Magnetization Processes in Ribbons of Soft Magnetic Amorphous Alloys

Using iron-based (Fe–B–Si–C; Fe–Ni–Si–B) and cobalt-based (Co–Fe–Ni–Cr–Mn–Si–B) soft magnetic alloys as examples, we have studied the dependences of the remanence measured using minor hysteresis loops on the maximum induction. The different degrees of stabilization of the 180° and 90° domain walls allows these dependences to be used to analyze the magnetization processes that occur in the rapidly quenched soft magnetic alloys. It has been established from the B_r(B_m) dependences that, in the ribbons of soft magnetic amorphous alloys, the processes of the rotation of the magnetization oriented perpendicular to the ribbon plane start before the end of the processes of the displacement of the walls of domains with planar magnetization. After the end of the magnetization rotation processes, the magnetization processes can be interpreted as the displacement of the domain walls with a planar magnetization accompanied by a decrease in their number and a transition to a bistable state.     

Temperature Dependence of Surface Tension of Sn-Ag Alloys

The surface tension of molten Sn-Ag alloys was measured using a specially developed high-accuracy sessile drop apparatus. In this apparatus, a molten sample is dropped onto a R-Al₂O₃ substrate in order to prevent any reaction between the sample and substrate during the heating process. The droplet shape was recorded from two perpendicular directions to confirm its symmetry. The oxygen partial pressure ( $ {P_{{{\text{O}}_2}}} $ ) was controlled by a Mg furnace to a value of about 10^?16 to 10^?15 Pa. The sample compositions used were Sn-20Ag, Sn-50Ag, and Sn-80Ag (at.%) and were alloyed from pure Sn (99.999%) and Ag (99.99%) in the dropping tube. The accuracy of the experimental results was confirmed by an extremely small scatter. The measured temperature dependence of the surface tension of the molten Sn-50Ag (at.%) alloy indicated a characteristic curve that changed from positive to negative with increasing temperature. Furthermore, the surface tension of the molten Sn-20Ag (at.%) alloy has a temperature dependence that changes from flat to negative, while the Sn-80Ag (at.%) alloy has a negative temperature dependence across the whole temperature range. Based on a theoretical discussion using Butler’s equation, these temperature dependencies can be determined by negative straight lines when assuming the surface composition.     

Influence of Deposition Current Density on the Magnetization Behaviour in Electrodeposited Ni-Mn Alloys

Ni-Mn alloys were electrodeposited at different current densities from sulphate baths and their magnetization behaviours at different fields were studied. The magnetization decreases with increase in deposition CD in the absence of additives. The magnetization behaviour of Ni-Mn is different from that of its counterpart i.e. the electrodeposited Fe-Mn system. The system is free from pronounced ferromagnetic coupling between Mn spins. The magnetic moments in high field regions are heavily influenced by the presence of Mn spins.     

In-plane Uniaxial Anisotropy and Magnetization Reversal Mechanism of FeCo Films by Strip Pattern

Strip-like Fe Co films were patterned by a traditional lithograph process from intrinsically isotropic continuous Fe Co films. The strip-patterned Fe Co film shows a strong in-plane uniaxial magnetic anisotropy with easy axis along the length direction of the strip. The angular dependences of remanence ratio, switching field, and coercivity indicate that the magnetization reversal mechanism of the strip-patterned Fe Co film is coherent rotation and domain wall depinning when the applied field is near the hard axis and easy axis, respectively. The consistency of the experimental hysteresis loops of the strip-patterned Fe Co film and calculated hysteresis loops with a simple in-plane uniaxial anisotropy model indicates that the strip-patterned Fe Co film behaves as a single domain. The absence of the domain wall and the strong in-plane anisotropy field make the strip-patterned Fe Co films have much potential for high-frequency application.     

