Papers by Author: Chihiro Iwamoto

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Authors: Chihiro Iwamoto, Shunichiro Tanaka
Abstract: In-situ HRTEM technique was applied to various substrates and the reaction processes between substrates and molten alloy were compared. Substrates used were SiC, Si3N4, Si wafers, an amorphous carbon film, and a carbon nanotube. Ti-containing Ag-Cu eutectic alloy foil was placed on the substrate and the combined specimen mounted on the heating holder of an HRTEM and heated in the microscope to melt the alloy foil. In the case of SiC, Si3N4, carbon materials, the molten alloy spreading on the substrates were observed after melting of the alloy. SiC polar plane nano-steps appeared with the SiC dissociation by the molten alloy. On the surface of the carbon nanotube, thin film precursor spreading was observed. In contrast, Si reaction with the molten alloy produced big holes at the contacted area and molten alloy spreading was not observed.
83
Authors: Chihiro Iwamoto, Shinobu Satonaka, Yoshihito Kawamura
Abstract: Recently, Mg96Zn2Y2 alloy was widely studied due to its excellent mechanical properties. These properties were considered to relate to the nanostructure of the alloy such as α-Mg matrix and bent long period stacking ordered (LPSO) structure. In this study, as the first step to the mechanical property control, we applied various spot welding methods to the Mg alloy to control the structure of the joints. The specimen used was an extruded Mg96Zn2Y2 alloy. The sheets were cut from this alloy rod for resistance spot welding. Three kinds of spot welding methods were applied to join the Mg alloy, such as spot welding with cover plates, long-time spot welding, and water-cooled spot welding. In the base metal, secondary phases extended along extruded direction at approximately 30μm intervals were produced in the α-Mg matrix. The secondary phase contained 14H-type LPSO structure. In the nugget of the joint welded with cover plates, a secondary phase was produced like a net in the α-Mg grain which was approximately 30μm in diameter. Both 14H-type and 18R-type LPSO were observed in the secondary phase. In the nugget produced by the long-time spot welding, a secondary phase tended to segregate to the grain boundary of the α-Mg grains. The structure of LPSO was 18R-type. In the water-cooled welding, strong directionality of the secondary phase texture was observed around the edge of the nugget. These results showed that the nugget nanostructure of Mg96Zn2Y2 dramatically varied depending on the above adopted methods of spot welding.
1181
Authors: Shinichi Yoshimitsu, Shinobu Satonaka, Yoshihiro Kawano, Chihiro Iwamoto, Dun Wen Zuo, Shunichi Yamashita
Abstract: This report describes a two-dimensional monitoring system for milling machines using small-diameter tools. Small-diameter tools are used for high-speed milling, and they are indispensable for high-quality and high-productivity manufacturing. However, tool breakage occasionally occurs, and this becomes a serious problem in automated production. This study aims to develop a system for monitoring the cutting state that can prevent tool breakage. The proposed system consists of two charge-coupled device (CCD) cameras, an image processing device, a man-machine controller (MMC), and a machining center with an open computer numeric (CNC). This monitoring system is connected to the machining center by Ethernet. It enables the precise measurement of tool deflection during high-speed milling. In an experiment, we applied this system to the end milling of a steel plate under different cutting conditions, and we examined the relationship between tool deflection and the cutting conditions. In addition, we applied this monitoring system to measure tool wear, and we examined the relationship between tool deflection and tool wear. It was found that the proposed system enabled in-process monitoring of the cutting state and tool wear.
433
Authors: Chihiro Iwamoto, Shinobu Satonaka, Yoshihito Kawamura
Abstract: Mg96Zn2Y2 is widely studied due to its high tensile yield strength and elongation. These excellent properties were considered to relate to the nanostructure of the alloy such as fine-grained α-Mg matrix and bent long period stacking ordered (LPSO) structure. In order to extend the application of this Mg alloy, development of the welding technique is indispensable. In the light of the reliability and productivity, resistance spot welding is an attractive method to join this Mg alloy. In this study, we joined the Mg alloys by the resistance spot welding with cover plates. Mechanical properties and structures of the nugget of the joints were investigated. In the case of the joints welded with cover plates, the welded region of the Mg alloy sheets were covered with steel plates to supply adequate heat for welding. Joints of extruded Mg96Zn2Y2 were obtained at relatively low welding current. The tensile strength of Mg96Zn2Y2 alloy was higher than that of the commercial Mg alloy AZ31B joints. Mg96Zn2Y2 base alloy had extended LPSO phase along extruded direction in α-Mg grains. At the nugget, net-like secondary phase was produced in the Mg grains. The relationship between the microstructure in the joints and mechanical properties were discussed.
