We investigated the microstructural and magnetic property changes of Nd-Fe-B sintered magnets with the application of simultaneous processing via powder doping and dip-coating, using DyF3 and/or DyH2. The simultaneous use of DyF3 powder doping and DyH2 dip-coating has a synergistic effect of improving the magnet's coercivity (Hc) while minimizing the reduction of remanence (Br). DyF3 powder doping suppresses the formation of the rare-earth segregated oxide phase (RE-rich phase, Dy-Nd-O or Nd-O), dramatically improving the grain boundary diffusion depth of Dy (from 250 to 600 μm) during the grain boundary diffusion process (GBDP). The RE-rich phase in Nd-Fe-B magnets is a major obstacle for the grain boundary diffusion of Dy because of the high surface energy of the RE-rich phase and the consumption by the non-stoichiometric RE-rich phase of diffused Dy to form a stoichiometric (Nd, Dy)2O3 phase. The slight reduction of the relative density of the as-sintered DyF3-doped magnet (from 98.1% to 97.5%) may have also helped to improve the grain boundary diffusion depth of Dy during the GBDP when the magnets were dip-coated with DyH2.
Bibliographical noteFunding Information:
This research was supported by the Technology Innovation Program funded by the Ministry of Knowledge Economy (MKE, South Korea) (No. 10043780 ), Republic of Korea.
© 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
- Core-shell microstructure
- Grain boundary diffusion depth of Dy
- Grain boundary diffusion process
- Nd-Fe-B sintered magnet
- Powder doping process
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys