Abstract: An extreme thin SiC buffer and Ga2O3 layer were deposited on silicon substrate
sequentially with a r.f. magnetron sputtering system. Then the sample was annealed in the ambiance of ammonia at high temperature. Nanowires were found when the sample was tested with scanning electron microscopy (SEM). The composition of the nanowires is found to be GaN when the sample was tested with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). A nanowire
was observed with transmission electron microscopy and it was even and uniform, with diameter of about 60nm. And the nanowire can be testified of wurtzite single crystal structure by electron diffraction (ED) analysis attached to the TEM. The high-resolution transmission electron microscopy (HRTEM) analysis to the nanowire indicates that the nanowire was single crystal with very good quality.
Abstract: Relaxor-based piezoelectric single crystals of lead indium niobate-lead titanate
(0.63Pb(In1/2Nb1/2)-0.37PbTiO3, abbreviated as PIN-PT), in the vicinity of the morphotropic phase boundary, were prepared by a flux method. The compositions of the flux, Pb3O4 or PbF2, play different role in perovskite stability and phase development. Thus, pure perovskite PIN-PT single crystals with the size of 2~5 mm were obtained by using Pb3O4 flux as well as a small amount of B2O3
additive. The microstructure and the phase development of the as-grown single crystals were investigated by scanning electron microscopy and transmission electron microscopy and X-ray diffraction. Furthermore, the dielectric properties of the <100>-oriented PIN-PT single crystals were measured in the temperature range between 20°C and 400°C.
Abstract: With area detector X-ray diffraction system, the orientation of superconductor films and their relationships with substrates can be easily examined. For YBCO high temperature superconductor films having complex crystalline orientation relationship fore and after melting process, 2-dimesional X-ray diffraction provides us much more information than common X-ray diffraction. This is very helpful for understanding the peritectic reaction during melting process because the growth mechanism of Y211 crystalline can be explained from its orientation information. Y211 phrase in the film and its orientation relationship with YBCO phase and MgO
substrate have been analyzed at first. It is found that Y211 crystalline is well match with both MgO substrate and YBCO parent phase. Then the melting process of YBCO has been discussed from the view of the orientation relationship between each phase.
Abstract: Under high impact energy, nano-structured surface layers of Hadfield steel and annealed AISI 1045 steel were investigated in the present paper. It has been observed that a so-called “black layer” for Hadfield steel and “white layer” for AISI 1045 steel has been formed, respectively. That definitely will give rise to a change of wear mechanism. The wear tests showed that the wear weight
loss curve of Hadfield steel will be bent down after some critical impact numbers. The wear curve of the AISI 1045 steel, however, shows a step-like characteristic with increasing impact numbers. It can be found from microstructural examination that high density twin bands of subsurface for Hadfield steel were produced, which have good plastic deformation coordination with bulk material. Cracks are usually initiated in the “black layer” underneath 12 µm in depth, and the worn debris
sizes were also observed in nano-scale. Nano scaled wear controls the whole wear process. For the annealed AISI 1045 steel, cracks are mainly initiated between the interface of the “white layer” and sub-surface deformation layer. Debris is in micron-scale and spalled in the flake-like style. The wear weight loss is, therefore, greater than that of Hadfield steel. The result showed from the wear tests of Hadfield steel and AISI 1045 steel that nanocrystalized process of subsurface becomes one of control factors to affect wear losses and wear mechanism under high impact energy.
Abstract: The fracture behavior under high-loading velocity and at high temperature was
investigated using tensile testing system for a shape memory alloy. Both SEM and X-Ray were used to examined the testing sample before and after tensile testing. It was found that the fracture behavior shows some similar tendency between at high-loading velocity and high-temperature. Based on the results, it can be confirmed that the shape memory alloy can be used to develop high performance intelligent material with high-impact resistance.
Abstract: Conventional multi-step extrusion processes with solid billet are examined by the
rigid-plastic finite element method in order to provide criteria for new process sequence for hollow parts. Two examples are taken for the analyses such as the current three-stage cold extrusion process for a hollow flange part and five-stage process for manufacturing an axle housing. Based on the results of simulation of the current three-stage and five-stage manufacturing processes, new design
strategy for improving the process sequences is developed simply by replacing the initial billet from solid to hollow one. The developed new process sequences are applied for simulation by FEM and they are compared with the existing processes to confirm the usefulness of new process sequences with hollow initial billets. The results of simulation show that the newly proposed process sequences
with hollow billet instead of solid one are more economical way to manufacture required parts, respectively.
Abstract: Nanoindentation test has been performed to characterize the mechanical properties of aluminium alloy foam cell wall. Two of the mechanical properties: hardness and Young’s modulus of cell wall material were evaluated using the stiffness of contact during both loading and unloading. Properties obtained from unloading stiffness were in better agreement with the conventional test result than those obtained from loading stiffness. The finite element analysis using nonlinear finite element code ABAQUS was performed to characterize the yield strength and the stress-strain curve of the cell wall material of the foam. Properties of foam cell wall material were found to be substantially different from the properties of the material before foaming. The methodology used in this paper can be effectively used to characterize the mechanical properties of cell wall of any cellular material.
Abstract: Radially extruded tubular components are adopted for the deformation analysis by
rigid-plastic finite element method. FE Simulations were conducted to investigate the influence of different geometric parameters and process condition, such as the ratio between inner and outer diameter of tubular components, gap height, die corner radius and friction factor, on metal flow into radial direction. The results of the simulations are discussed in terms of separation length, defined as the length that the material flow is separated away from the die in gap height, and maximum force
requirements for the radial forming process. Furthermore the pressure distributions exerted on the die-wall interfaces and deformation pattern was shown to obtain the features in producing sound radial extruded components. Finally some guidelines for basic design data in the radial extrusion process due to this simulation work might be drawn up.
Abstract: There is a need to destroy both military and civilian hazardous waste and urgency,
mandated by public concern over traditional waste handling methodologies, to safe and efficient alternative technologies. One very effective process for the destruction of such waste is supercritical water oxidation (SCWO). Nevertheless, corrosion of the materials of fabrication is a serious concern. This work intends to obtain the fundamental data for developing the corrosion resistant steel for the construction of SCWO system. The effects of various factors on the corrosion resistance of flat, welded, and U-bend 316L stainless steels in Trimsol solution were studied.
Corroded product on surface was composed of multi-layer with oxides and salts, and dealloying was observed. Major corrosion phenomena of 316L stainless steel under SCWO condition were intergranular corrosion, pitting corrosion, SCC, and erosion corrosion. This work focused on the elucidation of corrosion mechanism of 316L stainless steel in SCWO environment.
Abstract: In this study, the crack growth behavior in P92 steel (9%Cr-2%W) weldment was
investigated at 600ı under the load of trapezoidal wave shape with various holding times. The relationship between the crack growth behavior and holding time was studied and it was characterized using the ΔK and (Ct)avg parameters. The number of micro-voids/cavities at the crack tip and fracture modes were examined and the relationship between crack growth rate and holding time was investigated.