Oxidation and electrical behavior of AISI 430 steel coated with Ni–P–TiO2–ZrO2 composite for SOFC interconnect application

Abstract

AISI 430 stainless steel is used for interconnects in solid oxide fuel cells (SOFCs). One of the main problems with this steel is the formation of chromia scales during oxidation at high temperature and thus increasing electrical resistance. In order to solve such problems, a protective and conductive coating layer can be applied on interconnects. In this study, AISI 430 steel was coated by Ni–P–TiO2–ZrO2 composite coating. To evaluate the oxidation behavior, isothermal and cyclic oxidation tests were used at 800 °C. Area specific resistances (ASR) of uncoated and coated samples were also compared as a function of time during oxidation at 800 °C. Chemical composition and surface morphology of the samples were examined before and after oxidation by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). In isothermal and cyclic oxidation tests, coated samples showed lower weight gain due to the formation of Ni2P2O7, Ni3P2O8, and NiFe2O4 spinel. This spinel prevented outward Cr diffusion, and improved the oxidation resistance of the AISI 430 stainless steel substrate. The obtained result by cyclic oxidation revealed that the coated substrates were resistant against cracking and spallation. Also, the results showed that the formation of Ni2P2O7, Ni3P2O8, and NiFe2O4 spinel and also the presence of TiO2 and ZrO2 caused ASR reduction. ASR of Ni–P–TiO2–ZrO2-coated specimens after 300 h of oxidation at 800 oC (14.21 mΩ cm2) was lower than the uncoated specimens (41.84 mΩ m2) after the same time of oxidation.