Nanocomposite Magnets and their Preparation under High Pressure

This article reports current studies on nanocomposite magnets and a newly developed route for their preparation, known as crystallization of amorphous alloy under high pressure (CAAHP). The microstructure and magnetic properties of nanocomposite magnets prepared by CAAHP are presented, and the influences of pressure on the microstructures of the magnets are discussed. α‐Fe/Sm₂(Fe,Si)₁₇C_x nanocomposite magnets with a grain size <10 nm have been successfully prepared by CAAHP, and a maximum energy product of about 25 MGOe is obtained.     

Magnetic properties and microstructures of mischmetal-FeB-(Al, Ti and Al-Co) permanent magnets

The magnetic characteristics of anisotropic MM-FeB- (Al, Ti and Al-Co) permanent magnets have been investigated by using hot-pressing and die-upsetting process. The best magnetic properties obtained in these studies were H _C = 5.1 kOe, B _r = 5.4 kG with (BH)_max = 5.1 MGOe for hot-pressed MM-FeB-Al-Co magnets and H _C = 3.6 kOe, B _r = 6.7 kG, (BH)_max = 6.8 MGOe for die-upset MM-FeB-Al-Co magnets. Higher squareness of demagnetization curve was obtained in anisotropic die-upset MM-FeB- (Al, Al-Co) magnets. X-ray diffraction and STEM investigations revealed that the higher magnetic properties in die-upset magnets were resulted from alignment of the c-axis along the die-upsetting direction. The magnetic anisotropy of the die-upset magnets and the densification of the hot-pressed magnets were increased by partial substitution of Al and Al-Co for Fe.     

Computational Design of Rare-Earth Reduced Permanent Magnets

Multiscale simulation is a key research tool in the quest for new permanent magnets. Starting with first principles methods, a sequence of simulation methods can be applied to calculate the maximum possible coercive field and expected energy density product of a magnet made from a novel magnetic material composition. Iron (Fe)-rich magnetic phases suitable for permanent magnets can be found by means of adaptive genetic algorithms. The intrinsic properties computed by ab initio simulations are used as input for micromagnetic simulations of the hysteresis properties of permanent magnets with a realistic structure. Using machine learning techniques, the magnet’s structure can be optimized so that the upper limits for coercivity and energy density product for a given phase can be estimated. Structure property relations of synthetic permanent magnets were computed for several candidate hard magnetic phases. The following pairs (coercive field (T), energy density product (kJ·m⁻³)) were obtained for iron-tin-antimony (Fe₃Sn_0.75Sb_0.25): (0.49, 290), L1₀-ordered iron-nickel (L1₀ FeNi): (1, 400), cobalt-iron-tantalum (CoFe₆Ta): (0.87, 425), and manganese-aluminum (MnAl): (0.53, 80).     

Appreciable Magnetic Moment and Energy Density in Single-Step Normal Route Synthesized MnBi

We study the structural and magnetic properties of the MnBi intermetallic compound. The LTP (Low Temperature Phase) MnBi compound is successfully synthesized in single step by vacuum encapsulation technique and rapid quenching from phase formation temperature. The phase purity and the magnetic moments of MnBi are highly dependent on heat treating schedule. The best phase purity and the magnetic moment are found for a heat-treated sample at 310 °C for 48 h. Rietveld fitted X-ray diffraction (XRD) patterns revealed that the studied MnBi compound is crystallized in hexagonal P63/mmc space group with minute presence of unreacted Bi and Mn phases. The scanning electron microscopy (SEM) study is carried out to visualize the grains morphology and phase identification. The bulk MnBi powder showed appreciable magnetic moment of ～62 emu/g at 6 Tesla and maximum energy product BH _max of 4.01 MGOe at 6 Tesla. The magnetic properties of synthesized MnBi show that it could be a potential candidate for rare earth free permanent magnets.     

Effect of the Ce Content on the Magnetic Properties and Microstructure of CeCo<Subscript>5</Subscript>-based Sintered Bulk Magnets

