Magnetic and Microstructural Properties of DyF3-Coated Sintered Nd-Fe-B Magnets by Electrophoretic Deposition

The impact of the effective DyF3 content on the magnetic and microstructural properties of sintered Nd-Fe-B magnets by the grain boundary diffusion process using electrophoretic deposition (EPD) method was investigated. The coercivity increased gradually from 16.10 to 24.04 kOe, and then decreased with increasing the effective DyF3 content. A significant increment in coercivity of similar to 8.0 kOe was achieved with <1.3 wt.% Dy. During diffusion, Dy tended to diffuse into the magnet through the grain boundary and formed Dy-rich (Nd, Dy)(2)Fe14B phase in the outer region of Nd2Fe14B grains by substituting for Nd. The significant enhancement of coercivity was ascribed to the higher magnetocrystalline anisotropy of the core-shell phase and the improved decoupling by the continuous and thick grain boundary phase. The coercivity decreased with increasing the thickness of the magnets, and the increment of the coercivity was similar to 3.26 kOe for the DyF3 EPD-coated magnets with the thickness of 8.5 mm.