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Thermal stability improvement and microstructure optimization of high cobalt content Nd-Fe-B magnets via terbium grain boundary diffusion

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Journal of Rare Earths 2024年第8期42卷 1531-1538,I0004页

作者： Jiyuan Xu Ruiyang Meng Jing Liu Jiateng Zhang Rui Han yikun fang Shengzhi Dong Wei Li Division of Functional Materials Research Central Iron and Steel Research InstituteBeijing100081China

The substitution of Fe by Co in the 2:14:1 phase is an effective method to increase the Curie temperature and enhance the thermal stability of the Nd-Fe-B ***,the accumulation of Co ele ment at the grain boundaries(GBs) changes the GBs from nonmagnetic to ferromagnetic and causes the thinlayer GBs to become rare,In this paper,the method of diffusing Tb element was chosen to improve the microstructure and temperature stability of high-Co *** original sintered Nd_(28.5)Dy_(3)-CO_(x)e_(bal)M_(0.6)B_(i)(x=0,6 wt%,12 wt%;M = Cu,Al,Zr) magnets with different Co contents were diffused with Tb by grain boundary diffusion(GBD).After GBD,high-Co magnets exhibit more continuously distributed thin-layer GBs,and their thermal stability is significantly *** high-Co magnets(x=6 wt%),the absolute value of the temperature coefficient of coercivity decreases from 0.603%/K to0.508%/K in the temperature range of 293-413 K,that of remanence decreases from 0.099%/K to 0.091%/K,and the coercivity increases from 18.44 to 25.04 *** electron microscopy(TEM)characterization reveals that there are both the 1:2 phase and the amorphous phase in the high-Co magnet before and after GBD,EDS elemental analysis shows that Tb element is more likely to preferentially replace the rare earth elements in the 2:14:1 main phase than in the 1:2 phase and the amorphous *** concentration of Tb at the edge of the main phase is much higher than that in the 1:2phase and amorphous phase,which is beneficial to the improvement of the *** preferential replacement of Tb elements at the edge of the 2:14:1 phase and thin-layer GBs with a more continuous distribution are synergistically responsible for improving the thermal stability of high-Co *** study indicates that GBD is an effective method to improve the microstructure and thermal stability of high-Co magnets.

关键词： Nd-Fe-B magnets Coercivity Grain boundary diffusion Thermal stability Micro structure Rare earths

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Optimizing temperature coefficient of Sm2Co17-type magnets through adjusting the isothermal aging process

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Journal of Rare Earths 2024年第11期42卷 2097-2104页

作者： Chao Wang Die Hu Qiangfeng Li yikun fang Meng Zheng Lei Wang Hongsheng Chen Lei Zhao Haizhou Wang Minggang Zhu Wei Li Division of Functional Materials Research Central Iron and Steel Research Institute Shanghai Aerospace Control Technology Institute Beijing Advanced Innovation Center for Materials Genome Engineering Central Iron and Steel Research Institute Beijing Key Laboratory of Metal Materials Characterization Central Iron and Steel Research Institute

The high-temperature magnetic perfo rmance and micro structure of Sm1-xGdx(CobalFe0.09Cu0.09Zr0.025)7.2（x=0.3,0.5） magnets were *** the isothermal aging time decreasing from 11 to 3 h,the temperature coefficient of intrinsic coercivity in the temperature range of 25-500℃,β25-500℃,was optimized from -0,167%/℃ to-0.112%/℃ for x=0.3 *** noticeable enhancement（～33%） of temperature stability is correlated with the increased content of 1:5H cell boundary phase and its relatively high Curie temperature as ***,for the x=0.5 magnet,it is found that the presence of Sm5Co19phases and wider nanotwin variants hinder the formation of 1:5H cell boundary *** insufficient 1:5H is not beneficial to the proper redistribution of Cu in cell boundary,making the x=0.5 magnet difficult to achieve higher temperature ***,the approach of adjusting the isothermal aging process can offer guidance for attaining superior magnetic performance in the temperature range from 25 to 500℃ for Gd-substituted Sm2Co17-type magnets.

