Effect of In doping on the evolution of microstructure,magnetic properties and corrosion resistance of NdFeB magnets

The grain boundary phase affects the magnetic properties and corrosion resistance of sintered NdFeB magnets.In this work,a small amount of In was added to NdFeB magnets by induction melting to systematically investigate its effect on the evolution of the microstructure,magnetic properties and corrosion resistance of NdFeB magnets.Microstructural analysis illustrated that minor In addition generated more grain boundary phases and an abundant amorphous phase at the triple-junction grain boundary.While the addition of In failed to enhance the magnetic isolation effect between adjacent matrix grains,its incorporation fortuitously elevated the electrochemical potential of the In-containing magnets.Besides,during corrosion,an In-rich precipitate phase formed,hindering the ingress of the corrosive medium into the magnet.Consequently,this significantly bolstered the corrosion resistance of the sintered NdFeB magnets.The phase formation,magnetic properties and corrosion resistance of In-doped NdFeB magnets are detailed in this work,which provides new prospects for the preparation of high-performance sintered NdFeB magnets.

透射电镜强磁场原位样品台的研发及其应用

本文介绍了一种可施加水平强磁场的透射电镜样品台。通过降低磁场发生端面沿电子束方向的厚度,实现了增加磁场强度时较小的电子束偏折角度,在施加较强水平磁场的情况下仍然可以清晰地成像。在加速电压为200 kV的透射电镜中能够施加的最大磁场数值为075 T,远高于国际上现有装置的数值。利用该样品台成功观察了饱和磁场为06 T的AlNiCo磁体样品的磁化过程。

W对烧结NdFeB磁体的显微组织和磁性能的影响

主要研究了在烧结ＮｄＦｅＢ磁体的晶界添加Ｗ对显微组织和磁性能的影响。实验结果表明，随Ｗ添加量的增大，晶粒逐渐细化，剩磁稍有下降，而矫顽力逐渐升高。在含Ｗ为１％ｗｔ时，矫顽力达到峰值。扫描电镜的观察显示，加Ｗ磁体中在晶界区生成许多杆状相。能谱和Ｘ射线衍射分析均表明此相为ＷＦｅＢ化合物。

时效对NdFeB烧结磁体的矫顽力和显微组织的影响

本文主要研究了时效对ＮｄＦｅＢ烧结磁体的矫顽力和显微组织的影响。结果表明，６００℃左右的时效可显著提高烧结ＮｄＦｅＢ磁体的矫顽力。原因在于：①时效使主相晶界平直、规整，从而使反磁化畴难以形核。②晶界中的微粒相数量增多，强化了对晶界的钉扎。正是这两种因素的共同作用使得时效后磁体的矫顽力提高了。

纯石墨粉对NdFeB烧结磁体的显微组织和磁性能的影响

主要研究了在烧结 Nd Fe B磁体的晶界添加C对显微组织和磁性能的影响。实验结果表明 ,随 C添加量的增大 ,晶粒先粗化再细化 ,矫顽力呈先下降后上升再下降的趋势。当 C含量达到 0 .4 % wt时 ,晶界变得零乱而不规整。 X射线衍射分析表明此时磁体内生成了 Nd2 Fe17C相。矫顽力和晶粒尺寸的变化均与Nd2 Fe17C的生成有关。

高性能辐射取向环对圆柱型音圈电机的影响

对粉末冶金烧结和热压工艺制备的两种辐射取向环进行了磁环和装机对比测试。不同测试温度下,热压辐射环的静态磁性能均优于烧结辐射环。相同充磁电流下,同尺寸的热压辐射环圆周磁通比烧结辐射环提高近50%。将两种辐射环装入同一圆柱型音圈电机,相同测试条件下,热压环电机比烧结环电机增大了15%的推力,且到达80℃截止温度的时间延长一倍以上,测试结果表明高性能辐射环可有效提高圆柱型音圈电机的性能。

磁体阵列及性能对圆筒型直线电机的影响

研究了轴向、辐向及Halbach磁体阵列和性能对圆筒型直线电机的影响。磁通有限元分析表明,当主轴长度确定时,轴向或径向磁体阵列存在最佳的磁体对数,Halbach磁体阵列的磁通随辐向环剩磁的提高而增加。采用热压法和烧结法制造的磁体在晶粒微观结构上存在明显差别,热压环的剩磁、充磁后圆周和轴向磁通的大小和均匀性均优于烧结环。实验电机测试表明,相同电流下Halbach磁体阵列的推力比轴向磁体阵列的提高了近一倍,而采用高性能热压环的推力比烧结环的增加了15%。

