Recent progress in high temperature permanent magnetic materials

Permanent magnetic materials capable of operating at high temperature up to 500℃ have wide potential applications in fields such as aeronautics, space, and electronic cars. SmCo alloys are candidates for high temperature applications, since they have large magnetocrystalline anisotropy field （6-30 T）, high Curie temperature （720-920℃）, and large energy product （〉200 kJ.m-3） at room temperature. However, the highest service temperature of commercial 2：17 type SmCo magnets is only 300℃, and many efforts have been devoted to develop novel high temperature permanent magnets. This review focuses on the development of three kinds of SmCo based magnets： 2：17 type SmCo magnets, nanocrystalline SmCo magnets, and nanocomposite SmCo magnets. The oxidation protection, including alloying and surface modification, of high temperature permanent magnets is discussed as well.

A simple permanent deformation model of rockfill materials

Existing experimental results have shown that using a semi-log linear relationship between the permanent volumetric strain and cyclic number underestimates the volumetric deformation of rockfill materials with a large cyclic number, and that the error increases with the confining pressure. The existing permanent deformation models are not suitable for the seismic safety analysis of high dams during strong earthquakes. In this study, a series of large-scale triaxial cyclic loading tests of rockfill materials were performed, and a new permanent deformation model of rockfill materials was developed and validated with three kinds of rockfill materials. The results show that the proposed model can properly reflect the general features of the permanent deformation of rockfill materials. The main features of the model are as follows:(1) relations between the cyclic number and permanent volumetric/shear strain are described by hyperbolic functions, which can avoid underestimating the volumetric deformation occurring during strong earthquakes;(2) the model can capture the effect of the mean effective stress on the permanent volumetric strain, with greater confining pressure correlating to greater permanent volumetric deformation, and the permanent volumetric strain under low confining pressure near the dam crest can be well represented; and(3) the model can reflect the effect of the consolidation stress ratio on the permanent shear strain.

New shakedown criterion and permanent deformation properties of unbound granular materials

Unbound granular material specifications for road pavements in Australia are primarily based on physical material specification rather than mechanical characterisation. This simplified approach does not reflect the actual material performance under repeated dynamic traffic loads. There is a little information available on the influence of the local crushed rock properties and compacted layer properties on permanent deformation (PD). This study aims to characterise the local unbound granular materials in Victoria according to their PD behaviour under repeated loads and to develop a suitable shakedown criterion that could describe the PD of the tested materials to simplify the flexible pavement design. Repeated-load triaxial tests were conducted over several samples with a range of moisture contents, gradations, densities, and stress conditions. The laboratory test results showed that PD behaviour was influenced by several factors. In addition, the tested subbase-specified unbound granular materials reflect high PD resistance that is almost equivalent to basequality unbound granular materials. This may indicate that current requirements for the subbase-quality unbound granular materials are over-prescribe. Moreover, as the existing shakedown criterion was not applicable for the multi-stage repeated-load triaxial test and the local tested materials, a new shakedown criterion and new boundaries are proposed based on the PD behaviour. In the proposed criterion, the shakedown ranges are identified based on the curve angle of the PD vs. logarithm of the number of loading cycles, and this new criterion was validated using several materials from existing literature. The local tested base and subbase materials can be assigned as Range A when PD\1%, Range B when 1%\PD\3%, and Range C when PD[3%. The proposed criterion could provide a useful and quick approach to assess the PD of the unbound granular materials with both single and multistages of stresses.

Neural network-based model for prediction of permanent deformation of unbound granular materials

Several available mechanistic-empirical pavement design methods fail to include predictive model for permanent deformation(PD)of unbound granular materials(UGMs),which make these methods more conservative.In addition,there are limited regression models capable of predicting the PD under multistress levels,and these models have regression limitations and generally fail to cover the complexity of UGM behaviour.Recent researches are focused on using new methods of computational intelligence systems to address the problems,such as artificial neural network(ANN).In this context,we aim to develop an artificial neural model to predict the PD of UGMs exposed to repeated loads.Extensive repeated load triaxial tests(RLTTs)were conducted on base and subbase materials locally available in Victoria,Australia to investigate the PD properties of the tested materials and to prepare the database of the neural networks.Specimens were prepared over different moisture contents and gradations to cover a wide testing matrix.The ANN model consists of one input layer with five neurons,one hidden layer with twelve neurons,and one output layer with one neuron.The five inputs were the number of load cycles,deviatoric stress,moisture content,coefficient of uniformity,and coefficient of curvature.The sensitivity analysis showed that the most important indicator that impacts PD is the number of load cycles with influence factor of 41%.It shows that the ANN method is rapid and efficient to predict the PD,which could be implemented in the Austroads pavement design method.

