Evaluation of bias voltage effect on diamond‐like carbon coating properties deposited on tungsten carbide cobalt

Diamond‐like carbon (DLC) coatings are getting new trends for cutting tool applications. In this research work, the DLC coatings were deposited on 15 × 15 × 5‐mm tungsten carbide cobalt substrates with variation of bias voltage from 0 to 500 V. The DLC films of 400 nm were deposited using filter cathode vacuum arc system, and 100‐nm chromium interlayer was deposited by sputtering. The optimized conditions for plasma pretreatment at different argon flow rates and deposition rates with bias variation were found. The effect of bias voltage on microstructure, tribology, adhesion, and mechanical properties were evaluated. The characterization techniques employed were field emission electron microscopy, Raman spectroscopy, wear test, SEM, scratch test, and nano‐indentation. The effect of substrate pretreatment on film adhesion was also evaluated. It was observed that etching rate increased with the increase in Ar flow rate while DLC deposition and sputtering rates decreased with increase in the bias voltage. The characterization suggests the DLC coatings deposited at 0 V bias as optimum condition because of showing the best results among all other conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface oxidation process of a diamond‐like carbon film analyzed by difference X‐ray photoelectron spectroscopy

Difference X‐ray photoelectron spectroscopy (D‐XPS) revealed the surface oxidation process of a diamond‐like carbon (DLC) film. Evaluation of surface functional groups on DLC solely by the C 1s spectrum is difficult because the spectrum is broad and has a secondary asymmetric lineshape. D‐XPS clarified the subtle but critical changes at the DLC surface caused by wet oxidation. The hydroxyl (C―OH) group was dominant at the oxidized surface. Further oxidized carbonyl (C?O) and carboxyl (including carboxylate) (COO) groups were also obtained; however, the oxidation of C?O to COO was suppressed to some extent because the reaction required C―C bond cleavage. Wet oxidation cleaved the aliphatic hydrogenated and non‐hydrogenated sp² carbon bonds (C―H sp² and C―C sp²) to create a pair of C―OH and hydrogenated sp³ carbon (C―H sp³) bonds. The reaction yield for C―H sp² was superior at the surface, suggesting that the DLC film was hydrogen rich at the surface. Oxidation of aromatic sp² rings or polycyclic aromatic hydrocarbons such as nanographite to phenols did not occur because of their resonance stabilization with electron delocalization. Non‐hydrogenated sp³ carbon (C―C sp³) bonds were not affected by oxidation, suggesting that these bonds are chemically inert. Copyright © 2014 John Wiley & Sons, Ltd.     

Corrosion and tribocorrosion behaviour of super‐thick diamond‐like carbon films deposited on stainless steel in NaCl solution

Super‐thick diamond‐like carbon (DLC) film is a potential protective coating in corrosive environments. In the present work, three kinds of DLC films whose thickness and modulation periods are 4 µm and 3, 21 µm and 17 and 21 µm and 7, respectively, were fabricated on stainless steel. The effect of different thickness and modulation periods on corrosion and tribocorrosion behaviour of the DLC‐coating stainless steel was investigated in 3.5 wt% NaCl aqueous solution by a ball‐on‐flat tribometer equipped with a three‐electrode electrochemical cell. The DLC‐coating stainless steel served as a working electrode, and its OCP and potentiodynamic polarization were monitored before and during rubbing. The wear–corrosion mechanism of the DLC films was investigated by SEM. The results showed that the increasing thickness can prolong significantly lifetime of DLC films in NaCl aqueous solution. In particular, the modulation period has a significant impact on the tribocorrosion resistance of the DLC super‐thick films. The study suggested that the increasing thickness of compressive stress layer could suppress film damage by reducing crack propagation rate. Thus, the super‐thick DLC film with thickness of 21 µm and 7 periods presented the best tribocorrosion resistance among all studied films. Copyright © 2016 John Wiley & Sons, Ltd.     

