A dry powder deposition technique, namely electrostatic spray deposition (ESD), has been investigated for cathode fabrication of Li-ion battery. The specific features focused in this study were to prepare core/shell composite particles and examine their applicability for ESD. LiCoO2 (LCO) was chosen as a cathode active material. Around the LCO particle, carbon nanoparticles as conductive additive were coated, followed by PMMA nanoparticles as binder additive, producing core/shell composite particles. The nanoparticle-coated unevenness on the LCO was capable of significantly improving the fluidity of the cohesive LCO particles. The composite particles also showed a good electrostatic charging ability. In addition, the PMMA nanoparticles in the outermost layer of the composite particles played a crucial role on a stable electrostatic deposition. Thus, LCO-based cathode film was successfully fabricated by ESD using the composite particles.
Carbon fiber reinforced thermoplastics, which consisted of the polyamide 6 as the matrix and 20wt% carbon fiber, and A5052 plates were directly joined by the friction lap joining method. A continuous joined interface of A5052/CFRTP joint was obtained at various tool rotation speeds ranging from 1000 to 2500 rpm. These materials were joined by bonding of MgO oxide layer of A5052 and PA6 as the matrix of the CFRTP. Voids were observed in the CFRTP at the interface of the joint, and its quantity increased with increasing tool rotation speed. The tensile shear fracture load of the FLJ joint increased with increasing the tool rotation speed from 1000 to 2000 rpm, and then it decreased. The fracture mainly occurred at the joint interface, however, some joints joined at the tool rotation speed of 2000 and 2500 rpm showed the CFRTP base plate fracture.
Welding heat sources are determined by the welding processes. The distribution characteristics of welding heat sources have a significant influence on the welding molten pool and weld metal solidification process, which determine the microstructures and their mechanical properties. If interest is focused only on the temperature distributions and thermal cycles for the efficient analysis of welding thermal stress and strain, welding heat sources can be simplified to satisfy engineering applications. For this purpose, the basic heat source models for theoretical solutions and numerical analysis of heat conduction, nonlinear finite element methods for welding thermal stress/strain as well troubleshooting in numerical simulations are presented in this section.
The objectives of this study is to clarify the relationship between melt flow and spatters ejected from a molten pool during 10 kW laser welding of a pure titanium plate. Three-dimensional X-ray transmission in-situ observation of the weld molten pool with tungsten carbide tracers revealed that the melt flowed mainly along the bottom of the molten pool from the keyhole tip to the rear part and then from the rear to the front near the surface of the molten pool, while the melt in front of a keyhole flowed upwards along the keyhole wall at a velocity of less than 0.6 m/s and then was accelerated to 2.1 m/s at the height of about 2 mm above the keyhole inlet. One-way upward melt flows were continuously piled up at the tip of the elongated melt, resulting in spattering as droplets from the molten pool. Moreover, about 80 % of spatters were generated from melts of the front or sides of the keyhole at the speeds of less than 50 mm/s. When the welding speed increased from 50 100 mm/s to 300 mm/s, the ratio and the size of spatters occurring from the rear part of a keyhole increased from 20% to 80 % and became smaller than 1 mm.
Microstructures and mechanical properties of ultrafine grained twinning induced plasticity (TWIP) steels, which were welded by both friction stir (FS) welding and conventional tungsten inert gas (TIG) welding, were studied. The ultrafine grained microstructure was successfully obtained by cold-rolling to a reduction in thickness of 88 % and subsequent annealing at a warm temperature (620 °C). Kikuchi line analysis in Transmission Electron Microscope (TEM) clarified that most of the grain boundaries in the annealed specimen are high angle grain boundaries whose misorientation angle is larger than 15 °. The TIG welding of the ultrafine grained TWIP steel produces coarse grains whose mean grain size is 70 m. On the other hand, the joint of the FS welded sample exhibits ultrafine grains with a high density of dislocations, and retains high hardness of the base metal. These results suggest that FS welding is an appropriate process for the joining of the ultrafine grained TWIP steels. The microstructure evolution during the FSW was discussed with focus on the temperature dependence of the stacking fault energy of the TWIP steel. The tensile deformation of the parts of these joints were also examined at room temperature.
This research investigated the direct bonding mechanism of dissimilar materials such as metals and plastic by the conventional hot pressing process. The press area of 4 x 4 mm2 was used for direct bonding. The results of the study showed that titanium was completely bonded to polyamide 66. On the other hand, titanium was not bonded to polystyrene. In the case of bonding material of titanium with polyamide 66, and oxide layer of about 20 nm as reaction layer was confirmed on the bonding interface by transmission electron microscope observation. It was considered that the origin of this oxide layer was due to oxygen constituting amide groups with C=O double bond in the polyamide 66.
The cleaning action in AC TIG welding is attributed to the oxide film removal process caused by cathode spots. Clarifying the behavior mechanism of these cathode spots will enable the control of the cleaning action. However, the behavior mechanism of cathode spots has not yet been experimentally clarified. This study reports that observations by high-speed video camera revealed the absence of cathode spots at the center of the molten pool, when shot in the vicinity of a molten pool after AC TIG welding using helium as shield gas on aluminum plates.
