Design of experiments approach to the study of tribological performance of Cu-concentrate-filled PPS composites

The tribological performance of copper-concentrate (CC) mineral deposit as the filler in polyphenylene sulfide (PPS) was studied as a function of the filler proportions and sliding test variables. CC is a complex mixture of CuS, Fe_xO_y, SiO₂, Al₂O₃, and other trace materials. The design of experiments based upon L₉ (3⁴) orthogonal arrays by Taguchi was used. Sliding tests were performed in the pin-on-disk configuration against a hardened tool steel (55-60 HRC) disk. The improvement in wear resistance of PPS was considerable with the use of fillers. The lowest steady state wear rate of 0.0030 mm³/km was obtained for PPS+20%CC+15%PTFE composition. It was two orders of magnitude lower than that of unfilled PPS. The variations in steady state coefficient of friction with the changes in filler proportions and sliding test variables were small. The transfer film was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). X-ray photoelectron microscopy (XPS) was used to detect chemical reactive species developed during sliding, especially in the interface between transfer film and its counterface. Wear particles and the polymer worn surfaces were analyzed by energy dispersive spectroscopy (EDS) for elemental distribution.