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Zhao X.,Zhengzhou Institute of Aeronautics | Yang X.-L.,Zhengzhou Zhongxing Basic Constructions Development Co Ltd | Jing T.-F.,State Key Laboratory of Metastable Materials Science and Technology
Journal of Iron and Steel Research International | Year: 2011

The hot deformation characteristics of ductile iron are studied in the temperature range of 973 to 1273K and strain rate range of 0. 001 to 1 s-1 by using hot compression tests. Processing maps for hot working are developed on the basis of the variations of efficiency of power dissipation with temperature and strain rate. The results reveal that the flow stress of ductile iron is sensitive to strain rate. In the processing map under strain of 0. 7, a domain is centered at 1273 K and 1 s-1, and the maximum efficiency is more than 36%. According to the maps, the zone with the temperature range of 1173 to 1273 K and strain rate range of 0.1 to 1 s-1 may be considered as the optimum region for hot working. © 2011 Central Iron and Steel Research Institute.


Zhao X.,Zhengzhou Institute of Aeronautics | Yang X.-L.,Zhengzhou Zhongxing Basic Constructions Development Co. | Jing T.-F.,State Key Laboratory of Metastable Materials Science and Technology
Journal of Iron and Steel Research International | Year: 2012

In order to investigate the effect of initial microstructure on warm deformation behavior, some specimens of 45 steel were annealed and some quenched. Then the specimens were isothermally compressed on a Gleeble 3500 machine. The deformation temperature range was 550 to 700°C and the strain rate range was 0.001 to 0.1 s -1. An optical microscope (OM) and a transmission electron microscope (TEM) were used to study the microstructures. The results show that the microstructure of annealed specimens is ferrite and pearlite and that of quenched specimens is martensite. The flow stress of quenched specimens is higher than that of annealed ones at 550°C when strain rates are greater than 0.001 s -1. However, at 600 to 700°C and strain rate of 0.001 s -1, the whole flow curves of quenched specimens are below that of annealed ones. Under the rest conditions, the flow stress of quenched specimens is higher at the beginning of compression and then the opposite is true after the strain is greater than a critical value. The microstructure examination proves that the tempering and dynamic recrystallization easily occur in the specimens with martensite during warm compression, which results in the above phenomena. © 2012 Central Iron and Steel Research Institute.


Fu R.-D.,State Key Laboratory of Metastable Materials Science and Technology | Sun R.-C.,State Key Laboratory of Metastable Materials Science and Technology | Zhang F.-C.,Yanshan University | Liu H.-J.,Harbin Institute of Technology
Welding Journal | Year: 2012

The weld, ambient temperature, and direction of a friction stir welding (FSW) tool play roles as important as that of the welding parameters in the FSW process. On the assumption that the weld parameters are the same under different directions, the joint welded using a stir tool rotated in a counterclockwise direction exhibits better formation quality than does the joint welded in a clockwise direction. The formation quality of the joints welded underwater clearly improves compared with that of the joints welded in air. Excellent weld joints free from defects are obtained in the present range of the FSW parameters for joints welded underwater and the stir tool rotated in the counterclockwise direction. The investigation of the flow path of the softened metal around the FSW tool reveals that the flow pattern of the softened metal driven by the shoulder and the pin varies with the rotational direction of the FSW tool, weld ambient temperature, and weld parameters. An excessively high weld input is detrimental to sound flow and avoidance of weld defects. By contrast, moderately decreasing the ambient temperature around the weld zone can improve the formation quality of the weld joints, regardless of the other weld conditions.


Rui-dong F.,State Key Laboratory of Metastable Materials Science and Technology | Rui-dong F.,Yanshan University | Zeng-qiang S.,State Key Laboratory of Metastable Materials Science and Technology | Rui-cheng S.,State Key Laboratory of Metastable Materials Science and Technology | And 3 more authors.
Materials and Design | Year: 2011

Submerged friction stir welding (FSW) in cold and hot water, as well as in air, was carried out for 7050 aluminum alloys. The weld thermal cycles and transverse distributions of the microhardness of the weld joints were measured, and their tensile properties were tested. The fracture surfaces of the tensile specimens were observed, and the microstructures at the fracture region were investigated. The results show that the peak temperature during welding in air was up to 380 °C, while the peak temperatures during welding in cold and hot water were about 220 and 300 °C, respectively. The temperature at the retreated side of the joint was higher than that at the advanced side for all weld joints. The distributions of microhardness exhibited a typical "W" shape. The width of the low hardness zone varied with the weld ambient conditions. The minimum hardness zone was located at the heat affected zone (HAZ) of the weld joints. Better tensile properties were achieved for joint welded in hot water, and the strength ratio of the weld joint to the base metal was up to 92%. The tensile fracture position was located at the low hardness zone of the weld joints. The fracture surfaces exhibited a mixture of dimples and quasi-cleavage planes for the joints welded in cold and hot water, and only dimples for the joint welded in air. © 2011 Elsevier Ltd.


Fu R.,State Key Laboratory of Metastable Materials Science and Technology | Fu R.,Yanshan University | Xu H.,Yanshan University | Luan G.,Beijing FSW Technology Ltd Company | And 4 more authors.
Materials Characterization | Year: 2012

We characterized the microstructures on the top surface of friction-stir welding (FSW) joints of AA2524 aluminum alloys with Alclad. Types, distributions, dissolution and precipitation behaviors of the precipitates in different regions of the joints were investigated. The results show that the as-polished surface microstructures under the shoulder of the FSW tool exhibited "arc strip" feature. The Alclad on the outer surface of the plate was destroyed during FSW, and the residual Alclad was enriched in the retreating side of the FSW joint. The main precipitates in the FSW joint were composed of Guinier-Preston (GP) zones and θ′ (Al 2Cu), S′ (Al 2CuMg) and Fe-containing phases. In the heat-affected and thermal-mechanical-affected zones, coarsening occurred in some S′ phases. In the GP zone, some S″ phases were transformed into stable S′ or S phases. In the nugget zone, the density of the precipitates decreased due to the dissolution of some S′ or S phases back into the matrix during the weld-heating period, whereas during the weld-cooling period, the refined and dispersed unstable GP zones or S″ phases reprecipitated. © 2012 Elsevier Inc. All rights reserved.


