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1.
Two types of Gaussian distribution function (` θ type’ and `tan θ type') describing the degree of grain alignment in sintered NdFeB magnets have been compared in the distribution coefficient σ (or σg), the distribution probability P( θ) and the grain alignment dependence of coercivity. The results show that when the grain alignment is good (the ratio of remanence-to-saturation polarization Jr/ Js⩾0.90), σ( σg) and P( θ) for the two types of Gaussian functions have similar variation tendencies, the calculated values of normalized coercivity based on the starting field theory are basically the same and are consistent with experiments. When the grain alignment is not good ( Jr/ Js⩾0.80), the variation tendencies of σ and P( θ) are different. In addition, according to `tan θ type’ Gaussian function, the theoretical values of the normalized coercivity based on the starting field theory are still consistent with the experiments, but according to ` θ type’ Gaussian function, the theoretical values seriously deviate from the experiments. This means that the `tan θ type’ Gaussian function is a better texture function for describing the grain alignment. 相似文献
2.
The magnetic properties and microstructure were studied for bulk Nd 11.5Fe 72.4Co 9Nb 1B 6.1 magnets synthesized by hot-pressing and subsequent die-upsetting the melt-spun ribbons with additions of three kinds of low-melting-point metal (Zn, Al and Sn). Die-upset Nd 11.5Fe 72.4Co 9Nb 1B 6.1 magnets have low magnetic properties since they have an inhomogeneous microstructure with many coarse grains. The microstructure of die-upset magnets remains almost unchanged with Al and Sn additions, which only have negative effects on the magnetic properties. Different from Al and Sn additions, Zn addition changes the phase composition of the starting melt-spun powers due to the reaction of Zn and Nd 2Fe 14B during hot-pressing and hot-deforming and enhances the development of the desired [0 0 1] texture and improves the microstructure of die-upset magnets. As a result, an anisotropic magnet with good maximum energy product (221 kJ/m 3) and high coercivity (670 kA/m) is obtained by adding 2 wt% Zn to the Nd 11.5Fe 72.4Co 9Nb 1B 6.1 alloy. 相似文献
3.
It is difficult to obtain the crystallographic alignment for stoichiometric Nd 2Fe 14B alloys by applying the melt-spun and subsequent hot-pressing and hot-deformation techniques. However, the enhanced alignment and magnetic properties of die-upset nano-crystal Nd 2Fe 14B magnets have been obtained by Nb addition in the present paper. The magnetic properties studies show that Nb addition leads to the remarkable increase of remanence Br and intrinsic coercivity Hci, which is due to the improvement of c-axis texture and refinement of microstructure. Microstructure studies using transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that Nb atoms are enriched at grain boundary and the NbFeB phase is observed with increasing Nb content. Since some Fe atoms in the Nd 2Fe 14B phase participate in the formation of NbFeB phase, the excessive Nd atoms may be enriched at grain boundary, which may improve the physical property of grain boundary and provide a mass transport pass for preferential growth of oriented Nd 2Fe 14B grains, thus leading to the enhanced alignment and magnetic properties. 相似文献
4.
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 16.5Fe 77B 6.5 magnets has been enhanced about 40% by adding 3 wt% of the Dy-free compound of Nd 40Cu 30Al 30. 相似文献
5.
The Fe 65B 22Nd 9Mo 4 nanocomposite permanent magnets in the form of a rectangular cross sectioned rod have been prepared by annealing the amorphous precursors. The thermal behavior, structure and magnetic properties of the magnets have been investigated by differential scanning calorimetry, X-ray diffractometry, electron microscopy and magnetometry techniques. The as-cast Fe 65B 22Nd 9Mo 4 alloy showed soft magnetic properties, which changed into magnetically hard after annealing. Results provoke that the magnetic properties of the alloy are sensitive to thermal processing conditions. The optimum hard magnetic properties with a remanence ( Br) of 0.56 T, coercivity ( iHc) of 920.7 kA/m and maximum energy product ( BH) max of 50.15 kJ/m 3 were achieved after annealing the alloy at 983 K for 10 min. The good magnetic properties of Fe 65B 22Nd 9Mo 4 magnets are ascribed to the exchange coupling between the nano-scaled soft α-Fe, Fe 3B and hard Nd 2Fe 14B magnetic grains. 相似文献
6.
We have investigated the effect of lattice disorders near the surface of hard magnetic Nd 2Fe 14B grains on coercivity using artificial interfaces created by sputter depositing Nd on polished surface of Nd-Fe-B sintered magnets. The interfacial structure was manipulated by annealing the coated samples at 550 °C in vacuum with and without Ta cap. Nano-beam electron diffraction revealed a few nm thick disordered layer within the Nd 2Fe 14B phase at the Nd/Nd 2Fe 14B interface of a low coercivity sample, while a high coercivity sample showed a well-defined crystal structure of Nd 2Fe 14B near the NdO x/Nd 2Fe 14B interface. 相似文献
7.
