Papers by Author: Masaaki Otsu

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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: Yuji Kawakami, Fujio Tamai, Takashi Enjoji, Noboru Shikatani, Tatsuya Misawa, Masaaki Otsu, Kazuki Takashima
Abstract: Pulsed Current Sintering (PCS) process possesses some problems that need to be resolved. We, therefore aims at understanding phenomena of PCS process by presenting some basic data on in situ sintering behavior of PCS. In order to observe in situ sintering behavior of PCS, a special graphite mold equipped with thermo couple and electrodes were designed to measure the temperature, electric current and voltage inside the powder during PCS process. We apply three types of raw materials, especially for ZnO (thermoelectric material) as semiconductor, Al2O3 as non-conductor and WC (Tungsten Carbide) as good conductor. The observation succeeded and some valuable data were obtained. The results showed that the temperature in the Al2O3 powder is 100 K higher than the graphite mold at the temperature of 1473K and ZnO powder is 150 K higher than the graphite mold at the temperature of 1373K. The electric current and voltage were measured for each powder during PCS process. In addition, their electric resistance properties were calculated. The electric resistance showed different behavior.
Authors: Masaaki Otsu, Hiroshi Taniguchi, Kazuki Takashima
Abstract: Ti and Au foils with a thickness of 10μm were formed by indenting at a place neighboring another indented place sequentially by means of a hemispherical diamond tool with a radius of 5μm. In this forming method, forming dies are not necessary and commercial equipments for nanoindentation can be used. Forming load and pitch were changed in single line forming and forming direction, line pitch and line number were changed in plural line forming, and bending angle was investigated. From the experimental results, bending angle of Ti foil was greater than that of Au one when same working conditions were employed. As the forming pitch increased, bending angle decreased. When the forming line pitch was changed, bending angle had the maximum peak at a pitch of 30μm by one-way forming path and 25μm by two-way forming path. Bending angle by one-way forming path was larger than that by two-way forming path. As forming line number increased, although bending angle increased, increment of them became smaller.
Authors: Yuji Kawakami, Fujio Tamai, Takashi Enjoji, Kazuki Takashima, Masaaki Otsu
Abstract: In this investigation, functionally graded technique has been applied to prepare tungsten Carbide alloys (WC-Co alloys)-austenitic stainless steel to improve corrosion and wear resistance and reduce their fabrication costs. Two types of specimens were prepared by Pulsed Current Sintering (PCS) method. One is fabricated from WC alloy (WC-20 wt% Co, WC-20 wt% Fe-46Ni) powder and SUS316L stainless steel powder, and is designated “powder / powder process“. The other is fabricated from pre-sintered WC alloy and SUS316L plate, and is designated “bulk / bulk process”. Both types of specimens have four functionally graded layers. Mechanical properties of these specimens were evaluated by three points bending test, and microscopy observations were made to their microstructures. Although the proper bending strength of bulk / bulk process specimen was obtained, the optimum sintering condition is sensitive to the sintering temperature and function graded layers.
Authors: Yuji Kawakami, Fujio Tamai, Takashi Enjoji, Kazuki Takashima, Masaaki Otsu
Abstract: Austenitic stainless steel has been used as a corrosion resistance material in tough corrosive circumstance. However, austenitic stainless steel has poor wear resistance property due to its low hardness. Tungsten Carbide alloys (WC) are widely used as tooling materials, because of their high hardness and excellent wear resistance property. In this investigation, we apply powder composite process to obtain hard layer of Stainless steel. The composite material was fabricated from planetary ball milled WC powder and SUS316L stainless steel powder and sintered by Pulsed Current Sintering (PCS) method. We also added TiC powder as a hard particle in WC layer. Evaluations of wear properties were performed by pin-on-disk wear testing machine, and a remarkable improvement in wear resistance property was obtained. The weight loss rate of the composite was 1/10 of SUS316L. In addition, it was found that TiC hard particle addition has a positive effect on the wear resistance property. EPMA investigation showed good dispersion of WC hard phase and TiC hard particle with SUS316L matrix.
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