Characterization and mechanical/tribological properties of nano Au–TiO2 composite thin films prepared by a sol–gel process

Nano Au–TiO2 composite thin films on Si(1 0 0) and glass substrates were successfully prepared with a facile sol–gel process followed by sintering. The morphology and mircostructure of the films were investigated via X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The Au particles, of diameter 14–22 nm depending on the sintering temperatures used, were found to be well dispersed in the TiO2 matrix, with a small amount of the particles escaped from the film. The surfaces of the films were uniform, compact and crack-free. Hardness and elastic modulus of the films were measured by using the nanoindentation technique. Friction and wear properties were investigated by using a one-way reciprocating tribometer. It was found that the highest hardness and elastic modulus values were obtained for the films prepared with 500 °C sintering temperature. The films displayed superior antiwear and friction reduction performances in sliding against an AISI 52100 steel ball. With 5.0 mol% Au, the friction coefficient was only 0.09–0.10 and the wear life was more than 2000 sliding cycles. The friction coefficient and wear life decreased with increasing sliding speed and load. The failure mechanism of the Au–TiO2 films was identified to be light scuffing and abrasion. Those films can be potentially applied as ultra-thin lubricating coatings.