Corrosion investigation of nickel base superalloys in simulated high level waste medium using electrochemical impedance spectroscopy

67-72Nickel base superalloys (Alloy 600, 690 and 693) under as-received and heat treated (solution-annealed and sensitized) condition have been assessed by electrochemical impedance spectroscopic technique for their corrosion behavior in 3 M HNO3 and simulated high level waste medium at 25°C. All the alloys in all the conditions (as-received, solution-annealed and sensitized) show higher polarization resistance in 3 M HNO3 compared to simulated high level waste. The solution-annealed specimens for Alloy 690 and Alloy 693 show near capacitive behaviour in a larger ranger of frequency. Among the three alloys, Alloy 690 show highest polarization resistance followed by Alloy 693 and Alloy 600, due to the better stability of passive oxide layer. In contrast, the decreased polarization resistance for Alloy 600 specimens imply deterioration or reduction in the passive film stability