钕铁硼永磁晶界扩散技术和理论发展的几个问题

doi:10.11900/0412.1961.2020.00438

金属学报

2021, Vol. 57

Issue (9): 1155-1170 DOI: 10.11900/0412.1961.2020.00438

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钕铁硼永磁晶界扩散技术和理论发展的几个问题

刘仲武(

), 何家毅

华南理工大学材料科学与工程学院广州 510640

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

LIU Zhongwu(

), HE Jiayi

School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China

引用本文:

刘仲武, 何家毅. 钕铁硼永磁晶界扩散技术和理论发展的几个问题[J]. 金属学报, 2021, 57(9): 1155-1170.
Zhongwu LIU, Jiayi HE. Several Issues on the Development of Grain Boundary Diffusion Process for Nd-Fe-B Permanent Magnets[J]. Acta Metall Sin, 2021, 57(9): 1155-1170.

全文: PDF(4174 KB) HTML

摘要:

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。

关键词 ：永磁材料, 钕铁硼, 晶界扩散, 重稀土, 矫顽力

Abstract：

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 end-products. 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.

Key words： permanent magnet Nd-Fe-B grain boundary diffusion heavy rare earth coercivity

收稿日期: 2020-11-02

ZTFLH:

TM273

基金资助:国家自然科学基金项目(51774146);江西省重大科技研发专项项目(20203ABC28W006)

作者简介: 刘仲武，男，1971年生，教授，博士

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图1 烧结钕铁硼晶粒结构与晶界扩散示意图

图2 工业生产中涂覆晶界扩散剂的示意图与不同重稀土扩散剂(氟化物、氧化物、氢化物、金属与合金)对烧结磁体的扩散效果[16,20~28]

图3 通过掺杂与合金化提高扩散剂速率的原理图

图4 原位晶界扩散原理图及其对磁性能提升效果[39]

图5 放电等离子烧结磁体多层晶界扩散的第二象限退磁曲线和磁学性能

图6 三代晶界扩散剂的发展示意图

图7 重稀土晶界扩散的原理图

表1 不同重稀土扩散剂的优劣势

图8 轻稀土晶界扩散原理图及不同成分Pr-Al-Cu合金晶界扩散处理前后N50烧结磁体的退磁曲线[52]

图9 Cu的添加对烧结磁体微观组织的影响

图10 ZnO晶界扩散原理图与不同工艺ZnO扩散处理前后的退磁曲线[61]

图11 Pr7.03Nd21.84Ho2(Fe, M)balB0.95磁体和在不同方向进行DyHx扩散后磁体的退磁曲线[64]

图12 晶界扩散各向异性行为的微磁学模拟模型、晶粒结构以及磁化分布[67]

图13 晶界扩散与现存烧结工艺的结合：与气流磨结合的重稀土蒸气包覆、冷压前的双合金粉末混合、致密化成型前的扩散剂包覆和致密化成型后的扩散剂包覆(a) HRE vapor coating (b) diffusate coating(c) diffusate coating before sintering (d) diffusate coating after sintering

图14 原始磁体和Pr-Al-Cu、La-Al-Cu和Al-Cu扩散磁体的极化曲线及其腐蚀后的微观结构[49]

图15 Pr-Al-Cu合金扩散前后磁体的抗压曲线及断裂后的形貌[78]

图16 烧结和热变形Nd-Fe-B磁体之间的结构-性能关系对比图

图17 晶界扩散制备高矫顽力高剩磁黏结磁体的原理示意图

图18 超亚铁磁结构的示意图

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