The Production Management Improvement Model of Small and Medium-sized Permanent Magnetic Materials Manufacturing Companies

An integrated production planning and control model based on MRPⅡand JIT is put forward through analyzing the characteristics of magnetic materials manufacturing companies. Master Production Schedule with limited capacity and operational plan in workshop level based on the basic data of flow chart are formulated by this model which applied JIT idea and based on customer order demand. Push production is adapted during execution phase combined with process flow cards. The model is helpful to reduce inventory,keep certain flexbility of production and improve continuity and equilibrium of manufacturing process.

Design and Performance Analysis of Permanent Magnet Claw Pole Machine with Hybrid Cores

Permanent magnet claw pole machine(PMCPM) is a special kind of transverse flux permanent magnet machine. Compared with other electrical machines, it has the advantages of high torque density and high efficiency for high speed operation. However, because of its complex irregular structure, the manufacturing process using silicon sheets is complicated. Soft magnetic composite material(SMC) is manufactured by powder metallurgy technology, which can produce various shapes of stator core structures, so it is easier to produce various irregular shapes of the stator core. However, the raw SMC material is relatively expensive, and the mechanical strength of SMC is weak. In this paper, a PMCPM with hybrid cores is proposed. With the adoption of hybrid silicon sheet-SMC cores and amorphous alloy-SMC cores, the torque ability of PMCPM can be improved greatly and it can have higher efficiency for more wide operation frequency. Meanwhile, its mechanical strength has been improved and it can be designed for high torque direct drive applications as it is a modular machine. Furthermore, three methods are proposed to reduce the additional eddy current loss which resulted from the employment of hybrid cores in PMCPM.

An Empirical Study of CAPM’s Applicability to Rare Earth Permanent Magnet Material Stocks

China has the world’s largest reserves of rare earth elements.Rare earth permanent magnet material has always been one of the popular industries in the investment market.CAPM is the basic asset-pricing model in financial economics.There are a number of studies conducted to examine the applicability of CAPM to stock markets in different industries and to investigate the modification method to improve the model’s prediction accuracy.In this study,seven leading enterprises in China’s rare earth permanent magnet material industry listed on the A-share market were selected as the research subjects.Based on CAPM,regression analysis was conducted on the monthly data from March 2016 to February 2022.The results demonstrated that using the β coefficient to explain the risk of China’s rare earth permanent magnet industry is ineffective.The ultimate benefit was less affected by market indexes but mainly by non-systematic risks.CAPM has low applicability to China’s rare earth permanent magnet material industry and requires further improvement.Nevertheless,CAPM still has some guiding significance in making enterprise comparisons and investment decisions.

Effect of vertical stress rest period on deformation behaviour of unbound granular materials:Experimental and numerical investigations

Repeated load triaxial test is used to assess the deformation behaviour of unbound granular materials(UGMs) in flexible road pavements. Repeated load pulse characteristics(i.e. shape, loading period and rest period) are the stress configurations used in the experimental set-up to simulate the passing axle loads. Some researchers and standard testing protocols suggest a rest period of varying durations after a loading phase. A thorough review of existing literature and practises has revealed that there is no agreement about the effect of the rest period of vertical stress pulse on the deformation behaviour of the UGMs. Therefore,the main objective of this study is to investigate the effect of repeated stress rest period on the deformation behaviour of UGMs experimentally. Experiments are conducted, both with and without rest period, using basalt and granite crushed rocks from Victoria, Australia. Furthermore, in order to gain insight into the effect of the rest period, finite element modelling is also developed. Both the experimental and modelling results show that the rest period has a noticeable effect on both resilient and permanent deformation behaviours of UGMs. It is, therefore, recommended to take extra precautions while adopting a particular standard testing protocol and to supplement the results by additional tests with different loading configurations.

