Active, passive and transpassive dissolution of In-718 alloy in acidic solutions

The electrochemical behaviour of In-718 alloy in different compositions of binary and ternary solution mixtures of concentrated phosphoric, sulphuric, acetic acids and in different concentrations of aqueous and methanolic solutions of sulphuric acid has been studied by potentiostatic polarisation technique at 30 °C. The cathodic polarisation curves are almost linear and similar in all the solution mixtures and cathodic reaction is hydrogen evolution. The anodic polarisation curves reveal active, passive and transpassive behaviour in all the solution mixtures. In the transpassive region, a current plateau was observed in most of the cases in binary and ternary solution mixtures but electropolishing was not observed in any case. The results show that the existence of a current plateau is not the only sufficient condition for achieving electropolishing of the alloy.