Reduced area specific resistance for iron-based metallic interconnects by surface oxide coatings

The effects of various reactive-element coatings on the oxidation kinetics of two commercial iron-based alloys, Ebrite and ANSI 446, at elevated temperatures were investigated. Although NiO is not regarded as a reactive element oxide, it was chosen as a coating due to the enhanced conductivity of Cr2O3 by doping with NiO. Hot-dipping was used to make the desired coatings. The results consistently show a pronounced reduction in oxidation rate by either a Y2O3 coating or an equally mixed Y2O3/NiO double coating, particularly at low temperature, but only a slight influence by NiO coating. Examination of the scale microstructures revealed a continuous denser scale strongly bonded to the underlying metal for a Y2O3 coating, but visible micro-cracks for NiO coating. Electrical resistance measurements after a Y2O3 coating indicate a corresponding reduction in area specific resistance (ASR) with platinum and oxide electrodes, but an increase in ASR with oxide electrodes for a NiO coating. With a Y2O3/NiO double coating, a careful control of the NiO level in the scale has led to a denser, thinner and conducting Cr2O3 scale.