| Towards High Coercivities in Heavy Rare Earth Free Nd-Fe-B Ribbons Marko Soderžnik1; Matic Korent2; Urska Ročnik3; Boris Saje4; Spomenka Kobe5; 1JOžEF STEFAN INSTITUTE, Ljubljana, Slovenia; 2JOZZEF STEFAN INSTITUTE, LJUBLJANA, Slovenia; 3DEPARTMENT FOR NANOSTRUCTURED MATERIALS, JOžEF STEFAN INSTITUTE, Ljubljana, Slovenia; 4KOLEKTOR MAGNET TECHNOLOGY GMBH, Essen, Germany; 5JOSEF STEFAN INSTITUTE, Ljubljana, Slovenia; PAPER: 367/SISAM/Invited (Oral) SCHEDULED: 16:45/Fri. 25 Oct. 2019/Dr. Christian Bernard ABSTRACT: Reasonable magnetic performance to weight ratio makes polymer-bonded magnets indispensable in automotive applications [i]. The magnetic powders, used for bonded magnets are mainly produced by the gas atomization and melt-spinning [ii]. Several magnetic powders can be used for such purposes, namely ferrites, SmCo, Sm-Fe-N, Nd-Fe-B and/or combinations of all of them. Since the magnetic powder is blended with non-magnetic binder, the remanent magnetization is diluting as the volume percent of the binder is increasing. Therefore, they can be classified as medium-performance isotropic bonded magnets. The coercivity of the magnet, however, is not related to the magnetic powder/non-magnetic binder ratio but to the chemistry and microstructural features. Melt-spun ribbons of Nd-Fe-B material are composed of randomly oriented Nd<sub>2</sub>Fe<sub>14</sub>B grains within the size of single magnetic domain [iii]. Therefore, they have a huge potential for higher coercivity compared to sintered Nd-Fe-B magnets in which a typical grain size is measured in microns [iv]. There exist several ways to improve the coercivity of Nd-Fe-B magnets. One way is to decouple the Nd2Fe14B grains by infiltration of low eutectic Nd-based alloys which we propose within this study. Detailed microstructural analyses showed that non-ferromagnetic Nd<sub>70</sub>Cu<sub>30</sub> was successfully infiltrated between the grains, which prevented the physical contact between the grains leading to weaker intergrain exchange coupling. The results of such a process show more than 20 % improvement in coercivity while the remanence is increased as expected due to the lower amount of the ferro-magnetic phase. Significant increase in coercivity compensates lower remanence, and the energy product is also increased. In comparison to the basic powder, the coercivity at 150 °C is significantly improved, which enables these magnets to be used at a higher temperature. References: [i] J. J. Croat, 8-Major applications for rapidly solidified NdFeB permanent magnets, Woodhead Publishing Series in Electronic and Optical Materials (2018) 325–361.<br />[ii] G. Sarriegui, J. M. Martín, M. Ipatov, A. P. Zhukov, J. Gonzalez, Magnetic Properties of NdFeB Alloys Obtained by Gas Atomization Technique, IEEE Trans. Magn. 54 (2018) 2103105.<br />[iii] J. D. Livingston, Magnetic domains in sintered Fe-Nd-B magnets, J. Appl. Phys. 57 (1985) 4137–4139.<br />[iv] M. Soderžnik, M. Korent, K. Žagar Soderžnik, M. Katter, K. Üstüner, S. Kobe, Acta Mat. 115 (2016) 178–284. |
