Influence of nitrogen variation on the microstructrual, mechanical and tribological properties of CNx coatings deposited by dc unbalanced magnetron sputtering

Abstract

The increasing interest for new coatings with higher properties, opened the doors to research of carbon nitrides (CNx), these coatings are attractive for industrial applications due to its high recovery rates, low friction coefficients and wear rates, in addition to the self-lubricating properties of these coatings. In this research CNx coatings were deposited by DC magnetron sputtering, using a graphite target and a power density of 3KW/m2, deposition temperature was 523K, working pressure of 0.6Pa and a bias voltage of −70V, prior to the deposition a plasma cleaning process was carry out to clean the surface of the substrates. The nitrogen percentage was varied between 10% and 50% in the gas mixture, in order to evaluate the effect of nitrogen incorporation on microstructure, composition, mechanical and tribological properties. Thicknesses about 2000nm were obtained, SEM images revealed homogeneous, compact and columnar coatings. XRD analysis showed that all coatings are completely amorphous. The micro-Raman spectra are characteristic of carbon-rich samples, these clearly show D band (disordered aromatic rings) and G band (graphite). It was also possible to identify the band associated to CN triple bonds. The mechanical and tribological properties are affected by the nitrogen incorporation in the coatings, increasing the compressive residual stresses and hardness; all coatings show similar tribological behavior, with smooth friction records, low friction coefficients and wear rates.