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Vol.50, No.9, 659 ~ 668, 2012
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| Title |
| High-Temperature Corrosion Behavior of Alloy 617 in Helium Environment of Very High Temperature Gas Reactor |
| 이경근 Gyeong Geun Lee , 정수진 Su Jin Jung , 김대종 Dae Jong Kim , 정용환 Yong Whan Jeong , 김동진 Dong Jin Kim |
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| Abstract |
| Alloy 617 is a Ni-base superalloy and a candidate material for the intermediate heat exchanger (IHX) of a very high temperature gas reactor (VHTR) which is one of the next generation nuclear reactors under development. The high operating temperature of VHTR enables various applications such as mass production of hydrogen with high energy efficiency. Alloy 617 has good creep resistance and phase stability at high temperatures in an air environment. However, it was reported that the mechanical properties decreased at a high temperature in an impure helium environment. In this study, high-temperature corrosion tests were carried out at 850℃-950℃ in a helium environment containing the impurity gases H2, CO, and CH4, in order to examine the corrosion behavior of Alloy 617. Until 250 h, Alloy 617 specimens showed a parabolic oxidation behavior at all temperatures. The activation energy for oxidation in helium environment was 154 kJ/mol. The SEM and EDS results elucidated a Cr-rich surface oxide layer, Al-rich internal oxides and depletion of grain boundary carbides. The thickness and depths of degraded layers also showed a parabolic relationship with time. A normal grain growth was observed in the Cr-rich surface oxide layer. When corrosion tests were conducted in a pure helium environment, the oxidation was suppressed drastically. It was elucidated that minor impurity gases in the helium would have detrimental effects on the high- temperature corrosion behavior of Alloy 617 for the VHTR application. |
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| Key Words |
| metals, high temperature corrosion, microstructure, scanning electron microcopy, SEM, helium |
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