Achieving high-performance regeneration of grain boundary diffusion Nd-Fe-B sludge via an ultra-short process

The grinding sludge of grain boundary diffusion Nd-Fe-B magnet is rich in heavy rare earth and has a typical core–shell microstructure. In this work, an ultra-short process was developed to realize green, in-situ regeneration of the sludge and efficient reuse of heavy rare earth elements. The regenerated magnets showed excellent magnetic performance and good temperature stability which were fabricated after the purification of sludge, composition regulation with rare earth-rich compounds, Nd_42.1Fe_balB_0.79, NdH_x, (PrNd)H_x, and sintering. Especially, the magnet prepared by using Nd_42.1Fe_balB_0.79 alloy had significant property recovery, where remanence and coercivity were restored to 12.8 kG, and 20.6 kOe, respectively, reaching 97.7 % and 162.5 % of the original magnet. The magnetization reversal behavior and the coercivity mechanism were analyzed to keep the nucleation mechanism, and the high coercivity stemmed from the repair and optimization of the grain boundary by introducing rare earth-rich alloys, the full utilization of heavy rare earth elements, and the core–shell microstructure rooted in the sludge as well.