Structure and mechanical properties of magnetron sputtered Zr-Ti-Cu-N films

The article presents a detailed analysis of the structure-hardness relations in Zr-Cu-N and Zr-Ti-Cu-N films with low and high Ti content. These films were sputter deposited using a dc unbalanced magnetron equipped with a composed target, i.e. a round plate of diameter 100 mm made of ZrCu (90/10 at.%) alloy with a Ti (99.5%) fixing ring. The use of the Ti fixing ring of two internal diameters (70 or 50 mm) makes it possible to prepare Zr-Ti-Cu-N films with different Ti content, approximately with 15 or 50 at.%, respectively. The properties of the Zr-Ti-Cu-N films were compared with those of Zr-Cu-N films reactively sputtered from the same magnetron but equipped with a ZrCu (90/10 at.%) target in a mixture of argon and nitrogen at a total pressure p_T = p_Ar + p_N2 = 0.7 Pa. It was found that (i) nanostructured Zr-Cu-N and Zr-Ti-Cu-N films can form superhard materials with hardness H greater than 40 GPa, (ii) there is a strong correlation between the structure and the hardness of the films, (iii) the films with a maximum hardness H_max are composed of a mixture of grains of different crystallographic orientations and (iv) there is no correlation between H_max of superhard films, their stoichiometry x = N/(Zr + Ti) and Ti content in the film.