Adhesion and composite micro-hardness of DLC and Si-DLC films deposited on nitrile rubber

Thin films of hydrogenated diamond-like carbon (DLC) and silicon (Si) doped diamond-like carbon (Si-DLC) have been deposited on acrylonitrile butadiene rubber (NBR) using a closed field unbalanced magnetron sputtering ion plating system. A sputter cleaning process was integrated into the deposition process so as to reduce the likelihood of re-contamination between the cleaning and deposition stages. The deposited coatings showed excellent adherence with an adhesion rating of 4 A for films with a Si-C interlayer. The composite micro-hardness was highest for DLC films at 15.5 GPa for indentation load of 147.1 mN using a Vickers micro-hardness tester. Tribological tests undertaken under normal load of 5 N using a pin-on-disc tribometer for all of the samples of DLC and Si-DLC films, with and without Si-C interlayer, show a friction increase between 0.25 and 0.4 to between 0.45 and 0.6. This friction increase has been related to the micro-hardness of the films.     

Tribological performance of DLC films deposited on ACM rubber by PACVD

In this paper the tribological and adhesive performance of DLC films prepared by plasma assisted chemical vapor deposition on acrylic rubber (ACM) are studied. The effect of applied load and sliding velocity on the coefficient of friction and wear rate has been investigated. Effects of the rubber substrate and of ageing of the coated samples have also been explored. In addition, the adhesion of the DLC films to the rubber substrates is evaluated via stretch tests and the measured adhesion strength is larger than 40 MPa, indicating a superb adhesion to the substrate. It is shown that the tribological performance is greatly influenced by the viscoelastic properties of the substrate, and higher coefficients of friction are obtained at higher loads and velocities. The wear followed a similar trend, although very low in all the cases.     

DLC表面处理对高速钢耐磨性能的影响

经DLC表面处理的金属零件,其耐磨性会明显提高,因此DLC表面处理工艺在机械工业受到高度重视.以模具钢为对偶件,利用MM200磨损试验机比较了未经及经过DLC表面处理的高速钢在不同条件下摩擦磨损性能的差异,采用失重法评估耐磨性.试验结果表明:在高速和低速摩擦磨损试验条件下,无论在油润滑状态还是在干摩擦状态,经DLC表面处理后高速钢的耐磨性能都有明显的提高.同时还利用扫描电子显微镜(SEM)观察了磨痕微观形貌,并分析了磨损机理.     

Effects of N-doping on the microstructure, mechanical and tribological behavior of Cr-DLC films

We report on the effects of nitrogen doping on Cr-containing diamond-like carbon (Cr-DLC) films. DLC, Cr-DLC and N-doped Cr-DLC films were deposited on (100) Si substrates using a hybrid plasma-assisted CVD/PVD process. Film microstructure, composition and chemical state of elements were studied using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Mechanical and tribological properties were investigated using microhardness testing and pin-on-disc experiments. Analysis by TEM and XPS shows that the Cr-DLC films contain a dispersion of amorphous, Cr-rich nanoparticles. In the N-doped films, N combines with C and partly transforms the Cr-rich nanoparticles into chromium carbon nitrides, CrC(N), dispersed in the amorphous DLC matrix. Also, a significant portion of N is incorporated into the C network. The N-doped Cr-DLC films were found to possess higher hardness, lower intrinsic stresses and somewhat higher coefficient of friction and wear rate than Cr-DLC and DLC films. Such influence of the N-doping on the properties is attributed to the formation of CrC(N) nanoparticles and C-N bonds in the DLC matrix.     

Raman spectroscopy study of DLC films prepared by RF plasma and filtered cathodic arc

The build-up of intrinsic stress in carbon thin films deposited by vapour deposition can be a major cause of delamination. Arguably, this issue has been one of the main reasons why the industrial exploitation of carbon vapour deposited films has so far been of limited success. In the present study we deposited single and multilayer thin films of carbon and found that under certain deposition conditions, we were able to produce thin films free from delamination.Single and multilayer of films Diamond-like Carbon (DLC) were prepared by Plasma Immersion Ion Implantation and Deposition (PIIID) from two deposition systems: (1) Radio-Frequency (RF) plasma and (2) Filtered Cathodic Vacuum Arc (FCVA). Raman spectroscopy revealed a shift in the peaks previously identified as D and G band in the structures. The sp² and sp³ ratio contents were characterized by Raman spectroscopy.     

