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

Abstract

Polycrystalline nitride coatings TiAlCrN and TiAlCrYN have been grown by combined steered arc etching and unbalanced magnetron sputtering. The multicomponent coatings were found to exhibit superior wear resistance compared with commercial TiN and CrN coatings in dry-sliding conditions at low load, but similar wear rates at higher loads. An understanding of the wear mechanism was obtained by analytical transmission electron microscopy and scanning electron microscopy of the worn surfaces. The sliding wear was dominated by 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 minimal content. Below this, a thin layer of plastically deformed material was observed. Pre-existing peaks on the surface, arising from deposition defects, 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 with (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 deformation; and (d) more severe tribo-oxidation than found in the mild wear regime.