Melt-spun ribbons with composition Sm 2+Y(Co 0.8Fe 0.1Mn 0.1) 17B X ( X=0–1.0 and Y=0–0.2) were fabricated with a wheel speed of 50 m/s, followed by annealing in the temperature range of 500–800°C for 2.5–60 min. Our results show that all the ribbons annealed up to 800°C are composed of a TbCu 7-type phase as the main phase. The highest coercivity of 8.7 kOe is obtained in a Sm-rich sample with composition Sm 2.2(Co 0.8Fe 0.1Mn 0.1) 17 annealed at 750°C for 5 min. It is found that these magnets show a very promising high-temperature performance – much better than those of typical sintered 2 : 17 magnets. 相似文献
8.
构造了立方和不规则形状晶粒的各向异性纳米晶单相Pr 2Fe 14B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Pr 2Fe 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 相似文献
9.
The magnetic powders for sintered NdFeB magnets have been prepared by using the strip casting (SC), hydrogen decrepitation (HD) and jet milling (JM) techniques. The effects of powder flowability and addition of a lubricant on the alignment degree and the hard magnetic properties of sintered magnets have been studied. The results show that the main factor affecting powder flowability is the aggregation of magnetic particles for powders in a loose state, but it is the friction between the powder particles for powders that are in a compact state. The addition of a lubricant with suitable dose can slightly prevent the congregating of powders, obviously decrease the friction between the powder particles, improve the powder flowability, and increase the alignment degree, remanence and energy product density of sintered magnets. Mixing a suitable dose of lubricant and adopting rubber isostatic pressing (RIP) with a pulse magnetic field, we have succeeded in producing the sintered NdFeB magnet with high hard magnetic properties of Br=14.57 KG, jHc=14.43 KOe, ( BH) max=51.3 MGOe. 相似文献
10.
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 jHc=25.6 kOe, Br=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. 相似文献
11.
本文采用统计平均方法研究了软、硬磁性晶粒尺寸及相分布对Nd2Fe14B/α-Fe纳米复合永磁材料矫顽力的影响。计算结果表明:对于单相纳米硬磁材料,磁体矫顽力随着硬磁性晶粒尺寸的减小而降低;对于软、硬两磁性相组成的Nd2Fe14B/a-Fe纳米复合永磁材料,两相的随机分布将导致磁体矫顽力随硬磁性晶粒尺寸的减小呈现极大值。本文的计算结果还表明当硬磁性晶粒尺寸大于软磁性晶粒的最佳尺寸时(15nm),具有多层膜结构的Nd2Fe14B/a-Fe纳米复合永磁材料将比两相随机分布时具有更大的矫顽力。 相似文献
12.
Spontaneous demagnetization jumps are observed in sintered magnets (Nd0.6Dy0.4)16(Fe0.77Co0.23)78B6 in a constant magnetic field after a sharp decrease in an external magnetic field from the value corresponding to the saturation to a value close to the coercive force. It is shown that the number of the magnetization jumps is proportional to their amplitudes. A low value of the autocorrelation coefficient between the jump amplitude and the time of its appearance (R < 0.1) demonstrate the stochasticity of the jumps. It is found that the spectral jump density is independent of the frequency, i.e., a white magnetic noise is observed. The distribution of the magnetic field gradient has been obtained near the sample surface that makes it possible to distinguish domains and the grain magnetization in the dependence on the direction of the texturing of the sintered magnet. 相似文献
13.
Highly oriented films of ∼6 μm in thickness consisting of the Nd 2Fe 14B compound phase were obtained by a three-dimensional sputtering method at room temperature and the subsequent crystallization by annealing. The c-axis orientation and coercivity of film samples were sensitive to the sputtering parameters and annealing conditions. The optimum temperature and time for annealing were 650 °C and 30 min to show the highest coercivity without any deterioration for the orientation of Nd 2Fe 14B grains, and furthermore the degree of c-axis orientation was increased by decreasing the Ar gas pressure or input power for sputtering. The resultant film magnets with good magnetic properties of Br=∼1.06 T, HC=∼371 kA/m, and (BH) max=∼160 kJ/m 3 were obtained under the optimized parameters for sputtering. 相似文献
14.
Elements in atomic ratios Nd 2(Fe 0.9Mo 0.1) 14B were melted in an induction furnace and annealed in order to examine the effect of molybdenum during the preparation of Nd-Fe-B magnets. A phase analysis has been made from 57 Fe Mössbauer spectroscopic measurements in the temperature range of 100 to 700 K. It is found that two iron containing phases are formed, one Mo rich Fe alloy and the other Nd-Fe(Mo)-B isostructural to Nd 2Fe 14B. The Nd 1.1Fe 4B 4 phase usually found in Nd-Fe-B magnets is not observed in these samples. The Curie temperature, Tc, is found to be 605(5) K from the Mössbauer as well as vibrational sample magnetometer measurements on the same sample. At low temperatures, the average hyperfine field at Fe nuclei is found to show a decrease with respect to the value for Nd 2Fe 14B. 相似文献
15.