关键词： Isothermal aging process Rare earths Sm2Co17-type magnets Temperature coefficient of intrinsic coercivity

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Magnetic microstructure and coercivity mechanism of high performance Nd-Fe-B magnets

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Rare Metals 2006年第Z1期25卷 630-632页

作者： ZHU Minggang LIU Xingmin fang yikun LI Zhengbang LI Wei Central Iron & Steel Research Institute Beijing 100081 China Central Iron & Steel Research Institute Beijing 100081 China Central Iron & Steel Research Institute Beijing 100081 China Central Iron & Steel Research Institute Beijing 100081 China Central Iron & Steel Research Institute Beijing 100081 China

Magnetic microstructure of high performance Nd-Fe-B magnets was investigated by using magnetic force microscopy. The correlation between magnetic microstructure and coercivity for high performance Nd-Fe-B magnets was studied. It is found that the magnets with different coercivity mechanism take on different microstructures and magnetism. Moreover, the magnetic microstructures of high performance permanent magnets can be explained by the starting field theory model.

关键词： Nd-Fe-B permanent magnets magnetic domains reversal of magnetism starting field theory

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Correlation of mechanical anisotropy with fine grain strengthening for Sm_(2)Co_(17)-type sintered permanent magnets

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Journal of Rare Earths 2022年第10期40卷 1584-1591页

作者： Lei Wang Chao Wang Qiangfeng Li Youhao Liu yikun fang Xiaofei Yi Wei Li Division of Functional Materials Research Central Iron and Steel Research InstituteBejing 100081China State Key Laboratory of Rare Earth Permanent Magnetic Materials Hefei 231500China

The as-solution-treated Sm_(2)Co_(17)-type magnets exhibiting a single 1:7 H phase with different average grain sizes(D) were *** of bending strength(R_(bb))and compressive strength(R_(mc)) of the magnets were ***,the R_(bb) increases from 86 to 173 MPa with D decreasing from~52 to~18 μm for group c//h *** Hall-Petch correlation was employed to reveal the effect of grain size on mechanical properties of the magnets,giving deep understanding of the mechanical anisotropy *** relatively high Hall-Petch coefficient K^(Rbb)(0.79 MPa·m^(1/2)) gives rise to the largest R_(bb)(173 MPa) for group c//h *** mechanical anisotropy of the samples is well explained based on crystal structure and grain size features(grain boundaries).Grain refinement is an effective way to enhance the mechanical properties of Sm_(2)Co_(17)-type sintered magnets.

关键词： Sm_(2)Co_(17)-type permanent magnets Grain refinement Bending strength Compressive strength Anisotropy Rare earths

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Analysis of NdFeB multi-pole ring by SEM and MFM

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Rare Metals 2006年第Z1期25卷 489-492页

作者： LIU Xingmin LI Xiumei fang yikun ZHU Minggang HAN Baoshan LI Wei Central Iron & Steel Research Institute Beijing 100081 China Central Iron & Steel Research Institute Beijing 100081 China Central Iron & Steel Research Institute Beijing 100081 China Central Iron & Steel Research Institute Beijing 100081 China State Key Laboratory of Magnetism Institute of Physics and Center of Condensed Matter Physics CAS Beijing 100080 China Central Iron & Steel Research Institute Beijing 100081 China

Sintered multi-pole ring that is made in America and China was analysed by SEM and MFM. The results show that the average size of American multi-pole ring is much smaller than the Chinese one and has much better orientation degree. The magnetic field of American specimen is much higher than that of the Chinese one and its average value is about 500 Gs, and more uniform distribution of the Nd-rich phase has been obtained.

