The development of transfer layers and their role in polymer tribology

When polymers slide against metal counterfaces, transfer films are formed. This is also the case when sliding occurs between a polymer and another polymer. In the latter case, the transfer of material has been documented by infrared studies which show that material transfer occurs from a polymer of low cohesive energy density to one of higher cohesive energy density. The transfer film formed on a non-polymer counterface is governed by the counterface material and roughness, and of course the sliding conditions. The growth of transfer film with the number of passes is presented and the effect of counterface roughness is examined. The mechanism of wear is discussed with respect to the transfer film. It is shown that when polymers are modified, such as by the addition of fillers, the transfer film affects the tribological behavior. Some fillers affect the development of transfer film and enhance its adhesion to the counterface. Such fillers reduce the wear rate of polymer, often drastically. On the other hand, there are many fillers which have no such effect on the transfer film and wear in these cases is increased. The results of friction and wear behavior for both types of fillers are discussed in view of the transfer film characteristics. The analyses of transfer films as performed by XPS for a few cases are also presented.