Study On Tribological Properties Of Polyurethane-Metal And Interfacial Transfer Film Growth Under Water Lubrication

Water lubrication is sustainable and which is a low-cost,green and pollution-free lubrication method.The instead of traditional oil-lubricated bearings using water-lubricated bearings is not only efficient and environmentally friendly,but also can simplify the design of lubrication system and reduce manufacturing costs.High-performance water-lubricated bearings will play a more important role under the current strategic background of the the Belt and Road Initiative and the promotion of marine industry development.Polyurethane elastomers（PU）have been used as water-lubricated bearing materials since its excellent wear resistance,designability and low temperature resistance.However,the application of PU is greatly limited by its low carrying capacity,weak resistance to wear in case of insufficient lubrication,water absorption and stick-slip when it as water-lubricated material.Therefore,it is necessary to carry out corresponding modification research on polyurethane material to improve the overall performance and expand its application range.Regrettably,there are few studies on tribological property of PU,and the effect of functional fillers on its friction and wear mechanism has not been fully understood.This study is based on the design and preparation of high-performance PU bearing materials that can be used in the boundary lubrication state of water lubrication medium.The effect of various functional fillers on the tribological properties of PU matrix was investigated,and the formation mechanism of the transfer film between the PU-metal pair was analyzed in depth using advanced characterization methods.The main research contents are as follows:1.A series of PU composites filled with PEW and TiO₂ were designed and prepared.Tribological properties of PU composites were tested by MRH-3 ring-block tribometer.The results show that adding PEW into PU can reduce its friction coefficient significantly and improve its wear resistance slightly.The addition of TiO₂ particles improved the wear resistance of the composite effectively,but the reduce of friction coefficient unconspicuous.Surprisingly,the addition of PEW and TiO₂ into PU at the same time combines the advantages of both,and shows a synergistic effect on improve the tribological properties of PU.Among them,12PEW/1TiO₂/PU has the best tribological properties.Its friction coefficient is reduced by more than 40%and its wear resistance is increased by 10 times compared with neat PU.Through in-depth characterization and analysis of transfer film on the surface of metal pair rubbed with PU composite,it was found that the tribochemical reaction of PU will occur during the friction process to generate organometallic compounds,which will improve the adhesion of transfer film on the surface of the metal pair.The addition of PEW can promote the growth of transfer film,and provide lubrication between friction pairs based on its waxy shear properties.At the same time,TiO₂ also participated in the construction of the transfer film,significantly improving the carrying capacity of the transfer film.2.The effects of short carbon fiber（SCF）,glass fiber（GF）and aramid fiber（AF）on the tribological properties of PU were investigated.The tribological properties of three kinds of PU composites with different fiber additions were tested.The results shows that the best tribological properties of PU composites are obtained when the fiber addition is10%.The friction coefficient and wear rate of SCF reinforced PU composites are the lowest,is 0.22 and 4.88×10^-6 mm³/Nm respectively.And the friction coefficient of10SCF/PU is reduced by 33%,and the wear rate is reduced by two orders of magnitude compared with neat PU.Further characterization and analysis of the wear surface of composites and metal pairs found that the interface between GF and PU matrix was poor,and it was easy to fall on the friction interface to cause"three-body"wear.The further corrosion occurred in the water medium due to GF scratched the metal pairs seriously,and the friction corrosion products covered the wear surface hindered the formation of transfer film.AF has a good combination with PU matrix based on its polar group effect,but the transfer film containing AF has low strength.So that the transfer film unstable existence on the friction interface,and most of it is deposited in the groove by friction.In contrast,the transfer film composed of graphite carbon produced by SCF grinding at the friction interface is more stable,thus significantly improving the tribological properties of PU materials.3.The influence mechanism of gradient hardness inorganic functional fillers on the tribological properties of SCF reinforced PU composites was investigated.Among them,BN,Si C,and Sb₂O₃ have a positive effect on improving the tribological properties of SCF reinforced PU composites,while the addition of TiO₂ and Al N reduces the wear resistance of the materials to a certain extent.Compared with 10SCF/PU,10SCF/2Si C/PU materials have the most excellent tribological properties,with friction coefficients and wear rates reduced by 33%and 36%,respectively.Through in-depth characterization of friction interface and analysis of physical and chemical interaction,it is found that Si C will undergo friction hydrolysis reaction during friction.Its hydrolysate Si O₂ gel participates in the construction of hybrid transfer film at friction interface,which not only increases the binding force between transfer film and dual metal surface,but also improves the carrying capacity of transfer film,thus improving the tribological properties of PU composites.In this paper,the effects of PEW and TiO₂,different reinforced fibers and gradient hardness inorganic functional fillers on the tribological properties of PU materials under water boundary lubrication were studied.The microstructure and formation mechanism of the transfer film on the wear interface were deeply investigated through various characterization and analysis methods.Discuss the physical and chemical effects on the wear surface,providing an important reference for the development and preparation of PU composites for water-lubricated bearings.