Dependence of magnetic properties on microstructure and composition of Ce-Fe-B sintered magnets

In this paper,dependence of magnetic properties on microstructure and composition of Ce-Fe-B sintered magnets with Cu-doped Ce-rich alloy addition was investigated.It shows that the maximum energy product(BH)_(max) and coercivity H_(cj) of Ce-Fe-B sintered magnet are improved from 6.76 to 9.13 MGOe by 35.1%,and from 1.44 to 1.67 kOe by 16.0%,respectively,via adding 5 wt% liquid phase alloy of Ce_(35.58)Fe_(57.47)Cu_6 B_(0.95)(at%).Compared with the magnet without Cerich alloy addition,the volume fraction of the grain-boundary phase with low melting point increases in the magnet with Ce-rich alloy additio n,which is be ne ficial to imp roving the microstructure and promoting the coercivity enhancement of the magnet.In the Ce-Fe-B magnet with Ce-rich alloy addition,Cu and Ce enrich in the grain boundaries of the magnet after annealing,therefore the as-annealed magnet has a higher coercivity than the as-sintered magnet.A distinct Fe-rich layer with the average thickness of 60 nm is found in the grain boundaries in the magnet without Ce-rich alloy addition,but it seems that Fe-rich phase disappears in the magnet with Ce-rich alloy addition.The present work suggests that the further improvement of coercivity in the Ce-Fe-B sintered magnets is expectable by designing the composition and structure of added liquid phase alloys.     

Optimization of both coercivity and knee-point magnetic field of Sm2Co17-type magnets via solid solution process

It is confirmed that phase homogenization is very important for improving the magnetic properties of 2:17-type Sm–Co sintered magnets. In this work, the influence of solid solution process on microstructure and magnetic properties of the Sm(Co_balFe_0.233Cu_0.073Zr_0.024)_7.6 sintered magnets was systematically studied. With the solid-solution treating duration (t_s) increasing from 0 to 4 h, intrinsic coercivity (H_cj) increases from 12.83 to 36.54 kOe, magnetic field at knee-point (H_knee) increases from 2.76 to 19.14 kOe, and the maximum energy product increases from 19.79 to 29.48 MGOe. The electron probe microanalyzer results reveal that there mainly exist gray and dark regions besides “white” rare earth-rich phase, and the content of Sm, Fe and Cu elements for the two kinds of regions changes a lot for the specimens. Furthermore, with t_s increasing up to 4 h, the elements content deviation between the gray and dark regions becomes small gradually from 3.94 at% to 0.27 at%, 7.66 at% to 0.21 at% and 7.27 at% to 0.16 at% for Sm, Fe and Cu elements, respectively. Moreover, transmission electron microscopy results show that the distribution of cell size is much more concentrated for aged specimens when t_s is 4 h. It is also found that the Cu concentration at cell boundaries for the 4 h solid-solution treatment case shows relatively higher values and greater concentration gradient (1.94 at%/nm). It is verified that sufficient solution treatment duration is prerequisite to form these homogeneous microstructural features, which are the key points for obtaining both high H_cj and H_knee.     

工业生产高综合性能烧结 Nd-Fe-B永磁关键技术研究

通过优化合金成分设计和改进合金铸锭按需分配技术、磁场取向成型技术以及烧结技术，应用全部国产设备与国内通用的工业生产烧结Nd-Fe-B永磁的原材料，避免使用镓等稀有贵重金属元素，实现了N45H烧结Nd-Fe-B磁体的工业化生产，其典型磁性能为Br=1.386T(13.86kGs),BHc=1059kA/m(13.32kOe),JHc=1418kA/m(17.83kOe),Hk=1357kA/m(17.06kOe),(BH)max=364kJ/m^3(45.8MGOe)。，SEM观察和XRD分析结果表明，制造的N45H烧结Nd-Fe-B磁体具有良好的取向度和晶粒细小而均匀的显微组织。     

