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Coercivity enhancement of hot-deformed NdFeB permanent magnets with AlCuZn eutectic alloy grain boundary diffusion

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Rare Metals 2022年第1期41卷 226-231页

作者： Ye-Qi yu Kuo-She Li Hai-Jun Peng Xin-yuan Bai Ning-Tao Quan Kai-Wen Wu Yang Luo dun-bo yu National Engineering Research Center for Rare Earth Materials General Research Institute for Nonferrous MetalsBeijing 100088China GRIREM Advanced Materials Co.Ltd.Beijing 100088China

It is approved that grain boundary diffusion is an effective method to increase the coercivity of hot-deformed NdFeB magnet.In this paper,a new rare earth-free grain boundary diffusion source of hot-deformed magnet was studied.AlCuZn powders blended with commercial NdFeB powders were hot-compacted to obtain fully dense magnets,hot-deformed into anisotropic magnets and finally annealed to gain better homogeneity.Initially,the influences of annealing temperature and time on the magnetic properties of the specimens were studied and the optimal parameters of 600℃ and 60 min were achieved.Then,by changing the proportions of AlCuZn grain boundary diffusion,the coercivity,remanence and maximum energy product of the hot-deformed NdFeB magnets were examined.The result showed that with 1.0 wt%AlCuZn grain boundary diffusion and annealing at 600℃ for 60 min,the coercivity rose from 828 to 987 kA·m^(-1) without deteriorating the remanence.Microstructural analysis confirmed that AlCuZn diffused into the intergranular boundaries and the magnet diffused with AlCuZn possessed finer grains than that of without AlCuZn grain boundary diffusion.

关键词： AlCuZn Grain boundary diffusion Hotdeformed Coercivity enhancement

Structure,nitridation efficiency and magnetic properties of SmFe powders and its nitrides

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Rare Metals 2023年第6期42卷 1983-1988页

作者： Xiao-Xia Chen Yang Luo Zhou Hu Wen-Long Yan Ning-Tao Quan Shuo Lu dun-bo yu Jia-Jun Xie National Engineering Research Center for Rare Earth Grirem Advanced Materials Co.Ltd.Beijing100088China

The effect of annealing temperature(TA) at600-900℃ on structure and magnetic properties of the melt-spun Sm_(8.6)Fe_(85.9)Co_(4.3)Zr_(1.2) alloys and its nitrides was investigated.Results show that the melt-spun powder is TbCu7-type SmFe_(9) single phase.X-ray diffractometer(XRD) Rietveld refinement shows that the lattice parameter a increases,c and c/a decrease with the increase in T_(A) at600-700℃.This is due to the tendency of nitrogen entering into the 3f site(1/2,0,0) during the nitridation process,which is good for the magnetic properties.The phase transforms from TbCu7-type SmFe_(9) to Th_(2)Zn_(17)-type Sm_(2)Fe_(17) at above 800 0C.Scanning electron microscopy(SEM) images show that the amount of surface defects of melt-spun powder which are harmful for magnetic properties decreases at first and then increases as TA increases.The coercivity(H_(cj)) and maximum magnetic energy product((BH)_(max)) of its nitrides increase first and then decrease as a function of TA.And the remanence(B_(r))always shows a decrease.The optimal magnetic properties of H_(cj)=748 kA·m^(-1),B_(r)=0.92 T,(BH)_(max)=118 kJ·m^(-3) are obtained by annealing at 675℃ for 2 h and then nitriding at 460℃ for 10 h.

关键词： Melt-spun alloy Annealing temperature Magnetic property XRD Rietveld refinement

Hard magnetic properties of melt-spun nanocomposite Y_(16)Fe_(78)B_(6)ribbons

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Rare Metals 2023年第2期42卷 602-605页

作者： Liang Sun Kuo-She Li Hong-Wei Li dun-bo yu Yang Luo Jin-Ling Jin Shuo Lu Ning-Tao Quan GRIREM Advanced Materials Ltd General Research Institute for Nonferrous MetalsBeijing100088China

Melt-spun Y_(16)Fe_(78)B_(6)ribbons were prepared by the melt-spinning technique with pure elements Y,Fe and Fe-B alloy n argon.The ribbons are mainly composed of Y_(2)Fe_(14)B,YFe_(2)andα-Fe phases.Amorphous phase appears at the wheel velocity of>35 m·s^(-1).For the ribbons prepared at optimum wheel velocity and heat treatments,the coercivity,remanence and maximum energy product are239.5 kA·m^(-1),0.61 T and 32.7 kJ·m-3,respectively.By an investigation of Henkel plots of ribbons,it is found that intergrain exchange coupling leads to the enhancement of remanence.The coercivity mechanism of ribbons prepared at 35 m·s^(-1)is mainly controlled by inhomogeneous pinning of domain walls.The phase component and magnetic properties change with annealing temperature and time.The optimum magnetic properties are obtained with the ribbon quenched at 35 m·s^(-1)and annealed at 700℃for10 min.

