Development of Dual Multi-Phase Intermetallic Alloys Composed of Geometrically Close Packed Ni 3 X(X:Al and V) Structure
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0980-II08-02
Development of Dual Multi-Phase Intermetallic Alloys Composed of Geometrically Close Packed Ni3X(X:Al and V) Structures Takayuki Takasugi1,2 and Yasuyuki Kaneno1 1
Department of Materials Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka, 599-8531, Japan 2
Osaka Center for Industrial Materials Research, Institute for Materials Research, Tohoku University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka, 599-8531, Japan ABSTRACT Dual multi-phase intermetallic alloys composed of Ni3Al(L12)+Ni3V(D022) phases were developed, based on the Ni3Al-Ni3Ti-Ni3V pseudo-ternary alloy system. High-temperature tensile deformation, fracture behavior, and compression and tension creep were investigated using polycrystalline and single crystalline materials. The alloys with such a novel microstructure show extremely high yield and tensile strength with good temperature retention, and also reasonable tensile ductility. Also, creep test showed extremely low creep rate and long creep rupture time. The obtained results are promising for the development of a new-type of high-temperature structural material exceeding conventional superalloys. INTRODUCTION Multi-phase intermetallic alloys composed of geometrically close packed (GCP) Ni3X phases are expected to have highly coherent interface structure between the constituent phases and to have fine microstructure owing to their closely related crystal structures. Among these multi-phase intermetallic alloys, so-called dual multi-phase intermetallic alloys are composed of Ni3Al (L12) and Ni solid solution (A1) phases at high temperature annealing and are additionally refined by a eutectoid reaction at low temperature aging, according to which the Al phase is transformed into the Ni3Al (L12)+Ni3V (D022) phases. The dual multi-phase intermetallic alloys composed of Ni3Al (L12) and Ni3V (D022) were shown to exhibit coherent microstructures not only at the micron scale but also at the sub-micron scale, and also display high microstructural stability at high temperature [1,2]. In the present study, arc-melted material, forged material and single crystal are assessed over a wide temperature range by tensile test and creep test. EXPERIMENTAL PROCEDURES An alloy composition expressed by Ni75Al7.5Ti2.5V15(at.%) was chosen in this study. The forged material was doped with 500 wt.ppm boron. The arc-melted material was prepared by arc melting under an argon gas atmosphere on a copper hearth using a tungsten electrode. The hot-forged material was melted by an induction furnace under an argon gas, and then cast into a mould with a dimension of 68 mm in diameter and 70 mm in length. This billet was forged at about 1570 K where A1 (fcc Ni solid solution) phase is stable. A bulk single crystal was made by Bridgman technique in an argon atmosphere within an induction furnace. These materials were then sliced to several plates. According to the phase diagram reported in the previous study, sliced specimens were mostly annealed at 1573K for 10h→annealed 1373K for 10h→aged 1273K fo
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