Microstructure and its correlation to magnetic properties in 2:17 type (Sm,Gd)-Co-Fe-Cu-Zr alloys

Studies on the evolution of microstructure and phase transformation at various stages of thermal processing have been carried out in 2:17 type (Sm,Gd)-Co-Fe-Cu-Zr alloys. Microstructural studies reveal that during the solution heat treatment stage, a lamellar structure is formed and its volume fraction is found to be more at 1463 K for alloys without Gd, while at 1473 K for alloys with Gd = 25 wt% of Sm. It appears that the formation of the lamellar structure is closely associated with the phase transformation from Th₂Ni₁₇ (TbCu₇ + Th₂Zn₁₇) structure during the solution heat treatment. Magnetic measurements in isothermally aged (1123 K) samples showed that the replacement of 25% of Sm by Gd reduces the energy product from 180 to 136 kJ/m³. The Gd substitution is also found to reduce the temperature coefficient of magnetisation from 350 to 225 ppm/°C in the temperature range of 30–100°C.     

Fe掺杂及球磨处理对Sm_2Co_(17)合金结构和磁性的影响

用电弧熔炼法制备Sm2(FexCo1-x)17(x=0,0.3和0.7)母合金锭,均匀化退火后采用球磨方法制备纳米晶合金粉末。研究了Fe掺杂及球磨处理对Sm2(FexCo1-x)17合金结构、居里温度及永磁性能的影响。实验结果表明,随着Fe含量增多,合金中1∶5相逐渐减少,当x=0.7时,形成单相2∶17型化合物,同时居里温度从938℃(x=0)下降到590℃(x=0.7)。球磨处理过程有利于形成单相2∶17纳米合金粉,饱和磁化强度随着球磨时间的增加逐渐增大,同时内禀矫顽力和磁能积与球磨时间的关系呈两头下降的趋势。球磨时间在0.5~1 h时,纳米合金粉末的永磁磁性能达到最佳,Sm2Co17的最佳磁性能为4πMs=0.65 T,iHc=246.8 k A/m,(BH)max=25.5 k J/m3。     

The hydrogenation behaviour of the phases Sm2Co17 and Pr2Co17

The compounds Sm₂Co₁₇ and Pr₂Co₁₇ have been charged with hydrogen and the hydrogen compositions determined between pressures of approximately 2.5×10^–2 and 13 atm at temperatures of 150 and 200° C. Very low rates of hydrogen absorption were observed below 150° C so that solubility measurements have not been obtained below this temperature. The X-ray diffraction studies show that the structure of the metal lattice is unchanged by the hydrogenation process, i.e. the rhombohedral, Th₂Zn₁₇ structure type with space groupR¯3_m is maintained. As a result of the expansion the alloys become cracked and friable on hydrogenation.     

磁场下球磨处理各向异性纳米级Sm2Co17磁粉的制备与分析

2∶17型SmCo稀土永磁合金以良好的温度特性和较高的磁性能已成为不可或缺的高温永磁器件,通过球磨工艺,利用有机试剂庚烷和油酸对2∶17型Sm(CobalFe0.07Cu0.088Zr0.025)7.5磁粉表面包覆预处理,并在磁场强度为1.5T的外磁场下,对该磁粉进行细磨0.5～20h,制备得到厚度为20～100nm、具有各向异性能的纳米级磁片,其对应的磁性能(BH)m为127.36kJ/m3。     

Rapid quenching and nitrogenation of Sm2Fe17 alloys

The production of hard magnetic samarium-iron nitrides by rapid quenching of Sm₂Fe₁₇ alloys followed by a nitrogenation treatment is described and analysed. Rapid quenching of Sm₂Fe₁₇ produces almost pure Sm₂Fe₁₇ phase with 40 to 100 nm grain size. At low temperature (T465°C), the nitrogenation treatment under 1 bar N₂-H₂ (5%) mainly produces the definite compound Sm₂Fe₁₇N_3– and follows reasonably well an Arrhenius law, the reaction rate being limited by diffusion through the Sm₂Fe₁₇N_3– reacted layer. At higher temperatures (T465°C), disproportionation reactions simultaneously take place, which transform the metastable nitride into free iron and tiny SmN crystallites (about 10 nm wide). It is concluded that the nitrogenation treatment should be performed at about 400°C in order to reach a sufficient reaction rate for the nitride formation while (possibly) avoiding disproportionation reactions whose by-products (Fe and SmN) are deleterious for permanent magnet applications.     

