Influence of Al addition on microstructures of Cu−B alloys and Cu−ZrB2 composites

The influence of Al addition on the microstructure of Cu−B alloys and Cu−ZrB₂ composites was investigated using scanning electron microscopy, X-ray diffraction and first-principles calculation. The results show that the eutectic B in Cu−B alloys can be modified by Al from coarse needles to fine fibrous structure and primary B will form in hypoeutectic Cu−B alloys. As for Cu−ZrB₂ composites, Al can significantly refine and modify the morphology of ZrB₂ as well as improve its distribution, which should be due to its selective adsorption on ZrB₂ surfaces. The first-principles calculation results indicate that Al is preferentially adsobed on ZrB₂ (12(__)10), then on ZrB₂ (101(__)0), and finally on ZrB₂ (0001). As a result, smaller sized ZrB₂ with a polyhedron-like, even nearly sphere-like morphology, can form. Due to Al addition, the hardness of Cu−ZrB₂ composites is greatly enhanced, but the electrical conductivity of the composites is seriously reduced.     

平面流铸工艺中冷却辊流场和传热三维稳态模拟

平面流铸法是一种制备非晶和纳米晶薄带的先进技术。这项技术的难点不仅在于快速冷却以抑制薄带的晶化,还在于获得高表面质量的薄带。提出了一种用三维稳态模拟模型预测工业生产中广泛应用的2种单辊冷却结构的流场和传热系数分布的新方法。利用FLUENT软件,结合能量和动量方程,计算了2种结构的流速分布。预测了2种结构的对流换热系数分布。结果表明,水槽结构的速度分布无均匀性,也无周期性;水缝结构的速度分布无均匀性,但具有周期性。2种结构的对流换热系数分布不是中心对称的,水缝结构的冷却特性更为规则。预测了水缝结构的3个对称分布的合适区域,并通过连续生产多次验证。根据热平衡原理,描述了平面流铸法工艺的传热过程。对流换热系数的均匀分布可以作为冷却辊结构设计的依据之一。     

基于模糊支持向量机的继电保护状态在线评价

继电保护状态评价工作一直以来都是状态检修的重点和难点。提出一种基于模糊支持向量机的继电保护状态评价方法。首先,获取智能变电站继电保护装置的历史数据,从中选择合适的状态评价因素,再对状态评价因素进行数据预处理,并根据状态巡视及故障记录计算装置在各巡视点的百分比剩余寿命,生成训练样本集。然后通过模糊支持向量机回归训练生成模型,利用在线巡视记录,对装置状态进行在线评估。并根据最差指标,判定装置的当前状态,作为最终的在线状态评价结果。仿真分析表明,方法通过引入样本权重,能够区分本装置样本和同型号装置样本的不同,使得算法能够兼顾装置的个性和家族性共性,并具备一定的抗噪能力。     

Molecular dynamics simulation of Al–Co–Cr–Cu–Fe–Ni high entropy alloy thin film growth

Molecular dynamics (MD) simulations are used to study AlCoCrCuFeNi high entropy alloy (HEA) thin film growth on a silicon (100) substrate. Effect of the atomic composition is studied on morphology and atomic scale structure. Input data are chosen to fit with experimental operating conditions of magnetron sputtering deposition process. It is observed that the different structures are determined by the chemical composition and atomic size mismatch. The simulated results are in good agreement with the solid-solution formation rules proposed by Zhang et al. [1] for multi-principal component HEAs which based on the two parameters δ and Ω, respectively describing describe the comprehensive effect of the atomic-size difference in the n-element alloy and the effects of enthalpy and entropy of mixing on formation of multi-component solid-solutions. When Ω ≥ 1.1 and δ ≤ 6.6%, the multi-component solid solution phase could form. In contrast, the multi-component alloys forming intermetallic compounds and bulk metallic glasses (BMG) have larger value of δ and smaller value of Ω. The value of Ω for BMG is smaller than that of intermetallic compounds.     

Defect detection in magnetic tile images based on stationary wavelet transform

A novel approach using stationary wavelet transform (SWT) is proposed for automatically detecting low-contrast defects under various light conditions in magnetic tile images. In this method, the uneven background was removed by Sobel operation. Then the index low-pass filtering and the nonlinear enhancement were respectively used to eliminate the interference and enhance the target in subbands produced by SWT. To verify the validity of the proposed algorithm, extensive experiments were conducted in a novel machine vision based system. As the result shows, the proposed method achieves an accuracy rate of 92.86% in detecting various defects in magnetic tile surfaces with the average operation time of 0.5190 s, and is superior to traditional methods in terms of the high reliability and accuracy.     

