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Grain boundary diffusion in nanocrystalline Nd-Fe-B permanent magnets with low-melting eutectics

Sawatzki, Simon and Kübel, Christian and Ener, Semih and Gutfleisch, Oliver (2016):
Grain boundary diffusion in nanocrystalline Nd-Fe-B permanent magnets with low-melting eutectics.
In: Acta Materialia, Elsevier Science Publiching, pp. 354-363, 115, ISSN 13596454, [Online-Edition: http://dx.doi.org/10.1016/j.actamat.2016.05.048],
[Article]

Abstract

In order to combine the good thermal stability of nanocrystalline Nd-Fe-B magnets with the efficient grain boundary diffusion process (GBDP), low-melting eutectics have been mixed with Nd-Fe-B melt-spun ribbons, hot-compacted and subsequently die-upset. Transmission electron microscopy (TEM) analysis revealed the formation of 5–10 nm thick Dy-shells and a crystallography dependent diffusion into the individual solid grains on the nanoscale. Subsequent annealing at 600 °C leads to an enhanced diffusion but also some undesired Nd-O phases and induced grain growth depending on the annealing time, degree of deformation, strain rate and position within the sample. An optimized distribution of the low-melting eutectic was realized by milling the precursor powder and by using ternary alloys with reduced melting points. As a consequence a much higher effective increase in coercivity per wt%Dy was obtained compared to a homogeneous Dy-distribution which demonstrates the validity of this new approach.

Item Type: Article
Erschienen: 2016
Creators: Sawatzki, Simon and Kübel, Christian and Ener, Semih and Gutfleisch, Oliver
Title: Grain boundary diffusion in nanocrystalline Nd-Fe-B permanent magnets with low-melting eutectics
Language: English
Abstract:

In order to combine the good thermal stability of nanocrystalline Nd-Fe-B magnets with the efficient grain boundary diffusion process (GBDP), low-melting eutectics have been mixed with Nd-Fe-B melt-spun ribbons, hot-compacted and subsequently die-upset. Transmission electron microscopy (TEM) analysis revealed the formation of 5–10 nm thick Dy-shells and a crystallography dependent diffusion into the individual solid grains on the nanoscale. Subsequent annealing at 600 °C leads to an enhanced diffusion but also some undesired Nd-O phases and induced grain growth depending on the annealing time, degree of deformation, strain rate and position within the sample. An optimized distribution of the low-melting eutectic was realized by milling the precursor powder and by using ternary alloys with reduced melting points. As a consequence a much higher effective increase in coercivity per wt%Dy was obtained compared to a homogeneous Dy-distribution which demonstrates the validity of this new approach.

Journal or Publication Title: Acta Materialia
Volume: 115
Publisher: Elsevier Science Publiching
Uncontrolled Keywords: Permanent magnet, Nd-Fe-B, Hot-deformation, Grain boundary diffusion process (GBDP), Low melting eutectic
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Functional Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 08 Jul 2016 11:25
Official URL: http://dx.doi.org/10.1016/j.actamat.2016.05.048
Identification Number: doi:10.1016/j.actamat.2016.05.048
Funders: We thank Oliver Diehl for melt-spinning, Arne Grünewald for ONH analysis (both Fraunhofer IWKS) and the BMWi (Bundesministerium f. Wirtschaft und Technologie) via IGF (Industrielle Gemeinschaftsforschung), AiF (Allianz Industrie Forschung),, FVA (Forschungsvereinigung Antriebstechnik e.V.) FVA-Nr. 631 and the German federal state of Hessen through its excellence program LOEWE ″RESPONSE″ for financial support.
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