Ni对Fe_3Si软磁体磁性能影响的微观组织结构和电子结构研究

采用实验和第一性原理方法,从微观组织结构和电子结构研究了Ni浓度和退火时间对Fe_3Si软磁体磁性能的影响.结果表明Ni含量为3.125at.%时,软磁体具有最大的饱和磁化强度和最低的矫顽力值.但当浓度超过9.375at.%后,软磁体的饱和磁化强度减小,而矫顽力增大,说明适当添加Ni可提高Fe_3Si软磁体的磁性能.Ni元素从微观组织结构和电子结构两方面均对软磁体的磁性能产生较大的影响.     

Fe40—45Cr30—35Co20—25Mo0—4Zr0—2合金微观结构对矫顽力的影响

研究了高矫顽力型FeCrCo合金的磁性和微观结构.实验结果表明，适当的合金成分及热处理 条件可以明显提高FeCrCo合金的矫顽力.通过透射电镜、x射线衍射等手段得出结论：主体元 素含量的提高和微量元素的掺杂可以有效地控制相的组成，磁场热处理导致强磁性相和弱磁 性相的分离，回火后形成起磁硬化作用的调幅结构.该调幅结构中较大的两相成分差有利于 提高FeCrCo合金的矫顽力. 关键词： 矫顽力 调幅分解 磁场热处理 两相结构 成分差     

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     

粉末粒度离散性对NdFeB磁性能的影响

制备了一种NdFeB永磁材料,探讨了制粉前处理方式对粉末离散性、粒径及成品NdFeB永磁体结构与性能的影响。原材料经熔炼、粗破碎后,采用高速风选和高压氢爆2种制粉前处理方式,然后采用同样的成型、烧结和回火工艺制备得到(PrNd)32.3Nb0.70Al0.60Cu0.20B1.03Fe65.17合金,并系统研究了该合金的显微结构和磁性能。结果表明:高压氢爆处理后得到的粉末粒度呈单分散性,粉末粒径较细,所制备得到的磁体样品的微观结构均匀性也较好;高压氢爆处理后制得的磁体样品剩余磁通密度比高速风选制粉方式得到的磁体样品高0.047 T,内禀矫顽力高 193.4 kAm－1,最大磁能积高24.6 kJm－３。     

利用Pr_(70)Cu_(30)晶界扩散改善烧结钕铁硼废料矫顽力的研究

钕铁硼磁体制备过程中出现的部分块体废料由于矫顽力较低,性能难以满足使用要求.本文主要通过晶界扩散技术来提高废料磁体的矫顽力.采用Pr_(70)Cu_(30)合金作为扩散介质,对烧结钕铁硼废料磁体进行了晶界扩散处理,研究了扩散温度、扩散时间和回火时间对扩散后的磁体性能的影响.结果显示,800℃下扩散3 h,磁体的矫顽力从原来的7.88 kOe(1 Oe=79.5775 A/m)提升至11.55 kOe,提升幅度为46.6%,同时剩磁没有明显降低.扩散后回火对矫顽力的提升有一定的作用.800℃下扩散4h后的磁体在500℃回火3h后,最高矫顽力可达11.97 kOe,比原磁体废料提高了51.9%,接近成品磁体的水平.显微组织分析证实了晶界扩散的作用.扩散处理后的磁体中,主相晶粒间形成了连续晶间相,起到有效的磁隔离作用,有利于矫顽力的提高.研究还发现,Pr_(70)Cu_(30)晶界扩散虽然可以使磁体腐蚀电位上升,但也会增加腐蚀电流密度,不利于磁体抗腐蚀性的改善.本文工作对于提高材料的成品率具有重要意义.     

