Generation of self-healing and sliding wear resistant titanium surfaces by different pico-second laser induced periodic surface structures

Abstract

Selective and complete micro-patterning (μ-patterning) of α‑titanium surfaces were performed using a 1064 nm laser system. With a fluence of 0.6 J⋅cm−2 and a pulse duration of 10 ps, two different μ-patterns of laser induced periodic surface structures (LIPSS) were generated by mainly changing the number of pulses per spot and the spot-to-spot distance. A high number of pulses per spot and a large spot-to-spot distance of 60 μm gives selectively with LIPSS modified dimples. Their spatial period varies from 159 nm to a maximum of 620 nm inside the dimples. An increased fraction of TiO2 in the crystalline form of rutile gave improved wear resistance and a coefficient of friction COF of 0.20 ± 0.02. If the spot-to-spot distance is reduced to 6 μm and the number of pulses at one spot remains low, a completely rippled surface with slightly increased oxide fraction but still a metallic plastic behaviour was able to show volume expansion during sliding. The observed self-healing ability of this LIPSS pattern is correlated with the relief of compressive stresses in this study. As volume expansion operates against the sliding motion of the diamond tip, high COFs of 0.62 ± 0.11 for a normal load of 1.0 N and 0.45 ± 0.04 for a normal load of 0.5 N were measured. After further optimisation, such a tailored increase in COF and load stimulated volume expansion of the surface could be useful in order to act against implant loosening and undesired movements.