Duplex treatment: W-Ti-N sputtered coatings on pre-nitrided low and high alloy steels

Duplex treatment (plasma nitriding+PVD W-Ti-N coating) was applied to low and high alloy steels. The influence of nitriding layers, with different thickness (with and without "white layer" formation), on the properties of W-Ti-N films was studied. W-Ti-N coatings were deposited by dc reactive magnetron Sputtering using a W+20 wt.% Ti target varying the partial pressure of the reactive gas (N-2) and the ion bombardment conditions. The hardness of the coatings decreased when they were deposited on nitrided samples, whereas the critical load determined by scratch testing increased, even with the presence of a "white layer". These results were interpreted as a function of the residual stresses in the films induced by the deposition procedure and the ability of the substrate to support the applied load without suffering plastic deformation, together with changes on coatings characteristics. (c) 2005 Elsevier B. V. All rights reserved.