Project focuses on design of a novel and innovative high-performance green boundary film contacts that satisfy strict requirements on greenhouse emissions and hazardous materials, indispensably required in all future heavy loaded lubricated mechanical components.

Current emission legislation already severely affects industrial and automotive sectors, while restrictions that further increase with high pace will require abandoning key lubricant additives in next few coming years. However, new lubrication technology is not yet available. If efficient solutions will not be introduced on time, this may result in machinery performance deterioration and cause immense technical and economic consequences. This urgent need for replacement current technology has clearly set the development of green, high-performance lubrication to the uppermost priority in the field of tribology-related machine design, surface engineering and lubricant chemistry.

In this project, an efficient green contact interfaces were designed by combining tailored diamond-like carbon (DLC) coatings that possess very low-wear and low-friction properties, with harmless organic additives (alcohols, fatty acids). This new green concept, recently initiated by our group, is getting increased attention in academic and industrial research. To provide proof-of-concept for this project, we already possess supporting preliminary results, but further detailed evidence and basic understanding is indispensably missing for industrial implementation.

In order to achieve this goal, several tasks were tackled in this project; (1) Experiments, where a tribological tester was implemented in the neutron beam facility for “in-situ” sub-nano scale neutron reflectometry investigation of boundary film adsorption, were designed and performed. (2) Boundary film adsorption kinetics as a function of temperature and concentration, crucially required to understand mechanisms of interface bonding was determined using quartz crystal microbalance (QCM). (3) Verification under real-scale tribological contact conditions, in order to elucidate the ultimate answer on the lubrication performance and durability of additive-DLC interfaces, was performed. (4) Tribofilms were subjected to detailed nano-scale surface chemical analyses (XPS, AES, FT-IR, ToF-SIMS, AFM), which provided the last missing information to develop the new green lubrication technology. These goals, together with the new “DLC-Green additive” concept, enable a step-change in green lubrication technology and contact engineering, with significant impact on environmental, economic and social aspects.

The implementation of the project was carried out in accordance with the set work program and goals.

Neutron reflectometry “in-situ” tribo-adsorption: to determine the thickness and density of the adsorbed additive layers that form during tribological test.

In the framework of the WP2, most of the tasks have been implemented. We designed a unique tribological test rig for the implementation in the neutron reflectometer (WP2). In cooperation with Sulzer/Oerlikon Sorevi we have developed a new/special DLC coating technology for deposition of DLC coatings on atomic smooth surfaces, without intermediate layers (usually required to improve adhesion) and with exceptional small thickness (WP1). In cooperation with the research institute of Modena (CNR Nanoscience Institute, Unimore University of Modena, Dr. Alberto Rota), we also prepared Fe-coated samples that met all the requirements of neutron reflectometry (WP1). We also designed a new testing method on a neutron reflectometer in the presence of a tribological test rig.

Within the WP2 work package, a complete study of the interactions of the ZDDP additive with various DLC coatings (a-C, a-C:H, SiDLC) and Fe-coating was performed first. Experiments on the neutron reflectometer AMOR (PSI, Switzerland) were carried out under static and dynamic conditions (in the presence of tribological contact) at different temperatures and for various exposure times of coatings to the ZDDP solution. The results of this study were recently accepted for publication in the journal Frontiers in Mechanical Engineering. It should be mentioned that in-situ tribo-adsorption experiments with a neutron reflectometer have been planned in the second half of 2016, but due to the sudden and unexpected failure of the neutron target, they were cancelled and moved to the second half of 2017. For this reason, all subsequent experiments were delayed, which slightly affected the workflow and the subsequent acquisition of the results. Nevertheless, most of the measurements were accomplished and 2-3 articles are in preparation (stage).

Quartz Crystal Microbalance (QCM) studies: Determination of kinetics of adsorption layer formation (rate of adsorption, surface coverage, total adsorbed mass) under static conditions

Within the WP3 work package, we have completed most of the foreseen tasks. We prepared samples for the study of the formation of adsorbed layer’ kinetics. DLC coatings were applied to gold quartz crystals (WP1) as part of our collaboration with Sulzer/Oerlikon Sorevi. In the laboratory, we developed our own QCM system, which allows measuring the adsorption of additives from the viscous medium. With the help of this system and commercial QCM system (Open QCM), which was used to validate our system, we carried out preliminary tests for adsorption of ZDDP additives and hexadecanoic acid on various coatings. Detailed measurements of the adsorption of the studied organic friction modifiers were carried out with QCMD during the scientific visit in Total company in France. The results of these studies provide very valuable complementary information to the results from in-situ neutron reflectometry (WP2) and thus to understanding the adsorption mechanisms from the WP6 work package. The results were presented at the conference, the paper is being prepared.

Lubrication of macro contacts: study the macroscale friction behaviour and durability of the selected surface materials/coatings and additive combinations as a function of temperature in real-scale engineering contacts using conventional tribological facilities, and so validating the efficiency of new lubrication concept and interface design.

Within the WP4 work package, most of the planned tasks were realized. In cooperation with the Sulzer /Oerlikon Sorevi, we prepared samples of DLC coatings (a-C:H, a-C:H:F, a-C:H:F) on selected substrates (discs and balls from standard bearing steel) and carried out tribological experiments under different contact conditions (contact pressure, temperature, ...). First, we performed tribological tests using the ZDDP additive in various contact configurations with steel and DLC. A part of the results of this study (adsorption of ZDDP on steel and various coatings) was already published, while another larger part of the results of this study will be soon submitted to a tribological journal. The results of these studies were also presented at several international scientific conferences. In the second part following, tribological tests were carried out in the presence of organic friction modifiers at various temperatures (25, 50 and 100 °C) for steel/steel, a-C:H/aC:H and a-C:H:Si/a-C:H:Si contact configurations. This manuscript is in a preparation stage and will be submitted to journal by the end of 2019.

Chemical characterization of surface boundary films from three sub-studies within the work packages WP2-WP4 and WP7.

Within this work package (WP5), extensive characterization of surfaces and adsorbed/tribo layers from different work packages (WP2-WP4 and also WP7) were performed. A part of the analyses (XPS, TOF-SIMS, AES) were carried out in JSI, the project partner, and a part in the TINT laboratory (ATR FT-IR, AFM and optical interferometry). The results of these analyses contributed significantly to understanding the adsorption and lubrication mechanisms.