Nd-Fe-B永磁材料低磁时效机理研究

研究烧结Nd-Fe-B磁体的低磁时效问题.实验显示样品在室温293和353K经920d磁时效后，磁通量的衰减率分别为1.4%和13%，经老化处理后，磁通量的衰减率分别为6‰和6.9%，说明未做老化处理的磁体时间稳定性较差. 假设微观杂质运动临界能E₁、极微小杂质运动临界能E₂和移动原子对键取向转动临界能E₃对时间稳定性的影响最为显著，依据半经典的Boltzmann统计分布，导出的烧结Nd-Fe-B磁体的低磁时效所满足的规律.理论结果与实验相符. 关键词： 烧结Nd-Fe-B 低磁时效 临界能 时间稳定性     

烧结Nd-Fe-B磁体的微观结构和冲击韧性研究

对烧结Nd₁₅Fe_72-xCo_yNb_xB₈(y=0, 5;x=0, 05, 10, 15, 20, 25)永磁体的微观结构和冲击韧性及二者间的关系进行了研究.结果表明,添加Nb能够改善Nd-Fe-B磁体的微观结构,提高磁体的冲击韧性.当无Co磁体中Nb的原子百分含量为15%时,其冲击韧性达到最大;对于添加了Co的磁体,其冲击韧性的 关键词： Nd-Fe-B 冲击韧性 微观结构 晶界     

稀土含量对速凝工艺制备(Nd,Dy)-(Fe,Al)-B合金结构和磁性能的影响

采用双合金法制备了不同稀土含量的(Nd,Dy)-(Fe,Al)-B合金系列,研究了稀土含量的多寡对薄带和最终烧结磁体的微观结构和磁性能的影响.研究结果表明,适量的稀土含量(～3145%)不仅能改善速凝带主相(Nd,Dy)₂Fe₁₄B的单相性,还有利于富稀土(Nd,Dy)相在晶界的均匀分布.当主相薄带的稀土含量在接近2∶14∶1相稀土含量时,磁体的内禀矫顽力和磁能积显著提高.当稀土含量较少时,对速凝薄带的合适时效热处理将能有效地提高最终烧结NdFeB磁体的磁特性. 关键词： 双相烧结 速凝技术 微观结构 磁性能     

纳米晶永磁中面缺陷对畴壁钉扎机理的研究

畴壁钉扎模型的矫顽力可以表示为Hc=αpink2K1/μ0Ms-NeffMs，计算了微结构参数αpink随面缺陷内磁性参数A′和K′1的变化情况.结果表明，αpink可以在很宽的范围里取值.结合纳米单相Nd2Fe14B磁体，研究了晶粒边界的磁性参数和晶界厚度对αpink的影响，当A′/A=05，K′1/K1=01，以及晶界厚度r0＝332nm时，αpink最大.同时研究了纳米复相Nd2Fe14B/α-Fe磁体的αpink随α-Fe晶粒尺寸r0的变化情况，当r0＝7nm时，αpink最大. 关键词： 面缺陷 矫顽力 钉扎机理 纳米晶     

相分布和晶粒尺寸对Nd2Fe14B/ɑ-Fe纳米复合永磁材料矫顽力的影响

本文采用统计平均方法研究了软、硬磁性晶粒尺寸及相分布对Nd2Fe14B/α-Fe纳米复合永磁材料矫顽力的影响。计算结果表明：对于单相纳米硬磁材料，磁体矫顽力随着硬磁性晶粒尺寸的减小而降低；对于软、硬两磁性相组成的Nd2Fe14B/a-Fe纳米复合永磁材料，两相的随机分布将导致磁体矫顽力随硬磁性晶粒尺寸的减小呈现极大值。本文的计算结果还表明当硬磁性晶粒尺寸大于软磁性晶粒的最佳尺寸时(15nm)，具有多层膜结构的Nd2Fe14B/a-Fe纳米复合永磁材料将比两相随机分布时具有更大的矫顽力。     

