Book/Dissertation / PhD Thesis

FZJ-2020-02000

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Nanoscale investigation of high temperature oxidation mechanisms of high-Cr ferritic steels

Vayyala, A. (Corresponding author)FZJ*

2020
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-467-6

Please use a persistent id in citations: http://hdl.handle.net/2128/24992  urn:nbn:de:0001-2020060509

Abstract: Fe–22 Cr–0.5Mn based ferritic steels are being used as construction materials for interconnectsin solid oxide cells (SOCs). Oxidation resistance of these steels is critical for their performance and was investigated in the present work under conditions relevant for the interconnect operation. A set of ferritic steels of a Crofer family, including the commercial steel Crofer 22 H,were oxidized at 800 °C in Ar–O$_{2}$, Ar–H$_{2}$ –H$_{2}$O and Ar–CO–CO$_{2}$ model gases simulatingair and fuel sides of the fuel cells. The key factors controlling the high temperature oxidation behavior are addressed in the work, namely i) the effect of gas composition and ii) the role of alloying elements in the steels, especially minor additives. A set of analytical techniques was employed to characterize the oxidation process as well as the related structural changes in the steels. TG data were correlated with the results of the elemental analysis from GD–OES, phase analysis by XRD or Raman spectroscopy and microstructuralanalysis using SEM. A special focus in the work was put on high–resolution characterization methods such as TEM and APT, which enable to reveal the microstructure of the oxide scale and the elemental distribution at the nanoscale level and thereby investigate the mass transport processes through the oxide. APT was extensively used for obtaining atomic scale insight into the microstructure, particularly at grain boundaries, and the obtained information was employed to shed light on the oxidation mechanisms. The oxidation rate of these ferritic steels strongly depends on the oxygen partial pressure as well as on the alloy chemistry, even on small compositional changes. All studied alloys form a duplex oxide scale consisting of MnCr$_{2}$O$_{4}$ spinel on top of Cr$_{2}$O$_{3}$ in all atmospheres. Addition of Nb resulted in Nb–rich rutile–type oxide layer formation at the chromia–alloy interface. Subsequent addition of Si to Nb–containing alloy leads to disappearance of Nb–rich oxide layer and formation of a mesh–like SiO$_{2}$ layer at this interface. Ti addition promotes formation of the internal oxidation zone. [...]

Note: Dissertation, RWTH Aachen University, 2020

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Contributing Institute(s):

1. Analytik (ZEA-3)
2. Materialwissenschaft u. Werkstofftechnik (ER-C-2)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

Appears in the scientific report 2020

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Database coverage:
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