At high anodic potentials, two phenomena may generally occur on the surface of a passivated electrode: the oxygen evolution and the transpassive dissolution (at grain boundaries or generalized). For some materials, this anodic dissolution is postponed by the structural or chemical modification of the passive film. This phenomenon is characterized by a second plateau on anodic polarization curves. This latter informs about a limited further dissolution. This feature is commonly called the secondary passivation.

Generally, it is assumed that the passive film grown on Ni-Cr based alloys is mainly composed of chromium (Ⅲ) oxide. However, in certain circumstances, the formation of oxide with higher valence of chromium is related to the secondary passivation. It is of interest to investigate the role of alloying elements in the process of the secondary passivation to solve industrial applications or alloys design issues.

The aim of the present work is to study the electrochemical behaviour, especially the secondary passivation behaviour, of different Ni-Cr based alloys and pure Cr. This was mainly achieved by using successive electrochemical impedance spectroscopy (EIS) measurements. After 24h of immersion in borate buffer solution, EIS diagrams for different samples were successively recorded at different potentials from cathodic to anodic direction on a wide potential range. The step-by-step polarization curves (potentiostatic polarization) obtained from successive electrochemical impedance measurements was used as a complementary method to conventional polarization curves.

Besides, each impedance diagram was firstly analysed by enhanced graphical representation and complex capacitance representation to assess electrolyte resistance, constant phase element (CPE) parameters (α and Q), capacitance and thickness of the passive film. Since in most of the cases the CPE behavior observed for passive films could be attributed to a distribution of the resistivity through the film thickness. The power law model was used to adjust the experimental impedance diagrams. This model allows to study the trend of the resistivity profiles within the passive film as a function of the potential. Thus, the variation of the determined parameters related to the potential was presented for the different alloys. The use of this analytical approach in the secondary passivation domain was discussed.

To conclude, the role of the alloying elements on the process of the secondary passivation and especially on the chemical composition of the passive film was discussed.