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.