Fe73.5Cu1Nb3Si13.5B9非晶合金的激波纳米晶化速率和晶化度的对比研究

对Fe735Cu1Nb3Si135B9等非晶合金进行了退火和激波诱导两种方式的晶化实验以及XRD和DSC分析.着重对合金的晶化速率和晶化度等特性展开了研究和讨论.进一步证实了激波纳米晶化是一种包含着新机理的寓意丰富的晶化现象.也再次验证了作者曾经提出过的“激波流化相变”模型的合理性. 关键词： 非晶合金 激波 纳米晶化     

非晶合金Al88Ce2Ni9Fe1回火生成的纳米晶粒度分布与比内表面研究

采用小角X射线散射方法,结合差热分折及广角X射线衍射方法,对新型高强度、高韧性非晶合金Al₈₈Ce₂Ni₉Fe₁回火生成的纳米晶粒度分布和比内表面的改变进行了一系列分析研究,获得了关于纳米晶回转半径、Porod半径、散射积分不变量、粒度分布、结晶度、比内表面等方面的信息. 关键词：     

纳米晶Fe73.5Cu1Nb3Si13.5B9晶间非晶相结构弛豫与模量的振荡变化

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Fe-Cu-Si-B纳米晶合金的结构与性能

利用非晶晶化法制备了(Fe_0.99Cu_0.01)₇₈Si₉B₁₃纳米晶合金。发现其显微硬度H_v与晶粒尺寸d之间基本服从Hall-Petch关系。利用M?ssbauer谱研究了晶粒尺寸为30nm的材料中类金属原子的分布及其对晶化相电子结构的影响。 关键词：     

Fe基纳米晶合金晶粒尺寸反常变化的物理机制

晶粒尺寸在很大程度上决定了Fe基纳米晶合金的磁学性能,其随退火温度变化的物理机理是纳米晶领域重要的研究内容.研究了初始晶化温度与二次晶化温度之间退火1 h Fe基纳米晶合金晶粒尺寸随退火温度的变化,并建立了相应的模型.利用提出的模型分析了该温度范围内Fe基纳米晶合金晶粒尺寸随退火温度升高先减小后增大的物理机制. 研究发现,在初始晶化温度与二次晶化温度之间等时退火,当退火温度约为Fe基纳米晶合金熔点的0.6倍时其晶粒尺寸最小.在研究的温度区间内,理论研究结果与实验符合得较好. 本研究提供了一种快速获得小晶粒尺寸纳米晶合金的方法.     

铁基软磁非晶/纳米晶合金研究进展及应用前景

非晶合金通常是将熔融的金属快速冷却、通过抑制结晶而获得的原子呈长程无序排列的金属材料.由于具有这种特殊结构,铁基软磁非晶合金具有各向同性特征、很小的结构关联尺寸和磁各向异性常数,因而具有很小的矫顽力H_c,但可和晶态材料一样具有高的饱和磁感强度B_s.优异的软磁性能促进了铁基软磁非晶合金的应用研究.目前,铁基软磁非晶/纳米晶合金带材已实现大规模工业化生产和应用,成为重要的高性能软磁材料.本文回顾了软磁非晶合金的发现和发展历程,结合成分、结构、工艺对铁基非晶/纳米晶合金软磁性能的影响,介绍了相关基础研究成果和工艺技术进步对铁基软磁非晶/纳米晶合金研发和工业化应用的重要贡献.并根据结构、性能特征将铁基软磁非晶合金研发与应用分为三个阶段,指出了目前铁基软磁非晶合金研发与应用中面临的挑战和发展方向.     

高压下Zr70Cu30非晶合金的热稳定性和晶化相的变化

 用电阻测量及X射线衍射法研究了非晶Zr₇₀Cu₃₀合金在常压和高压下热稳定性以及晶化相的变化。结果表明压力提高了这种非晶合金的晶化温度并明显地改变了合金中的相平衡关系。在2 GPa压力下，平衡相为Cu₁₀Zr₇和α-Zr的混合物，而常压下为CuZr₂和少量α-Zr的混合物。     

AuCu249合金团簇热稳定性的原子尺度计算研究

采用基于嵌入原子法的NVT正则系综分子动力学方法,在原子尺度上计算了包含249个原子的金属间化合物AuCu₂₄₉合金团簇由固态转变为熔体的结构演化过程. 根据对分布函数、原子密度分布函数和主要原子键对数目随温度的变化,发现在温度从低温升到高温的过程中,合金团簇内伴随着原子的连续位置交换,团簇呈现由外及里的分阶段结构转变. 同时还发现在团簇内原子堆积结构转变过程中,Au原子出现由团簇内层向外层运动的趋势,而Cu原子则有由外层向内层运动的趋势. 关键词： 合金团簇 分子动力学 计算机模拟 相变     

