Abstract
The pitting corrosion behavior and the surface oxide layer for Ni-Ti alloy have been investigated by electrochemical techniques. According to potentiodynamic polarization measurement on physiological saline solution, the critical pitting potentials for Ni-dissolution are ＋0.9 V vs. Ag/AgCl for pure Ni, whereas the Ni-corrosion reaction for Ni-Ti is shifted more anodically at about ＋1.4 V. Thus it is suggested that the presence of Ti may significantly improve the corrosion resistance of the alloy. The pitting corrosion behavior was also examined by AC impedance measurement, ICP-atomic emission spectroscopy (AES) and scanning electron microscopy (SEM). The oxide layer on alloy surface was studied in strong basic media. At the Ni-Ti alloy electrode, the redox waves caused by Ni(Ⅲ)/Ni(Ⅱ) were observed near ＋0.5 and 0.45 V vs. Ag/AgCl, which is very similar to that observed on the pure Ni electrode. However, from the results of time dependence in voltammetric measurements, the interconversion of oxide phase from α-Ni(OH)2 to β-Ni(OH)2 was confirmed to be difficult, occurring on the Ni-Ti electrode surface compared with the Ni electrode. Therefore, it was suggested that the presence of Ti in alloy stabilized the microstructure of the passivation oxide layer and consequently improved its corrosion resistance.
