Investigation of Modified Ni – Cr – Mn Base Alloys for SOFC Interconnect Applications

Abstract

Two base alloys based on Haynes 230 were developed and evaluated against criteria relevant to solid oxide fuel cell (SOFC) interconnect applications, which included oxidation behavior under SOFC operating conditions, scale electrical conductivity, and thermal expansion. It was found that, when exposed to air at both sides, the alloys formed a scale, containing , etc.) spinels and as well as some . When exposed to air at one side and hydrogen at the other, however, the scales grown on these alloys at the air side were similar to the ferritic stainless steel Crofer22 APU, comprised of only a , etc.) spinel-rich top layer and -rich sublayer. The modified alloys demonstrated reasonable oxidation resistance under SOFC operating conditions, though the Mn additions increased the scale growth rate and thus sacrificed to some extent the oxidation resistance of the base alloy (Haynes 230). The formation of a spinel-rich top layer improved the scale conductivity, especially during the early stages of oxidation, but the higher scale growth rate resulted in a higher rate of increase in the area-specific electrical resistance. In addition, the base alloys demonstrated a coefficient of thermal expansion higher than that of anode-supported cells and ferritic stainless steel candidates.