Friction and wear behavior of PTFE composites filled with rare earth compounds under oil-lubricated conditions

Polytetrafluoroethylene (PTFE)-based composites, filled with CeO2, CeF3, an d La2O3 in volume contents of 5, 10, 15, 20, and 30%, were prepared. Then, the friction and wear behavior of these PTFE composites sliding against GCr 15 bearing steel under both dry and liquid paraffin-lubricated conditions w as evaluated using an MHK-500 ring-on-block wear tester. Finally, the worn surfaces and the transfer films of these PTFE composites were investigated using a scanning electron microscope (SEM) and an optical microscope. Exper imental results showed that filling CeO2, CeF3, and La2O3 into PTFE can red uce the wear of the PTFE composites by 1-2 orders of magnitude. When the co ntent of CeO2 in PTFE is 15%, the friction and wear properties of the CeO2- filled PTFE composite are the best. Meanwhile, when the content of La2O3 in PTFE is between 15 and 20%, the PTFE composite filled with La2O3 exhibits excellent friction and wear-reducing properties. However, the friction coef ficient of the CeF3-filled PTFE composite increases but its wear decreases with increase in the content of CeF3 from 5 to 30%. The friction and wear-r educing properties of CeO2-, CeF3-, and La2O3-filled PTFE composites can be greatly improved by lubrication with liquid paraffin, but the limit loads of the PTFE composites decrease with increase in the content of CeO2, CeF3, and La2O3 in PTFE (from 5 to 30%) under the same conditions. Investigation s of worn surfaces show that the interaction between liquid paraffin and th e CeO2-, CeF3-, and La2O3-filled PTFE composites, especially the absorption of liquid paraffin into the microdefects of the PTFE composites, creates s ome cracks on the worn surfaces of the PTFE composites and that the creatio n and development of the cracks reduces the mechanical strength and the loa d-supporting capacity of the PTFE composites. However, with increase of the content of CeO2, CeF3, and La2O3 in the PTFE, the microdefects in the PTFE composites also increase, which would lead to increase in the number of th e cracks on the worn surfaces of the PTFE composites under load and, so, in turn, lead to the reduction of the limit loads of the CeO2-, CeF3-, and La 2O3-filled PTFE composites under lubrication with liquid paraffin. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 78: 797-805, 1999.