Influence of precipitation on initial high-temperature oxidation of Ti–Nb stabilized ferritic stainless steel SOFC interconnect alloy

Oxidation phenomena on Laves phase forming Ti–Nb stabilized ferritic stainless steel (EN 1.4509) were studied at 650 °C by electron microscopic and electron spectroscopic methods. These investigations reveal a strong competition between Nb and Si for interfacial oxidation at the oxide–metal interface that is affected by different segregation rates of Nb and Si at elevated temperatures. In particular, formation of Si containing Laves (FeNbSi)-type intermetallic compounds in the bulk results in non-uniform distribution of Si oxide at the interface. This has direct implications to the electrical properties of this alloy in solid oxide fuel cell (SOFC) applications. Furthermore, these results provide better understanding to the controversial role of second phases (e.g. Laves, chi) on high-temperature oxidation (as recently discussed by Dae Won Yon, Hyung Suk Seo, Jae Ho Jun, Jae Myung Lee, Do Hyuong Kim, Kyoo Young Kim in Int J Hydrogen Energy 2011;36:5595–5603).

► Formation of Si containing Laves phase upon aging of EN 1.4509 at high-temperature.
► Strong competition between Nb and Si for oxidation at the oxide–metal interface.
► Laves phase results in non-uniform distribution of Si oxides at the interface.