Chen Renjie, Xia Xianshuang, Tang Xu, Yan Aru
CISRI & NIMTE Joint Innovation Center for Rare Earth Permanent Magnets, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China.
CAS Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China.
Materials (Basel). 2023 Jul 3;16(13):4789. doi: 10.3390/ma16134789.
High-performance Nd-Fe-B-based rare-earth permanent magnets play a crucial role in the application of traction motors equipped in new energy automobiles. In particular, the anisotropic hot-deformed (HD) Nd-Fe-B magnets prepared by the hot-press and hot-deformation process show great potential in achieving high coercivity due to their fine grain sizes of 200-400 nm, which are smaller by more than an order of magnitude compared to the traditional sintered Nd-Fe-B magnets. However, the current available coercivity of HD magnets is not as high as expected according to an empirical correlation between coercivity and grain size, only occupying about 25% of its full potential of the anisotropy field of the NdFeB phase. For the sake of achieving high-coercivity HD magnets, two major routes have been developed, namely the grain boundary diffusion process (GBDP) and the dual alloy diffusion process (DADP). In this review, the fundamentals and development of the HD Nd-Fe-B magnets are comprehensively summarized and discussed based on worldwide scientific research. The advances in the GBDP and DADP are investigated and summarized based on the latest progress and results. Additionally, the mechanisms of coercivity enhancement are discussed based on the numerous results of micromagnetic simulations to understand the structure-property relationships of the HD Nd-Fe-B magnets. Lastly, the magnetization reversal behaviors, based on the observation of magneto-optic Kerr effect microscopy, are analyzed to pinpoint the weak regions in the microstructure of the HD Nd-Fe-B magnets.
高性能钕铁硼基稀土永磁体在新能源汽车所配备的牵引电机应用中发挥着关键作用。特别是通过热压和热变形工艺制备的各向异性热变形（HD）钕铁硼磁体，由于其200 - 400纳米的细晶粒尺寸，在实现高矫顽力方面显示出巨大潜力，与传统烧结钕铁硼磁体相比，晶粒尺寸小了一个多数量级。然而，根据矫顽力与晶粒尺寸之间的经验关联，目前HD磁体的可用矫顽力并未达到预期，仅占钕铁硼相各向异性场全部潜力的约25%。为了实现高矫顽力HD磁体，已开发出两条主要途径，即晶界扩散工艺（GBDP）和双合金扩散工艺（DADP）。在本综述中，基于全球科学研究，对HD钕铁硼磁体的基本原理和发展进行了全面总结和讨论。基于最新进展和结果，对GBDP和DADP的进展进行了研究和总结。此外，基于大量微磁模拟结果讨论了矫顽力增强机制，以了解HD钕铁硼磁体的结构 - 性能关系。最后，基于磁光克尔效应显微镜的观察结果，分析了磁化反转行为，以确定HD钕铁硼磁体微观结构中的薄弱区域。
