Effect of rare earth compounds as fillers on friction and wear behaviors of PTFE-based composites

The friction and wear behaviors of polytetrafluoroethylene (PTFE)-based com posites filled with rare earth compounds CeO2, CeF3, and La2O3 in volume co ntent from 5 to 30% sliding against GCr15 bearing steel under dry friction conditions were evaluated by using an MHK-500 ring-block wear tester, The w ear debris and the worn surfaces of the PTFE composites were investigated b y using a scanning electron microscope (SEM), whereas the transfer films of the PTFE composites formed on the surface of GCr15 bearing steel were exam ined by using an optical microscope. Experimental results show that the ant iwear properties of the PTFE composites can be improved greatly by filling PTFE with different contents of CeO2, CeF3, and La2O3, and that the wear of the PTFE composites can be decreased by one to two orders of magnitude com pared with that of pure PTFE. The wear of the CeF3-filled PTFE composite de creases with the increase of the content of CeF3 from 5 to 30 vol %, but it s friction coefficient increases with the increase of the content of CeF3 i n PTFE. When the content of CeO2 in PTFE is 15 vol %, the friction and wear properties of CeO2-filled PTFE composite are the best. But when the conten t of La2O3 in PTFE is between 15 and 20 vol %, the PTFE composite filled wi th La2O3 exhibits excellent friction and wear-reducing properties. Microsco pe investigations show that rare earth compounds CeO2, CeF3, and La2O3 in P TFE not only inhibit the large-scale destruction of the banded structure of PTFE but also enhance the adhesion of the transfer films of the PTFE compo sites to the surface of GCr15 bearing steel, so they greatly reduce the wea r of the PTFE composites. With the increase of the content of CeO2, CeF3, a nd La2O3 in PTFE, the actions with which the rare earth compounds inhibit t he large-scale destruction of the banded structure of PTFE are enhanced; so the wear of the PTFE composites decreases. Meanwhile, because CeO2- and La 2O3-filled PTFE composites can easily form uniform transfer films on the su rface of GCr15 bearing steel, the friction and wear-reducing properties of CeO2- and La2O3-filled PTFE composites are better than those of CeF8-filled PTFE composites under dry friction conditions. (C) 1999 John Wiley & Sons, Inc.