G. Zambrano

Tungsten carbide/diamond-like carbon multilayer coatings on steel for tribological applications

Abstract Tungsten carbide/diamond like (W–C/DLC) multilayers have been investigated as low friction coatings on high-speed steel substrates. The coatings are composed of a W–C multilayer base and an upper lubricious DLC layer and they are obtained by reactive r.f. magnetron sputtering from a single target comprising of two equal halves; one-half carbon and the other half tungsten. The whole coating structure was obtained in situ, without any interruption of the sputtering process. Transmission electron microscopy (TEM) and SIMS were used to assess the multilayer structure and XPS, XRD, and Raman spectroscopy was used to analyze its composition. The tribological properties of the coatings in sliding wear were investigated by means of scratch test and ball-on-disc test measurements. It was found that the multilayer W–C base improves the adhesion of the upper DLC layer to steel substrates while maintaining its low friction coefficient.

Characterization of diamond-like carbon (DLC) thin films prepared by r.f. magnetron sputtering

Diamond-Like Carbon (DLC) thin films were deposited on stainless steel and silicon substrates by a r.f. (13.56 MHz) magnetron sputtering technique. A carbon target (99,99%) and a gas mixture of Ar/CH 4 were used. During the deposition process the plasma discharge was monitored by Optical Emission Spectroscopy (OES) in order to analyze the state of the chemical species present in the plasma. The films were characterized by Raman Spectroscopy and by Reflection Absorption and Transmission Infrared Spectroscopy. The morphology of the deposited layers was analyzed by Scanning Electron Microscopy (SEM). The Raman intensity of the diamond and graphite peaks (I D/IG) depends on the percentage of CH4 in the gas mixture. The relationship between the lines H α, and Hβ, intensities are a measure of the relative change of the plasma electronic temperature that, for the experiment conditions, does not depend significantly on the concentration of CH 4 in the mixture and its value was of the order of 1 eV. Optical Emission Spectroscopy shows that, besides of the atomic hydrogen peak (H α, Hβ, Hγ), emission spectra are dominated by neutral CH species and the most intense peak in the spectra correspond to CH (A 2 Δ → X 2 Π at 431,5 nm) which is supposed to be the precursor species in the diamond-like films, beside in the Transmission Infrared Spectroscopy analysis were observed the sp 3 CH2 symmetric and asymmetric at 2870 and 2960 cm -1 peaks. These peaks have been observed in diamond deposited at very high CH4 concentrations and also in diamond-like carbon (DLC) films.

Optical emission spectroscopy study of r.f. magnetron sputtering discharge used for multilayers thin film deposition

Abstract An investigation by Optical Emission Spectroscopy (OES) was performed on RF (13.56 MHz) magnetron sputtering discharge used for Tungsten Carbide/Diamond-Like Carbon (W-C/DLC) multilayer thin film deposition. The multilayer deposition is obtained from a single tungsten (99.99%) and carbon (99.99%) binary compound target by gradual variation of methane (CH4) concentration in the argon/methane (ArCH4) gas mixture. The optical emission spectra supply information about the chemical species present in the plasma, and the densities of these species can be correlated with the structure and composition of the deposited layers. The electron temperature dependence on gas pressure and methane concentration in ArCH4 gas mixture by using some Ar, W and H emission line intensities, are studied in the center of the discharge. A simple model for the excitation process of the Ar, W and H atoms allows us to calculate the density of sputtered atoms in the plasma. At high methane concentrations for deposition of DLC layers, OES shows that besides the atomic hydrogen peaks Hα (656.3 nm) and Hβ (486.1 nm) of Balmer series, emission spectra are dominated by neutral CH species and the most intense peak in the spectra corresponds to CH-band head at 431.5 nm, which is supposed to be the precursor species in the diamond-like films. Owing to the transport regime of the W and C sputtered species across the discharge, the existence of correlation between the target composition, tungsten density in the plasma, multilayer thin film composition, and microstructure determined by XPS, XRD, IR and Raman spectroscopy are studied.

Mechanical and tribological properties of tungsten carbide sputtered coatings

Tungsten carbide (WC) hard coatings have been obtained on steel substrates by an r.f. magnetron sputtering process. Two-layer coatings have been deposited in order to improve the adhesion on steel. The lower layer was tungsten metal and the upper WC layer was obtained by reactive sputtering of the tungsten target in an Ar and methane gas mixture. AES and SIMS confirmed that the WC layer composition depends on the reactive sputtering gas composition. Film microhardness was measured by microindentation, and the coating adhesion by microscratch. Measurement results showed that high hardness coatings can be prepared at a relatively low temperature and that good adhesion on steel is achieved with the two-layer coating. Nanowear measurements showed a noticeable dependence of this applied functional property on the coating compositions.