Quantitative measurements of sp content in DLC films with Raman spectroscopy

Hydrogenated and H-free diamond-like carbon (DLC) samples were prepared and 244 nm and 514 nm Raman spectra were collected and analyzed. Correlations between Raman spectra and sp³ content of DLC samples from this and previous studies have been analyzed. The dispersion rate of the G peak is shown to correlate linearly with the sp³ content of hydrogenated DLC samples, while the full-width-half-maximum of the G peak is shown to correlate nonlinearly with the sp³ content of H-free DLC samples. Quantitative relations are presented for measuring the sp³ content of both hydrogenated and H-free DLC.     

Use of near atmospheric pressure and low pressure techniques to modification DLC film surface

Diamond-like carbon (DLC) films have been use in numerous industrial applications due to its mechanical properties such as low friction coefficient, high hardness, and high adherence on different substrate materials. It has been demonstrated that the DLC surface can be modified with oxygen plasma treatment. The purpose of this paper is to study two kinds of surface treatments (atmospheric and low pressures) using oxygen gas for different etching exposure times in DLC films. Plasma durability along the time was also evaluated. DLC films were deposited using plasma enhanced chemical vapor deposition technique. The properties of DLC treated for both techniques in different exposure times were investigated through Raman, AFM and contact angle measurements. D band position slightly shifts toward lower wave numbers after oxygen plasma etching treatment whilst the surface becomes rougher, although the roughness values are still lower. A conventional wetting contact angle method was used to study the surface properties of DLC films with different treatments. The wetting contact angle reduced significantly due to the increase of carbon–oxygen sites on the surface.     

磁控溅射WSx/W/DLC/W多层膜的微观结构及摩擦学性能

采用磁控溅射技术在硅基底上交替沉积WS_x、W以及DLC膜层制备WS_x/W/DLC/W多层膜。利用X射线衍射仪、扫描电镜、纳米压痕仪等对多层膜的微观结构和力学性能进行了表征,使用球盘式摩擦磨损试验机测试了多层膜在大气中的摩擦学性能。结果表明:多层膜表面均光滑致密。随着周期中W单层厚度的增加,多层膜中出现α-W、W_2C和β-WC_(1-x)结晶相,多层膜的硬度大幅提高(6 nm时具有极大值17.3 GPa),摩擦因数呈下降趋势,结合力逐渐降低,磨损率先降低后升高。W单层厚度为6 nm的多层膜的耐磨性能最佳,磨损率约为1.4×10~(-14)m~3·N~(-1)·m~(-1)。     

Microstructure and chemical bonding of DLC films deposited on ACM rubber by PACVD

The microstructure and chemical bonding of DLC films prepared by plasma assisted chemical vapor deposition on acrylic rubber (ACM) are studied in this paper. The temperature variation produced by the ion impingement during plasma cleaning and subsequent film deposition was used to modify the film microstructure by controlling the different degrees of strain applied to the substrate. The film microstructure is studied by top view and cross sectional SEM. The observed patch sizes are correlated with the variation of temperature that occurred during deposition. Finally, the chemical bonding of the samples is studied by Raman spectroscopy. All the samples show similar spectra regardless the bias voltage used.     

Physical properties of chemical vapour deposited nanostructured carbon thin films

A simple thermal chemical vapour deposition technique is employed for the deposition of carbon films by pyrolysing the natural precursor “turpentine oil” on to the stainless steel (SS) and FTO coated quartz substrates at higher temperatures (700-1100 °C). In this work, we have studied the influence of substrate and deposition temperature on the evolution of structural and morphological properties of nanostructured carbon films. The films were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), contact angle measurements, Fourier transform infrared (FTIR) and Raman spectroscopy techniques. XRD study reveals that the films are polycrystalline exhibiting hexagonal and face-centered cubic structures on SS and FTO coated glass substrates respectively. SEM images show the porous and agglomerated surface of the films. Deposited carbon films show the hydrophobic nature. FTIR study displays C-H and O-H stretching vibration modes in the films. Raman analysis shows that, high ID/IG for FTO substrate confirms the dominance of sp³ bonds with diamond phase and less for SS shows graphitization effect with dominant sp² bonds. It reveals the difference in local microstructure of carbon deposits leading to variation in contact angle and hardness, which is ascribed to difference in the packing density of carbon films, as observed also by Raman.     

