Mechanical Properties Of Diamond-like Carbon Films Research Articles

Characterization of structural and mechanical properties of DLC films deposited on the surface of minute-scale 3D objects: Changes in the incident behavior of carbon ions

Diamond-like carbon (DLC) films have attracted great interest from the industry because they have beneficial mechanical properties such as low friction, high hardness, and wear resistance. DLC films have been used for the surface modification of various mechanical components, although many components that require surface treatments have complex three-dimensional (3D) surface structures. To date, 3D deposition of DLC films remains difficult using conventional methods. Particularly, uniform deposition technology on 3D components has not been developed for tetrahedral amorphous carbon (ta-C) films, which possess high CC sp3 bonds with high hardness. In this study, the filtered cathodic vacuum arc (FCVA) method was used to synthesize ta-C films on Si substrates placed on the sidewalls of trench-shaped and one-side tilted samples at various tilt angles and investigated their microstructure and hardness by Raman spectroscopy and nanoindentation. The results showed that the G peak position, full width at half maximum of G peak (FWHM (G)), and hardness of the ta-C film on the trench sidewall decreased as the depth from the top surface increased, similar to previous research. In contrast, ta-C films deposited on one-side tilted sample showed little depth dependence, and the film properties were determined by the tilt angle. We revealed that the film property dependence on the trench depth direction is due to the sputtered particles from the opposing trench sidewalls, resulting in graphitization of the film.

Effect of local pressure difference caused by argon flow on properties of DLC films on rubber

The application of a diamondlike carbon (DLC) coating on rubber surfaces is a promising method to enhance the tribological properties of rubber and alleviate its poor wear resistance. However, in the preparation of DLC films, accurate pressure detection in the sputtering region is challenging due to the single detection position in common sputtering systems. In this paper, the direct current magnetic sputtering method was used to prepare DLC films on nitrile butadiene rubber (NBR). A set of Faraday beam detection device (FBDD) was employed to monitor the current density in the sputtering region. It was found that even if the pressure at the detection position of the vacuum gauge is consistent, the actual pressure in the sputtering region may be different under different rates of argon flow based on the detection results from the FBDD. The surface energy of DLC films was also calculated and researched. According to the results of FBDD, a series of analytical characterization methods were selected to explore the influence mechanism of changing the Ar flow rate on the properties of DLC films on NBR when the initial sputtering pressure remained consistent. The results of FBDD show that the density of the beam in the sputtering region increases with the increase in the Ar flow rate introduced into the vacuum chamber. The surface energy of DLC films was also calculated and evaluated by a contact angle tester. Raman and x-ray photoelectron spectroscopy results indicate that the increase in the Ar flow rate leads to an increase in pressure, which is conducive to the formation of sp3 in DLC films, and the increase in sp3 improves the surface energy of DLC films. The highest sp3 content and surface energy among as-prepared DLC films are observed when the argon flow rate was 40 SCCM. Ball-on disk friction experiment was used to characterize the tribological performance of DLC films on NBR rubber and the adhesion between DLC films and NBR rubber was evaluated by a nanoscratching test. Combining the results of tribology and nanoscratching testing, it can be inferred that the Ar flow rate plays an important role in improving the mechanical properties of DLC films on NBR rubber. Furthermore, the results of scanning electron microscopy confirmed that the sputtering atoms can effectively fill in the grooves of the rubber substrate. This finding is of significance for controlling the sputtering process of preparing DLC on rubber and improving the frictional properties of rubber.

Structure and mechanical properties of diamond‐like carbon films prepared by pulsed laser‐induced cathodic vacuum arc technique

Diamond‐like carbon (DLC) films are prepared by pulsed laser‐induced cathodic vacuum arc technique with various arc voltages. The purpose of the research is to investigate the influence of the arc voltage on the structure, mechanical, and tribological properties of DLC films. The results from Raman spectra and XPS show that with increasing arc voltage from 180 to 280 V, the sp3 content in the DLC film increases from 43.2 to 56.9 at%, then follows by a significant decrease with further increasing arc voltage to 330 V. The trend in the mechanical properties of DLC films correlates well with the sp3 content in the films. The maximum hardness, modulus, and adhesion critical load (Lc) of the DLC film is obtained in the film deposited at 280 V; the values of that are 46.4 GPa, 380.6 GPa, and 620 mN, respectively. The friction coefficient of the films is between 0.1 and 0.2, and the film deposited at 280 V has the minimum wear rate with a value of 3.2 × 10−17 m3/m.N. It is concluded that the DLC films with high sp3 content (ta‐C, tetrahedral amorphous carbon) not only have good mechanical properties but also have excellent tribological properties, which provides a promising application for wear resistance parts.

