High performance sputtered carbon coatings for wear resistant applications

The Closed Field Un-Balanced Magnetron Sputter Ion Plating (CFUBMSIP) process is now routinely used in a production environment and is characterised by a high degree of flexibility in terms of the substrates and coating materials which can be used. Compared to classical magnetron sputtering the closed field system produces higher ion current density which gives high quality coatings and excellent adhesion. The ability to vary the deposition parameters over a wide range, permits the modification of not only the composition and the structure but also the morphology (density and growth mode) of the films. This paper describes, that in particular, a range of carbon coatings from transparent, electrically insulating to black, conductive coatings, can be produced. Tribological tests concerning adherence, hardness and wear properties in atmospheric and lubricated conditions are presented. The effects of the nature of the substrates with different hardness properties (M42, stainless steel and Al) are investigated.     

Intensity of stress singularity for the circumferential V‐shape corner front of a three‐dimensional diamond‐like defect

Three‐dimensional diamond‐like defects with circumferential V‐shape corner fronts are often contained in engineering materials. In this paper, generalized stress intensity factors are calculated for this type of defect using a modified advanced finite element method. A super corner front element model in the global coordinates is established to capture the stress singularities along the circumferential corner front. Three‐dimensional numerical series eigen‐solutions in the element have been transformed from asymptotic expressions in the local curvilinear coordinates. The element is suitable for a sharp V‐shape corner with arbitrary opening and inclination angle. Singular stress fields near various shapes of diamond‐like defects are systematically investigated. The interaction of an embedded defect with free surface or another identical defect is also investigated. The numerical results can be used as stress intensity parameters to predict fatigue strength at circumferential corner front of a diamond‐like defect.     

Designing multilayer diamond like carbon coatings for improved mechanical properties

New multilayer coatings were produced by incorporating alternating soft and hard DLC layers enabled by varying the bias voltage during deposition process while maintaining a constant hard-to-soft layer thickness ratio.These coatings were deposited onto a Cr/Cr Cxgraded layer by closed field unbalanced magnetron sputtering(CFUBMS).The cross-sectional analysis of the coatings showed that the multilayer coatings possess sharp interfaces between the soft and hard layers with the hard to soft layer thickness ratio(1:1.33)constant in all the coatings.Raman analysis uncovered the increasing sp³character of the DLC coatings as a result of decreasing ID/IGratio and increasing full width at half maximum(FWHM)values of the G band peak induced supposedly by an increase in bias voltage during hard layer deposition.Nanoindentation tests showed an increase in hardness of the DLC coatings which can be correlated with the increase in the sp³content of the coatings as well as decreasing sp²-C cluster size,as calculated from the ID/IGratio.Furthermore,the coatings exhibited excellent plastic deformation resistance and adhesion strength upon microindentation and scratch testing,respectively.Although further investigations are required to assess coating durability,the multilayer design could offer the DLC coatings with a rare opportunity to combine the high hardness with damage resistance with a constant bilayer thickness and without the need to introduce complex multilayer system.     

Realization of High Performance AR‐coatings with Dust‐ and Water‐Repellent Properties

Hydrophobic coatings enable the manufacture of easy‐to‐clean surfaces having dust‐ and water‐repellent properties. In this work, a hydrophobic coating is deposited as a top layer on an antireflective (AR) multilayer system to produce low reflectance optical surfaces at a normal incident angle in the visible spectrum with dust‐ and water‐repellent properties for applications in precision optics. It is shown that the hydrophobic coating can be considered, from an optical point of view, as two adjacent thin layers having specific thicknesses and densities. In fact, the hydrophobic layer is one monolayer comprising molecular chains with anchoring groups responsible for the chemical bond with the substrate material and functional groups responsible for the water‐ and oil‐repellent properties. Their optical constants are determined and included in the final coating design. High performance AR coatings having an average reflectance of 0.14% at 7° incident angle in the 400‐680nm spectral range together with a pleasing purplered reflex color are produced. Coated lenses exhibit an excellent abrasion resistance, environmental stability, resistance to cleaning agents, homogeneity and water repellence with contact angles against water higher than 110°.     

