Third Body Formation and the Wear of PTFE Fibre-Based Dry Bearings

Dry bearing tests have been made with a PTFE fibre/glass fibre/phenolic resin composite against stainless steel to examine the influence of time of sliding, counterface roughness and load. The worn surfaces were examined by optical and scanning electron microscopy, energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (ESCA). It is shown that the coefficient of friction and the rate of wear are strongly influenced by the formation of third bodies on both sliding surfaces. The structure and composition of these third bodies depend on the time of sliding and the load, but are independent of counterface roughness. Wear of the PTFE composite appears to occur on several scales, and considerable degradation of PTFE is evident within the third body (transfer film) on the counterface. The significance of these observations to the measured friction and wear rates is discussed.