Electrochemical behavior of Ni 3Al-based intermetallic alloys in NaOH

Abstract

The corrosion behavior of Ni 3Al-based intermetallic alloys in a 0.5 M NaOH solution was studied at 25 °C. The open circuit potential, cathodic and anodic potentiodynamic polarization, Tafel plots and linear polarization resistance measurements were used to characterize the corrosion behavior. For the Ni 3Al(B, Zr) alloy, potentiodynamic polarization curves showed a wide passive region that can be found between about −0.220 V SCE and 0.520 V SCE. On the other hand, a narrow passive region, in the range of potentials from about −0.180 V SCE to 0.180 V SCE, was observed for the Ni 3Al(B, Zr, Cr, Mo) alloy. Chromium, as an alloying element in the Ni 3Al(B, Zr, Cr, Mo) alloy, contributes to transpassive dissolution of the passive film at much lower anodic potentials and remarkably reduces the passivation region. The experiments indicated also that damaged passive films on alloys repairs itself and pits do not initiate. The surface of both alloys and passive films possess extremely high corrosion resistance in a studied solution. However, Tafel and linear polarization tests revealed that freshly exposed surfaces of the Ni 3Al(B, Zr) alloy exhibited better corrosion resistances than the Ni 3Al(B, Zr, Cr, Mo) alloy. Both methods, used for the determination of corrosion rates gave very similar results. The calculated corrosion rates are about 2.8 ·10 −3 and 6.0·10 −3 mm year −1 for the Ni 3Al(B, Zr) alloy and B, respectively.