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1.
Micro-arc oxidation (MAO), a plasma electrolytic surface process, has attracted much interest as an effective technique to improve the wear resistance of aluminum alloys by creating a relatively thick and hard alumina coating on the component surface. However, previous studies of MAO aluminum alloys have shown that as-deposited and polished alumina coatings have a relatively high friction coefficient, for example, values of 0.6 and 0.7 against WC/Co and AISI 52100 counterfaces in dry sliding tests, respectively.  相似文献   

2.
We report the experimental demonstration of fluorescence of CdSe quantum dots with surface plasmon excitation in deep-ultraviolet (deep-UV) region. Surface plasmon resonance in deep-UV is excited by aluminum thin film in the Kretschmann-Raether geometry. Considering the oxidation thickness of aluminum, the experimental results of incident angle dependence of reflectance show good agreement with Fresnel theory. Surface plasmon resonance with 19 nm-thick aluminum and 5 nm-thick almnina was excited at the incident angle of 48 degrees for 266 nm excitation. Fluorescence of CdSe quantum dots coated on this aluminum film was observed by the surface plasmon excitation.  相似文献   

3.
The metal aluminum (Al) is widely used because it has high reflectivity from the ultraviolet to the infrared band. But the new deposited Al films is exposed to the atmosphere, it forms transparent Al2O3 films on its surface at once. In this letter, the Al films is deposited on the quartz substrate by electron beam evaporation. The effect of Al films oxidation on refractive index and extinction coefficient is investigated by spectroscopic ellipsometry (SE). The optical constants of Al films change with the increase of oxidation time. The two parameters become stable when these films are exposed in air more than 2 days.  相似文献   

4.
黄伟其  刘世荣 《中国物理》2006,15(2):389-393
The investigation on the oxidation behaviour of Si自聚集锗 纳米结构 激光辅助氧化 PL光谱low-temperature oxidation, laser-assisted, nano-structure, PL spectraProject supported by the Natural Science Foundation of Guizhou Province, China (Grant No 3067(2004)).2005-04-202005-04-202005-10-08The investigation on the oxidation behaviour of Si1-xGex alloys (x=0.05, 0.15, and 0.25) is carried out. It is found for the first time that on the oxide film a germanium nano-cap with a thickness of 1.8-2.8nm and a few Ge nanoparticles with diameters ranging from 5.5 nm to 10 nm are formed by the low-temperatu.re laser-assisted dry oxidation of Si1-xGex substrate. A new scanning method on the decline cross-section of the multiple-layer sample is adopted to measure the layer thickness and the composition. Some new peaks in photoluminescence (PL) spectra are discovered, which could be related to the nano-cap and the nano-particles of germanium. A suitable model and several new calculating formulae with the unrestricted Hartree-Fock-Roothaan (UHFR) method and quantum confinement analysis are proposed to interpret the PL spectra and the nano-structure mechanism in the oxide.  相似文献   

5.
We investigate the oxidation behaviour of Si1-xGex alloys(x=0.05,0.15,and 0.25),The oxidation of SiGe films with different compositions was carried out in O2(dry)atmosphere at 800,900 and 1000℃,respectively,for various lengths of time,The thickness and property of the nanoparticle and nanolayer in oxide films and germanium segregation in oxidation of SiGe alloys are measured by using a high precision ellipsometer.The results are in good agreement with the Rutherford backscattering spectrometry,profile dektak instrument and high-resolution scanning transmission electron microscopy.We found that the Ge content in the oxide layer increases with the Ge content in SiGe alloys,and that the Ge content in the oxide film decreases with the increasing oxidation temperature and time,Rejection of Ge results in Piling up of Ge at the interface etween the growing SiO2 and the remaining SiGe,which forms a nanometre Ge-rich layer.Substantial interdiffusion of Si and Ge takes place in the remaining SiGe,which leads to the complicated distribution of Ge segregation.We find a nanometre cap layer over the oxide film after fast oxidation,in which there are many Ge nanoparticles,We analyse the kinetics and mechanism of the nanostructure of the oxide and Ge segregation in oxidation of Si1-xGex alloys.  相似文献   

