Long-term oxidation behavior of spinel-coated ferritic stainless steel for solid oxide fuel cell interconnect applications

Long-term electrical resistance tests were performed to evaluate the performance of AISI 441 ferritic stainless steel coated with a Mn–Co spinel protection layer as a candidate material for intermediate temperature solid oxide fuel cell interconnect applications. The tests indicated that, while uncoated AISI 441 shows a substantial increase in area-specific electrical resistance (ASR), spinel-coated AISI 441 exhibits much lower ASR values. The spinel coatings reduced the oxide scale growth rate and blocked outward diffusion of Cr from the oxide scale that grew between the coating and the steel substrate during the long-term tests. The oxide scale consisted of a chromia layer containing discrete regions of Mn–Cr spinel distributed throughout the layer. The presence of Ti in the chromia scale matrix and/or the presence of regions of Mn–Cr spinel within the scale may have increased the scale electrical conductivity, which would explain the fact that the observed ASR in the tests was lower than would be expected if the scale consisted of pure chromia.

► Ferritic stainless steel coated with Mn–Co spinel was tested for over 8000 h.
► The scale consisted of a chromia matrix containing regions of Mn–Cr spinel.
► Electrical resistance was lower than expected, possibly due to Ti in the scale.