Nd_2Fe_(14)B/α-Fe纳米双相复合永磁体研究进展

阐述了Nd2Fe14B/α-Fe纳米双相复合永磁体的磁学特性、制备方法及矫顽力机制;并结合近年来纳米复合永磁体研究的新进展,讨论了制备工艺,添加合金化元素,微结构与磁体性能的关系;最后指出了纳米复合永磁体目前存在的问题和今后的发展方向。     

声化学法与放电等离子烧结制备Nd-Fe-B/α-Fe纳米晶复合磁体

采用声化学法制备Nd-Fe-B/α-Fe型双相包覆磁粉，再经放电等离子烧结（SPS）制备成致密块状磁体．研究了不同α-Fe包覆含量对复合磁体磁性能及微观结构的影响．结果表明，声化学法可以制备均匀混和的双相纳米磁粉，α-Fe纳米粉均匀的包覆在硬磁相颗粒周围．烧结后的各向同性磁体有明显的剩磁增强，具有较高的磁性能．当α-Fe包覆量为2％（体积分数）时，磁体性能最佳，其（BH）max值为148．64kJ/m^3．     

高性能Nd-Fe-B复合永磁材料微磁结构与矫顽力机制

概述了近年来有关高性能Nd-Fe-B复合永磁材料矫顽力机制的研究进展,研究了工艺过程对矫顽力的影响机制和所适应的理论模型,重点探讨了双主相合金技术制备的高性能永磁材料的微结构特征与矫顽力的关系,尝试解释了双主相合金技术制备的高性能永磁材料的矫顽力机制 由传统的单合金或双合金工艺制备磁体的矫顽力机制可用发动场理论解释,且与实际相符较好.探讨了热压/热流变磁体各向异性的形成,展示了热退磁过程中烧结和热压/热流变磁体畴结构的演变规律.制备出最大磁能积约为424 kJ/m3的各向异性纳米品Nd-Fe-B磁体,研究表明,各向异性的产生主要源于再结晶过程中晶粒的择优生长和通过边界液相所促进的晶粒滑移和旋转.揭示出高性能各向异性纳米晶Nd-Fe-B磁体的典型磁畴结构是一种交换耦合畴.交换耦合畴的温度依赖关系是影响磁体使用温度的主要因素.     

Nd2Fe14B/α-Fe纳米复合永磁的制备和性能

用超声化学法制备纳米Fe颗粒包覆的Nd2Fe14B复合粉体,将其在Ar气保护下经放电等离子烧结(SPS),得到Nd2Fe14B/α-Fe纳米晶复合磁体.Fe名义质量分数为5%的烧结磁体具有较高的磁性能:Br=0.86 T,Hci=683.8 kA/m,(BH)max=95.92 kJ/m3.烧结前对复合粉末进行适当的高能球磨,能促进显微组织进一步细化,增强软磁相与硬磁相之间的交换耦合,使相同Fe含量和烧结工艺的磁体Br和(BH)max分别提高到0.94 T和113.6 kJ/m3.     

NdFeB纳米晶复合永磁材料的研究

自从NdFeB纳米晶复合永磁材料出现以来．由于其潜在的优异磁性能和巨大的商业价值,成为近几年来磁性材料领域研究的热点。本文重点论述添加合金元素和制备工艺对NdFeBN米晶永磁材料的微观结构和磁性能的影响,并概述近年来新的晶化工艺。     

Fe3B基纳米复合永磁材料的微结构和性能

利用差热(扫描)分析、X射线、透射电镜、振动样品磁强计研究了添加Co、Dy对Fe3B／Nd2Fe14B 纳米复合永磁材料的微结构和性能的影响．结果表明：添加适当的微量元素可以提高Nd4．5Fe77B18．5纳米复合永磁材料的内禀磁性，改进微结构，从而提高材料的永磁性能．在Nd4．5Fe77B18．5中添加1％-3％(原子分数)的Co、Dy明显地降低材料的晶化温度和最佳热处理温度、提高了2：14：1相的居里温度、改善了纳米复合永磁材料的微观结构，从而提高材料的永磁性能．与Nd4．5Fe77B18．5相比，Nd3．5Fe74Co3DylBl8.5的永磁性能为：Br=1.06T，jHc=328kA／m，(BH)max=108．9kJ／m^3，分别提高了26％，17％和104％．     

Nd2Fe14B/α-Fe纳米复相永磁合金微结构的形成

研究了使用不同快淬速度制备的Nd3 6Pr5 4Fe83Co3B5合金中Nd2Fe14B/α-Fe复合纳米晶结构的形成.采用X射线(XRD)、透射显微(TEM)分析技术和振动样品磁强计(VSM)观测和测量了材料的微结构和磁性.结果表明,使用最佳淬速(20m/s)形成的Nd2Fe14B/α-Fe复合纳米晶结构晶粒细小,晶粒尺寸均匀Nd2Fe14B相和α-Fe相的平均晶粒尺寸分别为14nm、16nm.合金中α-Fe相的体积分数为48.6%.纳米晶合金的磁性能为Jr=1.108T,Hc=446.5kA/m,(BH)max=193.6kJ/m3,剩磁比Jr/Js=0.736.     

