Role of surface texture and roughness parameters on friction and transfer film formation when UHMWPE sliding against steel

摘要

Abstract Understanding friction between material pairs is very crucial when utilizing the materials in various applications, including mechanical and biological systems. In the present investigation, tribological properties, such as coefficient of friction (COF) and transfer film formation, were investigated by varying surface texture and roughness features during sliding of Ultra High Molecular Weight Polyethylene (UHMWPE) pins against steel plates using an inclined pin-on-plate sliding tester. The roughness of the textures was quantified using optical profilometer. Scanning Electron Microscope was utilized to characterize the fracture features on the pin surface and transfer film formation on the plate surface. Results showed that the COF is significantly depend on surface texture when compared to surface roughness ( R _a) of the harder steel material. The transfer film formation is found to depend on the COF. Detailed analysis of friction components, namely adhesion and hysteresis, demonstrated that the effect of surface texture on the COF and transfer film formation was attributed to the variation of the hysteresis friction component. The variations in hysteresis friction with surface texture is attributed to the nature of constraints imposed by the surface textures at the asperity level during sliding conditions. Keywords Surface texture ; Roughness ; Friction ; Transfer film ; UHMWPE prs.rt("abs_end"); 1. Introduction Friction is a very important parameter that governs the selection of contacting materials in mechanical and biological systems because it affects numerous variables including the stresses, working conditions and the transfer film/debris formation [1] . There are several factors that influence friction and transfer film formation during sliding contact conditions. The surface topography is one of the key factors that affect the coefficient of friction (COF) and transfer film formation during sliding. Considerable efforts have been made to study the role of surface texture and roughness on friction of metallic materials [2] , [3] , [4] , [5] , [6] , [7] , [8] and [9] , polymeric materials [10] , [11] , [12] and [13] and ceramic materials [14] , [15] and [16] . As regards to the influence of surface texture and roughness on friction of polymeric materials, He et al. [10] studied the effect of surface textures on the friction of a polydimethylsiloxane. The results showed that the COF of pillar-textured surface was much lower than that on the smooth surface of the same material and this reduction of COF could be attributed to the reduced contact areas. The friction properties of molding thermoplastic materials are studied by Pouzada et al. [17] . The authors found that the COF at the ejection stage depended on the surface texture of the core. Santer and Czichos [18] investigated tribological behavior of several thermoplastic polymers under dry sliding condition and found that the COF decreases with increasing surface roughness of the steel counterface until a critical value is attained. For roughnesses above this critical value, the COF begins to increase. The reason for this variations are explained by the fact that for small values of the surface roughness adhesion forces dominate, however, abrasion plays a more important role at greater roughness values. The tribological properties of polytetrafluoroethylene (PTFE) composites against steel material of varying roughness under dry sliding conditions was investigated by Wieleba [19] . The surface characterization analysis showed that the roughness parameters related to the shape of the asperity profile ( S _m, Δ α and R _k) had the strongest influence on the COF. Attempts were also made to study the role of surface roughness on transfer film formation [20] and [21] . More specifically, the influence of counterface surface roughness on the transfer film formation during sliding against polymer materials was investigated by Bahadur [20] . The transfer film was developed due to adhesion and interlocking of the polymer at metal surface asperities, the extent of which depended on the surface roughness of the steel material. Jintang [21] investigated the friction and wear properties of various polymer–stainless steel pairs. The test results indicated that polymer transfer films were formed on all friction surfaces. The transfer film formation was influenced by polymer structure characteristics, tribochemical reactions and friction conditions. In literature, attempts were made to study the tribological properties of UHMWPE against steel under dry sliding and various lubricated conditions [22] , [23] and [24] . Xiong and Ge [22] studied the friction and wear properties of UHMWPE against Al₂O₃ ceramic under dry and different lubricating conditions. The friction and wear rate of UHMWPE were the highest under dry sliding and were the lowest under lubrication conditions. The wear mechanisms were differ