Si-containing Diamond-like Carbon Research Articles

Effect of tribologically-induced changes in surface termination of silicon-containing diamond-like carbon coatings on the resistance to biomolecule adsorption

Silicon-containing diamond-like carbon (DLC) is a class of thin-film materials with excellent mechanical properties, high thermal stability, and good tribological performance over a wide range of environmental conditions. While non-alloyed/non-doped DLCs also exhibit good biocompatibility and bioinertness, our understanding of the effect of silicon in DLCs on biomolecules/DLC interactions is still elusive. Here, we evaluated the structural, mechanical, and tribological properties of Si-containing DLC coatings with silicon content fraction of 11% and 16%. Tribological tests, performed by sliding a stainless steel pin on the coatings in water, indicated a low friction response (steady-state coefficient of friction <0.11), while quartz crystal microbalance experiments indicated no adsorption of a model biomolecule, namely adenosine triphosphate (ATP), on Si-containing DLCs. Near-edge X-ray absorption fine structure spectromicroscopy analyses performed after tribological experiments provided evidence for an increase in the fraction of silanol surface terminal groups formed in the worn region upon sliding in water without any significant sp3-to-sp2 rehybridization of carbon atoms. The fraction of surface hydroxyl groups in the worn region increases with the silicon content in Si-containing DLC, which leads to a decrease in friction. This tribologically-induced change in surface termination did not lead to the adsorption of ATP upon incubation of tribotested samples in ATP solutions for several hours. These findings open the path for the use of Si-containing DLC in applications requiring good tribological properties in aqueous solution and an excellent resistance to biomolecule surface adsorption that is maintained even after tribologically-induced variations in surface termination.

Mass Spectrometric Study on Ions and Radicals in Tetramethylsilane Plasma for Si-containing Diamond-Like Carbon Coating

Mass Spectrometric Study on Ions and Radicals in Tetramethylsilane Plasma for Si-containing Diamond-Like Carbon Coating

Si-containing diamond-like carbon coatings to improve the wear resistance of solid ceramic end mills

The study’s purpose is to determine the rational Si content in the DLC-Si external layer of (CrAlSi)N/DLC-Si coatings deposited on α/β-SiAlON + TiN ceramics. The influence of Si content on physical and mechanical properties of coatings such as microhardness, modulus of elasticity, and friction coefficient, and wear resistance of solid ceramic end mills in machining nickel alloy NiCr20TiAl is determined.

Development of DLC-Coated Solid SiAlON/TiN Ceramic End Mills for Nickel Alloy Machining: Problems and Prospects

The study is devoted to the development and testing of technological principles for the manufacture of solid end mills from ceramics based on a powder composition of α-SiAlON, β-SiAlON, and TiN additives, including spark plasma sintering powder composition, diamond sharpening of sintered ceramic blanks for shaping the cutting part of mills and deposition of anti-friction Si-containing diamond-like carbon (DLC) coatings in the final stage. A rational relationship between the components of the powder composition at spark plasma sintering was established. The influence of optimum temperature, which is the most critical sintering parameter, on ceramic samples’ basic physical and mechanical properties was investigated. DLC coatings’ role in changing the surface properties of ceramics based on SiAlON, such as microrelief, friction coefficient, et cetera, was studied. A comparative analysis of the efficiency of two tool options, such as developed samples of experimental mills made of SiAlON/TiN and commercial samples ceramic mills based on SiAlON, doped with stabilizing additives containing Yb when processing nickel alloys (NiCr20TiAl alloy was used as an example). DLC coatings’ contribution to the quantitative indicators of the durability of ceramic mills and the surface quality of machined products made of nickel alloy is shown.

Uniformity of Si-containing diamond-like carbon films deposited at different positions by mesh hollow cathode discharge