关键词： ring NdFeB SEM

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Superior corrosion resistance and corrosion mechanism of dual-main-phase (Ce_(15)Nd_(85))_(30)Fe_(bal)B_(1)M magnets in different solutions

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Journal of Rare Earths 2023年第1期41卷 122-129页

作者： Yaping Wu Minggang Zhu Qisong Sun Lele Zhang Peng Shen yikun fang Wei Li Division of Functional Materials Research Central Iron and Steel Research InstituteBeijing 100081China School of Materials Science and Engineering Northeastern UniversityShenyang 110819China

The electrochemical corrosion behavior of both (Ce_(15)Nd_(85))_(30)Fe_(bal)B_(1)M sintered magnets prepared with dual-main-phase method and N45-type magnets was studied in 3.5 wt% NaCl,1.1 wt% NaH_(2)PO_(4),and 2.5 wt% NaOH solutions,*** (Ce_(15)Nd_(85))_(30)Fe_(bal)B_(1)M sintered magnets perform superior corrosion resistance than N45-type magnets in the tested *** general,two kinds of magnets exhibit the best corrosion resistance property in 2.5 wt% NaOH solution,while the worst in 3.5 wt% NaCl *** of samples before and after corrosion were *** the addition of Ce by means of dual-main-phase method,which is conducive to facilitating low-temperature sintering and grain refinement,uniform grain size and(Nd,Ce)-rich phase distribution form,give rise to narrow and thin corrosion ***,the corrosion rate of the(Nd,Ce)-rich phase is lower than that of Nd-rich *** rdingly,corro sion re sistance of (Ce_(15)Nd_(85))_(30)Fe_(bal)B_(1)M sintered magnet is superior when compared with the commercial N45-type magnet which has comparable magnetic properties.

关键词： Sintered Nd-Fe-B magnet Electrochemical corrosion behavior Dual-main-phase method Electrolyte solution Corrosion mechanism Rare earths

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Magnetic properties,crystalline and magnetic microstructures of dual-main-phase(Nd,Ce)-Fe-B sintered magnets

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Journal of Materials Science & Technology 2023年第31期162卷 99-108页

作者： Yifei Xiao Lele Zhang Tao Liu Xiaolong Song Qisong Sun yikun fang Minggang Zhu Wei Li Division of Function Materials Center Iron and Steel Research InstituteBeijing 100081China

The(Nd,Ce)-Fe-B sintered magnets were prepared by a dual-main-phase(DMP)process under the same conditions using different combinations of Nd-Fe-B with Ce-Fe-B and(Nd,Ce)-Fe-B *** crystalline and magnetic microstructures of DMP(Nd,Ce)-Fe-B magnets with the remanence of 11.92-12.68 kGs,the intrinsic coercivity of 3.97-5.31 kOe,and the maximum energy product of 23.08-32.99 MGOe have been *** force microscope(MFM)investigations reveal that the DMP(Nd,Ce)-Fe-B magnets show maze-like patterns,which are like that of standard anisotropy Nd-Fe-B sintered magnets by and ***,much finer domain structures mixing with coarse ones can be observed obviously in DMP(Nd,Ce)-Fe-B sintered *** size distribution of the domain width of the DMP(Nd,Ce)-Fe-B magnet is not uniform *** average domain width is W=0.912μm,and the fine domain width has only 0.216μ*** smaller domain width and more branch domain patterns exist in poorer coercivity DMP *** is caused by the non-uniform Ce composition of poorer property DMP magnets and the grain boundary microstructure that is not conducive to improving the ***,it is found that some domains of rare-earth-rich grain boundary phases exhibit the characteristics of plate-like patterns rather than no-contrast by using MFM,indicating their *** correlations between the crystalline microstructure,chemical composition of phases,and magnetic structure were demonstrated for the DMP magnets.

关键词： Magnetic microstructures Dual-main-phase(DMP) (Nd,Ce)-Fe-B Core-shell structure Magnetic force microscope

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Microstructures and magnetic properties of Ce_(32.15)_Co_(49.36)Cu_(9.84)Fe_(9.65) magnet sintered at different temperatures

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Rare Metals 2012年第5期31卷 470-473页

作者： SUN Wei ZHU Minggang fang yikun PAN Wei LI Jiajie LI Yanfeng LI Wei Division of functional Materials Central Iron and Steel Research Institute Group Beijing 100081 China

