Lawrence Berkeley National Laboratory

An effective, dense and well adherent coating was produced on 430SS that has the result of significantly reducing the oxidation rate of this alloy at elevated temperatures. The coating is essentially a Mn-Co-O spinel, applied in powder form, and compacted to improve its green density. A simplified model is presented that allows an assessment of the effects of the contact and scale geometries. For 850oC, an ASR can be predicted of approximately 0.5 cm2, after 50,000hrs in air, taking into account a factor of 10 penalty for unfavorable contact geometries. The effect of the densified Mn-Co spinel coating is to reduce significantly Cr2O3 sub-scale formation, lower the thermal expansion mismatch, and increase the electronic conductivity of the scale. The findings point to several potential remedies for achieving coatings on 430 SS that allow for metal interconnects with a service life of 50,000hrs or more. Considering contact geometries, such service life is unlikely to be possible above operating temperatures of about 700oC, unless highly specialized alloys are used, with potential processing and cost penalties.