Dy与Co对HDDR粘结磁体的温度稳定性与磁性能的影响

添加微量元素Dy和Co后可使HDDR工艺制备的各向同性NdDyFeCoB粘结磁体的温度特性、磁性能以及微晶结构显著改善,从而得到一种具有实用价值的低温度系数、高内禀矫顽力粘结磁体.结果表明:添加适量的Dy和Co可使25—80℃时的磁通可逆温度系数α在-0043%℃左右,25—155℃时的磁通可逆温度系数α=-0056%℃;经155℃老化处理12h不可逆损失hirr为35%;最高内禀矫顽力Hci>1600kAm-1时,最大磁能积(BH)max仍可获得一个较好值. 关键词： HDDR工艺 温度特性 微结构 内禀矫顽力     

高性能纳米复合永磁材料的模拟计算研究

构造了在软磁相基体中析出规则形状硬磁相的各向同性和各向异性纳米复合永磁材料Pr2Fe14Bα-Fe.利用微磁学的有限元法，模拟计算了样品的磁滞回线.通过对剩磁、矫顽力和最大磁能积与软磁相厚度的关系分析，发现在软磁相厚度为0—12nm的范围内，复合磁体的矫顽力随软磁相厚度的增加而单调下降，而最大磁能积则是在适当的矫顽力和剩磁下达到最高.预计纳米复合Pr2(Fe,Co)14Bα-(Fe,Co)的各向同性磁体的最大磁能积最高可达248kJ/m3，而各向异性磁体则高达784kJ/m3. 关键词： 纳米复合永磁 矫顽力 剩磁 磁能积     

Nb_3Sn超导相的微观组织表征与Sn扩散的研究

CICC导体作为45T混合磁体外超导磁体的重要绕制材料,其所用的超导股线是由牛津公司提供的RRP法制备的高临界电流Nb_3Sn超导线材。由于Nb_3Sn超导相为典型的A15结构,其塑性非常差,所以在实际工程应用当中,往往是采用先绕制线圈,然后对绕制好的线圈进行热处理,进而生成Nb_3Sn超导相。因此,热处理制度的合理制定对于Nb_3Sn超导相的微观组织结构和超导性能具有非常重要的意义。为了验证热处理故障对超导磁体性能的影响,研究制定了三种不同的热处理制度,利用SEM方法对其生成的Nb_3Sn超导相进行微观组织的表征,通过EDS分析Sn元素的扩散;结合Ic值和RRR值的测定结果,对比分析不同热处理制度对Nb_3Sn股线微观组织与性能的影响。     

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Nd₁₀Fe_84-xB₆In_x(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. 关键词： 晶界 纳米复合材料 热处理 微量添加     

晶粒易轴取向度对纳米晶永磁Pr2Fe14B磁性的影响

构造了立方和不规则形状晶粒的各向异性纳米晶单相Pr₂Fe₁₄B磁体 .利用微磁学的有限元法，模拟计算了样品的磁滞回线.计算结果表明，随着磁体晶粒易轴取向度的变差， 磁体的剩磁、矫顽力均随之下降.不同晶粒尺寸的纳米晶单相Pr₂Fe_{14B磁体，其磁 性能随取向度的变化快慢不同，原因在于磁体中的晶间交换作用 (IGEC) 的强弱不同.随着 晶粒取向度的提高，纳米晶单相磁体的矫顽力逐渐增加，这完全不同于烧结磁体. 关键词： 纳米晶磁体 矫顽力 剩磁}     

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     

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.     

Effects of post-sinter annealing on microstructure and magnetic properties of Nd–Fe–B sintered magnets with Nd–Ga intergranular addition

We investigate the effects of post-sinter annealing on the microstructure and magnetic properties in B-lean Nd–Fe–B sintered magnets with different quantities of Nd–Ga intergranular additions. The magnet with fewer Nd–Ga additions can enhance 0.2 T in coercivity, with its remanences nearly unchanged after annealing. With the further increase of the Nd–Ga addition, the annealing process leads coercivity to increase 0.4 T, accompanied by a slight decrease of remanence. With the Nd–Ga addition further increasing and after annealing, however, the increase of coercivity is basically constant and the change of remanence is reduced. Microstructure observation indicates that the matrix grains are covered by continuous thin grain boundary phase in the magnets with an appropriate Nd–Ga concentration after the annealing process. However, the exceeding Nd–Ga addition brings out notable segregation of grain boundary phase, and prior formation of part RE6 Fe13 Ga phase in the sintered magnet. This prior formation results in a weaker change of remanence after the annealing process.Therefore, the diverse changes of magnetic properties with different Nd–Ga concentrations are based on the respective evolution of grain boundary after the annealing process.     

