Mechanisms of Formation of Polymeric Transfer Films*

When polymeric solids slide against other solids such as steel there appears to be no way to predict either the friction of the system or the wear life of the polymer from handbook data. Friction and wear vary over wide ranges when sliding speed, applied load and system temperature are varied. Neither have thermal analyses of the sliding system produced satisfying results, partly because of the difficulty in measuring temperatures in the sliding interface. However, there is some progress in these studies. Dowson [l] reports a thermal analysis of sliding by extrapolation from temperatures measured by thermocouple in several locations within the metal counterface. Lancaster [ 21 reports wear at low rubbing severity and attributes it to a fatigue mechanism. Finally, a number of authors of both research papers and test reports note that in some cases a polymeric film is transferred and remains firmly attached to the metal counter-face, with the apparent effect of reducing wear. This paper reports the results of some work to measure the properties of the transfer film and proposes a model for transfer film formation and behavior. The research reported consisted in the measurement of friction and wear rate over a wide range of load and speed together with measurements of temperatures in the vicinity of the sliding interface. Transfer films were