Si-DLC Films Research Articles

What Determines the Low-Friction Mechanism of the Silicon-Doped Diamond-like Carbon Film in a Water Environment: An Atomic-Level Understanding.

It is widely acknowledged that doping silicon can significantly enhance the friction performance of diamond-like carbon (DLC) films in a water environment. However, the mechanism of low friction caused by doped silicon is still highly controversial. Therefore, this article compares the interface interaction between DLC and Si-DLC films in a water environment through first-principles calculations of physisorption and chemisorption effects. The results indicate that water molecules are predominantly chemically adsorbed rather than physically adsorbed on the Si-DLC surface. Further study reveals that when OH-termination is formed on the Si-DLC surface, water molecules are predominantly physically adsorbed rather than chemically adsorbed on the Si-DLC hydroxylation surface. Consequently, a more stable hydration layer is formed on the surface through the hydrogen bond network formed by Si-OH groups, ultimately leading to lower friction. Moreover, molecular dynamics simulations further suggest that the lower friction coefficient of Si-DLC films in a water environment may be due to more water molecules at the friction interface and fewer interface covalent bonds. In short, the low-friction coefficient of the Si-DLC film in a water environment may be caused not only by the chemisorption of water molecules on its surface but also by the physisorption of water molecules on the Si-DLC film after surface hydroxylation.

Investigation of the Tribological Properties and Corrosion Resistance of Multilayer Si-DLC Films on the Inner Surfaces of N80 Steel Pipes

In order to solve the problem of the corrosion and wear of N80 metal pipelines exposed to corrosive media and abrasive sand during the development of petroleum resources, the proposed solution involves utilizing HC-PECVD technology to deposit a series of multilayer Si-DLC films with varying thicknesses on the inner surfaces of the N80 steel pipes. This investigation systematically explored the microstructure, mechanical properties, tribological features, and corrosion resistance of the multilayer Si-DLC films. Remarkably, after coating the multilayer (Si-DLC)40 film on the inner wall of the N80 tube, the friction coefficient decreased from 0.7~0.75 to 0.2~3, and the wear rate decreased by two orders of magnitude. In addition, the corrosion current decreased by 50%, and the impedance doubled in a 3.5 wt% NaCl solution saturated with CO2. Thus, the multilayer (Si-DLC)40 film on the inner wall of the N80 tube exhibited superior tribological properties and exceptional corrosion resistance. These findings are anticipated to furnish valuable data and technical insights for mitigating corrosion in N80 steel pipes during petroleum exploitation.

Corrosion behavior of Si-DLC film in simulant solutions containing CO2-H2S-Cl−

Tubing and casing failure due to corrosion is a common problem in the oil industry. The Si-DLC film deposited by plasma enhanced chemical vapor deposition (PECVD) technology is expected to protect the pipeline during oil and gas exploitation. Corrosion tests were carried out in different Na2S·9H2O concentrations and temperatures in order to evaluate the corrosion resistance and stability of Si-DLC film. The results show that the Si-DLC film significantly improves the corrosion resistance of the SS304 substrate. There is no significant change on the surface of Si-DLC film with the increase of temperature, and the XPS spectrum and Raman spectrum of DLC film after corrosion possess no obvious change, which indicates that Si-DLC film possesses a great high temperature stability. The Si-DLC film is denser and it possesses excellent protective effect on the substrate compared to the corrosion product layer. The as-deposited Si-DLC film possesses excellent corrosion resistance in CO2-H2S-Cl− environment and this study provides a promising protective material for the inner surface of the pipeline during oil and gas exploitation.

Binary elements (Si, Mo) co-doping strategy enhanced the tribological performance of diamond-like carbon films

To overcome the constraints posed by high internal stress and weak bonding forces, and achieve DLC films exhibiting exceptional tribological characteristics. Si and Mo co-doped DLC (Si-MoDLC) films were fabricated via the double-target co-sputtering technology. The results revealed that Si was mainly present in SiC and SiO forms, while Mo existed mostly in MoC and Mo forms. With an increase in Si content from 0 to 14.4 ± 0.2 at.%, the ratio of sp3/sp2 (peak area ratio) increase from 1.2 to 2.1. The hardness decreased first and then increased, while the adhesion increased first and then decreased. The Si-MoDLC film with 3.4 ± 0.2 at.% Si and 7.7 ± 0.2 at.% Mo exhibited the lowest hardness (13.4 GPa) and the highest adhesion (340 mN). The tribological properties of thin films were significantly affected by Si content and the testing environment. In the air, the Si-MoDLC film containing 14.4 ± 0.2 at.% Si displayed the lowest friction coefficient (0.07) and a low wear rate (1.1 × 10−7 mm3/N·m), while in a methanol environment, it showed the highest friction coefficient (0.21) and wear rate (14.6 × 10−7 mm3/N·m). These findings provide valuable insights into the microstructure and properties of Si-MoDLC films and offer guidance for the application of DLC films in alcoholic environments.

