Friction and wear characteristics of copper and its compound-filled PTFE composites under oil-lubricated conditions

Abstract

Four kinds of polytetrafluoroethylene (PTFE)-based composites, such as pure PTFE, PTFE + 30(v)%Cu, PTFE + 30(v)%Cu2O, and PTFE + 30(v)%CuS composite, were prepared. Then the friction and wear properties of the PTFE composites filled with Cu, Cu2O, or CuS sliding against GCr15-bearing steel under both dry and liquid paraffin-lubricated conditions were studied by using an MHK-500 ring-block wear tester. Finally, the worn surfaces and the transfer films of these PTFE composites formed on the surface of GCr15-bearing steel were investigated by using a scanning electron microscope (SEM) and an optical microscope, respectively. Experimental results show that the antiwear properties of these PTFE composites can be greatly improved by filling Cu, Cu2O, or CuS to PTFE, and the wear of these PTFE composites can be decreased by two orders of magnitude compared to that of pure PTFE under dry friction conditions. Meanwhile, CuS increases the friction coefficient of the PTFE composite, but Cu and Cu2O reduce the friction coefficients of the PTFE composites. However, the friction and wear properties of Cu, Cu2O, or CuS-filled PTFE composites can be greatly improved by lubrication with liquid paraffin. The friction coefficients of these PTFE composites can be decreased by one order of magnitude compared to those under dry friction conditions, while the wear of these PTFE composites can be decreased by one to two orders of magnitude. The PTFE + 30(v)%Cu composite exhibits excellent friction and wear-reducing properties under higher loads in liquid paraffin-lubricated conditions, so the PTFE + 30(v)%Cu composite is much more suitable for application under oil-lubricated conditions in practice. Optical microscope investigation of transfer films shows that Cu, Cu2O, and CuS enhance the adhesion of the transfer films 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 GCr15-bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. SEM examination of worn surfaces shows that the interaction between liquid paraffin and the PTFE composites, especially the absorption of liquid paraffin into the surface layers of the PTFE composites, creates some cracks on the worn surfaces of Cu2O or CuS-filled PTFE composites, the creation and development of the cracks reduces the load-carrying capacity of the PTFE composites; this leads to the deterioration of the friction and wear properties of the PTFE composites under higher loads in liquid paraffin lubrication. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1455–1464, 1998