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Mechanism of Decarburization of Alloy 617 at 1000°C in Helium Containing CO and CO2 as impurities

Published online by Cambridge University Press:  15 March 2011

Deepak Kumar  and
Gary S. Was
Deepak Kumar
Affiliation:
Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, U.S.A.
Gary S. Was
Affiliation:
Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, U.S.A.
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Abstract

The objective of this study was to determine the mechanism of decarburization of alloy 617 by investigating the surface and bulk stabilities of the alloy in helium gas containing only CO and CO2 impurities over the temperature range 900-1000°C. For this purpose, the alloy was pre-oxidized at 900°C for 150h in He + 15 ppm CO + 1.6 ppm CO2 gas mixture and subsequently decarburized at 1000°C for additional 100h. The reaction mechanism was corroborated through gas phase analysis, microstructural examination and micro-probe measurements. It was determined that decarburization of the alloy occurred via a reaction between the porous Cr2O3 scale (formed during pre-oxidation) and carbon in the alloy, resulting in chromium metal and carbon monoxide. The chromium diffused back into the matrix, whereas the carbon monoxide escaped the sample through existing cracks and pores in the oxide. Therefore, this study shows that decarburization of alloy 617 occurs in a helium gas containing only CO and CO2 impurities.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1125: Symposium R – Materials for Future Fusion and Fission Technologies , 2008 , 1125-R06-02
Copyright
Copyright © Materials Research Society 2009

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References

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