Effect of gas composition on the oxide scale growth mechanisms in a ferritic steel for solid oxide cell interconnects

• Published in: Corrosion science Vol. 221; p. 111317
• Main Authors: Vayyala, Ashok, Povstugar, Ivan, Naumenko, Dmitry, Quadakkers, Willem J., Hattendorf, Heike, Mayer, Joachim
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.08.2023
• Subjects: Atom probe tomography (APT); Grain boundary segregation; Oxide-film growth kinetics; SOFC; STEM; Oxide-film growth kinetics; Grain boundary segregation; Atom probe tomography (APT); SOFC; STEM
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2023.111317

The oxidation behavior of a ferritic steel Fe-23Cr-0.5Mn-0.6 Nb-0.1Ti (at%) considered for application in solid oxide cell (SOC) stack interconnects was studied at 800 °C. The oxidation kinetics and oxide scale microstructure formed in Ar-20%O2, Ar-4%H2-4%H2O and Ar-1%CO-1%CO2 atmospheres, simulating the SOC operation environments, were investigated by thermogravimetry (TG) in conjunction with electron microscopy (SEM/TEM) and atom probe tomography (APT). In all three environments multilayered oxide scales formed, consisting of Mn-Cr spinel on top of Cr2O3 and an additional Nb-rich oxide layer at the chromia-alloy interface. The initially faster oxidation in the low pO2 gases was attributed to formation of porous chromia scales compared to a dense scale formed in the high pO2 (Ar-O2) atmosphere. APT revealed segregation of minor alloying elements (Mn, Nb and Ti) to chromia grain boundaries in all three simulated SOC environments in quantitatively similar amounts, suggesting their similar effect on the ionic transport through the oxide scale. The findings indicate that oxygen activity in the test gas plays a dominating role in governing the oxidation kinetics and the oxide scale microstructure of the studied ferritic steel. [Display omitted] •.Studied high-Cr ferritic steel's oxidation in simulated solid oxide cell gases at 800 °C.•Early oxidation rates in low pO2 gases exceed high pO2, but later become similar or even slightly lower.•Oxide scales comprise outer Mn/Cr-spinel, inner chromia, and thin Nb(Cr,Ti)O2 layer at metal-chromia interface.•TEM revealed dense, fine-grained oxide in high pO2, and coarser, porous chromia scales in low pO2 atmospheres.•APT revealed Mn, Ti, Nb segregation at Cr2O3 boundaries in all gas tests. Growth rate differences aren't due to boundary transport.