Fundamental Investigation of Hydrogen Transport in Ferritic Stainless Steel for SOFC Interconnect Applications

• Published in: ECS transactions 2013-01, Vol.58 (2), p.199-205
• Main Authors: Zimny, Christopher I, Amendola, Roberta, Gannon, Paul E., Berry, Chaparral
• Format: Article
• Language: English
• ISSN: 1938-5862; 1938-6737
• DOI: 10.1149/05802.0199ecst

Ferritic stainless steel (FSS) is widely used to separate different gaseous environments in many energy conversion systems such as turbines, heat exchangers, and intermediate temperature solid oxide fuel cell (SOFC) stacks. This so called "dual atmosphere exposure" at elevated temperatures (650-800°C) is commonly believed to facilitate accelerated and/or anomalous corrosion. In SOFC stacks, FSS interconnects (ICs) separate individual cells in a stack and are simultaneously exposed to the fuel (H2) on one side and the oxidant (air) on the other. This study focuses on the effects of SOFC operating conditions on FSS AISI 441, which has been observed to exhibit significant dual atmosphere effects on air-side corrosion. Subsequent 100 hours of dual atmosphere exposure (separating moist H2 from moist air at 800°C) FSS 441 sample surfaces and polished cross sections were analyzed using a field-emission scanning electron microscope (FE-SEM) equipped with energy dispersive x-ray spectroscopy (EDX) for elemental analysis. The study confirms the results of previous studies exploring secondary phase precipitation at grain boundaries and within the grains of FSS 441. Additionally, large Ti-rich nodules were observed on the cross-section surfaces. Ongoing efforts to investigate phase composition and texture using electron backscatter diffraction (EBSD) are discussed with the aim to better understand hydrogen transport mechanisms and attendant dual atmosphere corrosion of FSS 441.