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Surface texturing has gained great attention in the tribological community since precisely defined surface features can help to reduce friction and/or wear irrespective of the acting lubrication regime. The ability to positively influence tribological performance under different lubrication conditions makes surface texturing particularly interesting for machine elements since they may experience different conditions over the lifetime or sometimes even over one cycle/stroke. However, despite the great effort by both researchers and industry to introduce surface texturing in machine elements, many questions remain unclear regarding the optimal design of surface textures, as well as the positive and negative effects on the component's performance. The aim of this review article is to critically summarize the state of the art of surface texturing applied to machine elements, with a special emphasis on piston rings, seals, roller bearings, and gears. After a brief introduction, the first section focuses on surface texturing in sliding components (piston rings and seals), whereas the second section deals with surface texturing in rolling components (roller bearings and gears). Based upon the main evidence from the literature, the final section provides more general design guidelines for surface texturing in machine elements.

The frictional behaviour of plane converging bearings was experimentally and numerically studied for four texture geometries fabricated by ultra-short pulse laser texturing (single pocket, line-, cross-and dot-like texture) and convergence ratios under full-film lubrication in the presence of thick oil films (up to 100 µm). Regarding the experiments, small variations in the spread of results between different textures and a general improvement over the untextured reference can be observed. Numerical simulations help to clarify the expected variations and conditions under which these occur. For high convergences, the simulations

Owing to MXenes’ tunable mechanical properties induced by their structural and chemical diversity, MXenes are believed to compete with state-of-the-art 2D nanomaterials such as graphene regarding their tribological performance. Their nanolaminate structure offers weak interlayer interactions and an easy-to-shear ability to render them excellent candidates for solid lubrication. However, the acting friction and wear mechanisms are yet to be explored. To elucidate these mechanisms, 100-nm-thick homogeneous multilayer Ti3C2T x coatings are deposited on technologically relevant stainless steel by electrospraying. Using ball-on-disk tribometry (Si3N4 counterbody) with acting contact pressures of about 300 MPa, their long-term friction and wear performance under dry conditions are studied. MXene-coated specimens demonstrate a 6-fold friction reduction and an ultralow wear rate (4 × 10–9 mm3 N–1 m–1) over 100 000 sliding cycles, outperforming state-of-the-art 2D nanomaterials by at least 200% regarding their wear life. High-resolution characterization verified the formation of a beneficial tribolayer consisting of thermally/mechanically degraded MXenes and amorphous/nanocrystalline iron oxides. The transfer of this tribolayer to the counterbody transforms the initial steel/Si3N4 contact to tribolayer/tribolayer contact with low shear resistance. MXene pileups at the wear track’s reversal points continuously supply the tribological contact with fresh, lubricious nanosheets, thus enabling an ultra-wear-resistant and low-friction performance.

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