Stanislava Rabadzhiyska

In our study, magnetron-sputtered vanadium nitride (VN) films were grown on 304 L stainless steel in an Ar/N2 atmosphere at a substrate bias voltage of 0 V, –50 V, –100 V,–150 V and – 200 V. The as-deposited VN coatings were characterized by X-ray dif-fraction (XRD), Fourier-transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The XRD and FTIR analysis exhibited a presence of VN crystalline phases. AFM and SEM exhibited that a decrease in the thickness and surface roughness with increasing the bias voltage to – 200 V. The VN coating, obtained at – 100 V, indicated a high hardness of 36.2 GPa. It was carried out that the friction coefficient is remarkably dependent by the film surface roughness. The lowest friction coefficients (0.42 and 0.44) for a loading force of 2 N and 5 N was evaluated for VN film, deposited at – 200 V which indicate a high degree of wear re-sistance. The electrochemical tests revealed that VN films, grown at a bias voltage of 0 V and – 200 V, have the most reliable protection against corrosion in aggressive elec-trolytes.

Vanadium nitride (VN) ceramic layers were deposited on 304L stainless steel specimens by direct current (DC) magnetron sputtering in an Ar/N₂ gas mixture at substrate temperatures of 250 °C, 300 °C, and 350 °C. The obtained films were evaluated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The results showed the existence of VN and V₂N phases in the as-deposited coatings. It was found that the surface roughness parameter (Ra = 10 nm) decreased with increasing substrate temperatures up to 350 °C. The highest hardness (10.6 GPa) was achieved in the layer produced at 300 °C. The low values of plastic and elastic deformation, as well as a low friction coefficient (0.38), led to an enhancement in the coatings’ tribological properties. The film’s thickness increased with increasing temperature due to the presence of nucleation centers in the films. The highest thickness (557 nm) was achieved in the layer deposited at 350 °C. The electrochemical tests exhibited reliable protection against corrosion in strongly aggressive electrolytes. It has been proven that the temperature significantly affects the ceramic coatings’ structural, morphological, tribological, and corrosion properties.

Vanadium nitride (VN) ceramic layers were deposited on 304 L stainless steel speci-mens by Direct Current (DC) magnetron sputtering in an Ar/N2 gas mixture at sub-strate temperatures of 250 oC, 300 oC and 350 oC. The obtained films were evaluated by X-Ray Diffraction (XRD), X-ray photoelectron spectrоscopy (XPS) and Atomic force microscopy (AFM). X-Ray diffraction patterns demonstrated the presence of (111), (200), (220) and (300) crystallographic orientations, corresponding to the VN and V2N phases, respectively. It was found out that the surface roughness (10 nm) diminishes as the temperature raises up to 350 oC. The highest hardness (10.6 GPa) was achieved in the layer, produced at 300 oC. The low values of the plastic and elastic deformation as well low friction coefficient (0.38) lead to enhancement of coatings wear resistance. The films thickness is increased with the raising of the temperature due to a presence of nucleation centres in the films. The highest thickness (500 nm) is achieved in the layer, deposited at 350 oC. The electrochemical tests exhibited a reliable protection against corrosion in strongly aggressive electrolytes. It was proved that the tempera-ture variation effects significantly the ceramic coatings structural, morphological, tribological and corrosion properties.

Zirconium nitrides films were synthesized on Ti6Al4V substrates at a bias voltage of −50 V, −80 V, −110 V and −150 V by the direct current (DC) reactive magnetron sputtering technique. The as-deposited coatings were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The wear and corrosion resistance of the obtained ZrN coatings were evaluated to determine the possibility for their implementation in modern biomedical applications. It was found that the intensity of the diffraction peak of the Zr-N phase corresponding to the (1 1 1) crystallographic plane rose as the bias voltage increased, while the ZrN coatings’ thickness reduced from 1.21 µm to 250 nm. The ZrN films’ surface roughness rose up to 75 nm at −150 V. Wear tests showed an increase in the wear rate and wear intensity as the bias voltage increased. Corrosion studies of the ZrN coatings were carried out by three electrochemical methods: open circuit potential (OCP), cyclic voltammetry (polarization measurements) and electrochemical impedance spectroscopy (EIS). All electrochemical measurements confirmed that the highest protection to corrosion is the ZrN coating, which was deposited on the Ti6Al4V substrate at a bias voltage of −150 V.

Coatings on the base of diamond-like carbon (DLC) were grown on 304 L stainless steel substrates at temperatures in range of 300 °C to 500 °C by electron-beam physical vapor deposition. X-ray photo electron spectroscopy (XPS) analysis was used to determine the binding energy and the phase composition of the obtained films. The surface morphology and roughness of the as-deposited samples were investigated via Atomic Force Microscopy (AFM). The XPS measurements indicated that the films contain high quantity of C-C bonds in sp³ state in the deposited DLC films. It was found that by increasing of the temperature from 300 to 500°C, the surface roughness of the produced films decreased from 27 nm to 15.6 nm. The friction coefficient and corrosion behavior of the DLC films deposited at different temperatures were also investigated. The results exhibited that the friction coefficient diminished with increasing of the temperatures and the lowest values of the friction coefficient were achieved in the films obtained at 400 °C and 500 °C. The studies on the corrosion resistance of three samples have been performed using 3 electrochemical techniques: open circuit potential (OCP), cyclic voltammetry (polarization measurements), and non-destructive electrochemical impedance spectroscopy (EIS). It can be concluded from the EIS studies that the most-corrosion resistant sample is DLC film produced at 500° C which was confirmed by OCP measurements.

In this study, we present the results of the effect of duplex surface modification of 304-L stainless steel substrates by an electron-beam treatment (EBT) and subsequent deposition of diamond-like carbon coatings on the surface roughness and corrosion behavior. During the EBT process, the beam power was varied from 1000 to 1500 W. The successful deposition of the DLC coatings was confirmed by FTIR and Raman spectroscopy experiments. The results showed a presence of C–O, C=N, graphite-like sp², and mixed sp²-sp³ C–C bond vibrations. The surface topography was studied by atomic force microscopy. The rise in the beam power leads to a decrease in the surface roughness of the deposited DLC coatings. The studies on the corrosion resistance of the samples have been performed using three electrochemical techniques: open circuit potential (OCP), cyclic voltammetry (polarization measurements), and non-destructive electrochemical impedance spectroscopy (EIS). The measured corrosion potentials suggest that these samples are corrosion-resistant even in a medium, containing corrosive agents such as chloride ions. It can be concluded that the most corrosion-resistant specimen is DLC coating deposited on electron-beam-treated 304-L SS substrate by a beam power of 1500 W.