Investigating the effect of nitrogen on the structural and tribo-mechanical behavior of vanadium nitride thin films deposited using RF magnetron sputtering

Magnetron sputtering is one of the most commonly used deposition techniques, which has received considerable attention in industrial applications. In particular, owing to its compatibility with conventional fabrication processes, it can produce and fabricate high-quality dense thin films of a wide range of materials. In the present study, nitrogen (N) was combined with pure vanadium in order to form binary nitride to improve its mechanical and tribological performance. To evaluate the influence of nitrogen on the structure of the as-deposited vanadium nitride (VN) coatings, the following techniques were used: XPS, XRD, SEM, AFM and optical profilometry. The residual stresses were determined by the curvature method using Stoney's formula. The hardness and Young's modulus were obtained by nanoindentation measurements. The friction behavior and wear characteristics of the films were evaluated by using a ball-on-disk tribometer. The obtained results showed that the N/V ratio increased with increasing the N-2 flow rate while the deposition rate decreased. The preferred orientation was changed from (200) to (111) as the N-2 flow rate increased with the presence of V-N and V-O binding energies as confirmed by XPS analysis. The nitrogen addition resulted in a columnar morphology and a fine structure with fine surface roughness. The VN thin film containing 49.5 at.% of nitrogen showed the best performance: highest mechanical properties (hardness = 25 GPa), lowest friction coefficient (mu = 0.37) and lowest wear rate (W-s = 2.72 x 10(-5) mm(3)N(-1) m(-1)). A good correlation between the film microstructure, crystallite size, residual stress and mechanical and tribological properties was observed.