Characterization and haemocompatibility of fluorinated DLC and Si interlayer on Ti6Al4V

Fluorinated diamond-like carbon (F-DLC) films were deposited on Ti6Al4V substrates by radio frequency plasma enhanced chemical vapor deposition (rf PECVD) technique using a mixture of methane (CH4) and tetrafluoromethane (CF4) gasses. A 100 nm Si interlayer was coated in advance by physical vapor deposition (PVD) to improve the adhesion between F-DLC and Ti alloy. A 200 nm TiN-coated specimen with the same Ti6Al4V substrate was also built by PVD as a benchmark. The structure and surface properties of F-DLC coatings, prepared with various fluorine flow ratios, were investigated by using X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, liquid drop goniometry, and electrochemical corrosion tests. The blood compatibility was evaluated by measuring haemolysis ratio and platelet-covered area in vitro. The films' spectroscopic results show that the CFx group and fluorine atomic concentration increase as CF4 flow ratio is promoted in the mixture. The surface energy is reduced due to the increased fluorine content. The modified surfaces are characterized by higher hydrophobicity, lower thrombogenicity, and better corrosive protection than the virgin and TiN ones.

► Fluorine atomic concentration increases with the CF4/CH4 ratio of the precursors.
► Etching mechanism becomes significant with higher CF4/CH4 ratio.
► F-DLC film's anti-corrosion capability is influenced by CF4/CH4 ratio and thickness.
► An F-DLC deposited Ti6Al4V produced by a smaller CF4/CH4 ratio is suggested.