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Oxidation of Metals

, Volume 67, Issue 5–6, pp 251–266 | Cite as

The Effect of Water Vapor on the Initial Stages of Oxidation of the FeCrAl Alloy Kanthal AF at 900 °C

  • H. GötlindEmail author
  • F. Liu
  • J.-E. Svensson
  • M. Halvarsson
  • L.-G. Johansson
Original Paper

Abstract

The effect of water vapor on the initial stages of oxidation of the FeCrAl alloy Kanthal AF is reported. Polished samples were exposed isothermally at 900 °C for 1, 24, 72 and 168 h in a well-controlled environment consisting of dry O2 or O2 + 40% H2O. The samples were investigated using a combination of gravimetry and several surface-analytical techniques, including XRD, SEM, EDX, FIB, AES and TEM. The presence of water vapor significantly accelerates oxidation during the first 72 h. A two-layered oxide forms in both the dry and wet environments. The bottom layer consists of inward-growing α-Al2O3 while the outer layer initially consists of outward-growing γ-Al2O3. A straight and narrow Cr-enriched band is present at the top of the lower (α-Al2O3) oxide, corresponding to the original sample surface. In dry O2, the top (γ-Al2O3) layer is converted into a mixture of γ-Al2−x (Mg,Fe) x O3−(x/2), MgAl2O4 and α-Al2O3. This transformation does not occur in O2 + H2O. The initial acceleration of oxidation by H2O is attributed to the stabilization of the outward-growing γ-alumina layer by the hydroxylation of the γ-Al2O3 surface. A schematic mechanism of the early stages of oxidation of FeCrAl alloys is presented, emphasizing the influence of water vapor.

Keywords

FeCrAl Water vapor Initial oxidation Transient alumina 

Notes

Acknowledgements

The work was performed within the Swedish High Temperature Corrosion Centre (HTC). The authors wish to acknowledge the support from Kanthal AB, Sandvik Materials Technology AB and the National Graduate School in Materials Science at Chalmers. A grant from Knut and Alice Wallenberg Foundation for acquiring the FEG-SEM instrument is gratefully acknowledged.

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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • H. Götlind
    • 1
    Email author
  • F. Liu
    • 2
  • J.-E. Svensson
    • 1
  • M. Halvarsson
    • 2
  • L.-G. Johansson
    • 1
  1. 1.Environmental Inorganic Chemistry Department of Chemical and Biological EngineeringChalmers University of TechnologyGoteborgSweden
  2. 2.Microscopy and Microanalysis Department of Applied PhysicsChalmers University of TechnologyGoteborgSweden

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