晶界扩散Dy60Co35Ga5合金对烧结钕铁硼磁体 磁性能及热稳定性的影响

研究了晶界扩散Dy₆₀Co₃₅Ga₅合金对烧结钕铁硼磁体磁性能及其热稳定性的影响.随着扩散温度的升高,磁体的矫顽力（H_cj）呈现出先增加后减少的趋势,并在890 ℃扩散3 h,480 ℃回火5 h的工艺条件下,矫顽力达到较优,从1 209 kA/m提高到1 624 kA/m,磁体的剩磁只有轻微的下降,从1.38 T降低到1.32 T.高温下测试磁体的磁性能,原始磁体和890 ℃晶界扩散Dy₆₀Co₃₅Ga₅合金磁体的矫顽力都呈下降趋势,但晶界扩散Dy₆₀Co₃₅Ga₅合金磁体的矫顽力在高温下要明显优于原始磁体.原始磁体及890 ℃晶界扩散Dy₆₀Co₃₅Ga₅合金磁体在不同温度下保温2 h的不可逆磁通损失分别为63 %和45 %.且DSC结果显示,890 ℃晶界扩散Dy₆₀Co₃₅Ga₅合金磁体的居里温度（T_c）要明显高于原始磁体的居里温度,这表明晶界扩散磁体的热稳定性得到了很大的改善. XRD图谱显示,890 ℃晶界扩散磁体RE₂Fe₁₄B相的衍射峰较原始磁体向右偏移,说明Dy原子及Co原子少部分已进入主相晶粒.      

烧结钕铁硼晶界扩散Dy微观组织分析

主要对渗Dy晶界扩散处理后的NdFeB磁体中的Dy元素分布特性进行了研究。经过蒸镀法渗Dy处理,磁体矫顽力从1060 kA/m提高至1630 kA/m,而剩磁几乎保持不变。ICP成分分析得知,虽然渗Dy处理后Dy含量从表到里逐渐降低,但与未处理的磁体相比,在最深的中心部仍有明显的Dy含量提高。SEM能谱和EPMA面分布结果显示,大部分Dy元素主要存在于角隅处富钕相,而贫钕晶界处Dy含量从表到里逐渐减少。Dy扩散过程在富钕相晶界处更易进行,钕铁硼磁体本身的富钕相分布和晶界结构对渗Dy过程起重要作用。     

晶界扩散中Tb对烧结NdFeB磁体微观组织和磁性能的影响

通过晶界扩散技术提升烧结钕铁硼(NdFeB)磁体矫顽力的方法已获得广泛应用,为了研究重稀土磁粉对磁体综合磁性能的影响,本文采用喷涂扩散的方法将重稀土Tb含量为6.0%(质量分数)的磁粉作为复合扩散源的一部分进行晶界扩散并制备了高性能烧结NdFeB磁体。结果表明,当主扩散源占比为60%(质量分数)时,Nd₄₀Tb₆₀对应扩散磁体的矫顽力最高达到21.52 kOe,矫顽力增幅明显。经过微观组织结构和XRD表征分析,重稀土元素Tb沿晶界相扩散进入磁体内部的同时发生了晶格取代反应,可在晶粒表层生成磁晶各向异性场更强的(Nd,Dy/Tb)₂Fe₁₄B硬磁相,显著增强了磁体矫顽力。当主扩散源占比为20%、40%和80%(质量分数)时,Nd₈₀Tb₂₀,Nd₆₀Tb₄₀和Nd₂₀Tb₈₀对应扩散磁体的矫顽力增幅较小,其中Nd₈₀Tb₂₀扩散...     

DyFe薄膜晶界扩散钕铁硼磁体的结构与磁学性能

采用磁控溅射在磁体易磁化面上沉积3μm厚度的Dy_xFe_1-x(x=30,50,80,100)合金薄膜层,并进行适当热处理制备晶界扩散型烧结钕铁硼磁体。当Fe含量为20%(原子分数)时,Dy₈₀Fe₂₀扩散磁体在基本不影响剩磁的情况下矫顽力能够达到15.70 kOe,接近Dy扩散磁体矫顽力,性价比更高。微观结构分析表明,重稀土元素Dy沿晶界相向磁体内部扩散的同时发生了晶格扩散,在晶粒表层生成了磁晶各向异性场更强的(Nd, Dy)₂Fe₁₄B硬磁壳层,因而磁体矫顽力增强。Dy扩散磁体经典核壳结构出现于100μm～300μm之间,且有效扩散深度小于500μm,而Dy₈₀Fe₂₀扩散磁体在100μm处便出现了明显的核壳且壳层可延续至500μm以上,说明Fe合金化可以有效缓解Dy在扩散磁体表面的聚集并提高有效扩散深度。在任意温度区间内,Dy₈₀Fe₂₀扩散磁体的α_B     