Diamond-like carbon (DLC) films exhibit exceptional tribological characteristics, but their practical application requires the development of scalable methods for uniform film deposition. For large-area DLC films, the properties of films deposited at different positions may be different, it is necessary to study the uniformity of DLC films. In this study, Si-containing DLC (Si-DLC) films were deposited by mesh hollow cathode discharge. The uniformity of the microstructure and mechanical properties of the DLC films deposited in the x, y, and z directions were studied. The Si-DLC films were characterized by scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and nanoindentation tests. The wear resistance was evaluated using a ball-on-disk tester and the wear scars were studied using a metalloscope. The thickness distributions of the Si-DLC films deposited in the x, y, and z directions exhibited thick middles and thin edges. However, the thickness distributions of the films deposited in the x and y directions were more uniform than the films deposited in the z direction. Compared with the films deposited in the z direction, the intensity ratio of the D and G peaks in the Raman spectra, the ratio of sp3 and sp2 carbons, the shift of the G peak position, and the full width at half maximum of the G peak of the films deposited in the x and y directions varied in a smaller range. Furthermore, the hardness, friction coefficient, and tribological performance of the films deposited in the x and y directions showed better uniformity than those of the films deposited in the z direction. Overall, mesh hollow cathode discharge provides good uniformity for films deposited in the x and y directions, but improved film deposition in the z direction is required. The study of the uniformity of Si-DLC films deposited at different positions by mesh hollow cathode discharge is benefit for understanding the working rule of mesh hollow cathode discharge, so as to prepare larger area and more uniform DLC film.

Tribological behavior of unlubricated sliding between a steel ball and Si-DLC deposited by ultra-high-speed coating employing an MVP method

Recently, with increasing demands for energy saving via friction reduction and lifetime extension via wear reduction, the applications of diamond-like carbon (DLC) are spreading gradually and steadily. It should be noted that the typical coating speed of DLC with such a conventional plasma chemical vapor deposition (CVD) is not very high, ~1μm/h, due to the employment of low-density plasma. In our previous work, we proposed that the plasma CVD with MVP (Microwave-sheath Voltage combination Plasma) is capable of coating a Si-containing DLC (Si-DLC) film at larger than 100μm/h. In this work, for achieving the design principle of Si-DLC by MVP, we studied the effects of process gas, which is a mixture of TMS, Ar, and one hydrocarbon gas, on the relationship between the film structure and the mechanical properties of Si-DLC films prepared by MVP. Si-DLC films were deposited by MVP with a hydrocarbon gas, CH4 or C2H2, where the TMS (tetramethylsilane)/hydrocarbon gas ratio was changed. The structure of DLC was estimated by Raman spectroscopy. The atomic composition of the films was evaluated by XPS for C, O, and Si, and RBS-ERDA for H/C. Friction tests were conducted using a ball-on-disk apparatus under dry condition.Si concentration in the films increased linearly with an increasing TMS/hydrocarbon ratio for both hydrocarbon gases, being the determining factor for the ID/IG ratio and SiC concentration of Si-DLC. In other words, we can determine the ID/IG ratio and SiC bond concentration in Si-DLC by controlling the TMS/hydrocarbon ratio. In addition, much higher deposition speed and higher H concentration are obtained by MVP using C2H2 than CH4. These findings, or the effect of gas source on the film structure of Si-DLC by MVP, would be an important design principle in designing Si-DLC for desired film structure and hardness, and better tribological performance.

Long-term thermal stability of Si-containing diamond-like carbon films prepared by plasma source ion implantation

The long-term stability of silicon-containing diamond-like carbon films was investigated. The samples were prepared by plasma source ion implantation with a mixture of tetramethylsilane (TMS) and acetylene (C2H2) using negative high voltage pulses. The film composition was changed by varying the flow rates of the TMS and C2H2 gases, resulting in a Si content from 0 to 44 at.%. After deposition the films were annealed at temperatures from 523 K to 773 K for 168 h in ambient air. The effect of the Si content on the structure, the mechanical and tribological properties of the DLC films was investigated. A silicon oxide layer is produced on the surface of the film which improves the thermal stability. Mechanical and friction characteristics of the Si-DLC were not much affected by the long-term thermal annealing if the temperature was kept below 573 K.

S1160405 成膜時残留ガスがPECVD-DLCのしゅう動特性に及ぼす影響

DLC (Diamond-Like Carbon) has excellent mechanical properties such as high hardness, low friction and high wear resistance. One of the main coating methods of DLC is PECVD, which enables ultra-high-speed coating at larger than 100 μm/h if combined with an appropriate high-density plasma represented by MVP (Microwave sheath-Voltage combination Plasma). For practically achieving high-throughput in DLC coating by MVP, not only coating time but also evacuation time should be shortened. If vacuum condition including not negligible amount of residual gases is allowed during coating, it leads to shorten the evacuation time before coating. Thus, in this research, in order to understand the effect of a residual gas, or water, during coating on Si-containing DLC (Si-DLC) deposited, we compared 3 Si-DLCs deposited under different 3 vacuum conditions; 1) evacuated down to 4×10^<-4> Pa with turbo-molecular pump, 2) evacuated down to 1 Pa only with rotary pump, and 3) water was added to the vacuum condition. Deposition of 3 Si-DLCs under the 3 vacuum conditions was conducted with not only MVP but also conventional DC plasma for comparison. As a result, it was observed in DC that 1) hardness decreased from 18.6 GPa to 10.8 GPa, 2) ID/IG increased from 0.25 to 0.41, 3) Si/C increased from 0.37 to 0.76, and 4) O/C increased from 0.02 to 0.42, with increasing of residual water during coating. Similar results were obtained in MVP, however, the increased/decreased ranges of the 4 parameters were decreased; in other words; the effect of residual water was suppressed by employing MVP instead of DC plasma. In spite of thus changes in films, friction coefficient in PAO oil was almost the same value from 0.08 to 0.1 in all specimens.

