Fabrication of a double-layered Co-Mn-O spinel coating on stainless steel via the double glow plasma alloying process and preoxidation treatment as SOFC interconnect

Abstract

To improve oxidation resistance, prevent Cr evaporation and maintain appropriate electrical conductivity of AISI 430 stainless steel (430 SS) as the solid oxide fuel cells' (SOFCs) interconnect, a double-layered Co-Mn-O spinel coating is fabricated successfully on 430 SS via a simple double glow plasma alloying process (DGPA) followed by heating in the air (preoxidation treatment). The double-layered Co-Mn-O spinel coating is composed of a thick MnCo2O4 spinel outlayer and a thin mutual-diffused (MnCoFe)3O4 oxide innerlayer. The isothermal and cyclic oxidation measurements are used to investigate the oxidation resistance, and the ASR test is performed to evaluate the conductivity for the coated and uncoated specimens. The coated specimen has a lower oxidation kinetics rate constant (9.0929 × 10−4 mg2 cm−4 h−1) than the uncoated one (1.900 × 10−3 mg2 cm−4 h−1) and the weight gain of the coated specimen (0.84 mg cm−2) is less than that of bare steel (1.29 mg cm−2) after 750 h oxidation. Meanwhile, the coated specimen holds a lower area specific resistance (0.029 Ω cm2) compared to the uncoated one (2.28 Ω cm2) after 408 h oxidation. Furthermore, the compact Co-Mn-O spinel coating can effectively impede Cr-volatilization. Additionally, the probable mechanism of the Co-Mn alloy conversion into spinel and the electronic conduction behavior in the spinel are discussed. The effects of mutual-diffused oxide innerlayer on oxidation behavior and conductivity are investigated.