Kang J.,Yanshan University | Fu R.-d.,State Key Laboratory of Metastable Materials Science and Technology | Fu R.-d.,Yanshan University | Luan G.-h.,Beijing FSW Technology Ltd Company | And 2 more authors.
Corrosion Science | Year: 2010

The surface corrosion behavior of an AA2024-T3 aluminium alloy sheet after friction stir welding was investigated by using an "in-situ observation" method. SEM observations showed that the density and degree of the pitting corrosion in the shoulder active zone were slightly larger compared to the other regions on the top surface. The origins of the pitting corrosion were in the regions between the S phase particles and the adjacent aluminium base. The effect of Al-Cu-Fe-Mn-(Si) intermetallic compounds on the pitting corrosion was attributed to their high self-corrosion potential which induced the anodic dissolution of the surrounding aluminium matrix. © 2009 Elsevier Ltd. All rights reserved.


Zhao X.,Zhengzhou Institute of Aeronautics | Jing T.F.,State Key Laboratory of Metastable Materials Science and Technology
Materials Science and Engineering A | Year: 2012

Specimens with ferrite+pearlite (F+P) and martensite (M) microstructures were compressed under warm conditions. The flow curves of quenched specimens were below those of annealed specimens at 873-973K (600-700°C) and a strain rate of 0.001s -1. This was due to the tempering and dynamic recrystallization of martensite. © 2012 Elsevier B.V..


Zhao H.,State Key Laboratory of Metastable Materials Science and Technology | Zhao H.,Yanshan University | Kiwi J.,Ecole Polytechnique Federale de Lausanne | Pulgarin C.,Ecole Polytechnique Federale de Lausanne | Yang J.,Yanshan University
International Journal of Applied Glass Science | Year: 2013

Fluorine-doped tin oxide (FTO) films were deposited on float glass to create low-emissivity glass (low-E glass) by atmospheric pressure chemical vapor deposition (APCVD). Heat treatments were carried out to assess its antioxidant properties. The surface morphology, crystal structure, and the oxygen and tin concentrations in the FTO films were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), Auger electron spectrometer (AES), and X-ray photoelectron spectroscopy (XPS), respectively. The results indicated that the electrical properties determined by the four-point probe method remained constant up to 600°C with increasing temperature. The FTO films exhibited nonstoichiometry with a ratio of [O]/[Sn] >2 on the top surface and <2 in the film. The sheet resistance of the film strongly depended on the oxygen concentration on the film surface. When the heating temperature reached 700°C, the sheet resistance increased rapidly from 9.4 to 86.7 Ω/□ with a concomitant increase in the oxygen concentration on the top surface. © 2013 The American Ceramic Society and Wiley Periodicals, Inc.


Ma Z.,Yanshan University | Shao G.,Yanshan University | Shao G.,State Key Laboratory of Metastable Materials Science and Technology | Wang G.,Yanshan University | And 2 more authors.
Journal of Solid State Chemistry | Year: 2014

Abstract The olivine-type niobium doping Li1-xNb xFePO4/C (x=0, 0.005, 0.010, 0.015, 0.025) cathode materials were synthesized via a two-step ball milling solid state reaction. The effects of Nb doping were charactered by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), galvanostatic intermittent titration technique (GITT), cyclic voltammetry (CV), electrochemical impedance spectra (EIS) and galvanostatic charge-discharge. It is found that Nb doping enlarges the interplanar distance of crystal plane parallel to [0 1 0] direction in LiFePO4. In other words, it widens the one dimensional diffusion channels of Li+ along the [0 1 0] direction. Electrochemical test results indicate that the Li0.99Nb0.01FePO4/C composite exhibits the best electrochemical performance with initial special discharge capacity of 139.3 mA h g-1 at 1 C rate. The present synthesis route is promising in making the solid state reaction method more practical for preparation of the LiFePO4 material. 7copy; 2013 Published by Elsevier Inc. All rights reserved.


Qin X.-J.,Yanshan University | Qin X.-J.,State Key Laboratory of Metastable Materials Science and Technology | Han S.-H.-Z.,Yanshan University | Zhao L.,Yanshan University | And 2 more authors.
Wuji Cailiao Xuebao/Journal of Inorganic Materials | Year: 2011

Al-doped ZnO thin films were prepared by aerosol-assisted chemical vapour deposition (AACVD) on glass substrates. The effect of Al content (2at%-8at%) on the structural, optical and electrical properties of Al-doped ZnO thin films was investigated in detail. The samples were tested by XRD, SEM, EDAX and UV-Vis spectrophotometer. The results indicate that the AZO films have a hexagonal (wurtzite) structure without preferential orientation along c-axis, and however no Al related phases are observed. The average transmittances of the AZO film is over 72% in the visible regions. The optical band gap for the AZO films becomes narrow with the increasing Al dopant. The four-point probe technique is used to characterize thin films electrically. The data shows that Al dopant decrease the sheet resistance. The ZnO films doped with 6at% Al exhibit a minimum of sheet resistance (18 Ω/□).

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