Effects of temperature, phase, elastic deformation and transformation on inhibition of localized corrosion of hydrogen-charged Ni-Ti superelastic alloy in NaCl solution

The effects of the solution temperature, phase, elastic deformation and the phase transformation on the inhibition of localized corrosion of a small amount of hydrogen-charged Ni-Ti superelastic alloy in 0.9% NaCl solution have been investigated by electrochemical measurements. No pitting potentials are observed in the anodic polarization curves obtained above room temperature and under static applied stress in the presence of parent or stress-induced martensite phases. In a dynamic cyclic tensile test in the elastic deformation region of the parent phase under various constant applied anodic potentials, the critical applied potential for an increase in the current density, which corresponds to the occurrence of localized corrosion, considerably shifts in the noble direction. At the stress plateau, i.e., in the superelastic region, caused by stress-induced martensite and reverse transformations, the critical applied potential for a marked increase in the current density slightly shifts in the noble direction. In the elastic deformation region of the stress-induced martensite phase, the critical applied potential for a marked increase in the current density shifts in the noble direction. The present results indicate that hydrogen charging is effective for inhibiting the localized corrosion of Ni-Ti superelastic alloy in NaCl solution at various temperatures, irrespective of the phase itself, under dynamic elastic deformation and the phase transformation.