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TitleTribological characterization of TiO2/Au decorative thin films obtained by PVD magnetron sputtering technology
Author(s)Abreu, C. S.
Matos, José C.
Cavaleiro, A.
Alves, E.
Barradas, N. P.
Vaz, F.
Faro, Marc Torrell
Gomes, J. R.
Decorativethin films
PVD sputtering
Issue date2015
Abstract(s)The aim of this work is to evaluate the tribological behavior of decorative thin film nanocomposites consisting of gold nanoparticles dispersed in a dielectric matrix of TiO2. The main focus is given to the changes in the friction coefficient and wear rate, as well as on the overall tribological features resulting from the morphological changes induced by annealing experiments in vacuum, at increasing temperatures up to 500ºC. In particular, the gold clustering, increase of grain size and the crystallization of the TiO2 dielectric matrix are correlated with the changes in the tribological parameters. Linearly reciprocating ball-on-flat sliding tests were performed under 0.1 N applied load and constant frequency of 1 Hz. AISI 52100 ball bearing steel was used as the opponent surface and the sliding occurred at room temperature, in the absence of external lubrication. It was found that the annealing process at different temperatures had no significant effect on the stoichiometric condition of the TiO2 matrix, deepness homogeneity of the Au nanoclusters and film thickness, but important changes occurred in terms of clusters size and crystallization of the film. Those structural changes resulted in distinct friction regimes and wear responses. Annealing at 300 ºC resulted in the best frictional response (f ~ 0.15 during an initial friction plateau) and good wear resistance (K ~ 2x 10- 6 mm3 N- 1 m -1). Thermal annealing at higher temperature had a detrimental effect on the tribological properties of the films due to important structural changes as increasing of crystallinityand nanoparticle gain size. Annealing at 500 ºC presented the worst tribological properties of the films (f ~ 0.22 and K ~ 4x 10- 5 mm3 N- 1 m- 1), with extensive early delamination. A direct correlation was found between the tribological properties of the TiO2/Au decorative thin films and the diffusion mechanisms induced by the thermal annealing.
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