Fe88Zr7B4Co1软磁纳米晶薄带的巨磁阻抗效应

利用熔旋快淬技术在铜辊速度为40 m/s的条件下制备了Fe88Zr7B4Co1薄带,分别经550、600、650、700、725、750℃退火处理30 min,形成纳米晶薄带.研究了退火温度、外磁场和驱动电流频率对巨磁阻抗效应的影响.发现存在一个最佳退火温度650℃.其bcc α-Fe相的晶粒尺寸为11.3 nm,在此温度下制备的Fe88 Zr7 B4 Co1纳米晶薄带具有最强的巨磁阻抗效应:在H=90 Oe下,频率约为1 MHz时Fe88Zr7B4Co1纳米晶薄带的磁阻抗△Z/Z0达到-52%.Fe88Zr7B4Co1纳米晶薄带具有比未掺杂的Fe88Zr7B4更强的巨磁阻抗效应.     

NdFeB/α-Fe合金快淬薄带表面微观形貌

采用快淬加后续晶化退火方法,制备了NdFeB/α-Fe双相纳米晶复合永磁合金的快淬态和晶化态薄带,用原子力显微镜(AFM)观察了薄带贴辊面和自由面的微观形貌,分析研究了薄带不同表面晶粒尺寸与均匀性的差异。贴辊面快淬时冷却速度快、结晶度高,快淬态主要由非晶体组成,退火时新相的析出以均匀形核的方式成核,晶化态晶粒数量少、平均尺寸(～70nm)大,但晶粒大小均匀。自由面快淬时析出了数量较多、尺寸较大的微晶,退火时以非均匀形核为主,成核率高,晶粒数量多、尺寸小,平均晶粒尺寸(～50nm)小于贴辊面,但由于微晶本身的长大,形成了超过100nm的粗大晶粒,使微观结构的均匀性变差。薄带不同表面微观形貌的差异将会对纳米晶复合永磁材料的磁性能产生直接的影响。     

制备条件对Finemet纳米晶软磁材料组织的影响

通过单辊快淬在真空和空气中制备了Finemet合金Fe73.5Si13.5B9Nb3Cu1的薄带,利用X射线衍射仪（XRD）和透射电镜（TEM）研究了薄带淬态和退火态的结构。利用差示扫描量热仪（DSC）研究了两种薄带的晶化动力学,结果表明,真空中制备的条带为完全非晶,空气中制备的薄带是由非晶相和少量!-Fe相组成。非晶中氧含量的升高使第一晶化峰温度升高,第二晶化峰温度降低,晶化激活能变大,但对等温退火后!-Fe的晶粒度无影响。     

退火对(Nd,Pr)_(12.8)Dy_(0.2)Fe_(77.4)Co_(4.0)B_(5.6)快淬薄带晶化行为的影响

采用高真空高纯氩DSC测量了(Nd,Pr)12.8Dy0.2Fe77.4Co4.0B5.6非晶快淬薄带以及不同温度退火薄带的连续加热曲线,计算了晶化激活能、频率因子、晶化体积分数、晶化速率,研究了预退火前后薄带的晶化动力学和晶化过程。结果表明(Nd,Pr)12.8Dy0.2Fe77.4Co4.0B5.6快淬薄带在30 K/min加热速度时DSC曲线起始晶化温度865.8 K、峰值晶化温度877.2 K、晶化结束温度901.7 K,居里温度转折点581.2 K,富稀土相的初始熔化点1003.6 K。在高于峰值晶化温度或晶化结束温度退火10 min的薄带非晶完全晶化,居里温度处形成吸热峰,而低于803.0 K退火处理的薄带以及快淬薄带在相近温度处只有DSC转折点。相对于快淬薄带直接晶化的特征,在低于起始晶化温度的693.0~743.0 K退火处理的薄带晶化峰形相近;803.0 K退火处理后薄带的晶化峰的温度范围增宽:在10~40 K/min相同加热速度下其起始晶化温度均降低1.4%,晶化结束温度在加热速度20~40 K/min时达到、甚至高于快淬薄带直接晶化结束温度;在低于快淬薄带直接晶化的峰值晶化温度之前存在一个具有相同晶化速率的临界温度,在低于该临界温度时,退火薄带比快淬薄带具有较高的晶化速率、更不稳定;而在高于该临界温度,退火薄带比快淬薄带具有较低的晶化速率。     

