Advances in the fabrication of rare earth-free and hybrid permanent magnets: from the nanostructuring of gas-atomized MnAlC and synthesis of tuned composites to additive manufacturing

Abstract

Additive manufacturing (AM) is attracting much interest in many high-tech sectors as it allows for fabricating complex objects with tuned properties and high performance [1]. For developing permanent magnets (PMs) by AM, it is necessary an increased filling factor and no deterioration of their PM properties during fabrication. Many works on AM of PMs focus on NdFeB [2], however it is of large scientific and technological interest to broaden the studies by including rare earth-free alternatives. Improved ferrites and the promising MnAl-based alloys are expected to partially cover the gap between conventional ferrites and NdFeB, provided successful development of PM properties. Moreover, they show high availability, low costs and environmental impact of extraction and processing of raw materials [3]. Composites (PM particles/polymer) were synthesized and extruded into homogeneous and continuous filaments. Gas-atomized τ-MnAlC, Sr-ferrite and hybrid (Sr-ferrite/NdFeB) particles were used for studying different alternative PM materials. The influence of particle size, fine-to-coarse particle ratio, polymer and fabrication parameters on the properties of the final products was analysed [4], being key factors for obtaining flexible filaments with a high filling factor (>80%) and length over 10 m. Magnetic measurements revealed non-deteriorated PMs properties of the particles after processing [4]. Optimized MnAlC-based filament (with a high MnAlC content above 80 wt.%) was used for 3D-printing objects as a proof-of-concept. Magnetic measurements carried out on the printed objects have proved that alternative PM materials can be efficiently synthesized and processed to develop new PMs by AM under controlled temperature, which might be used in sensing applications [4]. Acknowledgements Authors acknowledge fruitful collaboration and discussions with B. Skårman, H. Vidarsson and P.-O. Larsson from Höganäs AB (Sweden), and A. Nieto and R. Altimira from IMA S.L.U. (Spain). Authors additionally acknowledge financial support from EU M-ERA.NET and MINECO through the projects "NEXMAG" (M-ERA.NET Project Success Case, Ref. PCIN-2015-126) and "3D-MAGNETOH" (Ref. MAT2017-89960-R); Regional Government of Madrid through "NANOMAGCOST" project (Ref. P2018/NMT-4321); and Höganäs AB through the industrial contract "GAMMA".