日本金属学会誌

J. Japan Inst. Metals, Vol. 69, No. 8 (2005),
pp. 707-710

Creep Strength of Co-Free Ni-Base Single Crystal Superalloys

Toshiharu Kobayashi1, Hiroshi Harada1, Makoto Osawa1 and Atsushi Sato2,

1High Temperature Materials Group, National Institute for Materials Science, Materials Engineering Laboratory, Tsukuba 305-0047
2Department of Materials Science and Engineering, Shibaura Institute of Technology, Tokyo 108-0023

Abstract:

The Pebble Bed Modular Reactor (PBMR) is a small atomic power reactor which can be used in areas where the electric power transmission network is not well developed. It generates electricity by gas-turbines that used He-gas as a coolant. Ni-based superalloys are the primary materials used in gas-turbines. However if conventional Ni-base superalloys are to be used for PBMR, turbine maintenances will be difficult due to Co, as it can produce 60Co a recitative material that possesses a long half-life. Therefore, Co-free Ni-base superalloys are required for PBMR.
In this paper, a Co-free single-crystal (SC) superalloy, TMS-82+(-Co), was developed; it was the same chemical composition as the 2nd generation SC superalloy, TMS-82+, except that it is Co-free creep tests were performed on the developed alloy, TMS-82+, under three conditions; 900°C/392 MPa, 1000°C/245 MPa, and 1100°C/137 MPa; CMSX-4, a popular SC alloy, was used as comparison.
TMS-82+(-Co) displayed superior creep-rupture life in all creep tests; however, detrimental TCP were observed in the microstructure of the sample that underwent creep testing at 1100°C/137 MPa. This, the developed Co-free SC alloy should be further modified for long-term microstructural stability. Elimination of phase formation will allow the alloy to be utilized in the PBMR.


(Received 2005/4/26)

Keywords:

nickel-base superalloy, single crystal, creep, pebble bed modular reactor (PBMR), and cobalt free


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