DLC薄膜摩擦行为对微拉深工艺的影响

为了降低微成形中的摩擦尺寸效应,采用基于离子注入、沉积法和磁控溅射技术在模具表面分别镀上3种涂层（DLC、TiN和MoS2）。考虑试样在接触面的塑性变形,分析了表面涂层的摩擦行为。分析表明：当使用DLC涂层时,摩擦因数较低,并且在大应力应变条件下具有较高的抗磨损性能。当进行100次摩擦实验后,DLC薄膜出现石墨化。从摩擦功影响而导致能量降低的角度分析了石墨化机理。通过减小壁厚等研究了DLC薄膜的性能对微拉深件质量的影响。结果表明,DLC薄膜有助于改善微型构件的质量。     

Deposition and properties of Al-containing diamond-like carbon films by a hybrid ion beam sources

Metal incorporation is one of the most effective methods for relaxing internal stress in diamond-like carbon (DLC) films. It was reported that the chemical state of the incorporated metal atoms has a significant influence on the film internal stress. The doped atoms embedding in the DLC matrix without bonding with C atoms can reduce the structure disorder of the DLC films through bond angle distortion and thus relax the internal stress of the films. In present paper, Al atoms, which are inert to carbon, were incorporated into the DLC films deposited by a hybrid ion beams system comprising an anode-layer ion source and a magnetron sputtering unit. The film composition, microstructure and atomic bond structure were characterized using X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy. The internal stress, mechanical properties and tribogoical behavior were studied as a function of Al concentration using a stress-tester, nanoindentation and ball-on-disc tribo-tester, respectively. The results indicated that the incorporated Al atoms were dissolved in the DLC matrix without bonding with C atoms and the films exhibited the feature of amorphous carbon. The structure disorder of the films tended to decrease with Al atoms incorporation. This resulted in the distinct reduction of the internal stress in the films. All Al-DLC films exhibited a lower friction coefficient compared with pure DLC film. The formation of the transfer layer and the graphitization induced by friction were expected to contribute to the excellent friction performance.     

Mechanical and tribological properties of coatings sputtered from SiC target in the presence of CH4 gas

Amorphous hydrogen-free silicon carbide (a-SiC) coatings demonstrate good adhesion to different steel substrates, low intrinsic stress and high hardness however show quite high coefficient of friction in comparison with carbon-based coatings. Some addition of carbon to SiC can promote the decrease of friction coefficient.In the present work the amorphous hydrogenated silicon-carbide (a-SiC:H) films with different C/Si ratio were prepared at room temperature using DC magnetron sputtering in two ways: (i) sputtering of silicon target; (ii) sputtering of SiC target, both in the gas mixture of Ar and CH₄. In the latter case the films contained less hydrogen at the same C/Si ratio. The mechanical and tribological properties of these films were studied to find their optimum combination.The hardness, elastic modulus (nanoindentation), intrinsic stress (Stoney's formula) and coefficient of friction (pin on disc tribometer) were examined in dependence on the technological parameters, film structure and composition (Raman spectra, electron probe microanalysis). An increase of carbon in the films from 50 to 70 at.% resulted in decrease of hardness and friction coefficient. In the first case (i) the hardness decreased from 13 to10 GPa and in the second case (ii) from 23 to 16 GPa. Thus sputtering of SiC target in the gas mixture of Ar and CH₄ allows obtaining at room temperature the films with C/Si > 1 in which relatively high hardness (16-18 GPa) and low friction coefficient (~ 0.15) are combined.     

Microstructural, mechanical and tribological properties of tungsten-gradually doped diamond-like carbon films with functionally graded interlayers