X‐ray photoelectron analysis of surface functional groups on diamond‐like carbon films by gas‐phase chemical derivatization method

Oxygen‐related surface functional groups on diamond‐like carbon (DLC) films were derivatized with fluorine‐ and nitrogen‐related groups by the gas‐phase chemical derivatization (GCD) method, and the groups were analyzed quantitatively by X‐ray photoelectron spectroscopy (XPS). It is desirable that a derivatization reaction is unique to the target group; however, it usually causes undesirable side reactions which affect other groups. This diversity of the reactions has complicated the analysis. In this report, we have overcome the problem by applying a mathematical treatment which takes the side reactions into account. This improved analysis shows that it is no longer necessary to have derivatization reactions unique to the target groups. As a result, it is demonstrated that the carbonyl (C?O) group is the dominant surface functional group on both the DLC and its wet‐oxidized films, the carboxyl (COOH) group plays a minor role, and the presence of the hydroxyl (OH) group is logically denied. Considering the oxidation steps of these oxygen‐related surface functional groups, it is suggested that the C?O group on the DLC films requires the cleavage of the carbon–carbon bond with a relatively high activation energy barrier to change into the COOH group. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of sputtering current on the bonding structure and mechanical properties of diamond‐like carbon films deposited by MFPUMST

Diamond‐like carbon (DLC) films on glass wafers were produced by middle frequency pulsed unbalanced magnetron sputtering technique (MFPUMST) at different sputtering current. The chemical bonding of carbon characterized by Raman spectroscopy and X‐ray photoelectron spectroscopy (XPS) show that the sp³ fraction in DLC films increases with increasing sputtering current from 100 to 300 mA, and then decreases above 300 mA. Mechanical properties like nano‐hardness and elastic recovery for these films under different sputtering currents analyzed by a nano‐indentation technique show the same tendency that nano‐hardness and elastic recovery increase with increasing sputtering current from 100 to 300 mA, and then decrease with increasing sputtering current from 300 to 400 mA. These results indicate that the sp³ fraction in the prepared DLC films is directly related to nano‐hardness and elastic recovery. The results shown above indicate that the parameter of the preparation—sputtering current has a strong influence on the bonding configuration of the deposited DLC films. The mechanism of sputtering current on the sp³ fraction is discussed in this paper. Copyright © 2009 John Wiley & Sons, Ltd.     

Corrosion resistances of passive films on low‐Cr steel and carbon steel in simulated concrete pore solution

The passive ranges of carbon steel rebar and 3Cr steel rebar in saturated Ca(OH)₂‐simulated concrete pore solution with pH 12.6 were determined by means of cyclic voltammetry and potentiodynamic polarization curves. Chronopotentiometry was used to obtain steady‐state conditions for the formation of passive films on rebar samples at different anodic potentials. Electrochemical impedance spectroscopy, Mott–Schottky and X‐ray photoelectron spectrometer curves were employed to compare the formed passive films at different potentials. Additionally, cyclic polarization curves were used to compare the corrosion resistances of formed passive films on the two rebars in saturated Ca(OH)₂‐simulated concrete pore solution with different concentration of Cl^?. The results show that the passive ranges of the two rebars are all between ?0.15 and +0.6 V, and more stable passive films can be formed on both rebars at the anodic potential of +0.3 V. In the absence of Cl^?, the stability and corrosion resistance of the passive film formed on the 3Cr rebar are better than those of CS rebar. The passive film of 3Cr steel has the relatively better pitting corrosion resistance than carbon steel in saturated Ca(OH)₂‐simulated concrete pore solution that contains different concentration of Cl^?. Copyright © 2016 John Wiley & Sons, Ltd.     

The influence of anti‐wear additive ZDDP on doped and undoped diamond‐like carbon coatings

Diamond‐like carbon (DLC) coatings are recognised as a promising way to reduce friction and improve wear performance of automotive engine components. DLC coatings provide new possibilities in the improvement of the tribological performance of automotive components beyond what can be achieved with lubricant design alone. Lubricants are currently designed for metallic surfaces, the tribology of which is well defined and documented. DLC does not share this depth of tribological knowledge; thus, its practical implementation is stymied. In this work, three DLC coatings are tested: an amorphous hydrogenated DLC, a silicone‐doped amorphous hydrogenated DLC and a tungsten‐doped amorphous hydrogenated DLC. The three coatings are tested tribologically on a pin‐on‐reciprocating plate tribometer against a cast iron pin in a group III base oil, and a fully formulated oil that consists of a group III base oil and contains ZDDP, at 100 °C for 6 h and for 20 h in order to determine whether a phosphor‐based tribofilm is formed at the contact. The formation of a tribofilm is characterised using atomic force microscopy and X‐ray photoelectron spectroscopy techniques. The main findings of this study are the formation of a transfer film at the undoped, amorphous hydrogenated DLC surface, and also the tungsten amorphous hydrogenated DLC having a significant wear removal during the testing. The three coatings were found to have differing levels of wear, with the tungsten‐doped DLC showing the highest, the silicon‐doped DLC showing some coating removal and the amorphous hydrogenated DLC showing only minimal signs of wear. Copyright © 2015 John Wiley & Sons, Ltd.     

