Microstructure of explosively compacted Nd-Fe-B magnet by TEM

The microstructure of an explosively compacted Nd-Fe-B permanent magnet(Nd-Fe-B) was investigated by means of TEM and XRD. It is shown that there are three kinds of phases: Nd2 Fe14 B matrix phase, O-rich phases and Nd-rich phase with different structures and compositions in the magnet. The hard magnetic phase Nd2Fe14 B is tetragonal, which lattice parameters are determined to be a=0.88 nm and c=1.22 nm. The O-rich phase locates at the grain boundaries and the triple junctions has fcc structure whose lattice parameter is a=0. 559 nm. A dislocation is observed in this phase. It is also found that a large number of the block-shaped Nd-rich phases with hcp structure are embedded in the Nd2 Fe14 B matrix or at grain boundary. Their lattice parameters are determined to be a= 0. 395 nm and c=0. 628 nm.     

Coercivity,microstructure,and thermal stability of sintered Nd-Fe-B magnets by grain boundary diffusion with TbH_3 nanoparticles

Grain boundary diffusion technique with TbH_3 nanoparticles was applied to fabricate Tb-less sintered NdFe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematically studied. The coercivity and remanence of grain boundary diffusion magnet are improved by 112% and reduced by 26% compared with those of the original magnet, respectively. Meanwhile, both the remanence temperature coefficient(α) and the coercivity temperature coefficient(β) of the magnets are improved after diffusion treatment. Microstructure shows that Tb element enriches in the surface region of Nd_2Fe_(14)B grains and is expected to exist as(Nd,Tb)_2Fe_(14)B phase. Thus, the magneto-crystalline anisotropy field of the magnet improves remarkably. As a result, the sintered Nd-FeB magnets by grain boundary diffusion with TbH_3 nanoparticles exhibit enhanced coercivity.     

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

The isotropic nanocrystalline [(PrNd)_(0.8)MM_(0.2)]_(29.8)Fe_(68.7)Al_(0.1)Cu_(0.12)Co_(0.88)B 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 B_r=0.75 T,intrinsic coercivity of H_(cj)=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 R_2 Fe_(14)B 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(T_C) of 577 K,which is higher than that of SMP magnet.This result suggests that the T_C of the magnets can be promoted by double-main phase method and SPS.     

Microstructures and magnetic properties of Ce32.15Co49.36Cu9.84Fe9.65 magnet sintered at different temperatures

The microstructures and magnetic properties of Ce32.15Co49.36Cu9.84Fe9.65 magnet sintered at the temperatures ranging from 1005 to 1105 ℃ were investigated.The results on scanning electron microscopy and X-ray diffraction analysis indicate that the remanence Br of the magnets is mainly influenced by the degree of the easy-axis orientation when sintering temperature is less than 1085 ℃,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 ℃.Moreover,it is found that intrinsic coercivity Hci is strongly related to the content of copper in the matrix of the sintered magnets.The optimal sintering temperature is located in 1025～1055 ℃,the corresponding magnetic properties of the magnets are Br=0.685 T,Hci=350 kA·m-1,and maximum energy product (BH)m=85.6 kJ.m-3.     

Low-cost Sm_(0.7)Y_(0.3)Co_5 sintered magnet produced by traditional powder metallurgical techniques

RCo_5(R=rare earth) sintered magnets have good temperature stability,so it is still widely used in high temperature field.In this paper,by the method of adding liquid phase SmCo_(1.7) to the main phase,Sm_(0.7)Y_(0.3)Co_5 magnet was prepared by traditional powder metallurgical process.The results show the presence of a main phase RCo_5,a minor phase R_2 Co_7,and a R-rich phase in the magnet.Contrasting the results of the XRD(X-ray diffraction) in random and oriented directions,the magnet has a well-aligned(00l) orientated texture,which is consistent with the result of the electron backscattered diffraction(EBSD).The Sm_(0.7)Y_(0.3)Co_5 sintered magnet has good magnetic properties as remanence(Br) is 0.96 T,the coercivity(H_(cj)) is 1201.96 kA·m~(-1),and maximum magnetic energy product((BH)_(max)) is 175.16 kJ m~(-3).     

