Evaluation of adhesion and tribological behaviour of tantalum oxynitride thin films deposited by reactive magnetron sputtering onto steel substrates

Ta-O-N coatings (2-4 mu m thick) were deposited on high-speed steel by DC reactive magnetron sputtering. The 0, IN, ratio in the plasma was varied between 0.08 and 1.33. The (O+N)/Ta ratio in the Ta-O-N films varies between 1.27 and 2.78 and the oxygen fraction, f(O)=O/(O+N), between 0.06 and 0.96. The hardness decreases from 27 to 6 GPa with increasing (O+N)/Ta ratio in the films. The adhesion of the coatings to steel was evaluated by scratch tests. First cohesive failures occur at L-ct = 1-4 N for all the films. Most films with 2.16 <= (O + N) /Ta <= 2.77 fail by gross interfacial shell-shaped spallation at L-c2 = 3-5 N. Films with highest (O + N)/Ta= 2.78 are very brittle and exhibit a large area interfacial spallation already at low loads. At high loads (L-c3 = 22-26 N) all films fail via large scale interfacial spallation inside the track, resulting in coating delamination. The tribological behaviour of the coatings in pin-on-disk tests is discussed with respect to the metalloid content in the Ta-O-N. (c) 2005 Elsevier B.V. All rights reserved.