Fe₇₃Si₁₅Nb₃B₈Cu₁铁芯薄带的热处理工艺研究

本文对用Finemet型Fe73Si15Nb3B8Cu1快淬薄带制备的铁芯增加预退火处理,再在540 oC晶化退火处理得到退火铁芯。结果表明,随着预退火温度提高,预退火的薄带及再经晶化退火的薄带的韧性均逐渐降低,预退火后非晶薄带的第一晶化温度变化不大,而第二晶化峰值温度向高温方向偏移,预退火扩大了非晶薄带晶化退火的温度范围,有利于获得性能更加稳定的非晶纳米晶薄带;增加预退火处理的薄带的晶粒尺寸比直接晶化退火薄带的晶粒分布更均匀,其中在450 oC预退火的薄带经晶化退火后,晶粒尺寸在8~15 nm之间。增加预退火的铁芯样品,其振幅磁导率和铁损较直接退火的均有明显改善,其中经450 oC预退火的铁芯具有最大的振幅磁导率（μa=8.6×104, f=10 kHz）和最小的交流铁损（P0.5/10k=8.7 W/kg）,分别较直接退火的铁芯升高了16.0%,下降了17.1%。     

极端晶化条件下纳米双相永磁合金快淬薄带的晶化研究

在常规晶化退火工艺条件下纳米双相永磁合金快淬非晶薄带的晶化过程中,α-Fe相通常在低温优先析出,这导致了α-Fe晶粒过于粗大并严重损害了材料磁性能。针对这一问题,近期有一些学者对极端晶化条件下非晶快淬薄带的晶化行为和机制进行了仔细的研究。本文对这些研究进行了综述和分析。     

Fe89Zr7B4退火薄带的纳米晶结构、巨磁阻抗和磁导率变化

Fe89Zr7B4薄带在550℃～720℃的温度范围内分别退火20min，析出晶粒为13nm～17nm的α-Fe。720℃退火时有微量的第二相析出。Fe89Zr7B4纳米晶薄带的巨磁阻抗效应与退火温度紧密相关，存在一个最佳退火温度，约为650℃。进一步的实验结果显示：Fe89Zr7B4纳米晶薄带在直流磁场引导下横向磁导率的变化率在650℃存在最大值。经典电磁理论与磁谱结合的模型能较好地描述Fe89Zr7B4纳米晶薄带磁阻抗与频率的依赖关系。实验数据和理论计算结果均表明，巨磁阻抗效应与磁场引导的横向磁导率的变化紧密相关。     

Nb、Si、B含量的联动调整对Finemet型薄带结构及性能的影响

本文用V部分替代Nb并适当调整Si与B的含量,通过单辊快淬技术及退火工艺制备了原始成分为Fe73Si15Nb3B8Cu1和优化成分为Fe73Si15.5Nb1.1V2.4B7Cu1的Finemet型非晶纳米晶薄带。利用X射线衍射仪、透射电子显微镜、磁性能测试仪研究了薄带的结构及磁性能。结果表明：两种快淬态薄带主要为非晶结构,合金具有良好的非晶形成能力;采用Luborsky法评价薄带韧性,发现含V的快淬态薄带的断裂应变λt为5.05×10-2,其韧性较差;两种退火态薄带中的纳米晶晶粒大小分别约为14.8 nm与13.2 nm;与原始成分薄带相比,含V薄带的居里温度Tc,晶化起始温度Tx1有少量降低;含V薄带的饱和磁化强度略低于原始薄带,但是其矫顽力较小,其环形磁芯样品静态初始磁导率为1.269×105、静态损耗为1.748 J/m3,动态测试显示,随着频率的增加,含V薄带损耗较原始薄带小的优势更加明显。     

快淬速度对Nd2Fe14B/α-Fe纳米复合永磁材料结构和磁性能的影响

利用熔体快淬法制备了(Nd0.9Dy0.1)9(Fe0.9Co0.1)85.5B5.5快淬薄带,研究了快淬速度对晶化过程、晶化后薄带的结构及磁性能的影响.研究发现,快淬速度不同,薄带的非晶程度不同,晶化过程存在很大差异;在快淬速度为12m/s时,快淬薄带中已存在一定的晶态相,晶化后的晶粒细小均匀,磁性能较高;而当快淬速度达到18m/s和25m/s时,合金晶化后的晶粒粗大且不均匀,磁性能较低.     