A series of tungsten-gradually doped diamond-like carbon (DLC) films with functionally graded interlayer were prepared using a hybrid technique of vacuum cathodic arc/magnetron sputtering/ion beam deposition. With ‘compositionally graded coating’ concept, the deposition of wear-resistant carbon-based films with excellent adhesion to metallic substrate was realized. In the films, a functionally graded interlayer with layer sequence of Cr/CrN/CrNC/CrC/WC was first deposited onto the substrate, and then, a DLC layer doped with gradually decreasing content of W was coated on. The W concentration gradient along depth of the film was tailored by adjusting the W target current and deposition time. The characterized results indicate that the microstructural, mechanical and tribological properties of these films show a significant dependence on the W concentration gradient. A high fraction of W atom in carbon matrix can promote the formation of sp² sites and WC_1 − x nanoparticles. Applying this coating concept, strongly adherent carbon films with critical load exceeding 100 N in scratch test were obtained, and no fractures or delaminations were observed at the end of the scratched trace. The hardness was found to vary from 13.28 to 32.13 GPa with increasing W concentration. These films also presented excellent tribological properties, especially significantly low wear rate under dry sliding condition against Si₃N₄ ball. The optimum wear performance with friction coefficient of 0.19 and wear rate of 8.36 × 10⁻⁷ mm³/Nm was achieved for the tungsten-gradually doped DLC film with a graded W concentration ranging from 52.5% to 17.8%. This compositionally graded coating system might be a potentially promising candidate for wear-resistant carbon-based films in the demanding tribological applications.     

Tribological behaviour and residual stress of electrodeposited Ni/Cu multilayer films on stainless steel substrate

In the present study, [Ni (4.5 nm)/Cu (t_Cu = 2, 4 and 8 nm)] multilayers were pulse electrodeposited on stainless steel (AISI SS 304) substrate from sulphate based single bath technique. X-ray diffraction (XRD) was used to investigate the structure and stress of the Ni/Cu multilayer. The results from XRD analysis indicated that the deposited multilayers had a preferred crystal orientation of [111] and presence of satellite reflection suggested the formation of superlattice. The stress level within the deposited multilayers was found to be sensitive to the sublayer thickness. Sliding wear behaviour of electrodeposited Ni/Cu multilayer films has been investigated against a tungsten carbide (WC) ball as the counter body and compared with that of the constituents, Cu and Ni coatings. The wear tests were carried out by using a reciprocating ball-on-flat geometry at translation frequencies of 5 and 10 Hz, slip amplitude of 1 mm and at five different loads of 3, 5, 7, 9 and 11 N. Friction force was recorded on-line during the tests. At the end of the tests, the wear scars were examined by laser surface profilometry and scanning electron microscopy (SEM). Friction coefficient was found to be dependent on load and Cu layer thickness (t_Cu) and the values for multilayers were border between Ni and Cu. Among multilayers, sample with minimum t_Cu has shown the lowest friction coefficient and wear rate. With increasing t_Cu, the wear mechanism changes from pure abrasive wear at t_Cu = 2 nm, to particle entrapment at t_Cu = 4 nm to particle embedding at t_Cu = 8 nm. Detailed investigation of the wear scar morphology as well as wear rate measurement revealed that at low loads, (H/E) ratio and residual stress governed the wear rate and the principle wear mode was abrasive cutting. At intermediate loads, the role of residual stress became insignificant while wear was governed by (H/E) ratio and plastic deformation. However, at higher loads, plastic deformation played the major role.     

DLC and UHMWPE as hard/soft composite film on Si for improved tribological performance

The main purpose of this study is to explore the advantages of using a composite thin film of ultra high molecular weight polyethylene (UHMWPE) on a hard diamond like carbon (DLC) coating deposited on Si, for high wear life and low coefficient of friction. The experiments are carried out using a ball-on-disc tribometer at a constant linear speed of 0.052 m/s. A 4 mm diameter silicon nitride ball with a normal load of 40 mN is used as the counterface. The tribological results are discussed on the basis of hardness, elastic modulus, contact area, contact pressure and optical images of surface films. As a result of higher load carrying capacity (high hardness and elastic modulus), the wear life of Si/DLC/UHMWPE coated layer is approximately five times greater than that of Si/UHMWPE. Looking at the film thickness effect, UHMWPE film shows maximum wear resistance when the film is of optimum thickness (6.2 μm-12.3 μm) on DLC. Wear mechanisms of different UHMWPE thicknesses for Si/DLC/UHMWPE film are explained using optical microscopy of worn surfaces. Further, the use of perfluoropolyether (PFPE) ultra-thin film as the top layer on the composite coatings reduces the coefficient of friction to very low values (0.06-0.07) and increases the wear life of the films by several folds.     

