Magnetic and microstructural characteristics of DyF3/DyHx dip-coated Nd–Fe–B sintered magnets

Abstract We investigated the microstructural and magnetic property changes of DyF 3 /DyH x dip-coated Nd–Fe–B sintered magnets, as a function of the DyF 3 /DyH x mixing ratio. As the fraction of DyH x in a DyF 3 /DyH x mixed solution was increased (0 → 50 → 100%), there was a coincident gradual increase in coercivity (14.9 → 15.4 → 16.5 kOe). Similarly, the diffusion depth of Dy from the magnet surface also increased with an increasing fraction of DyH x . In the diffused region, we observed well-developed core–shell microstructures in the DyH x dip-coated magnet, but this was not seen in the case of the DyF 3 dip-coated magnet. Diffusion of Dy to the main phase was via lattice diffusion predominantly, rather than through grain boundary diffusion in the DyF 3 dip-coated magnet, but the opposite was observed in the DyH x dip-coated magnet, which is believed to be due to the different influences of F − and H + ions. Therefore, the use of DyH x solution is considered more suitable for developing a core–shell microstructure by encouraging grain boundary diffusion, and creating a Dy-saving effect in the dip-coating process.