Tribological performance of metal-reinforced ceramic composites selectively structured with femtosecond laser-induced periodic surface structures

The impact of femtosecond (fs) laser-induced periodic surface structures (LIPSS) on tribological properties was investigated for metal-reinforced ceramic composites (Al2O3-ZrO2-Nb). For this purpose, the metallic niobium (Nb) phase was selectively structured with LIPSS in an air environment with different values of the fs-laser peak fluence by near-infrared fs-laser radiation (lambda = 1025 nm, tau = 300 fs, f(rep) = 1 kHz), taking advantage of the different light absorption behavior of ceramic and metal. The tribological performance was evaluated by reciprocating sliding tests in a ball-on-disc configuration using Ringer's solution as lubricant. The surfaces were characterized before and after laser irradiation by optical microscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and by measuring the contact angle with Ringer's solution. The LIPSS formation resulted in an increased wetting of the surface with the lubricant. Moreover, the selectively structured composite surfaces revealed a coefficient of friction significantly reduced by a factor of similar to 3 when compared to the non-irradiated surface. Furthermore, the formation of a laserinduced oxidation layer was detected with NbO as the most prominent oxidation state. Selectively structured composites with outstanding mechanical properties and enhanced tribological performance are of particular interest for biomedical applications.