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Research Papers

Oxidation Parameters of Oxide Dispersion-Strengthened Steels in Supercritical Water

[+] Author and Article Information
Sami Penttilä

VTT Technical Research Centre of Finland Ltd.,
P.O. Box 1000, FI-02044 VTT Espoo, Finland
e-mail: sami.penttila@vtt.fi

Iva Betova

Department of Chemistry,
Technical University of Sofia,
Kl. Ohridski Blvd. 8, 1000 Sofia, Bulgaria
e-mail: iva_betova@tu-sofia.bg

Martin Bojinov

Department of Physical Chemistry,
University of Chemical Technology and Metallurgy,
Kl. Ohridski Blvd. 8, 1756 Sofia, Bulgaria
e-mail: martin@uctm.edu

Petri Kinnunen

VTT Technical Research Centre of Finland Ltd.,
P.O. Box 1000, FI-02044 VTT Espoo, Finland
e-mail: petri.kinnunen@vtt.fi

Aki Toivonen

VTT Technical Research Centre of Finland Ltd.,
P.O. Box 1000, FI-02044 VTT Espoo, Finland
e-mail aki.toivonen@vtt.fi

1Corresponding author.

Manuscript received May 28, 2015; final manuscript received July 16, 2015; published online December 9. Assoc. Editor: Thomas Schulenberg.

ASME J of Nuclear Rad Sci 2(1), 011017 (Dec 09, 2015) (8 pages) Paper No: NERS-15-1099; doi: 10.1115/1.4031127 History: Received May 28, 2015; Accepted July 23, 2015

The kinetic parameters of oxidation of two oxide dispersion strengthened (ODS) alloys, PM2000 and MA956, in supercritical water (SCW) are evaluated using an updated model that assumes that the growth of the outer layer is governed by the transport of interstitial cations through the inner layer. The model is able to reproduce quantitatively the depth profiles of individual constituent elements in the inner and outer layers, as well as in the diffusion/transition layer of the alloy between the inner layer and the bulk substrate. The rate constants and diffusion coefficients decrease with time, indicating oxide layer restructuring.

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Figures

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Fig. 1

Simplified scheme of the growth of the inner and outer layers of the film formed on a Fe-Cr-Al alloy according to the proposed approach

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Fig. 2

Atomic fractions of oxide constituents versus depth on MA956 (above) and PM2000 (below) oxidized for 2000 hr at 650°C. Left: major constituents; right: minor constituents. Sigmoid fits to determine the position of the alloy/oxide interface are shown as vertical solid lines

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Fig. 3

Comparison between the experimental (points) and calculated according to the model procedure (solid lines) fractions of metallic constituents (Fe, Cr, Al, Ni, Mn, Si, Ti, and Nb) in the oxide formed on (a) MA956 for 600 hr, (b) PM2000 for 600 hr, (c) MA956 for 2000 hr, and (d) MA956 for 2000 hr

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Fig. 4

Sensitivity study of the rate constants of oxidation at the alloy/inner layer interface (k1Fe, k1Cr, k1Al, k1Mn, k1Si, k1Nb, k1Ti, and k2) as well as the rate constant of production of trivalent chromium vacancies (k3Cr) for the oxide formed on MA956 for 1000 hr. Dashed lines represent variation of the respective parameters with 10%, respectively

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Fig. 5

Rate constants of inner layer growth (top), generation of cation vacancies (middle), and consumption of interstitial cations (bottom) expressed versus time of exposure

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Fig. 6

Diffusion coefficients of point defects in the inner layer of the oxide on PM2000 (top) and MA956 (bottom) expressed versus time of exposure

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Fig. 7

Diffusion coefficients of main constituents in the transition layer of PM2000 (top) and MA956 (bottom) expressed versus time of exposure

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Fig. 8

Comparison between the oxide thicknesses calculated from the model (open symbols) and the thicknesses estimated from the experimental GDOES depth profiles (closed symbols). Experimental thicknesses corrected by subtracting 0.05–0.1 μm of contamination layer

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