热压/热变形NdFeB磁体研究的新进展

Recent Research Progress in Hot-pressed and Hot-deformed NdFeB Magnets

热压/热变形钕铁硼磁体具有良好的纳米晶微结构、剩磁、磁能积以及高的抗腐蚀性和热稳定性等优点,受到人们的广泛关注。近年来Dy、Tb等重稀土的价格飙升,尤其是晶界扩散方法应用于热变形磁体使其矫顽力大幅度提高,热变形钕铁硼磁体的研究重新成为当前磁性材料研究的热点。本文从热压/热变形钕铁硼磁体的制备工艺、微观结构、元素掺杂等方面进行总结。介绍了几种提高热变形钕铁硼磁性能的工艺方法,对热变形钕铁硼的Nd元素含量、热变形温度、变形量、富Nd相的形状与分布、晶粒形状与修饰等进行探讨。并对多种低熔点共晶合金晶界扩散和压力扩散进行对比,采用添加轻稀土或者是添加高熔点合金的方式使得热变形钕铁硼仍然保持较优异的磁性能。此外,利用微磁模拟和透射电镜原位加场研究对热变形钕铁硼的磁化机理、晶粒耦合机制与矫顽力机制进行总结。这些机制包括主相晶粒间的交换耦合作用、晶间相的去磁耦合作用、钉扎理论、自钉扎理论、成核理论、成分关系理论、晶粒内部缺陷钉扎作用等相关理论。

Hot-deformed nanocrystalline NdFeB magnets with good microstructure,remanence,magnetic energy product,high corrosion resistance and thermal stability have attracted much attentions.In recent years,the prices of heavy rare earths such as Dy and Tb have soared and especially grain boundary diffusion method is applied to the hot-deformed NdFeB magets to enhanceing coercivity.So the hot-deformed NdFeB magnets have returned to centre stage in the field of magnetic materials.This paper summarizes the latest research progress in preparation method,microstructure and element doping of the hot-deformed NdFeB magnet.Several methods for improving the magnetic properties of hot-deformed NdFeB are introduced.The Nd element content,hot deformation temperature,deformation,shape and distribution of Nd-rich phase,grain shape and modification of hot-deformed NdFeB are discussed.The grain boundary diffusion of various low melting point eutectic alloys and pressure diffusion are compared,the addition of light rare earth or high melting point alloys makes the hot deformed NdFeB still maintain superior magnetic properties.In addition,the magnetization mechanism,grain coupling mechanism and coercivity mechanism of hot-deformed NdFeB were also summarized by micro-magnetic simulation and transmission electron microscopy in-situ field study.The mechanisms include exchange coupling between the main phase grains,the demagnetization coupling of the intergranular phase,the pinning theory,the self-pinning theory,the nucleation theory,the composition relationship theory and the internal defect pinning effect.