Effect of Ag nanoparticles on the tribological response of MAO coatings fabricated on plastically deformed titanium

The effect of silver nanoparticles (Ag-NPs) concentration in the electrolyte during micro-arc oxidation (MAO) of plastically deformed titanium of commercial purity (cp-Ti) on microstructure, adhesion and tribological performance of produced coatings was investigated within the present work. Although the effect of the Ag-NPs on the antibacterial properties and biocompatibility of MAO coatings has been barely investigated, the tribological behaviors such as sliding and fretting wear have been studied in detail. The application of phosphate-based electrolyte allowed to effectively incorporate the Ag-NPs into the MAO coating, particularly on their upper surface, without agglomeration, and in the areas close to the pores. Such a distribution of the Ag-NPs influences the scratch and wear resistance, delaying the cracking of the coating (by increasing L C1 critical load) and acting as a solid lubricant decreasing the coefficient of friction, respectively. A reduction in sliding wear rate was observed for the MAO coatings with added Ag-NPs, with a lowest value recorded for the material with 1 g/l of Ag-NPs suspended in the electrolyte (1.34·10 -6 mm 3 /N·m) as compared with the reference material without NPs (2.57·10 -6 mm 3 /N·m). A slight increase in wear rate was stated for 2 g/l (1.86·10 -6 mm 3 /N·m). The tribological response of the MAO coating with conductive Ag-NPs is governed by two competing phenomena: increasing amount of solid state lubricant (Ag-NPs) but increasingly more porous coating at the same time (due to more intense micro-arcing in the electrolyte of higher conductivity) deteriorating the wear resistance. • MAO coatings with Ag-NPs were deposited on cp-Ti substrates • Ag embed into MAO coating in original form on its upper surface and near porosity • Addition of Ag-NPs, acting as solid lubricants, reduced the friction coefficient • Wear rate reaches a minimum for the MAO coating with 1 g/l of Ag-NPs • Soft Ag-NPs on the upper surface helped to delay crack formation and propagation