Electropolymerized coatings of poly(o‐anisidine) and poly(o‐anisidine)‐TiO2 nanocomposite on aluminum alloy 3004 by using the galvanostatic method and their corrosion protection performance

Poly(o‐anisidine) (POA) and poly(o‐anisidine)‐TiO₂ (POA‐TiO₂) nanocomposite coatings on aluminum alloy 3004 (AA3004) have been investigated by using the galvanostatic method. The electrosynthesized coatings were characterized by FT ‐ IR spectroscopy, XRD, SEM ‐ EDX and SEM. The corrosion protection performance of POA and POA‐TiO₂ nanocomposite coatings was investigated in the 3.5% NaCl solution by using potentiodynamic polarization technique and electrochemical impedance spectroscopy. The results show that the corrosion rate of the nanocomposite coatings is about 900 times lower than the bare AA3004 under optimal conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Microstructure and anti‐ wear and corrosion performances of novel UHMWPE/graphene‐nanosheet composite coatings deposited by flame spraying

Ultra‐high molecular weight polyethylene (UHMWPE)/graphene‐nanosheet (GN, multiple layers of graphene sheets with the thickness of ~5–10 nm) coatings have been deposited by flame spraying. The structure of UHMWPE remained almost intact after the spray processing and addition of GNs resulted in a slightly decreased crystallinity and improved thermal stability of UHMWPE. In addition, the coating containing 1.0 wt.% GNs exhibited a reduction of ~20% in wear rate and 25% in friction coefficient (0.18 versus 0.24). Significantly enhanced anti‐corrosion performances of the UHMWPE–GN coatings were suggested by increased corrosion potential, corrosion current density, and impedance modulus value of the UHMWPE–GN coatings. The very well retained GNs are located mainly at the interfaces between UHMWPE splats and act as bridges connecting the splats, which mainly accounts for the enhanced properties of the composite coatings. The novel UHMWPE–graphene composite coatings show great potential for protecting engineering components for applications against corrosion. Copyright © 2013 John Wiley & Sons, Ltd.     

Size effect in the titanium/diamond‐like carbon bilayer films: effect of relative thickness on their structure and mechanical properties

Titanium/diamond‐like carbon (Ti/DLC) bilayer films with different relative thickness were fabricated by direct‐current and pulsed cathode arc plasma method. Microstructure, morphological characteristics, and mechanical properties of the films were investigated in dependence of the thickness of Ti and DLC layers by Raman spectroscopy, atomic force microscopy, Knoop sclerometer, and surface profilometer. Raman spectra of Ti/DLC bilayers show the microstructure evolution (the size and ordering degree of sp²‐hybridized carbon clusters) with varying the thicknesses of Ti interlayer and DLC layer. Nano‐scaled Ti interlayer of 12–20 nm thickness presents the largest size effect. The catalytic effect of the sublayer is most pronounced in the carbon layer of less than 106 nm. In these thickness ranges, the bilayer films possessed the highest micro‐hardness and reactivity between atoms at interface. Internal stress in the bilayer monotonically decreases, with the thickness of Ti interlayer increasing to 30 nm and then becomes stable with the thickness. These results are associated with the occurrence of atomic diffusion process at Ti/C interface, and they are of cardinal significance to optimize the structure and mechanical properties of carbon‐based multilayer films. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrochemical analysis of molybdate conversion coating on hot‐dip galvanized steel in various growth stages

The electrochemical behavior of molybdate conversion coatings in various growth stages was investigated by electrochemical impedance spectroscopy and equivalent circuits. The chemical composition and microstructure were characterized by SEM/energy dispersive spectroscopy, atomic force microscopy, and AES. Neutral salt spray tests complemented the information. The results indicated that the growth process of the molybdate conversion coating was accompanied by the growth of micro cracks, consisting of three stages: in the early and middle stages, the protective property of the coatings increased with increasing treatment time and then decreased when the cracks developed in the last stage. On the basis of the observation of the microstructure and the analysis of the electrochemical impedance spectra of the coatings in various stages, a simplified growth process model of the molybdate conversion coating on hot‐dip galvanized steel was created. Copyright © 2017 John Wiley & Sons, Ltd.     