High Performance of N‐Doped Graphene with Bubble‐like Textures for Supercapacitors

Nitrogen‐doped graphene (NG) with wrinkled and bubble‐like texture is fabricated by a thermal treatment. Especially, a novel sonication‐assisted pretreatment with nitric acid is used to further oxidize graphene oxide and its binding with melamine molecules. There are many bubble‐like nanoflakes with a dimension of about 10 nm appeared on the undulated graphene nanosheets. The bubble‐like texture provides more active sites for effective ion transport and reversible capacitive behavior. The specific surface area of NG (5.03 at% N) can reach up to 438.7 m² g^?1, and the NG electrode demonstrates high specific capacitance (481 F g^?1 at 1 A g^?1, four times higher than reduced graphene oxide electrode (127.5 F g^?1)), superior cycle stability (the capacitance retention of 98.9% in 2 m KOH and 99.2% in 1 m H₂SO₄ after 8000 cycles), and excellent energy density (42.8 Wh kg^?1 at power density of 500 W kg^?1 in 2 m KOH aqueous electrolyte). The results indicate the potential use of NG as graphene‐based electrode material for energy storage devices.     

Adhesion and degradation of hard coatings on poly (methyl methacrylate) substrates

The adhesion and time dependent crack growth behavior of polysiloxane based hard coatings on poly (methyl methacrylate) substrates were investigated. The adhesive fracture energies for different coatings were quantitatively characterized and varied between 1.4 J/m² and 22 J/m². Significant time dependent crack growth in various moist environments was observed and was consistent with a viscoelastic crack growth model. The effect of selected weathering treatments was also examined and resulted in a significant drop in coating adhesion. The coatings were analyzed using surface sensitive techniques; structural changes in the coatings resulting from various exposure doses were studied and mechanisms responsible for the observed degradation in adhesion were discussed.     

High performance graphene-poly (o-anisidine) nanocomposite for supercapacitor applications

Our previous exciting results on graphene (G)-conducting polymer (polyaniline (PANI) and polyethylenedioxythiophene (PEDOT)) supercapacitors have prompted the investigation of G-substituted conducting polymer nanocomposites used as electrode materials in supercapacitors. The solubility of ortho-substituted PANI derivatives in a few common solvents has allowed the fabrication of stretchable films by the casting technique. The G-poly (o-anisidine) (G-POA) nanocomposites were synthesized with different weight ratios of G to o-anisidine by chemical methods, and characterized by various techniques, such as, scanning electron microscopy, transmission electron microscopy, UV–visible spectroscopy, Raman spectroscopy, thermogravimetric analysis and cyclic voltammetry. The electrical conductivity and specific capacitance obtained for the G-POA nanocomposites were found to be dependent on the weight ratios of G to o-anisidine. The specific capacitance and the charging–discharging behavior of the POA and G-POA supercapacitors were investigated in a 2 M H₂SO₄, 0.2 M LiClO₄ and 1 M 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆) ionic liquid. The specific capacitance of 380 F g⁻¹ was calculated for the 1:1 weight ratio of G to o-anisidine based G-POA supercapacitor in 2 M H₂SO₄. The presence of the electron-donating group (–OCH₃) in the o-anisidine allows the electrons through the lone pair of nitrogen atoms to enhance the electronic charge transport inside the G-POA supercapacitor electrodes. However, the G-POA-based supercapacitors showed a 27% decrease in the specific capacitance in H₂SO₄ and 16% decrease in the ionic liquid (BMIM-PF₆) after 1000 cycles of charging and discharging. The higher stability and rate capability of the G-POA based supercapacitor in an ionic liquid (BMIM-PF₆) as compared to an aqueous electrolytic supercapacitor opens the door for the fabrication of stable supercapacitors for practical applications.     

Structure and mechanical properties of low temperature magnetron sputtered nanocrystalline (nc-)Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings

This paper reports on the structure and mechanical properties of ~ 2 μm thick nanocomposite (nc-) Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings deposited on 100Cr6 steel substrates, using low temperature (~ 200 °C) DC reactive magnetron sputtering. The carbon content was varied with acetylene partial pressure in order to obtain single layer coatings with different a-C:H carbon phase fractions. The nanocrystalline Ti(N,C) phase is approximately stoichiometric for all coatings and the a-C:H phase fraction increases from 31 to 47 at.% as the coatings stoichiometry changed from TiC_1.34 N_0.51 to TiC_2.48 N_0.48, respectively. TiC_1.34 N_0.51 coatings showed the highest nanoindentation hardness (H) of ~ 14 GPa and a modulus (E_r) of ~ 144 GPa; H reduced to < 6 GPa and E_r to < 70 GPa for TiC_2.48 N_0.48 coatings. nc-Ti(N,C)/a-C:H coatings are promising candidates for applications where better matching of the modulus between a relatively low modulus substrate, hard loading support layer and low modulus-high H/E ratio top layer is required.     