THE INFLUENCE OF SILICON ELEMENT-ADDED DLC FILM ON Ti-6Al-4V

Silicon added diamond-like carbon films fabricated from C2H2:TMS mixture were used to study the influence of silicon content on the deposition and tribological properties of films prepared on Ti-6Al-4V substrate by using plasma-based ion implantation (PBII). The structure of the film was analyzed by Raman spectroscopy. Hardness and elastic modulus of the film were measured by nano-indentation hardness tester. Tribological propertiesof the film were performed by using ball-on-disk friction tester. The results indicate that with the increasing silicon content in the pure DLC film, the friction coefficient increases. The hardness and elastic modulus of Si-DLC film can increase to a value of up to 31.1 GPa and 200.1 GPa with a silicon content of 13.1 at.%. This is because the greater C content. The Si-DLC films with Si content of 13.1 at.% (C:Si/1:2) and 14.3 at.% (C:Si/1:6) shows a low friction coefficient of 0.2, which is considerable improvement in the tribological properties. This is due to the high hardness and elastic modulus.

Predominant role of fatigue crack evolution and tribo-chemistry on tribological behavior of Si-DLC film under different relative humidity

With coupled mechanical-chemical field, the predominant role of fatigue crack evolution and tribo-chemistry on Si-DLC films were investigated under different relative humidity. Results show that incorporating Si stabilized friction interface and induced lubricating carbonaceous material transfer (0.053 under 20% RH), but the lubricating effect was deteriorated (0.12) by the iron oxide products on sliding shear stress. Furthermore, Si element aggravate overall wear rates than DLC film. Increasing relative humidity was beneficial to lowering wear rates of films with lower Si content, but aggravated the wear rates of films with higher Si content. The predominant role of tribo-chemistry on the friction coefficient (COF) was confirmed, meanwhile, critical impact of fatigue cracks evolution on surface wear is worse than that of tribo-chemistry.

Simultaneous deposition of DLC film on the internal surface of multiple pipes

Diamond-like carbon (DLC) film effectively prevent the corrosion and wear of the internal surface of the pipe. However, many related reports focus on the deposition of DLC film on internal surface of single pipe, ignoring the importance of mass production. In order to improve production efficiency and achieve single mass production in the industry, it is necessary to explore the deposition technology of multiple pipes. In this paper, multiple pipes were applied with the same negative bias voltage and the high-density plasma was generated through hollow cathode plasma enhanced chemical vapor deposition (HC-PECVD) technology. Multilayer Si-DLC films were deposited in each pipe under the same working pressure. The results show that when multiple pipes are deposited at the same time, the DLC films with high hardness (11–12 GPa), low friction coefficient (0.123–0.168), low wear rate (2.65 × 10−7–3.46 × 10−7 mm3 N−1 m−1) and low corrosion current density (more than an order of magnitude lower than SS304) are deposited in each pipe, and the DLC films on the internal surface of multiple pipes display good uniformity. The method mentioned in this study provides theoretical guidance for industrial production of DLC films on the internal surface of pipes.

Si-DLC films deposited by a novel method equipped with a co-potential auxiliary cathode for anti-corrosion and anti-wear application

