Optimal design of sintered Ce_9Nd_(21)Fe_(bal)B_1 magnets with a low-melting-point (Ce,Nd)-rich phase

A systemic investigation was done on the chemistry and crystal structure of boundary phases in sintered Ce9Nd21FebalB1 （wt%） magnets. Ce2Fe14B is believed to be more soluble in the rare-earth （RE）-rich liquid phase during the sintering process. Thus, the grain size and oxygen content were controlled via low-temperature sintering, resulting in high coercivity and maximum energy products. In addition, Ce formed massive agglomerations at the triple-point junctions, as confirmed by elemental mapping results. Transmission electron micros- copy （TEM） images indicated the presence of （Ce,Nd）Ox phases at grain boundaries. By controlling the composition and optimizing the preparation process, we successfully obtained Ce9Nd21FebalBx sintered magnets; the prepared magnets exhibited a residual induction, coerciv- ity, and energy product of 1.353 T, 759 kA/m, and 342 kJ/m3, respectively.

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

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.

Coercivity enhancement of hot-deformed Nd-Fe-B magnets with Pr-Cu alloy addition

Effects of low-melting Pr-Cu alloy addition on the microstructure and magnetic properties of the hot-deformation Nd-Fe-B magnets were investigated.A small amount of Pr-Cu addition enhances the coercivity of the hot-deformation Nd-Fe-B magnets obviously.The coercivity of the hotdeformation Nd-Fe-B magnets with 4.0 wt%Pr_(85)Cu_(15)addition increases to 1271 kA·m^(-1),75.69%higher than that of Pr-Cu-free magnet(723 kA·m^(-1)),and then decreases with5 wt%Pr_(85)Cu_(15)addition.It is observed that there a uniform RE-rich phase is formed wrapping the Nd2Fe14B main phase in the sample with 4.0%Pr_(85)Cu_(15)addition by scanning electron microscopy(SEM),which promotes the coercivity.The angular dependence of coercivity for the hot-deformation Nd-Fe-B magnets indicates that the coercivity mechanism is nucleation combined with domain wall pinning.The domain wall pinning is weakened,while the nucleation is enhanced after Pr-Cu addition.Theremanence,intrinsic coercivity,and maximum magnetic energy product of the original Nd-Fe-B magnet are 1.45 T,723 kA·m^(-1),and 419.8 kJ·m^(-3),respectively,and those of the sample with 4.0%Pr_(85)Cu_(15)alloy addition are 1.30 T,1271 kA·m^(-1),and 330.0 kJ·m^(-3),respectively.

Magnetic properties and structures of Y-substituted Nd-Y-Fe-B melt-spun ribbons

The nanocrystalline magnetic ribbons of(Nd_(1-x)Y_(x))_(14.5)Fe_(ba1)B(6)Co_(0.2)Al_(1)Cu_(0.15)(x=0,0.1,0.2,0.3,0.4) were prepared by melt-spinning technique.The magnetic properties and microstructures were systematically investigated for the ribbons.It is found that Y substituting Nd in the R_(2)Fe_(14)B main phase grains gives rise to the decrease in the crystal lattice constant.When Y content increases from x=0 to x=0.4,the remanence and intrinsic coercivity(H_(cj)) decrease from 0.80 to 0.71 T and1400 to 809 kA·m^(-)1,respectively,with the corresponding descent rate of 11.5% and 42.5%.It is impressed that the average grain size increases with Y content increasing.And the strong intergrain exchange coupling interactions exist in all the ribbons and could be enhanced with an appropriate Y substitution,such as x=0.4.Moreover,magnetization reversal mechanism is confirmed to be pinning type for the ribbons.The results provide valuable reference to the fabrication of Y-substituted Nd-Y-Fe-B sintered magnets.

Microstructure and magnetic properties of anisotropic hot-deformed magnet of different magnetic particle sizes

In this paper, the magnetic Nd-Fe-B particles of different sizes were conducted under vacuum by the hot pressing, then cooled quickly to room temperature. Finally hot deformation was performed to get the anisotropy Nd-Fe- B magnet at a deformation rate of 70 % in the protection of argon atmosphere. NIM-2000 was used for the measurement of hysteresis loop of the samples. Meanwhile, scanning electron microscopy （SEM） was used to observe the surface morphology of the magnetic particles with different sizes and hot-deformed magnets, energy spectrum analyzer to analyze the composition of magnetic particles. The effect of magnetic particle sizes on the microstructure and magnetic properties of the hot-deformed anisotropic magnet was investigated. Anisotropic hot-deformed magnets produced from the maximum particle size of 200-350 μm have the highest magnetic properties of Br = 1.465 T, Hcj = 1,157 kA.m-1, （Bn）max = 425 kJ.m-3.

