Flexible diamond-like carbon films on rubber: On the origin of self-acting segmentation and film flexibility

This paper reports an experimental approach to deposit flexible diamond-like carbon (DLC) films on hydrogenated nitrile butadiene rubber (HNBR) with plasma-assisted chemical vapor deposition and an analytical model to describe the self-segmentation mechanism of the DLC films. By making use of the substantial thermal expansion mismatch between the DLC films and the rubber substrate, a dense network of cracks forms in the DLC films and contributes to flexibility. The size of the microsegments can be controlled by tuning the temperature variation of the substrate during deposition through varying the substrate bias voltage. The formation mechanism of the crack network and its effect on the flexibility of DLC films coated on rubber are presented.     

Friction behaviour of diamond-like carbon films with varying mechanical properties

Diamond-like carbon (DLC) films deposited on silicon wafer with varying film thickness were investigated for their micro-scale friction behaviour. Films with three different thicknesses, namely 100 nm, 500 nm and 1000 nm, deposited by a radio frequency plasma-assisted chemical vapor deposition method on Si (100) wafer, were used as the test samples. The elastic modulus of the DLC samples increased with their film thickness. The micro-scale friction tests were conducted in a ball-on-flat type micro-tribotester, using soda lime glass balls with different radii (0.25 mm, 0.5 mm and 1 mm), and with varying applied normal load (load range: 1500 μN to 4800 μN). Results showed that the friction force increased with applied normal load, whereas with respect to the ball size, two different trends were observed. In the case of 100 nm thick sample, friction increased with the ball size at any given normal load, while for 500 nm and 1000 nm thick samples, friction had an inverse relation with the ball size at all applied normal loads. The friction behaviour in the case of the 100 nm thick film was adhesive in nature, whereas for the thicker films plowing was dominant. The friction behaviour of the test samples with the ball size, which was distinctly different, was discussed in terms of the contact area, influenced by their mechanical property, namely, the elastic modulus.     

Fracture mechanics of diamond-like carbon (DLC) films coated on flexible polymer substrates

Diamond-like carbon (DLC) films have been widely used for many industrial applications due to their outstanding physical properties such as high hardness, wear resistance and biological compatibility. The DLC films coated on polymer substrates have also been extensively used and investigated because recently, quite a few applications for the use of these polymer-DLC composites have been proposed and actively discussed. The applications range from DLC-coated Polyethylene Terephthalate film (DLC-PET), through DLC-coated Polycarbonate (DLC-PC) to other DLC-coated rubbers. In this work, thin DLC films coated on several polymer substrates possessing different chemical structures and Young's moduli were introduced. The DLC-polymer films were stretched to different strains and the extended surface was investigated by optical microscopy and scanning electron microscopy (SEM) to study the fracture mechanics of the DLC-coated polymer films. Horizontally and vertically aligned micro-cracks and micro-buckling were observed, constructing periodic lattice-like fracture patterns on the surface of the extended DLC-polymer films. It was found that the lattice patterns were significantly influenced by Young's moduli of polymer substrates and DLC films, and that the patterns were also dependent on the adhesion between the DLC films and the polymers.     

Adhesion improvement of hydrogenated diamond-like carbon thin films by pre-deposition plasma treatment of rubber substrate

For reduction of friction and enhancement of wear resistance of dynamic rubber seals, thin films of hydrogenated diamond-like carbon (DLC) have been deposited on hydrogenated nitrile butadiene rubber (HNBR) via magnetron-enhanced plasma chemical vapor deposition (ME-PCVD). Pre-deposition plasma treatment of HNBR substrate is proved to be crucial for the improvement of film performance due to enhanced interfacial adhesion. The columnar structure and the crack network formed during deposition enhance the flexibility of DLC thin films and exhibit strain tolerance up to 5%. Below 50% stretch strain and after unloading, thin DLC films of ∼ 300 nm thickness still adhere on the rubber substrates and no spallation or delamination is observed. The thin DLC film deposited on Ar-plasma pre-treated rubber at − 400 V substrate bias potential exhibits a very low coefficient of friction of 0.175 (compared to > 1 of uncoated HNBR rubber). After tribotests even under high normal load of 3 N, almost no wear can be seen on the films. Such tribological property is even better than that of 1 µm thick DLC or Me-DLC coated rubbers.     

