Presentation Information
[O5-2]Reduction of heavy rare earths in Nd-Fe-B-based magnets by diffusion source and application area optimization
*Imants Dirba1, Abdullatif Durgun1, Dominik Ohmer2, Matthias Katter2, Andreas Thul3, Hossein Sepehri Amin4, Oliver Gutfleisch1 (1. Functional Materials, Institute of Materials Science, Technical University of Darmstadt, 64287 Darmstadt, Germany (Germany), 2. Vacuumschmelze GmbH & Co. KG, 63412 Hanau, Germany (Germany), 3. Institute of Electrical Machines (IEM), RWTH Aachen University, 52062 Aachen, Germany (Germany), 4. National Institute for Materials Science, Tsukuba 305-0047, Japan (Japan))
Keywords:
permanent magnet,Nd2Fe14B,heavy rare earth,grain boundary diffusion,terbium
Reduction in critical heavy rare earth (HRE) elements such as Dy and Tb in NdFeB-based magnets for coercivity enhancement at the high operating temperature in E-motors is important for sustainable green energy transition. In this work, we maximize HRE utilization by selective hardening of areas in the magnet such as corners or edges that are highly susceptible to demagnetization, as demonstrated by Finite Element magnetostatics simulation on an internal permanent magnet synchronous traction motor for electric vehicles (Fig. 1a). Commonly industrially used HRE source TbHx as well as complex multi-component Tb-containing alloys such as Tb10Pr60(Cu,Al,Ga)30 are investigated on commercial grade NdFeB-based sintered magnets. For Tb hydride not only is the HRE utilization less efficient, but also the diffusion is more sluggish resulting in shorter diffusion depth. Highly efficient Tb utilization using small HRE amount comparable to trace elements added to commercial sintered magnets (e.g. Al, Cu, Ga) and good high-temperature performance is reached. Diffusing 0.4 wt.% Tb results in coercivity of 1014 kA/m at 120 °C with only minor reduction in remanence from around 1.45 T in the initial magnet to 1.43 T after GBDP. To shed light on the HRE diffusion and local magnetic hardening, spatial coercivity mapping was done to investigate the local coercivity enhancement. The results are graphically illustrated in Fig. 1b. Corners clearly show the highest coercivity reaching nearly 1600 kA/m corresponding to 587 kA/m enhancement compared to the initial magnet. As expected for a diffusion-governed process, coercivity decrease is proportional to the distance from the diffusion source (corners).
