Papers by Author: Peng Wan Chen

Abstract: In this investigation, thin Aluminum alloys 2A12 and Copper T2 composite plates which are both 1mm thick were obtained successfully by the method of explosive welding. The effect of annealing on the interface microstructures of the composite plates was investigated under different temperatures. Optical microscopy, scanning electron microscopy, micro-hardness test and bending test were performed. The results demonstrated that the Al/Cu composite plates were bonded well. The bonding interface of the Al/Cu composite plates had a wavy form. Micro-hardness measurements showed that the hardness of the composite plates near the interface was higher than other parts and the hardness of the whole composite plates was lower after annealing. The bending test showed the composite plates can be deformed or shaped.

Abstract: The research on the explosive compaction of reactive powders is a hot issue. In this work, unreacted Ti-Si block with high compactness has been successfully fabricated under explosive-driven compaction process. The precursors of Ti-Si powder with different stoichiometric ratios undergo pre-compaction shaping by hydraulic press and then shock loading treatment by using low-detonation-velocity explosives of varying loading conditions. The results show that the chemical reaction between Ti and Si powders are partly initiated even under low detonation pressures, indicating extremely low reaction threshold in the Ti-Si system. Meanwhile, optimal experimental conditions are displayed as the initial pressing compactness degree of 61%, and shock pressure of 11GPa. A compactness of 97% is achieved in the synthesized Ti-Si block with the lowest reactivity.

Abstract: AlN nanopowders are successfully synthesized via electrical Al wire explosion in liquid nitrogen. After pickling in 15 % HCl-ethanel, the purified AlN nanopowders are characterized by various techniques. It is observed that the synthesized AlN nanoparticles are hexagonal AlN (h-AlN) exhibiting various shapes, including sphere, spheroidicity, polygon and hexagon. The results show that the charging voltage affects on the AlN content and the morphology of samples, significantly. Further more, it is observed that synthesized AlN particles in the size of 100-300 nm are coated by an amorphous layer mostly resulted from the high cooling rate in liquid nitrogen.

Abstract: In the present research work the determination of residual stress distribution in welded non-oriented electrical steel samples is discussed. Tungsten Inert Gas and Electron Beam Welding were used as the welding methods. The residual stresses induced by welding estimated by the magnetic, non-destructive method of Barkhausen noise and were compared with the values resulting from the semi-destructive method of X-ray diffraction Bragg-Brentano (XRD-BB). In order to evaluate accuracy and reliability of the magnetic methods applied, the steel samples were subjected in both compressive and tensile stress and the magnetic noise values were correlated to residual stress values through an appropriate calibration curve. Furthermore, the fluctuations of the residual stresses in the welding zones of the welded samples were discussed on the basis of the experimental evidence and the microstructural changes occurring during welding. It was found that the residual stress determined by MBN method was in good agreement with the XRD-BB results. However, the residual stress determined by magnetic permeability method was not in good agreement with the XRD-BB results. In contrast to the XRD-BB method, the magnetic techniques required a precise calibration procedure in all zones with noticeably different microstructure.

Abstract: Explosive welding is an efficient method for metals welding. However, in explosive welding, the shock wave generated by the explosion can not only damage the sensitive structure in the area of the process, but also can actually destroy a welded joint immediately after its creation. By placing an additional structure (anvil) can reduce the influence of shock waves. The influence of different anvil on the explosive welding of aluminum and magnesium plates has been investigated by using AUTODYN Software in this paper. The results show that the steel anvil is much more appropriate than sand and magnesium.

