Corrosion Resistance of Multi-layered Ti/TIN Coatings on Surgical NiTi alloys in Artificial Saliva

It has been shown that orthodontic metal devices made by NiTi alloy may corrode in an acid- and chloride-rich intraoral environment. In the paper, pulsed bins arc ion plating (PBAIP) was conducted on NiTi to produce a multi-layered Ti/TiN coating to enhance the surface anti-corrosion properties. The corrosion behavior was monitored in an artificial saliva solution using electrochemical measurements techniques. The multi-layered Ti/TiN coating was found to improve the corrosion resistance of NiTi alloy considerably in the test solution, as manifested by the larger free corrosion potential, much lower passive current density, and no breakdown up to 1.5 V. The multi-layered Ti/TiN coating specimens exhibit larger impedance, lower porosity, and an exceedingly low metal ion release rate during 720 h immersion in the test solution. Visual inspection showed significant differences in the corrosion initiation and progress between the treated and ~untreated specimens after 720 h immersion. Our results reveal that the multi-layered Ti/TiN coating renders the NiTi orthodontic devices more corrosion resistant, as demonstrated by the long-term stability in the simulated immoral environment.