TY  - THES
AU  - Vayyala, Ashok
TI  - Nanoscale investigation of high temperature oxidation mechanisms of high-Cr ferritic steels
VL  - 491
PB  - RWTH Aachen University
VL  - Dissertation
CY  - Jülich
M1  - FZJ-2020-02000
SN  - 978-3-95806-467-6
T2  - Schriften des Forschungszentrums Jülich Reihe Energie & Umwelt / Energy & Environment
SP  - xix, 105
PY  - 2020
N1  - Dissertation, RWTH Aachen University, 2020
AB  - 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. [...]
LB  - PUB:(DE-HGF)3 ; PUB:(DE-HGF)11
UR  - https://juser.fz-juelich.de/record/875391
ER  -