Effects of various kinds of fillers on the tribological behavior of polytetrafluoroethylene composites under dry and oil-lubricated conditions

Polytetrafluoroethylene (PTFE)-based composites filled with various inorgan ic fillers in a volume fraction of 30% were prepared. The tribological beha vior of the PTFE composites sliding against AISI52100 steel under dry and l iquid paraffin-lubricated conditions was investigated on an MHK-500 model r ing-on-block test rig. The morphologies of worn surfaces and wear debris we re observed with a scanning electron microscope (SEM) and an optical micros cope. As the results, different fillers show different effects on the tribo logical behavior of the PTFE composites, while the composite shows much dif ferent tribological behavior under lubricated conditions as com pared with dry sliding. The tribological behavior of the PTFE composites under dry sli ding is greatly related to the uniformity and thickness of the transfer fil ms. Only the PTFE composites with a transfer film of good uniformity and pr oper thickness may have excellent tribological behavior. The PTFE composite s show much better tribological behavior under lubrication of liquid paraff in than under dry sliding, namely, the friction coefficients are decreased by 1 order of magnitude and the wear rate by 1-3 orders of magnitude. Obser vation of the worn composite surfaces with SEM indicates that fatigue crack s were generated under lubrication of liquid paraffin, owing to the absorpt ion and osmosis of liquid paraffin into the microdefects of the PTFE compos ites. The creation and development of the fatigue cracks led to fatigue wea r of the PTFE composites. This would reduce the mechanical strength and loa d-supporting capacity of the PTFE composites. Therefore, the tribological b ehavior of the PTFE composites under lubrication of liquid paraffin is grea tly dependent on the compatibility between the PTFE matrix and the inorgani c fillers. In other words, the better is the compatibility between PTFE and fillers the better is the tribological behavior of the composites. (C) 200 1 John Wiley & Sons, Inc.