In the research, samples made of AISI 4140 steel pre-treated by plasma nitriding and coated with different PVD coatings (TiN, TiAlN and ta-C) were investigated in terms of their microhardness, scratch adhesion and dry sliding wear resistance. Wear tests, in which duplex-treated pins were mated to hardened ball bearing steel discs, were performed with a pin-on-disc machine. To examine the influence of the nitrided zone on the performance of the coating-substrate composite, coatings were deposited on hardened as well as on plasma nitrided samples, prepared under different nitriding conditions. The results of the investigation showed improved mechanical and tribological properties of the plasma nitrided hard-coated specimens compared to the un-coated and pre-hardened ones. Furthermore, the compound laver was found to act as an intermediate hard layer leading to superior sliding wear properties of the composite. (C) 2001 Journal of Mechanical Engineering. All rights reserved.