Improving mechanical properties of Ni-W based nanocrystalline films by multilayered architecture

The applications of nanocrystalline pure Ni film are limited due to grain coarsen and a drop in the mechanical properties with exposure for a long time in ambient. The addition of W to nanocrystalline pure Ni films is a practical method to refine grain and increase hardness, which has attracted widespread attention in tailoring of mechanical properties. However, the lower toughness of Ni-W nanocrystalline film leads to relatively inferior wear resistance. Here, in order to synergistic improvement of hardness and tribological properties of Ni-based films, the NiW/NiWAl multilayer was deposited by co-sputtering, characterized microstructure using X-ray diffraction, atomic force microscopy, scanning electron microscopy and transmission electron microscopy, and evaluated mechanical properties by nanoindentation, scratch and wear test. With the occurrence of sharp periodical layer interfaces, grain refinement and smooth surface are achieved. Accordingly, significant hardness and scratch toughness are enhanced for NiW/NiAlW multilayer film in comparison of NiW and NiWAl monolithic films. For wear tests, the lowest average friction coefficient and wear rate are provided by multilayered film, and thus wear resistance is upgraded by superior mechanical properties of film with multilayered architecture.