放电等离子烧结制备高性能热变形Nd-Fe-B磁体

使用放电等离子烧结(SPS)可在短时间内将非晶Nd13.5Fe80.5B6粉末晶化,且可获得接近于全致密的各向同性磁体,其剩磁、矫顽力、最大磁能积分别为Br=0.8T,Hci＝1346kA/m,(BH)m=108kJ/m3.热变形后,随变形量的增加,硬磁相晶粒的取向度增加,Br及(BH)m大幅增加,在65%时达最大:B...     

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。     

热模压Nd-Fe-B磁体变形过程及其模拟研究

Nd-Fe-B快淬磁粉在真空中热压,继续进行不同变形温度和不同应变率的热模压处理.通过分析不同变形温度下的热变形过程中应力一应变率关系,对热模压Nd-Fe-B磁体的热变形行为进行了研究并由此得到了描述热变形过程的关键参数.为了清楚理解晶粒边界滑移和各向异性晶粒长大在变形过程中所起的作用,利用三维有限元软件(DEFORM...     

高性能各向同性及各向异性Nd-Fe-B/Fe复合磁体的制备

采用将Nd-Fe-B磁粉与Fe粉混合的方法,并结合真空感应热压烧结技术制得高性能的各向同性及各向异性复合磁体。研究了Fe粉含量对热压磁体磁性能的影响,以及温度和压力对磁体致密度和磁性能的影响。结果表明,适量的Fe粉添加(3%,质量分数)可提高热压磁体磁性能;升高温度或提高压力均可大幅提高磁体致密度,但过高的烧结温度使晶粒快速长大,恶化磁体磁性能,而温度过低磁体难易全致密化。在最佳热压温度及压力下制备的热压磁体具有最佳的磁性能:Br=0.852T,Hcj=798kA/m,(BH)m=131.5kJ/m3,磁体密度达7.72g/cm3;热变形后,最大磁能积达331kJ/m3。     

Ga对HDDR磁粉热变形磁体磁性能和微观结构的影响

利用HDDR工艺制备出Nd32FebalBGax(x=0.0、0.2%、0.4%、0.6%、0.8%(质量分数))磁粉,并且对HDDR磁粉进行热压/热变形处理制备出全密度各向异性磁体。研究了热变形温度和Ga含量对Nd-Fe-B热变形磁体磁性能的影响,观测了不同Ga含量热变形磁体的微观结构,探讨了微量元素Ga的添加对用HDDR磁粉制备的热变形磁体微观结构和磁性能的影响机制。研究发现,Ga的添加能够明显减小热变形磁体的主相晶粒尺寸,改善磁体的微观织构,并可以同时提高热变形磁体的剩磁和矫顽力。当Ga含量为0.6%(质量分数)时,热变形磁体的磁能积达到最大值228.3kJ/m3。     

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.     

各向异性致密(NdDy)_(11.5)Fe_(81.5)Nb_1B_6磁体的制备

采用热压热变形技术,制得了各向异性致密(NdDy)11.5Fe81.5Nb1B6+2%(质量分数)Zn磁体,并研究了热压及热变形磁体的微观结构以及不同形变量对磁体磁性能和微观结构的影响。结果表明,Zn的添加使热压磁体磁性能下降,但使热变形磁体磁性能大幅增加;热变形磁体磁性能的增加是由于良好c轴取向和微观结构的形成。此类磁体磁性能和微观结构随形变量的增加表现出与传统磁体类似的规律,即剩磁增加、矫顽力下降,c轴取向不断增强。尽管如此,在热变形的起始阶段,由于Zn的扩散使磁体矫顽力有较大幅度增加。磁体的形变量过大达75%时,磁体磁性能会因为晶粒严重长大而下降。     

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。     

单级热变形法制取各向异性Nd-Fe-B磁体的温度特性

单级热变形法(SSHD)是单步热压工艺,用Cu管代替压模能简化传统的模压工艺.     