6.
In this paper, a micro capacitive sensor with nanometer resolution is presented for ultra-precision measurement of micro components, which is fabricated by the MEMS (micro electromechanical systems) non-silicon technique. Based on the sensor, a micro capacitive tactile probe is constructed by stylus assembly and packaging design for dimension metrology on micro/nano scale, in which a data acquiring system is developed with AD7747. Some measurements of the micro capacitive tactile probe are performed on a nano positioning and measuring machine (NMM). The measurement results show good linearity and hysteresis with a range of 11.6 μm and resolution of better than 5 nm. Hence, the micro capacitive tactile probe can be integrated on NMM to realize measurement of micro structures with nanometer accuracy.  相似文献   

7.
陈凯  崔明启  郑雷 《中国物理 C》2008,32(8):673-676
The photo-absorption cross section of aluminum was obtained from the ratio of transmission of aluminum thin-films with different area densities from 50 to 250eV with synchrotron radiation monochromatic beam. Two samples with different area densities were used to minimize the uncertainty caused by the sample surface oxidation and systematic factors of the X-ray source, beamline, and detector. The experimental results are in good agreement with the published data and FEFF program calculations in general.  相似文献   

8.
黄伟其  刘世荣 《中国物理》2004,13(7):1163-1166
We report the investigation on the oxidation behaviour of Si_{1-x}Ge_x alloys (x=0.05, 0.15, and 0.25). It was found for the first time that a nanocap (thickness: 1.6-2.0nm) was formed on the oxide film after fast oxidation. Some new peaks in photoluminescence spectra were discovered, which could be related to the Ge nanocap, the Ge nanolayer (thickness: 0.8-1.2nm) and the Ge nanoparticles (with various diameters from 2.6nm to 7.4nm), respectively. A suitable model and several new calculating formulae combined with the Unrestricted Hartree-Fock-Roothaan (UHFR) method and quantum confinement analysis have been proposed to interpret the PL spectra and the nanostructure mechanism in the oxide and Ge segregation.  相似文献   

9.
By adjusting the anodization voltage periodically in the process of electrochemical oxidation of Muminum and subsequent chemical etching, anodic aluminum oxide membranes with a dual periodic layer-by-layer structure are prepared. Optical transmission spectra analyses prove that the dip position is dependent on the thickness of the layer and can be easily adjusted by the anodization voltage according to the Bragg-Snell formula. This result implies that the position and width of the stop band and the pass band in the visible and near infrared wavelength region can be designed and prepared arbitrarily. It is expected that these kinds of anodic aluminum oxide membranes may find applications in the fabrication of various optical devices.  相似文献   

10.
When two contacting solid surfaces are tightly closed and invisible to the naked eye,the discontinuity is said to be microscopic regardless of whether its length is short or long.By this definition,it is not sufficient to distinguish the difference between a micro-and macro-crack by using the length parameter.Microcracks in high strength metal alloys have been known to be several centimeters or longer.Considered in this work is a dual scale fatigue crack growth model where the main crack can be micro or macro but there prevails an inherent microscopic tip region that is damaged depending on the irregularities of the microstructure.This region is referred to as the"micro-tip"and can be simulated by a sharp wedge with different angles in addition to mixed boundary conditions.The combination is sufficient to model microscopic entities in the form of voids,inclusions,precipitations,interfaces,in addition to subgrain imperfections,or cluster of dislocations.This is accomplished by using the method of"singularity representation"such that closed form asymptotic solutions can be obtained for the development of fatigue crack growth rate relations with three parameters.They include:(1)the crack surface tightness*represented by o/=0.3-0.5 for short cracks in region I,and 0.1-0.2 for long cracks in region II,(2)the micro/macro material properties reflected by the shear modulus ratio*(=micro/macro varying between 2 and 5)and(3)the most sensitive parameter d*being the micro-tip characteristic length d*(=d/do)whose magnitude decreases in the direction of region I II.The existing fatigue crack growth data for 2024-T3 and 7075-T6 aluminum sheets are used to reinterpret the two-parameter da/dN=C(K)nrelation where K has now been re-derived for a microcrack with surfaces tightly in contact.The contact force will depend on the mean stress m or mean stress ratio R as the primary parameter and on the stress amplitude a as the secondary parameter.  相似文献   