1187
Authors: Seiichiro Ii, Chihiro Iwamoto, Shinobu Satonaka, Kazuyuki Hokamoto, Masahiro Fujita
Abstract: Bonding interface in aluminum (Al) and silicon nitride (Si3N4) clad fabricated by explosive welding has been investigated by transmission electron microscopy (TEM). The nanocrystalline region was clearly observed at the interface between Al and Si3N4. Electron diffraction pattern and energy dispersive X-ray spectroscopy (EDS) measurements across the interface revealed that this nanocrystalline region consist of the only aluminum.
3775
Authors: Takashi Saito, Tadahiko Furuta, Jung Hwan Hwang, Shigeru Kuramoto, Kazuaki Nishino, Nobuaki Suzuki, Rong Chen, Akira Yamada, Kazuhiko Ito, Yoshiki Seno, Takamasa Nonaka, Hideaki Ikehata, Naoyuki Nagasako, Chihiro Iwamoto, Yuichi Ikuhara, Taketo Sakuma
681
Authors: Shun Ichiro Tanaka, Chihiro Iwamoto
Abstract: Nanoscale singularity at the reactive wetting front on SiC (0006) was studied using video recorded in situ to clarify the dynamic atomistic behaviours of the brazing and the molten tip spreading on a high-temperature stage of a high-resolution transmission electron microscope. An atomistic process controls the wetting at the front of the spreading film where the classical macroscopic phenomenon never holds true and the singularities are observed in a precursor film. A 0.5-nm-thick precursor film spreading ahead of the main molten alloy on SiC (0006) at 1073 K and continuous spreading of the molten alloy were clearly observed on the SiC (0006) surface with a less than 1-nm-thick amorphous layer. Molten Ti and TiC nanolayers preceded the Ti5Si3 nanolayer at the tip and they traveled continuously at a velocity of 14 nm/sec on the plane perpendicular to SiC (0006). Since Ti atoms in the molten alloy diffuse sufficiently rapidly on the SiC surface to the tip, the formation of these layers may be the rate-determining step of spreading. Discontinuous spreading of the precursor tip on SiC (0006) with a thick amorphous film was observed in contrast to the continuous spreading on SiC with a thin film. This suggests that the spreading of the Ti molten alloy on SiC is also controlled by the dissolution of the amorphous layer.
269
Authors: T. Ichimori, Chihiro Iwamoto, Shigeru Tanaka
337
Authors: Shun Ichiro Tanaka, Chihiro Iwamoto
Abstract: Nanoscale singularity at the reactive wetting front on the 6H-SiC (0006) surface with amorphous oxide layer was studied using video recorded in situ to clarify the dynamic atomistic behaviors of the brazing and the molten tip spreading on a high-temperature stage of a high-resolution transmission electron microscope. A 0.5-nm-thick precursor film spreading ahead of the main molten alloy on SiC (0006) at 1073 K and continuous spreading of the molten alloy were clearly observed on the SiC (0006) surface with a less than 1-nm-thick amorphous layer. Molten Ti and TiC nanolayers preceded the Ti5Si3 nanolayer at the tip and they traveled continuously at a velocity of 14 nm/sec on the plane perpendicular to SiC (0006). Since Ti atoms in the molten alloy diffuse sufficiently rapidly on the SiC surface to the tip, the formation of these layers may be the rate-determining step of spreading. Discontinuous spreading of the precursor tip on SiC (0006) with a thick amorphous film was observed in contrast to the continuous spreading on SiC with a thin film. This suggests that the spreading of the Ti molten alloy on SiC is also controlled by the dissolution of the amorphous layer.
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