Mn-based permanent magnets

Mn-based intermetallic compounds have attracted much attention due to their fascinating structural and physical properties, especially their interesting hard magnetic properties. In this paper, we have summarized the magnetic and structural properties of Mn-based intermetallic compounds（Mn X, where X = Al, Bi, and Ga）. Various methods for synthesizing single phases of MnAl, MnBi, and Mnx Ga were developed in our lab. A very high saturation magnetization of 125 emu/g,coercivity of 5 kOe, and maximum energy product（BH）max of 3.1 MG·Oe were achieved at room temperature for the pure τ-Mn–Al magnetic phase without carbon doping and the extrusion process. Low temperature phase（LTP） MnBi with a purity above 95 wt.% can be synthesized. An abnormal temperature coefficient of the coercivity was observed for the LTP MnBi magnet. Its coercivity increased with temperature from 100 K to 540 K, reached a maximum of 2.5 T at about540 K, and then decreased slowly to 1.8 T at 610 K. The positive temperature coefficient of the coercivity is related to the evolution of the structure and magnetocrystalline anisotropy field of the LTP MnBi phase with temperature. The LTP MnBi bonded magnets show maximum energy products（BH）max of 8.9 MG·Oe（70 kJ/m^3） and 5.0 MG·Oe（40 k J/m^3） at room temperature and 400 K, respectively. Ferrimagnetic Mnx Ga phases with L10 structures（x 〈 2.0） and D022 structures（x 〉 2.0） were obtained. All of the above structures can be described by a D0（22） supercell model in which 2 a-Ga and 2 b-Mn are simultaneously substituted. The tetragonal D0（22） phases of the Mnx Ga show high coercivities ranging from 7.2 kOe for low Mn content x = 1.8 to 18.2 kOe for high Mn content x = 3 at room temperature. The Mn（1.2） Ga sample exhibits a room temperature magnetization value of 80 emu/g. The hard magnetic properties of coercivityiHc = 3.5 kOe, remanence Mr = 43.6 emu/g, and（BH）max = 2.5 MG·Oe were obtained at room temperature. Based on the above studies, we believe that Mn-based magnetic materials could be promising candidates for rare earth free permanent magnets exhibiting a high Curie temperature, high magnetocrystalline anisotropy, and very high coercivity.

A Study of Two-Phase Nanocrystalline Nd_(8.5)Fe_(75)Co_5Cu_1Zr_3Nb_1B_(6.5)Permanent Magnet

Nanocrystalline Nd 8.5 Fe 75 Co 5Cu 1Zr 3Nb 1B 6.5 ribbons were prepared by melt spun (18 m·s -1 ) and subsequent heat treatment (670 ℃/4 min). Excellent magnetic properties of the bonded magnet were achieved as follows: B r=0.68 T (6 8 kGs), J H c=620.3 kA·m -1 (7.8 kOe), ( BH ) max =74 kJ·m -3 (9 3 MGOe). The results of TEM photomicrographs confirm that the appearance of α Fe phase is earlier than that of Nd 2Fe 14 B phase during crystallization process. The addition of Cu and Zr elements shows to be advantageous to the improvement of an intrinsic coercivity and squareness of hysteresis loop, as well as energy product.

Rare earth permanent magnets prepared by hot deformation process

Hot deformation is one of the primary methods for fabricating anisotropic rare earth permanent magnets. Firstly,rapidly quenched powder flakes with a nanocrystal structure are condensed into fully dense isotropic precursors using the hot-pressing process. The prepared isotropic precursors are then hot-deformed to produce high-anisotropy uniaxial bulk rare earth permanent magnets and a highly textured structure is produced via this process. The resulting magnets possess many advantages such as near-net-shape, outstanding corrosion resistance, and ultrafine-grain structure. The influence of the preparation parameters utilized in the hot-pressing and deformation processes on the magnetic properties and microstructure of the permanent magnets are systemically summarized in this report. As a near-net-shape technique, the hot deformation process has notable advantages with regard to the production of irregular shapes, especially for radially oriented ringshaped magnets with high length-diameter ratios or thin walls. The difficulties associated with the fabrication of crack-free,homogeneous, and non-decentered ring-shaped magnets are substantially resolved through an emphasis on mold design,adjustment of deformation parameters, and application of theoretical simulation. Considering the characteristics of hotdeformed magnets which include grain shape and size, anisotropic distribution of intergranular phases, etc., investigation and improvement of the mechanical and electric properties, in addition to thermal stability, with the objective of improving the application of hot-deformed magnets or ring-shaped magnets, is of practical significance.