Co‐deposition behavior of alumina nanoparticles and properties of Ni‐Al2O3 nanocomposite coatings

The influence of adding alfa‐Al₂O₃ nanoparticles with different concentrations into Watt's bath under the application of ultrasound during electrodeposition was investigated by means of electrochemical impedance spectroscopy (EIS) in the galvanostatic mode. The characteristics of the double layer during nickel deposition were affected by the existence of Al₂O₃ nanoparticles in the electrolyte. In this study, the results of the impedance were correlated with the layer properties, e.g. the mean grain size, the incorporation of particles in the deposit and the strengthening performance. It became obvious that there is a good relationship between the EIS data and layer properties, which makes the impedance spectroscopy a reliable tool for predicting the properties in dispersion coatings. Copyright © 2015 John Wiley & Sons, Ltd.     

Corrosion resistance of amorphous AlPO4 coating in salty atmospheres

The objective of the present study was to introduce a cost-effective and environmentally friendly coating to improve the corrosion resistance of the structures located in salt water. The coating solution, based on amorphous aluminum phosphate composition, was synthesized by sol–gel process and applied to AISI 304 stainless steel by dip coating technique. X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy analyses were employed to investigate the phase composition and morphology of the coating. Corrosion behavior of the uncoated and coated samples was investigated using standard salt spray test, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. Salt spray test results for the bare substrate revealed a corrosion rate of six-time greater than that of the coated surface after 168 hr exposure time. Electrochemical test results declared that the amorphous AlPO₄ coating decreased the corrosion current density of the AISI 304 stainless steel by 10 orders of magnitude. Furthermore, according to the corresponding EIS measurements, the coated surface exhibited a superior anti-corrosion performance than uncoated sample. Overall, the results declared that the amorphous AlPO₄ coating could be a good choice for surface protection of stainless steel against electrochemical corrosion in salty environments.     

Hydrogen storage in porous structures of adamantane‐based nitrogen‐heterocyclic ring with diamond‐like structure

Using the density functional theory and molecular mechanics methods, we calculated the binding energy and parameters about the primitive cell designed by us with the adamantane and the nitrogen heterocyclic ring, the vibrational frequencies about the small complexes. Grand canonical Monte Carlo simulations were performed to predict the capacities for the hydrogen storage and adsorption isotherms. The results show the positive effects of bigger specific surface area and pore volume on hydrogen storage and isosteric heat. The gravimetric hydrogen uptake of adamantane‐based nitrogen‐heterocyclic ring of quaterpyridyl can reach 9.02 wt % at room temperature and 100 bar. But the volumetric H₂ capacities of the four materials are low at T = 298 K because of weak interaction between the materials and H₂ molecule. © 2014 Wiley Periodicals, Inc.     

Modification effects of short carbon fibers on mechanical properties and fretting wear behavior of UHMWPE composites

The present work comparatively studied the modification effects of short carbon fiber (CF) on the mechanical properties and fretting wear behavior of ultra‐high molecular weight polyethylene (UHMWPE)/CF composites. The interactions between CFs and UHMWPE interface were also investigated in detail. The results showed that, with the increase in fiber content, the compressive modulus and hardness of the composites increased, while its impact strength decreased. It was found that filling of CF can reduce the friction and wear of UHMWPE. In addition, the UHMWPE‐based composites reinforced with nitric acid‐treated CF exhibited better mechanical properties, lower friction coefficient, and higher wear resistance than those of untreated UHMWPE/CF composites. This was attributed to the improvement of interfacial adhesion and compatibility between CF and UHMWPE matrix caused by surface chemical modification of CF. Copyright © 2015 John Wiley & Sons, Ltd.     

