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 b y a dip-coating process from specialty formulated aqueous sols. The tribolo gical properties of the as-prepared thin films sliding against an Si3N4 bal l were evaluated on a one-way reciprocating friction and wear tester. The w orn surface morphologies and chemical compositions of the films were examin ed by means of atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), respectively. Thermograv imetric analysis (TGA) and differential scanning calorimetric analysis (DSC ) of dried sols were performed to explore the thermal events occurring duri ng 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 morph ologies. As the results, modified sol-gel Al2O3 films are of higher wear re sistance 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, th e longer the wear life of the sol-gel Al2O3 film. SEM observation of the mo rphologies of worn film surfaces indicates that wear of glass is characteri stic of brittle fracture and severe abrasion. Wear of unmodified Al2O3 film is dominated by microfracture and abrasion, while that of modified films b y plastic deformation and/or microcracking. (C) 2001 Elsevier Science Ltd. All rights reserved.