CeCo₅-based magnets have recently attracted much attention due to their moderate magnetic performance and low cost. Nevertheless, there have been few studies on the effects of Ce content on the magnetic properties and microstructures of CeCo₅-based magnets. In response to this, the magnetic properties of sintered bulk magnets with nominal compositions of Ce(Co_0.73Cu_0.135Fe_0.135) _z (z =?4.95, 5.15, 5.35, and 5.55), prepared by the conventional powder metallurgy method, were investigated here. Based on experimental findings, it was shown that Ce(Co_0.73Cu_0.135Fe_0.135)_5.15 sintered bulk magnets had comprehensive magnetic properties—maximum energy product of 80 kJ m^??3 (10 MGOe) and intrinsic coercivity (H _cj) of 452 kA m^??1 (5.69 kOe)—superior to those previously reported by us. For z =?5.35 and 5.55, due to the presence of the minor Ce₂Co₁₇ phase (which has a Curie temperature (T _c ) <?20 °C), magnets had low H _cj values. Based on x-ray diffraction and scanning electron microscopy observations, it was suggested that the volume fraction of the 1:5 matrix phase was the main factor determining the H _cj of CeCo₅-based sintered bulk magnets obtained with different Ce contents. Furthermore, the importance of the dispersion characteristics of the Ce₂O₃ phase within the matrix was emphasized. Uniform dispersion of the Ce₂O₃ phase can significantly improve the overall magnetic performance of CeCo₅-based magnets.     

Matrix effect in soft metal-bonded samarium-cobalt (SmCo5) permanent magnets

This paper discusses the preparation of samarium-cobalt (SmCo₅) alloy powders by reduction-diffusion process. These powders were blended with equal weight percentages of soft metal/alloy powders, such as indium, tin and solder alloy (Pb-17Sn), to prepare bonded magnets. Important magnetic properties such as remanence, coercivity and energy product of these magnets were measured. Effect of matrix metal/alloy on the magnetic properties of processed magnets is outlined.     

MAGNEQUENCH ND-FE-B MAGNETS

The advent of MAGNEQUENCH neodymium-iron-boron materials having excellent magnetic properties and potential economic advantages has initiated a new era in permanent magnet technology. These magnets have already been used in cranking motors, stepping motors, etc.

Different kinds of isotropic powders have been developed having high and low coercivities for use in varied applications. The properties of these powders are discussed. The properties of fully dense isotropic (MQ2) and anisotropic magnets (MQ3) are given. Anisotropic powders produced from hot deformed magnets are stable and it contrasts sharply with those prepared from sintered magnets. These anisotropic powders can be molded into bonded magnets with energy products of 15-17 MGOe.     

Novel Bimorphological Anisotropic Bulk Nanocomposite Materials with High Energy Products

Nanostructuring of magnetically hard and soft materials is fascinating for exploring next‐generation ultrastrong permanent magnets with less expensive rare‐earth elements. However, the resulting hard/soft nanocomposites often exhibit random crystallographic orientations and monomorphological equiaxed grains, leading to inferior magnetic performances compared to corresponding pure rare‐earth magnets. This study describes the first fabrication of a novel bimorphological anisotropic bulk nanocomposite using a multistep deformation approach, which consists of oriented hard‐phase SmCo rod‐shaped grains and soft‐phase Fe(Co) equiaxed grains with a high fraction (≈28 wt%) and small size (≈10 nm). The nanocomposite exhibits a record‐high energy product (28 MGOe) for this class of bulk materials with less rare‐earth elements and outperforms, for the first time, the corresponding pure rare‐earth magnet with 58% enhancement in energy product. These findings open up the door to moving from a pure permanent‐magnet system to a stronger nanocomposite system at lower costs.     

Structure and Magnetic Properties of Nd-Fe-B/a-Fe Nanocomposite Magnets by Co, Nb, Dy Substitutions

Structure and magnetic properties of the nanocomposite magnets prepared by mechanical alloying procedure with composition 55 wt pct Nd (Fe0.92B0.08)5.5+45 wt pct a-Fe, 55 wt pct Nd(Fe0.8-xCo0.12Nbx B0.08)5.5+45 wt pct a-Fe (x=0.00, 0.01, 0.03) and 55 wt pct (Nd0.9Dy0.1) (Fe0.77Co0.12Nb0.03B0.08)5.5+45 wt pct a-Fe were studied. It was found that substitution of Co for Fe could significantly improve the permanent magnetic properties of the nanocomposite magnets and typically, the maximum magnetic energy product was increased from 104.8 kJ/m3 (13.1 MGOe) to 141.6 kJ/m3 (17.7 MGOe). In contrast to the case of conventional nominally single-phase magnets, the addition of Nb results in promoting the growth of a-Fe grain and is thus unfavorable for the improvement of permanent magnetic properties of the nanocomposites. Although the addition of Dy can increase the coercivity of the magnets, the increase of magnetic anisotropy of hard phase leads to decrease of the critical grain size of soft phase. Additionally it causes the difficulty of preparing the nanocomposites because it is more difficult to control the grain size of soft phase to meet the requirement of appropriate exchange coupling between hard and soft grains.     