Abstract: High-temperature shock consolidation and under-water shock wave are two effective methods to eliminate cracks generated when shock wave propagating the powder bed. In this work, a novel assembly consists of a chemical furnace and a water column was used to fabricate tungsten-copper composites. The heat released from the reaction of a SHS reaction mixture was used as chemical furnace to preheat the precursor powder. The water column as well as the explosive attached was detached from the furnace by a solenoid valve fixed on the slide guide. So the explosive and water column was kept cooling during the preheating process. The W-Cu powders with the grain size of 2μm were first blended with mass ratio of 9:1 by mechanically alloying in a planetary ball mill. Prior to application of shock wave, the elemental powders were preheated at different temperatures, i.e. the highest temperature up to 1000°C. The intensity of the shock wave loading was under 10GPa. The consolidated specimens were then characterized by microstructure analysis and micro-hardness testing. The different micromechanical behaviors of W and Cu phase in the consolidated sample were studied by using in situ high-energy X-ray diffraction technique. The result showed that a fine-grained 90W/10Cu composite with no cracks could be compacted to a density of 16.44g/cm3 by hot-shock consolidation at a preheating temperature of 970°C.

Abstract: Moiré grating is a basic optical component, and can be used in various moiré methods. The conventional grating fabrication technology is based on photolithography and holographic interferometry, however, it requires complex optical components and is very difficult to put into practice. In this study, nanoimprint lithography (NIL), or rather, hot embossing lithography (HEL), is proposed for producing high frequency grating. Compared with silicon mold, holographic moiré grating mold costs less and is not easy to break, thus is chosen to be the mold in HEL. Using this mold and the hot embossing system, the grating structure can be transferred to the polymer after HEL process. Through a number of experiments, the process parameters were optimized and gratings were successfully fabricated. The multi-scale morphology of the fabricated gratings was then characterized by scanning electron microscope (SEM), atomic force microscope (AFM) and moiré interferometry. The microscale images observed by AFM and SEM show the regulate dots with equal spacing and the macroscale moiré patterns illuminate the excellent qualities of fabricated grating in a large area. The successful experimental results demonstrate the feasibility of the grating fabricated by HEL for the moiré measurement.

Abstract: A possible new phase of carbon nitride was synthesized by shock wave using a precursor of mixture of graphitic carbon nitride (g-C3N4) with iron powder in a weight ratio of 10:90 at the flyer velocity of about 3.0 km/s driven by explosive detonation. The results of XRD and TEM indicate that the new phase possesses four weak diffraction peaks at 2=36.06 (d=2.489Å), 41.90(d=2.154Å), 60.88(d=1.520Å) and 72.98(d=1.295Å) besides a strong diffraction peak of graphitic carbon nitride at 2=27.70 (3.218 Å) and shows a few tube-like structures in a diameter of about 200300nm and in a length of about 10003000nm with the exclusive element composition of carbon and nitrogen identified by EDX characterization.

Abstract: Different TiO2 precursors were impacted by detonation-driven high velocity flyers to obtain high-pressure phases of titania under instantaneous high temperature and pressure. The factors affecting high-pressure phase synthesis such as loading conditions and titanium dioxide precursors were also studied. The structure and phase composition of the shocked samples are determined by X-ray diffraction (XRD). The microstructure of TiO2 after shock treatment was observed by transmission electron microscopy (TEM).

Abstract: In this paper, nitrogen-doped titania was achieved by detonation-driven flyer impacting on the mixtures of TiO2 and different nitrogen precursors. XRD、UV-Vis and XPS spectra were employed to characterize the phase composition, N doping concentration and energy gap of recovered samples. N doping concentration can be effectively regulated by choosing different doping nitrogen resources, changing initial content of doping nitrogen resources and flyer velocity in order to regulate the energy gap of TiO2. The maximum concentration of nitrogen of doped TiO2 by shock loading at 3.37 km/s is 13.45 at%. The results show that anatase transforms to rutile and srilankite appears at a higher flyer velocity (1.9-2.52km/s), the concentration of doped nitrogen in the recovered samples increases with increasing flyer velocity, the maximum concentration of nitrogen is 13.45 at%. The edge adsorption wavelength of nitrogen-doped titania induced by shock wave is shifted from 435nm to 730 nm and the corresponding energy gap is reduced from 2.85 eV to 1.73 eV.