REACTIVE UNBALANCED MAGNETRON SPUTTER DEPOSITION OF POLYCRYSTALLINE TIN/NBN SUPERLATTICE COATINGS

An opposed dual-cathode unbalanced magnetron sputtering system was used to deposit polycrystalline TiN/NbN superlattice coatings, with periods between 2.5 nm and 150 nm, on M2 tool steel substrates. Analytical techniques including X-ray diffraction, Auger spectroscopy and transmission electron microscopy were used to characterize the structure of the superlattice coatings. These showed that well-defined TiN and NbN layers were obtained, but the interfaces were not perfectly planar or abrupt. The-mechanical properties of the superlattice coatings were characterized using a Vickers' microhardness tester and scratch tester. Microhardness values for the 6 mum thick superlattice coatings ranged from 1800 to 5200 kgf mm-2 (H v 0.05) and were strongly dependent on several deposition parameters such as superlattice period A, nitrogen partial pressure, the ratio of gas flow to each target, and the negative substrate bias V(s). The highest hardness values were obtained for A almost-equal-to 6 nm and V(s) = 150 V. The scratch adhesion critical load of superlattice coatings ranged from 1.8 kgf at V(s) = 200 V to 11 kgfat V(s) = 34 V.