Improvement of magnetic performance of Nd-Ce-Fe-B sintered magnets via Pr-Co-Ga grain boundary reconstruction

Grain boundary reconstruction is a commonly used method to improve the coercivity of Nd-Ce-Fe-B magnets but at the expense of a notable reduction in remanence. In this study, we present an effective approach to achieving a balance between remanence and coercivity of Nd-Ce-Fe-B magnets through Pr-Co-Ga grain boundary reconstruction. Compared to the original Nd0.7-Ce0.3-Fe-B magnet, the remanence of the magnet with 4 wt.% Pr-Co-Ga addition decreased only from 13.09 kGs to 12.8 kGs, while the coercivity remarkably increased from 10.95 kOe to 14.84 kOe. Additionally, the coercivity temperature coefficient (20–150°C) was improved from –0.606%/°C to –0.547%/°C, and the Curie temperature was increased from 278.4°C to 285.1°C, demonstrating excellent thermal stability. XRD refinement analysis showed a slight decrease in the main phase ratio, accompanied by a slight increase in orientation, resulting in a slight decrease in remanence. SEM and EPMA observations revealed that Pr preferentially replaced Ce on the grain surface, forming a "Pr-rich" shell with an enhanced anisotropy field. TEM analysis showed that the magnets with PCG addition exhibit a continuous Fe-lean grain boundary phase, weakening the exchange coupling of the adjacent grains. The synergistic effect of the "Pr-rich" shell formation and grain boundary optimization effectively enhanced the coercivity.