Development of Strip Casting Technology in Rare Earth Permanent Magnet Alloys and Hydrogen Storage Alloys in China

The SC technique is now being applied widely in material preparation, especially in rare earth functional materials in virtue of its advanced process and high performance product. The applications of SC technique in rare earth permanent magnet alloys and hydrogen storage alloys were analyzed integrative, on the basis of summary of SC technique development in this paper. The paper mainly includes development history of SC technology, effect of SC technology on alloy microstructure, application of SC technology in RE storage hydrogen alloy and sintered Nd-Fe-B alloy, development of SC equipment and SC product industry. At the same time, the paper points out the existing problem of SC products.

MAGNETIC DOMAIN STRUCTURE AND RELATED MAGNETIC PROPERTIES OF(NdPr)_(16)Fe_(76)B_8 PERMANENT MAGNET

The magnetic domain structure and related magnetic properties of (NdPr)_(16)Fe_(76)B_8 permanent magnet have been studied by colloid-SEM method.In thermally demagnetized state,the ma- trix grains in the magnet generally exhibit multidomain structure,i.e.,180° plate-like indi- vidual domain and a few spike-like or maze-like domains.The average width of the domain measured was 1.5μm.Grain size of single-domain was observed to be generally about 1μm and only a few up to 3μm.The results calculated are:the domain wall energy γ=36 MJ/m^2,the exchange constant A=4.5×10^(-11)J/m,the domain wall width δ=15.7nm, and the critical grain diameter of single-domain D_c=0.5μm.The dependence of high magnet- ic field gradient at grain boundaries in different magnetization directions in the adjacent mag- netic domains located on both sides of grain boundaries and the effect of microstructure on the values of K,A and δ were discussed.

Toward understanding the microstructure characteristics,phase selection and magnetic properties of laser additive manufactured Nd-Fe-B permanent magnets

Nd-Fe-B permanent magnets play a crucial role in energy conversion and electronic devices.The essential magnetic properties of Nd-Fe-B magnets,particularly coercivity and remanent magnetization,are significantly infuenced by the phase characteristics and microstructure.In this work,Nd-Fe-B magnets were manufactured using vacuum induction melting(VIM),laser directed energy deposition(LDED)and laser powder bed fusion(LPBF)technologies.Themicrostructure evolution and phase selection of Nd-Fe-B magnets were then clarified in detail.The results indicated that the solidification velocity(V)and cooling rate(R)are key factors in the phase selection.In terms of the VIM-casting Nd-Fe-B magnet,a large volume fraction of theα-Fe soft magnetic phase(39.7 vol.%)and Nd2Fe17Bxmetastable phase(34.7 vol.%)areformed due to the low R(2.3×10-1?C s-1),whereas only a minor fraction of the Nd2Fe14B hard magnetic phase(5.15 vol.%)is presented.For the LDED-processed Nd-Fe-B deposit,although the Nd2Fe14B hard magnetic phase also had a low value(3.4 vol.%)as the values of V(<10-2m s-1)and R(5.06×103?C s-1)increased,part of theα-Fe soft magnetic phase(31.7vol.%)is suppressed,and a higher volume of Nd2Fe17Bxmetastable phases(47.5 vol.%)areformed.As a result,both the VIM-casting and LDED-processed Nd-Fe-B deposits exhibited poor magnetic properties.In contrast,employing the high values of V(>10-2m s-1)and R(1.45×106?C s-1)in the LPBF process resulted in the substantial formation of the Nd2Fe14B hard magnetic phase(55.8 vol.%)directly from the liquid,while theα-Fe soft magnetic phase and Nd2Fe17Bxmetastable phase precipitation are suppressed in the LPBF-processed Nd-Fe-B magnet.Additionally,crystallographic texture analysis reveals that the LPBF-processedNd-Fe-B magnets exhibit isotropic magnetic characteristics.Consequently,the LPBF-processed Nd-Fe-B deposit,exhibiting a coercivity of 656 k A m-1,remanence of 0.79 T and maximum energy product of 71.5 k J m-3,achieved an acceptable magnetic performance,comparable to other additive manufacturing processed Nd-Fe-B magnets from MQP(Nd-lean)Nd-Fe-Bpowder.

