Papers by Author: Hideshi Miura

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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: Masaaki Otsu, Yasuhiro Ito, Akira Ishii, Hideshi Miura, Kazuki Takashima
Abstract: Pure titanium foils were bent by laser forming and the effect of c-d transformation and history of heat treatment of specimen on bending angle was investigated. The thickness of specimens was changed from 40 to 100om, the length of them was 20mm and the width of them was 10mm. The specimens were annealed at 600-1100oC for 30 minutes in argon atmosphere. A 20W YVO4 laser was employed and laser power was changed from 2 to 16W. From the experimental results, when laser power was increased, bending angle also increased and it was dramatically changed at the laser powers occurring c-d transformation and melting. Bending angle increased as grain size increased and it jumped up when grain size exceeded the foil thickness and then became constant. Bending angle decreased by annealing after forming and degree of decrease was greater when the annealing temperature before forming was lower.
Authors: Hideshi Miura, Hiroyuki Maeda, Makoto Uemura, Teruie Takemasu, Masaaki Otsu
Abstract: This paper investigates the characteristic of single-layered and multi-layered compacts made by selective laser sintering using titanium powder. The surface texture and tensile strength were investigated by using single-layered compacts. There were few defects in surface of specimen laser sintered in vacuum, and the roughness was smoother than that of the specimen laser sintered in argon. Maximum tensile strength of single-layered compact laser sintered in vacuum was about 200MPa. The shrinkage and mechanical strength were investigated by using multi-layered compacts. There was a unique tendency in the shrinkage of multi-layered compacts, which the density was around 75% and the adhesive bonding was not observed between layers, resulted in 70MPa of maximum bending strength and 50MPa of maximum tensile strength.
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: Yoshinori Itoh, Hideshi Miura, Kenji Sato, Mitsuo Niinomi
Abstract: The metal injection molding process was applied to produce Ti-6Al-7Nb alloys using 3 types of mixed powders. The first is a mixture of Ti and Al-Nb pre-alloyed powders, the second is a mixture of Ti, Ti-Al alloy and Nb powders, and the third is a mixture of elemental powders of Ti, Al and Nb. The sintered compacts using the first and second powders showed higher density and mechanical properties than the compacts using the third powder which showed many large pores formed due to the dissolution of Al particles during the sintering steps. Eventually, the compacts using a mixture of Ti+Al-Nb or Ti+Ti-Al+Nb powders showed tensile strength of above 800MPa and elongation of above 10%, which are similar to the properties of wrought materials.
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, Hyun Goo Kang, Yoshinori Itoh
Abstract: In this paper, two kinds of advanced powder processing techniques such as Metal Injection Molding (MIM) and Direct Laser Forming (DLF) were introduced to fabricate complex shaped Ti alloy parts which have been widely used for various industrial and medical applications because of their excellent characteristics of low density, high corrosion resistance and high biocompatibility but need high processing cost because of poor workability. The MIM process has been tried to strengthen Ti-6Al-4V alloy compacts by addition of fine Mo, Fe and Cr powders, and enhanced tensile strength of 1030 MPa with 15.1 % elongation was obtained by an addition of 4 mass%Cr because of the microstructural modification but also the solution strengthening in beta phase. DLF process has been tried to improve the honeycomb porous structure from Ti-6Al-7Nb powder material, and the honeycomb structure with 300 m holes showed good mechanical compatibility and superb biocompatibility in osteoblasts culturing.
Authors: Hideshi Miura, Kenta Okawachi, Hyun Goo Kang, Fujio Tsumori, Kosaku Kurata, Nobuhiro Arimoto
Abstract: Titanium and its alloys have been widely used for medical and aerospace applications because of their excellent attributes of light metal, high strength, high corrosion resistance and high biocompatibility. Especially, Ti-6Al-7Nb alloy has been developed as a more suitable biomaterial to replace Ti-6Al-4V alloy, because vanadium is toxic element to the biological body. However, it is not easy to fabricate the complex shaped and precise parts by the conventional methods due to their poor castability and machinability. In this study, laser forming technique has been applied to solve the above problems. The precise structure was obtained by optimizing the laser forming parameters. Using this technique, a honeycomb structure was fabricated effective to grow the neighboring tissue and also encourage osseointegration. Finally, mouse osteoblasts were cultured on the formed structures, resulted in the effectiveness of the honeycomb structure for biocompatibility.
Authors: Hideshi Miura, Hyun Goo Kang, Kensaku Sagara
Abstract: Ti-10V-2Fe-3Al is one of super elastic Ti alloys, which is the b type Ti alloy and shows the excellent properties such as high specific strength and corrosion resistance. By the combination of Cold working and heat treatment, high strength as same as the steels are obtained. Therefore, Ti-10V-2Fe-3Al is hoped to be a next generation’s spring material. In this study, Metal Injection Molding of super elastic Ti alloy materials are investigated by changing the process parameters such as powder type (mixed elemental or alloy), debinding and sintering conditions, and heat treatment conditions to obtain the excellent super elastic properties. Tensile strength of injection molded Ti-10V-2Fe-3Al compacts sintered at 1250 with mixed elemental powders showed approximately 85% of wrought materials. On the other hand, alloy powder compacts showed about 80% strength of wrought materials. Their super elastic behavior depended strongly on the heat treatment conditions.
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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