A fourfold interpenetrating diamond‐like three‐dimensional zinc(II) coordination polymer: synthesis,crystal structure and physical properties

Excellent fluorescence properties are exhibited by d¹⁰ metal compounds. The novel three‐dimensional Zn^II coordination framework, poly[[{μ₂‐bis[4‐(2‐methyl‐1H‐imidazol‐1‐yl)phenyl] ether‐κ²N³:N^3′}(μ₂‐furan‐2,5‐dicarboxylato‐κ²O²:O⁵)zinc(II)] 1.76‐hydrate], {[Zn(C₆H₂O₅)(C₂₀H₁₈N₄O)]·1.76H₂O}_n, has been prepared and characterized using IR spectroscopy, elemental analysis and single‐crystal X‐ray diffraction. The crystal structure analysis revealed that the compound exhibits a novel fourfold interpenetrating diamond‐like network. This polymer also displays a strong fluorescence emission in the solid state at room temperature.     

Study on the friction and wear behavior of surface‐modified carbon nanotube filled carbon fabric composites

The functionalization of multi‐walled carbon nanotubes (MWNTs) was achieved by grafting furfuryl amine (FA) onto the surfaces of MWNTs. Furthermore, the functional MWNTs were incorporated into carbon fabric composites and the tribological properties of the resulting composites were investigated systematically on a model ring‐on‐block test rig. Friction and wear tests revealed that the modified MWNTs filled carbon fabric composite has the highest wear resistance under all different sliding conditions. Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA) revealed that MWNTs were successfully functionalized and the modification led to an improvement in the dispersion of MWNTs, which played an important role on the enhanced tribological properties of carbon fabric composites. It can also be found that the friction and wear behavior of MWNTs filled carbon fabric composites are closely related with the sliding conditions such as sliding speed, load, and lubrication conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

Lower friction and higher wear resistance of fluorine‐incorporated amorphous carbon films

Plasma‐enhanced chemical vapor deposition was employed to fabricate hydrogenated amorphous carbon (a‐C:H) films and fluorine‐doped hydrogenated amorphous (a‐C:H:F) carbon films. For comparison purpose, the a‐C:H films were treated with CF₄ plasma. The bonding structure and tribological behavior of the films were investigated. The results indicate that the F presented mainly in the forms of C–F₃, C–F and C–F₂ groups in both the a‐C:H:F film and the surface CF₄ plasma processed hydrogenated amorphous carbon (F‐P‐a‐C:H) films. Moreover, the a‐C:H:F films, because of the transformation of sp³ to sp², possess a lower friction coefficient than that of the F‐P‐a‐C:H films. Copyright © 2013 John Wiley & Sons, Ltd.     

Bioactivity and mechanical properties of nickel‐incorporated hydrogenated carbon nanocomposite thin films

In this paper, the influence of nickel incorporation on the mechanical properties and the in vitro bioactivity of hydrogenated carbon thin films were investigated in detail. Amorphous hydrogenated carbon (a‐C:H) and nickel‐incorporated hydrogenated carbon (Ni/a‐C:H) thin films were deposited onto the Si substrates by using reactive biased target ion beam deposition technique. The films' chemical composition, surface roughness, microstructure and mechanical properties were investigated by using XPS, AFM, TEM, nanoindentation and nanoscratch test, respectively. XPS results have shown that the film surface is mainly composed of nickel, nickel oxide and nickel hydroxide, whereas at the core is nickel carbide (Ni₃C) only. The presence of Ni₃C has increased the sp² carbon content and as a result, the mechanical hardness of the film was decreased. However, Ni/a‐C:H films shows very low friction coefficient with higher scratch‐resistance behavior than that of pure a‐C:H film. In addition, in vitro bioactivity study has confirmed that it is possible to grow dense bone‐like apatite layer on Ni/a‐C:H films. Thus, the results have indicated the suitability of the films for bone‐related implant coating applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of clay and surface plasma‐treated carbon fiber on wear behavior of thermoplastic POM composites

In engineering applications, experimental data and insight from scientific investigations on wear properties of polyoxymethylene (POM) composites are important for engineers to understand how to design and formulate POM materials with high resistance to wear. In this work, clay and carbon fiber were utilized and incorporated into POM and the mechanical and wear properties, in specific wear rate, were then assessed. The experimental results suggested that the addition of clay increased the tensile modulus and strength. The mechanical and wear properties of POM composites were found to improve with the addition of the carbon fiber. Carbon fiber/clay/POM composite exhibited the lowest specific wear rate and friction coefficient.