Mechanical properties of the coating/substrate composite system: Nanostructured copper films on a LiF substrate

Abstract

The study of a series of composite structures (CSs) such as CS-1, CS-2, and CS-3 being “soft film/soft substrate” systems revealed much new information on the mechanical properties of these materials. The general and distinctive properties of CSs both within the series of СS-1, CS-2, and CS-3 and the properties of raw materials of Cu and LiF are considered. It is found that the deformation process passes through three main phases in a wide range of loads at the nanomicroindentation of Cu/LiF CSs: (1) when β = h/t < 0.5 (h is the indentation depth, t is the coating thickness) the plastic deformation is mainly concentrated in the film, and only a small elastic deformation can take place in the substrate; (2) at β ≈ 1.0 the deformation occurs in the film and in the interface zone; (3) when β > 1.0 the plastic deformation extends into the substrate bulk, capturing all the typical levels of the system (film–interface zone–substrate) naturally becoming more complex as the load increases. It is shown that the “film/substrate” CSs are complex systems with their highly individual properties even possessing the same chemical composition with the same production method, differing by only one parameter (the film thickness t).