Oxide modification by chi phase formed on oxide/metal interface of Fe-22Cr-0.5Mn ferritic stainless steel for SOFC interconnect

The effect of tungsten addition to Fe-22Cr-0.5Mn ferritic stainless steel on the oxidation, electric property and Cr evaporation is investigated for application to the solid oxide fuel cell interconnects. The mass gain, area specific resistance and Cr evaporation rate are evaluated to examine the feasibility of these alloys for an interconnect material. Addition of 4–6 wt.% W reduces the oxidation rate, evaporation rate of Cr vapor species and area specific resistance of Fe-22Cr-0.5Mn steel. When more than 4 wt.% W is added, chi (χ) phase particles are formed, especially beneath the interface between the oxide layer and substrate steel. These second phase particles are responsible for suppressing the fast diffusion of Cr, so that the surface Cr content is reduced while Mn content is increased. This reduction in Cr content at the surface is responsible for the lower Cr evaporation rate and area specific resistance.