The effects of deposition conditions on hydrogenation,hardness and elastic modulus of W-C:H coatings

The additions of C₂H₂, CH₄ and H₂ in hybrid PVD-PECVD of W-C:H coatings deposited using High Power Impulse Magnetron Sputtering (HiPIMS) and High Target Utilization Sputtering (HiTUS) were investigated to determine their effects on the content and chemical composition of the amorphous carbon-based boundary phase and mechanical properties of the coatings. Substantial differences were observed: CH₄ always produced higher concentrations of hydrogen and lower concentrations of carbon than C₂H₂ and HiPIMS resulted in higher contents of amorphous carbon-based boundary phase and higher levels of its hydrogenation than HiTUS. The detrimental effects of higher carbon and hydrogen contents in the boundary phase on hardness and indentation modulus were attributed to the consumption of CC bonds by CH bonds during hydrogenation and reduction of cross-linking of the polymeric network in the boundary phase. The HiPIMS W-C:H coatings deposited with acetylene and hydrogen exhibited medium (∼20 GPa) hardness and elastic modulus (200–220 GPa) with H_IT/E_IT > 0.1 suggesting improved toughness and wear resistance. These properties were attributed to the optimum combination of hydrogenation, hybridization and cross linking in the carbon-based boundary phase.     

HiPIMS induced high-purity Ti3AlC2 MAX phase coating at low-temperature of 700 °C

Ti₃AlC₂, one of Ti-Al-C MAX phases, has received extensive attention due to its unique nano-laminated structure and combined properties of metals and ceramics. However, ultra-high synthesis temperature exceeding 800 °C is a critical challenge for broad application of Ti₃AlC₂ coatings on temperature-sensitive substrates. In this study, Ti-Al-C coatings were deposited on Ti-6Al-4V substrates using high-power impulse magnetron sputtering (HiPIMS) and DC sputtering (DCMS) for comparison. Different from as-deposited amorphous Ti-Al-C coating by DCMS, nanocrystalline TiAl_x compound was achieved by HiPIMS deposition due to highly ionized plasma flux with high kinetic energy. Furthermore, HiPIMS promoted the generation of dense and smooth Ti₃AlC₂ phase coating after low-temperature annealing at 700 °C, while annealed DCMS coating only obtained Ti₂AlC. In-situ XRD demonstrated such Ti₃AlC₂ phase could be early involved in crystallization at 450 °C, lowest than synthesis temperature ever reported. The mechanical properties of Ti₃AlC₂ coating were also discussed in terms of structural evolution.     

Principles for designing sputtering-based strategies for high-rate synthesis of dense and hard hydrogenated amorphous carbon thin films

In the present study we contribute to the understanding that is required for designing sputtering-based routes for high rate synthesis of hard and dense hydrogenated amorphous carbon (a-C:H) films. We compile and implement a strategy for synthesis of a-C:H thin films that entails coupling a hydrocarbon gas (acetylene) with high density discharges generated by the superposition of high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). Appropriate control of discharge density (by tuning HiPIMS/DCMS power ratio), gas phase composition and energy of the ionized depositing species leads to a route capable of providing ten-fold increase in the deposition rate of a-C film growth compared to HiPIMS Ar discharge (Aijaz et al., 2012). This is achieved without significant incorporation of H (< 10%) and with relatively high hardness (> 25 GPa) and mass density (~ 2.32 g/cm³). Using our experimental data together with Monte-Carlo computer simulations and data from the literature we suggest that: (i) dissociative reactions triggered by the interactions of energetic discharge electrons with hydrocarbon gas molecules is an important additional (to the sputtering cathode) source of film forming species and (ii) film microstructure and film hydrogen content are primarily controlled by interactions of energetic plasma species with surface and sub-surface layers of the growing film.     

Tribological properties of DLC films with different hydrogen contents in water environment

Diamond-like carbon (DLC) films were deposited on silicon wafers by thermal electron excited chemical vapor deposition (CVD). To change the hydrogen content in film, we used three types of carbon source gas (C₇H₈, CH₄, and a CH₄+H₂) and two substrate bias voltages. The hydrogen content in DLC films was analyzed using elastic recoil detection analysis (ERDA). Tribological tests were conducted using a ball-on-plate reciprocating friction tester. The friction surface morphology of DLC films and mating balls was observed using optical microscopy and laser Raman spectroscopy.Hydrogen content in DLC films ranged from 25 to 45 at.%. In a water environment, the friction coefficient and specific wear rate of DLC films were 0.07 and in the range of 10⁻⁸–10⁻⁹ mm³/Nm, respectively. The friction coefficient and specific wear rate of DLC film in water were hardly affected by hydrogen content. The specific wear rate of DLC film with higher hardness was lower than that of film with low hardness. Mating ball wear was negligible and the friction surface features on the mating ball differed clearly between water and air environments, i.e., the friction surface on mating balls in water was covered with more transferred material than that in air.     

