Abstract
The anodic polarization behavior of equiatomic TiNi shape memory alloy with pure titanium as a reference material was investigated by means of open circuit potential measurement and potentiodynamic polarization technique. And the structure of passive films on TiNi intermetallic compounds was also conducted using AES and ESCA. While the dissolved Ni(II) ion did not affect the dissolution rate and passivation of TiNi alloy, the dissolved Ti(III) ion was oxidated to Ti(IV) ion on passivated TiNi surface at passivation potential. It has also been found that the Ti(IV) ion increases the steady state potential, and passivates TiNi alloy at a limited concentration of Ti(IV) ion. The analysis by AES showed that passive film of TiNi alloy was composed of titanium oxide and nickel oxide, and the content of titanium was three times higher than that of nickel in outer side of passive film. According to the ESCA analysis, the passive film was composed of $TiO_2$ and NiO. It seems reasonable to suppose that NiO could act as unstabilizer to the oxide film and could be dissolved preferentially. Therefore, nickel oxide contained in the passive film may promote the dissolution of the film, and it could be explained the reason of higher pitting susceptibility of TiNi alloy than pure Ti.
