Effect of fluorinated ethylene propylene copolymer on the wear behaviour of polytetrafluoroethylene

Abstract

The wear behaviour of polytetrafluoroethylene (PTFE) composites containing various fluorinated ethylene propylene copolymer (FEP) contents rubbing against an AA-7075 aluminium alloy has been evaluated. Wear tests were carried out on a modified pin-on-disc type wear machine under constant sliding conditions: applied stress, 1.87 MPa; sliding speed, 1.3 m s −1. The wear resistances of the PTFE composites were higher than for pure PTFE within the range of all the experimental FEP contents (5–40 wt.%). It is also shown that the PTFE composite with minimum wear rate contains about 35 wt.% FEP. In order to investigate the wear-reducing mechanism, microhardness tests, differential scanning calorimetry (DSC) and micrography have been carried out. The Vickers hardness showed little variation with FEP content. From the DSC results, the FEP peak was observed in the PTFE composites, but not in the wear debris. The molecular weight and crystallinity of PTFE contained in PTFE composites did not change with FEP content; however, those of the wear debris did change. The wear-reducing mechanism of PTFE composites containing various FEP contents is discussed in terms of the load-supporting action of FEP and the changes in the polymer film which are transferred onto the metal counterface.