Current Density Contour Map of TiNi Shape Memory Alloy in Sulfate Solutions

Abstract

In this study, a current density contour map of TiNi shape memory alloy in sodium sulfate solutions was constructed by potentiodynamic polarization technique. The current density contour map of TiNi alloy, constructed in a 0.5 M sodium sulfate solution over the pH range 1 to 13 at 37oC, showed only hydrogen evolution region, passive region, and oxygen evolution region. The localized corrosion region did not exist and the susceptibility of localized corrosion was not exhibited. We also investigated the effects of chloride ions on the pitting corrosion of TiNi alloy in sodium sulfate solutions. Pitting corrosion occurred with addition of 0.2 M NaCl in a sulfate solution. And it was observed that pitting potential got lower as the concentration of chloride ion went up. However, repassivation potential was not affected by the addition of chloride ion up to 0.5 M. It is concluded that a TiNi shape memory alloy exists as a passive state and a good corrosion resistance in sulfate solutions over the pH range 1 to 13, and the sulfate ion performs a role of inhibiting localized corrosion in chloride environment.