Simultaneous application of Dy–X (X = F or H) powder doping and dip-coating processes to Nd–Fe–B sintered magnets. (July 2015)

• Record Type: Journal Article
• Authors: Kim, Tae-Hoon; Lee, Seong-Rae; Kim, Hyo-Jun; Lee, Min-Woo; Jang, Tae-Suk
• Is Part Of: Acta materialia. Volume 93(2015)
• Page Start: 95
• Page End: 104
• Publication Date: 2015-07
• Subjects: Nd–Fe–B sintered magnet -- Core–shell microstructure -- Grain boundary diffusion depth of Dy -- Grain boundary diffusion process -- Powder doping process; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2015.04.019
• Languages: English
• ISSNs: 1359-6454

Abstract

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)2 O3 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 .