Magnetic and microstructural characteristics of DyF_3/DyH_x dip-coated Nd-Fe-B sintered magnets

摘要

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 micro-structures 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.