Surface modification of NiTi alloys using diamond-like carbon (DLC) fabricated by plasma immersion ion implantation and deposition (PIIID)

DLC films with various bias voltages were deposited on polished NiTi alloys by plasma immersion ion implantation and deposition (PIIID) using graphite as plasma precursor. Microstructure and nano-hardness of the DLC films were characterized by Raman spectroscopy and nano-indentation system, respectively. The electrochemical corrosion behavior of DLC coated and uncoated NiTi alloys is investigated in Hank’s solution by means of potentiodynamic polarization tests. The results show that on the one hand the corrosion resistance and surface hardness and elastic modulus of the NiTi alloys are remarkably improved due to the deposition of the DLC films, and on the other hand the sp3/sp2 ratio inferred from Raman spectra, hardness, elastic modulus and the corrosion resistance of the DLC films on the NiTi alloys first increase and then decrease with the increase of the bias voltage. It can be concluded that the corrosion resistance of the DLC films is influenced by their microstructure.