Microstructure and properties of TiAlCrN ceramic coatings deposited by hybrid HiPIMS/DC magnetron co-sputtering

TiAlCrN ceramic coatings were prepared utilizing a hybrid deposition technique consisting of High Power Impulse Magnetron Sputtering (HiPIMS) and Direct Current Magnetron Sputtering (DCMS). The chemical composition, phase structure, morphologies, mechanical and tribological properties of such coatings were systematically investigated. Results indicated that the content of Ti element increased monotonically from 0 at.% to 22 at.% with increasing of Ti target power. The TiAlCrN ceramic coatings presented a competitive growth tendency between (111) and (200) crystal plane through the energetic ion bombardment. Higher Ti target power resulted in stronger compressive intrinsic stress, which significantly suppressed the precipitation of hcp-AlN phase. With enhancing ion bombardment, diffusion energy and nucleation rate of adatoms on the growing surface increased, which caused a denser structure and ultra-smooth surface. The hardness and toughness also varied as a function of Ti target power, with the maximum hardness of 28.3 GPa under a Ti target power of 5 kW. Positive correlation between the adhesion strength (i.e., the critical load of the scratch test) and H³/E² ratio was discovered indicating a strong dependence of adhesion properties on toughness for the TiAlCrN ceramic coatings in this study, which agreed well with the literatures. As for the tribological behavior, the lowest wear rate of 8.9 × 10^-17 m³N^-1m^-1 was obtained for the TiAlCrN ceramic coating deposited at a Ti target power of 5 kW.     

Wear-resistant Ti–Al–Ni–C–N coatings produced by magnetron sputtering of SHS-targets in the DC and HIPIMS modes

The hard wear-resistant nanocomposite Ti–Al–Ni–C–N coatings were deposited by direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HIPIMS) in the Ar, Ar+15%N_2, and Ar+25%N₂ atmospheres. The structure of coatings was analyzed using the X-ray diffraction analysis, glow discharge optical emission spectroscopy, and scanning electron microscopy. Mechanical and tribological properties were measured using the nanoindentation and scratch testing as well as by tribological testing using the “pin-on-disc” scheme. Electrochemical corrosion resistance and oxidation resistance of coatings were investigated. The results suggest that the coatings are based on the FCC phases TiCN and Ni₃Al with crystallites size ~3 and ~15 nm, correspondingly. DCMS coatings with optimal composition were characterized by hardness 34 GPa, stable friction coefficient <0.26 and wear rate <5 × 10^-6 mm³N^-1m^-1. Application of HIPIMS mode allowed the increase of adhesion strength, tribological properties and corrosion resistance of coatings.     

Optimization of the mechanical properties of magnetron sputtered diamond-like carbon coatings

Diamond-like carbon coatings containing hydrogen, a-C:H, were deposited by use of reactive DC magnetron sputtering with an industrial deposition system. The reactive gas C₂H₂ was used in combination with carbon targets. Using Raman spectroscopy, nanoindentation and Rockwell C indentation, the mechanical properties of the coatings were optimized. Excessively high compressive stresses, which were measured with Raman spectroscopy, were found in the coatings with high hardness, resulting in poor adhesion to the substrates. By thermal annealing, these compressive stresses were reduced without altering the hardness, resulting in diamond-like carbon coatings with good adhesion.     