Comprehensive Classification of Near-Edge X-ray Absorption Fine Structure Spectra of Si-Containing Diamond-Like Carbon Thin Films

Structural analysis by the measurement of carbon K-edge near-edge X-ray absorption fine structure (NEXAFS) using synchrotron radiation was performed on 23 types of silicon-containing diamond-like carbon (Si-DLC) film fabricated by various synthesis methods. In addition, elementary composition in the Si-DLC films was determined by the combination of Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) using an electrostatic accelerator. In the C K-edge NEXAFS spectra of Si-DLC films, the σ* band shrunk and shifted to the lower-energy side, and the π* peak broadened with increasing silicon content in the Si-DLC film. The observed NEXAFS spectra of Si-DLC films were classified into four types.

Sliding velocity dependency of the friction coefficient of Si-containing diamond-like carbon film under oil lubricated condition

In this study we investigated the sliding velocity dependency of the coefficient of friction for a Si-containing diamond-like carbon (DLC-Si) film in an automatic transmission fluid (ATF) under a wide range of contact pressures. The DLC-Si film and a nitrided steel with a surface roughness, Rz JIS, of around 3.0 μm were used as disk specimens. A high-carbon chromium steel (JIS-SUJ2) bearing ball was used as a ball specimen. Friction tests were conducted using a ball-on-disk friction apparatus under a wide range of sliding velocites (0.1–2.0 m/s) and contact pressures ( P max: 0.42–3.61 GPa) in ATF. The friction coefficients for the nitrided steel had a tendency to decrease with an increase in sliding veloicity under all the contact pressure conditions; however, the friction coefficients for the DLC-Si film were stable with respect to sliding velocities under all the contatct pressures. These results indicate that the DLC-Si film suppresses the stick-slip motion during sliding againt steel in ATF, which is a desired frictional characteristic for the electromagnetic clutch disks used under lubrication. Furthermore, the DLC-Si film showed a higher wear resistance and lower aggression on the steel ball specimen than the nitrided steel. There were less hydrodynamic effects on the friction coefficient for the DLC-Si film possibly due to maintenance of the initial surface roughness and its poorer wettability with the fluid. X-ray photoelectron spectroscopy (XPS) analysis of the sliding surfaces revealed that the adsorption film derived from the succinimide on the sliding surfaces of the DLC-Si film and the mating steel ball also contributed to the sufficient and less sliding-velocity-dependant friction coefficients.

Effect of increasing hardness on Si-containing diamond-like carbon film during tribo-test

In this study, silicon-DLC film has been especially treated by plasma-enhanced chemical vapor deposition (PECVD) process at 500 °C in the same chamber without compound-layer for enhancement of hardness and adhesion. The effects of different levels of silicon content on the silicon-containing DLC films were tested in air condition at room temperature with relative humidity using a ball-on-disk tribometer. After the wear test, Raman spectrum analysis on the tested surface of silicon DLC showed the changed structure on the surface. Especially, it has shown the increasing hardness value in proportional to increase TMS gas rate after wear test. At the same time, it was shown that I D/ I G values increased higher G-peak values and positions on wear track of silicon-containing DLC surfaces. Therefore, the structure of the coated DLC surface changed between the wear-tested surface and the original surface. High silicon content DLC showed increased I G value with suddenly increased I D/ I G value after the wear test.