The Fe 63B 23Nd 7Y 3Nb 3Cr 1 nanocomposite magnets in the form of sheets have been prepared by copper mold casting technique. The phase evolution, crystal structure, microstructural and magnetic properties have been investigated in the as-cast and annealed states. The as-cast sheets show magnetically soft behaviors which become magnetically hard by thermal annealing. The optimal annealed microstructure was composed of nanosize soft magnetic α-Fe (19-29 nm) and hard magnetic Nd 2Fe 14B (45-55 nm) grains. The best hard magnetic properties such as intrinsic coercivity, jHc of 1119 kA/m, remanence, Br of 0.44 T, magnetic induction to saturation magnetization ratio, Mr/ Ms=0.61 and maximum energy product, (BH) max of 55 kJ/m 3 was obtained after annealing at 680 °C for 15 min. The annealing treatment above 680 °C results in non-ideal phase grains growth, which degrade the magnetic properties. 相似文献
16.
Recent studies have shown the effects of a post sintering heat treatment at 1000 °C for 24 h on the microstructure and magnetic properties of Pr-Fe-B/Nd-Fe-B magnets based on Nd 16Fe 76B 8 and Pr 16Fe 76B 8. In an attempt to understand the influence of environmental factors, an investigation into the effects of annealing under different degrees of vacuum for both types of sintered magnets has been carried out. The effect of annealing the Pr-Fe-B magnets at 1000 °C for 24 h resulted in a general increase in the magnetic properties, especially the intrinsic coercivity, although the degree of improvement appeared to be dependent on the initial annealing conditions (ambient pressure). Oxygen analysis of sintered and annealed magnets indicates a change in the nature of the grain boundary phases after the annealing treatment. The effect of annealing the Nd-Fe-B magnets at 1000 °C for 24 h resulted in a general decrease in the magnetic properties, especially the intrinsic coercivity. 相似文献
17.
The effect of gallium added by blending method on the magnetic properties, thermal stability and microstructure of Nd 16.5Dy 16.0Fe 53.45Co 13.0B 1.05 (wt%) sintered magnets was investigated. The experimental results show that an appropriate Ga addition can markedly increase the coercivity, reduce the irreversible loss and slightly enhance the remanence. For instance, by adding 0.5 wt% Ga, the coercivity is increased from 1232 to 1819 kA/m; the irreversible loss after being exposed at 200°C for 0.5 h is reduced from above 33% to below 5%. Microstructure analyses show that the grain boundaries of the magnets with and without Ga addition are substantially different. The grain boundaries of the Ga-free magnet are meandrous. On the other hand, most of the boundaries of Ga-containing magnets are straight and smooth. These characteristics can be explained by the appearance of new phases during sintering process. 相似文献
18.
用电弧熔炼法制备了Nd 3.6Pr 5.4Fe 83Co 3B 5合金铸锭,然后利用熔旋快淬法在铜辊转速V=20m/s下制备了Nd 3.6Pr 5.4Fe 83Co 3B 5薄带.快淬带主要由软磁相α-Fe和Nd 2Fe 14B型的硬磁相组成.采用直流退磁剩磁曲线方法分析了样品在反磁化过程中的可逆与不可逆磁化部分,并研究了软磁相和硬磁相的反磁化行为,得到样品的不可逆磁化形核场H no约为440kA/m.同时研究了样品的磁黏滞性,结果表明由于软磁相的存在使得热激活体积较大.
关键词: 相似文献
19.
The fabrication of Nd 11Dy 4Fe 76.5TM 2.5B 6 (TM=Co, Cu, Al, and Nb: at%) sintered magnets via a two-step sintering process was demonstrated. A densification of greater than 99% was achieved using the two-step sintering of the Nd-Fe-B powder. This process produced a sample with an average grain size of 6.2 μm in the Nd 2Fe 14B phase, resulting in an enhancement of the coercivity compared to that of the isothermally sintered sample. The suppression of grain growth was considered to be affected by the relatively low temperature during the two-step sintering and by the presence of a B-rich phase at the triple junction. Consequently, the two-step sintering process led to suppression of grain growth and a uniform grain size distribution, which resulted in improved magnetic properties, in particular in the intrinsic coercivity. 相似文献
20.
Sintered Nd 17 (Fe 1?x Co x) 75B 8 permanent magnetic alloys have been studied by Mössbauer effect, X-ray diffraction and electron probe micro-analysis, The results show that the alloys are composed of the tetragonal phase Nd 2(Fe,Co) 14B, the B-rich phase Nd 111(Fe,Co) 4B 4 and the Nd-rich phase Nd 80(Fe,Co) 19B. In the tetragonal phase, Co atoms occupy preferentially the k 2 and j 2 sites, and Fe atoms occupy randomly the k 1 site and preferentially the j 1 site while the e and c sites seem to be completely occupied by Fe atoms. 相似文献
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