烧结钕铁硼晶界扩散Dy工艺进展

烧结钕铁硼性能要求不断提高的今天,晶界扩散技术应运而生。通过该技术能用少量重稀土大幅提高矫顽力,且避免剩磁下降。本文对目前研究开发中的多种晶界扩散Dy工艺介绍总结,并就晶界扩散工艺提高矫顽力的机制做了简要分析。     

重稀土掺杂烧结钕铁硼磁体的晶界调控研究进展

随着低碳经济的提出,烧结钕铁硼磁体作为新能源汽车及其他高新技术的核心材料越来越受到人们的关注,同时对其性能也提出了更高的要求,高矫顽力、高剩磁和大磁能积的永磁体成为人们追求的目标。烧结钕铁硼磁体的磁性能与微观结构中晶界成分、分布以及体积分数等密切相关。利用新型工艺在合金中掺杂重稀土可以很好地调控磁体的微观结构,从而在保持剩磁不变的基础上,提高磁体的矫顽力和磁能积。本文在详细介绍两种新型掺杂技术的基础上,梳理了近几十年来国内外通过掺杂重稀土金属、重稀土化合物及重稀土合金来调控磁体晶界结构、提高磁体矫顽力方面的最新研究成果,为进一步提高烧结钕铁硼磁体性能提供参考。     

烧结Nd-Fe-B磁体晶界扩散TbH2高温稳定性及其机理

采用涂敷方式,在烧结钕铁硼表面均匀涂敷TbH₂粉末,经过不同的扩散温度处理,制备出晶界扩散磁体。研究了晶界扩散TbH₂对烧结Nd-Fe-B磁体常温磁性能及高温稳定性的影响,并分析了磁体矫顽力提升的机理。常温磁性能研究表明,扩散磁体经过890 ℃+490 ℃工艺处理后性能达到最优,矫顽力从1 383 kA/m提升到1 988 kA/m。高温磁性能结果显示,扩散磁体200 ℃的矫顽力温度系数|β|比原始磁体降低0.032%/℃,磁通不可损失hirr比原始磁体降低21.47%,扩散TbH₂明显提高了烧结Nd-Fe-B磁体的热稳定性。分析得出,晶界扩散TbH₂磁体矫顽力提升的机理是Nd₂Fe₁₄B晶粒外延层形成了（Tb, Nd）₂Fe₁₄B核壳结构,提高了磁晶各向异性场;同时改善了磁体的微观组织结构,有效地隔绝了晶粒之间的磁交换耦合作用。      

高Dy含量烧结Nd-Fe-B的晶界扩散处理研究

研究了晶界扩散处理对高Dy含量烧结Nd-Fe-B磁体性能和结构的影响。经蒸镀渗Dy晶界扩散处理,高Dy含量Nd-Fe-B磁体的矫顽力从1 713 kA/m提高至2 161 kA/m,而剩磁和最大磁能积基本没有下降,处理后磁体内Dy平均质量分数仅增加0.30%。不同深度片层分析表明,虽然磁体近表面片层比中心片层的Dy含量高,但是片层间矫顽力相差较少,而且所有片层的矫顽力均远高于未处理磁体片层的矫顽力。电子探针Dy元素面分布结果显示,在未处理高Dy含量磁体的晶界与主相中均存在Dy元素富集区且富集浓度较低,而经扩散处理后,晶界富Nd相中的Dy富集区浓度及所占比例明显提高;包括磁体芯部在内,磁体内大部分角隅处富Nd相内Dy含量明显增加,进一步提高了高Dy含量磁体内部各处的矫顽力。     

《晶界扩散钕铁硼永磁材料》国家标准制定依据和技术要求分析

为了促进晶界扩散钕铁硼永磁材料新工艺、新材料的应用,为生产企业和应用企业提供指南,制定了《晶界扩散钕铁硼永磁材料》国家标准。调查了钕铁硼永磁材料国际标准、国家标准和世界领头企业的技术标准,结合起草单位意见,确定了本标准涉及36个牌号作为技术要求对象。采用经验公式计算主要磁性能技术指标,并征集了参与企业样品测试数据加以验证。本标准G55SH、G52UH、G54UH、G48EH和G50EH等综合磁性能高于日本企业标准,本标准处于国际先进水平。     

液相扩散对钕铁硼磁体性能和组织结构的影响

用双合金工艺在Nd13.05Dy0.23Fe80.12B6.5铸片主合金中分别添加质量分数为3％～20％的富稀土铸锭辅合金Nd38.2Cc11.8Fe44.88Al4.12B,研究在钕铁硼永磁体中用Ce部分地取代Nd时对永磁体的磁性能的变化规律.实验结果表明,在一定的烧结及热处理工艺条件下,辅合金加入量介于8％ ～ 12％(质量分数)时,磁体的内禀矫顽力和磁能积相对较高,对剩磁的影响不大.显微成分分析表明,采用双合金法,使组织中细小的颗粒状富稀土相增多,形成了更多的对矫顽力有贡献的富稀土相,并且富稀土相分布于晶界上.     

