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 pT=pAr+pN2=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 Hmax are composed of a mixture of grains of different crystallographic orientations and (iv) there is no correlation between Hmax of superhard films, their stoichiometry x=N/(Zr+Ti) and Ti content in the film.