Formation mechanism and oxidation behavior of Cu–Mn spinel coating on ferritic stainless steel for solid oxide fuel cell interconnects

Buckling damage and spallation during oxidation are prime challenges in electroplated Cu–Mn oxide spinel coatings prepared for SOFC interconnects. (Cu,Mn)3O4 spinel coating is formed on AISI-430 stainless steel by oxidizing electroplated copper and manganese layers at 750 °C in air. Nickel strike deposition significantly reduces coating spallation. During oxidation at 750 °C, spinel coating hinders chromium migration and improves the oxidation behavior of the alloy by a decrease of 98.9% in the parabolic oxidation rate constant. Formation mechanism of the spinel is investigated, revealing that manganese initially forms MnO, Mn2O3, and Mn3O4. Over the time, copper oxidizes to CuO, and Mn2O3 replaces MnO and Mn3O4. Finally, (Cu,Mn)3O4 spinel forms after 6 h of oxidation by the co-existence of CuO and Mn2O3. It is concluded that manganese oxidation induces buckling damage due to a volume increase of up to 137% in the coating during the earliest stages of the oxidation.