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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.

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.

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.

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: 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.

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