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Anisotropic local hardening in hot-deformed Nd-Fe-B permanent magnets

Sawatzki, Simon and Schneider, Thorsten and Yi, Min and Bruder, Enrico and Ener, Semih and Schönfeldt, Mario and Güth, Konrad and Xu, Bai-Xiang and Gutfleisch, Oliver (2018):
Anisotropic local hardening in hot-deformed Nd-Fe-B permanent magnets.
In: Acta Materialia, Elsevier Sciene Publishing, pp. 176-183, 147, ISSN 13596454,
DOI: 10.1016/j.actamat.2017.12.059,
[Online-Edition: https://doi.org/10.1016/j.actamat.2017.12.059],
[Article]

Abstract

The diffusion of low-melting Nd-Cu alloys is very effective to increase coercivity in hot-deformed Nd-Fe-B permanent magnets without the use of heavy rare earth and to study the local hardening mechanism, especially the role of the Nd-rich grain boundary on the magnetic decoupling of the Nd-Fe-B grains on the nanoscale. In this study, we found that for a Nd-Cu diffusion parallel to the texture axis the increase in is higher than for a diffusion perpendicular to it and strongly depends on the diffusion depth whereas remanence develops in an inverse manner. We note the following three observations to explain This behavior results from: a) a higher overall Nd and Cu concentration for the parallel diffusion revealed by global energy dispersive X-ray (EDX) maps leading to a distinct change in the broadness of the interaction domains visualized by Kerr microscopy, b) a higher degree of misalignment of the Nd2Fe14B grains observed by electron backscattered diffraction (EBSD), and c) a more effective local hardening on the macroscopic scale governed by dipolar and exchange interactions as modeled by micromagnetic simulations. The misalignment and the incorporation of Nd and Cu also lead to a volume expansion of the magnet of around 0.6–0.8% as proven by in-situ thermo-optical measurements (TOM).

Item Type: Article
Erschienen: 2018
Creators: Sawatzki, Simon and Schneider, Thorsten and Yi, Min and Bruder, Enrico and Ener, Semih and Schönfeldt, Mario and Güth, Konrad and Xu, Bai-Xiang and Gutfleisch, Oliver
Title: Anisotropic local hardening in hot-deformed Nd-Fe-B permanent magnets
Language: English
Abstract:

The diffusion of low-melting Nd-Cu alloys is very effective to increase coercivity in hot-deformed Nd-Fe-B permanent magnets without the use of heavy rare earth and to study the local hardening mechanism, especially the role of the Nd-rich grain boundary on the magnetic decoupling of the Nd-Fe-B grains on the nanoscale. In this study, we found that for a Nd-Cu diffusion parallel to the texture axis the increase in is higher than for a diffusion perpendicular to it and strongly depends on the diffusion depth whereas remanence develops in an inverse manner. We note the following three observations to explain This behavior results from: a) a higher overall Nd and Cu concentration for the parallel diffusion revealed by global energy dispersive X-ray (EDX) maps leading to a distinct change in the broadness of the interaction domains visualized by Kerr microscopy, b) a higher degree of misalignment of the Nd2Fe14B grains observed by electron backscattered diffraction (EBSD), and c) a more effective local hardening on the macroscopic scale governed by dipolar and exchange interactions as modeled by micromagnetic simulations. The misalignment and the incorporation of Nd and Cu also lead to a volume expansion of the magnet of around 0.6–0.8% as proven by in-situ thermo-optical measurements (TOM).

Journal or Publication Title: Acta Materialia
Volume: 147
Publisher: Elsevier Sciene Publishing
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
11 Department of Materials and Earth Sciences > Material Science > Functional Materials
11 Department of Materials and Earth Sciences > Material Science > Mechanics of functional Materials
11 Department of Materials and Earth Sciences > Material Science > Physical Metallurgy
11 Department of Materials and Earth Sciences
Date Deposited: 12 Mar 2018 10:10
DOI: 10.1016/j.actamat.2017.12.059
Official URL: https://doi.org/10.1016/j.actamat.2017.12.059
Funders: We thank Juliane Thielsch for experimental advice on the Kerr-microscopy and the German federal state of Hessen through its excellence program LOEWE ”RESPONSE” for financial support., The authors also greatly acknowledge the access to the Lichtenberg High Performance Computer of TU Darmstadt.
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