Coercivity dependence of a Sm2(Co,Cu, Fe,Zr)17 type alloy on magnetic processing procedure

The results of an investigation into the effects of the magnetic processing procedure on the intrinsic coercivity of a Sm(Co_0.673Cu_0.080Fe_0.222Zr_0.025)_8.92 (217-type) alloy are reported. Two basic types of magnet were investigated: polymer-bonded fine powder magnets and cast (solid) magnets. The fine particles which were processed into polymer-bonded magnets were prepared by two different methods; i.e. by milling or by a hydrogen treatment. The cast magnets were manufactured from selected parts of solidified ingots exhibiting preferrred orientation and along directions parallel to the preferred orientation of magnetization. Magnetic properties and Vickers microhardness measurements on the solid solution treated (1170° C) and isothermally aged (800° C) samples, revealed that there was a clear similarity between the variations of the intrinsic coercivity and microhardness values versus ageing period. This suggests a coercivity mechanism for the present 217-type alloy which is predominantly controlled by general domain wall pinning by a critical dispersion of coherent precipitates. Certain aspects of the intrinsic coercivity against ageing time variations of the variously processed magnets as well as the corresponding microhardness variations have been attributed to a partial conversion of coherent precipitates to semi- or in-coherent particles during processing.     

Rheological and dynamic mechanical properties of polymer-bonded magnets based on Sm2Co17 and polyamide-12

The rheological and dynamic mechanical properties of polymer-based composites of Sm₂Co₁₇ and polyamide-12 with different particle loadings, sizes, and surface treatments are reported. Sm₂Co₁₇ particles were surface-treated with three different silanes: 3-glycidoxy(propyl)trimethoxysilane, 3-amino(propyl)trimethoxysilane (APTMS), and methyltrimethoxysilane (MTMS). It was shown, for the composites with untreated particles, that the viscosity and storage modulus increased with increasing filler content (0–60 vol%) and decreasing filler particle size. In addition, the glass transition temperature increased significantly and the damping decreased with increasing filler content. Of the silanes, the MTMS, which yielded only a thin surface layer, had in general the least effect on the rheological properties of the composite. The composite containing the APTMS-coated filler showed the highest storage modulus. The results give new insights on how to prepare polymer-bonded magnets with optimal process conditions (rheology) and dynamic mechanical properties, by varying the amount of particles, their size, and surface treatment.     

单相纳米晶Sm2Co17合金的制备与性能表征

提出了一种制备单相纳米晶Sm2Co17合金块体材料的新方法.利用XRD和TEM分析了制备出的纳米晶Sm2Co17合金的相结构和显微组织.研究表明制备的单相纳米晶Sm2Co17合金在室温下具有密排六方的晶体结构,与传统的菱方晶体结构的粗晶Sm2Co17合金具有不同的结构热稳定性.测定了单相纳米晶Sm2Co17合金的磁性能和力学性能,与同种成分的粗晶材料相比,单相纳米晶Sm2CO17合金的磁性能和力学性能均获得显著提高.     

Magnetic properties of a directionally solidified eutectic alloy containing Co17Sm2 fibres

An eutectic alloy containing 44% by volume Co₁₇Sm₂ fibres has been located in the Co-Sm-Sn system and directionally solidified at speeds of between 1.7 and 550 m sec^–1. The spacing , between the fibres and their diameter, d, as a function of the growth rate, R, show the following relations: ² R = 42 m³ sec^–1 d ² R = 10 m³ sec^–1.Fibre diameters ranging from 1.6 to 0.14m have been obtained and coercive forces of up to 2.3 kOe, for the finest fibres, measured. The behaviour of the coercive force with changing diameter is compared with that in a Bi-MnBi eutectic and in powders made from the same compounds. The results can be interpreted by means of a simple theoretical analysis which shows that the attainment of high coercive forces in powder is restricted by the microscopic surface-defect density introduced during preparation, whilst in eutectics it is limited by the difficulties of growing fine regular structures at high speed.     

