THE SLIDING WEAR OF ULTRAHIGH MOLECULAR-WEIGHT POLYETHYLENE IN AN AQUEOUS ENVIRONMENT

A study has been made of the tribological behaviour of ultrahigh molecular weight polyethylene (UHMWPE) during water lubricated reciprocating sliding wear. The experimental work has also been extended to study the effect of molecular weight, filler, lubrication, counterface roughness and sliding configuration on the polymer's transfer characteristics. Transfer of the UHMWPE material to the metal counterface during sliding wear involves interlamellar shear of the polymer and results in the development of a highly orientated transfer film. 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. An increase in molecular weight did not significantly improve the wear resistance of the UHMWPE but the additions of fillers did. Long term sliding with hard fillers leads to a reduction in R(a) of the counterface and a large increase in wear rate due to the absence of a transfer film. Coherent transfer films were not found when sliding parallel to the grinding direction on the steel counterface. The observed phenomena have been explained in terms of molecular morphology, mechanical interlocking and chemical bonding of the transfer film with the metal counterface.