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In situ study of real structure effects on the initial oxidation of FeCrAl alloys by two-dimensional high temperature X-ray diffraction

 
: Kodjamanova, P.; Fietzek, H.; Juez-Lorenzo, M.; Kolarik, V.; Hattendorf, H.

:

Taniguchi, S.:
High-temperature oxidation and corrosion 2005 : Proceedings of the International Symposium on High-temperature Oxidation and Corrosion 2005, Nara, Japan, 30th November - 2nd December 2005
Uetikon-Zuerich: Trans Tech Publications, 2006 (Materials Science Forum 522/523)
ISBN: 0-87849-409-X
ISBN: 978-0-87849-409-5
S.69-76
International Symposium on High-Temperature Oxidation and Corrosion <2005, Nara>
Englisch
Konferenzbeitrag
Fraunhofer ICT ()

Abstract
In order to contribute to a better understanding of the processes, which occur in the structure of FeCrAl alloys during oxidation, in situ - studies by two-dimensional high temperature X-ray diffraction (2D-XRD) using a global area detector and grazing incidence with a monocapillary have been performed. The 2D-XRD yields simultaneously with the identification of the oxides and their formation kinetics information about the grain size, grain shape, stresses, texture as well as grain movements during the oxidation process of both oxide and metal. Two commercial FeCrAl alloys with different reactive element additions were investigated in the temperature range of 850 degrees C to 1100 degrees C. In the range of 1100 degrees C already in the first 5 min the alloy grains become coarse and appear as single spots along the lateral profile in the 2D-XRD pattern. Dynamic displacement of these spots along the 20 - axis during the exposure indicates the formation of stresses, which differ from grain to grain. Initially, re-crystallisation and grain growth dominate and grains disappear and new grains appear. On further exposure the grains twist continuously with 1 degrees to 3 degrees per hour, depending on the alloy. The "dancing grain" effect of the alloy is probably related with growth stresses in the oxide scale and influenced by the bulging of the foil. Simultaneously, alpha-Al2O3 is detected from the first pattern after 5 min and shows an enhanced formation rate in the first 15 min of the oxidation. The alpha-Al2O3 grains are with 0.3 to 0.4 pin extremely fine and, a dense well adherent scale is observed even after I h.

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