Grain Growth Behavior in Sintered Nd-Fe-B Magnets

The Nd2Fe14B grain growth behavior in sintered Nd-Fe-B magnets was quantitatively described.The effects of sintering temperature and time,and alloy powder size and its distribution on grain growth process were analyzed.Hence,possible grain growth mechanisms in these magnets were qualitatively discussed.The Nd2Fe14B grain growth proceeded at quite a high rate in the initial 0~1 h of sintering and from then onwards the grain growth rate decreased.A large average particle size or a wide particle size distribution of initial alloy powders was found to remarkably accelerate the grain growth process and even result in the occurrence of abnormal grain growth.On the basis of experimental results,two grain growth mechanisms were considered to operate during sintering of Nd-Fe-B magnets,that is,dissolution and re-precipitation of Nd2Fe14B particles,and Nd2Fe14B particle growth by coalescence.It was believed that Nd2Fe14B particle growth by coalescence not only produced a large average grain size and a wide grain size distribution,but also was the fundamental reason for the formation of abnormally large grains in the microstructure of sintered Nd-Fe-B magnets.     

(Nd,Pr,Ce)-Fe-B磁体的组织与磁学性能

为开发低成本烧结钕铁硼磁体,用30% Ce替代(Nd_0.75Pr_0.25)_32.69Fe_66.25B_1.06磁体中的Nd和Pr,研究了磁体在烧结及回火过程中的组织结构和磁学性能变化.结果表明,取向压坯在1030~1080℃烧结2 h后,随烧结温度升高,磁学性能下降,烧结温度为1030℃时综合磁学性能均最好.烧结态Ce替代磁体的综合磁学性能优于未替代磁体.一级回火后,相组成和晶粒尺寸基本不变,边界结构也未发生明显变化,磁体性能基本不变,或有少量下降.二级回火后,晶界明显改善,获得较清晰且平直的晶界,磁体矫顽力均得到大幅提高.Ce替代磁体的剩磁、矫顽力和磁能积均稍低于未替代磁体.     

Design and fabrication of W-Mo-Ti-TiAl-Al system functionally graded material

To obtain a kind of functionally graded material (FGM) with a density gradient, the W-Mo-Ti-TiAl-Al system graded material was designed, and the powder metallurgy method was chosen for its fabrication. The sintering of W, W-Mo, and Mo-Ti alloys at low temperature was studied, and then the approximately wholly dense W-Mo-Ti-TiAl system FGM was achieved by one-step sintering at 1473 K for 1 hour under a pressure of 30 MPa. It was found that through sintering at 1473 K, mainly the mechanical mixtures of W and Mo were formed in W-Mo alloys. In Mo-Ti alloys, the newly designed Fe-Al sintering aids not only have an important effect on the densification of the alloys, but also contribute to the formation of the (Mo, Ti) solid solution. However, the solid-solution reaction that occurred in Mo-Ti alloys was still insufficient. During the sintering of Ti + TiAl, the chemical reaction of Ti + TiAl → AlTi₂ was induced within the sintered body. The W-Mo-Ti-TiAl-Al system FGM was finally fabricated by joining of the TiAl side of the sintered W-Mo-Ti-TiAl system FGM to metal Al with an Al-based brazing filler metal, and its density changed quasi-continuously within the large range from 17.15 to 2.70 g/cm³.     

Nd-Fe-B磁体热等静压烧结的实验研究

研究了热等静压烧结对Nd-Fe-B磁体的致密度、显微组织及磁性能的影响.结果表明:与常压烧结磁体相比,热等静压烧结磁体的内部存在较多的孔洞,致密度、晶粒取向度及磁性都有所降低.用加热Ar气热膨胀而产生热等静压进行烧结的办法不适于制造高性能的烧结磁体.     

