Surface Modification of Polyethylene by Nitrogen PIII: Surface Chemical and Nanomechanical Properties

摘要

Ultra-high molecular weight polyethylene (UHMWPE) was surface treated by nitrogen plasma immersion ion implantation (PHI), with the main aim of improving its wear resistance. Accelerating voltages (U) between 15 and 30 kV, fluences (F) between 1x10~(17) and 3x10~(17) cm~(-2) and fluence rates (FR) between 3x10~(13) and 7x10~(13) cm~(-2) s~(-1) have been applied. XPS was used to characterise the surface chemical composition and structure. Changes induced in the surface mechanical properties like hardness (H), reduced modulus (E) and in the tribological property of volume loss upon uniform wear test (V) were studied by nanoindentation and multipass wear measurements. The evolution of surface topography was followed by measuring the mean roughness (R_a). The macroscopic temperature (T) developed during the Pill-treatment was also studied. Incorporation of N and O took place into the surface layer. With the increase of U the surface N-content tended to decrease. The bulk plasmon loss energy of the C ls peak increased from 20 eV up to about 25 eV, suggesting densification and the formation of amorphous hydrogenated carbon nitride-like layer. H, T and R_a increased, and V decreased upon PHI treatment, while E either decreased or increased depending on the actual process parameter set applied. In the parameter range studied H_(max), E_(max) and R_(a,max) values have been observed at U_(max), F_(max) and FR_(min). V_(min) and T_(max) have been observed at U_(max), F_(min) and FR_(max), suggesting that the thermal effect is a dominant factor in determining the extent of reduction in the wear rate.