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NI-BASED, two-phase Ni3Al and Ni3V intermetallic alloys are composed of two intermetallic phases of Ni3Al (L12: a = 0.3572 nm) and Ni3V (D022: a = 0.3542 nm and c/a = 2.036). As predicted from the pseudo-binary phase diagram shown in Figure 1,[1] the alloys with a hypereutectoid composition have microstructures consisting of the primary Ni3Al precipitates and a Ni solid solution (A1 phase), serving as the channel region at high temperatures [above 1281 K (1008 C)]. Accordingly, the microstructure at high temperatures is similar to that observed in conventional Ni-based, c/c¢-type superalloys. At low temperatures, the Ni solid solution in the channel region is transformed into a lamellar-like microstructure consisting of Ni3Al and Ni3V phases DIASUKE EDATSUGI, formerly Graduate Student with the Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai 5998531, Japan, is now System Engineer with the Mazda Motor Corporation, Yamaguchi 747-0835, Japan. YASUYUKI KANENO and TAKAYUKI TAKASUGI, Professors, are with the Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University. Contact e-mail: [email protected] SATOSHI SEMBOSHI, Associate Professor, is with the Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, and also with the Kansai Center, Institute for Materials Research, Tohoku University, Gakuen-cho 1-1, Naka-ku, Sakai 599-8531, Osaka, Japan. Manuscript submitted August 22, 2015. Article published online January 14, 2016 998—VOLUME 47A, MARCH 2016

with a submicron size by the eutectoid reaction.[2–7] Here, the channel region behaves as a hard material, whereas the primary Ni3Al precipitate behaves as a soft material, in contrast to the ordinary c/c¢-type, Ni-based superalloys. These alloys have highly coherent crystal structures among the constituent phases and display high microstructural stability.[2–7] It was revealed from this feature that the Ni-based, twophase intermetallic alloys show specific high-temperature properties that have not been observed in the conventional Ni-based, c/c¢-type superalloys. The observed two-phase intermetallic alloys showed attractive mechanical properties.[5,6,8–11] Attempts have been made to improve the mechanical properties of the Ni-based, two-phase intermetallic alloys. Enhanced strength has been achieved by the addition of substitutional Ti,[2,3,8–10,12] Nb,[4–6, 11,12] and Ta[13,14] and interstitial C,[15,16] which behave as solid solution strengtheners in the constituent phases. It has also been recently shown that the hardness of the alloy containing Re was enhanced by annealing at temperatures below the eutectoid temperature, which was attributed to the precipitation of the Re-rich phase formed in the channel region.[13,14,17] Thus, the hardening mechanism in the alloys containing Re is different from that[18,19] suggested in the conventional Ni-based, c/c¢-type superalloys. It was suggested that the Re that is s