Hardness and morphological characterization of tungsten carbide thin films

Abstract Ni doped Tungsten Carbide thin films (WC+Ni) were deposited onto stainless steel, WC–Co and glass substrates by non-reactive d.c. magnetron sputtering process using a sintered WC–6% Ni target. The WC+Ni hard coating films had thicknesses between 0.6 and 1.5 μm and were deposited at temperatures between 300°C and 550°C. The structure of the films was characterized using X-ray Diffraction (XRD), Secondary Ion Mass Spectroscopy (SIMS) and Reflection Absorption Infrared Spectroscopy (RAIRS) techniques. A morphological analysis was carried out using Atomic Force Microscopy (AFM) and SEM, while the microhardness was measured by nanoindentation. Reflection Absorption Infrared Spectroscopy results confirm that the WC x formation was dependant on substrate temperature. AFM and SEM analysis indicated that the surface morphology is formed by rounded grains. Hardness values deduced from microindentation curves by statistical average on each sample is 18 GPa for all the samples, the same value that has been found from the microindentation measurements on the bare WC substrate.

Gas Temperature Determination of an AC Arc Discharge at Atmospheric Pressure in Air Using a Mach–Zehnder Interferometer

To determine the gas temperature of an alternating current (ac) (50 kHz) arc discharge at atmospheric pressure in air, a Mach–Zehnder type interferometer was built, utilizing an He-Ne

FTIR studies of tungsten carbide in bulk material and thin film samples

(lambda=6328 hboxAA)

Plasma characterization of Pulsed-Laser ablation process used for fullerene-like CNx thin film deposition

laser source with vertical polarization and a power of 5 mW. Upon introducing the arc discharge into one of the interferometer arms, a displacement of interference fringes takes place with respect to its position without the discharge. Keeping in mind that displacement of the fringes is related to the difference of the optical path with the variation of the refraction index and with temperature change in the discharge zone; the latter was determined from the displacements of the interference fringes. At the center of the discharge channel, a temperature near 3000 K was calculated, diminishing gradually to room temperature toward the discharge borders. This temperature value at the center of the channel agrees with results previously reported in similar discharges. This is an alternate method for the diagnosis of plasma parameters used in the production and treatment of materials.

Band Structure Dependence on the External Perpendicular Magnetic Field and Zn Concentration of Photonic Crystals Made of Co 1– x Zn x Fe 2 O 4 Nanoparticles

The use of Fourier transform infrared (FTIR) spectroscopy is proposed to characterize thin films of tungsten carbide (WC) coatings. For this reason, the IR reflection spectrum of a bulk sample was recorded and used as a reference. Three infrared bands were observed. They are located at 1067,1144, and 1220 cm{sup -1}. They were assigned to hexagonal and cubic phases of WC. These assignments are supported by XRD measurements. These results were used to characterize different WC films deposited on stainless steel substrates.

Influence of the microstructure on the electrochemical properties of Al-Cr-N coatings deposited by co-sputtering method from a Cr-Al binary target

An in situ Optical Emission Spectroscopy (OES) characterization was performed on Pulsed-Laser Ablation (PLA) process used for fullerene-like CNx thin film deposition at nitrogen pressures within the 5 ‐ 100 mTorr range. Plumes were generated by ablation of pyrolytic graphite (99.99%) target using a (500 mJ, 7 ns, 1064 nm) Nd: YAG-pulsed laser. The spectra from the plume show, essentially, the presence of the band heads of CN Violet vibrational/rotational B 2 § + - X 2 § + system and the characteristic C2 emission lines, belonging to the Swan A 3 ƒg - X ’ 3 ƒu system. These excited CN and C2 molecules were generated by laser ablation and by collisions of the plume with the substrate surface. Their vibrational temperatures were strongly dependent on nitrogen pressure during the deposition process and presented a decrease between 2.64 and 1.23 eV, as pressure increased from 5 to 100 mTorr. Synthesis of fullerene-like structures required high molecular temperatures at the condensation surface. High concentrations of CN radicals in the plasma promoted nitrogen incorporation into the films. The OES plasma characterization allowed for a correlation of the concentration and vibrational temperatures of CN and C2 species present in the plasma with the fullerene-like CNx film composition and bonding, determined by XPS, IR, and Raman spectroscopy.