Effect of bias voltage on the structure and the electrochemical corrosion behavior of hydrogenated amorphous carbon (a-C:H) films on NiTi alloys

Hydrogenated amorphous carbon films with different bias voltages were deposited on polished NiTi alloys by plasma immersion ion implantation and deposition (PIIID) using acetylene as precursor. Film composition and microstructure were characterized by X-ray photoelectron spectroscopy (XPS) and Raman scattering spectroscopy. The electrochemical behaviour of amorphous carbon films was investigated in Hankʹs solution by means of potentiodynamic polarization tests and atomic absorption spectrometry. The results show the a-C:H films improve the corrosion resistance of NiTi alloys, and the sp3/sp2 ratio and corrosion resistance of the a-C:H films on the NiTi alloys first increase and then decrease with the increase of bias voltage. Moreover, the relationship between the corrosion resistance and the structure of the a-C:H films is clarified.