TEM/STEM study of Zircaloy-2 with protective FeAl(Cr) layers under simulated BWR environment and high-temperature steam exposure

FeAl(Cr) thin-film depositions on Zircaloy-2 were studied using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) with respect to oxidation behavior under simulated boiling water reactor (BWR) conditions and high-temperature steam. Columnar grains of FeAl wi...

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Bibliographic Details
Published in:Journal of nuclear materials 2018-04, Vol.502 (C), p.95-105
Main Authors: Park, Donghee, Mouche, Peter A., Zhong, Weicheng, Mandapaka, Kiran K., Was, Gary S., Heuser, Brent J.
Format: Article
Language:English
Subjects:
Aluminum oxide
Boiling water reactors
Chemical precipitation
Computer simulation
Corrosion
Counterflow
Diffusion
Diffusion layers
Exposure
FeCrAl
Ferrous alloys
Grain
Intermetallic compounds
Iron aluminides
LWR cladding
Magnetron sputtering
Materials Science
Nickel ferrites
Nuclear Science & Technology
Oxidation
Porosity
Precipitates
Protective coatings
Scanning electron microscopy
Scanning transmission electron microscopy
Solid solutions
Steam
TEM
Temperature effects
Thin films
Transmission electron microscopy
Zircaloys (trademark)
Zirconium
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Summary:FeAl(Cr) thin-film depositions on Zircaloy-2 were studied using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) with respect to oxidation behavior under simulated boiling water reactor (BWR) conditions and high-temperature steam. Columnar grains of FeAl with Cr in solid solution were formed on Zircaloy-2 coupons using magnetron sputtering. NiFe2O4 precipitates on the surface of the FeAl(Cr) coatings were observed after the sample was exposed to the simulated BWR environment. High-temperature steam exposure resulted in grain growth and consumption of the FeAl(Cr) layer, but no delamination at the interface. Outward Al diffusion from the FeAl(Cr) layer occurred during high-temperature steam exposure (700 °C for 3.6 h) to form a 100-nm-thick alumina oxide layer, which was effective in mitigating oxidation of the Zircaloy-2 coupons. Zr intermetallic precipitates formed near the FeAl(Cr) layer due to the inward diffusion of Fe and Al. The counterflow of vacancies in response to the Al and Fe diffusion led to porosity within the FeAl(Cr) layer. •The oxidation behavior of FeAl(Cr) coatings on Zircaloy-2 in a simulated BWR environment and 700 °C steam exposure were studied.•The FeAl(Cr) coating was effective in forming a protective alumina layer and mitigated oxidation of the underlying Zircaloy-2 substrate.•The inward Fe and Al diffusion across the FeAl(Cr)-Zr interface resulted in the formation of Zr-based intermetallic phases.•The counterflow of vacancies in response to the Al and Fe diffusion resulted in porosity in the FeAl(Cr) coating.
ISSN:0022-3115
1873-4820
DOI:10.1016/j.jnucmat.2018.01.055