Papers by Author: Kazuhiro Nakata

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Authors: Takuya Tsumura, Taichi Murakami, Soong Keun Hyun, Hideo Nakajima, Kazuhiro Nakata
Abstract: Effects of pore directions on the profile of fusion zone for lotus-type porous magnesium by laser welding has been investigated by comparing the experimental observations and the results of numerical simulation. The three-dimensional finite element calculations were performed, which takes into account equivalent thermal properties and anisotropy of thermal conductivity. There is the pore anisotropy in the profile of fusion zone by laser beam irradiation and the good weldability was obtained when the growth direction of the original pore equaled to the direction of the laser beam irradiation. A good agreement was obtained between the calculated profile of the weld fusion zone and the experimental results.
Authors: Toshiya Okada, Souhei Uchida, Kazuhiro Nakata
Abstract: It was difficult to join dissimilar materials such as metallic material and polymer. Conventional joining processes of these materials were mechanical fastening, using adhesion, thermal pressing, laser welding and so on. These processes had disadvantages such as expensive apparatus, restriction of dimension of products and lack of anti-weather resistance.Friction Stir Welding (FSW), which was one of the solid state joinings, was available as a joining process for dissimilar metals. However, in case of joining metal and polymer, it was not available to use the tool for FSW. So we proposed Friction Lap Process to join a metallic material with a polymer and investigated mechanical and metallurgical properties of this dissimilar joint. Itwas described in this paper that joining mechanism is discussed with evaluation of microstructure at the interface between aluminum alloy and polymer. High density polyethylene was not able to be joined for as received aluminum alloy. Anodizing was effective to join with these materials.
Authors: Hyun Guen Kim, Kazuhiro Nakata, Takuya Tsumura, Masaharu Sugiyama, Takanori Igarashi, Masahiro Fukumoto, Hisamichi Kimura, Akihisa Inoue
Abstract: The Fe-based bulk metallic glass (Fe43Cr16Mo16C15B10) sprayed coating with the thickness about 220%m was successfully deposited on an aluminum alloy (A5052) metal substrate using an HVOF (High Velocity Oxygen Fuel) spraying process. All sprayed coating has still kept the amorphous state after spraying. The Fe-based bulk metallic glass coating shows good adhesion to the aluminum alloy metal substrate, and has a high hardness with HMV 913~1120. It has been found that better properties can be obtained in the sprayed coating by using finer powder.
Authors: Kazuhiro Nakata, Hirohisa Ikegami, Takuya Tsumura
Abstract: Lap joint of AZ31 Mg alloy extruded sheet can be successfully made by friction spot joining (FSJ) process. Joint strength was strongly affected by the probe thread, which increased the plastically deformed zone around a rotating probe and increased the tensile shear strength of the joint in comparison with the joint made by a thread-less probe.
Authors: Yuji Sakai, Kazuhiro Nakata, Takuya Tsumura, Mitsuji Ueda, Tomoyuki Ueyama, Katsuya Akamatsu
Abstract: Noncombustible magnesium alloy AMC602 (Mg-6mass%Al-2mass%Ca) extruded sheet of 2.0mm thickness was successfully welded using a fiber laser welding process at welding speed of 10m/min at 3kW laser power. Tensile strength of the welded joint was about 82 to 88% of that of the base metal. Vickers hardness, tensile strength and micro structural properties are also discussed.
Authors: Hwa Soon Park, Byung Woo Lee, Taichi Murakami, Kazuhiro Nakata, Masao Ushio
Abstract: The mechanical properties of the friction stir welds of the oxygen free copper (OFC) and 60%Cu-40%Zn copper alloy(60/40 brass) were investigated. The defect-free welds were obtained in a relatively wide range of welding conditions; the tool rotation speed had rpm of 1000 to 2000 in the OFC and 1000 to 1500 in the 60/40 brass, with the welding speed of 500 to 2000 mm/min. The SZ hardness values of the OFC welds were almost the same or slightly lower than those of the base metal. However, the SZ hardness values of the 60/40 brass in all welding conditions were much higher than those of the base metal. The SZ hardness values of both metals increase with a decrease in heat input. The tensile properties of the all-SZ showed relative correspondence to the variation of the SZ hardness values.
Authors: Kuk Hyun Song, Kazuhiro Nakata
Abstract: This study evaluated the microstructure and mechanical properties of friction stir welded lap joints. Inconel 600 and SS 400 as experimental materials were selected, and friction stir welding was carried out at tool rotation speed of 200 rpm and welding speed of 100 mm/min. Applying the friction stir welding was notably effective to reduce the grain size of the stir zone, as a result, the average grain size of Inconel 600 was reduced from 20 μm in the base material to 8.5 μm in the stir zone. Joint interface between Inconel 600 and SS 400 showed a sound weld without voids and cracks. Also, the hook, along the Inconel 600 alloy from SS 400, was formed at advancing side, which directly affected an increase in peel strength. In this study, we systematically discussed the evolution on microstructure and mechanical properties of friction stir lap jointed Inconel 600 and SS 400.
Authors: Kentaro Yamamoto, Manabu Tanaka, Shinichi Tashiro, Kazuhiro Nakata, Keiichi Suzuki, Kei Yamazaki
Abstract: It is important to consider the interaction between arc plasma and electrodes because melting of electrodes strongly affects arc plasma. Therefore, a GMA model will be developed, based on the unified model of TIG arc. As a first step, a TIG arc model with a calculation for molten cathode shape has been proposed. This model is calculated in two cases; molten W cathode and Calculation result of W cathode. In the case of W cathode, cathode shape change was found to affect the arc plasma property strongly. Calculated results of radial temperature distributions on electrode surface and arc pressure distributions at the anode surface are very similar to the experimental results.
Authors: Takuya Tsumura, Fu Xing Ye, Taichi Murakami, Hideo Nakajima, Kazuhiro Nakata
Abstract: Lotus-type porous metals, whose pores are aligned in one direction by unidirectional solidification, have a unique combination of properties. These are expected as revolutionary engineering materials with anisotropy of the properties. For the industrial use of the lotus-type porous metals, a reliable joining technology is required. We already reported the melting property of a few lotus-type porous metals by laser welding. These results indicated that these materials possessed anisotropy of melting property with the pore direction perpendicular and parallel to the specimen surface, especially remarkable anisotropy was obtained for the copper specimen owing to the difference of the laser energy absorption to the specimen surface. In this report, the three-dimensional heat transfer analyses, which take into account the difference of the laser energy absorption comparing with the anisotropy of thermal conductivity inherent to lotus-type porous metals, were performed by commercial code with user-defined subroutine. Predicted profile of weld fusion zone is in good agreement with the cross-sectional view obtained by experiments.
Authors: Masato Tsujikawa, S. Noguchi, N. Yamauchi, N. Ueda, T. Sone, Kazuhiro Nakata
Abstract: Surface layer hardness and concentration profiles of austenitic stainless steels after plasma carburizing and /or nitriding at 673 K were investigated. Carbon and nitrogen concentration were measured by glow discharge optical emission spectrometry (GDOES) and carbides or nitrides were detected by x-ray diffraction analysis (XRD) and TEM. The state of carbon at the treated surface was investigated by Raman spectroscopy. Separation of carburized layer and nitrided layer was observed in a simultaneous carburizing and nitriding plasma treatment.
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