烧结Nd-Fe-B磁体的磁性能一致性与其微观结构的关系

分析了微观结构和热处理工艺对矫顽力的影响,发现在矫顽力一定的情况下,磁体的微观结构越“差”,则保证不同批次磁体矫顽力变化不大于某一给定值所需的工艺条件就越严格;反之则越宽松.就同一炉产品而言,微观结构越好的磁体,其矫顽力受烧结(热处理)炉温度梯度的影响越小,其结果是该炉产品的一致性越高.反之,受温度梯度的影响越大,磁体的一致性也就越低.该研究结果说明:在条件许可的情况下,应首先考虑通过改善磁体的微观结构来提高磁性能一致性. 关键词： Nd-Fe-B永磁体 微观结构 内禀矫顽力 一致性     

高温超导线圈制备的绝缘技术研究

建立了电热耦合模型,根据热力学原理,以最大温度梯度为目标,对双饼线圈进行了三维有限元分析,为超导磁体的制备选择了一种性能良好的绝缘材料.为了探究仿真选型的绝缘材料对高温超导储能磁体电磁性能的影响,绕制了A、B两个双饼线圈进行了浸渍工艺实验研究,对线圈A、B分别采用了直接浸泡式和真空压力式浸渍进行绝缘处理,与浸渍固化前相...     

添加Nb在快淬NdFeB永磁体中的作用研究

系统研究了Nb元素的添加对快淬(Nd,Dy)_11.5Fe_82.4-nNb_nB_6.1(n=0,0.5,1,1.5,2)永磁体磁性能、温度特性及显微组织的影响. 结果表明：少量Nb元素的添加可以在不显著影响剩磁的情况下较大幅度提高磁体的内禀矫顽力，降低磁通不可逆损失. Nb在NdFeB磁体中的作用是使晶粒细小化、均匀化、规则化，提高交换耦合钉扎场H_p，减小材料内部的散磁场，显著降低磁通不可逆损失，改善NdFeB磁体在高温下的使用性能.     

Nd-Fe-B/FeCo多层纳米复合膜的结构和磁性

制备了Nd₂₈Fe₆₆B₆/Fe₅₀Co₅₀多层纳米复合磁性薄膜，对溅射态和650℃退火处理15 min试样的相成分分析和微结构的观察显示，溅射态薄膜呈非晶态，经650℃退火处理15 min后，薄膜主要相成分为硬磁性Nd₂Fe₁₄B相和软磁性相FeCo(110)相.Nd₂Fe₁₄B相呈柱状，其易磁化c轴垂直于膜面，尺寸约10 nm.在硬磁性相和软磁性相之间存在少量富Nd相和非晶态，富Nd相大小约7 nm.磁性测量和分析表明，1)该系列薄膜退火态具有垂直于膜面的磁晶各向异性.2)对于固定厚度(10 nm)层Nd-Fe-B和不同厚度(t_FeCo=1—100 nm)层FeCo多层纳米复合膜,剩磁随软磁相FeCo 厚度的增加快速增加，而矫顽力则减小.当t_FeCo=5 nm时，最大磁能积达到200 kJ/m³. 3)硬磁相Nd-Fe-B层和软磁相FeCo层之间交换耦合导致剩磁和磁能积增强. 关键词： Nd-Fe-B/FeCo多层纳米复合膜 交换耦合 磁各向异性     

晶粒边界对Nd2Fe14B/α-Fe纳米复合材料性能的影响

用快淬急冷技术制备了Nd10Fe84-xB6Inx(x=0和1)系列薄带磁体.利用添加和挥发微量In元素的方法从宏观表现上研究了晶粒边界对晶粒之间交换耦合和磁硬化等性能的影响.发现晶粒边界性质以不同方式影响着磁体矫顽力和剩磁比.某些晶界特性,像缺陷、应力等主要影响磁硬化机制;而另外一些性能,如晶界类型、边界处的自旋取向及结晶学相关性等则控制着交换耦合的强度.     

