Tribological Properties of Thermosetting Polyimide/TiO2 Nanocomposites Under Dry Sliding and Water-Lubricated Conditions

Thermosetting polyimide(PI)-based nanocomposites containing various contents of nano-TiO2 were fabricated via an in situ polymerization of monomer reactants (PMR) process. Under dry sliding and water-lubricated conditions the friction and wear behaviors of the PMR PI and its nanocomposites were evaluated and compared. The addition of nano-TiO2 in PI contributed to improving the friction and wear behavior considerably under dry sliding. The highest change ratio of wear rate was 61% with the optimum nano-TiO2 content of 3%, while the highest change of friction coefficient was 60% with the optimum nano-TiO2 content of 9%. Under water-lubricated condition, contrarily, the addition of nano-TiO2 in PI does harm to the tribological properties. Namely, the friction coefficient of the nanocomposites increased with increasing the nano-TiO2 content. These results may be caused by the following facts: the hardness of the PI matrix would be increased by adding the nano-TiO2 reducing the ability of elastic deformation of the nanocomposites; accordingly, the poor elastic deformation hindered the formation of a water-lubrication film on the surface. An investigation on the wear tracks indicated that the wear mechanism of PI/TiO2 nanocomposites under dry sliding condition proceeded from fatigue wear to a combination of fatigue wear and abrasive wear with increasing the mass fraction of nano-TiO2.