In-situ monitoring of the corrosion behaviour of austempered ductile iron (ADI) under cyclic salt spray exposure.

• Oxidation of the ADI in the salt fog cause the formation of a dense inner and porous outer corrosion products layers. • Corrosion of ADI in the salt fog has three stages: pitting corrosion of ferrite, inward and mixed oxidation of the matrix. • Goethite and lepidocrocite were found in the inner and outer layers of corrosion products. The corrosion behavior of austempered ductile iron (ADI) under cyclic salt spray exposure was studied using a specific three-electrode cell located in the salt fog chamber. Three steps were identified, namely pitting corrosion of ferrite (very first cycles), followed by inward oxidation of the ausferrite matrix and then (iii) mixed oxidation of the matrix associated with the formation of a rust layer at the specimen surface. Evolution of the corrosion rate calculated from in-situ electrochemical measurements was correlated with surface changes quantified from optical and field emission scanning electron (FE-SEM/EDS) microscopies. Corrosion products were identified by means of micro-Raman spectroscopy. [ABSTRACT FROM AUTHOR]