Hard and superhard Zr-Ni-N nanocomposite films

This article reports on the relationship between the structure and mechanical properties of Zr-Ni-N nanocomposite films prepared by d.c.-reactive magnetron sputtering of a ZrNi (90/10 at.%) alloyed target in a mixture of Ar and N₂ onto steel substrates using a planar round unbalanced magnetron with a diameter of 100 mm. The Zr-Ni-N nanocomposite films represent a new material of the type nc-MeN/metal composed of a hard nc-ZrN phase and a soft Ni phase, where nc- denotes the nanocrystalline phase of zirconium nitride. It was found that (i) there is a strong correlation between the structure of the film, the content of Ni in the nanocomposite and the film properties; (ii) Zr-Ni-N films can form superhard films with a high hardness up to 57 GPa; and (iii) Zr-Ni-N films with the same hardness (H > 40 GPa) can exhibit different structures and strongly differ in the size of nc-ZrN_x grains of which they are composed. Therefore, the superhard coatings with a hardness of H > 40 GPa are characterized either by the strong reflection from large (20-50 nm) ZrN_x grains with a preferential orientation or by many weak reflections from small, approximately 10 nm, ZrN_x grains. General relationships between the microhardness H, the reduced Young's modulus E* = E/(1 - v²), and the elastic recovery W_e, determined from loading/unloading curves measured using a Fisherscope microhardness tester are given; here E and v are the Young's modulus and the Poisson's ratio, respectively. The ratio H³/E*², which represents the resistance of the material to plastic deformation, is also given.