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Environmental awareness and especially the legislation that requires the reduction of polluting emissions are strong driving forces toward more sustainable engineering and greener solutions in the design, use and overall life span of machinery. However, providing novel concepts that will exclude non-environmentally adapted, but over many years developed and optimized solutions, is not an easy task. It clearly requires time if the same level of technical performance is to be maintained. Green tribology is one of the fields that has been closely involved in these actives in the past two decades. The research and use of tribology science and technology toward green and sustainable engineering include natural material usage, lower energy consumption, reducing natural oil resources, reducing pollution and emissions, fewer maintenance requirements and thus reduced machinery-investment cycles. This report is not an attempt to cover all the existing concepts, attempts or literature available in the field, but mainly those efforts that our group has been working on over the past 20 years, which mainly includes novel green-lubrication concepts that come from exploring and exploiting surface engineering through the use of diamond-like-carbon (DLC) coatings.

In this study we present a mechanism for the elastohydrodynamic (EHD) friction reduction in steel/steel contacts, which occurs due to the formation of oleophobic surface boundary layers from common boundary-lubrication additives. Several simple organic additives (amine, alcohol, amide, and fatty acid) with different molecular structures were employed as the model additives. It was found that the stronger chemisorption at 100 °C, rather than the physisorption at 25 °C, is more effective in friction reduction, which reaches 22%. What is more, EHD friction reduction was obtained in steel/steel contacts without use of the diamond-like carbon (DLC) coatings with their wetting or thermal effect, which was previously suggested as possible EHD friction reduction mechanism; yet about the same friction reduction of about 20% was obtained here—but with much simpler and less expensive technology, namely with the adsorbed oleophobic surface layers. A small variation in the additive’s molecular structure results in significant changes to the friction, indicating good potential in future EHD lubrication technology, where these additives could be designed and well optimised for notable reduction of the friction losses in the EHD regime.