Microstructural and compositional characterization of terbium-doped Nd-Fe-B sintered magnets
- Jozef Stefan Institute, Department for Nanostructured Materials, Jamova cesta 39, SI-1000 Ljubljana (Slovenia)
- Intermetallics Co. Ltd., Kyodaikatsura 303, 1-36 Goryo Ohara, Nishikyo-Ku, Kyoto-city 615-8245 (Japan)
Anisotropic sintered magnets based on the Nd{sub 2}Fe{sub 14}B phase doped with Tb were prepared using a grain-boundary diffusion process (GBDP) in order to enhance their coercivity. A FEGSEM microstructural analysis revealed that these GBDP magnets had a core-shell structure, where thin, Tb-rich, (NdTb){sub 2}Fe{sub 14}B shells are formed on the original matrix Nd{sub 2}Fe{sub 14}B grains after diffusion of the Tb. This shell thickness varies from a few tens of nanometres in the middle of the magnet up to a few micrometers near the edge. The exact chemical composition of these shells was determined using EDS and WDS electron-probe microanalyses, which were modified and optimized for submicrometer scale analyses. When analyzing the common Nd-L{alpha}, Tb-L{alpha} and Fe-K{alpha} lines a mutual multiple overlap in the EDS spectra is present and, as a result, an accurate quantitative analysis was only feasible when using WDS. Using this technique we were able to achieve a lateral analytical resolution of 0.4 {mu}m. A further improvement in resolution, down to 0.15 {mu}m, was realized with a dedicated set-up using low-voltage EDS, analyzing the 'atypical' low-energy Nd-M{alpha}, Tb-M{alpha} and Fe-L{alpha} lines. Quantitative analyses confirmed that the reaction phase (Nd{sub x}Tb{sub 1} {sub -x}){sub 2}Fe{sub 14}B is formed after the diffusion of Tb with the equilibrium concentration of Tb being equal to x Almost-Equal-To 0.5, i.e., with the atomic ratio of Nd/Tb equal to 1/1. We also found that a relatively sharp Tb concentration gradient from the shell to the core occurs within a length of Almost-Equal-To 0.5 {mu}m, while the Fe concentration remains unchanged. In terms of magnetic properties, the Tb-doping significantly increased coercivity by Almost-Equal-To 30% while the remanence remained at the same value as in the undoped Nd-Fe-B. - Highlights: Black-Right-Pointing-Pointer Nd-Fe-B sintered magnets were doped with Tb using grain-boundary diffusion process. Black-Right-Pointing-Pointer A tiny core-shell reaction phase was formed around the Nd{sub 2}Fe{sub 14}B matrix grains. Black-Right-Pointing-Pointer EDS and WDS analyses confirmed (Nd{sub 0.5}Tb{sub 0.5}){sub 2}Fe{sub 14}B equilibrium shell composition. Black-Right-Pointing-Pointer Coercivity of Tb-doped Nd-Fe-B increases by 30% without a drop in remanence.
- OSTI ID:
- 22066445
- Journal Information:
- Materials Characterization, Vol. 67, Issue Complete; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-5803
- Country of Publication:
- United States
- Language:
- English
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