Microstructure and magnetic properties of bulk magnets Nd_(14-x)Fe_(76+x)Co_3Zr_1B_6(x=0,0.5,1) prepared by spark plasma sintering

Melt-spun ribbons with nominal composition of Nd14-xFe76+xCo3Zr1B6(x=0,0.5,1) were consolidated into isotropic bulk magnets by spark plasma sintering method.It was found that the Nd content and sintering temperature had significant influence on the density and magnetic properties of the sintered magnets.Homogeneous microstructure and fine grain(50-100 nm) were obtained when sintering below 700 ℃,and the initial magnetization curve showed that the coercivity was controlled by the pinning mechanism.However,ab...     

Enhancement of terbium efficiency by gallium and copper co-doping in (Pr,Nd)-Fe-B sintered magnets

It is well known that Tb substitution for (Pr, Nd) in (Pr, Nd)-Fe-B based sintered magnetic materials is an effective way to increase intrinsic coercivity, but it is not quite clear whether the increment depends on the different matrix phases with various doping ingredient or not, which is essential to develop high quality magnets with high coercivity more efficiently and effectively with economic consumption of expensive Tb and other costly heavy rare earths. In this paper, we investigated the efficiency of Tb substitution for magnetic property in (Pr, Nd)-Fe-B sintered permanent magnets by co-doping Ga and Cu elements. It is shown that Ga and Cu co-doping can effectively improve the efficiency of Tb substitution to increase the thermal stability and the coercivity. The intrinsic coercivity increases up to 549 and 987 kA/m respectively by 1.5 wt% and 3.0 wt% Tb substitution in Ga and Cu co-doped magnets while the intrinsic coercivity increases up to only 334 and 613 kA/m respectively by the same amounts of Tb substitution in non-Ga and low-Cu magnets. In other words, it demonstrates that there is about 329–366 kA/m linear equivalent enhancement of intrinsic coercivity by 1.0 wt% Tb substitution for (Pr, Nd) in Ga and Cu co-doped magnets. The temperature coefficients of both intrinsic coercivity β and remanence α at 20–150 °C by 3.0 wt% Tb substitution for the magnets with Ga and Cu co-doping are −0.47%/K and −0.109%/K respectively, and in contrast those values are −0.52%/K and −0.116%/K respectively for the non-Ga and low-Cu magnets. It is the principal reason for more efficient enhancement of magnetic property by Tb substitution in the Ga and Cu co-doped magnets in which Tb atoms are expelled from triple junction phases (TJPs) to penetrate into the grain boundary phases (GB phases) and thus modify the grain boundary. It is prospected that the efficiency of Tb substitution would rely on different matrix phases with various doping constituents.     

粉末注射成形制备SmCo磁体烧结工艺对组织的影响

试验探讨了粉末注射成形方法制备2∶17型SmCo磁体在烧结时Sm的挥发与氧化对烧结后组织的影响。结果表明:当烧结炉的真空度良好(≥5×10-3Pa)时,Sm的挥发使烧结组织呈现清晰的层状结构,外层成分严重偏离设计成分,X射线分析显示为Co0.7Fe0.3及Fe2O3结构,从而影响内部组织的致密化。而当烧结炉的真空度较低(<1×10-2Pa)时,Sm的挥发与内部氧化的共同作用,使组织形成多层结构,Sm与氧元素的分布规律基本一致,而挥发的Sm与氧结合生成白色粉末状的Sm氧化物沉积在烧结炉中。烧结组织中层状结构的存在抑制烧结过程中心部的致密化,是导致烧结坯体的致密度较低的重要原因。     