铸锭组织及快淬工艺对R-Fe-B/α-Fe纳米双相永磁性能的影响

研究了名义成分为(Nd1-xPrx)9Fe84.85NbyCuzB5.5的R-Fe-B/α-Fe纳米双相永磁材料.利用扫描电镜和X射线衍射等手段研究了铸锭和快淬带的组织形态和相组成,并分析了铸锭组织和快淬工艺对快淬带和粘结磁体磁性能的影响.结果表明,无论是13kg铸锭还是50g铸锭,都是由基体(Nd(Pr))2Fe14B相,树枝状或颗粒状的α-Fe相,以及少量富Nd(Pr)相组成,只是小铸锭由于冷速快,组织比较细小.分别将13kg铸锭的柱状晶和中心等轴晶以及小铸锭以相同工艺制备成粘结磁体后发现,大铸锭制备的磁体性能略高于小铸锭,同时大铸锭不同部位制备的磁体性能相差约为10%.对于此成分合金,21m/s的快淬速度与700℃×10min的退火工艺是一个较好组合,制备的粘结磁体的最大磁能积为61kJ/m3.     

合金元素在Nd2Fe14B/α-Fe纳米复合永磁材料中的分布

主要利用三维原子探针研究了Nb和Zr等元素在Nd2Fe14B/α-Fe纳米复合永磁材料中的分布情况。研究发现，Nb、Zr等元素的添加改善了合金的微观结构，使得合金晶化后晶粒细小均匀，晶粒形状更为规则，合金的综合磁性能得到提高。三维原子探针分析结果表明，Nb元素不固溶于Nd2Fe14B硬磁性相，主要以NbFeB的形式在晶界处析出；Zr元素在Nd2Fe14B相内有较高的固溶度，与Nb、Fe在晶界处以成份接近（Zr，Nb）Fe2相的形式析出，富Nb相和富Zr相在晶界的析出阻碍了晶粒的长大，进而细化了晶粒，改善了磁性能。     

SmCo_5/α-Fe双相复合纳米晶磁体的结构与磁性研究

超声波分解Fe（CO）5的产物Fe纳米颗粒,通过非均相沉淀获得包覆型SmCo5/α-Fe双相复合磁粉,采用放电等离子快速热压技术（Spark Plasma Sintering,SPS）制备出全致密的各向同性Sm-Co5/α-Fe双相复合纳米晶磁体,研究发现,软磁相α-Fe添加后,磁体的剩磁Mr有所提高,矫顽力Hci则有所减小,随后通过对各向同性磁体进行热变形制备出各向异性磁体,形成了较好的C轴晶体织构。软磁相α-Fe名义含量为10%时,磁体磁性能为：μ0Ms=1.01T、μ0Mr=0.86T、Hci=0.1708T。     

Quasi-sheet multipole permanent magnets

A Rare-Earth Permanent Magnet design system with which a desired pure multipole field can be achieved by accurately deploying REPM blocks around a working region so as to generate magnetic sheet currents which follow the profile of a magnetically soft yoke is presented here. In addition to the general Quasi-Sheet Multipole model, examples of two small operating QSM quadrupoles together with a large QSM dipole are also described.     

ThMn12-Type Alloys for Permanent Magnets

Iron-rich compounds with the tetragonal ThMn₁₂-type structure have the potential to meet current demands for rare-earth-lean permanent magnets with high energy density and operating temperatures of 150–200 °C. However, while it is normal for magnet technology to lag behind the development of underlying magnetic material, this gap has always been unusually large for ThMn₁₂-type magnets. The gap has widened further in recent years, as excellent combinations of intrinsic magnetic properties have been obtained in compounds synthesized with a smaller amount of structure-stabilizing elements (e.g., SmFe₁₁V or Sm_0.8Zr_0.2Fe_9.2Co_2.3Ti_0.5) or with no such elements (i.e., SmFe_9.6Co_2.4 thin films). The search for promising compounds continues—with increasing help coming from theoretical calculations. Unfortunately, progress in the development of magnets beyond polymer-bonded interstitially modified powders remains marginal. The introduction of lanthanum (La) was found to stabilize low-melting-temperature minority phases in Sm(Fe,Ti)₁₂ alloys, thus allowing for liquid-phase sintering for the first time. The high reactivity of La, however, has apparently undermined the development of coercivity (H_c). A controlled crystallization of the initially suppressed ThMn₁₂-type phase makes “bulk” magnetic hardening possible, not only in Sm–Fe–V alloys (in which it has been known since the 1990s), but also is in La-added (Ce,Sm)(Fe,Ti)₁₂ alloys. The properties of the bulk-hardened alloys, however, remain unsatisfactory. Mechanochemically synthesized (Sm,Zr)(Fe,Si)₁₂ and (Sm,Zr)(Fe,Co,Ti)₁₂ powders may become suitable for sintering into powerful fully dense magnets, although not before a higher degree of anisotropy in both alloys and a higher H_c in the latter alloy have been developed.     