各向异性热压稀土永磁体的热变形机制及微磁结构研究

重点研究制备工艺对各向异性热压稀土永磁体性能的影响,探讨了热压永磁体的热变形机理和数学描述模型,并尝试从微磁结构的角度研究各向异性纳米晶Nd-Fe-B磁体,揭示纳米晶粒之间的静磁和交换耦合相互作用、磁化和反磁化、热退磁等微观机制。获得了最佳磁性能为:Hcj=1 157 kA/m,Br=1.465 T,(BH)max=426 kJ/m3纳米晶Nd-Fe-B磁体。     

Microstructure and magnetic properties in Mn-doped Nd-Fe-B magnets

The effect of the addition of antiferromagnetic element Mn on the local structure and the magnetic properties of Nd₉Fe₈₅B₆ magnets has been studied. It was found that the microstructure and local structure heavily depended on both the Mn addition and the quenched speed. The Mn additions could promote the order degree around Fe atom in as-spun samples. After appropriate annealing, the completely crystallized samples were obtained. It showed that the difference of the local structures around Fe atoms almost disappeared and the hard magnetic properties, especially the coercivity was enhanced. It is presumed that the enhanced hard magnetic properties were attributed to the enhancement of the exchange coupling, which is between the hard phases and the soft phases.     

The influence of densification temperature and the size of powder particles on the properties of isotropic Nd-Fe-B magnets made of quenched ribbons

The influence of densification temperature and the size of powder particles on magnetization of remanence J _r , coercivity _J H _c of hot-densified Nd-Fe-B magnets made of MQP-A quenched ribbons was investigated. A connection between magnetic properties, parameters of production process and microstructure of the magnet was confirmed. It was found that the remanence of isotropic magnet depends on temperature of hot densification process but is practically independent of the size of powder particles. On the other hand, the temperature of hot densification process and the size of powder particles have a substantial influence on coercivity.     

防氧化剂对烧结NdFeB永磁性能的影响

研究了防氧化剂的添加对Nd13.6Dy0.39Tb0.14FecalAl0.8B625的烧结永磁体的微观结构与磁性能的影响规律.结果表明,添加一定量防氧化剂后的主相晶粒尺寸较小且较为均匀,晶界清晰,空隙及缺陷较少.由于磁体微结构的改善,磁体的性能得到了较大的提高.同时发现防氧化剂复合添加的方式对磁性能的效果优于球磨或气流磨时单独添加防氧化剂时的效果.     

Effect of plasma treatment on thermal stability and magnetic properties of Nd-Fe-B series plastic magnets

In order to improve the thermal oxidative stability of the neodymium series (Nd₂Fe₁₄B) magnetic powder, plasma polymerization of benzene, styrene and acrylonitrile on the powder was carried out and its effect was examined. A strong hydrophobicity was revealed on the surface of the magnetic powder by the plasma treatment, and the thermal oxidative stability and magnetic properties of the powder were remarkably improved. Magnetic properties of the plastic magnets prepared with the magnetic powder coated with plasma polymer of acrylonitrile on the surface, were superior to plastic magnets prepared with untreated powder.     

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.     

Modelling of the material flow of Nd-Fe-B magnets under high temperature deformation via finite element simulation method

Abstract

Hot deformation of Nd-Fe-B magnets has been studied for more than three decades. With a good combination of forming processing parameters, the remanence and (BH)_max values of Nd-Fe-B magnets could be greatly increased due to the formation of anisotropic microstructures during hot deformation. In this work, a methodology is proposed for visualizing the material flow in hot-deformed Nd-Fe-B magnets via finite element simulation. Material flow in hot-deformed Nd-Fe-B magnets could be predicted by simulation, which fitted with experimental results. By utilizing this methodology, the correlation between strain distribution and magnetic properties enhancement could be better understood.     

Effect of Nb doping on microstructure and magnetic properties of hot-deformed Nd-Fe-B magnets with Nd-Cu eutectic diffusion

To restrict grain growth in coarse grain regions caused by the diffusion of Nd-Cu eutectic alloys, the Nb element was introduced into the precursor alloy to regulate the microstructure of melt-spun powder and die-upset magnets. The magnetic properties and thermal stability of die-upset magnets were appreciably improved through the addition of Nb. For the Nb-doped diffusion die-upset magnet, the grains inside the ribbons were refined and the coarse non-oriented surface crystallite got suppressed ...