied (gas-atomized τ-MnAlC, Sr-ferrite and hybrids —Sr-ferrite/NdFeB). Particle size and fine-to-coarse particles ratio (FP/CP) play a key role on the flexibility and powder loading of MnAlC filaments (length>10 m), reaching FF>80% and non-deteriorated PMs properties (Fig. 1) [4]. These results will be compared to the obtained for filaments based on Sr-ferrite (Hc=239 kA/m, FF=92%), NdFeB (Hc=812 kA/m, FF=93%) and hybrids (Hc=629 kA/m, FF=90%) (Fig. 2). MnAlC-based objects were 3D-printed under controlled temperature, proving that alternative PM materials can be efficiently synthesized and processed to develop novel PMs by AM (Fig. 1) [4].Acknowledgements. Authors acknowledge collaborations with B. Skårman, H. Vidarsson and P.-O. Larsson (Höganäs, Sweden) by the industrial contract GAMMA, and A. Nieto and R. Altimira (IMA, Spain), and financial support from: EU M-ERA.NET by COSMAG project (PCI2020-112143); MICINN by NEXUS project (PID2020-115215RB-C21); CM by NanoMagCOST project (P2018/NMT-4321).  Fig. 1. (a) Gas-atomized MnAlC, polymer, and composite; (b) SEM image of MnAlC particles and size distribution; (c), (d) image and SEM cross section of a MnAlC/ABS filament; (e) MnAlC-based 3D-printed object; (f) normalized magnetic response of MnAlC-based samples; and (g) magnetic flux density of a 3D-printed MnAlC-based disc.  Fig. 2. (a) SEM and EDX of a hybrid composite; (b) second quadrant of the hysteresis loops for the hybrid, Sr ferrite- and NdFeB-based materials. Insets show composite pellets and SEM cross section of a Sr ferrite-based filament.