The effects of annealing at 1000 °C for 24 h on the extrinsic properties of Pr-Fe-B and Nd-Fe-B-type sintered magnets

Recent studies have shown the effects of a post sintering heat treatment at 1000 °C for 24 h on the microstructure and magnetic properties of Pr-Fe-B/Nd-Fe-B magnets based on Nd₁₆Fe₇₆B₈ and Pr₁₆Fe₇₆B₈. In an attempt to understand the influence of environmental factors, an investigation into the effects of annealing under different degrees of vacuum for both types of sintered magnets has been carried out. The effect of annealing the Pr-Fe-B magnets at 1000 °C for 24 h resulted in a general increase in the magnetic properties, especially the intrinsic coercivity, although the degree of improvement appeared to be dependent on the initial annealing conditions (ambient pressure). Oxygen analysis of sintered and annealed magnets indicates a change in the nature of the grain boundary phases after the annealing treatment. The effect of annealing the Nd-Fe-B magnets at 1000 °C for 24 h resulted in a general decrease in the magnetic properties, especially the intrinsic coercivity.     

添加Dy元素对钕铁硼速凝片微观组织和磁特性的影响

本文讨论了不同含量的Dy元素对速凝条带微观组织的影响,得出Dy的添加量为1%—2%(at%)时条带的微观结构得到最优化,柱状晶生长均匀一致,具有良好的沿c轴取向度.同时,急冷面的细小等轴晶生长区域减少,氢破后相应的磁粉抗氧化性能增强. 关键词： 速凝片 织构 微观组织 氢破     

Effects of compositions on characteristics and microstructures for melt-spun ribbons and die-upset magnets of Nd12.8+xFe81.2−x−y−zCoyGazB6

The effects of varying Nd-contents on the magnetic properties of Nd_12.8+xFe_{81.2−x−y−z}Co_yGa_zB₆ ribbons and the resulting die-upset magnets have been investigated. It was found that the Nd content has a significant effect on both magnetic properties and texture of the die-upset magnets. An optimum Nd content exhibits good texture, while both Nd-lean and excessively Nd-rich Nd-Fe-B alloys lead to unsatisfactory textures. The magnetic properties and texture of the die-upset magnets strongly deteriorated with a further increase in the Nd-content. The thermo-mechanical characteristics and the formation mechanism of two kinds of cracks in backward-extruded ring magnets have also been investigated.     

Changes of microstructure and magnetic properties of Nd-Fe-B sintered magnets by doping Al-Cu

The microstructural and magnetic properties of Al_100−xCu_x (15at%≤x≤45 at%) doped Nd-Fe-B magnets were studied. The distribution and alloying effects of Cu or Al on the intergranular microstructure were investigated by thermodynamic analysis, differential scanning calorimetery and microscopy techniques. It was observed that when the Cu content of Al_100xCu_x exceeds to 25 at%, the (Pr, Nd)Cu and CuAl₂ phases form in these magnets. The formation of (Pr, Nd)Cu phase depends on the negative formation enthalpy of (Pr, Nd)Cu and the exclusive distribution of Cu in the intergranular regions. The eutectic reaction between (Pr, Nd)Cu phase and (Pr, Nd) occurs at 480 °C, which forms the liquid phase that dissolves the (Pr, Nd)₂Fe₁₄B surface irregularities and thus increases the quantities of (Pr, Nd)-rich phase at the grain boundaries. These changes benefit the grain boundary microstructure, especially the distribution of (Pr, Nd)-rich phase, which effectively improves the intrinsic coercivity _iH_c due to the decreases of exchange coupling between the (Pr, Nd)₂Fe₁₄B grains.     