A novel DLC film deposition method was proposed to realize the deposition of DLC film on the surface of complex shaped workpiece. Meanwhile, Si-DLC film was deposited on the surface of M2 high-speed steel (HSS M2) and 304 stainless steel (304SS), and the microstructure, surface roughness, mechanical properties, corrosion resistance and tribological properties of Si-DLC films were characterized in detail. Results show that Si-DLC film at different axial positions of the auxiliary cathode possesses similar microstructure, film thickness and surface roughness, and the as-deposited Si-DLC film shows the low intrinsic stress of < 0.3 GPa. Compared with the 304SS substrate, the Si-DLC film presents more noble corrosion potential, lower corrosion current density and higher polarization resistance, exhibiting higher corrosion resistance. Moreover, the Si-DLC film exhibits higher hardness, elastic factor and plastic factor than HSS M2 substrate and the corresponding adhesive strength is more than 10 N. The Si-DLC film sliding against GCr15 steel ball shows a lower friction coefficient than that of HSS M2 substrate and the wear rate of GCr15 steel ball sliding against the Si-DLC is lower than that of HSS M2 substrate. In addition, this novel method was used to deposit Si-DLC film on gears, drills and bearings without rotating sample racks. As a consequence, this method possesses great potential and can be generalized for the deposition of DLC film on the surface of complex shape workpiece.

Corrosion behavior and passive stability of multilayer DLC-Si coatings

In this research, multilayer DLC-Si films were effectively formed on the 2024 Al alloy utilizing cage-like hollow cathode discharge plasma-enhanced chemical vapour deposition (PECVD). A scanning electron microscopy (SEM), atomic force microscope (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and Nano Indenter G200 device were utilized to characterize the microstructural features of the coatings. Various electrochemical methods were used to investigate the anticorrosion performance of DLC films in 3.5 wt% electrolytic solution. The findings revealed that an increment in the bias voltage increases the condensation of the DLC layer and increments the thickness of the coatings. Furthermore, the outcomes revealed that the anodic current density and passive current decrements with an increment of bias voltage. This behavior is attributable to a good barrier impact of the amorphous DLC film. The multilayer film introduces new interfaces, resulting in the deterrence of Cl− ions penetrations. Further, the values of activation energy (∆E), enthalpy (∆H), and entropy of activations (∆S) for the samples in 3.5 wt% NaCl were determined and presented.

Compositional design of diamond-like carbon film for tribological performance at elevated temperature: Si and W co-doping

Silicon and tungsten co-doped diamond-like carbon (Si-W-DLC) films with W gradually increased from the top surface to the internal layer were deposited via reactive megnetron sputtering. The mechanical and high-temperature tribological properties of the films were investigated by nanoindentation tester and reciprocating sliding tribometer, respectively. The structures, surface bonding states of the wear tracks were examined by Raman and X-ray photoelectron spectroscopy (XPS), respectively. The results reveal that the gradual W incorporation increases the hardness and elastic modulus from 19.8 ± 0.5 GPa and 183.3 ± 2.8 GPa GPa for the Si-DLC film to 21.6 ± 0.6 GPa and 192.6 ± 3.0 GPa for the Si-W-DLC film, respectively. The Si-W-DLC film maintains a coefficient of friction (COF) below 0.1 and a wear rate of 6.4 × 10−7 mm3/N•m at 500 °C, while the Si-DLC film is worn out. The graphitization of the Si-W-DLC film confirmed by the increment of the ID/IG ratio from 2.26 at room temperature to 3.44 at 500 °C is beneficial to reduce the coefficient of friction (COF). WO3, WO2, WC and silicon oxides are detected on the wear track tested at 500 °C. It is proposed that the synergistic effect of film graphitization, WO3, WO2, WC and silicon oxides formed on the wear track and the improved mechanical properties attributed to the gradual W distribution are responsible for the well high-temperature tribological properties.

Effect of Bias Voltage on Characteristics of Multilayer Si-DLC Film Coated on AA6061 Aluminum Alloy

The multilayer Si-DLC films have been deposited on AA6061 aluminum alloy using a mesh hollow cathode plasma-enhanced chemical vapor deposition technique from acetylene and silane precursor gas at temperature 373 K. Low magnification electron microscopes, Raman spectroscopy, and Fourier transform infrared spectroscopy were employed for characterizing the coating film structure. The MFT-4000 scratch tester, G200 nano-indentation tester, and MS-T3001 tribology tester were utilized to evaluate the adhesion strength, mechanical properties, and friction coefficient. Potentiodynamic polarization and potentiostatic techniques were used to study the multilayer Si-DLC films electrochemical behavior in harsh solution 3.5 wt.% NaCl. The findings revealed that the increase in bias voltage to − 300 V led to the adhesion strength, hardness, elastic modulus, and friction coefficient around 18N, 9.89 GPa, 85.57 GPa, and 0.17, respectively. The polarization results showed a decrease in corrosion current density, increased polarization resistance, and decreased passive current almost 1.28×10−10 A/cm−2, 5.26×109 Ω cm2, and 24.3 nA cm−2, respectively. The findings are ascribed to reduce the internal stress and increase the overall content of sp3 bonds in the film. Moreover, the Si-doped DLC film forms a passive layer from SiOx at the film/solution interface to impede the charge transfer.

