Intergranular Melting of Ultrafine Grained Nd2Fe14B Studied by Means of Radiotracer Diffusion |
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Authors: | M. Eggersmann F. Ye S. Herth O. Gutfleisch R. Würschum |
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Affiliation: | (1) Institut für Nanotechnologie, Forschungszentrum Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany;(2) Institut für Festkörper- und Werkstofforschung Dresden, Germany;(3) Technische Universität Graz, Petersgasse 16, A-8010 Graz, Austria |
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Abstract: | Grain-boundary (Gb) diffusion was studied in ultrafine grained Nd2Fe14B-based permanent magnets below and above the melting transition of the Nd-enriched intergranular phase using the radiotracer technique with the isotope 59Fe. The product DGb of interface diffusion coefficient and interface thickness shows a substantial increase above the intergranular melting transition. Assuming a volume self-diffusivity as in -Fe, an analysis in the framework of grain-boundary diffusion kinetic of type B yields an Arrhenius-type behaviour DGb = 1.53 × 10–11 exp(–1.74 eV/kT) m3 s–1 below the intergranular melting transition. Similar values DGb are observed for ultrafine grained Nd-Fe-B with reduced Nd excess in the grain boundaries. The diffusion characteristics are compared with the kinetics of the hot-deformation which is of technical relevance for the processing of high-performance permanent magnets. |
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Keywords: | hard magnets diffusion intergranular melting NdFeB |
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