关键词： Melt spinning Permanent magnets Y-Fe-B alloys Magnetic hardening

Structural transformation and magnetic properties of Sm-Fe alloys with V doping

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Rare Metals 2022年第7期41卷 2349-2352页

作者： Yong-Jun Mao Jin-Ling Jin Jia-Jun Xie Yang Luo Kuo-She Li Wen-Long Yan dun-bo yu Hong-Wei Li National Engineering Research Center for Rare Earth Materials General Research Institute for Nonferrous MetalsBeijing 100088China Grirem Advanced Materials Co.Ltd. Beijing 100088China

A systematical investigation was carried out on structure and magnetic properties in SmFe_(9-x)V_(x)(x=0.4,0.8,1.2)compounds prepared by a single-roller quenching method.The high cool-down rate leads to metastable TbCu_(7) phase in the parent compound,which gradually transforms into equilibrium ThMn_(12) structure with V-doping content increasing.The Curie temperature increases from 470 to 590 K with V doping,which is consistent with the phase transformation.Surprisingly,simultaneous increase in both coercivity and remanence is resulted by V doping,reaching the highest value of 685 kA·m^(-1)and 44.8×10^(-3)A·m^(2)·g^(-1)in x=1.2 compound,respectively.This phenomenon can be explained by the combination of phase transformation and intergranular exchange coupling throughδM-H plots.

关键词： Phase transformation Magnetic properties Exchange coupling Element doping ThMn12-type phase

Preparation and properties of hot-deformed magnets processed from nanocrystalline/amorphous Nd-Fe-B powders

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Rare Metals 2021年第8期40卷 2033-2039页

作者： Peng Zhao Yang Luo dun-bo yu Hai-Jun Peng Wen-Long Yan Zi-Long Wang Xin-yuan Bai National Engineering Research Center for Rare Earth Materials General Research Institute for Nonferrous MetalsBeijing100088China Grirem Advanced Materials Co. LtdBeijing100088China

The hot-deformed magnets processed from nanocrystalline/amorphous Nd-Fe-B powders were preparedunderdifferenthot-pressingtemperatures(600-750℃,at intervals of 25℃)by the self-made hotpressing equipment.The microstructure and magnetic properties of hot-deformed magnets prepared at different temperatures were also investigated.When the temperature is above 650℃,the density of magnet reaches 7.5 g·cm^(-3).The optimum magnetic properties of magnetic induction intensity of B_(r)=1.3 T,optimum energy product of(BH)_(max)=282.5 kJ·m^(-3),intrinsiccoercivityof H_(cj)=1130.0 kA·m-1 of hot-deformed magnets are obtained at hot-pressing temperature of 650℃.X-ray diffractometer pattern shows that the(00 L)texture has been obtained.For the microstructural characteristic,on the one hand,the good magnetic performance is attributed to the fine platelet-like grains with an average length of 410-440 nm at the hot-pressing temperature range from625 to 675℃.On the other hand,the unaligned coarse grains are observed in all the samples.And the areal fraction of those is gradually increasing with the rise of the hot-pressing temperature,which tends to deteriorate the magnetic properties.The composition map shows the accumulation of Nd/Pr-rich phase in the coarse grains’region.

关键词： Nanocrystalline/amorphous powders Hotpressing temperature Hot-deformed Magnets Magnetic properties Microstructure

Crystal structure and magnetic properties of SmFe_(9-x)Co_x alloys

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Rare Metals 2014年第1期33卷 54-57页

作者： Yang Luo dun-bo yu Hong-Wei Li Wei-Dong Zhuang Kuo-She Li Wen-Long Yan National Engineering Research Center for Rare Earth Materials General Research Institute for Nonferrous Metals Grirem Advanced Materials Co. Ltd

The crystal structure and magnetic properties of SmFeg_xCox （x = 0, 1, 3, 5） alloys were studied by X-ray powder diffraction （XRD） and magnetic measurements. The Th2Znl7-type structure of the as-cast state is changed to TbCu7-type structure after quenching to a rotating molybdenum roll under certain velocity （12, 20, and 32 m.s-l）. The （002） XRD peak appears and ^-Fe phase disappears when the Co is added up to x = 5. Saturation magnetization of SmFe9 under different temperature shows 9 % change （112-102 A.m2.g-1） when the temperature is higher than 200 K. The saturation magnetization is 115 A.m2.g-1 and coercivity is 0.304 T at 5 K for SmFe9 alloys. Increased saturation magnetization and decreased coercivity can be obtained for Co added up to x = 5 at 5 K.

