含Ti和C的纳米复合Nd_2Fe_(14)B/α-Fe磁体研究EI北大核心

研究Ti和C添加对Nd9.4Fe79.6B11合金磁性能的影响规律。结果表明:Ti和C联合添加能够在不降低合金剩磁的情况下显著提高合金的矫顽力,最佳工艺条件下制备出的Nd9.4Fe75.6Ti4B10.5C0.5合金薄带的剩磁Br=0.91T,矫顽力Hcj=975.6kA/m,磁能积(BH)max=135.4kJ/m3。在磁体密度为6.1g/cm3时,黏结Nd9.4Fe75.6Ti4B10.5C0.5磁体剩磁Br=0.68T,内禀矫顽力Hcj=975kA/m,最大磁能积(BH)max=76 kJ/m3,性能和MQ-D磁粉制备的黏结磁体性能相当,具有低价位高性能的特点。     

含Ti和C的纳米复合Nd2Fe14B／α—Fe磁体研究

研究Ti和C添加对Nd9.4Fe79.6B11合金磁性能的影响规律。结果表明:Ti和C联合添加能够在不降低合金剩磁的情况下显著提高合金的矫顽力,最佳工艺条件下制备出的Nd9.4Fe75.6Ti4B10.5C0.5合金薄带的剩磁Br=0.91T,矫顽力Hcj=975.6kA/m,磁能积(BH)max=135.4kJ/m3。在磁体密度为6.1g/cm3时,黏结Nd9.4Fe75.6Ti4B10.5C0.5磁体剩磁Br=0.68T,内禀矫顽力Hcj=975kA/m,最大磁能积(BH)max=76 kJ/m3,性能和MQ-D磁粉制备的黏结磁体性能相当,具有低价位高性能的特点。     

NdH纳米助剂回收制备烧结钕铁硼永磁体的研究

采用NdH纳米掺杂的方法对废旧烧结钕铁硼磁体进行了回收制备。研究了不同NdH纳米粉掺杂量对再制造烧结钕铁硼磁性能的影响。随着NdH纳米粉末掺杂量的增多,烧结磁体矫顽力从926.54 kA/m增加到1 299.87 kA/m;剩磁首先相对稳定在1.296 T,在掺杂量2.0%(质量分数)后,剩磁逐渐下降。与原始磁体相比,2.0%(质量分数)NdH纳米粉掺杂磁体性能最佳,矫顽力回复97.5%,剩磁回复95.9%,磁能积回复89.7%。通过计算,掺杂3.0%(质量分数)NdH纳米粉后,再制造烧结磁体中富钕相体积分数从3.03%增加到5.70%,然而其晶粒尺寸从8.18μm增长至11.68μm。结合微观分析与磁性能,2.0%(质量分数)NdH纳米粉掺杂磁体性能最好。     

Nd-Fe-B永磁合金的组织与磁性

用金相显微镜、扫描电镜、X射线衍射,粉纹磁畴观察、磁测量等方法研究了性能为(B·H)_(max)=27～37MGOe,Br=11000～12500G、_MHc=13000～17000Oe的Fe74Nd18B8永磁合金的铸态、烧结,回火状态的磁性、显微组织、畴结构以及回火动力学曲线.结果表明:该永磁体的铸态组织是粗大的柱状晶.烧结、回火后组织为四方相和两种富Nd相(即富B相和富Nd相),回火后的组织形貌与烧结后的组织形貌没有显著变化,只是回火后富Nd相更富集在晶界上,永磁体磁化曲线具有形核场的特征,回火后矫顽力急剧增加而且随回火时间的延长出现峰值。磁畴是平行状多畴体.     

LiF与TbF3二元系晶界扩散改善Nd-Fe-B磁性能研究

采用LiF和TbF_3混合二元系作为扩散源,通过晶界扩散法研究了不同厚度钕铁硼磁体扩散后磁性能变化规律。结果表明,在最优扩散条件下,6 mm磁体的矫顽力从1.05×10~6 A/m提高到1.71×10~6 kA/m,10 mm磁体从1.05×10~6 A/m提高到1.52×10~6 A/m,且退磁曲线仍具有较高的方形度,剩磁与磁能积也没有显著的降低。SEM图像表明,晶界扩散与表面扩散的共同作用,影响重稀土元素Tb和晶界相在磁体内部的分布,从而使磁体的矫顽力获得较大幅度的提升。     

