Alloy design for reducing V content of dual two-phase Ni 3 Al-Ni 3 V intermetallic alloys
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Alloy design for reducing V content of dual two-phase Ni3Al-Ni3V intermetallic alloys Takahiro Hashimoto 1, Yasuyuki Kaneno 1 and Takayuki Takasugi1,2 Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho Naka-ku, Sakai, Osaka 599-8531, JAPAN 2 Kansai Center for Industrial Materials Research, Institute for Materials Research, Tohoku University, 1-1 Gakuen-cho Naka-ku, Sakai, Osaka 599-8531, JAPAN
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ABSTRACT The objective of this study is to establish alloy designing which can reduce the amount of V for a Ni-base dual two-phase intermetallic alloy, without degenerating the dual two-phase microstructure. It was demonstrated that the favorable dual two-phase microstructure will be maintained as far as the valence electron concentration (e/a) of the alloys added by Cr is not so much different from that of the base alloy (i.e. the alloy without additive elements). Consequently, it was found that the dual two-phase microstructure was maintained even though the amounts of V were reduced by 7 at.%, 7 at.%, and 10at.% by substituting of Cr for V, Cr for both of Ni and V, and Cr for Ni, respectively. The hardness of the alloys with reduced V content was higher than that of the base alloy. INTRODUCTION A dual two-phase Ni3Al-Ni3V intermetallic alloy is a new type of high temperature structural materials which have been developed in our laboratory. A feature of this alloy is its unique microstructure: the dual two-phase microstructure is comprised of upper two-phase microstructure with a micron scale and lower two-phase microstructure with a sub-micron scale. The upper two-phase microstructure is composed of primary cuboidal precipitates of Ni3Al (L12) and Ni solid solution (A1) at high temperature. Then, the prior A1 phase is decomposed into Ni3Al (L12) and Ni3V (D022) by a eutectoid reaction at low temperature, resulting in the lower two-phase microstructure in the channel region. It is found that the dual two-phase microstructures are highly coherent among primary cuboidal precipitates of Ni3Al (L12) phase and channel regions of Ni3V (D022) and Ni3Al (L12) phases, and display high microstructural stability at high temperature [1-4]. In addition, the dual two-phase intermetallic alloys are found to show excellent mechanical properties, e.g., higher high-temperature tensile and creep strength properties than many conventional superalloys, therefore promising for the development of a next generation-type high temperature structural material [4-6]. The dual two-phase intermetallic alloys however contain relatively high amount of vanadium which are inferior in the oxidization characteristic, density and cost. Therefore, it is a critical issue to reduce the content of constituent element V. The objective of this study is to establish alloy designing which can reduce the amount of V, without degenerating the dual two-phase microstructure, i.e., maintaining their superior mechanical and chemical properties. From the thermodynamic point of view to achieve this purpose, additive
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