Fe15.38Co61.52Cu0.6Nb2.5Si11B9纳米晶软磁合金的交流磁性

研究了退火温度对Fe_15.38Co_61.52Cu_0.6Nb_2.5Si₁₁B₉纳米晶软磁合金交流磁性的影响,并且分析了获得较好软磁性能的可能原因.合金的电阻率随着退火温度的增加逐渐降低.μ'f0值与饱和磁化强度M_s之间没有明显的正比关系,合金的旋磁比γ随退火温度的升高应呈不规则的 关键词： 纳米晶合金 软磁材料 品质因数 热处理     

Fe73.5Cu1Nb3B9Si13.5非晶态合金的激波纳米晶化研究

实验表明,非晶态合金在激波影响下会转变为纳米晶.最近的实验进一步发现,Fe_73.5Cu₁Nb₃B₉Si_13.5非晶态合金中的Cu,Nb在激波晶化中的细化作用被抑制,且样品在这种转变之后作进一步的退火处理,其晶粒度变大而晶格常数变小.在激波晶化机理分析中提出了“激波流体晶化”构想. 关键词：     

Highly anisotropic resin-bonded magnets processed with surfactant-coated SmCo5 nanocrystalline powders

Highly anisotropic SmCo₅ nanocrystalline powders with grain size in the range 5-20 nm were processed through surfactant and magnetic field-assisted milling. The SmCo₅ nanocrystalline powders so obtained by this method possess unusual characteristics such as reduction in particle size, platelet-structure and high remanence values. A possible mechanism for achieving remanence enhancement with the surfactant-coated SmCo₅ powders has been discussed. Besides, the resin-bonded magnets processed with the surfactant-coated SmCo₅ powders showed relatively higher density, induction remanence and energy product with strong anisotropic behavior than those of the magnets processed with the conventionally milled SmCo₅ powders. Maximum values of H_ci (16 kOe), B_r (4.66 kG) and (BH)_max (5.5 MG Oe) were achieved for the resin-bonded magnets processed with the surfactant-coated powders.     

A study on magnetic properties and structure of SmCo5 thin films on Ni-W underlayers

A systematic study on Ni-W alloy underlayers has shown that a highly textured (2 1 1)-Ni₄W can be formed after deposition at room temperature. Highly textured (0 0 0 1)-SmCo₅ with a high out-of-plane coercivity (over 10 kOe) and large perpendicular anisotropy can be obtained after deposition on the (2 2 1)-Ni₄W underlayer probably due to a small mismatch between (2 2 1)-Ni₄W and (0 0 0 1)-SmCo₅. Our study indicates that the surface roughness of the underlayers also plays a crucial role, that a smooth surface is favorable for a good crystallinity and high coercivity of SmCo₅. Moreover, we found that a highly textured Ni-(1 1 1) can be obtained on the top of the (2 1 1)-textured Ni₄W. The film structure of SmCo₅/Ni/Ni₄W may be interesting as the hard/soft double-layered film for perpendicular magnetic recording or for other applications after a further development.     

Microstructure and magnetic properties studies of SmCo5 thin films grown on MgO and glass substrates

In this work, SmCo₅ thin films are deposited on single crystal MgO (1 0 0) and amorphous glass substrates with a Cr underlayer at 400 °C by sputtering. A comparison study shows that the microstructures and magnetic properties are different in the two SmCo₅ films on the MgO (1 0 0) and glass substrates, respectively. An epitaxial growth of Cr-(2 0 0)〈1 1 0〉/SmCo₅-(1 1 2¯ 0)〈0 0 0 1〉 is achieved on the MgO (1 0 0) single crystal substrate with an average grain size of 20 nm for SmCo₅. On the amorphous glass substrate, no significant crystallographic texture is found in the Cr underlayer. After the deposition of SmCo₅, a weak texture of (1 1 2¯ 0) is observed with an average grain size of 8 nm. High remanence ratio value in this film is probably due to strong exchange coupling. Both SmCo₅ films show high in-plane coercivity, high in-plane anisotropy and remanence enhancement.     

Effects of surface-modification with Bi2O3 on the thermal stability and photoinduced charge property of nanocrystalline anatase TiO2 and its enhanced photocatalytic activity

Bi₂O₃ surface-modified TiO₂ nanoparticle has been synthesized by sol-hydrothermal processes, followed by post-treatment with an appropriate amount of bismuth nitrate solution, and also characterized by XRD, Raman, BET, TEM, FT-IR, XPS, UV-vis DRS and SPS techniques. The effects of the surface-modification with Bi₂O₃ on the thermal stability, photoinduced charge separation and photocatalytic activity for degrading rhodamine B (or phenol) under ultraviolet (or visible) irradiation are investigated in detail, along with their relationships and the activity enhancement mechanisms are also suggested. The results show that the modification with Bi₂O₃ can improve the thermal stability of the as-prepared anatase crystallites, consequently enhancing the anatase crystallinity so as to promote the photoinduced charge separation. And the modification with Bi₂O₃ also extends the optical response range. It can be concluded that the activity enhancement of surface-modified TiO₂ is mainly attributed to the increase in the photoinduced charge separation rate and to the extent of the optical response range, compared with un-modified ones. Moreover, the inhibition phase transformation mechanism related to Bi₂O₃ is suggested.     

