| Solid-liquid composite lubrication is a new technology that has attracted extensive attention of researchers in recent years.It can greatly improve the friction and wear properties of the material under extreme and variable working conditions and prolong the service life of the workpiece by combining self-replenishment,low-friction elastohydrodynamic lubrication characteristics of liquid lubricants and the high bearing capacity and antiwear properties of solid lubricating films.As the first industrialized nitride hard coating,TiN coating has been widely used in many industrial fields such as machinical processing and engines by its high hardness,high wear resistance and unique surface properties.However,with the continuous progress of industrial production for the complex and various use environment,the requirements for the mechanical and wear resistance of TiN coatings are becoming more and more stringent.On the other hand,the voice of developing solid-liquid composite lubrication technology with environmental adaptability lubrication characteristics and ultra-long wear-resistant life is getting higher and higher in order to meet the concepts of green environmental protection,clean production and efficient application.Thus,the thesis was devoted to design and construct a variety of solid-liquid composite lubricating systems based on TiN coatings by selecting liquid lubricants with special chemical properties which is based on the design idea of solid-liquid composite enhancement of tribological properties.A variety of solid-liquid composite lubricating systems were obtained in this thesis,and the chemical composition and structure of the lubricating film were systematically characterized by X-ray photoelectron spectroscopy（XPS）,Fourier transform infrared spectroscopy（FTIR）,Raman spectroscopy and other characterization methods.The mechanism of the solid-liquid composite lubricating system was evaluated to obtain for ultra-low friction and wear.The research results are expected to provide reference for realizing the effective lubrication of TiN coatings in different application environments.The main research contents and conclusions of the thesis are as follows:（1）The synergistic lubrication effect of TiN coating with a common lubricant additive,molybdenum dithiocarbamate（Mo DTC）,was investigated.Excellent tribological properties were observed on the TiN coating when lubricated by PAO6 oil containing Mo DTC,which is due to tribocatalytical effort by TiN coating for the formation of tribofilm containing Mo S2 by tribochemical degradation of Mo DTC in the friction process.Adding Ti O2 nanoparticles to Mo DTC-containing base oil can further improve the lubrication of Mo DTC on the surface of TiN coating,and macroscopically achieve ultra-low friction at contacting pressure of 1.3 GPa.The results enrich the research on the tribochemical degradation mechanism of Mo DTC,and provide some references for expanding the application of TiN coatings as low-friction and wear-resistant coatings for automobile engines.（2）A lubricating method was proposed to effectively improve the tribological properties of TiN coating by using carbon precursor molecules（cyclopropanecarboxylic acid）to in situ construct a carbon-based tribofilm on the surface of TiN coating.It was found that the cyclopropanecarboxylic acid,as an additive to polyalphaolefin（PAO）,was decomposed by the effect of rise of frictional temperature,contacting stress and tribocatalysis effort of TiN coating in the friction process.A carbon-based tribofilm was in situ formed in the contacting area to achieve an ultra-low friction.The tribochemical reaction mechanism of carbon-based tribofilms from cyclopropanecarboxylic acid molecules was systematically studied.The relationship between the size of the alkane ring in the cycloalkanecarboxylic acid structure and the thermal stability and tribological properties was established.（3）PAO6 base oil containing Cu-Ni bimetallic nanoparticles exhibited excellent lubricating properties on the surface of TiN coating.It was found that Cu and Ni have different roles in the friction process.Ni mainly plays a tribocatalytic role in the degradation of PAO6 molecules to form a carbon-based film lubrication layer at the friction interface,while Cu deposits in the contact area and plays a repairing role.The research results provide a reference for the design of novel bimetallic nano-additives with excellent tribological properties.（4）The TiN coating exhibits excellent tribological properties under lubrication of the glycerol as a green lubricant.The XPS analysis results of the tribofilm show that the glycerol degrades at the friction interface to form a Fe OOH-containing lubricating layer,The glycerol and the glycerol degradation products were further adsorbed on the surface of Fe OOH layer and formed a network structure through intermolecular hydrogen bonding to build a hydration layer with high lubricating properties.After incorporating Cu nanoparticles into glycerol,superlubricity can be macroscopically achieved at contacting pressure of 0.9 GPa.Cu nanoparticles were found to further catalyze the degradation of glycerol to generate a carbon-based film in the contact area.At the same time,Cu nanoparticles were deposited itself in the contact area,playing a repairing role. |
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