工质材料GdDyFe磁热效应的研究

对于磁制冷GdDyFe铸锭复合材料和快淬得到的纳米晶薄带的结构和磁热效应进行了研究和分析。结果表明，GdDyFe铸锭样品和纳米晶薄带样品的居里温度比GdDy合金高，分别由原来的260K升高到了275K和263K，并保留了较大的磁熵变。而且几种相变温度各不相同的铁磁物质复合的GdDyFe材料及其薄带样品的纳米晶结构使得样品的高磁熵变温区范围宽化。该材料适用于埃里克森循环，为磁制冷材料的实用化带来了希望。     

Effects of Ribbon Thickness on Structure and Soft Magnetic Properties of a High-Cu-Content FeBCuNb Nanocrystalline Alloy

The effects of ribbon thickness (t) on the structure and magnetic properties of a Fe_82.3B₁₃Cu_1.7Nb₃ alloy in melt-spun and annealed states have been investigated. Increasing the t from 15 to 23 μm changes the structure of the melt-spun ribbons from a single amorphous phase to a composite with dense α-Fe nanograins embedded in the amorphous matrix. The grain size (D_α-Fe) of the α-Fe near the free surface of the ribbon is about 6.7 nm, and it gradually decreases along the cross section toward the wheel-contacted surface. Further increasing the t to 32 μm coarsens the D_α-Fe near the free surface to 15.2 nm and aggravates the D_α-Fe ramp along the cross section. After annealing, the ribbon with t = 15 μm has relatively large α-Fe grains with D_α-Fe > 30 nm, while the thicker ribbons possessing the pre-existing nanograins form a finer nanostructure with D_α-Fe < 16 nm. The structural uniformity of the ribbon with t = 23 μm is better than that of the ribbon with t = 32 μm. The annealed ribbons with t = 23 and 32 μm possess superior soft magnetic properties to the ribbon with t = 15 μm. The ribbon with t = 23 μm exhibits a high saturation magnetic flux density of 1.68 T, low coercivity of 9.6 A/m, and high effective permeability at 1 kHz of 15,000. The ribbon with t = 32 μm has a slightly larger coercivity due to the lower structural uniformity. The formation mechanism of the fine nanostructure for the ribbons with suitable t has been discussed in terms of the competitive growth effect among the pre-existing α-Fe nanograins.     

B effects on crystallization and magnetic properties of Pr_（9.44）Fe_（90.56-x）B_x（x=7.16, 4.76） nanocomposite magnets

Magnetic properties, phase evolution and microstructures of Pr_9.44Fe_90.56-xB_x (x=7.16 and 4.76) nanocomposite magnets have been investigated. Both as-spun ribbons exhibit two-step demagnetization curves, indicating the feature of partial crystallization. By using differential scanning calorimeter (DSC) measurements, remained amorphous phase of ribbon with x=7.16 shows a higher crystallization temperature. At optimum annealing temperature of 650 ℃for 10 min, better magnetic properties, M_r=1.01 T, _jH_c=796 kA/m and (BH)_max=136 kJ/m³ were obtained in the sample with x=4.76. Transmission electron microscopy (TEM) observation confirms that the sample with x=4.76 possesses much finer grain size, which causing a better exchange coupling between soft and hard magnetic grains.     

Interaction of surface of ribbons of amorphous soft-magnetic iron-based alloys with vapor

The interaction with water vapor of the surface of ribbons of amorphous soft-magnetic iron-based alloys with positive saturation magnetostriction and an effect of the interaction on the magnetization distribution and magnetic properties have been investigated. The results of the investigation showed that, during in-air heat treatment, the interaction of the surface of ribbons of amorphous soft-magnetic alloys with water vapor upon the heating of samples and at the initial stage of isothermal holding exerts a substantial effect on the magnetization distribution and the level of magnetic properties formed. Preliminary room-temperature treatment of the ribbon surface in the as-quenched state with water vapor favors an increase in pseudo-uniaxial tensile stresses along the ribbon axis because, during annealing, the enhanced concentration of hydrogen and oxygen atoms introduced into the ribbon surface is formed in this direction. When certain regimes of heat treatment are used, this leads to an increase in the volume of domains with magnetization oriented along the axis of the ribbon in its plane and allows a significant enhancement in the efficiency of the in-air heat treatment.     

单相纳米晶Nd12.3Fe79.2Nb2.5B6合金的交换耦合作用与显微组织

采用熔体快淬及晶化退火工艺制备了含铌单相纳米晶Nd12.3Fe79.2Nb2.5B6合金,研究添加Nb对单相Nd2Fe14B纳米晶合金的磁性能、交换耦合和微观结构的影响规律.结果表明:Nb的添加提高了合金的非晶热稳定性,使得合金最佳晶化温度升高;合金晶化退火后,Nb可使晶粒尺寸分布均匀,并得到单一Nd2Fe14B相;晶粒边界比较完整,存在共格、半共格或大角度晶界,但没有观察到晶界相.上述结构可有效提高合金的磁性能,增强交换耦合作用.通过对Nd12.3Fe79.2Nb2.5B6合金磁性能分析可知:650 ℃晶化退火10 min后的合金性能最佳,交换耦合作用最强.     