Characterization of structural and mechanical properties of DLC films deposited on the surface of minute-scale 3D objects: Comparison of PECVD and FCVA deposition technique

Diamond-like carbon (DLC) films have received considerable attention owing to its excellent properties such as high hardness, low friction coefficient, high wear resistance, and chemical inertness. Because DLC film is considered an effective coating to improve the surface properties of materials, these films are used in various applications such as parts for automobile engines, hard disk surfaces, cutting tools and dies, and so on. The structure of the DLC film consists of a mixture of sp2- and sp3-bonded carbon atoms. Among them, the tetrahedral amorphous carbon (ta-C) film is known to be the hardest film owing to its diamond-like structure composed mainly of sp3-bonded carbon atoms. The most common deposition method for synthesizing ta-C is the filtered cathodic vacuum arc (FCVA) method. This method can remove the droplets that are non-ionic neutral species, and a high-quality film can be synthesized. However, the mechanical parts that require ta-C coating have a three-dimensional (3-D) shape, and it is difficult to coat the ta-C film on their entire surface conformity by the FCVA process. In this study, we deposited ta-C on three-dimensional parts by the FCVA method and evaluated the microstructure and surface morphology of the film in comparison with the plasma enhanced chemical vapor deposition (PECVD) method. Films were successfully coated over the entire surface of both millimeter- and nanometer-sized trench patterns. The film properties were investigated by Raman spectroscopy, SEM, nanoindentation tester and transmission electron microscopy.

Surface modification of 316L stainless steel by diamond-like carbon films

The diamond-like carbon (DLC) film on 316L stainless steel substrate was prepared by pulsed plasma-enhanced chemical vapor deposition, and the performance of the films was optimized by regulating the pulse voltage. Microstructure and properties of DLC film on 316L stainless steel were characterized by atomic force microscopy, field-emission scanning electron microscopy, Raman spectra, nano-indenter and electrochemical workstations. The results showed that DLC films with smooth and dense morphology have a low friction coefficient and high nano-indentation hardness, and the surface hardness of 316L stainless steel substrate was enhanced by more than 3 times. The mechanical properties of DLC films and their bond with 316L stainless steel could be further optimized by increasing pulse voltage. DLC films on 316L stainless steel substrate increased the self-corrosion potential by 0.173 V and decreased self-corrosion current by 99%, which significantly improved the anti-corrosive properties of 316L substrate.

Effects of carbide forming elements Me on residual stress and mechanical properties of DLC films by molecular dynamics simulation

In this paper, the structures of diamond-like carbon (DLC) films doped with carbide forming elements Me (MeTi, V, Cr, Zr, Nb, W) were designed firstly by molecular dynamics method. Then, the residual stress and mechanical properties of Me-DLC films were calculated. Meanwhile, the effect of doping carbide forming elements Me on DLC films were analyzed, which indicates the mechanism that the residual stress is decreased. The results show that the residual stress in Me-DLC films is compressive stress. With the increase of Me content, they are decreased firstly and then increased. Meanwhile, the smaller residual compressive stress of the DLC films is, the better their comprehensive mechanical properties are. By the structural analysis, it is found that the carbide forming elements Me are easily combined with the tri-coordinate C to increase the tetra-coordinate C content, which might affect the residual compressive stress. By the bond length and bond angle distribution analysis, it is observed that the CC bond length is relaxed and the CCC bond angle is deformed. By ELF analysis, it is found that a weak covalent bond is formed between the Me atom and the C atom, which lowers the bonding strength.

