Special Section “Current Research Trends and Tendencies in Tribology”

Tribology resembles a multi-disciplinary research discipline and connects with the understanding and design of interacting surfaces in motion under the effect of an applied external stress field. In this regard, this discipline, combining friction, wear and lubrication, relates to daily-life phenomena such as found the utilization of mechanical components (e.g., bearings, brakes and gears) as well as the usage of contact lenses and artificial joints or even when drinking/tasting wine and other food nutrients (e.g., active research fields connecting with bio-tribology).[1, 2] While a minimum level of friction and wear is essential for many processes (e.g., walking, writing with a pencil, among others), the quest to reduce both attributes to improve the resulting energy efficiency and durability has been around since the early days of human civilization. This aspect is well documented by early paintings and drawings from ancient Egypt, which unambiguously confirmed the concept and idea of using friction-reducing solutions (animal-based lubricants or sand) to move heavy stones for the construction of the pyramids. This can be interpreted as the initiation of all modern liquid lubricant solutions (oils and greases), which are decisive for the proper functioning and reliability of most mechanical components and systems nowadays.[1, 3] In today's world, friction- and wear-related processes and phenomena notably contribute to a downgraded energy efficiency. This aspect is well reflected by the fact that about 23% of the entire global energy is used to overcome friction and wear, while the biggest share can be found in transportation and the usage of heavy machinery. Irrespective of considering internal combustion engines or electric motors, the energy losses relating to friction and wear problems account for over 30%.[4] From an environmental point of view, decreasing resources (material and raw oil) and the need to reduce CO2 emissions to slow global warming urgently call for greener and more efficient solutions with the overall aim of improving friction and wear. Therefore, fundamental and applied research in tribology moves towards the design, development, and implementation of innovative solutions combining state-of-the-art principles of physics, chemistry, chemical engineering, mechanical engineering, and materials science. These new concepts and solutions may relate, but are not limited to, novel material pairings, innovative surface engineering, advanced coatings/coating systems, new lubricant/lubrication concepts, among others, which are exactly the topics to be covered in this Special Section. The articles published in this special collection cover a broad range of potential approaches to manipulate friction and wear under dry and/or lubricated conditions. Regarding dry conditions, Vezzelli et al. assessed the solid lubrication performance of black phosphorus coatings drop-casted on various substrates, including ISI 52 100 steel, aluminum, copper, and iron. The obtained tribological performance largely depended on the underlying substrate and tribological testing conditions, reflecting the greatest frictional and wear reduction for iron and aluminum surfaces, respectively (2401756). Staying in the world of 2D materials, Zambrano et al. demonstrated that the addition of graphene oxide and LiFePO4 can notably improve the friction and wear performance of base greases (2401762). Araya-Hermosilla et al. studied the possibility of chemically functionalizing multi-layer Ti3C2Tx nano-sheets with silanes and assessed the effect of the used sonication conditions. They verified that the dispersion and sonication treatment must be optimized to yield the best silanization result, which goes hand in hand with an improved structural quality and reduced amount of amorphous carbon (2500162). Regarding the development of advanced nanomaterials, Gautier di Confiengo and Faga holistically reviewed green synthetic approaches to design and tailor nanoparticles used for friction and wear reduction, thus underlining the overall potential of green nanomaterials in tribology and paving the way for future research in this direction (2500034). Liu et al. chose poly(methyl methacrylate) and ethyl cellulose as carbon sources to create nanocomposites making use of carbon-coated silica and hollow carbon spheres thus verifying the friction reduction capability when used as lubricant additives in PAO 10 (2500428). Ji et al. confirmed the self-repairing effect of nano-serpentine mineral powder when used as lubricant additive in base oil for steel/aluminum alloy tribo-contacts (2500035). Concerning surface engineering approaches, Lu et al. used high-power impulse magnetron sputtering to fabricate high-entropy nitride coatings. This demonstrated an excellent friction and wear performance under dry sliding conditions (2501226). Jenczyk et al. studied the nano-tribological response of zirconium carbide coatings, which were generated by physical vapor deposition sputtering. They demonstrated that coatings with a high amount of carbon showed reduced friction coefficients of about 0.08 (2500243). Kroiss et al. assessed the influence of the process parameters of high-pressure on the resulting surface topography and microstructure. They were able to verify differences in cutting depth and surface topography as well as microstructural changes depending on the adjusted grinding parameters (2401800). Raghuram et al. studied the scratch and wear performance of technical thermoplastics depending on temperature and polymer selected (2500139). Michalec et al. experimentally assessed the effect of the material selection for sliding surfaces to minimize damage in large-scale hydrostatic bearings under critical conditions (2401733). Related to computational studies or combined experimental and numerical studies, Liang et al. studied the fretting performance of textured TC4 alloys under punch/plane contact conditions by finite elements (2500203). Peesapati et al. combined an experimental and machine learning study to detect and predict the onset of chatter before inducing chatter marks on the workpiece (2500382). In the context of machine learning and artificial intelligence used in tribological research, Shah et al. presented a perspective article outlining successful examples of these approaches in tribological research, thus shedding light on potential research avenues for the next 5 to 10 years (2401944).