Materials Science Forum Vol. 750

Abstract: This study investigates the tensile properties of UACS (unidirectional arrayed chopped strands) laminates with different slit patterns. UACS composite is a kind of short fiber reinforced polymer by introducing slits into prepregs before the fabrication of laminates. Existing UACS composites have superior flowability but relatively low tensile strength compared to conventional CFRP (carbon fiber reinforced polymer). Consequently, many efforts have been made to improve the strength of UACS composites. In this study, two new discontinuous slit patterns, staggered pattern and bi-angled pattern, have been developed. Tensile tests reveal that two new UACS laminates with staggered and bi-angled slit patterns have higher strength and higher stiffness than existing UACS laminates with continuous slits. Discontinuity of slits plays an important role in inhibiting the development of delamination. Different slit patterns show different failure modes.

Abstract: Amorphous Pb(Zr0.52Ti0.48)O3 (PZT) thin films were deposited on LNO/SiO2/Si and Pt/Ti/SiO2/Si substrates by a sol-gel method and then crystallized by microwave irradiation in the microwave magnetic field. The crystalline phases and microstructures as well as ferroelectric property of the PZT films were investigated, and the effect of substrate on crystallization of PZT thin films heated by microwave annealing was discussed. The PZT films on LNO/SiO2/Si substrate show a highly (100)-preferred orientation, and better ferroelectric property than those on Pt/Ti/SiO2/Si substrate. The results demonstrated that LNO/SiO2/Si substrate is advantage for annealing of PZT thin films by microwave irradiation in the microwave magnetic field.

Abstract: Ab initio molecular dynamics (MD) calculations had been performed in this work to simulate the interactions of B with Fe, Al or Ca in metallurgical-grade silicon (MG-Si). The temperature of the MD simulations is 0K, the simulation time is 1ps. All the calculations were performed by using the CASTEP module of Materials Studio 4.3 software package. The geometry optimizations of impurities B with Fe, Al and Ca in MG-Si were performed with density functional theory (DFT) calculation. The Density of States of the optimized structures was calculated and the results have the potential application in guiding the boron removal from MG-Si by acid leaching.

Abstract: Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films rapidly crystallized by microwave irradiation were compared with those obtained by conventional furnace process. The PZT films under microwave irradiation at 650 °C for 60 s were crystallized well in to the perovskite phase, and showed butter electrical properties than those crystallized by conventional furnace annealing at 650 °C for 30 min. It is clear that microwave irradiation is effective for obtaining well-crystallized PZT films with good properties in a short process time.

Abstract: We investigated to add some high functionality to the brick by controlling the porous structure of the brick. It was succeeded in this study that a great many minute continuous pores which lead to capillary action were introduced inside of bricks in order to bring about “UCHIMIZU effect” for suppressing urban heat island phenomenon. But, as for the high water retainable pavement material like that brick, it is broken by water freezing in winter, and from this reason any pavement material with “UCHIMIZU effect” are not readily spread in through the all over Japan. Then, preparation of the brick which had both water retainability and frost resistance was tried by introducing much space into the brick inside to be able to permit the solidification expansion of water, and examined influence on properties of the brick by the quantity of porosity. From results, it was suggested that water retainability and frost resistance were able to be given to the brick at the same time by using the cavity formation materials.

Abstract: The unidirectional solidification process of magnesium alloy needs to establish a specific temperature gradient in casting mold, the direction of crystal growth and heat flow are in the opposite direction in the unidirectional solidification. The process can better control the grain orientation, and eliminate the horizontal grain boundary, so to attain columnar grain structure and excellent performance of magnesium alloy. In this paper, Numerical simulation is carried out by orthogonal experiments in order to obtain the optimal process parameters according to the actual experimental device. Different process parameters are taken into account, including pulling speed, cooling time and cooling intensity. FEM (finite element method) is employed to calculate the temperature field and reached a straight shape of temperature gradient distribution which is conductive to achieve unidirectional solidification microstructure. PFM(phase field method) is adopted into the microstructure calculation. The microstructure obtained by PFM is in agreement with the actual pattern by the optical microscope observation.

Abstract: In this study, a series of experimental studies was conducted to investigate the fatigue behavior of Ti-6Al-4V alloy at room temperature. Specifically, by inspecting the cylindrical specimens with a circumferential notch of different depths (20-200µm) and notch root radii (20-100µm), the notch effect was systematically investigated with tension-compression fatigue tests (R = –1). To quantify the effects of small notch, the -parameter model was adopted and its applicability for Ti-6Al-4V alloy was examined. Finally, the fatigue characteristics are discussed in conjunction with the behavior of small fatigue cracks at notches.

Abstract: Flaking and spalling caused by rolling contact fatigue associate with a small crack, and a special testing method and machine are required to study the small fatigue crack behavior under shear mode loading. It was found by authors that the behaviors of small shear-mode fatigue cracks from the inclusions and the artificial defects could be successfully observed by applying the fully-reversed torsion coupled with static axial compressive stress. However, the servo-hydraulic fatigue testing machine is quite expensive for purchase and maintenance, and large installation space is necessary for the hydraulic and cooling systems. Moreover, the presence of axial compression significantly lowers the frequency of torsional loading, which consequently results in low testing speed. In this study, a cost-effective, space-saving and high-speed fatigue testing method was newly proposed, and the shear-mode fatigue crack growth tests were carried out by using the developed machine. Based on the obtained experimental data, the potential of the new testing machine is discussed.

Abstract: A new conceptual technique for solar grade silicon (SOG-Si) purification was proposed in the present work. Most impurity elements in metallurgical grade silicon (MG-Si) exist in the grain boundary phases and their contents inside of silicon grains are extremely small, which is resulted from significant segregation during the solidification. Thus, the excellent purification was expected by selective ejection of grain boundary phases from silicon matrix. Such phases can be melted above the eutectic temperature of the system to form impurity-enriched liquid phase. In order to achieve the selective ejection of the liquid phase, its migration in the silicon matrix was investigated by conducting the heat treatment of silicon under the temperature gradient in this paper.

Abstract: Au-catalyzed growth of nanocrystalline Si by pulse jet chemical vapor deposition has been investigated. Au thin film was first deposited on thermally oxidized Si(100), then CH₃SiH₃ pulse jets were irradiated onto the Au/SiO₂/Si(100) surface. The irradiation of the CH₃SiH₃ jets at 1150 °C resulted in circular patterns with a diameter of ~40 µm on the sample surfaces. In the center of the circular patterns, agglomerations of Au were observed. It was found that the oxide layer was etched and that nanocrystalline Si with diameters ~500 nm was formed in the circular patterns. These results indicate that the nanocrystalline Si was grown by the VLS process in which Si atoms were supplied from the oxide layer, Si substrate, and CH₃SiH₃ molecules.