Characterization and tribological investigation of Al₂O₃ and modified Al₂O₃ sol-gel films

Thin films of Al₂O₃ and modified Al₂O₃ were prepared on a glass substrate by a dip-coating process from specially formulated aqueous sols. The tribological properties of the as-prepared thin films sliding against an Si₃N₄ ball were evaluated on a one-way reciprocating friction and wear tester. The worn surface morphologies and chemical compositions of the films were examined by means of atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), respectively. 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 Al₂O₃ films. The wear mechanisms of the films are discussed based on SEM observation of the worn surface morphologies. As the results, modified sol-gel Al₂O₃ films are of higher wear resistance than the unmodified one. Meanwhile, the wear life of the modified films is correlated to the additive amount in the starting aqueous sol. In other words, the higher the additive amount in the starting aqueous gel, the longer the wear life of the sol-gel Al₂O₃ film. SEM observation of the morphologies of worn film surfaces indicates that wear of glass is characteristic of brittle fracture and severe abrasion. Wear of unmodified Al₂O₃ film is dominated by microfracture and abrasion, while that of modified films by plastic deformation and/or microcracking.