Deformation behavior of nanocrystalline Co-Cu alloys
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Deformation behavior of nanocrystalline Co-Cu alloys Motohiro Yuasa1, Hiromi Nakano2, Kota Kajikawa1, Takumi Nakazawa1, Mamoru Mabuchi1 1
Graduate School of Energy Science, Kyoto University, Yoshidahonmachi, Sakyo-ku, Kyoto, 606-8501, Japan 2 Cooperative Research Facility Center, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 440-8580, Japan ABSTRACT Three kinds of nanocrystalline Co-Cu alloys: a nanocrystalline Co-Cu alloy with nanoscale lamellar structure, a supersaturated solid solution Co-Cu alloy and a nanocrystalline two-phase Co-Cu alloy were processed by electrodeposition, and their mechanical properties were investigated at room temperature. These nanocrystalline Co-Cu alloys showed the high hardness and the low activation volume. The mechanical properties of the nanocrystalline Co-Cu alloys strongly depended on the grain boundary characteristics. Molecular dynamics simulations were performed in the two-phase nanocrystalline Co-Cu alloy to investigate the dislocation emission at the Co/Cu interface. The MD simulations showed that the stacking faults, which are generated by the intense geometrical strain at the Co/Cu interface, play an important role in the dislocation emission. INTRODUCTION Co alloys are one of promising metallic materials because they exhibit high heat resistance, ferromagnetism and so on. For various applications, it is desirable to improve the mechanical properties of Co alloys. Nanocrystallization can give rise to a significant enhancement of mechanical properties in metallic materials. However, nanocrystalline metals tend to be very brittle with a ductility of less than a few percent in tensile tests [1,2], due to the absence of dislocation activity [3]. It is accepted that nanocrystalline metals show the high hardness (high strength) and the low activation volume [4-9]. These features of nanocrystalline metals are attributed to emission of dislocations at the grain boundaries, and the grain boundaries play a critical role in deformation of nanocrystalline metals. Hence, it is required to develop nanocrystalline Co alloys with unique grain boundaries for enhancement of the mechanical properties. In the present work, three kinds of nanocrystalline Co-Cu alloys are processed by electrodeposition, and their mechanical properties are investigated at room temperature. In addition, molecular dynamics (MD) simulations are performed in the nanocrystalline two-phase Co-Cu alloy to investigate the dislocation emission at the Co/Cu interface. EXPERIMENTAL Three kinds of nanocrystalline Co-Cu alloys, that is, a nanocrystalline Co-Cu alloy with nanoscale lamellar structure, a supersaturated solid solution Co-Cu alloy and a nanocrystalline
two-phase Co-Cu alloy were processed by electrodeposition [10]. The electrolyte composition was CoSO4・7H2O (1 M) and CuSO4・5H2O (0.025 M). Microstructure of the Co-Cu alloys was investigated by transmission electron microscopy. Mechanical properties of the Co-Cu alloy were investigated by the hardness and tensile tests
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