Ultralow Friction and Wear of Polymer Composites under Extreme Unlubricated Sliding Conditions

Dependence of the tribological behaviors of polyimide- and polyetheretherketone-based composites on pv (pressure x speed) factors is investigated in air ambience. It is demonstrated that the hybrid composites filled with nanosilica/carbon fibers/graphite exhibit ultralow friction and wear under extreme conditions. In particular, the friction coefficients of the hybrid nanocomposites at 40 MPa m s(-1) are in the range of 0.03-0.04, which are even lower than those obtained with poly alpha olefin lubrication. Moreover, the friction coefficients are lower than those of carbon fibers reinforced polymer composites ever reported in literatures. In order to reveal the underlying mechanisms of ultralow friction and wear, tribochemistry and tribofilms' nanostructures are comprehensively analyzed. It is identified that chelation of polymeric molecular radicals with steel counterface occurs enhancing tribofilm's bonding strength. Striking orientation of the molecules of remnant polymer in tribofilm is indicative that the film exhibits an easy-to-shear characteristic under extreme pv conditions. Nanosilica released onto sliding interface and iron oxide particles abraded from the counterface are thereafter tribosintered into a compact layer, which accounts for the high load-carrying capability of the tribofilm.