Friction and wear characteristics of fiber- and whisker-reinforced PTFE composites under oil lubricated conditions

Four kinds of polytetrafluoroethylene (PTFE)-based composites, such as pure PTFE, PTFE + 30(vol.)% carbon fiber, PTFE + 30(vol.)% glass fiber, and PTFE + 30(vol.)% K₂Ti₆O₁₃ whisker composite, were prepared. The friction and wear properties of these fiber- and whisker-reinforced PTFE composites sliding against GCr15-bearing steel (SAE52100 steel) under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester (Timken wear tester). Then the worn surfaces of these PTFE composites and the transfer films formed on the surface of GCr15-bearing steel were investigated by using a Scanning Electron Microscope (SEM) and an Optical Microscope, respectively. Experimental results show that the friction and wear properties of the PTFE composites reinforced with carbon fiber, glass fiber, and a K₂Ti₆O₁₃ whisker can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of these PTFE composites can be decreased by one order of magnitude compared to those under dry friction conditions. Meanwhile, the wear of the fiber- and whisker-reinforced PTFE composites in liquid paraffin lubrication increases with the increase of load, but the friction coefficients of these PTFE composites first decrease with the increase of load, and then increase with the increase of load. The variations of friction coefficients with load for these PTFE composites in liquid paraffin lubrication can be described properly by the Stribeck's curve as given in this article. However, when the load increases to the load limits of the PTFE composites, their friction and wear increase sharply. SEM and optical microscope investigations show that the interactions between liquid paraffin and the PTFE composites, especially the absorption of liquid paraffin into the surface layers of the PTFE composites, create some obvious cracks on the worn surfaces of the PTFE composites. The creation and the development of the cracks reduce the load-carrying capacity of the PTFE composites, and therefore lead to the increase of the friction and wear of the PTFE composites under higher loads. Meanwhile, the transfer of the fiber- and whisker-reinforced PTFE composites onto the counterfaces can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1393–1402, 1998