摘要
目的采用Dy、Tb等重稀土元素晶界扩散是制备高性能钕铁硼磁材的重要技术手段,但现阶段工业化晶界扩散生产过程的工艺模式仍然较为粗放,对重稀土等国家战略性资源的极致利用还远不够精细。方法采用直流磁控溅射镀膜技术在牌号42SH钕铁硼磁体表面沉积约10μm厚Tb涂层,然后在高真空扩散炉中对镀Tb磁体进行晶界扩散处理,研究了一步扩散法和梯度扩散法工艺模式变化对Tb渗入效率和提高磁体内禀矫顽力实际效能的影响,尝试性地建立了重稀土渗入效率、单位重稀土渗入量产生的实际效能、单位重稀土沉积量产生的实际效能的计算方法,结合电子探针分析了不同扩散模式下重稀土渗入磁体的分布特征。结果一步扩散法的重稀土渗入效率由86%提高到91%和95%,而梯度扩散法达到96%。梯度扩散法的单位浓度Tb渗入量的内禀矫顽力提升量可达到21.42 kOe/wt.%Tb,单位浓度Tb沉积量的内禀矫顽力提升量可达到20.5 kOe/wt.%Tb,换算成单位内禀矫顽力提升量需要的Tb沉积量则为0.049wt.%Tb/kOe,该指标可为不同内禀矫顽力提升量的生产需求预测出合理的重稀土沉积量。结论在梯度扩散模式下,有更多的Tb原子沿晶界相渗入至磁体更深位置,在更多的Nd2Fe14B主相晶粒表面形成具有更高磁晶各向异性场核壳结构(Nd,Tb)2Fe14B硬磁层,所以梯度扩散模式下矫顽力提升量最大。
With the booming development of new energy automobiles and wind power generation,high remanent magnetism,high coercivity and high thermal stability of NdFeB magnets have reached tens of thousands of tons of annual market demands.The grain boundary diffusion process(GBDP)of heavy rare earth elements(HRE)such as Dy and Tb is an important technological means to meet the demand of the above high-performance Nd-Fe-B magnets.However,the utilization of HRE in the present GBDP production lines is still far from being fine enough and there is a lack of quantitative assessment in its efficacy.In this work,DC magnetron sputtering coating technology is used to deposit a Tb film approximately 10μm thick on the surface of grade 42SH Nd-Fe-B magnets,and then a high vacuum diffusion furnace is used to carry out grain boundary diffusion on the Tb-coated magnets.After optimizing the best one-step diffusion process parameters of 950℃×9 h,the effects of the different process modes of one-step vacuum diffusion with holding temperature at 750,850 and 950℃ for 9 h and gradient vacuum diffusion with holding temperature at each of the three levels of temperature for 3 h on the enhancement of the magnets are investigated.Several quantitative equations such as the HRE infiltration efficiency into the magnet,the actual efficacy per unit of infiltrated HRE on the coercivity enhancement,the actual efficacy per unit of consumed HRE on the coercivity enhancement are defined,the corresponding values under different diffusion modes are calculated and compared.Meanwhile,the distribution characteristics of Tb infiltrating into the magnets under different diffusion modes are analyzed by electron probe microanalyzer(EPMA).The results show that for one-step diffusion with the same holding time of 9 h,the Tb infiltration efficiency increases from 86% to 91% and 95% when the diffusion temperature increases from 750℃ to 850℃ and 950℃,respectively,and the infiltration efficiency of Tb in the gradient diffusion mode is even higher,reaching 96%.In terms of the effect of magnetic properties enhancement by GBDP,the gradient diffusion mode is also the most significant.In the gradient diffusion mode,the coercivity enhancement per unit infiltrated Tb can reach 21.42 kOe/wt.%Tb,and the coercivity enhancement per unit deposited Tb can be 20.5 kOe/wt.%Tb,this means that per kOe of coercivity increase needs at least 0.049wt.% of Tb deposition.The EPMA composition analysis shows that in the one-step diffusion even at higher temperature of 950℃,due to the simultaneous occurrence of Tb atoms diffusing along the grain boundary phases and into the main phase grains,the infiltrated Tb is prone to enrichment at the surface and shallow surface layers of the magnet,and resulting in a lower Tb content in the longitudinal depth of the magnets.But in the gradient diffusion mode,the staged holding at 750℃×3 h and 850℃×3 h helps the Tb atoms to diffuse firstly along the grain boundaries to the longitudinal position of the magnet,and then,undergoing the third stage of 950℃×3 h,forming a core-shell structure(Nd,Tb)_(2)Fe_(14)B hard magnetic layer with higher magnetic crystal anisotropy field around more main-phase grains located at the deeper position of the magnets,thus the coercivity enhancement in the gradient diffusion mode is the largest.
作者
田广科
张希
崔光宇
王瑜
许亿
夏原
TIAN Guangke;ZHANG Xi;CUI Guangyu;WANG Yu;XU Yi;XIA Yuan(National Engineering Research Center for Technology and Equipment of Environmental Deposition,Lanzhou Jiaotong University,Lanzhou 730070,China;Baotou Jinshan Magnetic Material Co.,Ltd.,Inner Mongolia Baotou 014000,China;Institute of Mechanics,Chinese Academy of Sciences,Beijing 100083,China)
出处
《表面技术》
北大核心
2025年第16期221-230,共10页
Surface Technology
基金
国家重点研发计划项目(2021YFB3500100)。
关键词
钕铁硼永磁体
重稀土晶界扩散
磁性能
微观组织与结构
成分
定量评估
Nd-Fe-B permanent magnets
heavy rare earth grain boundary diffusion
magnetic property
microstructure
composition
quantitative assessment
作者简介
通信作者:田广科。
