A tribological study of the hybrid lubrication of DLC films with oil and water

This paper reports on the results of a tribological study that compared the friction coefficient and wear volume of titanium alloy (Ti6Al4V) and 316L stainless steel samples, with and without DLC films, in contact with humidity, water and oils. Distilled water (DW), and synthetic motor oil (SO) were applied to some of the sample surfaces, while others were left uncoated or coated only with DLC. The DLC films were grown by using a Pulsed DC Plasma Enhanced Chemical Vapor Deposition (PE-CVD) technique. The friction coefficient and wear volume of various sample pairs were studied as a function of applied load with constant sliding speed, using sphere-on-flat configuration in the reciprocating mode. The sphere wear was measured using a very small pin approach, in agreement with the ASTM G99 norm. Also, the film's atomic arrangements and graphitization level before and after tribotests were analyzed by Raman scattering spectroscopy. Tribotests showed that the friction coefficient and the wear depend on boundary lubrication, suggesting that the chemistry of the fluid lubricant is an important parameter to be considered. Results showed that the lowest friction coefficient and no wear were obtained to DLC/DLC pair in contact with synthetic oil. The most significant aspect of our work is that with just one friction surface with DLC film it is possible to obtain a 56% reduction in the friction coefficients and no measurable wear, resulting in a 50% reduction in production cost. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.