Crystallization process and soft magnetic properties of nanocrystalline (Fe0.5 Co0.5 ) 86 Hf7 B6 Cu1 alloy used in elevated temperature applications

Nanocrystalline (Fe0.5 Co0.5 )86 Hf7 B6 Cu1 HITPERM alloy was investigated as the candidate of soft magnetic material for high temperature applications, compared with Fe86 Hf7B6 Cu1 NANOPERM alloy. Amorphous alloy ribbons were prepared by single-roller melt-spinning technology. Crystallization process of as-quenched ribbon was investigated using differential scanning calorimeter at different heating rates. The coercivity was determined from quasi-static hysteresis loop measured at room temperature using a computerized hysteresis loop tracer. X-ray diffraction with Cu Kα radiation was used to determine the structure. The vibrating sample magnetometer was usedto measure the magnetization as a function of temperature of the nanocrystllized alloys. That Co substitution for Fein alloy enhances the Curie temperature of amorphous alloy and the magnetization of nanocrystalline alloy at hightemperature. After annealing amorphous precursor, the optimum nanocrystalline alloy obtained shows the local minimum coercivity. The coercivity increases with the increasing annealing temperature corresponding to the formation of ferromagnetic phase in the secondary crystallization.     

带厚对FeCuNbSiB纳米晶铁芯性能的影响

采用标称成分为Fe73.5Cu1Nb3Si15.5B7(原子百分数)、带厚分别为18 μm、22 μm和26 μm的带材制成环形铁芯,经过560℃保温1h热处理后测试其性能,发现铁芯损耗随带材厚度的减小而降低,实验中用18μm和22 μm厚带材制备的铁芯与在共模电感方面处于国际领先地位的VAC公司生产的同规格铁芯在电感...     

Effect of Ca addition on soft magnetic properties of nanocrystalline Fe-based alloy ribbons

The effect of Ca addition on the magnetic properties of a nanocrystalline Fe-based alloy was investigated. A small amount of Ca (0.06 wt%) was added to the Fe-based alloy, which was then melt spun to fabricate thin ribbons with a thickness of ∼30 μm. These ribbons were heat treated to obtain a nanocrystalline structure with a grain size of ∼10 nm, and the crystallization behavior was studied to optimize the grain structure. The characteristics of the ribbon alloys were analyzed using a B-H meter, a 4-point probe, a transmission electron microscope (TEM), and a scanning electron microscope (SEM). As a result, the optimum permeability and minimum core loss were obtained for the alloy containing Ca, when annealed at 520 °C for 1 h. The analyses revealed that a reduced core loss could be attributed to the high electrical resistivity and suppressed grain growth, which were caused by the Ca element distributed along the grain boundary. Based on the results, Ca addition to Fe-Si-B-Nb-Cu base nanocrystalline alloy was very effective in controlling the grain size, minimizing the eddy current loss, inducing an improved magnetization behavior, and reducing the core loss.     

Precipitation of a-Fe from Fe84-xSi4B12+x (x=1,3) Amorphous Alloys Under High Magnetic Field Annealing

This work aims to investigate the effects of high magnetic field annealing (HMFA) on the precipitation of α-Fe from Fe84-xSi4B12+x (x =1,3) amorphous precursors.Isothermal annealing process for Fe81Si4B15 and Fe83Si4B13 amorphous ribbons has been performed with and without the magnetic field.The magnetic field shows the effects of increasing the nucleation rate and decreasing the grain size of α-Fe crystals simultaneously,during the crystallization processes of the investigated amorphous alloys.By applying HMF,α-Fe crystals with more homogeneous distribution and smaller grain size are achieved in the amorphous matrix,which is crucial helpful to improve the magnetic properties for Fe-Si-B amorphous alloys.The mechanism of HMFA affecting the crystallization microstructure is also discussed in the present work.     

Magnetization distribution in a soft magnetic amorphous alloy ribbon in as-quenched state and efficiency of heat treatment

The effect of heat treatment in air on the formation of magnetic properties has been studied based on the example of soft magnetic Fe₇₇Ni₁Si₉B₁₃ and Fe₈₁B₁₃Si₄C₂ amorphous ribbons characterized by positive magneto-striction. The magnetization distribution in the ribbons in the as-quenched state was shown to affect the efficiency of annealing. Under certain conditions, heat treatment, which results in the formation of mainly amorphous state of ribbon surface, is more efficient for samples characterized by high volume of orthogonally magnetized domains. This can be related to high in-plane tensile stresses, which are induced by hydrogen and oxygen atoms introduced into the ribbon surface upon its interaction with atmospheric water vapor.