Hard nanocomposite Zr–Y–N coatings, correlation between hardness and structure

The article reports on structure and mechanical properties of Zr–Y–N nanocomposite films containing two immiscible elements (Zr, Y) as metals. Films were prepared by d.c.-reactive magnetron sputtering of alloyed targets ZrY (80/20 at.%) and ZrY (93/7 at.%) in a mixture of Ar+N2 using round planar unbalanced magnetrons of diameter 100 mm. It was shown that: (i) there is a strong correlation between the structure of the film and its hardness, H; (ii) the film structure can be controlled with the interlayer inserted between the substrate and the Zr–Y–N film; and (iii) the film hardness depends on the ratio N/(Zr+Y) in the film and the crystallographic orientation of ZrN grains. Superhard nanocomposite films with hardness greater than 40 GPa were prepared. These films are characterized by (i) the X-ray reflection from ZrN(200) grains and no reflection from the second phase containing Y; and (ii) the ratio N/(Zr+Y)≈1. Also, it was found that the incorporation of nitrogen into the pure ZrY alloy film results in dramatic changes of its mechanical properties. The Zr–Y–N film can be very hard (up to 47 GPa), exhibits the high elastic recovery (We up to 83%) and the high resistance to plastic deformation [H3/E*2 up to approx. 0.75, where E*=E/(1−ν2), E is the Young’s modulus and ν is the Poisson’s ratio]. On the contrary, the ZrY alloy film is soft (H≈6 GPa) and exhibits a low elastic recovery (We=32%).