纳米晶复合Nd9.5Fe76Co5Zr3-xNbxB6.5（x=0～3.0）粘结磁体的磁性能和温度系数的研究

采用熔体快淬法及真空退火工艺制备了Nd9.5Fe76Co5Zr3-xNbxB6.5(x=0～3.0)粘结磁体,研究了其磁性能及温度系数。结果表明,随着Nb含量的增加,合金剩磁逐渐提高,磁能积和矫顽力呈现先增大后减小的趋势。Zr元素与Nb元素复合添加,能够有效地改善矫顽力温度系数β。经最佳条件退火处理后制备的Nd9.5Fe76Co5Zr1.5Nb1.5B6.5的粘结磁体,具有最优的综合磁性能:Br=0.717T,Hcj=773kA/m,(BH)max=82kJ/m3,α20～150℃=-0.111%/℃,β20～150℃=-0.356%/℃。     

放电等离子烧结制备块状纳米晶SmCo5烧结磁体

采用放电等离子烧结（SPS）技术制备了致密纳米晶SmCo5烧结磁体，研究了磁体的结构和磁性能。X衍射结果表明，烧结磁体具有CaCu5结构，说明SPS过程可以获得稳定的1：5相。TEM观察显示，磁体由平均晶粒尺寸约为30nm的1：5相构成。室温时磁体的矫顽力高达2208kA/m，而剩磁比高达0，7，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，773K时的矫顽力为456kA/m，矫顽力温度系数β为-0．212％/K。     

回收制备烧结Nd-Fe-B磁体的磁性能与耐热性能

以废旧钕铁硼磁体为原料,采用短流程回收制备技术制备了烧结Nd-Fe-B磁体,通过添加镨钕混合稀土研究了磁体的磁性能和耐热性能。结果表明,在回收磁体中添加2%PrNd,制备的烧结Nd-Fe-B磁体的剩磁为1.31T、矫顽力为1 474.86kA/m、磁能积为353.90kJ/m~3。与一次成品相比矫顽力恢复到102%,剩磁恢复到95%,磁能积恢复到90%。在293~393K范围内未掺杂PrNd磁体的矫顽力温度系数为-0.589 9%/K,掺杂2%PrNd磁体的矫顽力温度系数为-0.556 4%/K,提高了磁体在高温下的耐热性能。这是由于添加混合稀土PrNd增强了主相晶粒间的去磁交换耦合作用,提高了主相的磁晶各向异性场,从而提高了磁体的矫顽力和耐热性能。     

回收制备烧结Nd-Fe-B磁体的磁性能与耐热性能

以废旧钕铁硼磁体为原料,采用短流程回收制备技术制备了烧结Nd-Fe-B磁体,通过添加镨钕混合稀土研究了磁体的磁性能和耐热性能.结果表明,在回收磁体中添加2％ PrNd,制备的烧结Nd-Fe-B磁体的剩磁为1.31T、矫顽力为1 474.86 kA/m、磁能积为353.90 kJ/m3.与一次成品相比矫顽力恢复到102％,剩磁恢复到95％,磁能积恢复到90％.在293～393 K范围内未掺杂PrNd磁体的矫顽力温度系数为-0.589 9％/K,掺杂2％PrNd磁体的矫顽力温度系数为-0.556 4％/K,提高了磁体在高温下的耐热性能.这是由于添加混合稀土PrNd增强了主相晶粒间的去磁交换耦合作用,提高了主相的磁晶各向异性场,从而提高了磁体的矫顽力和耐热性能.     

利用混合稀土制备稀土永磁体的工艺研究

用富含La,Se的混合稀土代替部分PrNd合金作为原料,按(NdPr)18.2(MM)13.6Fe66.22B1.08Cu0.2Al0.7(质量分数)进行配料,以甩带熔炼方式形成薄带状合金,合金经氢破碎后,用气流磨制成粉末,最后经压制、烧结得到一种廉价稀土永磁体.用磁性测量仪测量了样品的磁性能;用定氧仪考察了防氧化剂对粉体氧含量的影响,用SEM观察了烧结样品的组织形貌.该永磁体的剩余磁感应强度为1.16～1.2 T,内禀矫顽力为960～1 000 kA/m,磁能积为248～264 kJ/m3.该磁体性能与N33,N35钕铁硼磁体性能相当.     

一次回火温度对烧结NdFeB永磁材料组织和性能的影响

探讨了880~900℃、910~930℃、940~960℃温度区间下1h回火处理对Nd30Dy3.5Al0.2B1合金显微组织和磁性能的影响。研究表明,温度低于910℃时,晶界富Nd带过厚且积聚,主相体积分数小,矫顽力、磁能积低;温度高于930℃时,晶粒尺寸过大,晶界面积变小,晶界富Nd带加厚,矫顽力、磁能积均下降;910~930℃时晶粒尺寸趋向均匀,晶界富Nd带呈薄层状分布,磁性能最佳。     

Properties improvement and structural optimization of sintered NdFeB magnets by non-rare earth compound grain boundary diffusion

