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 + N-2 using round planar unbalanced magnetrons of diameter 100 mm. It was shown that: (i) there is a strong correlation between the structure of the him 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) approximate to 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 (W-e up to 83%) and the high resistance to plastic deformation [H-3/E*(2) up to approx. 0.75, where E* = E/(1 - v(2)), E is the Young's modulus and v is the Poisson's ratio]. On the contrary, the ZrY alloy film is soft (H approximate to 6 GPa) and exhibits a low elastic recovery (W-e = 32%). (C) 2000 Elsevier Science S.A. All rights reserved.