Sm2Co17永磁体的显微组织及其对矫顽力的影响

探讨了Sm(CobalFe0.197Cu0.049Zr0.026)7.5,Sm(CobalFe0.197Cu0.062Zr0.034)7.5永磁体的显微组织及其对矫顽力的影响.Sm2Co17永磁体由2:17相和1:5相两相所形成的胞状组织构成,并影响材料矫顽力的大小.在高矫顽力磁体的单晶表面有大量取向一致的沟痕,而不同晶粒内部的沟痕取向不同;沟痕较多时,磁体内所形成的1:5相增多,对畴壁的钉扎能力增强,有利于内禀矫顽力的提高.磁体表面的白色物质含Sm较多时可降低矫顽力.     

Optimization of microstructures and magnetic properties of Sm(CobalFe0.227Cu0.07Zr0.023)7.6 magnets by sintering treatment

Magnetic properties and microstructures of Sm(Co_(bal)Fe_(0.227)Cu_(0.07)Zr_(0.023_)_(7.6) sintered magnets were optimized by sintering treatment. Results show that the knee-point magnetic field, Hknee, is twofold up and the intrinsic coercivity Hcjincreases by 40%, ranging from 21.64 to 30.39 kOe at the cost of a little decrease of Brfrom 10.84 to 10.31 kGs with sintering temperature decreasing from 1488 to 1473 K. And the average domain width is narrower and more uniform for the specimen sintered at 1473 K than that of the specimen sintered at 1488 K. It is impressive that the density of lamellar phase increases from ~0.050 to ~0.058 nm~(-1) with the sintering temperature decreasing from 1488 to 1473 K. Moreover, the average cellular size is about ~84 nm for the magnets sintered at 1473 K, which is 80% of that of the magnets sintered at 1488 K(~97 nm). And the cell boundary width of the magnets sintered at 1473 K(~7 nm) is only half average width of the magnets sintered at 1488 K(~14 nm). It is found that the Cu content in the cell boundaries is much higher(~17 at%) in the magnets sintered at 1473 K compared to that of the magnets sintered at 1488 K(~10 at%). It can be concluded that smaller cells and narrower cell boundaries together with higher gradient of Cu content are key points for obtaining the optimum Hkneeand Hcj.     

Electrochemical synthesis,structure characterization and magnetic properties of Tb_xFe_7Co_3(x=0,0.6,0.8) nanowires

Highly ordered Tb_xFe_7 Co_3(x=0,0.6,0.8) nanowires were synthesized in alumina templates by electrochemical deposition method.Here,the effects of Tb content and annealing treatment on the phase composition,morphology,crystalline structure and magnetic properties were investigated.The asdeposited Tb_0 Fe_7 Co_3 nanowires comprise Fe_7 Co_3 phase.While after adding Tb,the diffraction peaks slightly shift left,indicating the infiltration of Tb atoms into Fe_7 Co_3 phase.After annealing,Tb_0 Fe_7 Co_3 nanowires still consist of Fe_7 Co_3 phase with a slight enhancement on coercivity.While the annealed nanowires with Tb doped present a complex phase composition containing Fe3 Tb,Fe_2 Tb,Co_3 Tb,Co_(17)Tb_2,TbFeO_3 and Fe_2 O_3 phases distribute in the central portion,and Co_(0.72)Fe_(0.28) at the nanowire outer walls.The annealed Tb_xFe_7 Co_3(x=0.6,0.8) nanowires show higher magnetic performance owing to the formation of hard magnetic phases,the interfacial elastic coupling between hard and soft phases and the coherent Fe3 Tb/Co_3 Tb interface which restrain the domain wall motion.To be specific,the coercivity and remanence ratio of TbxFe_7 Co_3(x=0.6,0.8) nanowires significantly enhance with increasing Tb content.     

高温永磁Sm(CoCuFeZr)z的研究现状

综述了高温永磁体的现状,总结了影响高温磁体使用温度的关键因素,介绍了永磁体Sm(CoCuFeZr)z的发展状况,分析了成分对高温永磁体Sm(CoCuFeZr)z使用温度(内禀矫顽力Hci和温度系数β)的影响,概括了其矫顽力机理,并探讨了其今后的研究方向.     

