THE GROWTH AND BONDING OF TRANSFER FILM AND THE ROLE OF CUS AND PTFE IN THE TRIBOLOGICAL BEHAVIOR OF PEEK

Sliding experiments on the PEEK composites filled with CuS and PTFE powders while rubbing against tool steel surfaces were performed under ambient conditions in a pin-on-disk configuration. A constant sliding velocity of 1 m s(-1) and a contact pressure of 0.654 MPa were used in all experiments. The steel counterfaces were finished by abrasion to a surface roughness of 0.11 mu m R(a). The optimum CuS proportion for minimum wear rate as determined experimentally was 35 vol.%. With the addition of CuS, the coefficient of friction increased. The addition of PTFE to these composites reduced both the wear rate and the coefficient of friction. The wear rate of the different compositions depended upon their ability to form transfer films on the steel counterfaces. The study of the transfer film growth by scanning electron microscopy revealed that it was a mechanical process in which the fragments of the material removed were locked into the crevices of counterface asperities. The compositional changes in the transfer film were studied by XPS analysis of the top surface of the transfer film and also closer to the steel substrate. It was found that Cu ions and the compounds of FeF2, FeSO4 and FeS were formed near the interface of the transfer film with its steel substrate. These compounds contributed to enhanced bonding between the transfer film and the counterface. Of the various mechanisms of wear, the cracking and delamination of the transfer film will also be affected by the bonding of transfer film to the counterface.