Higher Order Assembly of Virus‐like Particles (VLPs) Mediated by Multi‐valent Protein Linkers

Two‐ and three‐dimensional assembly of nanoparticles has generated significant interest because these higher order structures could exhibit collective behaviors/properties beyond those of the individual nanoparticles. Highly specific interactions between molecules, which biology exploits to regulate molecular assemblies such as DNA hybridization, often provide inspiration for the construction of higher order materials using bottom‐up approaches. In this study, higher order assembly of virus‐like particles (VLPs) derived from the bacteriophage P22 is demonstrated by using a small adaptor protein, Dec, which binds to symmetry specific sites on the P22 capsid. Two types of connector proteins, which have different number of P22 binding sites and different geometries (ditopic linker with liner geometry and tetratopic linker with tetrahedral geometry) have been engineered through either a point mutation of Dec or genetic fusion with another protein, respectively. Bulk assembly and layer‐by‐layer deposition of P22 VLPs from solution was successfully achieved using both of the engineered multi‐topic linker molecules, while Dec with only a single binding site does not mediate P22 assembly. Beyond the two types of linkers developed in this study, a wide range of different connector geometries could be envisioned using a similar engineering approach. This is a powerful strategy to construct higher order assemblies of VLP based nanomaterials.     

Diamond like carbon coatings deposited by microwave plasma CVD: XPS and ellipsometric studies

Diamond-like carbon (DLC) films were deposited by microwave assisted chemical vapour deposition system using d.c. bias voltage ranging from −100 V to −300 V. These films were characterized by X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry techniques for estimating sp ³/sp ² ratio. The sp ³/sp ² ratio obtained by XPS is found to have an opposite trend to that obtained by spectroscopic ellipsometry. These results are explained using sub-plantation picture of DLC growth. Our results clearly indicate that the film is composed of two different layers, having entirely different properties in terms of void percentage and sp ³/sp ² ratio. The upper layer is relatively thinner as compared to the bottom layer.     

A perspective on the optimisation of hard carbon and related coatings for engineering applications

Hard carbon coatings hold the key to improved performance for many types of products. However the achievement of these improvements requires the selection of the appropriate type of carbon coating and therefore the correct process and appropriate deposition parameters. The huge range of properties achievable in carbon coatings is mainly due to the ability of carbon to form different types of interatomic bonds, to take up different sites, and to adopt different structures. In addition to intrinsic material properties, other factors must also be considered for each application, such as the adhesion level achievable and coating cost. This complex situation explains why the number of applications for hard carbon films is still more limited than originally expected. Despite the considerable progress achieved during the last decade in hard coating technologies, practical results often appear conflicting, with differences in properties occurring even within the same types of coatings. Furthermore, the many different deposition systems and processes which have been developed introduce further complications in regard to (for example) achievable coating uniformity and deposition rates. Thus, there is often confusion in the use of certain fundamental principles, especially regarding the growth mechanisms and the effects which produce more dense homogeneous and stable coating materials. This is especially true for the improved properties of tetrahedral amorphous carbon films, which are different from previously reported diamond-like carbon materials, and can be created by adapting and improving existing industrial processes, to offer advantages compared to earlier coatings, and hence possibilities for important new applications. This paper discusses issues relating to intrinsic material properties, and practical aspects such as adhesion, to provide a framework for the development, selection and use of hard carbon coatings in practical situations.     

原位聚合导电高分子包混对硬碳性能的影响

采用原位聚合方法对硬碳材料进行了导电聚合物包混,并测试了导电聚合物包混硬碳材料的电化学性能.利用扫描电镜,拉曼光谱,电导率仪及恒电流法研究了导电聚合物包混的硬碳材料的结构以及充放电特性.研究发现,聚苯胺、聚吡咯和聚噻吩等均能通过原位聚合包混在硬碳表面.其中,采用噻吩在硬碳表面原位聚合增强了硬碳材料的导电性.经聚噻吩包混的硬碳首次充电容量达到了385mAh g-1以上,高于未包混的硬碳(320mAh g-1).循环20周以后聚噻吩包混硬碳的容量仍保持在325 mAh g-1以上,而未包混硬碳的容量则降低到290 mAh g-1以下.     

