Individual Layer Thickness Dependence of Microstructure and Mechanical Properties of Magnetron Sputtering Mo-W-Doped Ni/Ni3Al Multilayers

The mechanical properties of nanocrystalline pure Ni films are degraded due to grain coarsening with exposure for a long time in ambient. In order to further improve the mechanical properties of Ni-based thin films, as-sputtered Mo-W co-doped Ni/Ni3Al multilayered structures were constructed. When the individual layer thickness (h) is lower than 40 nm, both the average grain sizes and the crystallinity degrees are degraded, showing a tendency for the formation of the amorphous phase. With h = 40 nm, nano-twins were observed as (111) twining interfaces for the multilayers due to the reduction of the stacking fault energy by the co-doping of Mo-W, whereas the nucleation and growth of the nano-twins were limited, without observations for the Mo-W co-doped Ni/Ni3Al multilayer with h = 10 nm. The hardness of the multilayers was enhanced, and the elastic modulus was reduced at a lower h, owing to the grain refinements and layer interface barriers for strengthening, and the existence of the amorphous phase with the inferior modulus, respectively. The resistance against the fracture was enhanced due to toughening by the lamellar structure for the Mo-W doped Ni/Ni3Al multilayer at h <= 40 nm. Comprehensively, the Mo-W-doped Ni/Ni3Al multilayer with 10 nm displays a superior mechanical performance.

Automated summary

The mechanical properties of nanocrystalline pure Ni films degrade due to grain coarsening when exposed for a long time. In order to improve the mechanical properties, Mo-W co-doped Ni/Ni3Al multilayered structures were constructed. The average grain sizes and crystallinity degrees decrease when the individual layer thickness is below 40 nm. At 40 nm, nano-twins are observed due to the reduction of stacking fault energy. The hardness of the multilayers is enhanced and the elastic modulus is reduced. The best mechanical performance is observed in the Mo-W-doped Ni/Ni3Al multilayer with a thickness of 10 nm.