关键词： TbCu7-type Crystal structure SmFe Magnetic properties

Magnetic properties optimization of nanocomposite Nd_9Fe_(85)B_6 magnets by controlling microstructure of as-quenched ribbons

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Rare Metals 2014年第3期33卷 299-303页

作者： yu-Chao Liu Hong-Wei Li Kuo-She Li dun-bo yu Jin-Ling Jin Yang Luo Liang Sun Ning-Tao Quan National Engineering Research Center for Rare Earth Materials General Research Institute for Nonferrous Metals

To optimize the magnetic properties of nanocomposite Nd9Fe85B6 magnets, the as-quenched ribbons with different microstructures were prepared at six wheel velocities from 10 to 30 m s^-1through rapid quenching,followed by a series of annealing treatments at 550-800 °C for 5-10 min. It is found that both the large initial grains at low cooling rate and high content of amorphous phase at high cooling rate cause a-Fe grains coarsening, which leads to a decline in the strength of exchange coupling interaction and the deterioration of magnetic properties. In order to optimize the magnetic properties, the as-quenched ribbons should be chosen with relatively small initial grains as well as a small amount of amorphous phase. For nanocomposite Nd9Fe85B6 materials, the optimized magnetic properties of Hcj= 446 kA m^-1, Br= 0.86 T,（BH）max=80 kJ m^-3are obtained for ribbons prepared at 18 m s-1after annealing at 620 °C for 5 min.

关键词： Nanocomposite Rapid quenching Microstructure Grain sizes

Permanent magnetic properties of Nd-Fe-B melt-spun ribbons with Y substitution

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Rare Metals 2020年第1期39卷 55-61页

作者： Cao-Huan Zhang Yang Luo dun-bo yu Ning-Tao Quan Gui-Yong Wu Ya-Kun Dou Zhou Hu Zi-Long Wang National Engineering Research Center for Rare Earth Materials General Research Institute for Nonferrous MetalsBeijing100088China Grirem Advanced Materials Co.Ltd Beijing100088China

Phase constituents,microstructures and magnetic properties of melt-spun Nd12-xYxFe81B6 Nb ribbons were investigated systematically.The influence of Y substitution for Nd on the phase stability,grain size and magnetic exchange coupling was analyzed.It is found that all the ribbons crystallize in the tetragonal 2:14:1 structure,i.e.,with single hard magnetic phase at the roll speed of25 m s-1.With the increase in Y doping,Curie temperature(Tc)increases,while the coercivity decreases monoclinic ally.However,remanence magnetization(Br)and maximum energy product((BH)max)fluctuate and the maximum value is obtained at certain amount of Y.The optimum magnetic properties of intrinsic coercivity of intrinsic coercivity(Hcj)=908.2 kA·m-1 and(BH)max=118.52 kJ·m-3 are achieved when x=1.0.It can be attributed to the strengthened exchange coupling between the neighboring nanograins in Nd-Y-Fe-B meltspun powder based on the Henkel curves.Furthermore,Y substitution also significantly improves the temperature stability of magnetic performance.The coercivity temperature coefficient ofβ=-0.157%·℃-1 and remanence temperature coefficient ofα=-0.32%·℃-1 are gained,which are greatly reduced compared with those of the undoped Nd-Fe-B compounds.

关键词： Rapid quenching (Nd,Y)-Fe-B alloy Exchange coupling Thermal stability

Structure and magnetic properties of TbCu_7-type melt-spun Sm–Fe–B alloys

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Rare Metals 2019年第2期38卷 151-156页

作者： Chuan-Jiang Zheng Yang Luo dun-bo yu Wen-Long Yan Hong-Wei Li Yong-Jun Mao Shuo Lu Ning-Tao Quan National Engineering Research Center for Rare Earth Materials General Research Institute for Nonferrous Metals Grirem Advanced Materials Co. Ltd.

The melt-spun SmFe_(12)B_x(x = 0, 0.50, 0.75,1.00, 1.25 and 1.50) ribbons were prepared at 40 m·s^(-1),and their structure and magnetic properties were studied by powder X-ray diffraction(XRD), vibrating sample magnetometer(VSM) and transmission electron microscopy(TEM). XRD results indicate that SmFe_(12)B_x alloys with 0.50 ≤ x ≤ 1.00 are composed of single-phase TbCu_7-type structure. Moreover, it is found that the boron addition can inhibit the emergence of soft magnetic phase a-Fe and result in the increase in the axial ratio c/a. After annealing at 650 ℃ for 0.5 h, the metastable phase TbCu_7 initially decomposes into the stable phase Sm_2Fe_(14)B(Nd_2Fe_(14)B-type) and a-Fe. The value of magnetic moment per Fe atom increases slightly from 1.75 uB for boron-free sample to 1.80 uB for the x = 0.75 sample and then decreases again.In addition, the best magnetic properties of maximum energy product [(BH)_(max)] of 14.56 kJ·m^(-3), coercivity(H_(cj))of 172.6 kA·m^(-1) and remanence(B_r) of 0.45 T are obtained for the SmFe_(12)B_(1.00) alloy. Based on transmission electron microscopy(TEM) results, the average size of grains is around 197 nm for B-free sample and decreases to 95 nm for x = 1.00 sample, indicating that the addition of boron can refine grains.

关键词： TbCu7-type structure Sm-Fe-B ribbons Phase formation Magnetic moment Microstructure