Action of transfer film in improving friction and wear behaviors of iron- and copper-filled poly(ether ether ketone) composites

The composites of poly(ether ether ketone) (PEEK) filled with micrometer-sized Cu and Fe particles were prepared by compression molding. The friction and wear behaviors of the composites were examined on a pin-on-disc friction-and-wear tester by sliding PEEK-based composites against tool steel at a sliding speed of 1.0 m s^-1 and a normal load of 19.6 N. Optical microscopic analysis of the transfer film and of the worn pin surfaces and wear debris was performed to investigate the wear mechanisms of the composites. It was found that Cu and Fe used as filler considerably decreased the wear rate of PEEK. A thin, uniform, and tenacious transfer film was formed when Cu was used as the filler, and a nonuniform and thick transfer film was formed when Fe was used as the filler. The transfer film played a key role in increasing the wear resistance of the PEEK composites. Plastic deformation was dominant for wear of PEEK-Cu, while abrasion and adhesion were dominant for wear of PEEK-Fe. Because of the strong affinity between Fe as filler and its identical counterpart in the counterface tool steel surface, the adhesion between the PEEK-Fe composite surface and the counter-face tool steel surface was thus severe. This contributed to the generation of a thicker transfer film for PEEK-Fe.