11.
Cathodic plasma electrolytic (CPE) techniques are new groups of coating processes, which can be used for fabrication of nanostructured layers on surface of a wide range of metallic substrates. The most exciting visible feature of these atmospheric-based plasma techniques is continuous sparking on processed surface inside an electrolyte. Unlike the anodic part of plasma electrolysis (usually known as plasma electrolytic oxidation (PEO) or micro arc oxidation (MAO)), which is commonly used for oxidation of light metals/alloys such as aluminum, titanium and magnesium, CPE techniques can clean and coat different metals and alloys such as steel, copper, and light metals/alloys with formation of wide range of nanostructures including complex carbides, carbonitrides, intermetallics, and even oxides. It has been observed that the properties of obtained layers depend on the characteristics of achieved nanostructures such as average size, distribution and average coordination number of nanocrystallites. Furthermore, the properties of the processed surface can be tailored by tailoring the nanostructure characteristics. There is limited literature available on the mechanism of CPE and its connection to the morphology of nanostructured layers. This article addresses the two important aspects of CPE, namely characterization of nanostructured layers and mechanism of cathodic plasma electrolysis, which are reviewed in accordance to the morphology of fabricated nanostructures.  相似文献   

12.
Plasma electrolytic oxidation (PEO) is a cost-effective technique that can be used to prepare ceramic coatings on metals such as Ti, Al, Mg, Nb, etc., and their alloys, but this promising technique cannot be used to modify the surface properties of steels, which are the most widely used materials in engineering. In order to prepare metallurgically bonded ceramic coatings on steels, a combined technique of arc spraying and plasma electrolytic oxidation (PEO) was adopted. In this work, metallurgically bonded ceramic coatings on steels were obtained using this method. We firstly prepared aluminum coatings on steels by arc spraying, and then obtained the metallurgically bonded ceramic coatings on aluminum coatings by PEO. The characteristics of duplex coatings were analyzed by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The corrosion and wear resistance of the ceramic coatings were also studied. The results show that, duplex Al2O3/aluminum coatings have been deposited on steel substrate after the combined treatment. The ceramic coatings are mainly composed of α-Al2O3, γ-Al2O3, θ-Al2O3 and some amorphous phase. The duplex coatings show favorable corrosion and wear resistance properties. The investigations indicate that the combination of arc spraying and plasma electrolytic oxidation proves a promising technique for surface modification of steels for protective purposes.  相似文献   

13.
对管状铝质材料的等离子体电解沉积行为进行了研究.测试了不同工作电压和不同电极放置模式条件下铝管内部不同位置的电位分布,并通过显微分析观察,对比了不同电极放置模式对铝管内外壁陶瓷沉积层生长情况的影响.结果表明,不同的电极放置模式下,铝管内外壁陶瓷沉积层生长情况有很大差异.这是因为不同的电极放置模式对铝管内的电场分布具有很大影响,进而影响到铝管内外壁陶瓷层的沉积过程.只有外电极时,由于电场屏蔽作用,不能在铝管内壁形成均匀陶瓷层;在铝管内部加入辅助中心电极后,铝管内部产生均匀电场,这有利于在其内壁形成均匀的陶瓷层. 关键词: 等离子体电解沉积 铝管 表面改性 陶瓷层  相似文献   

14.
The paper presents the results of oxidation tests of Fe3Al-based alloys containing additions of Cr, Zr, B, and C, with and without an aluminide coating. The coating was formed by a pack cementation process in which the surface of material got enriched in aluminum. The Al-rich layer was intended to enhance the tendency of Al2O3 formation. The slow-growing Al2O3 scale provides the best corrosion protection for structural materials at high temperatures. The cyclic oxidation tests were performed in laboratory air at 1373 K. The structure and composition of oxide scales as well as their adherence were evaluated and compared for the materials with and without aluminide coatings. Surface enrichment in aluminum and effect minor addition of Zr on oxidation behavior was discussed.  相似文献   

