Microstructure and mechanical properties of multi-constituent superlattice coatings

Superlattice nitride coatings with four different layer constituents, i.e., ZrN, MoN, NbN and AlN, were synthesized using an unbalanced closed-field magnetron sputtering coater. At small superlattice modulation periods, both MoN and AlN layers adapted to the cubic B1 structure due to a template effect, and the coatings exhibited a strong (2 0 0) preferred orientation. Increasing the modulation period above a critical value led to the formation of hexagonal MoN and AlN layers with diminishing (2 0 0) preferred orientation. These microstructure changes were reflected in the coating mechanical properties. Relatively high hardness and Young's modulus values were obtained at small modulation periods, which decreased dramatically above the critical modulation period. The effects of substrate bias on the layer crystallographic structure, coating preferred orientation and mechanical properties were similar to those of the modulation period.