The tribological behaviors of the polyurethane coating filled with nano-SiO2 under different lubrication conditions

The tribological behaviors of polyurethane (PU) composite coatings filled with nano-SiO2 were investigated using a ring-on-block wear tester under different friction conditions, and the worn surfaces of nano-SiO2 filled PU coating and transfer films formed on the surface of the counterpart ring were investigated by scanning electron microscopy (SEM) and optical microscope (OM), respectively. The results show that the tribological behaviors of SiO2 filled PU coating are very sensitive to the formation of transferred films. The wear life of the SiO2 filled PU coating under water lubrication is the lowest and under liquid paraffin lubrication is the highest. The OM analyses indicated that a lubricating film can be more easily formed on the frictional surfaces under liquid paraffin lubrication; thus the lubrication condition at the rubbing surfaces can be greatly improved, leading to the decrease of the friction and wear of nano-SiO2 filled PU coating. However, water hinders the formation of transferred films and might penetrate and corrode the filler–matrix interface, which lead to the worst anti-wear property of nano-SiO2 filled PU coating.