Surface physical and chemical changes of pure iron after molybdenum ion implantation and their effects on the tribological behaviour II: Tribological behaviour

The components of tribological systems are all quite sensitive to the surface chemistry and microstructure of the tribological material which may be dramatically changed by ion implantation. This paper is aimed at studying the effect of surface physical and chemical changes caused by molybdenum ion implantation on the friction and wear behaviours of pure iron. For this purpose, the wear tests of unimplanted and implanted specimens were conducted on an SRV fretting wear machine in air, at room temperature and with or without lubrication. The surface morphology, composition and chemical state of the wear tracks were also examined using electron probe microanalysis, Auger electron spectroscopy and X-ray photoelectron spectroscopy. The experimental results indicate that the wear resistance of pure iron is largely improved by molybdenum ion implantation. Under dry friction conditions, the wear resistance of the specimen implanted with a dose of 3 × 10 17 is increased to 2.8 times that of unimplanated pure iron since the anti-adhesion, anti-abrasion and anti-deformation abilities are improved as a result of the increase in microhardness. When liquid paraffin is used as a lubricant, the wear resistance of the implanted specimen is 4.8 times as high as that of the unimplanted one. This further increase in wear resistance compared with that for dry friction is mainly due to the boundary lubricating film provided by liquid paraffin, which reduces the adhesion between the wear counterpart and molybdenum atoms in the implanted specimen. When liquid paraffin plus sulphurized olefin is used as a lubricant, the wear resistance of the implanted specimen is 2.8 times as high as that of the unimplanted one. It can be seen that the increasing value of the wear resistance is lower than that of the sample lubricated with liquid paraffin. The reason is that the compounds FeS and FeSO 4 formed between the element of the wear specimen and the active elements of the lubricant in the wear process play an anti-wear role. However, the presence of a molybdenum element in the implanted specimen decreases the atomic ratio of iron, and thus decreases the amount of FeS and FeSO 4 and the wear resistance.