Effect of working pressure on the structure and the electrochemical corrosion behavior of diamond-like carbon (DLC) coatings on the NiTi alloys

DLC coatings with different working pressure (2 × 0− 2, 6 × 10− 2 and 8 × 10− 2 Pa) were deposited on polished NiTi alloys by plasma immersion ion implantation and deposition (PIIID) using graphite as plasma source. The results of Raman spectra and X-ray photoelectron spectroscopy (XPS) indicate the sp3/sp2 ratio is decreased with the increase of the working pressure. The cross-section microstructure of the DLC coated NiTi alloys indicates that the DLC coating is dense and compact. The corrosion results show that the corrosion resistance of the NiTi alloys is improved by the DLC coating, and the corrosion resistance of the DLC coatings on the NiTi alloys is decreased with the increase of the working pressure. It can be concluded that the sp3/sp2 ratio has obvious effect on the corrosion resistance of the DLC coatings.