Electrochemical Behaviour of Al, Al—In and Al–Ga–In Alloys in Chloride Solutions Containing Zinc Ions

The electrochemical behaviour of Al, Al—In and Al–Ga–In alloys in 0.6 m NaCl solutions with and without Zn²⁺ was investigated. The study was performed by means of open circuit potential, potentiodynamic polarization, potentiostatic current-time and electrochemical impedance spectroscopy measurements as well as by SEM-EDAX examination. It was found that the Al—In alloy exhibits the highest negative open circuit potential in 0.6 m NaCl and the corrosion resistance of the tested electrodes decreases in the following order: Al > Al–Ga–In > Al—In. The greater activity of the Al—In alloy was interpreted on the basis of the autocatalytic attack by indium. The potentiostatic current–time measurements in Zn²⁺ containing electrolyte at potentials above the pitting potential revealed that Zn²⁺ has an insignificant influence on the Al electrode, while it enhances the corrosion of the Al–Ga–In alloy and improves the attack morphology of the Al—In alloy. Furthermore, the impedance spectra recorded under open circuit conditions showed a decrease in the polarization resistance of Al—In and Al–Ga–In alloys in presence of Zn²⁺ indicating the activating effect of Zn²⁺ ions.     

On the observation of inductive high-frequency impedance behaviour during the electrodeposition of Au—Sn alloys

Inductive high-frequency impedance behaviour is often observed in metal electrodeposition systems. This behaviour is typically attributed to equipment limitations or non-idealities in the cell set-up and electrical connections. Such instrumental artefacts would nevertheless be relevant to a frequency range which is expected to be well above that in which inductive behaviour is in fact observed (down to a few tens of Hz). In this paper some results on an acidic Au—Sn electrodeposition system are reported. Electrochemical impedance and potentiostatic transients were measured. These results suggest that the high-frequency inductive behaviour may be related to metal nucleation processes. A correlation is proposed between the pseudo-inductive potentiostatic nucleation transients and the pseudo-inductive behaviour of the impedance spectra.     

Electrodeposition, composition and structure of Zn—Cr alloys

The effect of polyethylene glycol (PEG 1500) as additive and of deposition conditions on Zn—Cr alloy electrodeposition from an acidic sulfate electrolyte at room temperature, without agitation was investigated. PEG polarizes the overall cathodic reaction and inhibits Zn deposition. Cr codeposition with Zn starts at a cathodic potential of about –1,95 V vs Hg/Hg₂SO₄, which is reached at current density of about 20 A dm^–2 in galvanostatic conditions. Zn—Cr alloy coatings containing up to 28 at % Cr were obtained depending on the plating conditions. SEM observations showed an island-like structure, formed by the local growth of crystals, which covered the surface during further deposition. In the first stages of electrodeposition the powder diffraction spectra contain lines of b.c.c. -(Zn,Cr) phase (a 3.02 Å). After 30 s deposition time weak lines of Zn-based phase (a 2.67 Å, c 4.90 Å) appear, and become clearly visible in coatings deposited for 90 s. The average Cr content in the alloy coatings decreases with advancing deposition. The as-plated surface contains C in organic compounds and Zn(OH)₂. After 50 min sputtering, Zn and a mixture of Cr, Cr₂O₃ and Cr₇C₃ were found. The presence of organic C and O, probably from inclusions of PEG, were also detected.     

A study of the potentials achieved during mechanical abrasion and the repassivation rate of titanium and Ti6Al4V in inorganic buffer solutions and bovine serum

Titanium alloys in orthopaedic implants are susceptible to mechanical disruption of the passive film (fretting corrosion). To study this effect, open-circuit potential (ocp) measurements before, during and after mechanical disruption of the passive film in a tribo-electrochemical cell on commercial pure titanium and Ti6Al4V alloy in inorganic buffer solutions in the pH range from 2.0 to 12.0 and calf bovine serum at pH 4.0 and 7.0 are reported. Additionally, the effect of pH, electrolyte and sample composition on the repassivation rate has been investigated. The potentials achieved during the abrasion of Ti6Al4V are the same as those characterizing pure titanium, which indicates that the corrosion current of both materials in the active state is due to the oxidation of titanium. However, commercial pure titanium displays a tendency to repassivate faster than Ti6Al4V in inorganic buffer solutions thanks to the lower critical current density and the higher catalytic activity towards the hydrogen evolution reaction observed on the pure metal in comparison with the alloy.Proteinaceous solutions like bovine serum, significantly slow down the anodic dissolution and the cathodic reactions both on titanium and the alloy. However, the repassivation rate of the Ti6Al4V is not affected by serum, while that of cp titanium significantly decreases both at pH 4.0 and 7.0.     

电沉积非晶态合金镀层磁性的控制

磁性元件薄膜化促进了磁性镀层的开发与应用。综述了镀液及镀层成分、电沉积工艺、镀层厚度及热处理对电沉积非晶态镀层性能的影响，以便在实际应用中控制非晶态合金镀层的磁性。