Superhard Nb–Si–N composite films synthesized by reactive magnetron sputtering

By means of the reactive magnetron sputtering method, a series of Nb–Si–N composite films with different Si contents were deposited in an Ar, N2 and SiH4 mixture atmosphere. These films’ chemical composition, phase formation, microstructure and mechanical properties were characterized by the energy dispersive spectroscopy, X-ray diffraction, transmission electron microcopy, atomic force microscopy and nanoindentation. The experimental results showed that the silicon content in the Nb– Si–N composite films can be conveniently controlled by adjusting the SiH4 partial pressure in mixed gas. The hardness and elastic modulus of the Nb–Si–N films were remarkably increased with a small amount of silicon addition and reached their maximum values of 53 and 521 GPa, respectively, at 3.4 at.% Si. Such an obvious enhancement of mechanical properties is related to the increment of crystal defects in the Nb–Si–N films. With silicon content increasing in the films further, the mechanical properties decreased gradually to somewhat a bit lower than those of the NbN film.