Grain boundary diffusion using rare earth (RE)-containing compounds has recently become an effective approach for improving the coercivity and reducing the heavy RE content in sintered NdFeB magnets. Here we report the enhancement of magnetic properties and corrosion resistance of NdFeB magnets by a non-RE compound diffusion process. The Dy-free sintered NdFeB magnets were coated with an MgO layer by magnetron sputtering, followed by solid diffusion heat treatment. With the successful diffusion of MgO into the magnet, the coercivity increasing from 1094 to 1170 kA/m and the maximum energy product increasing from 240 to 261 kJ/m³, together with the enhanced temperature stability and corrosion resistance, have been demonstrated. The underlying mechanisms for these enhancements have been analyzed. Microstructural investigations show that MgO entered mainly into the intergranular regions and modified the composition and structure of the grain boundary phase. The intergranular Nd–O–Fe–Mg phases observed in the MgO diffused magnet contribute to the improved performance. The current non-RE compound grain boundary diffusion process has significance in further minimizing the use of rare earth (RE).     

Tuning magnetic properties,thermal stability and microstructure of NdFeB magnets with diffusing Pr-Zn films

Grain boundary diffusion process(GBDP) serves as a promising approach in improving magnetic properties and thermal stability of Nd FeB permanent magnets. Herein, non-heavy rare earth Pr-Zn films deposited on the magnet surface using DC-magnetron sputtering system are reported. The thermal stability and coercivity enhancement mechanism of Pr-Zn GBDP magnets were investigated. Results show that the coercivity of Pr-Zn GBDP magnet increases from 963.96 kA m~(-1) to 1317.14 kA m~(-1) without any remanence reduction. Notably, the demagnetization curve of Pr-Zn GBDP magnet still remains a high squareness ratio. The temperature coefficient of coercivity and anti-demagnetization ability of Pr-Zn GBDP magnet under high temperatures are improved after GBDP treatment. The well-optimized rare earth-rich(RE-rich) grain boundary phases and high effective anisotropy field of(Nd,RE)2 Fe14 B magnetic hardening layers surrounding main grains are the key factors to impact the magnetic properties and thermal stability of Nd FeB permanent magnets via GBDP treatment.     

High coercivity (Nd8Y3)–(Fe62Nb3Cr1)–B23 magnets produced by injection casting

High coercivity (Nd₈Y₃)–(Fe₆₂Nb₃Cr₁)–B₂₃ magnets in rods have been produced by copper mold injection casting. Magnetic properties, microstructure, and phase evolution in the as-cast and annealed states have been presented and discussed. The (Nd₈Y₃)–(Fe₆₂Nb₃Cr₁)–B₂₃ alloys show hard magnetic properties in the as-cast state. Annealing induces ideal microstructure containing magnetically hard and soft phases with hard/soft volume ratio of 73/27. Exchange coupling between magnetically hard (Nd,Y)₂Fe₁₄B phase and soft α-Fe (Fe₃B) phase leads to excellent hard magnetic properties. Highest coercivity of 1230 kA/m in (Nd₈Y₃)–(Fe₆₂Nb₃Cr₁)–B₂₃ magnet originates from the large amount of hard phase with high magnetocrystalline anisotropy, formation of thin grain boundary phase and refinement of magnetic grains. Nb and Cr doping modify the magnetic phases. Annealed magnetic rods with a diameter of 2 mm and 36 mm in length demonstrated the maximum magnetic properties i.e., _iH_c of 1230 kA/m, B_r of 0.49 T, and (BH)_max of 45.6 kJ/m³.     

Role of lanthanum in microstructure evolution and enhanced magnetic properties of cerium-containing sintered magnets

In this study, lanthanum was applied to strip cast Ce−Fe−B alloy to improve its phase composition and microstructure. The results reveal that lanthanum doping can significantly enhance the proportion of 2 : 14 : 1 phase and improve the microstructure of Ce−Fe−B alloy. Besides, the influence of the starting alloys structure on the microstructure and magnetic properties of final multi-phases cerium-containing magnets was also systematically investigated. Compared to the multi-phases magnet without lanthanum addition, a pronounced coercivity increment could be distinguished in lanthanum-doping multi-phases magnet, which could be attributed to the finer grain size together with ideal grain boundary. In this work, the superior performance of H_cj = 701.28 kA/m B_r = 1.30 T, and (BH)_max = 313.70 kJ/m³ were obtained by blending Nd−Fe−B alloy with (La_0.35Ce_0.65)-Fe−B alloy to meet 25.0 wt.% lanthanum-cerium utilization content, suggesting that the possibility to develop high abundant rare earth permanent magnetic materials.     

