Advanced Materials Research Vols. 706-708

Abstract: The response characteristics of noble metal (platinum and palladium) modified TiO2 gas sensors were investigated, respectively. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the sensing films. In addition, the resistance of sensors response to oxygen partial pressure was discussed by Kroger–Vink model. The response properties indicated that Pt modified TiO2 was providing excellent response properties when the sensor exposed to hydrogen and oxygen. The response mechanism was suggested to arise from the activation energy (E) of the modified sensing films.

Abstract: Gas response properties of lithium doped (1%~8%) SnO2 sensing films were investigated when exposed to hydrogen gas. Sensors were prepared by thick film technique. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the crystal structure and grain size of the prepared materials. The gas response properties indicated that the response time reduces obviously with the Li-doping. It was found that 4 mol% Li-doped sensing film exhibits the best response characteristics. The response mechanism was suggested to arise from the conduction holes ionized by Li and the surface potential barrier change in target gas.

Abstract: The Ultimate Strength of 93WNiFe alloy was investigated by dynamic tensile testing with temperature ranges from 10 to 900 degrees. The ultimate strength of 93WNiFe alloy declined gradually as the temperature increased, and it appeared a protruding at the temperature 400~700°C. Deposition of ternary system alloy make the W-W, W-M interface of tungsten alloy improved.It was the reason of the protruding appeared in tungsten alloy.

Abstract: The growth kinetics and morphology of intermetallic compound (IMC) between Sn-3Ag-0.5Cu -xFe (x= 0, 0.5wt.%, 1wt.%) composite solders and Cu substrate were investigated in the present work. The Sn-Ag-Cu-Fe/Cu solder joint were prepared by reflowing for various durations at 250°C. During soldering process, Fe particles quickly deposited in the vicinity of IMC, resulting in the formation of Fe-rich area. It was shown that Fe could effectively retard the growth of interfacial Cu6Sn5 and Cu3Sn layers during liquid-state reaction and reduce the size of Cu6Sn5 grains. Small cracks were observed in the Cu6Sn5 grains of Sn-Ag-Cu/Cu interface after reflowing for 30 min while they were not found in the other composite solders.

Abstract: Ion beam etching can achieve nanometer size easily, processing in nanometer size, then put forward higher requirements on the workpiece surface. Ion beam etching is based on the Sigmund sputtering principle to remove the material, and the defects such as vacancies and interstitials in substrate material atomic lattice will be produced in this process. When these defects are enough, they lead to material damage. This paper is based on this effect to explore the effect of the processing parameters like Ar ion incident energy and incident angle of plasma beam on the implantation depth and the lattice change, through the SRIM software simulation which Ar ions used to the silica etching, moreover, forecast and put forward the suitable parameters for ion beam etching of nanocrystals on the workpiece, to produce the smaller nanowires damage.

Abstract: In this paper a phase transformation model with the temperature has been used to predict the percentage of phase at different temperature for TA15 titanium alloy during heat treatment. Heat treatment tests were conducted on TA15 samples at different temperatures ranging from 850°C to 1000°C. The material parameters were determined by using the test results and an Evolutionary Programming (EP)-based optimization method. Good agreements between the experimental and computed results were obtained.

Abstract: In this paper, for heat conductivity identification of three dimension steady heat transfer model of composite materials, a new hybrid Tikhonov regularization mixed multiscale finite-element method is present. First the mathematical models of the forward and the coefficient inverse problems are discussed. Then the forward model is solved by mixed multiscale FEM which utilizes the effects of fine-scale heterogeneities through basis functions formulation computed from local heat transfer problems. At last the numerical approximation of inverse coefficient problem is obtained by Tikhonov regularization method.

Abstract: PET-Ti composites have already been preliminarily used in the medical area due to the benefit of moderate biocompatibility of PET and the excellent mechanical properties of Ti. The connection of these materials always utilizes various technologies. Comparing to other methods, laser joining has the ability to achieve a clean weld and heat up materials in a spatially localized area only the material parts to be welded. This article describes how pulse shape, peak power and pulse-width affect the welding quality. And, make a conclusion that pulsed laser shapes, no matter with ramped-down waveform or ramped-up waveform, can be used to minimize the degradation of PET causes the decrease of gas bubbles that influence the bond strength and width.

Abstract: Aiming at enhancing the internal quality of 37Mn5 steel, a two-dimensional heat transfer mathematical model is established based on Finite Element Method. The synchronization between computing time and casting time is implemented by use of slice moving method. The reasonable of the model is verified by tested temperature. The process of solidification and shell formation is simulated for 37Mn5 steel ∅210mm round billet. The studied results indicate that: after optimization, the internal quality of billet is improved significantly; the defects such as center porosity, shrinkage cavity, intermedium cracks and center cracks were decreased obviously; defects above grade 1 were basically avoided.

Abstract: The effects of the different heat-treatments on the eutectic carbides in HSS cast strip are studied. The microstructure of the high speed steel(HSS) is analysized by means of optical microscopy and SEM. The results show that the heat treatment can make M2C and M6C metastable phase decompose. After comparison we can find that the optimized heat treatment processing of HSS cast strip is at 1200°Cfor 6 h, under which the fine and uniform carbides can be obtained.