Simultaneous application of Dy-X (X = F or H) powder doping and dip-coating processes to Nd-Fe-B sintered magnets

Tae Hoon Kim, Seong Rae Lee, Hyo Jun Kim, Min Woo Lee, Tae Suk Jang

Research output: Contribution to journalArticlepeer-review

56 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)95-104
Number of pages10
JournalActa Materialia
Volume93
DOIs
Publication statusPublished - 2015 Jul 1

Keywords

  • 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

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