Deposition of diamond-like films of hydrogenized carbon

Diamond-like films of hydrogenized carbon on metal substrates were produced by deposition from methane activated by capacitive electric discharge (AD) within the frequency range of 5–250 Hz and with a relative pulse duration of the charge of 1.5–17. Variations in the charge parameters (frequency, relative pulse duration, current density, methane pressure, the value of gas flow), substrate temperature, and geometry of the vacuum chamber affect the deposition rate, properties, and structures of films within a wide range. Diamondlike films of hydrogenized carbon represented nanocomposite material. The size of sp ² clusters was 5–6 nm, whereas the sp ³/sp ² ratio of carbon and the content of bound hydrogen decreased with increasing substrate temperature and current density and decreasing methane pressure.     

The development and application of diamond-like carbon films

A considerable amount of research has been conducted over the years on diamond-like carbon films. Due to its mechanical, optical, thermal, electrical, tribological, and biomedical properties, it has shown tremendous potential for use in military and commercial applications. R. Jethanandani earned his B.S. in metallurgical engineering at Regional Engineering College in 1993. He is a graduate student at the University of Cincinnati.     

Pin-on-disc testing of PE-CVD diamond-like carbon coatings on tool steel substrates

The present study deals with the tribological behaviour and the wear mechanisms of 2-μm thick diamond-like carbon coatings. The examined coatings were deposited by plasma-enhanced chemical vapour deposition (PE-CVD) on three tool steel substrates, of different hardnesses. Tribological studies against alumina were performed using a pin-on-disc apparatus under various normal loads (2–20 N) and sliding speeds (0.1–0.3 m s⁻¹), while the relative humidity of the environment was kept constant, equal to 25%. The influence of the testing parameters (normal load and sliding speed) and the mechanical properties of the substrate on the wear lifetime of the coatings was determined and the involving wear mechanisms were identified. It was found that both the sliding conditions and the hardness of the substrate affect strongly the wear rate and the wear lifetime, but have no significant influence on the value of the friction coefficient, which was found to be lower than 0.15 for all the testing parameters.     

Structural and nano-mechanical properties of nanostructured diamond-like carbon thin films

The effect of self bias on structural and nano-mechanical properties of nanostructured diamond-like carbon (ns-DLC) thin films is explored. These films are grown at different negative self biases ranging from ?100 V to ?200 V using radio frequency (13.56 MHz) plasma enhanced chemical vapor deposition technique. The generation of nanostructured morphology at room temperature in these films is confirmed by scanning electron microscopy, whereas change in microstructure produced by varying the self biases is confirmed by Raman analysis. These ns-DLC films exhibit very high hardness, which varied from 16 GPa to 31 GPa. With the help of load versus displacement curves, various other important nano-mechanical parameters such as elastic modulus, elastic recovery etc are also estimated. The nano-mechanical properties are further correlated with the Raman and SEM analyses. Owing to their versatile nano-mechanical properties, these ns-DLC films may find application as hard and protective coatings.     

Thermal stability of diamond-like carbon films with added silicon

Diamond-like carbon (DLC) films with added silicon content from 0 to 19.2 at.% were deposited using r.f. PECVD (radio frequency plasma enhanced chemical vapor deposition). Fourier transform IR (FTIR) spectrometry, Raman spectrometry and X-ray photoelectron spectrometry (XPS) were used to determine the structural change of the annealed DLC films in ambient air. By increasing the annealing temperature the CH_n and Si–H groups in the FTIR spectra decrease because of hydrogen evolution, whereas the intensities of CO and Si–O peaks increase owing to oxidation. From Raman spectra, the integrated intensity ratio I_D/I_G of the pure DLC films and the silicon-doped films increases at 300 and 400 °C, respectively, whereas the observable shoulder of the D band occurs at 400 and 500 °C, respectively, which indicates that the addition of silicon improves the thermal stability of DLC films. Using XPS analysis, a surface reaction for the annealed films is investigated.     