The effect of CNT content on the surface and mechanical properties of CNTs doped diamond like carbon films

The carbon nanotubes (CNTs) doped diamond like carbon films were carried out by spinning coating multi-walled carbon nanotubes (CNTs) on silicon covered with diamond like carbon films via PECVD with C₂H₂ and H₂. The results show that the I_D/I_G and sp²/sp³ ratios are proportional to the CNT contents. For wettability and hydrogen content, the increase of CNT content results in more hydrophobic and less hydrogen for CNT doped DLC films. As for mechanical properties, the hardness and elastic modulus increases linearly with increasing CNT content. The residual stress is reduced for increasing CNT content. As for the surface property, the friction coefficient is reduced for higher CNT content. For CNT doped DLC films, the inclusion of horizontal CNT into DLC films increases the hardness, elastic modulus and reduces the hydrogen content, friction coefficient and residual stress. Like the light element and metal doping, the CNT doping has effects on the surface and mechanical properties on DLC which might be useful to specific application.     

Nanostructure,mechanical and tribological properties of reactive magnetron sputtered TiCx coatings

This study describes the correlation between microstructure, mechanical and tribological properties of TiC_x coatings (with x being in the range of 0–1.4), deposited by reactive magnetron sputtering from a Ti target in Ar/C₂H₂ mixtures at ~ 200 °C. The mechanical and tribological properties were found to strongly depend on the chemical composition and the microstructure present. Very dense structures and high hardness, combined with low wear rates and friction coefficients, were observed for coatings with chemical composition close to TiC. X-ray diffraction and X-ray photoelectron spectroscopy analysis, used to evaluate coating microstructure, composition and relative phase fraction, showed that low carbon contents in the coatings lead to sub-stoichiometric nanocrystalline TiC_x coatings being deposited, whilst higher carbon contents gave rise to dual phase nanocomposite coatings consisting of stoichiometric TiC nanocrystallites and free amorphous carbon. Optimum performance was observed for nanocomposite TiC_1.1 coatings, comprised of nanocrystalline nc-TiC (with an average grain size of ~ 15 nm) separated by 2–3 monolayers of an amorphous a-DLC matrix phase.     

Micromechanical properties of BN and B–C–N coatings obtained by r.f. plasma-assisted CVD

We have obtained highly transparent and hard BN films in a capacitively coupled r.f. plasma-assisted CVD reactor from three different gas mixtures: B₂H₆–H₂–NH₃, B₂H₆–N₂ and B₂H₆–N₂–Ar. It was found that the films were smooth, dense, and had a textured hexagonal structure with the basal planes perpendicular to the film surface. The microhardness, friction coefficient and adhesion of these coatings were measured by nanoindentation and microscratching. BC_xN_y films were also prepared in the same plasma-assisted CVD reactor from B₂H₆–N₂–CH₄ gas mixtures. The carbon content in the films was varied by using different CH₄ flow rates. These films had a less ordered structure. The mechanical properties of these films had been compared to those of hexagonal BN films. Microhardness measurements showed that there is a correlation between film composition and hardness of the BCN films.     

Deposition,structure and tribological behavior of silver–carbon nanocomposite coatings

Silver–carbon nanocomposite coatings were deposited by plasma-enhanced chemical vapor deposition and d.c. magnetron sputtering of a silver target. Coatings with various metal concentrations were prepared by changing of acetylene and argon gas mixture ratio (C₂H₂/Ar), and concentrations of more than 40 at.%Ag was achieved in this study. Transmission electron microscope revealed that silver metallic grains with typically 15 nm were dispersed in amorphous carbon host matrix. Size of the grains increased with decrease of the gas mixture ratio due to secondary or triangularly formed metal grains. Tribological behavior of the coatings was investigated using reciprocating tribometer with in-situ electrical contact resistance measurement. Low and stable friction coefficient was achieved in the specimen with relatively low Ag concentration. Elemental mapping results on the ball after the friction tests reveal that tribofilm was formed on the ball when low and stable friction was achieved, and the tribofilm was mainly composed of C and Ag. It can be concluded that formation of the tribofilm is necessary for achieving low and stable friction.     

In situ diagnosis of chemical species for the growth of carbon nanotubes in microwave plasma-enhanced chemical vapor deposition

A synthesis of multi-wall carbon nanotubes (MWNTs) by microwave plasma-enhanced chemical vapor deposition using CH₄/H₂/NH₃ gases on Ni/Cr-coated glass at low temperature, was investigated by optical emission spectroscopy (OES) and quadrupole mass spectroscopy (MS). It was observed that the MWNTs were grown within a very restrictive range of the gas compositions. Optical emission lines were observed primarily from atomic hydrogen H_α, molecular hydrogen, and CN radicals. The quadrupole mass spectrum also showed the formation of C₂H₂ and HCN. An addition of a small amount of NH₃ resulted in a decrease of C₂H₂, which could be used to estimate amounts of carbon sources present in the plasma for the growth of MWNTs, and increases of CN and H_α radicals acting as etching species of amorphous carbon. These results show that the etching species of amorphous carbon as well as the growth species are necessary and the ratio between two species have to be in appropriate condition for the synthesis of carbon nanotubes at low temperature. The optimum C₂H₂/H_α ratio in the gas mixture for the growth of MWNTs at low temperature was found to be 1:5 in this study.     

