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Morishita M.,Kobe Steel | Ishida H.,Kobe Steel | Yoshida M.,Kagami Memorial Laboratory for Materials Science and Technology
Keikinzoku/Journal of Japan Institute of Light Metals | Year: 2010

In order to develop high quality aluminum alloy products, modeling to predict a behavior of solute distribution in dendrite and precipitation within the inter-cell region quantitatively is important. However Scheil's and Brody-Flemings's equations can't find the precipitation behavior during solidification because a diffusion in liquid phase is not considered. Numerical analysis methods typified by "Phase Field" are more effective but a calculation time has not been enough short to apply industrial use, yet. Consequentially a mathematical model is developed based on the Matsumiya's calculus of finite differences for analyzing inter-cell microsegregation and precipition. Diffusion of solutes in both the solid and liquid is taken into consideration, and realistic mesh shape to calculate microsegregation is conducted for finite difference calculation at this Matsumiya's model. But the calculus hardly predict precipitation behavior, since liquid concentration shift by precipitation during solidification is not considered. Then we improved the model to estimate precipitation of intermetallic compounds by thermodynamics database in this work. Additionally evaluation method of microsegregation used by EPMA was developed Consequently, we built a new segregation model, which could predict both the microsegregation and the kinds and amount of intermetallic compounds. Source


Morishita M.,Kobe Steel | Abe M.,Kobe Steel | Yoshida M.,Kagami Memorial Laboratory for Materials Science and Technology
Keikinzoku/Journal of Japan Institute of Light Metals | Year: 2010

The cooling water used in vertical aluminum DC casting is generally induced to just under the mold to prevent molten aluminum break out. However, the cooling water leaks into the air gap between the mold and the surface of ingot, so water splashes over the top of the molten aluminum, resulting in uneven cooling. But the quantitative survey on the splash break behavior and the change in the cooling condition has not been conducted. Hence, to quantify the splash break condition and the cooling capability, we have made the "Cooling water simulator" capable of freely controlling the potential splash causing factors such as temperature of cooling water, water flow rate, air gap amount, and angle of the water flow, reproducing the splash, and measuring the heat transfer value. The experimental result reveals that the temperature of cooling water is not a factor highly influencing on heat flux and splash, but the splash behavior highly depends on three factors which are the water flow rate, the angle of water flow, and the distance between the cooling water hit point level and the cooling water exit level. And that the heat flux also increases when splash occurs. In addition, the splash break parameter was drawn based on the above three factors, and the correlation between splash break parameter and heat flux was clarified. Use of splash break parameter enables setting of the casting condition where the maximum heat flux is obtained while preventing splash. Source


Nishinaga J.,Waseda University | Nishinaga J.,Kagami Memorial Laboratory for Materials Science and Technology | Horikoshi Y.,Waseda University | Horikoshi Y.,Kagami Memorial Laboratory for Materials Science and Technology
Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics | Year: 2010

C60-multivalent metal composite layers (aluminum, gallium, and germanium) are grown on GaAs and quartz glass substrates by molecular beam epitaxy. The structural properties of the C60-metal composite layers are investigated by reflection high-energy electron diffraction and transmission electron microscopy measurements, and it is confirmed that these layers have an amorphous structure. Mechanical properties of the layers are investigated by Vickers hardness test, and the values of the C60-metal composite layers are confirmed to be dramatically increased. The structural change and the hardness enhancement are induced by the bonding between C60 molecules and multivalent metal atoms. Optical properties of the layers are measured by the absorption coefficient spectra. The absorption peaks in C 60-Ge composite layers become less pronounced with increasing Ge concentration and the intensity in visible light spectrum is increased. Pure C60, C60-Al, and C60-Ga composite layers are confirmed to be insulators in air. In contrast, the conductivity of a C 60-Ge composite layer is found to be 0.02 Ω-1 cm-1 at room temperature with an activation energy of 120 meV. These enhancements of absorption coefficient and conductivity are very important for solar cells applications. © 2010 American Vacuum Society. Source

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