Papers by Author: Akimichi Kojima

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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: 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: Haruhiko Atsumi, Hisashi Imai, Shu Feng Li, Yoshiharu Kousaka, Akimichi Kojima, Katsuyoshi Kondoh
Abstract: The purpose of this research is the development of a high strength α-β brass (Cu-40Zn) with additions of elements of small solid solubility in brass. Cu-40Zn with 0.6 wt.% Tin (Sn), 0.73 wt.% Chromium (Cr) and 0.51 wt.% Iron (Fe) were prepared by casting (Cu-40Zn-CrFeSn). The yield stress (YS) and ultimate tensile stress (UTS) of extruded Cu-40Zn-CrFeSn was 291 MPa and 601 MPa, 23 % and 36 % higher than that of extruded binary Cu-40Zn alloy. Vickers micro hardness of 158 Hv was higher than that of extruded Cu-40Zn alloy (131 Hv). In addition, the elongation of extruded Cu-40Zn-CrFeSn was 35 %. The strengthening mechanisms of these alloys were considered as follows; one was a solid solution strengthening of Cr, Fe and Sn additives which were identified by SEM-EDS. The other was increasing of the area ratio of β-phase in Cu-40Zn-CrFeSn, compared to that of Cu-40Zn.
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