Effects of silicon on microstructure and corrosion resistance of diamond-like-carbon film prepared on 2024 aluminum alloy by plasma-enhanced chemical vapor deposition

Effects of silicon on microstructure and corrosion resistance of diamond-like-carbon (DLC) film prepared on 2024 aluminum alloy by plasma-enhanced chemical vapor deposition were investigated. It was found that the content of silicon has significant influence on the microstructure and corrosion resistance of Si-DLC film. When the content of silicon is 0%, the exchange of charges on the surface of the film was facilitated because of more sp2 bonds were formed within the film. The corrosion resistance of the Si-DLC film with the addition of 2% silicon was improved because of the changes in the content of sp3 and sp2 bonds within the film. However, with the content of silicon was increased to 10%, massive nanopores were formed within the film. The corrosion resistance of Si-DLC film with the addition of 10% silicon is decreased. The optimal addition of silicon into the DLC film in order to improve the corrosion resistance in the present work is 2%. The influence mechanism of the content of silicon on corrosion resistance of Si-DLC film and the formation mechanism of nanopores within Si-DLC film are also discussed.

Deformation mechanisms of Si-doped diamond-like carbon films under uniaxial tension conditions

Element-doped diamond-like carbon (DLC) films have been fabricated to achieve excellent mechanical properties but their elastic/plastic deformation mechanisms are unclear due to experimental limitations in characterizing the deformation process. This study investigates the deformation mechanisms of Si-doped DLC films by simulating their uniaxial tensile tests. It is found that these films show many strain-localized regions under tensile deformations. The coordination number (CN) of Si atoms in such regions decreases even with a small tensile strain. The sp3-sp2 bonding transition of C atoms also happen in these regions with a large tensile strain. As a result, these regions show highly-degraded structures with weak mechanical strength and can be regarded as the defects in the Si-DLC films. In this case, the tensile forces are mainly undertaken by the networks formed of both sp3C atoms and Si atoms with large CN, and hence such networks can be regarded as backbones of Si-DLC films. Their fracture finally initiates in the strain-localized regions. Furthermore, Si-DLC films with an increased Si content show large fraction of sp3C atoms but still exhibit a decreased strength due to the rapid presence of strain-localized regions.

Friction and wear behaviors of different DLC films sliding against SiC and Si3N4 balls under high relative humidity

In this paper, the Pure-DLC, B4C-DLC and Si-DLC films were deposited on the AISI 304 stainless steel by unbalanced magnetron sputtering method. The tribological behaviors of the films sliding against SiC and Si3N4 balls were tested by a ball-on-disc tribometer under high relative humidity (90%). The results showed that the tribological behaviors for the films sliding against SiC exhibits more excellent than the corresponding film sliding against Si3N4, mainly showing lower friction coefficients and wear rates, narrower wear widths as well as lower fluctuant friction curves. There are two main reasons for the results. On the one hand, the films sliding against SiC ball exhibit the superior graphitization degree, smaller size of microcrystalline graphite and smaller disorder and sp2 hybrid bond content. On the other hand, the films sliding against Si3N4 ball show more abrasive particles during the friction process, which leads to the adsorbate of films on the surface to be more easily desorbed so that the σ bond reacted easily with water vapor and oxygen is more exposed and forms a strong covalent bond.

Structure and properties of different elements doped diamond-like carbon on micro-arc oxidation coated AZ31B Mg alloy

To further improve corrosion and wear protection of micro-arc oxidation (MAO) to magnesium (Mg) alloys, a pure diamond-like carbon (DLC), H-DLC, Si-DLC, and Cr-DLC film was deposited the MAO coated-Mg alloys using closed field unbalance magnetron sputtering system, respectively. The microstructure and properties of the coatings were investigated. Results indicated that DLC films cannot completely seal the surface micropores of MAO coatings but can reduce their number and pore size. The duplex MAO/DLC films significantly improved the tribological properties of the MAO coating. The MAO/Si/Si-DLC film showed the lowest friction coefficient (0.17) and wear rate (3.18 × 10−6 mm3/(m·N)). The electrochemical test results showed that the lowest corrosion current density (icorr)of the MAO/Si/H-DLC is 3.26 × 10−7 A/cm2 but the icorr of other duplex films is higher than that of the MAO (4.27 × 10−7 A/cm2) coated sample. This indicated that the H-DLC can enhance the anti-corrosion properties of the MAO coating on magnesium alloys. However, the NSS test results indicated that the long-term anti-corrosion properties of duplex H-DLC/MAO coating is not good as that of MAO coating due to the conductivity of the H-DLC.