高温稀土永磁Sm2(Co,Cu,Fe,Zr)17 的制备和性能

制备了高温稀土永磁材料Sm(Coba1Fe0．26Cu0．05Zr0．026)7．0，研究了磁性能与工艺条件的关系．结果表明：提高烧结温度可使材料的Br和(BH)max增大，但是使Hci降低；适当提高真空预烧温度，可使材料在较低烧结温度下致密化，具有较高的Hci和(BH)max和温度稳定性．真空预烧温度过高使性能的急剧降低，其主要原因是Sm的析出．在最佳工艺条件下材料的磁性能参数分别为：Br1．08T3Hci2286kA／m，Hcb932kA／m，(BH)max220．8kJ／m^3；β20-200℃为-0．19％／℃．     

Structural change in Sm2Fe17 alloys during homogenization and HD processing

The evolution of phase compositions, phase change and microstructure in Sm₂Fe₁₇ alloys during anneal and hydrogenation–disproportionation processing has been studied systematically using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The results indicate that, after annealing at 1050 °C for 24 h, the main phase in the as-homogenized ingot is Sm₂Fe₁₇ with a rhombohedral Th₂Zn₁₇-type structure, together with a negligible amount of α-Fe phase. A minor phase, SmFe₃/SmFe₂, is barely detectable. The Sm₂Fe₁₇ alloy first absorbs the hydrogen in the hydrogenation atmosphere with a pressure of 0.1 MPa. Disproportionation begins at T ≥ 500 °C, and large amounts of SmH_x and α-Fe phases are formed, partly in microcrystalline or amorphous structures. As the temperature increases, the microcrystals and amorphous structures transform into a fully crystalline structure, the transformation becoming complete at 750 °C. The resultant crystal grain size is about 50–100 nm.     

Some structural and magnetic properties of Fe-Al-C and Fe-Mn-Al-C alloys

The remanence and coercivity of Fe-Al-C and Fe-Mn-Al-C alloys have been measured and studied as a function of ageing at 623 K. The resulting formation and growth of carbide precipitates of Fe₃AlC and Mn₃AlC in the same samples have been investigated by transmission and scanning electron micoscope techniques. The addition of Manganese to the Fe-Al-C alloy is shown to be severely deleterious to the magnetic properties of the resulting quaternary alloy; however, simultaneously, the electron diffraction and microscopic studies demonstrate that the structural order of the carbide precipitates is considerably improved. It is concluded that this observed decline in the magnetic properties of this alloy system is related to the formation of Mn₃AlC in preference to Fe₃AlC carbide precipitates.     

Sm2Co17二元复合粘结永磁材料的研究

系统研究了Sm2Co17磁粉含量对NdFeB、AlNiCo、Ferrite粘结复合磁体磁性能的影响,并通过多项式拟合的方法分析了实验结果.结果表明:Sm2Co17和其它三种永磁材料粘结复合时,磁粉之间的相互作用对矫顽力的影响较强.添加Sm2Co17来获得高矫顽力的粘结复合永磁材料从经济上来说是不可行的.     

Optimization of soft magnetic properties in nanoperm type alloys

In the present paper, it was shown that soft magnetic properties of the group of amorphous alloys Fe–X₂–B₂₂ (X=Cr, Zr and Nb) can be optimized (magnetic permeability increases about five times) by applying 1-h annealing at temperatures: 600, 600, 650 and 700 K for the Fe₇₈B₂₂, Fe₇₆Cr₂B₂₂, Fe₇₆Zr₂B₂₂ and Fe₇₆Nb₂B₂₂ alloys, respectively. This effect is attributed to annealing out of free volumes formed into material during fabrication and for the Fe₇₆Zr₂B₂₂ alloy also to a formation of a nanocrystalline phase. Using isothermal measurements of magnetization (magnetic balance), it was shown that the process of formation of nanocrysalline phase can be described by Johnson–Mhel–Avrami kinetic. Activation enthalpy of this process was deduced as 3.2 eV and the power law exponent 3.4.     