The microstructures and magnetic properties of Ce-32.15Co_49.36Cu_9.84Fe_9.65 magnet sintered at the temperatures ranging from 1005 to 1105 °C were investigated. The results on scanning electron microscopy and X-ray diffraction analysis indicate that the remanence B r of the magnets is mainly influenced by the degree of the easy-axis orientation when sintering temperature is less than 1085 °C, the rapidly increasing amount of the secondly phase (5:19 phase) gives rise to the deterioration of the magnetic properties of the magnet above 1085 °C. Moreover, it is found that intrinsic coercivity H ci is strongly related to the content of copper in the matrix of the sintered magnets. The optimal sintering temperature is located in 1025~1055 °C, the corresponding magnetic properties of the magnets are B_r =0.685T, H_(ci) =350kA·m^-1 , and maximum energy product (BH)_m =85.6 kJ·m 3 .

关键词： Ce-Co permanent magnet sintering temperature coercivity

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Cellular microstructure modification and high temperature performance enhancement for Sm2Co17-based magnets with different Zr contents

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Journal of Materials Science & Technology 2022年第25期120卷 8-14页

作者： Chao Wang Peng Shen yikun fang Shuai Wang Qiangfeng Li Lei Wang Wei Li Minggang Zhu Division of Functional Materials Research Central Iron and Steel Research InstituteBeijing 100081China

Influence of Zr contents on high-temperature magnetic performance of Sm(CoFeCuZr)(x=0.025,0.03,0.035,0.04) magnets were *** x increases from 0.025 to 0.04,the temperature coefficient of intrinsic coercivity(H) is optimized from-0.1673% K^(-1)to-0.1382% K^(-1)and the Hat 773 K gradually increases from 556.32 kA m^(-1)to 667 kA m^(-1).The microstructure and microchemistry of different Zr-content magnets were revealed by a transmission electron microscope equipped with *** increasing Zr content induces that the average size of cells decreases from ~76 nm to ~56 nm and the weight fraction of 1:5 H cell boundary phase increases from ~25% to ~37% as well,resulting decreasing of the average Cu content at cell boundaries from 13.59 at% to ~8.52 at%.It is found that the Cu-lean characteristic at cell boundary phase is the reason that gives rise to higher magnetic properties at elevated temperatures for x=0.04 magnet.

关键词： Sm2Co17-type magnets Zr content High temperature magnetic properties FROC diagram

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Optimization of microstructures and magnetic properties of Sm(Co_(bal)Fe_(0.227)Cu_(0.07)Zr_(0.023))_(7.6) magnets by sintering treatment

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Journal of Rare Earths 2019年第2期37卷 171-177页

作者： Kuikui Songa Wei Suna yikun fang Shuai Wang Nengjun Yu Meiling Zhang Minggang Zhu Wei Li Division of Functional Materials Research Central Iron and Steel Research Institute

Magnetic properties and microstructures of Sm(Co_(bal)Fe_(0.227)Cu_(0.07)Zr_(0.023_)_(7.6) sintered magnets were optimized by sintering treatment. Results show that the knee-point magnetic field, Hknee, is twofold up and the intrinsic coercivity Hcjincreases by 40%, ranging from 21.64 to 30.39 kOe at the cost of a little decrease of Brfrom 10.84 to 10.31 kGs with sintering temperature decreasing from 1488 to 1473 K. And the average domain width is narrower and more uniform for the specimen sintered at 1473 K than that of the specimen sintered at 1488 K. It is impressive that the density of lamellar phase increases from ~0.050 to ~0.058 nm^(-1) with the sintering temperature decreasing from 1488 to 1473 K. Moreover, the average cellular size is about ~84 nm for the magnets sintered at 1473 K, which is 80% of that of the magnets sintered at 1488 K(~97 nm). And the cell boundary width of the magnets sintered at 1473 K(~7 nm) is only half average width of the magnets sintered at 1488 K(~14 nm). It is found that the Cu content in the cell boundaries is much higher(~17 at%) in the magnets sintered at 1473 K compared to that of the magnets sintered at 1488 K(~10 at%). It can be concluded that smaller cells and narrower cell boundaries together with higher gradient of Cu content are key points for obtaining the optimum Hkneeand Hcj.

关键词： Sm-Co magnets Sintering Coercivity Microstructure Rare earths

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