MTA与iRoot BP Plus行直接盖髓术治疗龋源性露髓恒磨牙临床疗效分析

目的:观察成熟恒磨牙去龋未净时露髓使用无机三氧化物聚合体(Mineral trioxide aggregate,MTA)和生物陶瓷类材料(iRoot BP Plus)行直接盖髓术的临床疗效,探讨此类术式的可行性及其影响因素,比较两种盖髓剂疗效的差异。方法:选取2018年4月-2019年10月就诊于笔者科室符合纳入标准的53例患者,共53颗患牙,随机分为M组和B组,分别使用MTA与iRoot BP Plus行直接盖髓术,术后定期复查,比较两组的临床疗效。结果:共计45例患者(45颗患牙)完成2年随访,总体成功率84.4%;M组和B组分别为85.7%、83.3%,两组比较差异无统计学意义(P>0.05)。性别、年龄、露髓孔大小等因素对疗效均无显著影响(P>0.05)。结论:成熟恒磨牙术中露髓时使用MTA或iRoot BP Plus行直接盖髓术均可获得良好疗效;相较于性别、年龄、露髓孔大小等因素,如何简单准确评判牙髓状态及避免龈下微渗漏更加值得关注。

全球Nd-Fe-B稀土永磁材料产业的发展与趋势

在总结Nd-Fe-B稀土永磁材料发展历程的基础上,预测未来该产业的发展趋势。Nd-Fe-B稀土永磁材料,被称作是第3代稀土永磁材料,凭借其优越的性价比和不断提升的性能成为产业化和增长速度最为迅速的一种稀土永磁材料。当前国际上的Nd-Fe-B永磁材料发展具有高增长、高牌号、高附加值和全球化的特征。

纳米晶Nd-Fe-B基稀土永磁体的磁性能的微磁量子理论计算

从微磁学理论出发，利用铁磁体总自由能极小的变分法，导出了取向各向异性磁体的磁化强度满足的Ｂｒｏｗｎ方程，对取向的纳米晶双相交换耦合磁体，该方程类似于量子力学中的定态Ｓｃｈｒｄｉｎｇｅｒ方程，利用中心场问题的求解方法推导了Ｎｄ－Ｆｅ－Ｂ基稀土永磁体的成核场同时随两相晶粒尺寸的变化关系。数值计算结果表明，当两相晶粒尺寸小于某一临界尺寸时，可以获得磁性能优异的纳米晶稀土永磁体。所得结果可用于定性解释实验结果和指导巨磁能积纳米晶永磁体的制备。

轴向磁力轴承结构综述

按照悬浮力的产生方式将轴向磁力轴承分为主动型、被动型和混合型,主动型的优点是能够产生可控电磁力,被动型的优点是结构简单,混合型兼顾了主动型和被动型的特点。在研究同心单环结构的基础上,分析了具备冗余性的同心多环冗余结构及叠片式冗余结构,从电磁力角度看,整体式同心双环结构优于同心三环结构,叠片式六环结构优于叠片式四环结构和叠片式八环结构。最后,对轴向磁力轴承在结构、控制及工业应用方面的发展前景进行了展望,轴向磁力轴承的结构应当朝着更具备冗余性和重构能力的方向优化。

Nd-Fe-B烧结永磁材料的车削加工研究

对Nd-Fe-B烧结永磁材料的车削加工进行了试验研究。用线性断裂力学的方法建立了硬脆材料车削加工时的材料去除模型。探讨了车削过程中背吃刀量、进给量和车削速度对车削力及加工表面质量的影响,采用多元回归分析方法得出了主车削力的经验公式,并给出了用于检验回归结果与试验结果符合程度的误差评判参数。分析了Nd-Fe-B烧结永磁材料车削过程中刀具的磨损状况,以及刀具几何参数对加工质量的影响。

Nd-Fe-B永磁材料氢脆过程及Al+Al_2O_3阻氢涂层研究

从材料保护的角度出发,在分析了Nd Fe B永磁材料的氢脆过程及氢脆的特点后,用RF磁控溅射制备一定厚度的Al薄膜并在一定条件下进行氧化处理,得到了Al+Al2O3复合涂层。用SEM和XRD分析了涂层形貌和组成,并用高压气相充氢的方式测试了涂层的阻氢性能。研究表明,厚度为8.0μm复合涂层的阻氢性能为:在10MPa的H2环境中(25℃),阻氢时间达65min,且对磁体的磁性能无不良影响。