The microstructure and improved mechanical properties of Ag/Cu nanoscaled multilayer films deposited by magnetron sputtering

The Ag/Cu nanoscaled multilayer films, which had a constant thickness of Ag layer (about 15 nm) and various thicknesses of Cu layer from about 4 to 20 nm, have been deposited by magnetron sputtering technique. The phase composition, microstructure, surface topography and mechanical properties of these films were investigated, respectively. XRD results revealed that both Ag and Cu layers in multilayer films had a polycrystalline fcc structure with preferred growth of (1 1 1) orientation. The crystallite sizes decreased greatly compared with that of pure Ag film. High-resolution TEM analysis indicated that the multilayers exhibited obvious interfaces between Ag and Cu layers and had dense and columnar grain morphology. AFM analysis showed that all the multilayers with various thicknesses of Cu layers were much smoother than their constituent Ag and Cu pure films. As compared to that of pure Ag (1.7 GPa) and Cu (2.1 GPa) films, as well as, the hardness values calculated from the rule-of-mixtures, a remarkable increase of hardness was observed for all the multilayer films. The maximum hardness value of 4.3 GPa was obtained for the multilayer film with about 20 nm Cu layer. The vacuum ball-on-disk tribotest results suggested that the multilayer film with highest hardness showed a slight decrease in friction coefficient and notable increase in wear resistance. Especially, these results about mechanical and tribological properties were discussed as a function of the film microstructure.