Characterization and Tribological Investigation of Sol–Gel Titania and Doped Titania Thin Films

Abstract

Titania (TiO2) and doped TiO2 ceramic thin films were prepared on a glass substrate by a sol–gel and dip‐coating process from specially formulated sols, followed by annealing at 460°C. The morphologies of the original and worn surfaces of the films were analyzed with atomic force microscopy (AFM) and scanning electron microscopy. The chemical compositions of the obtained films were characterized by means of X‐ray photoelectron spectroscopy (XPS). The tribological properties of TiO2 and doped TiO2 thin films sliding against Si3N4 ball were evaluated on a one‐way reciprocating friction and wear tester. The AFM analysis shows that the morphologies of the resulting films are very different in nanoscale, which partly accounts for their tribological properties. XPS analysis reveals that the doped elements exist in different states, such as oxide and silicate, and diffusion took place between the film and the glass substrate. TiO2 films show an excellent ability to reduce friction and resist wear. A friction coefficient as low as 0.18 and a wear life of 2280 sliding passes at 3 N were recorded. Unfortunately, all the doped TiO2 films are inferior to the TiO2 films in friction reduction and wear resistance, primarily because of their differences in structures and chemical compositions caused by the doped elements. The wear of the glass is characteristic of brittle fracture and severe abrasion. The wear of the TiO2 thin film is characteristic of plastic deformation with slight abrasive and fatigue wear. The doped TiO2 thin films show lower plasticity than the TiO2 thin film, which leads to large cracks. The propagation of the cracks caused serious fracture and failure of the films.