Tribological behavior of sol-gel TiO₂ films on glass

TiO₂ thin films were grown on a glass substrate by sol-gel and dip-coating processes from specially formulated sols, followed by annealing at 460°C. Thermogravimetric analysis (TGA) and differential scanning calorimetric analysis (DSC) of dried sols were performed to explore the thermal events occuring during the annealing process of the sol-gel TiO₂ films. The chemical states of some typical elements in the target films were detected by means of X-ray photoelectron spectroscopy (XPS). The morphologies of the original and worn surfaces of the samples were analyzed by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM). The tribological properties of TiO₂ thin films sliding against AISI52100 steel and Si₃N₄ ball were evaluated on a reciprocating friction and wear tester. As the results, the target film was obtained and reaction may have taken place between the film and the glass substrate. TiO₂ films are superior in reducing friction and resisting wear compared with the glass substrate. SEM observation of the morphologies of worn surfaces indicates that the wear of glass is characteristic of brittle fracture and severe abrasion. Differently, abrasion, plastic deformation and micro-crack dominate the wear of TiO₂ films. The superior friction reduction and wear resistance of TiO₂ films are attributed to slight plastic deformation as well as good adhesion of the film to the substrate.