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.     

Preparation of rare earth-cobalt magnet alloy by reduction-diffusion process

Preparation of rare earth-cobalt alloys by reduction-diffusion (R-D) process is described. The process essentially involves mixing of the rare earth oxide and cobalt/cobalt oxide powders in proper proportion and high temperature reduction of the charge in hydrogen atmosphere, followed by aqueous leaching of the reduced mass to yield the alloy powder. Comparison is made of the magnetic properties of the R-D powder with those of the powder prepared by the direct melting (DM) route and it is observed from the reported values for SmCo₅ that the energy product of the R-D powder (∼ 22 MGOe) is only marginally lower than that of the Directly Melted alloy (∼ 25 MGOe). The paper also includes the results of studies carried out at the Bhabha Atomic Research Centre on the preparation of misch metal-cobalt alloy by the R-D process.     

Grain boundary optimization induced substantial squareness enhancement and high performance in iron-rich Sm-Co-Fe-Cu-Zr magnets

Increasing iron content has been witnessed an essential method to improve the remanence of 2:17-type Sm-Co-Fe-Cu-Zr magnets,however,the inferior squareness factor accompanied with the increased iron content turns into a neck sticking problem.In this work,the grain boundary optimization induced sub-stantial squareness enhancement from 63.4％to 91.4％,and consequently an excellent maximum energy product of 32.63 MGOe have been achieved in iron-rich Sm-Co-Fe-Cu-Zr magnets via tuning solution process.It is clearly revealed that the grain boundary(GB)phases as well as the micro-twins'density in grain interiors can be controlled and interprets the enhancement mechanism of squareness.     

Magnetic properties of a mischmetal-cobalt alloy

The magnetic properties of a mischmetal-cobalt alloy are studied. A mischmetal-64% cobalt alloy was melted in induction furnace under a protective atmosphere of argon. The melt was solidified in a magnetic field of 7 kOe, and cooled to a temperature of 950° C and was thereafter quenched in water. Specimens of suitable dimensions were machined, heat-treated in the temperature range 1000–1100° C for various lengths of time and the magnetic properties evaluated. The (BH)_max value was 10·3 MGOe which was associated with aB _r value of 7 kG and H_c value of 5 kOe. The results obtained offer feasibility to design new MM-Co₅ magnets through developments in processing technique.     

Magnetic properties and microstructure of radially oriented Sm(Co,Fe,Cu,Zr)z ring magnets

Radially oriented Sm(Co,Fe,Cu,Zr)_z ring magnets are prepared by powder metallurgy with appropriate magnetic field molding, sintering process and aging treatment. The results indicate that radially oriented Sm(Co,Fe,Cu,Zr)_z ring magnets have obvious anisotropy of thermal expansion and sintering shrinkage, which easily lead to the splits and deformation of the ring magnets. So, slow heating, vacuum pre-sintering in sintering process and various quenching processes at different steps during quenching are adopted. The magnets have excellent magnetic properties: B_r = 10.8 kGs, H_cj = 27.6 kOe, BH_max = 28.1 MGOe. Besides, there is a uniform magnetization field on the surface of the ring magnets. The average surface magnetization field () is 1.502 kGs. The deviation from average (α) is only 4.2%. The microstructure of the magnets consists of a mixture of homogeneous cellular and lamella structures.     

Spark plasma sintered Sm(2)Co(17)-FeCo nanocomposite permanent magnets synthesized by high energy ball milling

Nanocomposite Sm(2)Co(17)-5?wt% FeCo magnets were synthesized by high energy ball milling followed by consolidation into bulk shape by the spark plasma sintering technique. The evolution of magnetic properties was systematically investigated in milled powders as well as in spark plasma sintered samples. A high energy product of 10.2?MGOe and the other magnetic properties of M(s) = 107?emu?g(-1), M(r) = 59?emu?g(-1), M(r)/M(s) = 0.55 and H(c) = 6.4?kOe were achieved in a 5?h milled and spark plasma sintered Sm(2)Co(17)-5?wt% FeCo nanocomposite magnet. The spark plasma sintering was carried out at 700?°C for 5?min with a pressure of 70?MPa. The nanocomposite showed a higher Curie temperature of 955?°C for the Sm(2)Co(17) phase in comparison to its bulk Curie temperature for the Sm(2)Co(17) phase (920?°C). This higher Curie temperature can improve the performance of the magnet at higher temperatures.     