Crystal structure and thermal stability of martensite in Cu-25Al-3Mn alloy

The martensite structure in Cu-25Al-3Mn alloy and its thermal cycling and aging behavior are studied. It is convinced that the M2H martensite can be obtained by water-quenched, and the atoms distribution on the basal plane of the mart ensite is: Ⅰ(corner)-Al; Ⅱ(center of the plane)-Cu; Ⅲ(middle of b- side)-22/25Cu+3/25Mn. The lattice parameters are determined to be a=0.445 9 nm, b=0.527 9 nm, c=0.424 1 nm, β=88.64°. The triangle and other complicated configurations consisting of the variant group in the martensite are discovered. It is showed that the tested alloy has a high thermal stability when aging at average temperature in the parent phase, and the thermoelastic martensite amount is up to 90% af ter aging for 96 hat 400 ℃. The thermal cycling has a little influence on the transform ation temperature (Ms). When the number of thermal cycles is up to 1000, the increasing of Ms is only 8 ℃.     

Effects of oxygen and carbon on the magnetic properties and microstructure of Sm2Co17 permanent magnets

The research on the sintered Sm2Co17 permanent magnets prepared by metal injection molding is still at the exploratory stage. Carbon and oxygen are two key factors that influence the magnetic properties. In this article, the effects of oxygen and carbon on the properties and microstructure of the magnets have been studied. The results indicate that oxygen consumes the effective Sm content of the magnets and forms Sm2O3-the non-magnetism phase, which result in the deterioration of the magnetic properties. Besides, the magnetic properties decrease in evidence with increasing carbon content. The main factor that affects the magnetic properties is the deterioration of the microstructure of the magnets. The Sm（Co, Cu）5 phase decreases, whereas the cell size increases with the increase of the carbon content. When the carbon content is above 0.43 wt.%, the Sm（Co, Cu）5 phase is not enough to form a uniform cellular microstructure. Thus the magnetic properties disappear. ZrC is detected in the magnets by XRD when the carbon content is above 0.21 wt.%. ZrC also reduces the properties of the magnets.     

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

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.     

Microstructure and magnetic properties of sintered CeCo4.3252-xCu0.675Fex magnets

Anisotropic CeC o4.325-xCu0.675Fex(x = 0.475-0.875) sintered magnets were prepared by traditional powder metallurgical method. Influence of ball-milling time and iron content on microstructure and magnetic properties of the CeC o4.325-xCu0.675 Fexsintered magnets were investigated. It is shown that the properties of the magnet produced by magnetic powders ball-milled for 40 min are better than that for 30 min. With iron content increasing, remanence Brand maximum energy product(BH)mincrease first and then decrease.The optimal magnetic properties are obtained for the CeC o3.65Cu0.675Fe0.675 sintered magnet: Br= 0.685 T, the intrinsic coercivity Hci= 350 kA ám-1, and(BH)m=85.6 kJ ám-3. The increase of Bris 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 C 0.775.     

Chemically synthesizing exchange-coupled SmCo_5/Sm_2Co_(17)nanocomposites

A new strategy to chemically synthesize exchange-coupled SmCo_5/Sm_2 Co_(17) nanocomposites by in situ decomposition of SmCox(5 x 8.5) is reported in this work.Our synthesis starts with the fabrication of Co/Sm_2 O_3(Sm to Co atomic ratio of Sn/Co=1:4.2),which can be reduced into 40-nm SmCo_5 single crystal nanoparticles by Ca under the protection of CaO,showing a high coercivity of 2.85 T and saturation magnetization(M_s) of 0.0671 A·m~2·g~(-1).By changing the Sm/Co to 1:4.5,1:4.8 and 1:5.2,SmCo_5/Sm_2 Co_(17) nanocomposites with different proportions were acquired using the same process.Owing to the in situ decomposition of SmCo_x intermediate,the small size(both of their size less than 10 nm) and uniform phase distribution were achieved in our nanocomposites.Thus,the as-prepared nanocomposites display a strong exchange-coupling interaction.As a consequence,SMCo_5/Sm_2 Co_(17)(Sm/Co=1:5.2) exhibits a coercivity of 1.23 T and enhanced M_(7 T)(magnetization at 7 T) of 0.0812 A·m~2·g~(-1),increasing by 21% than pure SmCo~5.Our synthesis provides a new protocol to prepare exchange-coupled high-performance nanocomposites.     