Tribological properties of Si-containing diamond-like carbon film under ATF lubricated condition

Recent years have seen a rise in social needs regarding safety and the environment, and this has placed increasing importance on product development for automotive parts that leads to smaller sizes, higher capacity, and lower costs. Diamond-like carbon (DLC) coating technology is being focused on as an effective solution to such issues. This paper reports on the tribological properties of a Si-containing diamond-like carbon film under an automatic transmission fluid (ATF) lubricated condition, which dramatically improves the performance of an electromagnetic clutch used in electronically controlled All-wheel-drive (AWD) coupling. The Si-containing DLC film maintains its rough sliding surface while simultaneously exhibiting extremely low aggression against mating materials. Thus, the boundary lubrication state of the initial friction stage is maintained, while also displaying a positive μ– v slope with excellent anti-shudder performance and a satisfactory friction coefficient as demanded by the drive train. Based on time-of-flight secondary ion mass spectrometry (TOF-SIMS) of sliding surfaces, it was speculated that the mechanism behind the good tribological properties of a sliding material coated with Si-containing DLC film under fluid lubrication are in part connected to the material properties of the DLC-Si film and an adsorbate such as a succinimide-based dispersant.

Evaluation of DLC-Si Film Damage due to Friction under ATF Lubricated Condition

Diamond-like carbon (DLC) coating technology has been receiving increasing attention in recent years for its application to automotive sliding parts. As it is critical to evaluate the adhesion strength between a film and a substrate for assessment of the reliability of DLC films, a practical method to assess film damage under repeated sliding motions is needed. This research clarified the conditions under which damage is generated on Si-containing DLC films by analyzing damage modes such as wear, spalling, and cracking of the films under an automatic transmission fluid (ATF) lubrication condition and repeated sliding friction. The research also confirmed the effectiveness of the evaluation method. The test results indicated that the Si-containing DLC film has the highest reliability compared to the other types of films tested using the same test method.

Characteristics and tribological properties in water of Si-DLC coatings

Si-containing diamond-like carbon (Si-DLC) coatings with a Si content ranging between 0 (DLC) and 10 at.% were deposited by thermal electron excited plasma CVD method, and their characteristics and the tribological properties in water environment were investigated. The results showed that doped Si had little effect on the hardness and Young's modulus of the coatings. Increasing Si content reduced the friction and the wear of the mated ball, although the wear of the coatings increased. The wear of the counter ball occurred mainly in the early stage of rubbing. The Raman and XPS analysis revealed that the tribochemical reaction of Si-DLC coating occurred in water, and SiO x(OH) y gel was formed on the mated ball surface. It is considered that the tribochemical reaction is also responsible for the tribological properties of the Si-DLC coating and the counter ball, and the reaction may be accelerated by increasing the Si content. Failure-resistant capability is strongly governed by the characteristics of the coating, and can be improved by doping Si. There is an optimum Si content for increasing the failure-resistant capability and it was 6.6 at.% in this work.

Structural analysis of Si-containing diamond-like carbon

We have investigated the structures of silicon-containing diamond-like carbon (DLC-Si) films with various silicon contents. The DLC-Si films were deposited on steel substrates at 773 K by direct current plasma-enhanced chemical vapour deposition (DC-PECVD). The Si content in the films was controlled in the range of 4–28 at.% by adjusting the ratio of methane (CH 4) and tetramethylsilane (Si(CH 3) 4) as the precursor gases. Several typical spectroscopic measurements provided the film information: elastic recoil detection analysis (ERDA), hydrogen content; electron probe microanalysis (EPMA), carbon and silicon content; Fourier transform infrared (FT-IR), chemical bonding; and Raman scattering, networking due to the sp 2 carbon (Csp 2). In addition, solid-state 13C nuclear magnetic resonance (NMR) measurements were able to quantify the two types of hybridized carbon atoms, Csp 2 and Csp 3. The cross-polarization technique provided more precise environments for the carbon atoms bonded to hydrogen atoms, suggesting that the environment of Csp 2 is quite different depending on the silicon content. The 29Si NMR measurement was also carried out to provide the circumstance of the four-coordinate Si atoms. In addition, the mechanical property of the films (hardness) was evaluated by the nanoindentation method in order to compare it with the film structure.

Friction and Wear of Various DLC Films in Water and Air Environments

Three types of diamond-like carbon (DLC) films, pure DLC, F-containing DLC, and a Si-containing DLC film, were deposited on a WC–Co substrate by a plasma-enhanced CVD technique. Friction and wear properties were determined using a ball-on-plate type reciprocating friction tester in water, comparing the water results to those in ambient air. The friction coefficient of DLC and F–DLC films in water was considerably lower than that in air. With Si–DLC, the friction was almost the same level in both water and air, and was less than 0.1. The specific wear rate of films in water was much smaller than that in air and varied around the low level of 10−8 mm3/Nm in water, The mating ball wear was also less than 10−8 mm3/Nm. With DLC and F–DLC films, the transferred amount of material on the friction surface of a mating ball was larger in a water environment than that in air. With a Si–DLC film, the difference in the transferred amount when exposed to either the water or air environment was negligible.

