Investigation on the grain boundary diffusion of Dy2O3 film prepared by electrophoretic deposition for sintered Nd-Fe-B magnets

Highlights: • Dy₂O₃ film prepared by electrophoretic deposition is used as diffusion source for grain boundary diffusion. • Core-shell structure and optimized structure and distribution of RE-rich phase contribute to increased properties. • Thermal stability and corrosion resistance are improved significantly by grain boundary diffusion. • The relation of processes-microstructure-magnetic properties is investigated in details. -- Abstract: Based on the diffusion source of Dy₂O₃ film prepared by electrophoretic deposition (EPD), grain boundary diffusion (GBD) is performed to improve properties of sintered Nd-Fe-B magnets. Effects of EPD and GBD processes on microstructure and magnetic properties are investigated in details. The studied results show that 30 s of EPD time is the most suitable for the preparation of diffusion source, and the optimal magnetic properties with H_ci of 934 kA/m, B_r of 1.41 T and (BH)_max of 349 kJ/m³ can be achieved under GBD condition of 800 °C/6 h followed by 500 °C/1 h, enhancing by 27.6%, 0.7% and 13.7%, respectively, comparing to those of as-prepared magnet. The formation of (Nd, Dy)₂Fe₁₄B shell surrounding Nd₂Fe₁₄B core and improved distribution and structure of rare earth-rich (RE-rich) phase jointly contribute to the improvement of coercivity. Moreover, Thermal stability (temperature coefficient of remanence and coercivity) is improved considerably. Dense Dy₂O₃ film and formed filamentous substance covering the surface together promote the improvement of corrosion resistance.