Phase composition and magnetic properties of Pr-Nd-MM-Fe-B nanocrystalline magnets prepared by spark plasma sintering

The isotropic nanocrystalline[(PrNd)0.8MM0.2]29.8Fe68.7Al0.1Cu0.12Co0.88B magnets(MM:mischmetal)were prepared by single-main phase and double-main phase methods using spark plasma sintering(SPS).Melt-spinning method was used to prepare initial powder and avoid component deviations caused by longtime ball milling.The magnetic properties of the magnet prepared by double-main phase method(called double-main phase magnet,DMP magnet)are remanence of Br=0.75 T,intrinsic coercivity of Hcj=909.83 kA·m-1,maximum magnetic energy product of(BH)max=95.48 kJ·m-3,which are better than those of the magnet prepared by single-main phase method(called singlemain phase magnet,SMP magnet).The diffraction peaks of the main phase of DMP magnet split in X-ray diffractometer(XRD)pattern,indicating that R2 Fe14B phases with different distributions of La/Ce elements exist in the magnet.This speculation is confirmed by transmission electron microscopy(TEM)observation.The La/Ce-rich main phase and La/Celean main phase are present in DMP magnets.The heterogeneity of rare earth elements suppresses the magnetic dilution effect in DMP magnet,and the magnetic properties are improved.Though the DMP magnet contains different main phases,it presents unitary Curie temperature(TC)of 577 K,which is higher than that of SMP magnet.This result suggests that the TC of the magnets can be promoted by double-main phase method and SPS.

Preparation of Sintered(Ce_(1-x)Nd_x)_(30)Fe_(bal)Cu_(0.1)B_1 Magnets by Blending Powder Method

Magnets with nominal compositions of （ Nd1-x Cex ） 30 Febal Cu0.1 B1 （x = 0, 0.15, 0.3 and 0.4, mass% ） have been fabricated by blending powder method. The remanence （B r）, intrinsic coercivity （He） and maximum en- ergy product （BH） of the RE2Fe14B type magnets deteriorated when Nd was replaced by Ce. The chemical composition and crystal structure of magnet were investigated systemically. Backscattered electron （BSE） and energy dispersive spectroscopy （EDS） results revealed that Ce-rich and Ce-lean matrix grains coexisted in the magnets. The magnetic coupling mechanism among the double hard magnetic phases was discussed. Low melting point RE-Cu phase was in favor of the formation of uniform continuous grain boundary. Transmission electron microscopy （TEM） investigation showed the presence of fcc （Nd,Ce）Ox phase in the grain boundary. When the Ce content was 15% of the total amounts of all the rare earth, the maximum energy product of the sintered magnet was 359.8 kJ/ms.

Overview of composition and technique process study on 2:17-type Sm-Co high-temperature permanent magnet

Sm-Co permanent magnets are widely used in aerospace equipments,tubes,sensors and hybrid electric vehicles due to their excellent magnetic properties at both room and high temperatures.Compared to that of Nd-Fe-B magnets,the capability of reliably operating at temperatures up to 500℃ is the biggest preponderance of Sm-Co permanent magnets.However,the reliable high-temperature magnetic properties are susceptible to composition and technique processes.So,appropriate composition and matched technique processes are prerequisites for good high-temperature magnetic properties.This review mainly emphasizes the influences of Sm,Fe,Cu and Zr contents and technique processes on development of high-temperature performance and discusses the controversial hightemperature coercivity mechanism of 2:17-type high-temperature Sm-Co magnets.

Numerical simulation of single roller melt spinning for NdFeB alloy based on finite element method

The numerical simulation model of single roller melt spinning for rapid quenching process of NdFeB alloy was built,and the vacuum chamber,cooling roller and sample were taken into account as a system.The existing mature technology was in order to verify the correctness of simulation.The rapid quenching ribbons with different roll speeds were used as the simulation objects.The results of the numerical simulation and experiments show that the validity of the model has been testified and the reasons of the formation of complete quenching ribbons and by-product have been explained.The experimental thickness of the ribbons is proportional to the theoretical thickness.In the same spray condition,with the roll speed increasing,the thickness decreases linearly.At the speed range of25-30 m·s^(-1),the simulated calculation date is close to the experimental date,which can be considered as an ideal technological parameter.

