Chapter 17 – Polytetrafluoroethylene matrix nanocomposites for tribological applications

: Solid lubricants comprise an important class of materials and find use in applications where the use of more traditional lubrication techniques is undesirable or precluded. Polytetrafluoroethylene (PTFE) is a notable solid lubricant material, being known for its reputably low friction coefficient, high thermal range and chemical resistance, but a high wear rate limits its application in moving mechanical systems. The use of microfillers can reduce the wear rates to more acceptable values, but large particle size, high filler concentration, increased abrasion and increased friction coefficient all contribute to limit the performance of the composite. The use of nanofillers has been shown to provide further improvements in wear rates without introducing detrimental effects on its other beneficial properties. This work outlines recent studies of the wear resistance mechanisms in these novel systems. Several key wear resistance mechanisms have been identified: (1) bonding and strength at the filler/matrix interface, (2) dispersion and mechanical effects of load support and crack deflection, (3) morphological effects of nanoparticles on the matrix, (4) fibrillation and toughening, (5) transfer film coverage, (6) transfer film orientation and (7) chemical degradation. It is found that the about 1000× improvement in wear resistance that trace loadings of nanofillers impart to PTFE is due to a synergism of wear resistance mechanisms that is activated by the small filler size.