A simulation study of rapid solidification and crystal configuration of Cu70Ni30 alloy

A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu₇₀Ni₃₀ adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2×10¹² K/s, the Cu₇₀Ni₃₀ formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be, further understood.     

Numerical simulation on dendritic growth of Al-Cu alloy under convection based on the cellular automaton lattice Boltzmann method

A numerical model is developed by coupling the cellular automaton (CA) method and the lattice Boltzmann method (LBM) to simulate the dendritic growth of Al-Cu alloy in both two and three dimensions. An improved decentered square algorithm is proposed to overcome the artificial anisotropy induced by the CA cells and to realize simulation of dendritic growth with arbitrary orientations. Based on the established CA-LBM model, effects of forced convection and gravity-driven natural convection on dendritic growth are studied. The simulation results show that the blocking effect of dendrites on melt flow is advanced with a larger number of seeds. The competitive growth of the converging columnar dendrites is determined by the interaction between heat flow and forced convection. Gravity-driven natural convection leads to highly asymmetric growth of equiaxed dendrites. With sinking downwards of the heavy solute, chimney-like or mushroom-like solute plumes are formed in the melt in front of the columnar dendrites when they grow along the gravitational direction. More details on dendritic growth of Al-Cu alloy under convection are revealed by 3D simulations.     

Double-ceramic-layer thermal barrier coatings based on La2(Zr0.7Ce0.3)2O7/La2Ce2O7 deposited by electron beam-physical vapor deposition

Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3) and La₂Ce₂O₇ (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO₃ is formed due to the chemical reaction between LC and Al₂O₃ which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs.     

一种改进的多速双向行人流元胞自动机模型

考虑行人的位置交换、侧向前进和后退行为,建立了一种改进的元胞自动机模型,用于研究地下通道中具有多种运动速度的双向行人流.将改进的元胞自动机模型与Weng的模型进行了比较.计算机模拟表明,改进的模型具有提高系统中行人的平均速度并降低行人占据密度的倾向. 关键词： 双向行人流 元胞自动机 计算机模拟     

Improvement of magnetic properties and read/write characteristics in SmCo5 perpendicular thin films

An SmCo₅ alloy is a promising candidate for ultra-high density magnetic recording media because of its strong uniaxial magnetocrystalline anisotropy, whose constant, K_u, is more than 1.1×10⁸ erg/cm³. Recently, we successfully obtained high perpendicular magnetic anisotropy for a sputter-deposited SmCo₅ thin film by introducing a Cu/Ti dual underlayer. However, it is necessary to improve magnetic properties and read/write (R/W) characteristics for applying SmCo₅ thin films to perpendicular magnetic recording media. In this study, we focused on reduction of magnetic domain size and change of a magnetization reversal process of SmCo₅ perpendicular magnetic thin films by introducing carbon (C) atoms into the constituent Cu underlayer. The magnetic domain size became small and the ratio of coercivity (H_c) against magnetic anisotropy (H_k) which is an index of the magnetization reversal process was increased by adding C atoms. We also evaluated the R/W characteristics of SmCo₅ double-layered media including C atoms. The medium noise was decreased and signal-to-noise ratio increased by introducing the C. The addition of C into the Cu underlayer is effective for changing the magnetization reversal process, reducing medium noise and increasing SNR.     

Probing the anisotropy constants of SmCo5 and PrCo5 by Hall resistance measurements in pulsed high magnetic fields up to 47 T

In order to assess the anisotropy constants of highly anisotropic thin film samples with anisotropy fields well above 10 T, Hall resistance measurements were conducted in pulsed magnetic fields. These measurements also deliver the anomalous Hall data, which are proportional to the perpendicular magnetisation. This specific approach combines the high field values obtainable by pulsed fields with a measurement technique sensitive enough to be applied to thin film samples. Two epitaxial Rare Earth-Cobalt thin films with large in-plane uniaxial magnetocrystalline anisotropy at room temperature were studied. The resulting anisotropy fields and constants are discussed with respect to measurements on single crystals and similar films investigated in quasi-static magnetic fields well below the anisotropy field. The present technique proved to be very valuable to highly anisotropic samples, as the approach to saturation is fully monitored and the data thus provides a more extended view on the hard axis magnetisation process.