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 composites filled with rare earth compounds CeO2, CeF3, and La2O3 in volume content 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 wear debris and the worn surfaces of the PTFE composites were investigated by using a scanning electron microscope (SEM), whereas the transfer films of the PTFE composites formed on the surface of GCr15 bearing steel were examined by using an optical microscope. Experimental results show that the antiwear 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 compared with that of pure PTFE. The wear of the CeF3-filled PTFE composite decreases with the increase of the content of CeF3 from 5 to 30 vol %, but its friction coefficient increases with the increase of the content of CeF3 in 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 content of La2O3 in PTFE is between 15 and 20 vol %, the PTFE composite filled with La2O3 exhibits excellent friction and wear-reducing properties. Microscope investigations show that rare earth compounds CeO2, CeF3, and La2O3 in PTFE 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 composites to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composites. With the increase of the content of CeO2, CeF3, and La2O3 in PTFE, the actions with which the rare earth compounds inhibit the large-scale destruction of the banded structure of PTFE are enhanced; so the wear of the PTFE composites decreases. Meanwhile, because CeO2- and La2O3-filled PTFE composites can easily form uniform transfer films on the surface 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.