| As a kind of common metal materials, carbon steel is widely used in industrial production and daily life. Its tribological performance directly affects the use scope of materials and service life. Therefore, a lot of researchs in the field of tribology are focused on how to effectively reduce the friction and wear of materials. It is reported that micro/nano surface texturing on materials can decrease real contact area of friction pairs, thus significantly improve the tribological properties of metal materials. At the same time, organic film, deposited on the surface by using the self-assembled technology, can also effectively reduce surface energy and friction of the contact. In fact, the organic combination of the two technologies can not only greatly improve the surface hydrophobic properties, but also improve the tribological properties of the surface by using the anti-friction effect of surface texture and the nanometer lubricating effect of self-assembly layer.However, only a few studies are reported to combine surface texturing to self-assembled technologies in order to further reduce friction and wear of the materials. This thesis is devoted to this area. Here, the particular micro-nano surface texture is generated on steel by using chemical etching and sol-gel technology, respectively, above which a stearic acid monolayer is deposited by using self-assembled technology to further reduce surface energy. In this way, a super or high-hydrophobicity film can be obtained which shows excellent friction-reducing and anti-wear performance. The surface morphology, formation mechanism, wettability and the tribological behavior of the high-hydrophobicity films were characterized. The influence of preparation conditions on the tribological properties of the films and the effect of temperature and UV irradiation to the films’tribological and wettability properties are further investigated. The main results are showed as the follows:(1) A simple two-step process was developed to render steel with lower friction and longer durability. The hydrophilic nanotextured steel was firstly fabricated by immersing steel in HNO3solution at room temperature for10min. Stearic acid film was then deposited on etched steel to acquire high hydrophobicity by using self-assembled technology. The static contact angle is142°.The high hydrophobic film shows excellent tribological performance,.remaining low friction coefficient (less than0.2) for a relatively long period (longer than7,200s) before the experiments stop. However, bare steel shows high friction coefficient (-0.6) only by5s sliding. Preparation conditions, such as etching agent composition, stearic acid modified time and fatty acids, were found to affect the tribological properties of the high hydrophobic film. If the film is heated or irradiated by UV, the organic film was damaged with rapid decrease of contact angle and increase of friction coefficient.(2) The three different etchants are used to fabricate the surface texture on steel. The etched steel are coated by stearic acid film by self-assembled technologies to reduce friction and wear of steel. The results show that the different textured steel surface are prepared by different etchants. However, when stearic acid film is deposited on textured surfaces, surfaces are superhydrophobic with static contact angle of about150°. However, they show different friction-reducing performance. Comparing to surface etched by hydrochloric acid and hydrofluoric acid, surface etched by sodium hydroxide solution have the best tribological property. At load of4N, the superhydrophobic surface preserve low friction coefficient and wear resistance property for7200s sliding time.(3) The anatase TiO2hydrophilic film, prepared on steel surface via a sol-gel method, shows better friction-reducing performance. Enhanced wear resistance were clearly obtained after functionalization of stearic acid on the TiO2surface. Wettability was changed from hydrophilic to hydrophobic. Much better friction reduction and wear resistance, higher hydrophobic are also observed for the steel substrate after duplex surface-modification with metal Ni or Cu ion doped TiO2surface obtained by sol-gel method and top layer of stearic acid.In brief, this thesis is devoted to decrease the friction and wear of steel substrate by combining the effects of nano lubrication from self-assembled monolayer, surface texture from chemical etching and TiO2film from sol-gel technologies. The as-prepared hydrophobic organic compound films show excellent low friction and long wear resistance. The results are important to develop steel materials with low friction and high wear resistance. |
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