Microstructure and magnetic properties of sintered CeCo_(4.3252-x)Cu_(0.675)Fe_x magnets

Anisotropic CeCo4.325_xCuo.675Fex （x ： 0.475- 0.875） sintered magnets were prepared by traditional powder metallurgical method. Influence of ball-nfilling time and iron content on microstructure and magnetic properties of the CeCo4,325-xCuo.675Fex sintered magnets were investigated. It is shown that the properties of the magnet produced by mag- netic powders ball-milled for 40 min are better than that for 30 rain. With iron content increasing, remanence Br and maxi- mum energy product （BH）m increase first and then decrease. The optimal magnetic properties are obtained for the CeCo3.65Cuo.675Feo.675 sintered magnet： Br=0.685 T, the intrinsic coercivity Hci = 350 kA.m-1, and （BH）m ： 85.6 kJ.m-3. The increase of Br is mainly influenced by iron content of 1：5 matrix which can properly increase the saturation induction Bs; the rapid increase of the amount of Ce-rich phase and 5：19 phase gives rise to the deterioration of the magnets when x ≥ 0.775.

Development of Ce-based sintered magnets: review and prospect

Ce-based magnets have attracted extensive attention in both academia and industry due to their excellent property-price ratio and distinctive phase structures.Characteristically,Ce-based sintered magnets have widely tunable magnetic properties with changing Ce contents.Therefore,they can be used to meet many different application requirements from packaging market to driving motors,etc.The intrinsic magnetic properties,phase composition,and microstructures of the Ce-based sintered magnets with different Ce contents have been summarized.The service performances such as temperature stability,corrosion resistance,mechanical properties and thermal expansion of commercial Ce-based sintered magnets are introduced.The research and development trends of the Ce-based magnets in the future are pointed out.

Preparation of Nanoscale Sm_2Co_(17)Flakes by Ball Milling in Magnetic Field

A new preparation method of Sm2Co17 nanoflakes was investigated. Hard magnetic Sm2 Co17 nanoflakes with thickness of 20-100 nm were obtained by milling in heptane and oleic acid under a magnetic field of 1.5 T for 0.5-20 h. It was shown that higher anisotropic magnetic properties would be induced by the flake-shape anisotropy when the prepared Sm2 Colt particles are milled with a magnetic field. The magnetic anisotropy of flakes after being aligned under the magnetic field of 1.5 T could be further enhanced, and the value of （BH）m was 128 kJ · m a Both anisotropy and properties are better than those of the nano-particles milled without a magnetic field.

Identification of optimal solid solution temperature for Sm_(2)Co_(17)-type permanent magnets with different Fe contents

It is confirmed that the solid solution temperature range to obtain optimal magnetic properties is different for the magnets with different Fe contents,and the correlation between magnetic properties and microstructures influenced by solid solution temperature(Ts)has been systematically studied.The optimal solid solution temperature range is 1413-1463 K for the Sm(Co_(bal)Fe_(0.213)Cu_(0.073)Zr_(0.024))_(7.6)magnet,which is higher than that of the Sm(Co_(bal)Fe_(0.262)Cu_(0.073)Zr_(0.024))_(7.6)magnet(1403-1453 K),and the optimal T_s range is about 50 K for both of the magnets.The solid solution temperature range shifting toward relatively high temperature is due to the increase in a phase transition temperature.The magnet solution-treated at proper temperature exhibits 1:7 H single phase,and intact cell structure and high Cu concentration(23.12 at%)in the cell boundary are found after aging process,which makes the magnet shows high intrinsic coercivity(H_(cj))and magnetic field at knee-point(H_(knee)).At a lower solid solution temperature,the 2:17 H,1:5 H and Zr-rich precipitation phases appear,which affects the cell structure,density of lamellar phase and Cu concentration in the cell boundary,leading to the reduced magnetic properties.However,at a higher solid solution temperature,there exist obviously light gray and dark regions with different Sm,Cu and Fe contents in scanning electron microscopy observation,and the magnet shows low pinning field in the two regions and incomplete cell structure,resulting in an inferior H_(cj)and H_(knee).