微波烧结温度对CNTs/Cu复合材料结构和性能的影响

结合液相混合方法、微波烧结技术和冷轧技术制备碳纳米管增强铜基（carbon nanotubes reinforced copper-matrix,CNTs/Cu）复合材料,研究不同烧结温度对于CNTs/Cu复合材料微观形貌、力学性能及物理性能的影响。结果表明,采用液相混合法制备出粒径为200~500 nm、碳纳米管质量分数为0.5%的CNTs/Cu复合粉体,碳纳米管均匀分散在铜颗粒中,并与之形成良好结合界面。CNTs/Cu复合材料的相对密度、硬度、电导率随着烧结温度的升高先增大后减小,在烧结温度为1000℃时达到最佳。制备的碳纳米管质量分数为0.5%的CNTs/Cu复合材料组织均匀、孔隙数量及尺寸较少,相对密度为95.79%,硬度为HV 80.9,电导率为81.8% IACS。经冷轧处理后,CNTs/Cu复合材料拉伸强度达到218 MPa,延伸率保持37.75%。由此可见,微波烧结技术是一种制备高性能CNTs/Cu复合材料的理想方法。     

Gel-Combustion Synthesis of Nanocrystalline Cerium Oxide and Its Powder Characteristics

Nanocrystalline ceria powders were prepared by using citrate gel combustion. The influence of the composition of the combustion mixture on the characteristics of the final product was investigated. Ceria powders obtained by calcining the combustion residue in air at 1073 K were characterized for their specific surface area (SSA), X-ray crystallite size (XCS), bulk density (BD), particle size distribution (PSD) and residual carbon. The dependence of these properties on the fuel to oxidant ratio (R) of the initial mixture was investigated. The microstructure of the calcined ceria powders prepared from a mixture with R = 0.25 was investigated by using high resolution transmission electron microscopy. All the calcined powders were pelletised and sintered at 1473, 1673 and 1873 K, and their sinterability was compared by measuring the density of the sintered pellets. A maximum sintered density of 98 % theoretical density could be achieved at a temperature as low as 1473 K for the first time for the powder prepared from a mixture with R = 0.75. The systematic dependence of the properties of these powders on the composition of the initial mixture is being reported for the first time. Powders obtained from a mixture with an R value 0.25 showed a linear increase in sintered densities with the sintering temperature. Other powders exhibited anomalous decrease in the sintered density at high temperature, probably due to irregular grain growth coarsening.     

Coercivity of 2:17 Based Permanent Magnets

High-quality permanent magnets either are based on large nucleation fields or strong pinning forces of domain walls (dws). In the case of 2:17 based magnets depending on the temperature range considered both hardening mechanisms have been discussed. The dominant hardening mechanisms at temperatures below around 700 K are repulsive or attractive pinning of domain walls at the cell walls (1:5 structure) between the nanostructured pyramidal cells (2:17 structure). Micromagnetic calculations of the pinning forces sensitively depend on the shape of the interaction potential between the dw and the microstructure. In the case of the 2:17 based magnets these calculations become rather complex if the domain wall width is of the order of the potential width. In this case the domain wall is modified due to the space dependent local anisotropy which changes from K₁^2:17 to K₁^1:5 of the cell boundary phase over a distance D of the intergranular phase boundary. Using the K₁(r)-profiles as determined from the chemical composition obtained by high-resolution EDX measurements the coercive field due to domain wall pinning is determined self-consistently as a function of the pinning-potential parameters taking into account the modification of the domain wall by the space dependent material parameters. It is shown that the coercive field of the high-temperature magnets as a function of the width of the cell boundary phase varies between 3 T for a sharp boundary (D = 0 nm) and 1 T for a wide boundary (D = 4 nm). On the basis of micromagnetism the condition for the dominance of pinning or nucleation is investigated. It is shown that in the case of 2:17 based high-temperature magnets with increasing temperature the hardening mechanisms change from repulsive to attractive pinning and nucleation starts at around 700 K. The temperature ranges where the transitions take place sensitively depend on the Cu content and on the annealing parameters.     