Effects of Sintering Temperature on Microstructure and Magnetic Properties of Nd–Fe–B Magnets

The sintered Nd–Fe–B (neodymium–iron–boron) magnet has been used for many applications in various fields such as acoustics, communications, and automation due to its excellent properties including high remanence, high coercivity, and large energy product. Especially high-coercivity sintered Nd–Fe–B magnets have been extensively applied in the field of permanent magnet motors. In the present work, the effects of sintering temperature on the structural and magnetic properties of a Nd₁₅Fe₇₇B₈-type magnet have been investigated. Sintered permanent magnets were produced from a Nd₁₅Fe₇₇B₈ commercial alloy. The magnetic properties were evaluated using an Automatic Magnet Tester. The magnets were successfully produced at different temperatures. It was seen that the best magnetic properties were obtained for the magnet produced at 1050 ^°C for 1 h. The structural evolution of the magnets has also been examined by means of X-ray diffraction (XRD) and polarized optical microscope. Nd₂Fe₁₄B, Fe₃B and some α-iron phases were observed by X-ray diffraction results.     

添加润滑剂对烧结钕铁硼磁体性能的影响

研究了烧结钕铁硼永磁材料的粉末流动性及添加润滑剂对粉末流动性与磁体取向度和磁性能的影响.结果表明:影响松装状态磁粉流动性的主要因素是粉末颗粒团聚,影响密实磁粉流动性的主要因素是颗粒间的摩擦力.添加适量的润滑剂可以防止粉末颗粒团聚、明显地减小摩擦力,改善粉末流动性,提高磁体的取向度、剩磁与磁能积.采用添加润滑剂和橡皮模等静压制成型工艺,批量生产的烧结钕铁硼磁体性能达到:Br=1.457 T,jHc=1148 kA/m(14.43 kOe),(BH)max=408 kJ/m3(51.3 MGOe).     

Exchange Coupling and Magnetic Behavior of SmCo_(5-x)Sn_x Alloys

Exchange coupling and magnetic properties of SmCo5 alloys containing different amounts of Sn were investigated in sintered magnets.X-ray diffraction analysis revealed the formation of Sm2Co17 and Sm2Co7 phases in SmCo5 matrix.Exchange coupling mechanism was evaluated by switching field distribution,dcdemagnetization and magnetization curves as function of reverse applied field.Energy product of 59.2 kJ/m 3(7.4 MGOe),remanent magnetization to maximum magnetization ratio of 0.97 and remanence coercivity to intrinsic coercivity ratio of 1.75 were achieved for 0.2 at.% Sn.     

HDD法制备各向异性NdFeB磁粉的研究

本文探讨了用吸氢—歧化—脱氢(HDD)工艺制取各向异性NdFeB永磁粉末的可能性。研究了成份、氢处理工艺以及后处理等对各向异性现象的影响。研究结果表明,在Nd_xFe_(87)-x-yCo_6B_7Zr_y的合金中经适当的氢气处理,初步获得了各向异性磁粉,由M115型振动样品磁强计所测磁粉的磁性能为:B_r=0.92emu/gm,iH_c=720kA/m(9kOe),(BH)_(max)=112kJ/m~3(14MGOe)。由该粉与3％(重量百分比)的环氧树脂混合制成的各向异性粘结磁体的磁性能为B_r=0.65T,iH_c=744kA/m(9.3kOe),(BH)_(max)=64k3/m~3(8MGOe)。本文还观察了各向异性粉的微观结构。     

The Influence of Co and Nb Additions on the Magnetic Properties and Thermal Stability of Ultra-high Intrinsic Coercivity Nd-Fe-B Magnets

The effect of Co and Nb additions on the magnetic properties and thermal stability of ultra-high intrinsic coercivity Nd-Fe-B magnets has been investigated. The results show that the remanence (B _r ) and maximum energy product (BH)_max of sintered Nd-Fe-B magnets first increases, and reaches a maximum, then starts to decrease with increasing Co content. The intrinsic coercivity and temperature coefficients of remanence (α) decrease, and the temperature coefficients of coercivity (β) increase with increasing Co content. The minimum reversible magnetic flux loss, temperature coefficients of reversible magnetic flux, total magnetic flux loss and irreversible magnetic flux loss are obtained when the Co content is 7.5 at.%. The temperature coefficients of coercivity (β) and remanence (α) for sintered Nd₉Dy₆Fe_79?x Nb _x B₆ magnets from 300 K to 513 K are 0.36 %/K and 0.127 %/K respectively when the content of Nb is 1.0 at.%. The reasons for the variation on magnetic properties and temperature coefficients were analyzed.