Tribological performance of sub-100-nm femtosecond laser-induced periodic surface structures on titanium

•Large areas covered with sub-100nm LIPSS (HSFL) were manufactured by fs-laser irradiation on titanium surfaces.•Tribological performance of HSFL covered areas was qualified in reciprocal sliding tests in two different lubricating oils.•HSFL on titanium do not endure the tribological tests.•For a beneficial tribological performance, the tribological sample deformation must be smaller than the LIPSS modulation depth. Sub-100-nm laser-induced periodic surface structures (LIPSS) were processed on bulk titanium (Ti) surfaces by femtosecond laser pulse irradiation in air (30fs pulse duration, 790nm wavelength). The laser peak fluence, the spatial spot overlap, and the number of overscans were optimized in a sample-scanning geometry in order to obtain large surface areas (5mm×5mm) covered homogeneously by the LIPSS. The laser-processed regions were characterized by optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM). The friction coefficient of the nanostructured surfaces was tested during 1000 cycles under reciprocal sliding conditions (1Hz, 1.0N normal load) against a 10-mm diameter ball of hardened 100Cr6 steel, both in paraffin oil and in engine oil used as lubricants. Subsequently, the corresponding wear tracks were qualified by OM, SEM, and energy dispersive X-ray analyses (EDX). The results of the tribological tests are discussed and compared to that obtained for near wavelength-sized fs-LIPSS, processed under somewhat different irradiation conditions. Some constraints for a beneficial effect of LIPSS on the tribological performance are provided.