Improvement of flow strength and scratch resistance of Ti/Cu nanocrystalline metal multilayer thin films by tailoring layer thickness and modulation ratio

In this work, nanocrystalline Ti/Cu multilayer thin films were fabricated using direct current magnetron sputtering with different layer thicknesses, namely 250, 100, 50, 25 and 5 nm. Additionally, a group of the film specimens were prepared with various modulation ratios where each bilayer was set to 100 nm. The sizedependent deformation behavior of the films was studied using the nano-indentation and nano-scratching techniques. The results showed that the flow strength of the films tended to increase as the layer thickness decreased. Moreover, the strength and scratch resistance of the films can be further enhanced by tailoring the thicknesses of two adjacent layers, while keeping the thickness of each bilayer unchanged. Finally, the sizedependent strengthening mechanism was discussed by recourse to microscopic examination.