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Corrosion behavior of dual-main-phased(Nd_(0.8)Ce_(0.2))2Fe_(14)B magnets with and without annealing process

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Rare Metals 2023年第2期42卷 585-590页

作者： Xiao-Ning Shi Ming-Gang Zhu Rui Han Li-Wei Song Wei Li Division of Functional Material Central Iron&Steel Research InstituteBeijing100081China

In this work,the corrosion behavior of the sintered Nd_(2)Fe_(14)B in which Nd was substituted by Ce to form dual-main-phased magnet with/without annealing process was studied.The mass loss of as-sintered magnets(SM)is larger than that of as-annealed magnets(AM)in the accelerated corrosion tests.In particular,the mass loss of SM increases sharply when the corrosion time increases to48 h.The free corrosion current of the SM samples is larger than that of AM in 0.1 mo1·L^(-1)HCl;this is due to that the content of RE-rich phase at the intergranular triple junctions(TJs)of the SM samples is larger than that of AM samples and the corrosion rate of the RE-rich phase at the TJs is higher than that at grain boundaries.But the free corrosion current of the SM samples is smaller than that of AM samples in 3.5 wt%NaCl as the electron transfer resistance(R_(ct))of SM is larger than that of AM.Inductive loop in the Nyquist diagrams at low frequency of SM is observed,which originated from the pitting.It shows that pitting of SM occurs more easily than that of AM.Corrosion morphology of samples indicates that the corrosion area of SM is bigger and deeper than that of AM after accelerated corrosion for 60 h.Through the annealing process,the distribution of rare-earth-rich phase becomes more uniform,which changes the free corrosion current and effectively suppresses the occurrence and propagation of pitting.

关键词： ndfeb magnet Annealing process Intergranular corrosion Pitting corrosion

Influence of the electroplating pretreatment on corrosion mechanism of ndfeb magnets

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Journal of Rare Earths 2016年第2期34卷 152-157页

作者：周巧英李刚刘壮郭帅闫阿儒李东李建忠 Key Laboratory of magnetic Materials and Devices Ningbo Institute of Material Technology and Engineering Chinese Academy of Sciences Ningbo Permanent magnetics Co. Ltd.

The electroplating pretreatment of ndfeb magnets was simulated in this study, and the effect of the pickling process on element, matrix morphology and texture was discussed. The results showed that in the ordinary circumstance the acid solution con-centration should be below 4 mol/L and the pickling time was within 120 s. However the concentration was lower than 1 mol/L and the time was about 30 s in the ultrasonic environment. The precoating technology sequentially was studied. The results revealed that there were two main reactions of the corrosion and displacement in the precoating process, and these two reactions were more obvi-ous in the grain boundary. The electrochemical analysis illustrated that the corrosion and displacement reactions were affected obvi-ously by the current density and the precoating solution temperature, usually the current density was controlled about 0.3 A/dm2, and the temperature was about 318 K in the precoating process.

关键词： ndfeb magnet pickling precoating corrosion pretreatment rare earths

Relationship between controllable preparation and microstructure of ndfeb sintered magnets

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Journal of Rare Earths 2014年第7期32卷 628-632页

作者：李岩峰朱明刚李安华冯海波黄书林李卫杜安齐岩 Division of Functional Materials Central Iron and Steel Research Institute College of Science Northeastern University

The double hard magnetic phase magnets with nominal compositions of Nd30–xDyxFe69B1（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 Nd2Fe14 B 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.

关键词： ndfeb magnet double hard magnetic phase structure Dy content coercivity rare earths

Experimental and Numerical Analysis of Surface magneto-Hydrodynamic Propulsion Induced by ndfeb magnets

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Fluid Dynamics & Materials Processing 2021年第2期17卷 427-439页

作者： Zongkai Liu College of Automation Nanjing University of Science and TechnologyNanjing210094China Nanjing Yue Bo Power System Co. Ltd.Nanjing210094China

The so-called surface magneto-hydro-dynamic(MHD)propulsion relies on the Lorentz force induced in weak electrolyte solutions(such as seawater or plasma)by ndfeb magnets.The Lorentz force plays an important role in such dynamics as it directly affects the structures of flow boundary layers.Previous studies have mainly focused on the development of such boundary layers and related fluid-dynamic aspects.The main focus of the present study is the determination of electromagnetic field distributions around the propulsion units.In particular dedicated experiments and numerical simulations(based on the finite volume method)are conducted considering a NACA0012 airfoil immersed in seawater.The results show that,along the propulsion unit,the field strength undergoes a rapid attenuation in the direction perpendicular to the wall.

关键词： Vector finite element method edge element method ndfeb magnet Lorentz force

MICROSTRUCTURE AND magnetIC HARDENING OF SINTERED ndfeb magnetS DOPPED WIHT Dy OR Dy_2O_3

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Acta Metallurgica Sinica(English Letters) 1992年第11期5卷 351-356页

作者： ZHOU Shouzeng ZHANG Jin MA Deqing GAO Maolin University of Science and Technology Beijing,Beijing,China

The magnetic properties,microstructure and magnetic hardening of sintered (Nd_(1-x)Dy_x)_(16)Fe_(77.2)B_(6.8) and Nd_(16)Fe_(77.2)B_(6.8)+ywt-%Dy_2O_3 magnets have been stud- ied.As an addition of Dy to the magnet during smelting,Dy atoms may enter the matrix phase Nd_2Fe_(14)B,so as to enhance H_A,refine grains and improve boundary struc- ture,as well as to increase H_(ci)of the magnet.If Dy_2O_3 is added to powder material prior to sintering,Dy atoms diffuse into the epitaxial layer of grains of matrix phase causing enhancement of K′_1,also refinement of grains and improvement of boundary structure.The ndfeb based permanent magnets with higher H_(ci) and greater(BH)_m may be produced by adding about 2—3 wt-% Dy_2O_3 which make a favourable condition for lower cost.

