Oxidation resistance of chromium steels is due to the formation of Cr 2 O 3 on the surface. However, this surface layer destabilizes above 1,000°C and does not protect the metal. In this study, three types of coatings were applied to AISI 304 stainless steel (SS), and the microstructure and oxidation resistance of the coatings were investigated. Aluminum coating, silicon coating, and the codeposition of Al and Si were deposited on an SS substrate by the pack cementation method. The microstructure of the samples was then examined by SEM and EDS, and phases were identified by XRD. The oxidation resistance of these samples was studied in air at 1,050°C. The results showed that the best resistance to oxidation was obtained, in order, from the codeposition of Al-Si, Al coating, and Si coating.
An issue associated with chromia-scale formation on ferritic stainless steels is an associated increase in electrical resistance over time, due to the oxide growth. Further, the migration of chromium via chromia-scale evaporation into solid oxide fuel cell (SOFC) cathodes can result in degradation in cell electrochemical performance. In this research, manganese and cobalt were deposited by the pack cementation method onto Crofer 22 APU ferritic stainless steel. Isothermal and cyclic oxidation was carried out to evaluate the role of coating materials during oxidation. Area-specific resistance (ASR) of the Mn-Co-coated substrates was also tested at 800°C. The results demonstrate that the coating layer transforms to MnCo 2 O 4 , CoFe 2 O 4 , CoCr 2 O 4 , and Co 3 O 4 spinels during oxidation. This scale is protective, and acts as an effective barrier against chromium migration into the outer oxide. Mn-Co oxide and cobalt oxides also cause a reduction in ASR, in comparison to that of bare steel.
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