Friction and wear characteristics of ceramic particle filled polytetrafluoroethylene composites under oil-lubricated conditions

Five kinds of polytetrafluoroethylene (PTFE)-based composites were prepared : PTFE, PTFE + 30 vol % SiC, PTFE + 30 vol % Si3N4, PTFE + 30 vol % BN, and PTFE + 30 vol % B2O3. The friction and wear properties of these ceramic pa rticle filled PTFE composites sliding against GCr15 bearing steel under bot h dry and Liquid paraffin lubricated conditions were studied by using an MH K-500 ring-block wear tester. The worn surfaces and the transfer films form ed on the surface of the GCr15 bearing steel of these PTFE composites were investigated by using a scanning electron microscope (SEM) and an optical m icroscope, respectively. The experimental results show that the ceramic par ticles of SiC, Si3N4, BN, and B2O3 can greatly reduce the wear of the PTFE composites; the wear-reducing action of Si3N4 is the most effective, that o f SiC is the next most effective, then the BN, and that of B2O3 is the wors t. We found that B2O3 reduces the friction coefficient of the PTFE composit e but SiC, Si3N4, and BN increase the friction coefficients of the PTFE com posites. However, the friction and wear properties of the ceramic particle filled PTFE composites can be greatly improved by lubrication with liquid p araffin, and the friction coefficients of the PTFE composites can be decrea sed by 1 order of magnitude. Under lubrication of liquid paraffin the frict ion coefficients of these ceramic particle filled PTFE composites decrease with an increase of load, but the wear of the PTFE composites increases wit h a load increase. The variations of the friction coefficients with load fo r these ceramic particle filled PTFE composites under lubrication of Liquid paraffin can be properly described by the relationship between the frictio n coefficient (mu) and the simplified Sommerfeld variable NIP as given here . The investigations of the frictional surfaces show that the ceramic parti cles SiC, Si3N4, BN, and B2O3 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. However, the transfer of the PTFE composites onto the surface of the GCr15 bearing steel can be greatly reduc ed by lubrication with liquid paraffin, but the transfer still takes place. Meanwhile, the interactions between the liquid paraffin and the PTFE compo sites, especially the absorption of Liquid paraffin into the surface layers of the PTFE composites, create some cracks on the worn surfaces of the cer amic particle filled PTFE composites; the creation and development of these cracks reduces the load-supporting capacity of the PTFE composites. This l eads to the deterioration of the friction and wear properties of the PTFE c omposites under higher loads in Liquid paraffin lubrication. (C) 1999 John Wiley & Sons, Inc.