Corrosion properties of materials coated with Cr{sub}2O{sub}3/NiCr and with Cr{sub}2O{sub}3 + NiCr functionally gradient materials

摘要

This paper studied the corrosion properties of five kinds of Cr{sub}2O{sub}3 coated materials: the SUS3I6L austenitic stainless steels respectively coated with the Cr{sub}2O{sub}3 layer (Cr{sub}2O{sub}3/316), Cr{sub}2O{sub}3 and 80Ni-20Cr layers (Cr{sub}2O{sub}3/80NiCr/316), Cr{sub}2O{sub}3 and 50Ni-50Cr layers (Cr{sub}2O{sub}3/50NiCr/316), Cr{sub}2O{sub}3+80Ni-20Cr functionally gradient materials (Cr{sub}2O{sub}3 + 80NiCr FGM), and Cr{sub}2O{sub}3 + 50Ni-50Cr FGM (Cr{sub}2O{sub}3 +50NiCr FGM). All the coatings were made by atmospheric pressure plasma spraying method (APPS). The corrosion resistance of the coated materials was analyzed by immersion tests and electrochemical evaluations. A mechanism of the corrosion failures for these kinds of coated structures was proposed. The different coating structures for improving the adhesion between ceramics and substrates were assessed, and the effect of Cr content in the NiCr coatings on the corrosion property was discussed. The ceramic coatings with the 50Ni-50Cr intermediate layer possessed a better corrosion resistance than that with 80Ni-20Cr. The FGM structures appeared to offer weaker resistance to corrosion attack than that with the intermediate layer in general. Under corrosion test conditions, the corrosion-proof abilities of the coated structures were, respectively: the Cr{sub}2O{sub}3/50NiCr/316 in the best rank; the Cr{sub}2O{sub}3/316, Cr{sub}2O{sub}3/80NiCr/316, and Cr{sub}2O{sub}3 + 50NiCr FGM in the second rank; and the Cr{sub}2O{sub}3 + 80NiCr FGM in the last rank. This means that applying the 50NiCr intermediate layer under the Cr{sub}2O{sub}3 ceramic coating can further improve the corrosion resistance of Cr{sub}2O{sub}3/316. Porosity analysis was used to explain the difference of corrosion resistance between the Cr{sub}2O{sub}3/50NiCr coated material and the Cr{sub}2O{sub}3+50NiCr FGM. The porosity in each layer of the Cr{sub}2O{sub}3 + 50NiCr FGM was higher than that in the Cr{sub}2O{sub}3/ 50NiCr coating, and as a result the corrosion resistance of Cr{sub}2O{sub}3/50Ni Cr/316 is better than Cr{sub}2O{sub}3 + 50NiCr FCM.