Effect of various inorganic fillers on the friction and wear behaviors of polyphenylene sulfide

The friction and wear behaviors of polyphenylene sulfide (PPS) filled with various particulate inorganic fillers were studied. The fillers were Ag₂S, NiS, PbSe, and PbTe in varying proportions. Friction wear tests were performed in a pin-on-disc configuration at a sliding speed of 1.0 m s^-1 and a load of 19.6 N. The pins were made of PPS-based composites and the discs of hardened tool steel. X-ray photoelectron spectroscopy (XPS) was used to study the interface of the transfer film and its steel substrate for the possible chemical changes occurring during sliding. It was found that Ag₂S and NiS as the fillers decreased the wear rate of PPS very effectively, while PbSe and PbTe increased it dramatically. XPS analysis revealed that chemical reactions occurred during sliding between the fillers and the counterface metal iron in the cases of Ag₂S and NiS, while there was no such chemical reaction when PbSe or PbTe was used as the filler. The chemical reactions in the cases of Ag₂S and NiS contributed to enhancing the adhesion of transfer film to the counterface, and thus led to reduced wear. These observations led to the conclusion that the fillers that reduced wear had to be chemically active to the counterface metal. The Gibbs free energy criterion was suggested to test this hypothesis.