Modern advanced mechanical systems need to operate under evermore demanding working conditions, such as high loads, speeds, temperatures and aggressive environment, and typically, better performance is expected than it was in the past. Under lubricated conditions, this suggests that contact conditions are changing toward mixed or boundary lubrication regime, where successful operation depend on properties of the surfaces and their ability to form wear-protective and low-friction boundary films, which is typically achieved with lubricant additives and/or advanced surface coatings. However, conventional advantages of typical surface coatings or additives, are often not sufficient for the most advanced tribology systems, which in addition, need to consider demands on greener operation. New concepts, which require smart nanoscale interface design by combining unique surface coatings, specific surface-tailored additives, fully-exploiting topography features and tribofilms response, call for extreme surface layers. However, which contact-design rules and approaches are available today to respond on these demands? Various tribology aspects and surface phenomena that could lead to far-improved future performance are discussed.
B.04 Guest lecture
COBISS.SI-ID: 15698715We have studied the effect of counterbody on formation of ZDDP tribofilm on hydrogenated diamond-like carbon coating after 1 and 6 hours sliding for ball on disc contact. Formation of tribofilm was evaluated in terms of surface roughness, tribofilm thickness, coefficient of friction and wear for both surfaces in contact for all four tribopairs (steel/steel, DLC/steel, steel/DLC, DLC/DLC). Results show that the presence of steel counterbody is unnecessary for formation of tribofilm on DLC surface. Furthermore, it turned out that it is very important whether steel surface in contact is used as a ball or disc. In case of steel/DLC tribopair, almost no tribofilm was formed on DLC disc and the amount of film decreased with sliding on both surfaces of tribopair. On the contrary, more tribofilm was detected on DLC ball in DLC/steel tribopair and the amount of tribofilm increased with sliding on both surfaces in tribopair.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 16089883Neutron reflectometry has proven to be indispensable analytical tool for providing direct evidence with quantitative information on the additive adsorption. In fact, it enables in-situ measurement of depth profiles of thin films and interfaces during surfaces exposure to additivated lubricants with sub-nanometer precision. This is especially important in studying delicate interfaces, such as for instance DLC coating/tribofilm, whereby the evidence of surface-to-additive interactions can be lost due to required sample cleaning before analysis and/or work in vacuum. Using this technique we have studied the adsorption of the ZDDP additive onto a hydrogenated DLC (a-C: H) coating at different temperatures and different exposure times. In addition, the influence of tribological contact on the growth/removal of a priori formed ZDDP film was investigated for the first time with the neutron reflectometry. For this purpose, tribological tester designed especially for the implementation into in a neutron reflectometer was used.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 16380443Although it has become obvious that wettability is an important characteristic in tribology, there is still no information on how additives and their different molecular structure change the wetting behaviour of oil, if at all. This work reports on the influence of some simple organic friction modifiers like fatty acids, amides, alcohols and amines on static and dynamic (i.e. advancing, receding contact angle, CAH) wetting of oil. The influence of additive molecular structure was investigated by varying additive chain length and polarity. Using both static and dynamic wetting parameters we wanted to determine which of them is the most appropriate for evaluating wetting behaviour of oil on steel.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 16377115Organic Friction Modifiers (OFMs) are additives that work through adsorption of the polar headgroup to the surface. Despite numerous literature, there are no studies to investigate the adsorption of OFM from a commercial lubricating oil. In order to develop new, better and more environmentally friendly additives, the understanding of both adsorption and wetting is of key importance. In collaboration with TOTAL company (France), we performed adsorption measurements for simple OFM using a quartz microbalance (QCM). Although it has become obvious that wettability is an important characteristic in tribology, there is still no information on how additives and their different molecular structure change the wetting behaviour of oil, if at all. Studies have reported that the most commonly used static contact angle to describe the wettability of oil on steel might be inappropriate parameter. In this work, we studied the influence of the molecular structure of some simple OFMs (fatty acids, alcohol and amine) on their adsorption from lubricating oil and how the adsorbed film affects the static and dynamic wettability of the oil. By evaluating the wettability with the parameters of static and dynamic wetting (advancing and receding contact angle and the contact angle hysteresis CAH), we wanted to determine, which of them is the most appropriate for evaluating wetting behaviour of oil on steel.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 16380955