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《International Journal of Heat and Mass Transfer》2007,50(9-10):1805-1822
The effects of turbulence on momentum, heat, and mass transfer during laser welding of a copper–nickel dissimilar couple are studied by carrying out three-dimensional unsteady Reynolds Averaged Navier Stokes (RANS) simulations. The turbulent transport is modelled by a suitably modified high Reynolds number k–ε model. The solid–liquid phase change is accounted for by a modified enthalpy porosity technique. In order to demonstrate the effects of turbulence, two sets of simulations are carried out for the same set of processing parameters: one with the turbulence model, and the other without activating the turbulence model. The enhanced diffusive transport associated with turbulence is shown to decrease the maximum values of temperature, velocity magnitude, and copper mass fraction in the molten pool. The effects of turbulence are found to be most prominent on the species transport in the molten pool. The composition distribution in turbulent simulation is found to be more uniform than that obtained in the simulation without turbulent transport. The nickel composition distribution predictions, as obtained from the present turbulence model based simulations, are also found to be in good agreement with the corresponding experimental results. 相似文献
84.
Vladimir An Farabi Bozheyev Franck Richecoeur Yuri Irtegov 《Materials Letters》2011,65(15-16):2381-2383
Tungsten and molybdenum disulfides were produced in direct self-sustained combustion in argon between elementary sulfur and metal (W, Mo) nanopowders prepared by electrical explosion of wires. The results of XRD analysis show that the main phases of the synthesized nanopowders are hexagonal WS2 and MoS2. According to SEM and TEM observations, they are agglomerated nanolamellar particles of thickness 40–150 nm and width 100–3000 nm. 相似文献
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In this study, microstructures and mechanical properties of A356 aluminum alloy obtained by expendable pattern shell casting process with vacuum and low pressure (EPSC-VL) were investigated. Meanwhile, microstructures and mechanical properties of A356 alloy among EPSC-VL, expendable pattern shell casting process under gravity casting (EPSC-G), lost foam casting with vacuum and low pressure (LFC-VL) and lost foam casting under gravity casting (LFC-G) were compared. The results showed that the microstructure of A356 alloy fabricated by EPSC-VL was finer and denser than the products from EPSC-G, LFC-G and LFC-VL processes, and its grain size was only 147.2 μm compared to LFC-G (327.1 μm). Moreover, its porosity defects were greatly reduced (0.16%) compared to LFC-G (1.97%). The tensile strength, elongation and hardness of castings produced by EPSC-VL were all considerably higher than the products from EPSC-G, LFC-G and LFC-VL. The A356 alloy made by EPSC-VL exhibited morphology of dimple fracture that was very deep and well-distributed. In addition, the castings produced by EPSC-VL process had better surface quality compared to LFC castings. 相似文献
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The aim of this research was to examine the effect of microstructural parameters on the tensile properties of dif- ferent compositions of tungsten heavy alloys. The microstructural parameters (grain size, connectivity, contiguity, and solid volume fraction) were measured and were found to have a significant effect on the tensile properties of tungsten-based heavy alloys. The microstructural parameters of W-Ni-Fe alloys are sufficiently different to present a range of me- chanical properties. It is concluded that the mechanical properties of tungsten heavy alloys largely depend on the micro- structural parameters and their ductility is particularly harmed when grains are contiguous. 相似文献
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Bismuth selenide thin films were grown on Pt substrate via the route of electrochemical atomic layer epitaxy (ECALE) in this work for the first time. The electrochemical behaviors of Bi and Se on bare Pt, Se on Bi-covered Pt, and Bi on Se-covered Pt were studied by cyclic voltammetry and coulometry. A steady deposition of Bi2Se3 could be attained after negatively stepped adjusting of underpotential deposition (UPD) potentials of Bi and Se on Pt in the first 40 deposition cycles. X-ray diffraction (XRD) analysis indicated that the films were single phase Bi2Se3 compound with orthorhombic structure, and the 2:3 stoichiometric ratio of Bi to Se was verified by EDX quantitative analysis. The optical band gap of the as-deposited Bi2Se3 film was determined as 0.35 eV by Fourier transform infrared spectroscopy (FTIR), which is consistent with that of bulk Bi2Se3 compound. 相似文献