Mechanical and tribological properties of multilayered PVD TiN/NbN coatings

The tribological performance of thin hard coatings is, for a given substrate material, mainly governed by the coating hardness, coating fracture resistance, the contact temperature and chemistry (in the prevailing tribosystem). For a given application, an improved tribological performance can therefore, for example, be accomplished by increasing the coating fracture resistance while retaining the hardness, or vice versa. Four different PVD TiN/NbN multilayer coatings were deposited on high speed steel and cemented carbide substrates. Homogeneous TiN and NbN coatings were used as references. The coated composites were investigated with respect to coating thickness, morphology and microstructure, adhesion, hardness, residual stress and resistance to abrasive and erosive wear. The investigation showed that the deposition process works well for the deposition of well adhering, multilayered TiN/NbN coatings. The highest fracture resistance was found for the multilayer coating deposited with the thinnest (5-10 nm) individual layers of TiN and NbN. This implies, in combination with the high hardness of the 10/5 coating, that a multilayered coating has the potential to be both tougher as well as harder than a single-layered coating provided that the multilayer consists of very thin (approximate to 5-10 nm) layers.