Tribological and corrosive investigations of perfluoro and alkylphosphonic self-assembled monolayers on Ti incorporated carbon coatings

This paper presents tribological and corrosion properties of perfluoro and alkylphosphonic self-assembled monolayers formed on Ti incorporated carbon coatings. The Ti-DLC incorporated coatings were deposited on Ti6Al4V substrates by Radio Frequency Plasma Enhanced Chemical Vapour Deposition (RF PECVD) method using combination of methane (CH4) and titanium (IV) isopropoxide (Ti [OCH(CH3)2]4) atmospheres. The obtained coatings were subsequently modified by perfluoro and alkylphosphonic self-assembled layers having hydrocarbon or perfluorocarbon chains (DP and PFDP). Presented results show that application of these compounds on the top of Ti-DLC coatings significantly improves their tribological properties. After 1000 m of ball-on-disc test the DP- and PFDP- modified coatings presented low coefficient of friction, showing particularly more stable and lower value in case of PFDP while the unmodified coating was worn out already after 160 m of the test under the same conditions. The corrosion tests show varied results for both modifiers. In the case of PFDP an increased reactivity of the coating is observed, whereas for DP the results prove the anti-corrosive effect of this self-assembled layer.