关键词： ndfeb magnet coercivity microstructure Dy Dy_2O_3

Microstructure and magnetic properties of bulk magnets Nd_(14-x)Fe_(76+x)Co_3Zr_1B_6(x=0,0.5,1) prepared by spark plasma sintering

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Journal of Rare Earths 2009年第6期27卷 1023-1026页

作者：马毅龙刘颖李军杜慧龙高静 College of Materials Science and Engineering Sichuan University

Melt-spun ribbons with nominal composition of Nd14–xFe76+xCo3Zr1B6(x=0,0.5,1) were consolidated into isotropic bulk magnets by spark plasma sintering method.It was found that the Nd content and sintering temperature had significant influence on the density and magnetic properties of the sintered magnets.Homogeneous microstructure and fine grain(50–100 nm) were obtained when sintering below 700 ℃,and the initial magnetization curve showed that the coercivity was controlled by the pinning mechanism.However,ab...

关键词： spark plasma sintering ndfeb magnet magnetic properties microstructure rare earths

Investigation of the coercivity mechanism for Nd-Fe-B based magnets prepared by a new technique of strip casting

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Rare Metals 2004年第2期23卷 152-156页

作者： LIBo HUJifan WANGDongling GUOBinglin WANGXinlin DepartmentofFunctionalMaterials CentralIron＆SteelResearchInstituteBeijing100081China DepartmentofPhysics ShandongUniversityJinan250100China

The coercivity mechanism of Nd-Fe-B based magnets prepared by a new techniqueof strip casting was investigated. Different from the traditional magnets, α-Fe phases aredifficult to be found in Nd-Fe-B magnets prepared by strip casting. Meanwhile, the rich-Nd phasesoccur not only near the grain boundaries of main phases, but also within the main-phase grains.Investigation on the magnetizing field dependence of the coercivity for the(Nd_(0.935)Dy_(0.065))_(14.5)Fe_(79.4)B_(6.1) magnet and the temperature dependence of thecoercivity for the Nd_(14.5)Fe_(79.4)B_(6.1) magnet hav been done. Results show that coercivitiesfor strip casting magnets are controlled by the nucleation mechanism.

关键词： ndfeb magnet coercivity mechanism nucleation mechanism strip casting

Time-stability of sintered Nd-Fe-B permanent magnet with lower oxygen content

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Journal of Rare Earths 2010年第S1期28卷 396-398页

作者：刘国征姚宏福夏宁赵明静李波喻晓军 Research Center of Functional Materials Baotou Research Institute of Rare Earth Department of Functional Materials Advanced Technology and MaterialsChina Iron & Steel Research Institute Group Shenyang General magnetic Co. Ltd.

Time-stability of sintered Nd-Fe-B magnet with lower content of oxygen at different temperatures and humidity conditions for 400 d was investigated.Results showed that the magnetic flux loss was-0.68% for the non-electroplating samples and-0.43% for the electroplating samples at room temperature and average humidity was 25% during 400 d,respectively.The magnetic flux loss of the plated samples was lower than non-plated samples under the conditions of room temperature and with the average humidity of 54%,but the magnetic flux loss of the plated samples was larger than that of the non-plated sample at 80 oC.The magnetic flux loss of electroplated and non-electroplated sintered Nd-Fe-B magnets was less than 1% for 400 d,which showed that the N40SH grade magnets have good time stability.

关键词： ndfeb magnet rare earth magnet magnetic flux loss time stability

Investigation of Coercivity Mechanism for Nd-Fe-B magnets Prepared by Combination of Strip-Casting with Hydrogen Decrepitation Techniques

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Journal of Rare Earths 2003年第5期21卷 555-557页

作者：李波胡季帆王东玲郭炳麟王新林 Department of Functional Materials Central Iron & Steel Research Institute Department of Physics Shandong University

The coercivity mechanism of Nd Fe B magnets prepared by combination of strip casting with hydrogen decrepitation techniques was investigated. The microstructure of (Nd 0.935 Dy 0.065 ) 14.5 Fe 79.4 B 6.1 magnet was observed. The average grain size is about 6～12 μm. The magnetizing field dependence of the hardmagnetic properties for the (Nd 0.935 Dy 0.065 ) 14.5 Fe 79.4 B 6.1 and the temperature dependence of the coercivity for the Nd 14.5 Fe 79.4 B 6.1 were investigated. Results show that the coercivity for magnets prepared by the combination of strip casting with hydrogen decrepitation techniques is controlled by the nucleation mechanism.

关键词： metal materials ndfeb magnet strip casting hydrogen decreipitation nucleation mechanism rare earths