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Unusual SEM Image Contrast from Corrosion Oxide Films of Zr-2.5%Nb Pressure Tube Alloy

Published online by Cambridge University Press:  02 July 2020

Y. P. Lin  and
J. DeLuca
Y. P. Lin
Affiliation:
Materials Department, Ontario Hydro Technologies, Toronto, OntarioM8Z 5S4, Canada
J. DeLuca
Affiliation:
Materials Department, Ontario Hydro Technologies, Toronto, OntarioM8Z 5S4, Canada
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Extract

Zr-2.5wt%Nb alloy is used as the pressure tube material in CANDU reactors. The pressure tube microstructure consists primarily of α-Zr (< l%Nb) grains elongated in the axial direction of the pressure tube and typically 0.3-0.5 μm thick in the radial direction. The α-Zr grains are partially surrounded by a thin layer of Nb-rich β-Zr phase (≈ 20%Nb). During corrosion, α-Zr is converted primarily to monoclinic ZrO2 with minor amounts of tetragonal ZrO2. Oxidation of α-Zr is complicated by the metastable nature of the phase below 863K. A detailed understanding of the nature of oxidized β-Zr remains a topic of on-going investigation, although some information have recently become available. Present SEM observations shed some lights on the charging characteristics of the oxidized β-Zr compared with ZrO2.

Oxide films on pre-polished surfaces perpendicular to the radial direction of the pressure tube were grown in steam at 673K in an autoclave; the treatment corresponds to the last stage of the pressure tube production.

Type
Oxidation, Corrosion, and Protective Coatings
Information
Microscopy and Microanalysis , Volume 3 , Issue S2: Proceedings: Microscopy & Microanalysis '97, Microscopy Society of America 55th Annual Meeting, Microbeam Analysis Society 31st Annual Meeting, Histochemical Society 48th Annual Meeting, Cleveland, Ohio, August 10-14, 1997 , August 1997 , pp. 781 - 782
Copyright
Copyright © Microscopy Society of America 1997

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References

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This work was supported by funding from Ontario Hydro.Google Scholar