Enhancement of Magnetic Properties in Anisotropic Nd-Fe-B Sintered Magnets Fabricatied by Spark Plasma Sintering

Abstract

Nd-Fe-B sintered magnets are widely utilized in various high-performance fields such as traction motors in electric vehicles (EVs), industrial robotics, and wind power generation, owing to their high magnetic performance. To ensure reliable operation under elevated temperatures, it is necessary to enhance coercivity through the incorporation of heavy rare earth (HRE) elements such as Tb and Dy. However, the limited supply and high cost of these elements significantly constrain their use. In this study, anisotropic Nd-Fe-B sintered magnets were fabricated by aligning jet-milled Nd-Fe-B powders under an external magnetic field prior to sintering. The oriented green compacts were then densified using the spark plasma sintering (SPS) process. The short sintering time of SPS effectively suppressed grain growth. Post-sintering heat treatment promoted the formation of continuous grain boundary phases, resulting in a significant improvement in coercivity. Furthermore, grain boundary diffusion (GBD) was performed to enhance coercivity while maintaining remanence. TbH was x selected as the diffusion source. Two GBD approaches were applied to the SPSed magnets. The first approach employed a conventional GBD method, while the second approach utilized an internal GBD method. The effects of the two diffusion processes on the formation of core-shell structures and the resulting magnetic properties were analyzed and compared.