Macroscopic and local electrochemical studies of austempered ductile iron in perchlorate solutions

The corrosion behavior of austempered ductile iron (ADI) in alkaline environment has been investigated at the microscale by means of the electrochemical microcell technique, surface analysis methods, and at the macroscale using classical electrochemical techniques. Local electrochemical investigations have revealed that the matrix (ausferrite), far from spheres, undergoes passivation in 1 M NaClO4, pH 10 solution within a wide potential range, from the corrosion potential (of about - 280 mV/SCE) until 800 mV/SCE. Surface observations combined with local electrochemical analysis have shown that corrosion of ADI first occurs in the close vicinity of some graphite spheres and then around oxide inclusions. The oxidized regions are richer in oxygen than the matrix located far from spheres. X-ray photoelectron spectroscopy analysis has revealed that the electrochemical dissolution of ADI in 1 M NaClO4, pH 10, leads to the formation of corrosion products containing mainly iron oxides and hydroxide. (c) 2006 The Electrochemical Society.