**7. Summary**

High-rate laser texturing was presented as a powerful method for advanced surface engineering and functionalization. By combining high-power laser systems with polygon mirror based scan techniques for ultrafast surface texturing, a maximum area processing rate up to 3.8 m2/min could be achieved. This unprecedented processing rate was experimentally realized by single pass raster scanning the laser beam at 950 m/s scan speeds producing microscopic surface features over a large area on stainless steel metal sheets. The effective area processing rate decreased noticeably when a higher number of scan passes was required to fabricate a distinct surface topography for a specific surface functionality, as demonstrated by a regular ripple structure where the effective area processing rate was 0.13 m2/min.

The laser textured surfaces were analyzed regarding their frictional performance by using a standardized friction test method. The highest static COF was found of μ<sup>20</sup> = 0.68 for the laser textured cross pattern that is about + 126% higher than that obtained for the fine grinded reference contact system. The static COF determined for self-organizing cone-like protrusions was μ<sup>20</sup> = 0.44 while a little effect on the tribological performance was observed for LSFL textured contact surfaces with μ<sup>2</sup> = 0.41 at the very beginning of the measurement. The effective area processing rates for both self-organizing and deterministic laser surface textures were typically achieved in the range between 0.04 cm2/min and 43 cm2/min.

Finally, the ultrashort pulse laser made microscopic surface features were tested for the first time in a shaft-hub connection. For the line pattern textured on the shaft surface, the COF increased to μmax = 0.35 that is + 75% higher than the reference value. Even though further optimization on the surface texture is needed for this special machining example, the high potential of laser textured microscopic surface features could be demonstrated for advanced tribological functionality by a real-world application. Moreover, in addition to the increase of the static coefficient of friction presented here, the laser textured surfaces may also provide great potential to enhance adhesive strength and stability for bonded joints and hard coatings, e.g., on forming and milling tools that will be investigated in the ongoing study.

**Author Contributions:** Conceptualization, J.S., F.R.; methodology, L.S., J.S., F.R., S.S., S.H., J.P.; investigation, L.S., J.S., F.R., S.S., S.H.; validation, all authors; resources, U.L., J.S., E.L., J.P.; writing—original draft preparation, J.S., F.R., S.S., S.H., S.M.; writing—review and editing, all authors. All authors have read and agreed to the published version of the manuscript.

**Funding:** The presented study was funded by the German Federal Ministry of Education and Research (grant numbers 03FH037PX4 and 03PSIPT1A) and by the Federal Ministry of Economic Affairs through the German Federation of Industrial Research Associations (AiF grant numbers 17229 BR/1 and 18500 BR/1).

**Conflicts of Interest:** The authors declare no conflict of interest.

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