Structure, deformation and fracture of arc evaporated Zr–Si–N hard films

Abstract

Zr–Si–N films with varying Si contents were grown on WC–Co substrates by reactive cathodic arc deposition technique. The resulting microstructures of the films correlate to dominant variation in mechanical properties and deformation mechanisms. Si forms a substitutional solid solution in the cubic ZrN lattice up to 1.8at.% exhibiting a fine columnar microstructure. Further Si additions result in precipitation of an amorphous (a)-SiNx phase and evolution of a nanocomposite microstructure (nc ZrN/a-SiNx) which completely suppresses the columnar microstructure at 6.3at.% Si. The rotation-induced artificial layering during film growth is used as a marker to visualize the deformation of the film. A dislocation-based homogeneous plastic deformation mechanism dominates the columnar microstructure, while grain boundary sliding is the active mechanism mediating heterogeneous plastic deformation in the nanocomposite microstructure. Film hardness increases with increasing Si content in the columnar microstructure due to an effective solid solution strengthening. The deformation mechanism of localized grain boundary sliding in the nanocomposite microstructure results in a lower hardness. When cracking is induced by indentation, the fine columnar microstructure exhibits pronounced crack deflection that results in a higher fracture resistance compared to the nanocomposite films.