Mechanical properties of fluorinated DLC and Si interlayer on a Ti biomedical alloy

Fluorinated amorphous 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) process to improve the adhesion between F-DLC and Ti alloy. The structure and surface properties of F-DLC coatings, prepared by various fluorine flow ratios, were investigated by using X-ray diffraction spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The mechanical properties were evaluated by nano-indentation, and the adhesion, by micro-scratch. The results showed that a moderate incorporation of the fluorine content in the DLC films can still maintain acceptable mechanical properties, which, on the other hand, obtains remarkable benefits of blood compatibility and anti-corrosion.

► F-DLC’s sp2 carbon cluster increases with the precursors’ CF4/CH4 ratio. ► F-DLC’s reduced elastic modulus and hardness decrease with the CF4/CH4 ratio. ► F-DLC film’s adhesion strength degrades as the CF4/CH4 ratio elevated. ► An F-DLC deposited Ti6Al4V produced by a smaller CF4/CH4 ratio, 1-3, is suggested.