Fabrication, microstructure and tribological behavior of pulsed laser deposited a-CNx/TiN multilayer films

a-CN_x/TiN multilayer films were deposited onto high-speed steel substrates by pulsed laser ablation of graphite and Ti target alternately in nitrogen gas. The composition, morphology and microstructure of the films were characterized by energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The tribological properties of the films in humid air were investigated using a ball-on-disk tribometer. The multilayer films consist of crystalline TiN, metallic Ti and amorphous CN_x (a-CN_x). With an increase in thickness ratio of CN_x to bilayer, the hardness of multilayer film decreases, friction coefficient decreases from 0.26 to 0.135, and wear rate increases. The film with thickness ratio of CN_x to bilayer of 0.47 exhibits a maximum hardness of 30 GPa and excellent wear rate of 2.5 × 10^− 7 mm³ N^− 1 m^− 1. The formation of tribo-layer was observed at contact area of Si₃N₄ ball. The film undergoes the combined wear mechanism of abrasion wear and adhesion wear.     

High temperature tribological behavior of W-DLC against aluminum

Diamond-like carbon (DLC) coatings are well suited for applications that require minimum adhesion and low coefficient of friction (COF) against aluminum alloys. These properties however deteriorate rapidly at elevated temperatures, and coating wear occurs. In this study, tribological behavior of W containing DLC (W-DLC) were studied as a function of testing temperatures up to 500 °C, and the sliding-induced surface and subsurface damage at these temperatures was investigated. Pin-on-disk tests performed on W-DLC run against 319 Al showed a low COF of 0.2 at 25 °C, whereas between 100 °C and 300 °C, a high average steady-state COF of 0.60 was recorded. At 400 °C the COF decreased to 0.18, and this reduction in COF continued with increasing the temperature to 500 °C (0.12). It was observed that the formation of transferred material layers on 319Al was the governing mechanism for the low COF. The Raman analysis revealed that at room temperature these layers were rich in carbon, whereas at 400 °C the transfer layers consisted of tungsten oxide. According to transmission electron microscopy (TEM), and X-Ray photoelectron spectroscopy (XPS), of the coatings tested at 400 °C and 500 °C a thin (20 nm) tungsten oxide layer was formed on their top surface. This in turn led to the formation of tungsten oxide rich transfer layers that is believed to reduce the COF at temperatures above 400 °C.     

Effect of metal ion implantation on thermal instability of diamond-like carbon films

In this work, molybdenum and tungsten ions were implanted onto the DLC films deposited by filtered cathodic vacuum arc. We investigated the effects of ion species and doses on carbon related bonding property such as the ratio of sp³ carbon to sp² phase, the chemical composition and tribological properties of the DLC films in the range of 200 to 600 °C. The oxidation starting temperature decreased with an increasing ion dose and ion mass owing to higher sp² carbon fraction. Oxidation of the implanted-metal element, however, keeps the DLC film from carbon sublimation by oxidation, offering stable tribological characteristics by covering it with a metal oxide layer at the high temperature.     

Corrosion performance and mechanical stability of 316L/DLC coating system: Role of interlayers

In the present work, the corrosion performance and mechanical stability of diamond-like carbon (DLC) coatings were investigated in the context of their biomedical applications. DLC was prepared by radio-frequency (RF) plasma-enhanced chemical vapor deposition (PECVD) onto medical grade 316L stainless steel. Interlayers of amorphous hydrogenated silicon-based materials such as a-Si, a-SiN_x, a-SiC_x, and a-SiC_xN_y, and a nitrided interlayer, were studied in order to optimize its adhesion strength. Potentiodynamic polarization tests were performed to evaluate the corrosion performance of the 316L/DLC coating system. Electrochemical impedance spectroscopy (EIS) was used to determine the stability of the coating system during long-term tests of exposure to a simulated body fluid solution. The evolution of EIS spectra was monitored during two years of immersion in Ringer's solution. In addition to providing the best adhesion, the a-SiN_x interlayer was found to significantly improve the corrosion resistance of the DLC system since it is highly impervious to the liquid. This is demonstrated by a two-order of magnitude improvement in the corrosion current density compared to the DLC with the nitrided interlayer. The a-SiN_x interlayer substantially enhances the mechanical stability of the DLC coating system in the simulated body fluid environment, indicated by a slight reduction (less than 20%) in the adhesion strength and fivefold increase in the charge transfer resistance after two years of immersion. Moreover, Si-doped DLC coatings show improved corrosion barrier properties, due to the formation of a passive silicon oxide film at the electrode/electrolyte interface.