This study reports on the role of nano-scale topography and chemical composition of thin films on microfrictional properties. To alter the surface chemistry from hydrophilic to hydrophobic, silicon oxide and fluorocarbon thin films were deposited on Cr-N coatings with different pyramid-like, crater-like and hemisphere-like morphologies. The structured surfaces always exhibit lower friction than smooth ones. Among the structured surfaces, the crater-like morphologies show lower friction; however, no significant friction differences were observed between crater-like structures with different roughness values. In contrast, friction increases on the pyramid-like and hemisphere-like structured surfaces with decreasing surface roughness. The effect of the relative humidity is not as pronounced on nanostructures as it is on the smooth surface. Among the structured surfaces the pyramid-like structures show a stronger dependence on the relative humidity than the others. For hydrophobic and hydrophilic structures, the friction force decreases with increasing sliding velocity, whereby the slope depends on type and size of the structural features.
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