New kind of NdFeB magnet prepared by spark plasma sintering

We have produced an anisotropic Nd/sub 15.5/Dy/sub 1.0/Fe/sub 72.7/Co/sub 3.0/B/sub 6.8/Al/sub 1.0/ magnet by the spark plasma sintering (SPS) technique and compared it with a magnet of the same composition processed by the conventional sintering method. We investigated magnetic properties, microstructure, and constituents by a B-H loop-line instrument, a scanning electron microscope, and an energy-dispersive X-ray detector, and studied the effects of processing conditions on the magnetic properties, dimensional precision, and density. We also examined the magnet's electrochemical properties in electrolytes and its corrosion behavior in oxidizing environments. We found that the microstructure of the SPS NdFeB magnet is different from that of the conventional one. In the SPS-processed magnet, the grain size is fine and uniform while the distribution of the Nd-rich phase is heterogeneous. The SPS NdFeB magnet has a maximum energy product of 240 kJ/m/sup 3/ and a coercive force of 1260 kA/m. The density of the magnet reaches 7.58 g/cm/sup 3/, and its dimensional precision is about 20 /spl mu/m. The electrochemical properties and the corrosion resistance of the SPS NdFeB magnet are better than those of the conventional one. The SPS process is a promising method for the production of NdFeB magnets with ideal overall performance.     

Microstructural and magnetic studies on P/M processed (Nd14.9Dy1.9)(Fe65.0Co8.0Cu1.0Ga1.0Nb0.7) B7.5 alloy

Sintered samples of (Nd_14.9 Dy_1.9) (Fe₆₅ Co₈ Cu_1.0 Ga_1.0 Nb_0.7)B_7.5 were prepared and subjected to stepwise annealing in the temperature range 875 K–675 K. The XRD and metallographic (optical and electron microscopy) studies reveal a multi-phase microstructure with each phase showing different solubility of the alloying additions. This alloy has T _C of 705 K with an intrinsic coercivity of 1000 kA/m and energy product of 250 kJ/m³ at RT. Solubility of Co into the matrix phase and that of Ga and Cu into the Nd-rich grain boundary phase are considered to be the main contributing factors for the significant enhancement in T _C and H _ci respectively of the multi-component alloy when compared to those of ternary NdFeB, wherein H _ci = 720 kA/m and T _C = 585 K.     

Microstructure and properties of Nd-Fe-B magnets prepared by spark plasma sintering

Abstract

Anisotropic Nd₁₅.₅Dy₁.₀Fe_BalCo₃.₀B₆.₈Al₁.₀ magnets were produced by the spark plasma sintering (SPS) technique. The effects of processing conditions on the microstructure, magnetic properties, dimensional precision and density of the magnets were studied. The magnetic properties, microstructure and constituents were investigated by means of a magnetic flux density - magnetic field strength (B-H) loopline instrument, scanning electron microscopy and energy dispersive X-ray analysis. The density of the magnets was determined by the Archimedes method, and the dimensional precision of the magnets was measured by micrometer. It was found that the microstructure of SPS processed Nd-Fe-B magnets is unique; the grain size is fine and uniform while distribution of the neodymium rich phase is heterogeneous. The optimal magnetic properties of SPS processed Nd-Fe-B magnets obtained so far are maximum energy product of 240 kJ m^-3 and coercive force of 1260 kA m^-1. The dimensional precision of the magnets is ~ 20 μm, and the density of the magnets reaches 7.58 g cm^-3.     

Study of the morphological and magnetic microstructure of SmCo5 magnets

In this paper, high-coercivity sintered SmCo₅ permanent magnets were investigated. The study of the morphological microstructure was performed by scanning electron microscopy (SEM) using backscattered electron imaging and energy dispersive X-ray (EDX) microanalysis, and the magnetic microstructure was observed with magnetic force microscopy (MFM) in the thermally demagnetized state of the magnets at the surface perpendicular to the alignment axis. In addition to the main SmCo₅ phase, an appreciable amount of a mixture of the Sm₂Co₇ and Sm₅Co₁₉ phases, pores, Sm oxides and carbon was detected. The grains exhibited magnetic domains. Except for rare cases, the domains were continuous from grain to grain, indicating good magnetic alignment of the individual grains.     

混合合金法添加DyH_x对烧结Nd-Fe-B磁体性能和微观结构的影响

以Nd31.5FebalB6.0Co1.2Cu0.04(质量分数,%)为母合金,添加不同含量DyHx粉研究Dy对Nd-Fe-B磁体性能和微观结构的影响。研究发现,Dy未扩散到主相晶粒中,主要分布在晶界相中;Dy使磁体晶粒得到细化、均匀化,异常长大晶粒基本消失,晶粒边界结构得到改善;添加0.5%(质量分数)的DyHx粉可以明显提高磁体矫顽力Hcj,但添加量超过1.0%(质量分数),磁体矫顽力Hcj增幅变小,磁体密度严重下降。