基于烧结钕铁硼永磁稳定性的纳米技术调控

Sintered NdFeB magnets have a broad application prospects in the field of hybrid/electric cars and wind turbines due to their strongest magnetic property. However, the disadvantages of poor thermal and chemical stability of the magnets seriously restrict their further development and application. Here we provide a structural model for the sintered magnets with both ideal magnetic properties and high stability. The magnets are composed by Nd2Fe14B main phase with high magnetization, (Dy/Tb)2Fe14B grain boundary phase with high magnetocrystalline anisotropy and non-magnetic rare earth rich boundary phase with high corrosion-resistant. First, powder metallurgy, nanoparticles doping and surface diffusion, and electrophoretic deposition technologies are used to prepared the new sintered NdFeB magnets which are consistent with the theoretical model. Second, the microstructure, magnetic properties of the magnets are analyzed and measured, and effect of phase composition, phase distribution, and interface structure of the magnets on their magnetic properties, temperature and chemical stability are studied. The studies are focused on diffusion thermodynamics and kinetics, as well as final distribution characteristics of rare earth and other metallic nanoparticles in the process of sintering and heat treatment. The magnetic property variation at different temperature and the corrosion behaviors in different conditions are measured. Finally, we will buildup the relation among the microstructure and stability of the magnets, and provide the scientific guidance for preparing sintered NdFeB magnets with excellent all-around property.

烧结钕铁硼是当前磁性能最强的永磁材料，在电动汽车、风力发电等领域有广泛的应用前景。但是烧结钕铁硼永磁的温度和化学稳定性较差，对其应用造成很大影响。对此，本项目提出了兼具高磁性能和高稳定性的烧结钕铁硼结构模型，即磁体由高磁化强度主相、高磁晶各向异性主相晶粒边界层相，及高耐蚀非磁性富稀土边界相组成。首先，采用粉末冶金、纳米颗粒包覆和表面渗镀、电泳沉积技术，研制与上述理论模型一致的新型烧结钕铁硼永磁；在此基础上，分析、测定磁体微结构特征以及各项磁性能参量；进一步，深入研究新型磁体的相组成、相分布及界面结构对磁性能、温度及化学稳定性的影响。重点考查所添加的稀土及非稀土纳米颗粒在烧结和热处理过程中的扩散热力学、动力学及其最终分布特征；考查磁体的磁性能随温度变化规律及其在不同环境下的腐蚀行为。最终建立新型磁体的微结构与其稳定性之间的构效关系模型，为研制综合性能优异的烧结NdFeB永磁提供科学指导。

烧结钕铁硼是当前磁性能最强的永磁材料，在电动汽车、风力发电等领域有广泛的应用前景。但是烧结钕铁硼永磁的温度和化学稳定性较差，对其应用造成很大影响。本项目分别针对传统烧结钕铁硼磁体、废旧钕铁硼磁体以及高丰度铈基磁体进行了纳米技术调控，提高了磁体的矫顽力和耐蚀性。采用TbH3纳米颗粒进行晶界扩散，获得了矫顽力为47.1kOe，最大磁能积为38.5MGOe的超高磁性能钕铁硼磁体。磁畴观察结果表明晶界扩散形成的核壳结构抑制了反磁化畴形核过程，从而有效提高了磁体的矫顽力和综合磁性能。通过掺杂CuZn5合金粉末，成功制备出高耐蚀性烧结钕铁硼磁体。在高压加速腐蚀中（121℃，2 atm，500 h），掺杂量为3.5 wt.%的烧结钕铁硼磁体腐蚀失重率仅为1.00 mg/cm2，腐蚀速率远低于未掺杂磁体（106.14 mg/cm2）。为改善再生烧结钕铁硼磁体的磁性能，研究了稀土纳米颗粒掺杂以及晶界扩散的方式对再生钕铁硼磁体磁性能与显微组织的影响。DyH3纳米颗粒掺杂可大幅度提高再生磁体的矫顽力，当掺杂量为1.0 wt.%时，其矫顽力已高于原始磁体。DyH3纳米颗粒晶界扩散再生钕铁硼磁体的矫顽力由14.99 kOe提升至27.35 kOe。对稀土镧和铈的合理利用，不仅有利于降低烧结钕铁硼的成本，而且可以平衡利用资源。(Nd0.6Ce0.4)33Fe66B烧结磁体的矫顽力较低，通过TbH3纳米颗粒晶界扩散可以实现对(Nd0.6Ce0.4)33Fe66B磁体的磁硬化。TbH3纳米颗粒晶界扩散烧结磁体矫顽力较原始磁体提升71.72%。上述研究结果可为研制综合性能优异的稀土永磁材料提供科学指导。