Structure and magnetic properties ofhigh-performanced Sm2（Co, Fe, Cu, Zr）17 alloys

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Effect of Fe on Microstructure and Coercivity of SmCo-Based MagnetsEI北大核心CSCD

High-temperature permanent magnets have an important application in the aerospace and other high-tech fields, among which 2:17-type SmCo magnets have become the first choice for high-temperature permanent magnets due to the strong magnetic anisotropy and high Curie temperature. Although there are studies on the effect of Fe on the remanence and coercivity, the role that Fe plays on coercivity mechanism of SmCo magnets is still unclear. In this work, Sm(CobalFexCu0.08-0.10Zr0.03-0.033) z (x= 0.10-0.16, z=6.90 and 7.40) magnets are prepared and the magnetic properties under different temperatures are investigated. The magnets with an intrinsic coercivity of 603.99 kA/m and a maximum energy product of 87.30 kJ/m(3) at 500 degrees C. are obtained. It is revealed that at room temperature the coercivity of the magnets increases with increasing Fe content, however, at 500 degrees C. the coercivity shows an opposite dependency on Fe content. Moreover, the effect of Fe on coercivity is more obvious at low z value. The phase structure and composition analyses were characterized by XRD and TEM. The results show that with the increase of Fe content, the size of the 2: 17R cell phase increases, the volume ratio of cell boundary 1: 5H phase decreases, and furthermore, both Fe content in the 2: 17R phase and Cu content in the 1: 5H phase increase. The variations of Fe and Cu contents in both phases lead to the change of the domain wall energy difference. With the increase of Cu content of 1:5H phase, the domain wall energy of 1: 5H phase (gamma(1:6)) drops faster at room temperature, the coercivity is determined by gamma(2:17)-gamma(1:5), so the coercivity increases with increasing Fe content. While at 500 degrees C, due to gamma(1:6) at its Curie temperature, the coercivity is mainly determined by the domain wall energy of 2: 17R phase (gamma(1:17)), which decreases with increasing Fe content. The increase of Fe content at the low z value results in a smaller growth of cell size, which leads to a more significant change in coercivity.     

Nanocrystalline Nd2Fe14B／α—Fe permanent magnet

Nd8.5Fe75Co5Cu1Zr3Nb1B6.5bonded magnet was prepared by melt-spinning(vs=18m/s)and subsequent heat treatment(670℃，4min).Excellent magnetic properties of the bonded magnet were achieved:Br=0.68T,iHc=620.3kA/m,(BH)max=74kJ/m^3.The addition of Cu and Zr elements shows to be advantageous in improving an intrinsic coercivity and squareness of hysteresis loop,as well as energy product.In has a remarkable remanence enhancement and the isotropic saturation remanence ratio Mr/Ms is 0.83.     

烧结钕铁硼(Al+Cu)含量对晶界扩散的影响

本研究对(Al+Cu)含量分别为0.25%的钕铁硼基体和0.5%基体进行Dy晶界扩散,并分析了矫顽力、Dy含量分布和微观结构。通过比较两种磁体的成分、性能发现,在Dy增加量基本相同的情况下,高(Al+Cu)磁体扩散后的矫顽力提高量相较于低(Al+Cu)磁体高37kA/m~43kA/m。进一步进行成分、矫顽力的梯度分析发现,基体的(Al+Cu)含量变化并没有改变扩散后磁体内部Dy元素随扩散深度的浓度分布,但是矫顽力梯度分析结果显示高(Al+Cu)的各片层矫顽力提升量均比低(Al+Cu)片层高40 kA/m~80 kA/m。后续的EPMA的Dy面分布图显示,高(Al+Cu)基体扩散后Dy在晶界处富集条纹更清晰、连续,而TEM的EDX分析结果也显示高(Al+Cu)样品中晶界附近Dy含量更高。(Al+Cu)含量的提高,使得晶界相的流动性增强,Dy更加连续包裹主相晶粒,使得Dy增加量相同的情况下进一步提升矫顽力。     

热扩渗DyZn合金膜层对烧结钕铁硼磁性能与耐热性能的影响

采用直流磁控溅射的方法,在烧结NdFeB磁体表面制备了DyZn薄膜,研究了热扩渗处理磁体前后的磁性能、温度稳定性及微观组织结构变化。结果表明,晶界扩散渗DyZn处理后,磁体在保持剩磁基本不降低的情况下,矫顽力大幅度提升,矫顽力从原来的963.68 kA/m提高到1544.60 kA/m,增幅达63.31%。晶界扩散处理可以改善磁体的温度稳定性,在293~453 K范围内,剩磁温度系数基本不变,而矫顽力温度系数由–0.5533%/K降低为–0.4885%/K。通过对样品微观组织结构观察发现,Dy元素沿着晶界液相扩散,主要富集在晶界相和晶粒外延层处,晶界相结构与成分的优化、及晶界和晶粒之间(Nd,Dy)_2Fe_(14)B过渡层的形成是矫顽力大幅度提升的主要原因。     

