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 occurring 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.