Grain boundary reconstruction for high-performance regeneration of Ce-abundance sintered Nd-Ce-Fe-B magnet scraps

Abstract

In this study, we focus on the short-process regeneration of high-Ce content sintered Nd-Ce-Fe-B magnet scraps, aiming to enhance the coercivity and overall magnetic properties through the reconstruction of grain boundaries (GBs) based on the analysis of rare earth (RE) loss and proportions at each stage of the regeneration process. CeHx, (Nd0.75Pr0.25)Hx, and their mixtures were added as intergranular additives to produce sintered magnets. When 2.31 wt% of (Nd0.75Pr0.25)Hx is added, a high-performance magnet is obtained with the remanence of 11.72 kG, coercivity of 11.56 kOe, and maximum energy product of 32.23 MGOe, reaching performance recovery rates of 98.8%, 103.5%, and 98%, respectively, of the original magnets. It is indicated that the intergranular additives were beneficial to the formation of continuous smooth RE-rich GBs. In addition, a portion of Nd/Pr diffused into the 2:14:1 phase as a partial replacement for Ce, resulting in the migration of Ce from the interior of the grains to the outer region. This led to the formation of new RE-rich triple junction phases on the exterior, thereby reducing the magnetic dilution effect of Ce in the primary phase and enhancing the magnetic crystal anisotropy. These findings offer new insights into the regeneration of high-Ce sintered Nd-Ce-Fe-B scraps.