Effect of Ti addition on the electric and ionic property of the oxide scale formed on the ferritic stainless steel for SOFC interconnect

Ferritic stainless steels with Ti addition are considered as promising candidates for SOFC interconnect application. In this study, the effect of Ti addition on the electrical conductivity and Cr evaporation resistance was discussed in terms of microstructure and ionic property of the oxide scale by using TEM analysis and asymmetry polarization method. Ti addition induced the generation of ionic defects in the oxide layer and modified the growth kinetics of Cr2O3 and MnCr2O4, but in different manner depending on Ti amount. Ti content in a range of 0.05–0.07 wt% was effective for reducing the oxidation rate and electrical resistance. Addition of 1 wt% Ti promoted fast Cr2O3 growth due to the excess ionic defect in Cr2O3 matrix. However, the formation of the outermost MnCr2O4 layer was accelerated by Ti segregation near the scale/alloy interface and it reduced Cr evaporation effectively. Co-addition of a small amount of Ti and La enhanced Ti segregation without generation of excess ionic defect and improved both the electric conductivity and Cr evaporation resistance.

► Ti modified the growth kinetics of scale differently depending on the Ti amount.
► Presence of Ti (0.06 wt%) in Cr2O3 matrix retarded the oxidation rate of steel.
► A high amount (1 wt%) of Ti in Cr2O3 matrix generated excess ionic defect.
► The addition of high amount (1 wt%) of Ti accelerated the oxidation rate of steel.
► Co-addition of Ti and La reduced both electric resistance and Cr evaporation.