Effects of grain boundary diffusion of PrCu alloy on microstructure and coercivity of hot deformed(Nd,Ce)-Fe-B magnets

The technology of using high abundance rare earth element Ce in permanent magnets has attracted many concerns.In this work,the magnetic properties and microstructures of hot deformed(Nd_(1-x)Ce_x)_(13.8)Fe_(76.1)Co_4 Ga_(0.5)B_(5.6) magnets and a selective magnet treated with PrCu grain boundary diffusion process(GBDP) were investigated systematically.It is found that Ce is beneficial to improving the plastic deformation ability of NdFeB magnets.The strongest c-axis orientation is achieved in the HD magnets with Ce concentration of x=0.3,resulting in good comprehensive magnetic properties of B_r=13.00 kGs,H_(cj)=10.12 kOe,(BH)_(max)=38.42 MGOe.Based on that,the GBDP was implemented on the magnets with the best orientation using Pr_(68)Cu_(32) ribbons and the magnetic properties of B_r=12.87 kGs,H_(cj)=15.65 kOe,(BH)_(max)=37.48 MGOe were obtained.The results of composition distribution and Curie temperature test of the GBDPed magnets illustrate that Pr diffuses into the(Nd,Ce)_2(Fe,Co)_(14)B grains to substitute Ce,which not only improves the Curie temperature of the grains,but also enhances the magnetic performance of the magnets.Through GBDP,the thermal stability of magnets has also been improved.     

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.     

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。     

Antioxidation Study of Sm（Co, Cu, Fe, Zr）z-Sintered Permanent Magnets by Metal Injection Molding

2∶17type Sm(Co ,Cu ,Fe ,Zr)zpermanent mag-nets originatedfromthe investigationinthe 1970s .Sm(Co ,Cu ,Fe ,Zr)zpermanent magnets have excellentintrinsic magnetic properties such as very high Curietemperature , high anisotropy fields , and relativelyhigh saturation magnetizations[1 ~4]. Hence the mag-nets play an i mportant role in national defence andmodernindustry .Because of the high brittleness of Sm(Co ,Cu ,Fe ,Zr)zpermanent magnets ,theirtransfor-mationinto complex,small ,precision …     

Coercivity enhancement of Ce-Fe-B sintered magnets by low-melting point intergranular additive

Ce-Fe-B sintered magnets with enhanced coercivity were prepared by the powder metallurgy method. The mechanism of the coercivity enhancement in Ce-Fe-B sintered magnets with the low-melting point intergranular additive was discussed in details. It was speculated that the low coercivity of Ce-Fe-B sintered magnet was related to the irregular sharps and relatively low magneto-anisotropy field of the matrix phase. After introducing a 20 wt.% Nd-based intergranular additive, the coercivity markedly increased from 108 Oe to 2560 Oe due to the formation of thin and continuous grain boundary layers and the surface modification of the matrix phase grains. Additionally, the formation of the high anisotropy field(Nd,Ce)_2Fe_(14)B shell was beneficial to the increase of the coercivity as well. This work suggested that adding low-melting point intergranular additives was effective to fabricate the practical Ce-Fe-B sintered magnets.     

Effects of cerium substitution on phase components,microstructures and magnetic properties of Nd-Fe-Ti-B alloy

(Nd_(1-x)Ce_x)_(12)Fe_(77)Ti_5B_6(x = 0,0.2,0.3,0.4,0.6,0.8)alloys were prepared by melt-spinning and annealing techniques.The phase constitutions,microstructures and magnetic properties were investigated by powder X-ray diffraction(XRD),a differential scanning calorimeter(DSC),a vibrating sample magnetometer(VSM)and a transmission electron microscope(TEM).It is found that with the increase of Ce content,the coercivity of the(Nd_(1-x)Ce_x)_(12)Fe_(77)Ti_5B_6 alloys reaches maximum first and then decreases.The maximum coercivity reaches 18.5 kOe obtained in the sample of 20% Ce substituted which is 34%higher than the Ce-free sample.TEM results reveal that the micro structure refinement effect is responsible for the coercivity improvement.This phenomenon implies that in some cases,Ce and Ti co-doping is more beneficial to improving of the coercivity than Ti single doping in Nd-Fe-B alloys.With further Ce addition,magnetic properties deteriorate due to the formation of CeFe_2 and TbCu_7-type phases.     

Effects of cobalt addition on microstructure and magnetic properties of PrNdFeB/Fe_7Co_3 nanocomposite

The permanent magnetic nanocomposite PrNdFeB/Fe_7Co_3 ribbons were prepared by directly quenching, and the microstructure and magnetic influence of composite materials with Co substitution were studied. The phase identification and the magnetic properties were measured by X-ray diffraction(XRD) and vibrating sample magnetometry(VSM). Microstructure observation was performed using scanning electron microscopy(SEM). The crystallization temperatures of the hard magnetic phase and the soft magnetic phase were measured using differential scanning calorimetry(DSC). The experimental results showed that Co addition improved the Curie temperature of magnets. When the ribbons were melt-spun at 35 m/s, the added content of Co was 4 at.%, and the magnetic properties were the best, which were remanence(Br) of 0.379 T, coercivity(Hci) of 344.4 kA/m, the maximum magnetic energy product(BH)max of 32.6 kJ/m~3. Besides, the activation energy of each phase was calculated by Kissinger equation, which was 310.4 kJ/mol of Fe_7Co_3 phase and 510.2 kJ/mol of 2:14:1 phase, respectively.     