15.
Experimental results on the melting of aluminum nitride heated by an electric arc burning in a nitrogen atmosphere at a pressure of 0.2–0.3 MPa are presented. A qualitative explanation of the dissociation suppression mechanism under arc heating is proposed. It has been shown that the suppression is possible at atmospheric pressure due to the photoactivation of aluminum on the sample surface by resonant radiation of aluminum vapors present in the electric arc.  相似文献   

16.
57Fe Mössbauer spectroscopy and scanning electron microscopy measurements of precursor phases formed during catalyst preparation and of the catalysts, themselves, demonstrate that the preparation of Raney iron from iron aluminum alloys involves the formation of Fe(OH)2 and Fe3O4 as intermediate phases. The metallic Fe is formed from subsequent reduction of Fe3O4 by hydrogen generated by the oxidation of aluminum metal by hydroxide ions. Precursors to Urushibara iron U?Fe (III) are found to consist of Fe?Zn alloys when Zn is used as a reductant and of epitaxial deposits of Fe on aluminum when Al is the reductant. The material resulting from the reduction of the iron salt by aluminum is not a hydrogenation catalyst; the absence of catalytic activity is related to the absence of any alloying of the iron and aluminum. A consideration of the preparation of Raney iron, Urushibara iron, ammonia synthesis and Fischer-Tropsch catalysts leads to the conclusions that catalytic activity is highly correlated to the existence of intermediate mixed-crystals phases and the presence of intimate mixtures of at least two phases in the final catalyst.  相似文献   

17.
Rapidly solidified aluminum alloys are promising materials with very fine microstructure. The microscopy observation of these materials is complicated due to overlay of fcc-Al matrix and different intermetallic phases. A possible way to solve this problem is to dissolve the Al matrix. By this process powder formed by single intermetallic phase particles is obtained. In this paper a new aqueous based dissolving agent for Al-based alloy is presented. The influence of oxidation agent (FeCl3) concentration on quality of extraction process was studied.  相似文献   

18.
Ion implantation was adopted to change the surface potentials of samples made of aluminum bronze. The interactions between the SiO2 particles and the sample surfaces in water were changed from attractive to repulsive. According to the surface element integration method, this interaction was simulated and the electrostatic double layer force was considered to be the dominated factor. This long range repulsive interaction was proved to have effect on preventing micro particles approaching the alloy surface by the fluorescent particles adhesion experiment, and the technology of ion implantation may have potential applications in adhesion resistance and abrasion reduction for alloys running in water.  相似文献   

19.
Iron alloys and aluminum were nitrogen implanted in a controlled oxygen atmosphere and the role of hydrogen on the surface etching mechanisms studied. The surface composition was analyzed by in situ photoemission electron spectroscopy (XPS). In iron alloys, hydrogen strongly etches oxygen, improving nitrogen retention on the surface. On the other hand, hydrogen removes nitrogen from aluminum surfaces, with a deleterious effect on the nitriding effectiveness. The oxygen removal in iron alloys is associated with the catalytic effect of electrons in d-orbitals and the nitrogen removal in aluminum is associated with a steric effect.  相似文献   

20.
Micro-arc oxidation (MAO) is an effective approach to improve the properties of aluminum and its alloy by forming ceramic films on the surface. However, the oxide layers often have a porous surface structure, which exhibits relatively high friction coefficients. In this work, in order to enhance the surface and mechanical properties of the films produced by micro-arc oxidation, Al2O3 coatings embedded with Fe micrograins of different thicknesses were produced on aluminum alloys by adding Fe micrograins into the electrolyte during MAO. Compared to the Al2O3 coatings without Fe micrograins, the MAO Al2O3 coatings with Fe micrograins are much denser and harder, and the wear resistance is also improved significantly. The enhancement can be attributed to the enhancement of the surface structure and morphology of the MAO Al2O3 coatings with embedded Fe micrograins.  相似文献   

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