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  4. Grain boundary diffusion in nanocrystalline Nd-Fe-B permanent magnets with low-melting eutectics
 
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2016
Journal Article
Titel

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

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.
Author(s)
Sawatzki, S.
Kübel, C.
Ener, S.
Gutfleisch, O.
Zeitschrift
Acta Materialia
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DOI
10.1016/j.actamat.2016.05.048
Language
English
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Fraunhofer-Institut für Silicatforschung ISC
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