Effects of grain boundary diffusion process on magnetic properties enhancement and microstructure evolution of hot-deformed Nd-Fe-B magnets

Grain boundary diffusion(GBD) process is an important approach for producing Nd-Fe-B magnets with high coercivity and high thermal stability.The GBD for hot-deformed Nd-Fe-B magnets with nanocrystalline micro structure is more complicated compared to sintered magnets.Here,we investigated the effects of different GBD methods,i.e.,intergranular addition(in-situ GBD 1#),in-situ GBD from magnet surface during hot pressing and hot deformation(in-situ GBD 2#),and conventional GBD,on the magnetic prope...     

Effect of aluminum on microstructure and magnetic properties of sintered Nd-Fe-B magnets processed by grain boundary diffusion of Tb-Al

The grain boundary diffusion process(GBDP) of Tb can improve the coercivity of sintered Nd-Fe-B magnets.In this study,the effect of AI on the diffusion of Tb in the GBDP was investigated.The content of diffused Tb-Al was precisely controlled by adjusting the magnetron sputtering process.The Tb equivalent of Al was also studied.Results show that AI promotes the diffusion of Tb deeper into the magnet,reducing the thickness of the shell in the core-shell structure.This study is helpful for further ...     

Effect of grain boundary diffusion of terbium on mode of mechanical fracture of sintered NdFeB magnets

Grain boundary diffusion process(GBDP) is a widely used method of increasing the coercivity of sintered NdFeB magnets.In this study,the effects of the GBDP on the bending strength and microhardness of sintered NdFeB magnets and the fracture mode were investigated.Results show that the bending strength of magnets is reduced by pickling and heat treatment and greatly recove rs after heavy rare earth element(Tb) grain boundary diffusion.The pickling and the heat treatment cause a slight decrease in...     

Influence of Pr-Al-Co alloy diffusion source on magnetic properties and microstructure of sintered Nd-Fe-B magnets processed by grain boundary diffusion

In this study, the influence of the content of Al and Co in the diffusion source on the magnetic performance and microstructure of the diffused magnet was studied by grain boundary diffusion treatment with Pr₇₀Al_30–xCo_x (x = 0 at%, 10 at%, 15 at%, 20 at%, 30 at%) alloys. When the Co content in the diffusion source increases from 0 at% to 10 at%, the coercivity enhancement in the Pr₇₀Al₂₀Co₁₀ diffused magnet is the highest, increased from 1.62 to 2.24 T, higher than 2.01 T of the Pr₇₀Al₃₀ diffused magnet. With further increase of Co content in the diffused source, the coercivity of the diffused magnet decreases gradually, the coercivity of Pr₇₀Al₁₅Co₁₅, Pr₇₀Al₂₀Co₁₀ and Pr₇₀Co₃₀ diffused magnet is 2.15, 1.99 and 1.81 T, respectively. Microstructural analysis shows that plenty of continuous grain boundary phases (CGBPs) can be formed in the Pr₇₀Al₂₀Co₁₀ diffused magnet under the synergistic effect of Al and Co, which leads to the enhancement of magnetic isolation between more adjacent grains. However, the amount of CGBP in the diffused magnets gradually decreases with the further increase of Co content in the diffusion source.     

Tailoring the mechanical anisotropy of sintered NdFeB magnets by PrCu grain boundary reconstruction

Pr_(83)Cu_(17)(wt%) grain boundary reconstruction was applied to prepare sintered NdFeB magnets. The effects of addition amount and annealing on the bending strength were investigated. The results show that Pr_(83)Cu_(17) can not only effectively enhance the bending strength, but also change the mechanical anisotropy in two directions parallel and perpendicular to c-axis. The bending strength perpendicular to c-axis reaches 404 MPa in 10 wt% addition magnet, higher than 348 MPa along parallel direction. This change is attributed to the preferred distribution of boundary phases, i.e., ductile(Nd,Pr)-Fe-Cu phase along perpendicular direction to c-axis and(Nd,Pr)-Fe phase along parallel direction. Moreover, the Cu migration during 480 ℃ annealing is found to be related to this boundary phase distribution.     