Modification of tribological performance of DLC films by means of some elements addition

The elements added diamond-like carbon films (hydrogen, fluorine, and sulfur) fabricated from C₂H₂:H₂, C₂H₂:CF₄ and C₂H₂:SF₆ mixtures were used to compare and study the effects of element contents on the deposition and tribological properties of films prepared by plasma-based ion implantation (PBII). The structure of the films was analyzed by Raman spectroscopy. Hardness and elastic modulus of films were measured by nano-indentation hardness testing. Contact angle and surface energy of films were measured by contact angle measurement. Tribological characteristics of films were performed using a ball-on-disk friction tester. The results indicate that with the increasing element contents, the hardness and elastic modulus, and surface energy of all films decreases, while the surface angle tends to increase. Additionally, H-DLC films at C:H flow rate ratio of 1:4 shows a friction coefficient of 0.08 under ambient air, which are considerable improvement in the tribological properties. This is due to the formation of a transfer films on the interface and high hydrogen contents. For F-DLC films and S-DLC films, does not show a significant decrease in the friction coefficient with the fluorine and sulfur contents under ambient air. The decrease in the friction coefficient is greater under high vacuum than under ambient air.     

Molecular dynamics simulations for the growth of diamond-like carbon films from low kinetic energy species

In this study, molecular dynamics simulations using the Brenner potential for hydrocarbons have been used to simulate the formation of diamond-like carbon (DLC) films grown from low-energy hydrocarbon radicals (<2 eV). With these simulations, insight is gained in the processes occurring in this type of deposition. The initial surface is a previously deposited DLC surface; impinging particles include Ar⁺ ions, with an energy of 2 eV, as well as several carbon radicals and molecules, and hydrogen atoms, with an energy of 1 eV. Two different radical flux compositions were examined: in the first condition, only C, C₂, and CH were used as growth species, as well as a large flux of H atoms. In the second condition, the same carbon radicals were considered, as well as the C₂H radical and C₂H₂, C₄H₂, and C₆H₂ molecules, but without the H atom flux. These fluxes are similar to different experimental conditions in an expanding thermal Ar/C₂H₂ plasma (expanding thermal plasma, or ETP), using different influxes of acetylene. Several properties of the resulting films will be presented, focusing mainly on the carbon coordination and the bonding network. The simulations suggest that lowering the acetylene influx results in films having a more extensive bonding network, but with more H incorporated. This leads to more polymeric films having a less diamond-like character, as is expected also from experiments. The aim of this work is twofold. The first objective is to compare the structural composition of the simulated films to the structure of the experimentally deposited films by applying similar conditions. Second, the simulations can give us valuable information about the key mechanisms in the deposition process.     

Synthesis of organo-functionalized mesoporous silica hollow nanospheres via in situ generated template method

A facile one-pot method has been developed for the synthesis of organo-functionalized mesoporous silica hollow nanospheres using TEOS, (R′O)₃Si-R-Si(OR′)₃ or R-Si(OR′)₃ as silane precursors and CTAB as surfactant in ethanol–water/ammonia medium. The study shows that silica nanospheres formed by TEOS acts as in situ generated “soluble” template for the formation of hollow nanostructures. Different kinds of organic moieties such as –CH₂CH₂–, –C₆H₄–, –CH₂C₆H₄CH₂–, –CH₂CH₂CH₂NHCH₂CH₂CH₂–, –CH₂CH₂CH₂NH₂ could be successfully incorporated in the framework of hollow nanospheres.     