Sm3(Fe,Co,Ti)29合金HD和HDDR处理研究

深入研究了合金Sm3Fe18.5Co9Ti1.5的HD和HDDR处理过程.HD过程分别于350、400和450℃处理4h;HDDR过程于800℃处理2h.试验发现HD和HDDR法均可有效的对合金进行破碎处理,HDDR法由于其形核长大机制可有效的用于制备纳米晶复合材料;350℃时HD法可以有效的进行,随着温度的升高试样发生分解反应.给出了HD及HDDR处理后合金所表现的典型形貌.     

HO2Fe17-xAlx合金晶体结构及磁性能的研究

采用真空电弧炉熔炼制备了HO2Fe17-xAlx(x=4.0、5.0、5.5、5.8、5.9、6.0、6.1、6.2)系列合金,通过X射线衍射(XRD)、热重分析仪(TG)和振动样品磁强计(VSM)分析了其晶体结构、居里温度以及磁性能.结果表明,合金表现为软磁性,随着Al含量的增加,饱和磁化强度Ms大幅度降低,居里点Tc下降,通过成分微调可使其居里温度降至室温附近.     

Co对Nd-Fe-Al大块非晶合金的晶化行为和磁性能的影响

采用示差扫描量热法(DSC)，X射线衍射(XRD)和振动样品磁强计(VSM)研究了Co对Nd—Fe-Al大块非晶合金的非晶形成能力，晶化行为和磁性能的影响。结果表明：加入Co元素后可以显著提高Nd—Fe-Al大块非晶合金的非晶形成能力以及提高合金的居里温度。Nd60Fe30-xAl10Cox(z=0、5、10)大块非晶合金在室温有较高的内禀矫顽力，具有硬磁性。内禀矫顽力随着Co含量的增加变化不大．但是饱和磁化强度和剩磁则随着Co含量的增加有所下降。Nd60Fe3-xAl10Cox(x=0、5、10)大块非晶合金具有的硬磁性能来自于非晶相。合金少量晶化后，磁性能变化不大。完全晶化后合金的硬磁性迅速消失。     

Phase transformation and impact properties of type 17-8-2 austenitic weld metals

The influence of stress relieving and ageing treatments in the range 600 to 900° C on the phase transformations and change in room temperature impact properties has been studied for two manual metal arc 17-8-2 weld metals. The transformation of the-ferrite in the range 600 to 800° C was found to conform to a classical Johnson-Mehl equation; the initial precipitates were M₂₃C₆ carbides followed by the intermetallic-phase. At higher temperatures a slower transformation rate was found suggesting a C curve type of behaviour and the dominant intermetallic phase changed to. Room temperature impact toughness values were found to change with ageing time. Below 800° C there was a consistent fall in these values which became very marked when the-phase developed at the/-boundaries, Above 800° C, spherodization of the carbides and intermetallic phases delayed the fall in the impact values, and led to significant increases in the early stages of ageing. Scanning electron microscopy confirmed that the change from ductile to brittle fracture mode was normally associated with the development of the and phases, but at 600° C the fall in impact properties could be atrributed to carbide development.     

Hierarchical assembly of Sm2Co7/Co magnetic nanoparticles into highly stable and uniform nanospheres

Hierarchical assembly of colloidal Sm2Co7/Co clusters in the form of nanospheres has been processed through a polyol process. The SmCo nanospheres are found to be robust, uniform ( 100 nm) and tend to self-assemble in the form of ordered superstructures. Each nanosphere consists of large number of discrete fine particles ( 6.0 nm), having two-phase structure of both Sm2Co7 and Co-phases. Upon annealing, these phases transform into Sm2Co17 phase with very high magnetization (169 emu/g). A possible mechanism on the formation of nanospheres from the individual Sm2Co2o7 and Co nanoparticles is also discussed.