Evaluation of pulse electroplated cobalt/yttrium oxide composite coating on the Crofer 22 APU stainless steel interconnect

Abstract

Ferritic stainless steels have been evaluated as favorable materials for utilization in SOFC interconnects. However, there are difficulties in utilizing these metallic interconnects, including the quick decrease of their electrical conductivity and cathode poisoning due to the evaporation of Cr species. In this work, Co and Co/Y2O3 composite coatings have been deposited onto Crofer 22 APU stainless steels by the pulse current electrodeposition method and the oxidation and electrical properties of uncoated and coated steels have been evaluated. Cyclic oxidation was performed in air at 800 °C for 500 h, oxidation rates were calculated, and oxide layer microstructures were examined. SEM–EDS and XRD investigations exhibited the created oxide layer on both coated samples made up of two scale after oxidation. The internal thin scale was composed of Cr and O and the external scale comprised of Co, Mn, Cr, Fe, and O. Y2O3 was observed as dispersed particles in the external oxide scale after the cyclic oxidation test. The thicknesses of internal oxide scale were reduced and oxidations rates also were meaningfully decreased for Co/Y2O3-coated steels relative to uncoated and Co-coated steels. Finally the ASR values of coated and uncoated substrates was also tested as a function of temperature and time in air. Results showed that the ASR value of the Co/Y2O3-coated steel was 13.1 mΩ cm2 after 500 h of cyclic oxidation at 800 °C, which was significantly lower than that of bare steel and the Co-coated sample.