Investigation On The Microstructure And Tribological Performance Of TiO₂ Films By Sol-gel Method

Some low friction and good wear-resistance nanoceramic TiO2 thin films were designed and prepared by sol-gel process. The tribological properties of those films at room temperature were investigated and their wear mechanisms were discussed. The following main conclusions are reached:1. The surfaces of the TiO2 films by traditional sol-gel were compact, uniform, crack-free and disfigurement-free, with low roughness. The thickness can be controlled in the range of nanoscale. The sol-gel films exhibited relatively low friction coefficient and long wear life.2. The TiO2 thin films were prepared by surface sol-gel process on the glass substrates. Their structure, composition, surface morphology and tribological properties were investigated. Results show that, compared with traditional bulk sol-gel derived TiO2 thin films, the tribological properties of thin films had been significantly improved. This is due to several drying process which can avoid structural defects resulting from instantaneous output of large volumes of solvent residues during drying and heat treatment via traditional bulk Sol-Gel process, Improvement of friction and wear performance was attributed to a higher compactness.3. The doped sol-gel films were obtained by combination of TiO2 and mutually-soluble dopants SiO2, or TiO2 and self-lubricating materials Ag, effect of doped content on surface morphology structure, composition, surface morphology and tribological properties have been investigated. Results show because the Ag+ ions introduced by the sol-gel process are unable to enter TiO2 lattice to form a stable solid solution, effect of Ag content on surface morphology and wear resistance is much apparent, but without a single linear relationship. With low Ag content, enhancing tribological properties is predominant; but with high Ag content, decreasing tribological properties is apparent due to deteriorating surface morphology. For SiO2 doped TiO2 films, the suitable addition of silica into TiO2 film can effectively prevent the growth of TiO2 grains and ensure the durability of TiO2 due to formation of Si-O-Ti hetero linkages. Additionally, the presence of SiO2 can greatly increases the adhesion and mechanical stability of thin film on substrates. All these effects contributed to the excellent antiwear and friction-reduction performance of mutually-soluble TiO2-17.9SiO2 film over pure TiO2 film in sliding against Si3N4 under low load. However, excessive SiO2 seriously deteriorates wear resistance of film due to phase separation.4. Under low load and sliding speed, the wear mechanisms of those doped films by optimized control were mainly characterized by slight scuffing and abrasion; while pure TiO2 film and excessive dopants by severe plastic deformation and abrasion, separately, even by brittle fracture and peeling.