Microstructures and magnetic properties of Sm(Co_(bal)Fe_(0.245)Cu_(0.07)Zr_(0.02))_(7.8)sintered magnet solution-treated at high temperature

Sm(CoFeCuZr)zsintered permanent magnet has been attracting a great deal of attention by virtue of its high-temperature magnetic properties,low temperature coefficient and good corrosion and oxidation resistance.The microstructures and magnetic properties of Sm(Co_(ba1)Fe_(0.245)Cu_(0.07)Zr_(0.02))_(7.8)sintered permanent magnet prepared by a traditional powder metallurgy method were investigated.Tunable magnetic properties,especially the maximum magnetic energy product,(BH)max,were obtained through adjusting solution-treated temperatures.With solution-treated temperature increasing from 1155 to 1195℃,remanence(Br)almost keeps constant and knee point coercivity(Hk),magnetic induction coercivity(H_(cb))and(B_(H))maxfirst increase and then decrease.The intrinsic coercivity(H_(cj))of magnet solution-treated at 1195℃is 738 kA·m^(-1),which is less than 2/5 that of magnet solution-treated at 1183℃(>1927 kA·m^(-1)).The reason that magnet solution-treated at 1195℃shows lower Hcjthan magnet solution-treated at 1183℃is considered to be mainly related to the fact that there are a lot of cells with abnormally small size.In addition,the lattice constant of Sm(Co_(bal)Fe_(0.245)Cu_(0.07)Zr_(0.02))_(7.8)sintered permanent magnet solution-treated at 1195℃,given by indexing highresolution transition electron microscope(HRTEM)results,is considered to be related to the formation of cells with abnormally small size which decreases H_(cj).

Relation between microstructure and magnetic properties of shock wave-compressed Nd-Fe-B magnets

The relationship between the microstructure and magnetic properties of Nd-Fe-B sintered magnet compressed by shock wave with 6.26 GPa≤p≤7.16 GPa was investigated.It reveals that Nd-Fe-B magnets show a demagnetization behavior after compressed by shock wave.The intergranular fracture is the main occurring phe-nomenon in the shock wave-compressed magnets.The coercivity of the shock wave-compressed Nd-Fe-B magnets could be recovered after repeating the annealing process.It suggests that only the morphology change just like the intergranular fracture occurs,and there is no structural change in the grain boundary phase in the shock wave-compressed magnet.Matrix phase grain interconnection,microcracks and pores,and alterant orientation relationship between matrix phase and grain boundaries phase are con-sidered as induced factors of demagnetization.

Oxygen content and magnetic properties of composites La_(0.75)Sr_(0.25)MnO_(3±δ) dcalcined at different temperatures

The effects of the calcination temperature on the oxygen content and magnetic properties of the nano- crystalline perovskite manganite Lao.75Sro.25MnO3±δ pre- pared by the sol-gel method were investigated. The highest temperatures at which the samples were calcined were 973, 1073, 1273, and 1473 K. The X-ray diffraction （XRD） analyses indicate that all the samples have only a single phase with the R3c perovskite structure. As the calcination temperature and calcination time increase, the oxygen content in the samples increases from being deficient to being in excess of that in the stoichiometric formula. The crystallite size also increases from 23 to 283 nm. Magnetic measurements indicate that the sample calcined at 1073 K has the highest Curie temperature. This is owing to the fact that the crystallite cores of this sample have stoichiometric oxygen content. The dependence of the Curie temperature and the saturation magnetization on the calcination tem- perature are successfully explained.

Microstructures and coercivity mechanism of 2:17-type Sm-Co magnets with high remanence

Sm(Co_(bal)Fe_(0.245)Cu_(0.07)Zr_(0.02))7.8(at%)sintered magnets with high remanence(B_(r)~1.15 T)were prepared using a traditional powder metallurgy method.Tunable magnetic properties,especially intrinsic coercivity(H_(cj)),were obtained through adjusting isothermal procedure parameters.H_(cj)of the magnets increases from 305 to 752 kA·m^(-1)with isothermal annealing time increasing from 3 to 20 h,while B_(r) of the magnets almost keeps constant.From the bright field transmission electron microscopy(TEM)images,it is found that:(1)there is dispersed precipitated phase with very small size in the magnet annealed for 3 h,while the magnets annealed for 20 h have distinct and intact cellular structure;(2)the number density of Z-phase in magnet annealed for 20 h is bigger than that for 3 h.Besides,the finer microstructures were studied with high-resolution transmission electron microscopy(HRTEM).