Sintered Nd-Fe-B magnet with core–shell structures fabricated through the intergranular addition of ultra-fine as-disproportionated (Nd,Dy)–Fe–B–Cu powder

Ultra-fine as-disproportionated (Nd,Dy)–Fe–B–Cu powder was fabricated through mechanically activated disproportionation and was incorporated into sintered Nd–Fe–B magnets through a “two-powder” method. The microstructure–coercivity relationships of the magnets were discussed. Results revealed the successful fabrication of bulk Nd–Fe–B magnet with core–shell structures through this process. The coercivity of the magnet was increased by 54.7% from 15 to 23.2 kOe when 20wt% as-disproportionated Dy-containing powder was added. This rapid coercivity enhancement was attributed to the enhanced local anisotropy field of the grain outer regions and the well-decoupled 2:14:1 grains. The increment of coercivity here was higher than that of the magnets obtained by using other Dy sources as the intergranular additives for the similar starting magnet and Dy concentration. Therefore, this work showed a promising fabrication method for a Nd–Fe–B magnet with high coercivity and Dy utilization efficiency.