On the nature of the transfer film at the interface of a water lubricated sliding polymer-metal couple

Abstract

A range of ultra-high molecular weight polyethylenes have been subjected to water-lubricated, reciprocating sliding wear against a stainless steel counterface under a pressure of 10 MPa at a frequency of 2.5 Hz and a maximum speed of 0.4 m s-1. Transfer of material to the metal counterface during sliding wear involves interlamellar shear of the polymer and results in the development of a highly oriented transfer film. The deformed surface layers of the polymer and the resultant wear debris have been examined using both optical and scanning electron microscopy, differential scanning calorimetry, infrared spectroscopy and x-ray diffraction. Significant differences have been found in the degree of crystallinity, crystallite size and orientation in the deformed surface layers of the polymer and debris compared with those of the bulk polymer. The worn surface of the polymer shows slightly increased crystallinity but the crystallinity of the debris is much higher than that of the bulk whilst the crystallite size is much reduced.