Influence of film thickness and ArN2 plasma gas on the structure and performance of sputtered vanadium nitride coatings
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Date
2019-11-25
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Abstract
We investigated the effect of film thickness on the structure and properties of V-N coatings deposited by magnetron sputtering in an argon and nitrogen atmosphere. The nitrogen percentage was changed between 10 and 20%. Firstly, structural and morphological properties of VN films were observed, analyzed and subsequently followed by a detailed investigation on the mechanical and tribological properties of these coatings.
It has been shown that film structure, hardness and wear resistance significantly changed with varying the film thickness and the nitrogen percentage. In the case of films deposited under 10%N2, the presence of V2N phase was evident. With increasing nitrogen ratio in the deposition chamber from 10 to 20%, the structure was changed from (hc)V2N to multi phases of V2N and (fcc) V-N (formation of different vanadium nitrides). The thick films containing more nitrogen were slightly dense compared to the thinner ones presenting rough surface and columnar morphology.
Nanoindentation measurements showed that film mechanical behavior depends on its thickness, nitrogen percentage and microstructural features. The film hardness first increased with its thickness and then decreased. The highest hardness of 26.2 GPa was obtained for the film deposited under 20%N2, which is correlated with its dense structure and film stoichiometry.
The film thickness has a significant effect on the tribological properties of V-N films. The minimum friction coefficient of 0.4 was found for the thickest film of 2500 nm. The wear rate gradually decreased with increasing the film thickness, due to the high hardness, presence of VN phase and the strong adhesion between film and substrate.
Description
Experimental setup
The V-N films were deposited on Si (100) (1 × 1 cm2, 450 μm) and XC100 steel substrates (Ø 15 × 3 mm) by the magnetron sputtering technique (NORDIKO type 3500, 13.56 MHz). V-N films were obtained by sputtering of vanadium target (99.9% purity, 10.6 cm of diameter and 3 mm thick) in an argon and nitrogen atmosphere. The nitrogen to argon ratios were: N2/Ar = 11.1 and 25% corresponding to gas flow rates of 10:90 sccm and 20:80 sccm, respectively. These both configurations led to obtain binary films .
Chemical composition
The chemical composition (determined by EDS and XPS analysis) and film thickness (determined by SEM) of V-N coatings, deposited under two different mixture atmospheres (N2/Ar = 11.1 and 25%) are shown in Table 1. As the nitrogen percentage increased from 10 to 20%, the V content decreased from (65–64.3) to (47–50.1) at. %. This is mainly due to the uptake of nitrogen by the deposited metal with the increase of the concentration of reactive nitrogen gas compared with argon and the target..