INTERNATIONAL JOURNAL OF ELECTROCHEMICAL SCIENCE, vol.9, pp.5352-5374, 2014 (SCI-Expanded)
The effect of Rhenium (Re) additions (2.4, 3.5, and 6%) to a standard Inconel 718 alloy (IN718) on the uniform and pitting corrosion processes of IN718 was studied. Measurements were conducted in 1.0M H2SO4 solutions without and with 0.1M, 0.3M, or 0.6M NaCl at 25 oC, employing various electrochemical techniques, complemented with SEM/EDS and AFM examinations. The corrosion behavior at equilibrium (corresponding to immersion of samples without polarization) was studied as a function of alloy composition by monitoring the open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS) measured at the corrosion potential (Ecorr), and by polarization studies around Ecorr (Ecorr±250 mV). The anodic behavior of the tested alloys was also studied in 1.0M H2SO4 solutions without and with Cl-, based on potentiodynamic anodic polarization measurements. A potentiostatic technique (current vs. time measurements at a given potential) was also employed to access the role of the alloyed Re in the kinetics of pit initiation and growth induced by Cl-. Experimental findings showed that the rates of the uniform and pitting corrosion processes decreased when Re content increased from 2.5% to 3.5%. However, further increase in alloyed Re content (up to 6%) has resulted in an obvious enhancement in the rates of uniform and pitting corrosion processes. Potentiostatic measurements in presence of Cl- showed that nucleation of pit (initiated by Cl- at anodic potentials very close to and beyond the pitting potential, Epit) takes place after an incubation time (ti). The rate of pit nucleation (ti-1) increases with increase in Cl- concentration and applied anodic potential (Ea). The results of potentiostatic measurements also revealed that ti-1 suppressed when Re content in the alloy increased up to 3.5%, but enhanced in presence of 6%Re.