热压过程对热变形钕铁硼磁体磁性能影响的研究

介绍了利用快淬粉制备全密度、高性能、各项异性钕铁硼稀土永磁体的有效方法—热压、热变形方法。成功制备出了磁能积BHm约3.44×105T·(A/m),剩磁Br约1.352T,矫顽力Hcj约1×106A/m的热变形钕铁硼磁体。利用XRD、VSM、PPMS、SEM等材料表征手段对样品磁性能的各项异性以及取向度进行了分析,并讨论了工艺参数对样品磁性能的影响。

Improvement of coercivity thermal stability of sintered 2:17 SmCo permanent magnet by Nd doping

The effects of Nd doping on the microstructures and magnetic properties of Sm_(1-x)Nd_(x)(Co_(0.695)Fe_(0.2)Cu_(0.08)Zr_(0.025))7.2(x = 0, 0.3, 0.5, 0.7, 1.0) permanent magnets are studied. The scanning electron microscope(SEM) analysis of the solid solution states of the magnets shows that with the increase of Nd content, the distribution of elements becomes inhomogeneous and miscellaneous phase will be generated. Positive temperature coefficient of coercivity(β) appears in each of the samples with x = 0.3, 0.5, and 0.7. The corresponding positive β temperatures are in ranges of about 70 K–170 K,60 K–260 K, 182 K–490 K for the samples with x = 0.3, 0.5, and 0.7, respectively. Thermomagnetic analysis shows that spin-reorientation-transition(SRT) of the cell boundary phase is responsible for this phenomenon. On the basis of this discovery, the Sm_(0.7)Nd_(0.3)(Co_(0.695)Fe_(0.2)Cu_(0.08)Zr_(0.025))7.2magnet possessing thermal stability with β ≈-0.002 %/K at the temperature in a range of 150 K–200 K is obtained.

基于Maxwell的电磁阀导磁部件分析与优化

利用电磁场有限元分析软件Maxwell建立电磁阀二维模型,研究电磁阀导磁部件的结构和材料属性对电磁阀性能的影响。通过对电磁阀的铁心直径、气隙、线圈位置、材料属性等关键参数进行静态/动态仿真分析,计算不同参数下行程与磁力的关系,经过对比得出优化参数。在保持同样大小电压输入前提条件下,在行程为0时,优化后的电磁阀模型电磁力增大了约2倍,且体积减小5.2%。与初始模型相比,该模型能耗低、制造成本低、电磁力大、响应速度快。

Sm_2Co_(17)永磁材料力学各向异性机理分析

烧结Sm2Co17型永磁材料以其优良的磁性能、良好的耐腐蚀性和温度稳定性得到广泛应用。但其脆性较大,不仅给机械加工带来困难,也限制了材料在一些领域的应用。从Sm2Co17永磁材料微观晶体结构入手,分析了Sm2Co17永磁材料力学特性各向异性的机理。研究表明,Fe、Cu和Zr等掺杂元素、界面效应以及主相晶体结构导致了Sm2Co17永磁材料力学性能的各向异性,其中主相晶体结构的特性对力学性能各向异性起关键作用。研究结果为改善2:17型钐钴永磁材料的力学特性提供了理论指导。

基于Ansoft Maxwell的电磁阀二维仿真可靠性验证

利用Ansoft Maxwell软件二维/三维建模对电磁阀进行仿真分析被广泛应用于电磁阀设计。采用Maxwell建立电磁阀三维模型和二维轴对称模型,保持三维模型和二维模型求解参数一致,进行仿真分析。通过对比不同行程下三维模型和二维模型轴对称模型的仿真结果,验证了二维/三维模型电磁力大小的一致性,并且发现二维轴对称模型相比三维模型收敛次数少,仿真耗时短,计算精度高。采用二维模型代替三维模型对轴对称的电磁阀进行仿真计算,大大提高计算效率、缩短研发周期、降低研发成本。

