钕铁硼永磁晶界扩散技术和理论发展的几个问题

Several Issues on the Development of Grain Boundary Diffusion Process for Nd-Fe-B Permanent Magnets

钕铁硼永磁在新能源、信息通讯和智能制造等领域有着广泛的应用。电动汽车驱动电机、风电系统发电机等对钕铁硼磁体的高温性能和矫顽力提出了更高的要求。重稀土Tb和Dy可以显著提高钕铁硼磁体的各向异性场,但降低了剩磁,增加了成本。21世纪初出现的晶界扩散技术是稀土永磁制造领域的一项重大进展。它通过将重稀土元素或稀土合金以晶界扩散的方式渗透入磁体,在有效提高磁体矫顽力的同时,大幅降低重稀土含量,提高性价比。晶界扩散技术发展至今,引起业内的广泛关注并已实现工业化,但在技术和理论层面上仍存在一些关键问题。本文基于国内外最新进展和作者团队的研究工作,总结了晶界扩散工艺目前亟需解决的问题及可能的解决措施。对厚磁体的晶界扩散技术、晶界扩散中各向异性行为的利用、低成本扩散剂的选择、晶界扩散与现存工艺的结合、晶界扩散对其他服役性能的影响以及晶界扩散的相关理论发展等问题进行了阐述,并对晶界扩散的未来发展趋势进行了展望。

Nd-Fe-B based permanent magnets have been widely used in many industries,including renewable energy,information and communication,and intelligent manufacturing.The applications in the electric vehicle drive motors and wind power system generators set high requirements on the elevated temperature performance and coercivity for Nd-Fe-B magnets.Heavy rare earth(HRE)of Tb and Dy have been frequently used to substitute Nd to enhance the anisotropy field of the magnets.However,introducing these HRE elements reduces the remanence of magnets and increases the total price of endproducts.The grain boundary diffusion(GBD)process,invented at the beginning of this century,is a significant progress in the field of rare earth permanent magnet manufacturing.The coercivity can be significantly improved by diffusing HRE elements or rare earth alloys into the magnet along the grain boundary.Simultaneously,the reduced heavy rare earth consumption and enhanced performance-cost ratio can also be realized.Although the GBD process has attracted much attention and has been quickly industrialized since its appearance,some key issues still exist on technical and theoretical levels.Based on the latest domestic and overseas developments and the research results from the authors􀆳group,this paper summarizes the urgent problems and feasible solutions for the GBD process.Several issues are described in this report,including the GBD process for thick magnets,utilization of anisotropic behavior of GBD,selection of low-cost diffusion sources,combination of GBD with the existing process,influence of GBD on the service performance,and advancement of GBD related theories.The challenges and opportunities in the future development of the GBD process for Nd-Fe-B based magnets are also highlighted.