Effects of copper and zirconium contents on microstructure and magnetic properties of Sm(Co,Fe,Cu,Zr)_z magnets with high iron content

The evolution of the microstructure,microchemistry and magnetic properties of the Sm(Co_(bal)Fe_(0.28)-Cu_yZr_x)_(7.6) magnets with different Zr and Cu contents was investigated.It is found that the coercivity of the Sm(Co,Fe,Cu,Zr)_z magnets is sensitive to Zr content.The deficiency of Zr content causes heterogeneity of Cu and Fe distributions,while an excessive Zr content leads to the formation of a SmCoZr impurity phase.The cellular structure and distribution of Cu concentration.gradient between the cell boundary phase and cell pha se are destroyed by inappropriate Zr content,which results in a reduction of coercivity.The Cu concentration difference between the cell boundary phase and cell phase increases with increasing Cu content.The coercivity of the Sm(Co_(bal)Fe_(0.28)Cu_yZr_(0.02))_(7.6) magnets increases from 10.4 to 25.4 kOe for y=0.05 and y=0.07.However,the excess of Cu element destroys the cell boundary phase and enlarges the cell size,resulting in a significant decrease of squareness and energy density.The optimum performance(remanence of 11.4 kG,coercivity of 2 5.4 kOe,maximum magnetic ene rgy product of 30.4 MGOe) was obtained for the Sm(Co_(0.63)Fe_(0.28)Cu_(0.07)Zr_(0.02))_(7.6) magnet.     

不同配比铁基预合金粉的胎体性能研究

对湿法冶金工艺制备的两种铁基预合金粉(Fe_(43)Co_(24)Cu_(33)和Fe_(56)Co_(14)Cu_(30),以下简称A和B)进行了性能研究,对其粉末颗粒的形貌和氧含量进行了对比分析,并经过750、800、850、900、950℃五种烧结温度制备热压烧结试样。通过阿基米德排水法测定烧结试样密度,利用HR-150A型洛氏硬度计测量烧结试样的显微硬度,利用三点弯曲法测定烧结试样的抗弯强度,使用扫描电子显微镜观察烧结试样的断口形貌。结果表明:随着烧结温度的提高,两种烧结试样的密度都呈增加趋势,当温度超过850℃后,密度变化逐渐趋于平缓;烧结试样的硬度都随着温度的升高先增加后降低,烧结试样B硬度在850℃以前要高于烧结试样A,且在800℃时达到最大值,当温度高于850℃时烧结试样A的硬度要高于烧结试样B;两烧结试样的抗弯强度都随温度的升高而增大;预合金粉A的烧结试样对温度敏感性较小,当温度达到850℃以后,晶粒几乎不在长大,预合金粉B的烧结试样对温度敏感性比较大,随着温度的升高,晶粒不断地长大。     

Spark Plasma Sintering Nd-Fe-B Permanent Magnets With Good All-Around Property

In present study, sintered Nd-Fe-B permanent magnets with different compositions were fabricated by using both Spark Plasma Sintering (SPS) technique and conventional sintering technique. Microstructure and compositions of both magnets are observed by scanning electron microscope with energy dispersive X-ray detector. Magnetic properties, mechanical properties, and chemical stabilities of both Nd-Fe-B magnets are investigated. Compared with the conventional sintered magnets, SPS Nd-Fe-B magnets possess comparable magnetic properties, better corrosion resistance and mechanical properties. Further investigation shows that the good all-around properties of the SPS magnets result from their unique microstructure. In detail, the grain size of Nd₂Fe₁₄B main phase is fine and uniform, only a few Nd-rich phase forms along the grain boundaries of Nd₂Fe₁₄B, while most of them agglomerates into the triple junctions. As a result, SPS process is expected to be a promising method for the production of new Nd-Fe-B magnets with good all-around properties.     

