Effect of transfer film structure, composition and bonding on the tribological behavior of polyphenylene sulfide filled with nano particles of TiO2, ZnO, CuO and SiC

The tribological behavior of polyphenylene sulfide (PPS) filled with inorganic nano particles was studied. The fillers investigated were TiO₂, ZnO, CuO and SiC whose sizes varied from 30 to 50 nm. The polymer composites were compression molded with varying proportions of these fillers. Wear and friction tests were performed in a pin-on-disk configuration at a sliding speed of 1.0 m/s, nominal pressure of 0.65 MPa, and counterface roughness of 0.10 μm Ra. The polymer composite pins slid against hardened tool steel counterfaces. The transfer films of the composite materials formed on the counterfaces during sliding were studied by optical microscopy and X-ray photoelectron spectroscopy (XPS) and the adhesion between the transfer film and counterface was measured in terms of the peel strength. It was found that the wear rate of PPS decreased when TiO₂ and CuO were used as the fillers but increased with ZnO and SiC fillers. The optimum wear resistance was obtained with 2 vol.% CuO or TiO₂. These filled composites had the coefficients of friction lower than that of the unfilled PPS. The wear behavior of the composites is explained in terms of the topography of transfer film and adhesion of transfer film to the counterface as observed from peel strength studies. There is a good correlation observed between the transfer film-counterface bond strength and wear resistance.     

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.     

The role of transfer film and back transfer behavior on the tribological performance of polyoxymethylene in sliding

The role of transfer films formed during the sliding of polymer composites against steel counterfaces was studied in terms of the tribological behaviors of the composites. The composites were prepared by compression molding and sliding tests were run in pin-on-disk sliding configuration. The counterface was made of tool steel hardened to 55–60 HRC and finished to a surface roughness of 0.09–0.10 μm Ra. Wear tests were run for 6 hrs at the sliding speed of 1.0 m/s and contact pressure of 0.65 MPa. Transfer films formed on the counterfaces during sliding were investigated using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The results showed that as the transfer film became smooth and uniform, the wear rate decreased. The examination of worn surfaces using Energy Dispersive Spectroscopy (EDS: dot mapping mode) showed the back-transfer of the steel counterface material to the polymer pin surface. This behavior is believed to strengthen the polymer pin surface during sliding thereby contributing to the decrease in wear rate. This paper was recommended for publication in revised form by Associate Editor Jae Cheon Lee Minhaeng Cho received his B.S. and M.S. degrees in Mechanical Engineering from Chung-Ang University, Seoul in 1993 and 1995, respectively. He received his M.S. degree in Materials Science and Engineering from Oregon State University in 2000, and his Ph.D. in Mechanical Engineering from Iowa State University in 2004. Dr. Cho is currently an Assistant Professor at the School of Mechanical Engineering at Chung-Ang University in Seoul, Korea. His research interests are in the area of tribology, surface phenomena, and functional surfaces such as laser surface texturing and ultra-thin coatings.     

Effect of surface coating and tin plating on friction characteristics of P-110 tubing for different thread compounds

Design factor problems related to galling failure have become an increasing concern for deepwater offshore wells. This paper presents the results of an experimental study conducted to determine friction characteristics of P-110 tubing coated with manganese phosphate and plated with tin. Six repeated tests were run to investigate the effect of lubrication type on friction characteristics of P-110 tubing by using thread compounds of API modified Threadkote-706, Shell Type-3 and Graphite/PTFE at a rotational speed of 5 rpm. In each test the bearing load was increased monotonically to a maximum value of 625 kN. The results of this study clearly indicate the importance of tin-plating in reducing the coefficient of friction.