Nano-scale mechanical characteristics of epitaxial stabilization ZrTiN/NbN superlattice coatings

Abstract

Protective hard thin films are necessary in industrial engineering under extreme condition. In that regard, superlattices with epitaxial stabilization have shown to be a potential approach. The ZrTiN/NbN system was chosen due to the similar lattice parameter and crystal structure. The phase transition from c-NbN to h-NbN was presented while NbN sub-layer was relatively thick in the superlattices, owing to higher VEC (valence electron concentration) of NbN. HRTEM images confirmed that h-NBN led to the loss of epitaxial growth, and thus the coatings demonstrated polycrystalline structure. The superlattices showed no cracks after indentation, possessing stronger crack resistance than ZrTiN (Kc = 3.22 MPa √ m) and NbN (Kc = 2.70 MPa √ m) monolayers. A 3-scan procedure was conducted and multilayers exhibited the staircase-like curve during scratching. The wear volume of multilayers was significantly lower than monolithic films, however, the existence of h-NbN would deteriorate the wear resistance and elastic recovery of the coatings. It can be concluded that epitaxial ZrTiN/c-NbN superlattices exhibited not only favorable mechanical performance but also excellent tribological behavior.