Sawatzki, Simon ; Kübel, Christian ; Ener, Semih ; Gutfleisch, Oliver (2016):
Grain boundary diffusion in nanocrystalline Nd-Fe-B permanent magnets with low-melting eutectics.
In: Acta Materialia, 115, pp. 354-363. Elsevier Science Publiching, ISSN 13596454,
[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 ; Kübel, Christian ; Ener, Semih ; 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 |
| Journal 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 |
| URL / URN: | 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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