Chromium nitride/niobium nitride nano-scale multilayer coatings deposited at low temperature by the combined cathodic arc/unbalanced magnetron technique

Abstract

CrN/NbN nano-scale multilayered coatings have been successfully grown at a deposition temperature of 250 °C. The coatings have been grown by the combined cathodic arc/unbalanced magnetron technique (Arc Bond Sputter) and were deposited at two different thicknesses namely ∼1.0 and ∼3.0 μm at bias voltages UB between −75 and −150 V. In all cases the stresses were compressive and increased from −4.4 GPa at UB=−75 V to −9.5 GPa at UB=−150 V. Coatings in all cases developed a pronounced {111} texture that tended to a maximum at a bias voltage of −95 V. The experiments indicated that the {111} texture developed by a competitive growth mechanism from a randomly oriented or {100} initial starting texture. Measurements of coefficients of friction and sliding wear show a decrease in the coefficients of friction and sliding wear with increasing bias voltage. The coefficient of friction decreases from μ=0.7 at UB=−75 V to μ=0.5 at UB=−150 V while in parallel the coefficient of sliding wear decreased by an order of magnitude from 1.3×10−14 at UB=−75 V to 2.8×10−15 at UB=−150 V. These decreases in coefficients of friction and sliding wear appear to mirror the increases in intensity of the {111} texture. The adhesion as measured by scratch test shows a distinct maximum of 72 N at a bias voltage UB of −95 V, which is a remarkably high value for a low temperature process in a coating with a compressive stress of −5.4 GPa.