Microstructure and magnetic performance of Nd–Y–Ce–Fe–B sintered magnets after annealing

Annealing has been widely recognized as a crucial approach to modify the microstructure and enhance the coercivity of Nd–Fe–B magnets. However, in the context of Nd–Y–Ce–Fe–B magnets with multiple rare earths (REs) exhibiting different diffusion behaviors, annealing effects on the magnetic properties become more complicated and remain unknown. In present work, through a comparative study between as-sintered and annealed Nd–Y–Ce–Fe–B magnet upon 50 wt% Y–Ce co-substitution of total REs, we found that annealing process surprisingly enhances the remanence from 1.17 to 1.20 T, with simultaneous coercivity increment from 612.9 to 660.7 kA·m⁻¹, resulting in drastically improved maximum energy product from 242.0 to 263.5 kJ·m⁻³. Such a peculiar remanence enhancement is closely correlated to the preferential Y/Nd infiltration into RE₂Fe₁₄B main phase and Ce segregation into REFe₂ intergranular phase, which consequently improve the intrinsic magnetism, as evaluated by Curie temperature (T_C), saturation magnetic polarization (J_S) and magnetocrystalline anisotropy field (H_A). Present work delights that different metallurgical behaviors of Nd/Y/Ce exert influential effects on the intrinsic and extrinsic magnetic properties and provide a novel approach toward high-performance 2:14:1-type permanent magnets based on abundant RE mixtures.

Graphic abstract

摘要

退火已被广泛认为是改善Nd-Fe-B磁体微观组织和增强矫顽力的重要途径。然而, 在Nd-Y-Ce-Fe-B磁体中不同稀土元素的扩散行为各异, 退火对磁性能的影响更加复杂。本工作通过对比研究烧结态和退火态的50 wt% Y-Ce共取代磁体, 发现退火使剩磁从1.17 T提高到1.20 T, 同时矫顽力从612.9 kA·m⁻¹ 提高到660.7 kA·m⁻¹, 最大磁能积从242.0 kJ·m⁻³提高到263.5 kJ·m⁻³。研究发现, 退火过程中Y/Nd优先进入RE₂Fe₁₄B主相, 而Ce更易富集于REFe₂晶界相。这种元素扩散行为提高了退火态Nd-Y-Ce-Fe-B磁体的本征磁性能(包括居里温度T_C, 饱和磁极化强度J_S, 磁晶各向异性场H_A), 从而导致剩磁的异常提升。本工作发现稀土元素Nd/Y/Ce的不同扩散行为会显著影响磁体的内禀和外禀磁性能, 为制备高性能2:14:1型混合稀土永磁提供了新的途径。