Development of amorphous carbon protective coatings on poly(vinyl)chloride

The great versatility of polymers has promoted their application in a series of ordinary situations. The development of specific devices from polymers, however, requires modifications to fit specific stipulations. In this work the surface properties of thin films grown onto polyvinylchloride (PVC) were investigated. Hydrogenated amorphous carbon films were deposited onto commercial PVC plates from acetylene and argon plasmas excited by radiofrequency (13.56 MHz, 70 W) power. The proportion of acetylene in the gas feed was varied against that of argon, keeping the total pressure constant at 2.5 Pa. Deposition time was 1800 s. Film elemental composition was analyzed by X-ray photoelectron spectroscopy, XPS. Water contact angle measurements were performed using the sessile drop technique. The root mean squared roughness was derived from 50 × 50 µm² surface topographic images, acquired by scanning probe microscopy. Nanoindentation and pin-on-disk techniques were employed on the determination of film hardness and sliding wear, respectively. Oxidation resistance was obtained through the etching rate of the samples in oxygen radiofrequency (1.3 Pa, 50 W) plasmas. From XPS analysis it was detected oxygen and nitrogen contamination in all the samples. It was also found that sp³/sp² ratio depends on the proportion of argon in the plasma. At lower argon concentrations, hardness, wear and oxidation resistances were all improved with respect to the uncoated PVC. In such conditions, the surface wettability is low indicating a moderate receptivity to water. This combination of properties, ascribed to a balance between the ion bombardment and deposition processes, is suitable for materials exposed to rigorous weathering conditions.     

Automatically inf − sup compliant diamond‐mixed finite elements for Kirchhoff plates

We develop a mixed finite‐element approximation scheme for Kirchhoff plate theory based on the reformulation of Kirchhoff plate theory of Ortiz and Morris [1]. In this reformulation the moment‐equilibrium problem for the rotations is in direct analogy to the problem of incompressible two‐dimensional elasticity. This analogy in turn opens the way for the application of diamond approximation schemes (Hauret et al. [2]) to Kirchhoff plate theory. We show that a special class of meshes derived from an arbitrary triangulation of the domain, the diamond meshes, results in the automatic satisfaction of the corresponding inf ? sup condition for Kirchhoff plate theory. The attendant optimal convergence properties of the diamond approximation scheme are demonstrated by means of the several standard benchmark tests. We also provide a reinterpretation of the diamond approximation scheme for Kirchhoff plate theory within the framework of discrete mechanics. In this interpretation, the discrete moment‐equilibrium problem is formally identical to the classical continuous problem, and the two differ only in the choice of differential structures. It also follows that the satisfaction of the inf ? sup condition is a property of the cohomology of a certain discrete transverse differential complex. This close connection between the classical inf ? sup condition and cohomology evinces the important role that the topology of the discretization plays in determining convergence in mixed problems. Copyright © 2013 John Wiley & Sons, Ltd.     

Sensitivity analyses of FORM‐based and DRM‐based performance measure approach (PMA) for reliability‐based design optimization (RBDO)

In gradient‐based design optimization, the sensitivities of the constraint with respect to the design variables are required. In reliability‐based design optimization (RBDO), the probabilistic constraint is evaluated at the most probable point (MPP), and thus the sensitivities of the probabilistic constraints at MPP are required. This paper presents the rigorous analytic derivation of the sensitivities of the probabilistic constraint at MPP for both first‐order reliability method (FORM)‐based performance measure approach (PMA) and dimension reduction method (DRM)‐based PMA. Numerical examples are used to demonstrate that the analytic sensitivities agree very well with the sensitivities obtained from the finite difference method (FDM). However, as the sensitivity calculation at the true DRM‐based MPP requires the second‐order derivatives and additional MPP search, the sensitivity derivation at the approximated DRM‐based MPP, which does not require the second‐order derivatives and additional MPP search to find the DRM‐based MPP, is proposed in this paper. A convergence study illustrates that the sensitivity at the approximated DRM‐based MPP converges to the sensitivity at the true DRM‐based MPP as the design approaches the optimum design. Hence, the sensitivity at the approximated DRM‐based MPP is proposed to be used for the DRM‐based RBDO to enhance the efficiency of the optimization. Copyright © 2009 John Wiley & Sons, Ltd.     

Nano-mechanical properties and nano-tribological behaviors of nitrogen-doped diamond-like carbon (DLC) coatings

Diamond-like carbon (DLC) coatings doped with different nitrogen contents were prepared by an ECWR-CVD deposition technique, and their chemical compositions, nano-mechanical properties and nano-tribological behaviors were characterized using Auger Electron Spectrometer and Hysitron Triboindenter, respectively. The results have shown that, higher nitrogen contents in the N-doped DLC coatings can be obtained by increasing the N2 flow rate in the reactive gas mixture. The nitrogen addition in the DLC coatings decreases evidently the nano-mechanical properties, including nano-hardness and reduced modulus. In addition, the depths for the scratched tracks produced during the scratch testing depend heavily on the nitrogen content in the N-doped DLC coatings, and, at the same applied loads, the higher the doped nitrogen content, the deeper the resulting scratched tracks. For the DLC coatings doped with different nitrogen contents, however, the frictional coefficients (LF/INF) deduced from nano-scratch testing at same loads are similar, and, therefore, seem to be independent of the added nitrogen content.