Oxidation behaviour of an Alloy 617 in very high-temperature air and helium environments

The oxidation characteristics of Alloy 617, a candidate structural material for the key components in the very high-temperature gas-cooled reactor (VHTR), were investigated. High-temperature oxidation tests were conducted at 900 and 1100 degrees C in air and helium environments and the results were analysed. Alloy 617 showed parabolic oxidation behaviour at 900 degrees C, but unstable oxidation behaviour at 1100 degrees C, even in a low oxygen-containing helium environment. The SEM micrographs also revealed that the surface oxides became unstable and non-continuous as the temperature or the exposure time increased. According to the elemental analysis, Cr-rich oxides were formed on the surface and Al-rich discrete internal oxides were formed below the surface oxide layer. After 100 h in 1100 degrees C air, the Cr-rich surface oxide became unstable and non-continuous, and the matrix elements like Ni and Co were exposed and oxidized. Depletion of grain boundary carbides as well as matrix carbides was observed during the oxidation in both environments. When tensile loading was applied during high-temperature oxidation, the thickness of the surface oxide layer, the internal oxidation, and decarburization were enhanced because of the increase in diffusion of oxidizing agent and gaseous reaction products. Such enhancement would have detrimental effects on the high-temperature mechanical properties, especially the creep resistance of Alloy 617 for the VHTR application. (c) 2007 Elsevier Ltd. All rights reserved.
Publisher
ELSEVIER SCI LTD
Issue Date
2008-06
Language
ENG
Keywords

DYNAMIC RECRYSTALLIZATION; ELEVATED-TEMPERATURES; INCONEL-617; SUPERALLOY; 1000-DEGREES-C; CORROSION; 800H

Citation

INTERNATIONAL JOURNAL OF PRESSURE VESSELS AND PIPING, v.85, no.6, pp.368 - 377

ISSN
0308-0161
URI
http://hdl.handle.net/10203/4547
Appears in Collection
NE-Journal Papers(저널논문)
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