Surface corrosion enhancement of passive films on NiTi shape memory alloy in different solutions

• TiO2 in passive film improved the corrosion resistance of NiTi shape memory.
• NiTi alloy showed excellent passivated properties in sodium chloride solution.
• Corrosion resistance of NiTi alloy decreased with increasing passivated potential.

The corrosion behaviors of NiTi shape memory alloy in NaCl solution, H2SO4 solution and borate buffer solution were investigated. It was found that TiO2 in passive film improved the corrosion resistance of NiTi shape memory. However, low corrosion resistance of passive film was observed in low pH value acidic solution due to TiO2 dissolution. Moreover, the corrosion resistance of NiTi shape memory alloy decreased with the increasing of passivated potential in the three solutions. The donor density in passive film increased with the increasing of passivated potential. Different solutions affect the semiconductor characteristics of the passive film. The reducing in the corrosion resistance was attributed to the more donor concentrations in passive film and thinner thickness of the passive film.