Properties of Anisotropic Nd(Fe,Co)B Type Sintered Magnets Produced by Powder Injection Moulding

Abstract

Anisotropic Nd(Fe,Co)B type sintered permanent magnets were fabricated by powder injection moulding (PIM) using paraffin wax as a binder. A conventional process was also used in order to compare the resultant properties with those of sintered magnets produced by PIM. Magnetic properties, microstructure, and constituents were investigated by dc fluxmeter, scanning electron microscopy, X-ray diffractometry, wavelength dispersive X-ray analysis, and ir absorption analysis. Effects of particle alignment of the sintered magnets on the magnetic properties and anisometric linear shrinkage ratios were studied. Particle alignment of sintered magnets produced by PIM was 4% lower than that of the conventional process. The PIM sintered magnet exhibited a maximum energy product of 232 kJ m^?3. The residual carbon after debinding affected the magnetic properties and sintering characteristics by contaminating the liquid phase during PIM sintering. PM/0782     

烧结温度对高速压制制备弥散强化铜材料导电率的影响

弥散强化铜材料具有高强度和高导电性的特性,孔洞是影响导电率的重要因素.本文采用高速压制成形技术,对Al₂O₃质量分数为0.9%的弥散强化铜粉压制成形,研究了压制速度对生坯的影响.当压制速度为9.4 m·s^-1时得到密度为8.46 g·cm^-3的生坯.研究了烧结温度对烧结所得Al₂O₃弥散强化铜试样导电率的影响.当生坯密度相同时,烧结温度越高,所得试样的导电率也越高.断口与金相分析表明:烧结温度为950℃时,烧结不充分,颗粒边界以及孔洞多而明显,孔洞形状不规则;烧结温度为1080℃时,颗粒边界消失,孔洞圆化,韧窝出现,烧结坯的电导率为71.3%IACS.     

Mechanical Properties of β–Ti-35Nb-2.5Sn Alloy Synthesized by Mechanical Alloying and Pulsed Current Activated Sintering

A developed Ti-35?pct Nb-2.5?pct Sn (wt pct) alloy was synthesized by mechanical alloying using high-energy ball-milled powders, and the powder consolidation was done by pulsed current activated sintering (PCAS). The starting powder materials were mixed for 24 hours and then milled by high-energy ball milling (HEBM) for 1, 4, and 12 hours. The bulk solid samples were fabricated by PCAS at 1073?K to 1373?K (800 °C to 1100 °C) for a short time, followed by rapid cooling to 773?K (500 °C). The relative density of the sintered samples was about 93?pct. The Ti was completely transformed from ?? to ??-Ti phase after milling for 12 hours in powder state, and the specimen sintered at 1546?K (1273 °C) was almost transformed to ??-Ti phase. The homogeneity of the sintered specimen increased with increasing milling time and sintering temperature, as did its hardness, reaching 400?HV after 12 hours of milling. The Young??s modulus was almost constant for all sintered Ti-35?pct Nb-2.5?pct Sn specimens at different milling times. The Young??s modulus was low (63.55 to 65.3 GPa) compared to that of the standard alloy of Ti-6Al-4V (100 GPa). The wear resistance of the sintered specimen increased with increasing milling time. The 12-hour milled powder exhibited the best wear resistance.     

高能球磨-放电等离子烧结法制备双晶分布钛

以平均粒径约150μm的球形钛粉为原料,采用高能球磨结合放电等离子烧结技术制备由双尺度晶粒组成的高致密纯钛块体材料,研究高能球磨过程中钛粉的形貌、尺寸及显微组织的变化,分析球磨钛粉放电等离子烧结时的致密化行为和显微组织的演变规律,测试烧结钛块体材料的室温压缩性能。结果表明:钛粉在球磨初期发生剧烈的塑性变形并相互焊合,形成层片状团聚粉末。球磨10 h时,钛粉的部分晶粒细化至40~100 nm。放电等离子烧结过程中,随烧结温度升高和烧结时间延长,烧结钛的密度逐渐增大。在烧结温度为800℃、保温时间为4 min、烧结压力为50 MPa的条件下,烧结钛的密度达到4.489 g/cm3,接近全致密,其显微组织由双尺度的等轴晶组成,细晶区晶粒尺寸为1~2μm,粗晶区晶粒尺寸为5~20μm,二者呈层状交替分布;该试样在室温压缩条件下的综合力学性能与铸锻Ti-6Al-4V合金相当。