烧结Nd-Fe-B中的热力学影响

在烧结Nd-Fe-B中，各种相的形成，添加元素原子的替代、对磁体的微结构和性能的影响以 及大多数工艺与热力学都有密切联系.Al，Cu，Ga，Sn，Zn等与B均具有正的混合焓，在主相 中的浓度都很低，与富 Nd相反应改善磁体的微结构. Zi,Ti，Nb，W，Mo，V等与Nd有很大的 正的混合焓，与B具有很大的负的混合焓，能优化磁体的微结构和稀释磁体.参考热力学，系 统讨论了各种常用添加元素对烧结Nd-Fe-B的微结构、性能和制造工艺的影响. 关键词： Nd-Fe-B永磁体 混合焓 烧结     

Effect of adding non-ferromagnetic nanoparticles to grain boundary on coercivity of sintered Nd-Fe-B magnet

In this work, we investigated the influence of additional compounds of Nd-Cu-Al, Dy-Nb-Al, Dy-Zr-Al and Nb-Cu-Al on coercivity of sintered Nd-Fe-B magnets. The additional nanoparticles with size in the range of 40–80 nm was mixed with the micrometer Nd-Fe-B powder before sintering process. The results show that the coercivity of the sintered Nd-Fe-B magnets can be improved by introducing additional nanoparticles to their grain boundaries. The improvement of the coercivity of the magnets is clearly dependent on composition and fraction of the additional compounds. While the Dy-Nb-Al, Dy-Zr-Al and Nb-Cu-Al compounds degrade the coercivity of the sintered Nd-Fe-B magnets, the Nd-Cu-Al nanoparticles considerably improve this quantity. The coercivity the sintered Nd_16.5Fe₇₇B_6.5 magnets has been enhanced about 40% by adding 3 wt% of the Dy-free compound of Nd₄₀Cu₃₀Al₃₀.     

Nb含量对烧结NbFeB永磁体磁性能及显微结构的影响

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Investigation of the domain structure of sintered Nd-Fe-B permanent magnets by Bitter-pattern method

The conventional Bitter-pattern technique and the colloid-scanning electron microscopy (colloid-SEM) method were used to study the domain structure of polycrystalline sintered Nd-Fe-B permanent magnets. In the thermally demagnetized state most of the grains are multidomain and the domain structures resemble those observed in bulk uniaxial crystals with strong magnetocrystalline anisotropy. Investigations of the magnetic microstructure during magnetizing cycle showed that the domain walls can easily be moved within the grains and that the magnetization reversal in sintered Nd-Fe-B magnets occurs predominantly by the nucleation and expansion of reverse domains at structural imperfections near the grain boundaries. It is also shown that the colloid-SEM method is more surface sensitive and reveals the domain structure with better resolution than the conventional Bitter technique. Thanks to the application of digital image processing systems, clear and high contrast domain images were obtained. The work was supported by the Lódź University within Research Grant 505/694 (2004).     

Study of high-coercivity sintered NdFeB magnets

Magnetic powders for sintered NdFeB magnets have been prepared by using an advanced processing method including strip casting, hydrogen decrepitation, jet milling and rubber isotropic press. The effects of Dy, Ga and Co addition on the microstructure and magnetic properties of sintered magnets have been investigated. By adopting a suitable component ratio and adjusting proper technological parameters, we have prepared high-coercivity sintered NdFeB magnets with hard magnetic properties of _jH_c=25.6 kOe, B_r=13.2 kG and (BH)_max=39.9 MGOe. The temperature coefficient of coercivity of the magnets (between 20 and 150 °C) is –0.53%/°C. The magnetic properties at high temperature satisfy the needs of permanent magnet motors.     

烧结Nd-Fe-B永磁合金矫顽力机制的理论与实验研究

从理论和实验上研究了烧结Ｎｄ－Ｆｅ－Ｂ永磁合金的矫顽力随取向磁场的变化规律。指出磁体反磁化过程主要是晶粒边界软磁性区的反磁化成核以及反磁化核长大成畴并向晶粒内部不可逆畴壁位移的过程。比较了成核场与退钉扎场的大小及其随磁场方向的变化，并得出结论：退钉扎场是决定烧结Ｎｄ－Ｆｅ－Ｂ磁体矫顽力的主要机制。 关键词：     

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.