Effect of yttrium substitution on magnetic properties and microstructure of Nd-Y-Fe-B nanocomposite magnets

The phase evolution,microstructure and magnetic properties of Nd9-xYxFe72Ti2Zr2B15(x=0,0.5,1,2) nanocomposite ribbons were investigated.It was found that substitution of Y enhanced glass forming ability of the over-quenched ribbons and stabilized the amorphous phase during post annealing treatment.Appropriate content of Y substitution effectively refined the microstructure and enhanced the remanence of the annealed samples.The residual amorphous intergranular phase in the annealed sample improved the square...     

Relationship between controllable preparation and microstructure of NdFeB sintered magnets

The double hard magnetic phase magnets with nominal compositions of Nd_30–xDy_xFe₆₉B₁(x=2, and 4) (wt.%) were prepared. The magnetic properties of the magnets were measured with a NIM-2000H hysteresigraph. The crystalline structures of the magnets were identified by X-ray diffraction (XRD). The Rietveld refinement was carried out using the FULLPROF software. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were carried out in order to investigate the microstructure of the magnets. It showed that the magnets consisted mainly of Nd₂Fe₁₄B phase, and some Nd-rich phase. Two types of matrix-phase grains in dark grey and light grey were found in the magnets with x=2 and 4. The Dy content was obviously different in the two types of grains, which proved that the double hard magnetic phases (Dy-rich and Dy-lean phases) coexisted in the magnet. It revealed that the Nd-rich phases in junction regions had fcc structure, with the unit cell parameter of about 0.52–0.56 nm. The weak superlattice spots were found in the SAD patterns of the junction Nd-rich phases with large scale. The double hard magnetic phase structure seemed to improve the magnetic properties of NdFeB magnets with high coercivity, while decrease the consumption of Dy element, compared with the single alloy magnet.     

Dependence of magnetic properties on microstructure and composition of Ce-Fe-B sintered magnets

In this paper,dependence of magnetic properties on microstructure and composition of Ce-Fe-B sintered magnets with Cu-doped Ce-rich alloy addition was investigated.It shows that the maximum energy product(BH)_(max) and coercivity H_(cj) of Ce-Fe-B sintered magnet are improved from 6.76 to 9.13 MGOe by 35.1%,and from 1.44 to 1.67 kOe by 16.0%,respectively,via adding 5 wt% liquid phase alloy of Ce_(35.58)Fe_(57.47)Cu_6 B_(0.95)(at%).Compared with the magnet without Cerich alloy addition,the volume fraction of the grain-boundary phase with low melting point increases in the magnet with Ce-rich alloy additio n,which is be ne ficial to imp roving the microstructure and promoting the coercivity enhancement of the magnet.In the Ce-Fe-B magnet with Ce-rich alloy addition,Cu and Ce enrich in the grain boundaries of the magnet after annealing,therefore the as-annealed magnet has a higher coercivity than the as-sintered magnet.A distinct Fe-rich layer with the average thickness of 60 nm is found in the grain boundaries in the magnet without Ce-rich alloy addition,but it seems that Fe-rich phase disappears in the magnet with Ce-rich alloy addition.The present work suggests that the further improvement of coercivity in the Ce-Fe-B sintered magnets is expectable by designing the composition and structure of added liquid phase alloys.     

Influence of gadolinium on microstructure and magnetic properties of sintered NdGdFeB magnets

The effect of Gd content on microstructure and magnetic properties of sintered Nd33.03-xGdxFe65.65B1.32 (x=0-2) was studied in this paper to improve the thermal stability of NdFeB and to reduce the raw material cost. The results showed that better magnet performance could be obtained by adding Gd (0-1.5 wt.%) with partial substitution of Nd in Nd33.03-xGdxFe65.65B1.32. It was also found that the Nd33.03-xGdxFe65.65B1.32 magnets showed the best performance when Gd addition increased to 1.0 wt.%. The temperature coefficient Br (α) could be improved from -0.15%/oC to -0.063%/oC (maximum work temperature 120 oC) and the Curie temperature could be improved from 315 oC to 323 oC because the Gd2Fe14B had positive temperature coefficient Br (α) and higher Curie temperature than that of Nd2Fe14B. The coercivity could be improved from 10.2 to 11.48 kOe and the microstructure was close to ideal microstructure. The magnetic performance decreased sharply by adding Gd (above 2 wt.%) with partial substitution of Nd in Nd33.03-xGdxFe65.65B1.32 because the Gd element concen-trated in the grain boundaries.