Internal stress reduction by incorporation of silicon in diamond-like carbon films

Si-containing diamond-like carbon (DLC) films deposited using CH 4+SiH 4 by an electron beam excited plasma (EBEP) CVD system were investigated for internal stress, dynamic hardness and structural properties. As the SiH 4 flow ratio was varied from 0 to 36.4%, the internal compressive stress linearly decreased from 2.5 to 1.0 GPa while the dynamic hardness remained nearly constant. From the correlations between the internal stress and the structural properties, it is suggested that SiH bonds formed by silicon incorporation can play the role of reducing the compressive stress. Also, the formation of SiH bonds is accompanied by a reduction in unbound hydrogen, which may cause the compressive stress reduction.

Tribological characteristics of Si-containing diamond-like carbon films under oil-lubrication

Tribological behaviors of Si-containing diamond-like carbon (DLC) and DLC films deposited by an electron beam excited plasma (EBEP)–CVD system were investigated for applications to mechanical components. The ball-on-disc tests against bearing steel with oil-lubrication were performed for the Si-containing DLC and the DLC-coated carburized Cr–Mo steel discs. Two different oils with and without zinc dialkyldithiophosphate (Zn-DTP) additives were used as lubricants. The Si-containing DLC films deposited at SiH 4 flow ratios of 2.8 and 12.5% showed low coefficients of friction and wear resistance when lubricated in the oil with additives. The results from X-ray photoelectron spectroscopy (XPS) analysis indicated that it was due to the effect of formation of a boundary lubrication film including ZnO, ZnS, FePO 4, FeS and FeS 2 compounds on the lubricated contact region.

The effects of Si incorporation on the electrochemical and nanomechanical properties of DLC thin films

Silicon-doped diamond-like carbon (DLC) films with a Si content of up to 20.2 at.% were grown on Al2O3–TiC substrate by plasma-enhanced chemical vapour deposition. The influence of Si addition on the bonding structure, nanomechanical and corrosion behaviour of the DLC films was investigated by Raman and X-ray photoelectron (XPS) spectroscopy, nano-indentation, potentiodynamic and electrochemical impedance spectroscopy (EIS). Silicon addition promoted the formation of sp3 bonding and reduced the hardness. The deterioration of the nanomechanical properties is related to the increased hydrogen content in the films, leading to the formation of a polymeric sp3 CHn structure. The high hydrogen concentration in the Si-containing DLC samples was established by the increased Raman background slope. The EIS were analysed within the context of an equivalent circuit, which incorporated two time constants representing the DLC coating and the solution/Al2O3–TiC interface. Introduction of Si in the DLC led to significant improvements in the corrosion resistance of DLC, as revealed by increase in the charge transfer resistance and reduction in the anodic current of the polarisation curves. Films with a thickness of 20 nm remained intact after the polarisation scan when the Si concentration was increased above 11.8 at.%. The improvements in corrosion resistance are related to the formation of a passivation layer, which fills the pores present in the films.

Comparative study of the tribological moisture sensitivity of Si-free and Si-containing diamond-like carbon films

Diamond-like carbon (DLC) has become one of the most widely used wear-protective low-friction coatings due to its outstanding mechanical and tribological properties. However, a major disadvantage of DLC is the deterioration of its lubricating properties at high relative humidity, limiting its use in certain tribological applications for which ambient humidity may be subject to significant variations. The addition of small amounts of Si to DLC has been reported as an effective method for reducing friction coefficient at high humidities. In this paper we have characterised the tribological behaviour of a reference DLC coating prepared using a PACVD technique in the relative humidity range 5–85%, sliding against steel, alumina and DLC counterfaces, and directly compared this to similar coatings alloyed with small amounts of Si (<6 at.%). Commercially available DLC coatings were also studied for comparison. Our results confirm that the addition of Si can significantly improve the humidity sensitivity of a given coating and show that by adjusting the Si content, the friction behaviour can be tailored to suit the expected humidity operating range or counterface materials. However, the addition of Si also produces a reduction in coating wear resistance by a factor as high as 4. Results indicate that the nature of the counterface is an important factor for frictional behaviour, and the DLC/steel friction pair was shown to be particularly sensitive to the presence of Si, displaying a threefold reduction in friction coefficient at high relative humidities and an inversion in humidity sensitivity (i.e. higher friction coefficients under dry conditions).