Wear mechanisms of monolithic and multicomponent nitride coatings grown bycombined arc etching and unbalanced magnetron sputtering

Polycrystalline nitride coatings TiAlCrN and TiAlCrYN have been grown by co mbined steered arc etching and unbalanced magnetron sputtering. The multico mponent coatings were found to exhibit superior wear resistance compared wi th commercial TiN and CrN coatings in dry-sliding conditions at low load, b ut similar wear rates at higher loads. An understanding of the wear mechani sm was obtained by analytical transmission electron microscopy and scanning electron microscopy of the worn surfaces. The sliding wear was dominated b y a surface film of Fe-based oxides. formed through material transfer from the tool steel counterface. For the TiN, this layer contained a significant contribution from the coating, while for the TiAlCrYN there was only a min imal content. Below this. a thin layer of plastically deformed material was observed. Pre-existing peaks on the surface, arising from deposition defec ts, were preferentially removed during the early stages of wear, resulting in locally more severe surface deformation and consequent delamination. At higher load or low speed, more severe wear modes were observed associated w ith (a) cracks due to friction traction; (b) delamination sheets resulting from coalescence of cracks perpendicular and parallel to the worn surface; (c) cohesive cracking and detachment of the film due to substrate deformati on, and (d) more severe tribo-oxidation than found in the mild wear regime. (C) 2001 Elsevier Science B.V. All rights reserved.