Presentation Information
[O7-5]Strategy for producing Nd-Fe-B permanent magnets with short-loop recycling methods for high-performance applications
Gatien Bacchetta1, *Frederico Orlandini Keller1, Olivier Tosoni2, Cyril Rado2, Sorana Luca2 (1. Orano Projets, Permanent Magnets Dpt, Montigny-le-Bretonneux 78180, France (France), 2. Univ. Grenoble Alpes, CEA LITEN, Grenoble 38000, France (France))
Keywords:
Critical Raw Materials,Sintered Nd-Fe-B,High-performance magnets,Short-loop recycling,Industrial-scale
High-performance Nd-Fe-B permanent magnets contain approximately 30 wt% of Rare Earth (RE), which are listed as critical by the European Union (EU) [1]. To address RE criticality, recycling methods have been developed to use End Of Life (EOL) permanent magnets as a secondary supply source of RE. Moreover, EOL magnets from high-performance applications (e.g. Electric Vehicles Traction Motors), contain non-negligible amounts of Heavy Rare Earth (HRE), such as Tb and Dy, elements that are scarce and subjected to high supply risks in the EU. Short-loop recycling methods concentrate more and more attention. Indeed, they are energy, time and resource saving – not to mention resilient from a strategic standpoint – when compared to the conventional fabrication process or the long-loop recycling process, which relies on the oxide-to-metal conversion step.
Most of the short-loop recycling routes use hydrogen treatments to convert the EOL magnets directly into powder and subsequently refabricate sintered magnets (magnet to magnet). To address impurities and composition variations in recycled materials, the known methods consist in using additional RE-rich alloys and/or intermetallics blended with recycled powders to control the final performances of the magnet. Besides, a strict control of the EOL feedstocks composition is required to achieve optimum magnetic properties [2,3]. Considering the variabilities in the input materials, it might be challenging to implement these methods on an industrial scale to fabricate high-performance magnets with constant quality. Another approach is the magnet to alloy method. It consists in melting EOL permanent magnets to refabricate an alloy for the manufacturing of recycled magnets. This method is more energy consuming compared to the magnet to magnet route. Nevertheless, it has the advantage to homogenize and easily adjust the composition while resetting the microstructure of the recycled alloy. Furthermore, the melting enable to remove a large part of oxygen contamination from the EOL feedstock and allow to obtain high-quality input material for magnet fabrication.
Several studies focus on near 100 % recycled material [4], enabling to manufacture magnets with magnetic performances highly dependent on the input feedstock. We show in this study a method to thoughtfully fabricate sintered Nd-Fe-B magnets for high-performance applications incorporating at least 25 % of recycled materials. Indeed, this approach meets the objectives of the EU Critical Raw Materials act [1]. This method combines both melting- and hydrogen-based short-loop recycling routes. This process is specifically tuned to recycle HRE-rich EOL magnets and use these materials as primary source of HRE. The main objective is to optimize the use of HRE while maximizing the coercivity improvement by fine-tuning the alloy composition and tailoring the magnet microstructure. Microstructural characterizations by SEM, TEM, WDS and numerical simulations bring new insights on the evolution of the microstructure along the recycling process. This study paves the way to an industrial-scale fabrication of high-performance recycled sintered magnets. These results are demonstrated on Orano’s pre-industrial pilot line installed at CEA Grenoble (France). This complete pilot line, rare in Europe, possesses the complete fabrication equipment from strip casting to the final sintered magnet. This work is partly funded by the MAGELLAN European project and the MAGNOLIA French project.
References:
[1] European Commission, Publications Office, LU, 2020. https://data.europa.eu/doi/10.2873/865242.
[2] M. Schönfeldt, et al., J. Alloys Compd. 939 (2023) 168709.
[3] G. Bacchetta, et al., Adv. Eng. Mater. (2024) 2400234.
[4] M. Zakotnik, C.O. Tudor, Waste Manag. 44 (2015) 48–54.
Most of the short-loop recycling routes use hydrogen treatments to convert the EOL magnets directly into powder and subsequently refabricate sintered magnets (magnet to magnet). To address impurities and composition variations in recycled materials, the known methods consist in using additional RE-rich alloys and/or intermetallics blended with recycled powders to control the final performances of the magnet. Besides, a strict control of the EOL feedstocks composition is required to achieve optimum magnetic properties [2,3]. Considering the variabilities in the input materials, it might be challenging to implement these methods on an industrial scale to fabricate high-performance magnets with constant quality. Another approach is the magnet to alloy method. It consists in melting EOL permanent magnets to refabricate an alloy for the manufacturing of recycled magnets. This method is more energy consuming compared to the magnet to magnet route. Nevertheless, it has the advantage to homogenize and easily adjust the composition while resetting the microstructure of the recycled alloy. Furthermore, the melting enable to remove a large part of oxygen contamination from the EOL feedstock and allow to obtain high-quality input material for magnet fabrication.
Several studies focus on near 100 % recycled material [4], enabling to manufacture magnets with magnetic performances highly dependent on the input feedstock. We show in this study a method to thoughtfully fabricate sintered Nd-Fe-B magnets for high-performance applications incorporating at least 25 % of recycled materials. Indeed, this approach meets the objectives of the EU Critical Raw Materials act [1]. This method combines both melting- and hydrogen-based short-loop recycling routes. This process is specifically tuned to recycle HRE-rich EOL magnets and use these materials as primary source of HRE. The main objective is to optimize the use of HRE while maximizing the coercivity improvement by fine-tuning the alloy composition and tailoring the magnet microstructure. Microstructural characterizations by SEM, TEM, WDS and numerical simulations bring new insights on the evolution of the microstructure along the recycling process. This study paves the way to an industrial-scale fabrication of high-performance recycled sintered magnets. These results are demonstrated on Orano’s pre-industrial pilot line installed at CEA Grenoble (France). This complete pilot line, rare in Europe, possesses the complete fabrication equipment from strip casting to the final sintered magnet. This work is partly funded by the MAGELLAN European project and the MAGNOLIA French project.
References:
[1] European Commission, Publications Office, LU, 2020. https://data.europa.eu/doi/10.2873/865242.
[2] M. Schönfeldt, et al., J. Alloys Compd. 939 (2023) 168709.
[3] G. Bacchetta, et al., Adv. Eng. Mater. (2024) 2400234.
[4] M. Zakotnik, C.O. Tudor, Waste Manag. 44 (2015) 48–54.