Chapter 2 - The effect of nanoparticle fillers on transfer film formation and the tribological behavior of polymers

Abstract

Sliding systems in which a polymer component slides against a metallic counterface are commonly used in practice because of the light weight of polymers, corrosion resistance, low cost and low friction and wear behavior even in nonlubricated applications. The tribological behavior in these systems is greatly influenced by the polymer transfer film that is formed on the metallic counterface during sliding. This chapter discusses key sliding parameters that affect the transfer film characteristics, as well as the role that transfer films play in the wear of polymers. Nanocomposites made by filling the polymers with nanosized inorganic materials have great potential because of their enhanced wear resistance and ease of manufacturing. These fillers have been reported to enhance the bonding and uniformity of the transfer film, both of which are considered to be key factors for enhancing tribological performance. This chapter deals with the nanoparticle filler materials that have been shown to improve the tribological behavior as well as the fillers that degrade performance. Interestingly, nanosized particles show optimal wear benefits at much lower volume fractions than are required when using microsized filler materials. This chapter proposes two primary mechanisms to describe the effects that nanoparticle fillers have on transfer film bonding to the counterface. The first is mechanical interlocking of polymer and nanoparticle debris within the counterface asperities, thus leading to deposition of transfer film and a smoothening of the wear surface. The second mechanism of bond enhancement by nanoparticle fillers is their chemical degradation or chemical reaction with the counterface material. The chapter reports on much of the work done in using nanoparticle fillers and how these fillers affect transfer films and thus the wear resistance.