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Liu G.,National Key Laboratory for Precision Hot Processing of Metals | Liu G.,Harbin Institute of Technology | Wang J.,National Key Laboratory for Precision Hot Processing of Metals | Tang Z.,Nanjing University of Aeronautics and Astronautics | Wu Y.,National Key Laboratory for Precision Hot Processing of Metals
Key Engineering Materials | Year: 2014

A process with gas pressure up to 70MPa is introduced, which is called High Pressure Pneumatic Forming (HPPF), comparing to superplastic forming (SPF) with pressure lower than 5MPa. HPPF process can be used to form tube blank at lower temperature with high energy efficiency and also at higher strain rate than SPF. With Ti-3Al-2.5V Ti-alloy tube, the potential of HPPF was studied through experiment in the temperature range of 700~850?. To know the formability of the Ti-alloy tube, HPPF experiments of a large expansion tube and a square cross-section tube were carried out at different temperature and pressure. The limit expansion ratio and limit radius were measured to evaluate the forming limit of Ti-3Al-2.5V tube within HPPF. The results show that the lower the pressure, the better formability and the lower efficiency. At a constant pressure, the strain rate increases exponentially with bulging time during the free bulging procedure, but decreases exponentially during the small corner calibration. Through EBSD pictures, the deformation mechanism of the corner forming process in HPPF was analyzed. Because of a nonconstant strain rate deformation state and complicated stress and strain state during HPPF, the microstructure at the transition zone of the components are also nonhomogenous, but the grains are refined to a certain extent. © (2014) Trans Tech Publications, Switzerland. Source

Liu Z.,National Key Laboratory for Precision Hot Processing of Metals | Shuai J.,University of Houston | Geng H.,Harbin Institute of Technology | Mao J.,University of Houston | And 6 more authors.
ACS Applied Materials and Interfaces | Year: 2015

Microstructure has a critical influence on the mechanical and functional properties. For thermoelectric materials, deep understanding of the relationship of microstructure and thermoelectric properties will enable the rational optimization of the ZT value and efficiency. Herein, taking AgSbSe2 as an example, we first report a different role of alkaline-earth metal ions (Mg2+ and Ba2+) doping in the microstructure and thermoelectric properties of p-type AgSbSe2. For Mg doping, it monotonously increases the carrier concentration and then reduces the electrical resistivity, leading to a substantially enhanced power factor in comparison to those of other dopant elements (Bi3+, Pb2+, Zn2+, Na+, and Cd2+) in the AgSbSe2 system. Meanwhile, the lattice thermal conductivity is gradually suppressed by point defects scattering. In contrast, the electrical resistivity first decreases and then slightly rises with the increased Ba-doping concentrations due to the presence of BaSe3 nanoprecipitates, exhibiting a different variation tendency compared with the corresponding Mg-doped samples. More significantly, the total thermal conductivity is obviously reduced with the increased Ba-doping concentrations partially because of the strong scattering of medium and long wavelength phonons via the nanoprecipitates, consistent with the theoretical calculation and analysis. Collectively, ZT value ∼1 at 673 K and calculated leg efficiency ∼8.5% with Tc = 300 K and Th = 673 K are obtained for both AgSb0.98Mg0.02Se2 and AgSb0.98Ba0.02Se2 samples. © 2015 American Chemical Society. Source

Fan Z.,Harbin Institute of Technology | Yu H.,Harbin Institute of Technology | Yu H.,National Key Laboratory for Precision Hot Processing of Metals | Li C.,Harbin Institute of Technology | Li C.,National Key Laboratory for Precision Hot Processing of Metals
Journal of Materials Processing Technology | Year: 2016

Magnetic pulse cladding (MPC) technology, which is based on sequentially impact welding portions of long tubes, offers the distinct advantage of utilizing only a small amount of energy stored on the capacitor to fabricate bi-metal tubes. It remains necessary, however, to develop a method for successfully controlling and enhancing cladding quality during MPC. This paper provides insight into the plastic deformation behavior of bi-metal tubes subjected to progressive magnetic pulse force, using experiments with the FE method. The effect of the field shaper on the plastic deformation was also investigated to facilitate the field shaper design, where the parameters considered are the geometrical characteristics, known as the inclined angle α1 and α2 on the work zone of a field shaper. Results show that a bamboo-like shape produced on the outer surface of the clad tube was a result of inharmonious plastic deformation behavior. The modification of a field shaper by setting an inclined angle α2 works more effectively than shortening the feeding length in terms of improving bamboo-like shape, due to change in the magnetic field during the second step of the MPC process. Additionally, two kinds of typical plastic deformation responses corresponding to local and progressive collision patterns were identified during MPC. It was found that the inclined angle α2 and actively setting of inclined angle α1 at 3°on the work zone proved critical factors in determining plastic deformation response in the MPC process. These results demonstrate that the proposed numerical approach successfully elucidates fundamental details on critical behaviors during the MPC process, and can be used to assist process design. © 2015 Elsevier B.V. All rights reserved. Source

Yu H.,National Key Laboratory for Precision Hot Processing of Metals | Yu H.,Harbin Institute of Technology | Fan Z.,Harbin Institute of Technology | Li C.,National Key Laboratory for Precision Hot Processing of Metals | Li C.,Harbin Institute of Technology
Journal of Materials Processing Technology | Year: 2014

Bi-metal tubes, which combine the advantageous properties of two different metals, are desirable in industries where corrosion resistance is important. A new cladding method named magnetic pulse cladding (MPC) was used to form bi-metal tubes. A cladding of mild steel tube by aluminum alloy (AA3003) was achieved. The effect of the geometry of the field shaper on cladding quality was investigated as well as other main process parameters, such as, feeding size, radial gap and discharge voltage. The mechanical property was evaluated by compression-shear test and a maximum strength of 79.2 MPa and an average of 29.7 MPa were attained to by the following process settings: profiled field shaper, feeding size of 12 mm, radial gap of 2.0 mm and discharge voltage of 15 kV. OM and SEM images show a smooth integral interface and a small wavy one. EDS mapping reveals the interfacial diffusion zone up to 50-μm wide. The results show that the proposed MPC process is able to form sound cladding bonds and could be applicable to a tubular clad component with a high axial length. © 2013 Elsevier B.V. All rights reserved. Source

Liu W.,Harbin Institute of Technology | Liu W.,National Key Laboratory for Precision Hot Processing of Metals | Hao J.,Harbin Institute of Technology | Liu G.,Harbin Institute of Technology | And 4 more authors.
International Journal of Advanced Manufacturing Technology | Year: 2016

Hole hydro-piercing-flanging is a new hybrid technology by using high internal pressure as the support medium instead of rigid die. By this process, holes can be punched and flanged successively on hydroformed tubular parts without secondary positioning and fabrication. However, punch shape as an important factor has not been concerned enough so far. In this study, the influence of punch shape on geometrical profile and quality of holes was investigated both by experiments and simulations with three different shapes of transition zone between the piercing punch and the flanging punch. Results show that the geometrical size of roll-over depth, straight-wall height, and thickness varied with punch shapes. Considering the quality of the hole’s edge, ellipsoidal punch is the best one with the largest smooth zone and the least damage, but the conical punch gives the worst results. Finally, the mechanism of hydro-piercing-flanging process affected by the punch shape was clarified by the stress and strain distribution during plastic deformation by finite element analysis. © 2016 Springer-Verlag London Source

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