A core–shell anode consisting of nickel–gadolinium-doped-ceria (Ni–GDC) nanocubes was directly fabricated by a chemical process in a solution containing a nickel source and GDC nanocubes covered with highly reactive {001} facets. The cermet anode effectively generated a Ni metal framework even at 500 °C with the growth of the Ni spheres. Anode fabrication at such a low temperature without any sintering could insert a finely nanostructured layer close to the interface between the electrolyte and the anode. The maximum power density of the attractive anode was 97 mW cm–2, which is higher than that of a conventional NiO–GDC anode prepared by an aerosol process at 55 mW cm–2 and 600 °C, followed by sintering at 1300 °C. Furthermore, the macro- and microstructure of the Ni–GDC-nanocube anode were preserved before and after the power-generation test at 700 °C. Especially, the reactive {001} facets were stabled even after generation test, which served to reduce the activation energy for fuel oxidation successfully.
In the present study, to increase the carrier density of n-GaN, the formation of N-vacancies are attempted by interfacial reaction and by Ar ion irradiation. The microstructure and electrical properties after the interfacial reaction and Ar ion irradiation were then analyzed by TEM and DC conduction tests. The TEM result indicates that Ti2N is formed adjacent to the GaN substrate after the deposition of Ti film. The Ti2N formation indicated that a huge amount of N-vacancies is formed within the subsurface of GaN. The electrical conduction profile reveals that even with the formation of Ti2N, ohmic conduction is achieved. It is likely due to the formation of N-vacancies by interfacial reaction to form Ti2N and Ar ion irradiation. By prolonging the Ar ion irradiation, further improvement of electrical conductivity is achieved. This result indicated that the amount of N-vacancies formation within the GaN subsurface are depending to the Ar ion irradiation times. However, by performing Ar ion irradiation for 3600 s, no further improvement is achieve. It is likely due to phase transformation from GaN to Ga-rich phase at the GaN subsurface. The Ga-rich phase enhance the Ga-Ti compound, which increase the height and width of the Schottky barrier, thus reduce the electrical conductivity.
We present here analysis of the discharge characteristics of a non-thermal plasma jet, where the surrounding gas condition of the plasma jet is precisely controlled in open air. The mixing of the surrounding gas into the plasma jet markedly changes the discharge characteristics: the optical emission intensity of N2+ linearly increases with an increase in gas flow ratio of N2 to O2 in the surrounding gas. Our experiments clearly demonstrate that the plasm jet could be controlled from O2 main discharge to N2 main discharge by changing the surrounding gas condition even in open air.
In this study, the effect of adding 0.5 and 1 wt% In to Sn–58Bi solder on intermetallic compound (IMC) layers at the interface and the microstructure of the solder alloys were investigated during reflow and thermal aging by scanning electron microscopy. The results showed that the addition of minor elements was not effective in suppressing the IMC growth during reflow; however, the addition of 0.5 wt% In was effective in suppressing the IMC layer growth during thermal aging. The results also showed that the minor addition of In can significantly suppress the coarsening of the Bi phase.
Welding residual stresses are one of the main factors influencing the engineering properties of welded structures, and should be taken into account during designing and manufacturing different products such as ships, bridges, etc. The contour method is one of the new powerful stress measurement techniques that is used for measuring residual stresses. In this method a welded component is cut normal to the weld line. Displacements normal to the cut surface are measured. Using the finite element method (FEM), residual stresses before the cut are then reconstructed from the measured displacements. However after cutting the part of interest, only displacements normal to the cut surface can be measured while in-plane displacements cannot be measured. Therefore, the main objective of this paper is to examine the influence of in-plane displacements on the quality of reproduced residual stresses using numerical simulation. In this paper, a computational approach is developed to numerically simulate the contour method. Welding residual stresses are evaluated when conventional and low transformation temperature (LTT) weld wires are used. Phase transformation is considered for LTT welds. The developed computational approach is then used to simulate the contour method and reconstruct the residual stresses using 1) both normal and in-plane displacements, and 2) using only normal displacements. Simulation results show a very good agreement between welding residual stresses as originally computed and the reproduced stresses when in-plane displacements are considered. Additionally, application of only the displacement normal to the cut surface; reproduces stresses with a good agreement with welding residual stresses and those reproduced considering in-plane displacements.
Ceramic dendrite structures with geometrically ordered lattices had been created successfully by using a laser scanning and micro patterning stereolithography of spatial joining techniques. Micro rods of alumina, zirconia, titania and hydroxyapatite were connected to realize four, six, eight and twelve coordination numbers for fluctuation modulations of electromagnetic wave, electronic current propagation, heat diffusion, stress distribution, liquid flow and gas dispersion. Intensity profiles of these energy fields and material densities were visualized theoretically though finite element methods to compare with measured results. Technological concepts of these ceramic dendrites will be applied to novel censor devices, composite materials, solid electrodes and biological implants in near future industrial and medical fields. In this paper, fabrication processes of ceramic dendrites and numerical simulations of spatial gas flows, electromagnetic wave propagations and biological fluid flows will be discussed for novel energy harvesting devices and biocompatible implants.
