ORALS

SESSION: SISAMFriPM2-R3 F: Metastability & sustainability	Kobe International Symposium on Science of Innovative and Sustainable Alloys and Magnets (5th Intl. Symp. on Science of Intelligent and Sustainable Advanced Materials (SISAM))
Fri Oct, 25 2019 / Room: Dr. Christian Bernard
Session Chairs: Michael J. Zehetbauer; Session Monitor: TBA

16:45: [SISAMFriPM211] Invited
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 Id: 367 [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 Nd₂Fe₁₄B 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 Nd₇₀Cu₃₀ 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.\n[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.\n[iii] J. D. Livingston, Magnetic domains in sintered Fe-Nd-B magnets, J. Appl. Phys. 57 (1985) 4137–4139.\n[iv] M. Soderžnik, M. Korent, K. Žagar Soderžnik, M. Katter, K. Üstüner, S. Kobe, Acta Mat. 115 (2016) 178–284.