Coercivity enhancement of sintered Nd–Fe–B magnets by grain boundary diffusion with Pr_(80-x)Al_(x)Cu_(20)alloys

A grain boundary diffusion(GBD)process with Pr_(80-x)Al_(x)Cu_(20)(x=0,10,15,20)low melting point alloys was applied to commercial 42M sintered Nd–Fe–B magnets.The best coercivity enhancement of a diffused magnet was for the Pr_(65)Al_(15)Cu_(20)GBD magnet,from 16.38 kOe to 22.38 kOe.Microstructural investigations indicated that increase in the Al content in the diffusion source can form a continuous grain boundary(GB)phase,optimizing the microstructure to enhance the coercivity.The coercivity enhancement is mainly due to the formation of a continuous GB phase to separate the main phase grains.Exchange decoupling between the adjacent main phase grains is enhanced after the GBD process.Meanwhile,the introduction of Al can effectively promote the infiltration of Pr into the magnet,which increases the diffusion rate of rare-earth elements within a certain range.This work provides a feasible method to enhance coercivity and reduce the use of rare-earth resources by partial replacement of rare-earth elements with non-rare-earth elements in the diffusion source.

Effect of TbF_(3)diffusion on the demagnetization behavior and domain evolution of sintered Nd-Fe-B magnets by electrophoretic deposition

We studied the magnetic properties and domain evolution of annealed and TbF3-diffused sintered Nd-Fe-B magnets using the electrophoretic deposition method.After TbF_(3)diffusion,the coercivity increased significantly by 9.9 kOe and microstructural analysis suggested that Tb favored the formation of the(Nd,Tb)_(2)Fe_(14)B shell phase in the outer region of the matrix grains.The first magnetization reversal and the dynamic successive domain propagation process were detected with a magneto-optical Kerr microscope.For the TbF_(3)-diffused magnet,the magnetization reversal appeared at a larger applied field and the degree of simultaneous magnetization reversal decreased compared with an annealed magnet.During demagnetization after full magnetization,the occurrence of domain wall motion(DWM)in the reproduced multi-domain regions was observed by the step method.The maximum polarization change resulting from the reproduced DWM was inversely related to the coercivity.The increased coercivity for the diffused magnet was mainly attributed to the more difficult nucleation of the magnetic reversed region owing to the improved magneto-crystalline anisotropy field as a result of Tb diffusion.

Effect of CeO_(2)doping on the coercivity of 2:17 type SmCo magnets

The effects of CeO_(2)doping on the magnetic properties and microstructure of 2:17 type SmCo magnets are studied.With the increase of CeO_(2)from 0 wt.%to 3 wt.%,the coercivity of the magnets increases from 22.22 kOe to over 29.37 kOe,which is an increase of more than 30%.When the doping content is lower than 1 wt.%,the remanence and magnetic energy product of the magnets remain almost constant.Both decrease sharply as the doping concentration further increases.After CeO_(2)doping,the oxide content in the magnet increases significantly and the Ce element is uniformly distributed in the magnet.Observing the magnetic domains reveals that doping with CeO_(2)can refine the magnetic domains and make the magnetic domain wall more stable,resulting in a significant increase in the coercivity of the magnets.

Effect of spin-reorientation transition of cell boundary phases on the temperature dependence of magnetization and coercivity in Sm_(2)Co_(17) magnets

Four Sm_(2)Co_(17)magnets with spin-reorientation transition(SRT)of cell boundary phases(CBPs)are prepared by liquid-phase sintering.The temperature of the SRT of CBPs(T_(SR)^(1:5))is regulated from 125 K to 195 K by adding 0 wt.%,3 wt.%,6 wt.%and 9 wt.%Dy_(88)Cu_(12)alloy powder.The effect of SRT of Sm_(2)Co_(17)magnet CBPs on the temperature dependence of the magnetization(M-T)and coercivity(H-T)is systematically investigated.The temperature dependence of the magnetization is influenced by the SRT of CBPs.The M-T curves measured during the heating process are larger than those measured during the cooling process when T<T_(SR)^(1:5).When T=T_(SR)^(1:5)there is a bifurcation point.When T>T_(SR)^(1:5)the M-T curves overlap and the M-T derivation curve shows that the magnetization of the magnet has low temperature dependence of magnetization above T_(SR)^(1:5).With increasing T_(SR)^(1:5),the initial temperature of the low temperature dependence of magnetization shifts towards a higher temperature.The coercivity temperature coefficient becomes positive as the SRT effect increases,and the temperature range of the positive coercivity temperature coefficient moves towards higher temperatures as T_(SR)^(1:5)increases.This reveals that SRT of CBPs has little effect on the temperature dependence of magnetization above T_(SR)^(1:5),while the temperature dependence of coercivity is optimized.The temperature range of magnetization and coercivity with low temperature dependence tends towards higher temperatures,which is conducive to the preparation of magnets with a low temperature coefficient at higher temperatures.