Enhanced maximum energy product of(Sm_(1-y)Y_y)_2Fe_(17)N_x caused by abundant yttrium doping

Replacement of samarium(Sm) with abundant yttrium(Y) can help solve the potential shortage of Sm in the preparation of promising Sm_2 Fe_(1)7 N_x magnets.In this article,phase composition,microstructure and magnetic properties of(Sm_(1-y)Yy)_2 Fe_(17)N_x(y=0,0.2,0.4,0.6,0.8,1.0) were investigated.Maximum energy product(BH)_(max) is improved when less than 40 at% Y is doped in(Sm_(1-y)Y_y)_2 Fe_(17)N_x powder.In particular,when 20 at% Y replaces Sm,(BH)_(max) of(Sm_(1-y)Y_y)_2 Fe_(17)N_x powder increases by 15.1% from 131.7 to151.6 kJ/m~3.The effect of annealing temperature on the structural properties of high Y doping(Sm_(0.6)Y_(0.4))_2 Fe_(17) and the magnetic properties of the corresponding nitrides were subsequently investigated.In the RE_2 Fe_(17) phase grain combination process,the interlaced structure of the rhombohedral Th_2 Zn_(17)-type structural phase and the hexagonal Th_2 Ni_(17)-type structural phase is formed.Due to shortrange exchange coupling,the nitride with the highest content of two interlaced RE_2 Fe_(1)7 phases has the highest magnetic properties:B_r=1.23 T,H_(cJ)=443.9 kA/m and(BH)_(max)=197.6 kJ/m~3.     

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.     

Magnetic Microstructures of 2:17 Type Sm(Co,Fe,Cu,Zr)z Magnets Detected by Magnetic Force Microscopy

The magnetic microstructures of 2:17 type Sm(Co,Fe,Cu,Zr)z magnets were detected by magnetic force microscopy.Comparing the microstructures of the specimens coated with and without Ta thin film before and after heat-treatment, it is found that: (a) as a protection layer, Ta coating layer about 20 nm thick can effectively restrain Sm volatilization under high temperature;(b) the stress built in the 2:17 type Sm-Co magnets during specimen preparation only affects some local parts of the domain structures;(c) the magnetic microstructures vary largely for specimens heat-treated at high temperature without Ta film coating due to Sm volatilization.In addition, by comparing with high coercivity Fe-Pt point tips, it is found that the Co-Cr thin-film tips are not suitable for detecting the magnetic microstructures of strong permanent magnets.     

High coercivity Nd-Ce-Fe-B nanostructured ribbons prepared from melt spinning technique

The Ce-substituted(Nd_(1-x)Ce_x)_(12.2) Fe_(81.6) B_(6.2)(x=0.0, 0.2, 0.4, 0.6) nanocrystalline ribbons were prepared by annealing amorphous ribbons from melt spinning. It is found that all ribbons are in a multiphase state consisting of a-Fe phase, Nd(Ce)-rich phases and RE_2 Fe_(14) B(RE = Nd, Ce) phases. However, the coercivity of all annealed ribbons can reach a considerably high value without doping any heavy rare earth or other coercivity enhanced elements. A strong intergranular exchange coupling appears in these nanocrystalline ribbons. The Nd_(12.2) Fe_(81.6) B_(6.2) ribbons with multiphase have a coercivity of about 11.3 k Oe, and the coercivity decreases slightly with increasing Ce content. A coercivity of 7.5 kOe can be obtained when60 at% of Nd is replaced by Ce(x = 0.6) due to the grain refinement and the strong intergranular exchange coupling. This provides a practical approach of fabricating high coercivity Ce-substituted Nd-Fe-B materials.     

Magnetic Microstructures of 2：17 Type Sm（Co,Fe,Cu,Zr）z Magnets Detected by Magnetic Force Microscopy

The magnetic microstructures of 2：17 type Sm （Co, Fe, Cu, Zr）z magnets were detected by magnetic force microscopy. Comparing the microstructures of the specimens eoated with and without Ta thin film before and after heat-treatment, it is found that： （a） as a protection layer, Ta coating layer about 20 nm thick can effectively restrain Sm volatilization under high temperature; （b） the stress built in the 2.17 type Sm-Co magnets during specimen preparation only affects some local parts of the domain structures; （c） the magnetic microstructures vary largely for specimens heat-treated at high temperature without Ta film coating due to Sm volatilization. In addition, by comparing with high coercivity Fe-Pt point tips, it is found that the Co-Cr thin-film tips are not suitable for detecting the magnetic microstructures of strong permanent magnets.     