Microstructure and mechanical properties of hafnium carbide coatings synthesized by reactive magnetron sputtering

Hafnium carbide coatings with different carbon contents were synthesized in Ar–C₂H₂ mixture by reactive magnetron sputtering. Energy-dispersive X-ray, X-ray diffraction, scanning electron microscopy, atomic force microscopy, and nanoindentation were employed to characterize their microstructure and mechanical properties. The effects of C₂H₂ partial pressure on the composition, phase, microstructure, and mechanical properties of the coatings were investigated. The results show that hafnium carbide coatings can be synthesized at a low partial pressure of C₂H₂. The single-phase HfC coating with columnar crystal and favorable mechanical properties is obtained when the proportion of C₂H₂ partial pressure is only about 3.0% in the mixture, and the highest hardness and modulus are 27.9 and 255 GPa, respectively. The coating contains metal Hf and HfC phases and obtains low hardness under lower C₂H₂ partial pressure. When the C₂H₂ partial pressure is higher, the hardness and elastic moduli of acquired amorphous coatings decrease significantly.     

On adsorption and electro-oxidation of some compounds on tungsten carbide; their effect on hydrogen electro-oxidation

Adsorption and electro-oxidation of carbon monoxide, ethylene, acetylene, and hydrogen sulphide on tungsten carbide, in solutions of these compounds in 1 N H₂SO₄, have been investigated. It was found that CO, C₂H₄, and C₂H₂ do not undergo adsorption and oxidation and do not affect adsorption and electro-oxidation of hydrogen. H₂S does not oxidise as well, and it does not displace adsorbed hydrogen in any measurable amounts, though it does inhibit electro-oxidation of molecular hydrogen. Methanol is inert on tungsten carbide like carbon monoxide and hydrocarbons. Electro-oxidation of formaldehyde and formic acid proceeds without apparent WC-surface coverage by the adsorbed compound.     

Über die Säuren HOOCCH(SX)CH(SX)COOH (X  CH2COOH,C6H5) und ihre Methylester

The Acids HOOCCH(SX)CH(SX)COOH (X  CH₂COOH, C₆H₅) and their Methyl Esters The acids HOOCCH(SX)CH(SX)COOH with X  CH₂COOH and C₆H₅ and their methyl esters have been prepared by addition of thiols to acetylene dicarboxylic acid as salt and methyl ester. The structures and configurations have been discussed.     

Stress and structural properties of diamond-like carbon films deposited by electron beam excited plasma CVD

Diamond-like carbon (DLC) films prepared using CH₄ or C₆H₆ with varying deposition parameters by an electron beam excited plasma CVD system were investigated for the internal stress, dynamic hardness and structural properties such as the film density, total, bonded and unbound hydrogen contents, sp³ ratio and graphite crystallite. From the correlations between internal stress and structural properties, the following conclusions were derived. The fraction of unbound hydrogen to total hydrogen content was the most influential factor for the compressive stress of the DLC films deposited from CH₄. It is suggested that unbound hydrogen may be trapped into the disordered microstructure of graphite crystallites embedded in the network of film. For the DLC films deposited from C₆H₆, it was shown that the compressive stress was correlated with not only the fraction of unbound hydrogen content but also the degree of cross-linking between graphite crystallites in the film.     

Improvement of anhydrous catalyst stability in acetylene dimerization by regulating acidity

BACKGROUND: Loss of the active CuCl component occurs during acetylene dimerisation to monovinylacetylene (MVA) catalysed by an anhydrous catalyst with the formation of a dark red precipitate. Acidic species can reduce the loss of CuCl but have an unfavorable influence on acetylene dimerisation. This study aims to determine the precipitate composition and regulate the acidity of the catalyst to find a balance between reaction rate, MVA selectivity and catalyst life. RESULT: The precipitate composition was 2CuCl·3C₂H₂·1/3CH₃CH₂NH₂·1/7C₃H₇NO, formed by the combination of DMF, CH₃CH₂NH₂, C₂H₂ and the [Cu]‐acetylene π‐complex, which is an intermediate in the reaction. From an overall consideration of the loss of CuCl, conversion of acetylene, and selectivity of MVA, the reaction temperature and acetylene space velocity were optimized at 65 °C and 200 h^?1, respectively. The introduction of HCl into the catalyst with a rate of 3.2 h^?1 could reduce CuCl loss by 73.5%, whereas conversion of acetylene was only lowered by 9.0%. CONCLUSION: Acidity regulation of the anhydrous catalyst by optimising the reaction temperature, acetylene space velocity, and rate of addition of HCl shows little negative effect on acetylene conversion and selectivity to MVA but can reduce CuCl loss significantly. © 2012 Society of Chemical Industry