类金刚石膜在模具中的应用

阐述了类金刚石膜的结构和力学性能,介绍了类金刚石膜在各种模具上的应用。类金刚石膜能有效提高模具使用寿命,降低模具使用成本。分析了目前类金刚石膜在模具上的应用和推广中存在的障碍。     

Effect of metallic interfacial layers on the properties of diamond-like carbon thin films

Diamond like carbon (DLC) thin films with metallic interfacial layers of aluminum and nickel-chromium (Al and Ni-Cr) were grown using a low cost hybrid technique involving a resistive heating thermal evaporator and radio frequency plasma enhanced chemical vapor deposition techniques. Stress, hardness, elastic modulus, bonding, phase, and electrical conductivity of these films were investigated. Introduction of interfacial Al and Ni-Cr layers in DLC led to drastic improvement of its conductivity along with a significant reduction in residual stress but with some reduction of hardness and the elastic modulus. The structural and surface properties of thin films were studied using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy techniques.     

中频对靶磁控溅射制备含铬类金刚石薄膜

利用新型中频对靶磁控溅射在硅和M2高速钢基体上沉积了一系列无氢含铬类金刚石膜.考察了类金刚石膜的表面形貌、显微结构、硬度、结合力和摩擦磨损性能.结果表明：合成的类金刚石薄膜具有优良的综合性能,硬度为30-46GPa、结合力Lc达50-65N、大气环境下摩擦系数约为0.1.     

Mechanical properties and antibacterial activity of copper doped diamond-like carbon films

A hydrogenated diamond-like carbon (a-C:H) with a copper dopant (Cu/a-C:H) was deposited on glass substrates using a combined radio-frequency plasma and magnetron sputtering deposition process under various Ar/CH₄ gas mixtures. The effects of the Cu content on the structure and properties of the a-C:H matrix were investigated using X-ray diffraction (XRD), Raman transmission electron microscopy, high-resolution transmission electron microscopy (TEM), and nano-indentation. The bacterial activity of a Cu/a-C:H film was evaluated with Escherichia coli (E. coli). TEM images and XRD spectra demonstrated that composite films containing copper nanoparticles embedded in the a-C:H were deposited on the glass substrates. The Raman spectra showed the structure of a-C:H film was substantially changed by the incorporation of Cu. The Cu/a-C:H films offered superior antibacterial activity against E. coli indicating that they could be suitable for surface coatings in cardiovascular applications.     

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.     

不同沉积气压对MPCVD法制备的类金刚石膜性能的影响

采用微波等离子体化学气相沉积法,以玻璃作为基底,通入CH4和H2,在改变沉积气压的条件下研究类金刚石(DLC)薄膜的生长情况。再利用紫外–可见–近红外分光光度计、激光Raman光谱仪和场发射扫描电子显微镜分别对制备出的DLC薄膜的光透过率、质量以及表面形貌进行表征与分析。结果表明:随着沉积气压的逐渐增大,可见光范围内的光透过率随之增大,类金刚石粒径逐渐减小,膜表面的团聚体尺寸逐渐减小、平整度提高。     

Thickness dependence of the structure of diamond-like carbon films by Raman spectroscopy

The thickness dependence on structure of Diamond-like carbon films of a-C:H deposited by ECR-CVD and ta-C by FCVA has been studied by visible and UV Raman spectroscopy. The results show that the evolution of structure as a function of the thickness for a-C:H films contains two stages: when thickness is less than 50 Å, the film contains less sp³ sites and not continuous; and when thickness is up to 50 Å, the film contains more sp³ sites and become continuous. However, for ta-C films, it includes three stages. In the first stage of thickness lower than 20 Å, the film is not continuous, and also contains less sp³. In the second stage of thickness between 20 Å and 50 Å, the sp³ site abruptly shifts a higher value in 20 Å and then keeps stable. In the third stage of thickness over 50 Å, the sp³ site has a little increase and then almost not changed. Thus, the fundamental limitation thickness in using DLC as an ultrathin overcoat for ta-C films is 20 Å (> 10 Å), and for a-C:H films is 50 Å. The implications of result on the mechanisms proposed for the film growth mode were also discussed.     

Microstructure analysis of MoS2 deposited on diamond-like carbon films for wear improvement

A compound solid lubricating film containing a MoS₂ top layer deposited on DLC interlayer by UBM sputtering technique was investigated for its tribological applications in humid environments. TEM, Raman and XRD analysis revealed the amorphous nature of the MoS₂ film which contains only short-range order in its lattice structure. The as-deposited MoS₂ compound films showed well-bonded interfaces. The MoS₂, however, is very susceptible to humidity and oxidation, which resulted in higher friction coefficients and lower wear life. A friction coefficient of 0.05 was measured between steel balls and MoS₂ in atmosphere of 90% RH. Excessive abrasive wear was identified, as a result of the wear debris and the oxidized transfer layers between MoS₂ and its counterpart. The inclusion of a supportive DLC interlayer has effectively improved the wear behavior of MoS₂ films under various loading conditions. The overall wear mechanism of MoS₂ was complicated due to its oxidation problem which needs to be resolved for successful usage of MoS₂ in humid environments.     

