Adhesive Wear of Duplex-Treated Tool and Structural Steels

Thin ceramic coatings deposited on the surface of tools and machine parts by PVD methods improve considerably their tribological properties. However these hard brittle coatings can be damaged rapidly if plastic deformation initiates in the substrate near the coating-substrate interface when subject to a relatively high load. The logical way how to treat such problems is improvement of the mechanical characteristics of subsurface layers by heat treatment or thermo-chemical treatment such as plasma nitriding. The typical duplex process involves plasma nitriding and PVD coating treatment of steels. Thickness of the nitride layers depends on the activity of nitrogen in the plasma, process temperature and time. The type and thickness of nitrides can influence considerably the quality of the deposited PVD coatings and their adhesion to a nitrided substrate. High-speed steels and Cr-V ledeburitic steels were plasma nitrided and duplex-coated (pulse plasma nitriding + PVD TiN or CrN coating) at various combinations of processing parameters. The wear resistance of the non-nitrided, PVD coated and duplex-coated steel surface was examined by ring-on-plate and plate-on-plate tribological testers. The effect of subsequent PVD–coating performed on plasma nitrided specimens can be considered as very positive when the specimens were severe loaded. The tested duplex treated low-alloy steel 31CrMoV9 was pulse plasma nitrided and then coated by different PVD coatings (TiN, CrN, TiAlN and (CrN-TiN)x3). The results of tribological tests (ring-on-plate tribometer) confirmed the high wear resistance of duplex treated steels.