Fe含量对高温稀土永磁Sm(CobalFexCu0.1Zr0.03)7.5 (x=0.09～0.21)磁性能的影响

采用粉末冶金工艺制备了高温稀土永磁Sm(CobalFexCu0.1Zr0.03)7.5 (x=0.09～0.21),研究了Fe含量对磁体磁性能的影响.结果表明:随着Fe含量的增加,剩磁Br和最大磁能积(BH)max逐渐增加,在x=0.21时获得最大值,分别为0.96 T和176.7 kJ/m3;内禀矫顽力Hci先增加后降低,在x=0.15时获得峰值2276.6 kA/m.最佳工艺制备(x=0.15)的磁体温度稳定性良好,B-H退磁曲线在温度为500 ℃时保持为直线;内禀矫顽力温度系数β为-0.16%/℃,最高使用温度(OT)max达到533 ℃.     

HDDR各向异性NdFeB矫顽力机理的研究

研究了HDDR各向异性NdFeB永磁材料的矫顽力机理。通过对材料磁化过程的研究以及对其显微组织结构的观察分析，发现其矫顽力机制起源于畴壁挣脱主相Nd2Fe14B晶粒边界以及晶粒团边界富钕相的钉扎机制，其中富钕相对材料畴壁的钉扎是决定其矫顽力的关键因素。通过理论计算，其结果与材料实际的矫顽力十分接近。此外，还进行了验证性实验并提出了改善材料矫顽力的途径。     

块状纳米晶SmCo5烧结磁体的结构及其磁性能

采用放电等离子烧结(SPS)技术制备致密块状纳米晶SmCo5烧结磁体,研究磁体的结构和磁性能.XRD结果表明:球磨粉末基本为非晶结构,烧结磁体具有CaCu5结构.TEM结果表明:磁体获得晶体均匀分布的组织结构,平均晶粒尺寸约为30 nm.电子选区衍射(SAED)分析表明:磁体主相为SmCO5相.室温时磁体的矫顽力高达2.28 MA/m,而剩磁比Mr/Ms高达0.7,并通过剩磁曲线-M-H及其变化趋势,说明在纳米晶之间存在强烈的晶间交换耦合作用.烧结磁体具有良好的高温性能,773 K时其矫顽力为0.72 MA/m,矫顽力温度系数β为-0.146%/K.     

Preparation of isotropic Sm2Fe17Nx magnetic powders and their bonded magnets

The isotropic Sm2Fe17Nx magnetic powders were prepared by Hydrogenation-Disproportion-Desorption-Recombination (HDDR) process. The phase and microstructure evolutionary process of Sm-Fe alloy during the solidification, homogenization, HDDR and nitration processes were investigated by means of XRD, SEM, EDX and AFM. The results show that the homogeneous Sm2Fe17 alloy wassuccessfully obtained and the impurity phases and residual stress were well removed by heated at 1050 ℃ for 24 h. When heated at 800 ℃ for 1h in H2 of 0.1 Mpa, the alloy turns into SmHx and α-Fe with plenty of nanocrystals. After vacuumized at 800 ℃ for 2h the alloy recombines into Sm2Fe17 with a crystal grain size of about 85 nm.The lattice constant of the alloy increases and the expanding of the crystal cell reaches 6.28% after nitrified at 500 ℃ for 5 h. The magnetic property of isotropic bonded Sm2Fe17Nx magnets is Br=0.6704 T, Hcj = 1015 kA·m-1,( BH )max =73.7 kJ·m-3 with a density of 6.04 g·cm-3 .     

Effect of preannealing on crystallization process of amorphous Sm5Fe80Cu1Si5B3C2.5Zr3.5 alloy

In the view of crystallization activation energy of amorphous alloy,the mechanism of coarse grain in annealed Sm5Fe80Cu1Si5B3C2.5ZR3.5 amorphous alloy was analyzed.It reveals the e4ffect of preannealing on the process crystallization.The results show that preannealing can be used to change the crystallization behavior of the α-Fe phase in the Sm5Fe80Cu1Si5B3C2.5Zr3.5 amorphous alloy,whick is helpful for forming α-Fe phase grains;and it is not large for Sm2Fe17Cx phase.