Optimization of core-shell structure distribution in sintered Nd-Fe-B magnets by titanium addition

In view of the uneven distribution of the core-shell structure of sintered Nd-Fe-B magnets after grain boundary diffusion,this study proposes to use high-melting-point and reactive element titanium(Ti) as an additive to increase the diffusion channels and to enhance the diffusion of heavy rare earth elements along the grain boundary phase.By adding Ti element,the diffusion depth and hence the intrinsic coercivity of magnets are increased significantly.The addition of Ti increases the coercivity ...     

Tremendous enhancement of magnetic performance for Sm(CoFeCuZr)z magnet based on multiscale copper redistribution

Microstructure and magnetic properties were studied for the commercial Sm(CoFeCuZr)_z magnets before and after post annealing treatment. The results show that the phases composition and orientation of the magnet do not change after post annealing treatment, but the substantial redistribution of Cu element within multiscale (the microscale crystal grain and the nanoscale cellular structure) is observed simultaneously. In detail, along with the Cu redistribution, the thickness of the Cu-rich Sm(Co,Cu)₅ cell boundary becomes thinner, and the Cu concentration in the boundary increases sharply. The pinning field of domain walls and corresponding coercivity increase remarkably with slight remanence and maximum energy product loss, and the overall magnetic performance of (BH)_max (MGOe)+H_cj (kOe) increases by 54.3% as a result. Moreover, the thermal stability of the magnet improves as well. On the other hand, Cu-lean phenomenon was observed along the grain boundary region, triggering to magnetic domain reversal process and slightly undermining the squareness of the demagnetization curve of the magnet.     

Enhanced magnetic properties in chemically inhomogeneous Nd-Dy-Fe-B sintered magnets by multi-main-phase process

Homogeneous substitution of Dy for Nd in the hard magnetic 2:14:1 phase can effectively enhance coercivity to ensure the high temperature operation,however,inevitably deteriorate remanence at expense.In this work,we performed a comparative investigation of the two magnets prepared by multimain-phase(co-sintering Nd_2 Fe_(14)B and(Nd,Dy)_2 Fe_(14)B powders) and single-main-phase(sintering(Nd,Dy)_2 Fe_(14)B powders) approaches.The comparative investigation reveals that at the same Dy substitution level(2.16 wt%),such chemically inhomogeneous multi-main-phase magnet possesses better roomtemperature magnetic properties as well as thermal stability than those of the single-main-phase one with homogenous Dy distribution in the matrix grains.Room-temperature magnetic properties H_(Cj)=1664 kA/m,B_r=1.33 T and(BH)_(max)=350.4 kJ/m~3 for the multi-main-phase magnet are all better than those for the single-main-phase magnet with H_(Cj)=1536 kA/m,B_r=1.29 T and(BH)_(max)=318.4 kj/m3.In addition,over the temperature range from 295 to 423 K,both the temperature coefficients of coercivity and remanence for the multi-main-phase magnet are also lower than that for the single-main-phase magnet.Such superior magnetic performance is attributed to the short-range magnetic interactions inside individual 2:14:1 phase grains and the long-range magnetostatic interactions between adjacent grains with inhomogeneous Dy distribution.Our work provides a feasible approach of enhancing coercivity and retaining energy product simultaneously in the Nd-Dy-Fe-B permanent magnets.     

Influence of Fe Content on Microstructure and Magnetic Properties of Melt-Spun SmCo-Based Alloy Ribbons

The microstructure and magnetic properties of melt-spun Sm(Co_0.88-xFe_xCu_0.10Zr_0.02)_7.5 (x = 0.1 and 0.2) alloy ribbons have been studied. The results showed that the as-spun ribbons were in a single phase, SmCo₇, with the Cu₇Tb structure. When aged in the temperature range from 720 to 900 °C, the SmCo₇ phase transformed into Sm₂Co₁₇, SmCo₅, and CoFe(Zr) phases with a minor Sm₂Co₃ phase. For the x = 0.1 alloy, a large coercivity, H_c = 8.7 kOe, was observed although the soft magnetic CoFe(Zr) phase was present in the alloy. The volume fraction of the CoFe(Zr) phase increased when the ageing temperature increased from 720 to 760 °C. At higher ageing temperature, the CoFe(Zr) phase was partially re-dissolved. With an increase in the Fe content in the alloy, the CoFe(Zr) phase increased significantly, causing the coercivity to decrease.