High Entropy Alloys,Miscibility Gaps and the Rose Geometry

Recent review articles on high entropy alloys (HEAs) provide little information about miscibility gaps in multicomponent systems, especially about how to respond with alloying should they be found. Also, there is a lack of information about how miscibility gaps might appear on calculated or measured multicomponent phase diagrams. In this work concepts concerning miscibility gaps that form in binary and ternary systems are reviewed. Then the work is extended to alloys with more components including HEAs. The previous work predicts that there are significant differences between binary systems and those with three or more components. For example, miscibility gaps do not form in binary systems that have a negative heat of mixing, but they do form in ternary systems. Also, ternary systems with a positive heat of mixing can have their stability temperature lowered by adding ternary components that add positive heats of mixing. The morphology and topology of multicomponent/multiphase miscibility gaps differ from typical phase diagrams, as well. For example, one type of miscibility gap is said to have the rose geometry, because of its floral design. Normally only 2-phase miscibility gaps can form in binary and ternary systems. However using the Graph Method it is suggested that 3-phase miscibility gaps might form in HEA systems, even while trying to avoid them. A conclusion of this investigation is that with additional computational and experimental work it may be possible to expand the boundaries of where HEAs can be found.     

Composition Dependence of the Kinetics and Mechanisms of Thermal Oxidation of Titanium-Tantalum Alloys

The oxidation behavior of titanium-tantalumalloys was investigated with respective concentrationsof each element ranging from 0 to 100 wt.%. Alloys wereexposed to argon-20% oxygen at 800 to 1400°C. Theslowest oxidation rates were observed in alloys with5-20% Ta. The oxidation kinetics of alloys containingless than approximately 40% Ta were approximatelyparabolic. Pure Ta exhibited nearly linear kinetics. Alloys containing 50% or more Taexhibited paralinear kinetics. The activation energiesfor oxidation ranged between 232 kJ/mole for pure Ti and119 kJ/mole for pure Ta, with the activation energies of the alloys falling between these values andgenerally decreasing with increasing Ta content. Theactivation energies for oxidation of the end members, Tiand Ta, agree well with published values for the activation energies for diffusion of oxygenin -Ti and Ta. Scale formation in the alloys wasfound to be complex exhibiting various layers of Ti-,Ta-, and TiTa-oxides. The outermost layer of the oxidized alloys was predominately rutile(TiO₂). Beneath the TiO₂ grew avariety of other oxides with the Ta content generallyincreasing with proximity to the metal-oxide interface.It was found that the most oxidation-resistant alloys hadcompositions falling between Ti₅Ta andTi-15Ta. Although Ta stabilizes the -phase of Ti,the kinetics of oxidation appeared to be rate limited byoxygen transport through the oxygen-stabilized -phase.However, the kinetics are complicated by the formationof a complex oxide, which cracks periodically. Tantalumappears to increase the compositional range ofoxygen-stabilized -phase and reduces both the solubilityof oxygen and diffusivity of Ti in the - and-phases.     

Dependence on the Chromium Content of the High-Temperature Oxidation Behavior of Ta-Rich Nickel-Based Cast Alloys

The high-temperature stability of primary tantalum carbides is a problem of importance for chromium-rich cast alloys, based on cobalt or nickel. The focus of this study was nickel-based alloys, as these alloys are particularly sensitive to a lack of TaC in the as-cast state and by dissolution due to high-temperature exposure. In this work, a possible way for promoting the formation of many TaC precipitates by changing from the usual 30 wt% chromium content was investigated. Five alloys with Cr content varying from 10 to 50 wt% were prepared and then subjected to microstructure characterization and to oxidation tests. In contrast with what was expected, decreasing the Cr content in comparison with the Ni–30Cr–0.4C–6Ta reference alloy did not succeed in obtaining more TaC precipitates, but instead had the opposite effect. Concerning the high-temperature oxidation behavior at 1127 and 1237 °C, loss of resistance was observed only for a Cr content at the lower level of 10 wt%. It was noticed that a subscale CrTaO₄ developed during oxidation and seemed to promote oxide spallation during cooling.     

环境因素对铝合金大气腐蚀的影响及其动态变化规律研究

采用灰关联分析法分别计算了环境因素与三种铝及铝合金在1、3、6、10年大气暴露后平均腐蚀速率的关联度,并进行了排序.对LY12cz、LY12、L6M材料在不同暴露时间的主要环境影响因素及其动态变化规律进行了分析.结果表明,SO2、Cl-、T、RH>80%等环境因素对铝及铝合金腐蚀作用显著;尤其是SO2,而NH3和非水溶性降尘(D)的影响基本可忽略.RH>80%影响的加强可促进Cl-对铝合金腐蚀的影响,且T影响强时,Cl-和SO2有协同作用.灰关联度计算结果与各试验站实际的大气腐蚀结果相一致.     

