Papers by Author: Katsuyoshi Kondoh

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Authors: Hisashi Imai, Hiroyasu Yamabe, Katsuyoshi Kondoh, Junko Umeda, Anak Khantachawana
Abstract: Dependence of the mechanical properties of PM extruded titanium with the silicon nitride (Si3N4) on solid phase decomposition of Si3N4 was investigated. Si3N4 particles within Ti composite powder were decomposed during spark plasma sintering at 1223 K with 30 MPa pressure for 3.6 ks; and then, decomposition by-products of nitrogen and silicon atoms were defused into titanium matrix. The extruded Ti-1.0 mass% Si3N4 composite showed ultimate tensile strength (UTS) of 1139 MPa, and yield stress (0.2%YS) of 1065 MPa. UTS and 0.2%YS of P/M extruded Ti-1.0 mass% Si3N4 composite were 2 and 2.5 times compared to extruded pure Ti powder material, respectively. It was considered that the solid solution strengthening of both nitrogen and silicon originated from Si3N4 caused the high strength of PM extruded Ti-1.0 mass% Si3N4 composite.
Authors: Ritsuko Tsuzuki, Katsuyoshi Kondoh, Wenbo Du, Tatsuhiko Aizawa, Eiji Yuasa
Authors: Shu Feng Li, Hisashi Imai, Akimichi Kojima, Yoshiharu Kosaka, Koji Yamamoto, Motoi Takahashi, Haruhiko Atsumi, Katsuyoshi Kondoh
Abstract: The effect of heat treatment on phase transformation, precipitation behavior and micro-hardness response of Cu40Zn-1.0Ti brass was investigated via powder metallurgy method. The volume fraction of α phase increased with elevated temperature, equaled to that of β phase at 400 °C, and reached to a maximum value of 55.9% at 500 °C. The solid solubility of Ti in Cu40Zn brass matrix decreased with elevated heat treatment temperature, showed high chemical potential for precipitates reaction in Cu40Zn brass. The micro-hardness of the BS40-1.0Ti brass was primarily dependent on the solid solubility of Ti, but also dependent on the phase ratio of α and β phase.
Authors: Patcharawat Khemglad, Julathep Kajornchaiyakul, Katsuyoshi Kondoh, Anak Khantachawana
Abstract: In the present work, the strengthen mechanism of Ti-Si-N ternary alloys prepared by Spark Plasma Sintering (SPS) was investigated. Ti, Si and TiN substrate powders were prepared in order to obtain nominal composition of Ti-0.35Si-1TiN and Ti-0.7Si-1TiN (wt %). Homogenization was performed before extrusion. Microstructure and phase identification were analyzed by Optical Microscope (OM) and X-ray diffraction (XRD). In order to evaluate the mechanical properties of extruded specimens, micro hardness test and tensile test were carried out. The XRD results show that no Si and TiN particles are remained after SPS and no any reaction caused of intermetallic compound during heat treatment and extrusion processes. It is found that the abnormal phase with high N-content was observed in matrix phase. It is also obvious that increasing Si from 0.35Si to 0.7Si (wt %) can increase yield stress and ultimate tensile stress from 1006±15 to 1092±5 MPa and 1089±10 to 1170±10 MPa, respectively. Hence, the strengthening mechanism by addition Si content into Ti-1TiN (wt %) is only solid solution mechanism.
Authors: Hisashi Imai, Shu Feng Li, Yoshiharu Kousaka, Akimichi Kojima, Haruhiko Atsumi, Katsuyoshi Kondoh
Abstract: Copper-40mass%zinc (Cu-40Zn) brass alloy powder containing 1.0 mass% Cr was prepared by the water atomization. Graphite particles, having a mean particle size of 5 μm, were added to the as-atomized powders by the ball milling equipment for 4h under 120 rpm. Spark plasma sintering process was used to consolidate the above elemental mixed powders (sintered material). Sintered materials were heat-treated for the precipitation of much Cr (HT material). The machinability of Cu-40Zn brass alloys was evaluated by a drilling test using a drill tool under dry conditions. The matrix hardness of sintered material was higher than that of HT material. On the other hand, the machinability of sintering material was higher than that of HT material. There is no trade-off relationship between the matrix hardness and machinability of the brass alloys. SEM-EDS observation indicated that Cr content dissolved in the brass matrix of sintered material and HT one was 0.42 mass% and 0.19 mass%, respectively. As the reason why machinability of HT material lowered, the precipitation of the hard Cr particle or generation of Cr-C compound caused to inhibit the machinability.
Authors: Shu Feng Li, Bin Sun, Katsuyoshi Kondoh, Takanori Mimoto, Hisashi Imai
Abstract: Ti metal matrix composites (Ti–MMCs) reinforced by vapor grown carbon nanofiber (VGCF) and graphite particle (Gr) were prepared via powder metallurgy and hot extrusion. Ti with 0~0.4wt% VGCF/Gr mixture powders were consolidated by using spark plasma sintering (SPS) at 800 °C. Hot extrusion was then performed at 1000 °C with an extrusion ratio of 37:1. Microstructures and mechanical properties of the as-extruded Ti composites were investigated. Tensile strength of Ti–VGCF/Gr composites was steadily augmented when additions of VGCF/Gr were increased from 0.1 to 0.4 wt%. YS and UTS were increased 40.2% and 11.4% for Ti–0.4wt%VGCF as compared to pure Ti, while those values were 30.5% and 2.1% for Ti–0.4wt%Gr. The strengthening mechanism including grain refinement, carbon solid solution strengthening and dispersion hardening of TiC/carbon was discussed in detail.
Authors: Ritsuko Tsuzuki, Katsuyoshi Kondoh
Abstract: Super light and high performance Mg2Si/Mg composites, which had excellent mechanical properties, were developed via the combination of solid-state synthesis and hot extrusion process. In this study, cold compacting (CP) and repeated plastic working (RPW) were firstly carried out for the mixture of Mg-Si powders, and the refinement of both Mg grains and dispersoids. Each specimen was evaluated by observation of microstructure and tensile test. As a result, it was understood that Mg2Si dispersoids were refined and dispersed into Mg matrix, and were flowed along extrusion direction. And their mechanical properties were higher than the conventional die casting alloys. Also the effect of RPW as the improvement of properties and the decrease of synthesis temperature were confirmed.
Authors: Wenbo Du, Katsuyoshi Kondoh, Eiji Yuasa, Ritsuko Tsuzuki, Tatsuhiko Aizawa
Authors: Katsuyoshi Kondoh, Masashi Kawakami, Junko Umeda, Hisashi Imai
Abstract: In fabricating metal matrix composites, it is important to evaluate the coherence at the interface between the reinforcements and the matrix metal. Titanium particulates were selected as suitable reinforcements in this study because they had high hardness and Young’s modulus compared to the magnesium alloys used as the matrix, and also showed better ductility than those of ceramic particles. The wettability in the combination of pure magnesium and pure titanium was investigated in this study. The sessile drop method indicated that the contact angle in the case of Mg-Ti was 40°at 1073K in argon gas atmosphere, and showed an excellent wettability of pure titanium by molten pure magnesium. No intermetallic compound at the interface between them was detected. Titanium particulate could be effective reinforcements of magnesium composite materials. Water-atomized magnesium composite powders including titanium particles were used as raw materials, and consolidated by cold compaction and hot extrusion. When including about 3 mass% Ti particles, the magnesium composites reinforced with them showed significantly improved yield stress and tensile strength, while having good elongation.
Authors: Shigeharu Kamado, Trevor B. Abbott, Junichi Koike, Katsuyoshi Kondoh, Yoshihito Kawamura
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