عنوان مقاله [English]
In this paper, heat treated Nickel Aluminium Bronze (C95520) was used as received and exposed to sea water for 75 days. Metallographic investigations were carried out on exposed specimens prepared under as received and heat treated conditions in order to study their microstructures using optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy dispersive x-ray analysis (EDAX). To determine the resistance of the passive layer on specimen surfaces, an advanced and novel electrochemical noise technique via zeo resistance ammeter (ZRA) together with linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) were utilized. With respect to the passivation potentials extracted from polarization diagrams and polarization resistance (Rp) determined from Nyquist diagrams for all specimens, it was found out that the target sample was under concentration polarization effect. The target sample, coded as sample 14, was heat treated at 675 oC for 45 minutes and normalized in air. The lower starting passivation potential for the target sample indicated a better condition from passivation point of view. Data analysis of electrochemical noise measurements using an evaluation of the last measured 40 potentials and current data of the specimens exposed to sea water for 75 days showed that the corrosion current for as received specimen was found to be twice that of the target specimen. According to the metallographic micrograph, the pearlitic zones in target specimens were attacked much less than similar sites in as received specimen. It was further observed that the corrosion attack on passive layer occurred on selective phases leading to pitting corrosion.