**On the Role of a ZDDP in the Tribological Performance of Femtosecond Laser-Induced Periodic Surface Structures on Titanium Alloy against Di**ff**erent Counterbody Materials**

**Jon Joseba Ayerdi 1,2,\*, Nadine Slachciak 2, Iñigo Llavori 1, Alaitz Zabala 1, Andrea Aginagalde 1, Jörn Bonse <sup>2</sup> and Dirk Spaltmann <sup>2</sup>**


Received: 3 July 2019; Accepted: 30 August 2019; Published: 3 September 2019

**Abstract:** Laser-induced periodic surface structures (LIPSS, ripples) with ~500–700 nm period were produced on titanium alloy (Ti6Al4V) surfaces upon scan processing in air by a Ti:sapphire femtosecond laser. The tribological performance of the surfaces were qualified in linear reciprocating sliding tribological tests against balls made of different materials using different oil-based lubricants. The corresponding wear tracks were characterized by optical and scanning electron microscopy and confocal profilometry. Extending our previous work, we studied the admixture of the additive *2-ethylhexyl-zinc-dithiophosphate* to a base oil containing only anti-oxidants and temperature stabilizers. The presence of this additive along with the variation of the chemical composition of the counterbodies allows us to explore the synergy of the additive with the laser-oxidized nanostructures.

**Keywords:** lubricant additives; laser-induced periodic surface structures (LIPSS); wear; friction