Direct silanol analysis of tribological surfaces using synchrotron radiation

A new direct detection technique for silanol is needed for tribological materials containing silicon. We focused on near-edge X-ray absorption fine structure (NEXAFS), which uses synchrotron radiation as a method for directly detecting silanol. Model samples were prepared, and their spectra were obtained by NEXAFS. The Si and the O K-edge spectra of silanol exhibited peaks at approximately 1843 eV and 535 eV, respectively. Then the surfaces of silicon-containing diamond-like carbon (DLC-Si) films were measured. The amount of silanol on high-silicon-doped DLC, which had a low friction coefficient, was found to be greater than that on low-silicon-doped DLC. In this research, we demonstrated that the silanol on the surface of DLC-Si films can be directly detected and identified by NEXAFS.

Improving high temperature tribological performances of Si doped diamond-like carbon by using W interlayer

Diamond-like carbon films (DLC) with different silicon contents combined with W interlayer are deposited by plasma-assisted reactive magnetron sputtering. The structures and high-temperature tribological properties of the films are investigated. The results reveal that the pure DLC film is worn out at 400 °C because of graphitization, while the Si-DLC film with Si content of 4.56 at.% keeps low friction coefficient (0.2–0.05) at high temperature up to 500 °C. The 14.56 at.% Si-DLC film failed at 500 °C induced by the formation of SiO2. The improved high-temperature tribological performance of the 4.56 at.% Si-DLC film is attributed to the tribochemistry of W interlayer at 500 °C which formed a film composed of tungsten oxides and carbide.

Modulation of Si on microstructure and tribo-mechanical properties of hydrogen-free DLC films prepared by magnetron sputtering

Modulation of Si on microstructure and tribomechanical properties of hydrogen-free DLC films was studied by preparing Si-DLC films through a hybrid HiPIMS and middle-frequency magnetron sputtering deposition technique. Atomic force microscope, scanning electron microscope, transmission electron microscope, Raman spectrometer and X-ray photoelectron spectroscopy were used to investigate film chemical composition and microstructure. Hardness and elastic modulus were characterized by a nanoindenter. Friction coefficient was measured by a ball-on-disk tribometer. 3D surface profiler, optical microscope and Raman spectrometer were applied to study the tribological behaviors of Si-DLC films. Films surface roughnesses (Ra) are in the range of 1.18–3.15 nm. Si-DLC layer presents a Si-rich/Si-poor multilayer microstructure with a period of about 4 nm. With the rise of Si content in Si-DLC film, sp3 content, hardness and elastic modulus increase. Most Si atoms are interspersed in the amorphous carbon matrix and bond with carbon atoms forming Si-C bonds. The lowest wear rate of 3.5 × 10-7 mm3/Nm is obtained as Si content in Si-DLC film is 14.8%. Varying Si contents in Si-DLC films generated different bonding states of wear tracks, leading to the different wear behaviors of Si-DLC films.

Characterization of Si-DLC films synthesized by low cost plasma-enhanced chemical vapor deposition

Diamond-like carbon (DLC) coatings offer versatile applications in surface engineering due to high hardness and strength, chemical and radiation resistance, biocompatibility and low friction coefficient. When doped with Si, such coatings demonstrate even more beneficial properties, such as lower friction coefficient and higher thermal stability. We demonstrate the instrumental developments of a plasma-enhanced chemical vapor deposition (PECVD) method and the use of an original low-cost set-up aimed to synthesize Si-doped DLC films using polyphenylmethylsiloxane (PFMS) precursors. These films on the surface of glass substrate were characterized by means of XPS, AFM, Raman spectroscopy, and nanoindentation. Dry fiction coefficient was found to be reduced for Si-doped DLC for 4–6 times in comparison with glass substrate.

Effect of Water in Lubricated Oil on Friction Property of DLC-Si Films

Effect of Water in Lubricated Oil on Friction Property of DLC-Si Films