Matrix effect in soft metal-bonded samarium-cobalt (SmCo5) permanent magnets

This paper discusses the preparation of samarium-cobalt (SmCo₅) alloy powders by reduction-diffusion process. These powders were blended with equal weight percentages of soft metal/alloy powders, such as indium, tin and solder alloy (Pb-17Sn), to prepare bonded magnets. Important magnetic properties such as remanence, coercivity and energy product of these magnets were measured. Effect of matrix metal/alloy on the magnetic properties of processed magnets is outlined.     

The effects of the air gap between pancake windings on the central magnetic field in a high temperature superconducting magnet

In an HTS magnet consisting of pancake windings, an air gap between the pancake windings can be used to increase the central magnetic field because the air gap increases the critical current of pancake windings. The effects of an air gap on the central magnetic field of an HTS magnet are discussed in this paper according to the various number of turns and also to the number of pancake windings. Results of calculation show the air gap could increase the central magnetic field and the field uniformity simultaneously. The optimum air gap which maximized the central magnetic field was about 4 mm at eight pancake windings and 50 turns per pancake winding. The central magnetic field increased 6.2% from 0.225 T (no air gap) to 0.239 T (4 mm air gap) at that case.     

中国NdFeB磁体产业的10周年

中国NdFeB磁体的研制始于1983年,此后全国如此众多的大学和研究所均介入NdFeB磁体的研究与开发。与此同时,NdFeB磁体的生产也迅速增长。今天中国NdFeB磁体的产量仅次于日本,位居世界第二。本文评述中国NdFeB磁体产业的发展现状和前景,以作为我国NdFeB磁体产业10年历程的纪念。     

Research in High Magnetic Fields: The Installation at the University of Nijmegen

For research in the highest continuous and pulsed magnetic fields large, complex and powerful installations are needed. This paper describes the new 20 MW installation for continuous high magnetic fields that has been built at the University of Nijmegen. The ultra-low ripple power converter provides the capability to perform experiments up to 33 T with resistive magnets (up to 40 T with the hybrid magnet system under construction) and will be of great value for investigations in physics, chemistry and biology at the forefront of fundamental and applied research. Typically during experiments, the magnetic field is slowly varied or held constant for a period lasting from a few minutes to an hour. The cooling installation is designed to allow uninterrupted operation at maximum power for 3 hours, and when the magnetic field is being swept between zero and full field the cooling plant does not pose limits to the operation. When much higher fields are required, there is the option to go to pulsed magnetic fields with duration in the tens of milliseconds.     

高性能各向异性Sm2Fe17Nx磁粉的制备

本文研究了高性能各向异性Ｓｍ２Ｆｅ１７Ｎｘ磁粉的制备工艺路线与工艺参数。优化了制备与工艺参数。已制备出磁性能达到：Ｂｒ＝１．３９Ｔ，Ｈｃｉ＝８５０ＫＡ／ｍ和（ＢＨ）ｍ＝２３６ＫＪ／ｍ＾３的各向异性Ｓｍ２Ｆｅ１７Ｎ２．８８磁粉，该磁粉的各向异性场ＨＡ达到２０Ｔ。     

Preparation of rare earth-cobalt magnet alloy by reduction-diffusion process

Preparation of rare earth-cobalt alloys by reduction-diffusion (R-D) process is described. The process essentially involves mixing of the rare earth oxide and cobalt/cobalt oxide powders in proper proportion and high temperature reduction of the charge in hydrogen atmosphere, followed by aqueous leaching of the reduced mass to yield the alloy powder. Comparison is made of the magnetic properties of the R-D powder with those of the powder prepared by the direct melting (DM) route and it is observed from the reported values for SmCo₅ that the energy product of the R-D powder (∼ 22 MGOe) is only marginally lower than that of the Directly Melted alloy (∼ 25 MGOe). The paper also includes the results of studies carried out at the Bhabha Atomic Research Centre on the preparation of misch metal-cobalt alloy by the R-D process.     

稀土类永磁材料的发展及研究动向

介绍了稀土类永磁材料R-Co系、R-Fe-B系和R-Fe-N系3个发展阶段的研究及应用现状,并讨论了通过交换耦合机制改善稀土永磁材料性能的最新研究动向.