Papers by Author: Toshiko Osada

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Authors: Bin Liu, Makoto Saisho, Yuya Nagatomo, Takuya Oka, Toshiko Osada, Hideshi Miura, Osamu Furukimi, Shinji Munetoh
Abstract: Poly-crystalline Ba8Cu6Ag2Si38 clathrates were synthesized by the arc-melting method and a subsequent annealing treatment. The main phase of all the samples was type-I clathrate. However, there were some precipitates which rich in Cu, Ag or Si in the grain boundary of the as-synthesized sample and the precipitates gradually reduced with the increase of annealing time. The transition metal content in the clathrate increased with the annealing time because of the diffusion of the Cu and Ag atoms from precipitates phase into clathrates phase. The as-synthesized sample was n-type material. For the 576 hours annealed sample, the carrier type changed from n-type to p-type because of the increase of Cu and Ag content in the clathrate.
Authors: Hyun Goo Kang, Toshiko Osada, Hideshi Miura
Abstract: The direct metal laser sintering process was applied to produce density gradient materials of stainless steel 316L. In order to understand the mechanism of forming porous structure, the influence of laser power, scan rate and scan pitch on the porosity were investigated by measuring density of produced samples and observing cross-sectional microstructures. Laser power greatly affected to the porosity by forming clusters of melted metal powders. It was found that the size change of clusters plays a role in forming porous structure. Eventually, three dimensional sample owing density gradient structures was manufactured.
Authors: S. Virdhian, Toshiko Osada, Hyun Goo Kang, Fujio Tsumori, Hideshi Miura
Abstract: Titanium and its alloys have been widely used for medical and aerospace applications because of their excellent attributes of high specific strength, corrosion resistance, and biocompatibility. However, it is not easy to produce the complex shaped parts due to their poor castability and machinability. Metal injection molding (MIM) is one of suitable processing technique to produce the complex shaped parts in order to reduce the manufacturing cost. In this study, complex shaped Ti-6Al-4V compacts was prepared by MIM process for airplane application. The effects of high molecular binder content and different compact’s set-up during thermal debinding on the distortion of complex shaped compacts were measured and evaluated. The binder with 10 % APP (Atactic polypropylene) was found to have better shape retention for the parts. Furthermore the results indicate that high distortion occurs at early stage of thermal debinding process. The use of supports during thermal debinding can significantly reduce the distortion of the final parts.
Authors: Toshiko Osada, Hideshi Miura, Takanobu Yamagami, Kazuaki Nishiyabu, Shigeo Tanaka
Abstract: Gas surface treatment is considered to be especially effective for Titanium because of its high reactivity. In this study, we investigated the gas nitriding mechanism in titanium sintered parts produced by metal powder injection molding (MIM) process. In MIM process, gas nitriding can be surface-treated subsequently after debinding and sintering process. Then, the microstructure and nitrogen content of sintered MIM parts are considered to be greatly influenced by not only nitriding conditions but also sintered conditions. In this study, the effects of sintering time on microstructure such as nitrided layer thickness and hardness was investigated. Focus was given to the effects of specimen size on nitriding process, because the size of micro metal injection molding (μ-MIM) product is so small and the specific surface of that product is so large that the mechanical and functional properties can be subject to change by nitriding.
Authors: Hideshi Miura, Toshiko Osada, Shigeo Tanaka, Makoto Uemura
Abstract: In this study, gas nitriding was processed for various sizes of Ti specimens which were produced by metal injection molding (MIM) process, for the sake of enabling the high functionality at low processing cost. It was shown by the nitriding treatment that the hardness of the surface increased extremely and the microstructure changed to the TiN and acicular α-Ti phase. With respect to the effect of the nitriding on the size of parts, micro dumbbell specimen had around five times higher content of nitrogen than the block ones. It was suggested that the size of μ-MIM products is so small that the surface treatment can contribute significantly to improve the properties, and then gas nitriding process may be one of effective surface treatment methods for high functionality of μ-MIM Ti products.
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