超导环的磁化性质研究

计算了双结超导π环、零环及规则超导环阵列的自由能随外加磁场及温度的变化,给出了超导转变温度附近的系统相图。针对高温超导体及低温超导体中出现的顺磁迈斯纳效应,用π结、零结概念,给出了一种简单的理论解释。     

Compositional Dependence of Surface Morphology and Electrical Properties of GaInAsSb Alloys Grown by Metalorganic Chemical Vapor Deposition

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Effect of Al2O3 on the Microhardness of AMg2/Graphite Nanocomposite Powder Gas Dynamic Coatings on Aluminum Alloys

Metal Science and Heat Treatment - Mechanically synthesized hybrid powders of the AMg2/graphite + Al2O3 system and coatings deposited by cold gas dynamic spraying from these powders are studied....     

纳米复合永磁材料最新进展

纳米复合永磁材料由于具有潜在的优异性能和商业价值而倍受青睐。本文综述了纳米复合永磁材料近几年来的研究进展,主要说明通过成分优化和工艺改进以获得均细小的组织和优异的磁性能。     

Magnetization of superparamagnets in the state of mechanical anisotropy

The internal energy of magnetic anisotropy in some particles dominates over the thermal energy, even at room temperature. The existence of strong magnetic anisotropy of nanoparticles can significantly affect the process of magnetization of superparamagnets. However, if the axes of magnetic anisotropy of nanoparticles are randomly oriented, then their presence does not affect the process of magnetization, which occurs according to the classical Langevin theory. However, if the axes of nanoparticles are polarized (mechanical anisotropy), then the magnetization curve of a superparamagnet under the conditions of mechanical anisotropy lies between the Langevin curve and the curve of hyperbolic tangent and with increasing anisotropy moves progressively farther from the Langevin curve and approaches the curve of hyperbolic tangent. It has also been shown that, in the case of powder superparamagnets, the presence of mechanical anisotropy leads to significant changes in the Curie constant.     

用于铝合金晶粒细化的中间合金研究

晶粒细化是提高合金质量的重要途径之一，综述了用于铝合金晶粒细化的中间合金研究与应用进展，同时就其发展历史、分类和生产方法进行介绍，最后指明了铝合金晶粒细化剂的发展方向。     

Ti添加对快淬Pr基永磁合金磁性能与显微结构的影响

采用快淬法制备了Pr基(Nd,Pr)10.5Fe81.5-xTixCo2B6(x=0.0,1.0,2.0,3.0,4.0,5.0)系列粘结磁体,研究了添加Ti元素对快淬合金显微结构和磁性能的影响。Ti元素能有效细化合金的晶粒,添加3at%Ti的合金,晶粒细化到约70nm,且大小均匀;添加量超过3at%,晶粒进一步细化,但均匀性变差。含Ti3at%的(Nd,Pr)10.5Fe78.5Ti3Co2B6合金,粘结磁体磁性能达到最佳值,Br=0.655T,Hci=681kA/m,(BH)m=68kJ/m3。Ti元素低于3at%,合金晶粒粗大,磁性能较低;超过3at%后,富Ti的晶间相加厚,晶粒间的交换作用和剩磁增强效应减弱,且晶粒大小不均匀,合金的内禀矫顽力虽然增加,但剩磁Br和最大磁能积(BH)m降低。     

Dependence of Microstructure and Hardness of Nanocomposite Coatings of nc-(Ti_(1-x)Al_xN)/a-Si_3N_4 on Aluminum Contents

HARD COATINGS are finding a widely applicationin machining industries as tools and moulds since1980s[1].Hard coatings consisting of a variety of thetransition metal nitrides,for instance,TiN,TiC,TiCN,TiBN,TiAlN,CrN etc,usually service as a protectioncoatings that requires some better properties ofwear-resistance,corrosion-resistance and also highfatigue-strength especially at elevated temperature(formore details see Ref.2-6).The generic concept for the design of novelsuper-hard(>40G…