Rare earth-cobalt permanent magnets

This paper reviews the historical background and the development of rare earth-cobalt-based permanent magnets from basic science studies on rare earth-transition metal alloys in the 1960's to today's broad spectrum of commercial magnet types and their applications. It puts the RE-Co magnets in perspective relative to older magnet types and also traces the path to the subsequent development of the related Nd-Fe-B magnets. The treatment is qualitative, with emphasis on the relationship between fundamental properties of the compounds and the interaction between microstructure and magnetic domain walls that makes high coercivity and the exceptional hard magnetic properties of the rare-earth magnets possible. The various kinds of RE-Co magnets in production and use today, some of their engineering properties, and economic aspects governing their applicability, cost and availability are also discussed. Many references provide a guide to the special literature regarding the physics, metallurgy, manufacture, product selection and properties of rare earth-cobalt magnets.     

烧结NdFeB断裂方式及其断面的微观结构

 经熔炼、制粉、成型、烧结和回火等工序制备了成分为Nd₃₃Fe_65.95B_1.05（质量分数）的烧结NdFeB磁体,将铸锭样品和烧结磁体样品折断,并采用扫描电子显微镜和金相显微镜对二者的断裂方式和断面的微观结构进行了对比分析。结果表明：烧结NdFeB铸锭的断裂方式为沿晶断裂,断面处有较多的层状富钕相,多边形的主相较为完整;烧结NdFeB磁体既有沿晶断裂也有穿晶断裂,但是以沿晶断裂为主。分析造成烧结NdFeB磁体断裂的原因为：（1）其微观结构中有大量的孔洞等缺陷,这是外部原因;（2）微观结构中占主要成分的主相的维氏硬度为6 235.94 N·mm^-2,富钕相的维氏硬度为5 947.42 N·mm^-2,二者有较大的差距,这是本征因素。针对磁体中孔洞和夹杂等缺陷存在而造成的断裂提出了相应的解决措施。     

Effect of die-upset level on the mechanical properties and microstructure of Nd-Fe-B magnets prepared by spark plasma sintering

The mechanical properties and microstructure of Nd-Fe-B magnets produced at various die-upset levels have been investigated. The results showed that the Vickers hardness and the fracture toughness of Nd-Fe-B magnets first increased, and then rapidly decreased with the increase in die-upset level. The optimum Vickers hardness and the fracture toughness were obtained at the die-upset level of 40%. The peak intensity of the (1 0 5) peak is the maximum value, the relative intensities of the (2 1 2), (2 1 4) and (3 1 4) peaks decline and the relative intensity of the (0 0 6) peak increases with the increase in die-upset level. The microstructures show that the variation in the size of small spherical grains is not obvious, and the volume fraction of small spherical grains declines gradually with the increase in die-upset level.     

Effects of terbium sulfide addition on magnetic properties,microstructure and thermal stability of sintered Nd-Fe--B magnets

To increase coercivity and thermal stability of sintered Nd–Fe–B magnets for high-temperature applications, a novel terbium sulfide powder is added into(Pr_(0.25)Nd_(0.75))_(30.6)Cu_(0.15)Fe_(bal)B_1(wt.%) basic magnets. The effects of the addition of terbium sulfide on magnetic properties, microstructure, and thermal stability of sintered Nd–Fe–B magnets are investigated.The experimental results show that by adding 3 wt.% Tb_2S_3, the coercivity of the magnet is remarkably increased by about 54% without a considerable reduction in remanence and maximum energy product. By means of the electron probe microanalyzer(EPMA) technology, it is observed that Tb is mainly present in the outer region of 2:14:1 matrix grains and forms a well-developed Tb-shell phase, resulting in enhancement of HA, which accounts for the coercivity enhancement.Moreover, compared with Tb_2S_3-free magnets, the reversible temperature coefficients of remanence(α) and coercivity(β) and the irreversible flux loss of magnetic flow(hirr) values of Tb_2S_3-added magnets are improved, indicating that the thermal stability of the magnets is also effectively improved.