非平衡磁控溅射Ti掺杂类金刚石薄膜的基本特性

利用非平衡磁控溅射技术在镜面抛光的SCM415渗碳淬火钢基片上沉积了无掺杂类金刚石(DIE)薄膜和不同含量Ti掺杂类金刚石(Ti-DIE)薄膜.利用AFM、SEM、TEM对薄膜的微观结构与形貌进行了观察,利用纳米硬度计、摩擦磨损试验仪及纳米划痕仪测试了薄膜的显微硬度、摩擦系数及薄基结合强度.结果表明:随着Ti的掺杂,薄膜硬度先迅速降低,然后保持不变,在Ti含量为25at%时薄膜硬度出现回升,膜基结合强度随Ti的掺杂呈单调增强趋势.与无掺杂类金刚石薄膜相比,掺杂Ti后薄膜表面微观凸凹增多,摩擦系数增大.对于Ti-DIE薄膜来说,随着Ti掺杂量的增加,摩擦系数出现减小的趋势.其原因在于Ti掺杂量的增加使Ti-DLC薄膜变得更加致密,同时Ti的掺杂还有利于弥补基体表面的凸凹缺陷,使薄膜变得更平滑.     

Tribological behaviors of hydrogenated diamond-like carbon films in different testing environments

Hydrogenated diamond-like carbon (DLC) films were deposited on Si substrate using plasma enhanced chemical vapor deposition(PECVD) technique with CH4 plus H2 as the feedstock. The tribological properties of the hydrogenated DLC films were measured on a ball-on-disk tribometer in different testing environments (humid air,dry air, dry O2, dry Ar and dry N2 ) sliding against Si3 N4 balls. The friction surfaces of the films and Si3 N4 balls were observed on a scanning electron microscope (SEM) and investigated by X-ray photoelectron spectroscopy (XPS). The results show that the tribological properties of the hydrogenated DLC films are strongly dependent on the testing environments. In dry Ar and dry N2 environments, the hydrogenated DLC films provide a superlow friction coefficient of about 0. 008 -0.01 and excellent wear resistance (wear life of above 56 km). In dry air and dry O2, the friction coefficient is increased to 0. 025 - 0.04 and the wear life is decreased to about 30 km. When sliding in moist air, the friction coefficient of the films is further increased to 0. 08 and the wear life is decreased to 10. 4 km. SEM and XPS analyses show that the tribological behaviors appear to rely on the transferred carbon-rich layer processes on the Si3 N4 balls and on the friction-induced oxidation of the films controlled by the nature of the testing environments.     

Surface modification of 6150 steel substrates for the deposition of thick and adherent diamond-like carbon coatings

Because of the high residual compressive stress normally accompanying the growth of diamond-like carbon (DLC) coatings and the large mismatch in the thermal expansion coefficient between DLC and steel, it is difficult to grow DLC coatings much thicker than 0.25 μm on steels. This paper describes our attempt to overcome this thickness limitation by a sequence of carbonitriding, carburizing and equilibration pre-treatments of the steel surface, followed by DLC coating deposition, all conducted within the same deposition system without breaking vacuum. These pre-treatments resulted in a surface with a graded composition and hardness profile. Such a graded interface is expected to reduce the interfacial energy, decrease thermal mismatch between the coating and the substrate, and thus improve coating adhesion. X-ray diffraction revealed the formation of various hard carbide and nitride phases. Raman spectroscopy showed that the modified steel surface just before DLC deposition exhibits local carbon bonding characteristics similar to DLC. Pulsed dc plasma-enhanced chemical vapor deposition was used to deposit one-micron thick DLC on these steel surfaces. The coating hardness was ~ 18-19 GPa. Its adhesion on the steel substrate was measured by scratch testing and was found to be comparable to thick, adherent DLC coatings deposited by other methods.