热渗温度对表面Al合金化Nd-Fe-B烧结磁体的性能及结构的影响

采用表面热渗Al工艺,实现了对Nd-Fe-B烧结磁体的表面保护和优化高温磁性能。通过在Nd-Fe-B烧结磁体表面热渗Al,在磁体表面形成了与基体冶金结合的致密的Al合金层。在Al合金层的保护下,表面热渗Al磁体的耐腐蚀性能得到了明显改善且磁性能保持良好。在高压加速老化测试168 h后,Al-700磁体的单位表面积增重量(3.40 mg·cm^(-2))远低于基体(14.28 mg·cm^(-2))。利用电化学工作站测试了表面热渗Al磁体的极化曲线,其腐蚀电流密度值较基体明显降低。显微组织分析表明,Al合金化层的厚度随热渗温度的增加而增加。在700℃的热渗温度下,晶界内形成了均匀连续的富Al相,从而获得了较优异的综合性能。根据XRD相分析,热渗过程中,随着温度的升高,Al、Fe和Nd原子在合金层中相互扩散越剧烈,磁体表面相继形成Al-Fe相和Nd-(Al,Fe)相。该研究为提高Nd-Fe-B烧结磁体的耐蚀性能和性价比提供了新的思路。

低失重烧结钕铁硼磁体的研究进展

烧结钕铁硼永磁材料被发明以来,以其优越的磁性能得到了广泛的应用,目前成为永磁产业的支柱。但是其耐腐蚀性能差,大大限制了其使用范围。因此,近20多年来如何改善其抗腐蚀性能成为烧结钕铁硼材料生产和使用的重要问题。总结了烧结钕铁硼腐蚀失重的机制,制备低失重烧结钕铁硼的方法和工艺,对如何提高烧结钕铁硼磁体的耐腐蚀性,降低腐蚀失重进行了综述。从磁体成分设计和微观结构方面总结了几条提高烧结钕铁硼磁体耐蚀性的原则,其关键是对晶界相的成分和微观结构进行合理的控制。

Phase constitution and microstructure of Ce–Fe–B strip-casting alloy

The strip-casting technique plays an important role in fabricating high coercivity sintered magnet. In this paper, we investigate the phase constitution and the microstructure of rapidly solidified Ce-Fe-B alloy fabricated by strip-casting. We find that the Ce2FelgB phase coexists with Fe, Fe2B, and CeFe2 phases in the Ce-Fe-B strips. The eutectic stucture consisting of Fe and Fe2B is encased in Ce2Fe14B grains, which is blocked by the CeFe2 grains at triple junctions, indicating that the microstructure of Ce-Fe-B strip is characteristic of a peritectic solidification. Thermal analysis indicates that the large supercooling of Ce2Fe14B results in the residual Fe and Fe2B. The microstructural optimization in Ce-Fe-B strips without Fe and Fe2B could be achieved by a heat treatment of 1000 ℃.

高丰度稀土永磁材料的研究进展与展望

稀土永磁材料的大量使用导致低丰度、高成本稀土元素Pr,Nd,Dy,Tb等过度消耗,而高丰度稀土元素La,Ce,Y未得到充分利用,导致稀土元素利用的严重失衡,不利于中国稀土资源利用的健康持续发展。出于国家战略安全和原材料成本角度考虑,低成本、高性能的高丰度稀土永磁材料的研究与开发势在必行。本文对高丰度稀土永磁材料的研究现状进行归纳总结,分别介绍了富Ce磁体、富La,Ce磁体及富Y磁体的微观结构特征及其性能调控技术,并对高丰度稀土永磁材料的开发进行了讨论和展望。