Effect of SiNx interlayer thickness on adhesion and friction properties of diamond-like carbon films

A suitable interlayer thickness is critical to reduce film mismatch and roughness. In this text, diamond-like carbon (DLC) films with different SiNx interlayer thicknesses were successfully synthesized on Si (100) substrates by radio frequency (RF) and direct current (DC) magnetron sputtering method. The effect of SiNx interlayer thickness on surface morphology, adhesion, tribological and mechanical properties of DLC films was investigated. The results show that, due to the use of SiNx interlayer in the DLC films, the adhesion is significantly enhanced, the surface roughness is increased, and the sp3 content and modulus are lowered. When the SiNx interlayer is introduced, the internal stress and the roughness decrease first decrease and then increase. The reason may be related to the accumulation of nitrogen vacancy centers (NVC). A sample of about 10 nm SiNx interlayer was found to have the best combination of tribology, mechanical properties, and surface roughness.

The friction and wear performance of DLC coatings deposited on plasma nitrided AISI 4140 steel by magnetron sputtering under air and vacuum conditions

Diamond-like-carbon (DLC) coatings with high hardness and low friction coefficient exhibit excellent tribological performance under air and vacuum conditions. However, adhesion and cold welding problems in vacuum conditions lead to increase friction coefficient values. These negative effects can be eliminated by different methods such as forming interlayers between coating and substrate or ion treatment of the substrate. In this work, DLC coatings were deposited on untreated and plasma nitrided (at 400°C, 500°C and 600°C for 1h and 4h) AISI 4140 steel substrates by magnetron sputtering technique. The effects of plasma nitriding treatment on the friction and wear properties of DLC coatings under air and vacuum conditions were investigated. The structural and mechanical properties of DLC films were examined by XRD, SEM, and microhardness tester, respectively. The friction and wear properties were determined by a tribotester under air and vacuum conditions. The microhardness of samples increased after surface treatments and the highest value was obtained from the sample plasma nitrided at 600°C for 4h plus DLC coated sample. The wear resistance of samples increased with increasing plasma nitriding time and temperature. Also, it was observed that the samples tested under vacuum condition showed better wear resistance than the samples tested under ambient air. Furthermore, increasing plasma nitriding time and temperature improved the wear performance of the material regardless of the test environment.

The correlation between optical and mechanical properties of amorphous diamond-like carbon films prepared by pulsed filtered cathodic vacuum arc deposition

Diamond-like carbon (DLC) films were deposited by pulsed filtered cathodic vacuum arc (FCVA) deposition. The microstructure, mechanical and optical properties of DLC films have been investigated as functions of the variation in the substrate negative direct current bias voltage (Vbias) from 0.0 to 1.5 kV. Raman and X-ray photoelectron spectroscopy results show a correlation between the ID/IG ratio and the microstructure in terms of the sp3/sp2 ratio to Vbias. This fact shows that a significant change in the sp3 content, which is attributed to the transformation from graphite-like to diamond-like, is accompanied by a decreasing ID/IG ratio. The relatively high mass density of the films in the range of 2.51 to 2.79 g/cm3 can be obtained with biasing. The mechanical properties, i.e., the hardness and elastic modulus, were 13–25 and 114–145 GPa, respectively. The improvement of the mechanical properties is due to the formation of the compressive residual stress and the local density depending on Vbias. The relationship between the refractive index and the ID/IG ratio agree well with the microstructure and mechanical properties of DLC films. All of these results indicate a vital role of Vbias in determining the DLC properties.

Tribological behavior of DLC films and duplex ceramic coatings under different sliding conditions

Diamond-like carbon (DLC) films are effectively utilized to improve the tribological properties of materials due to their low friction coefficient, good wear resistance and high hardness. In recent years, different pre-treatments such as plasma assisted diffusional processes have been used to increase long-term durability of these coatings. In the present work, DLC films were deposited on untreated and plasma nitrided AISI 4140 low-alloy steel samples using physical vapor deposition method (PVD). The effect of nitride layers on the structural and mechanical properties of DLC films was examined by XRD, SEM, microhardness tester and reciprocating tribotester. The wear tests were performed under dry, saltwater and lubricant environments. The microhardness results indicated that surface hardness considerably increased after duplex treatment and this caused to increase plastic deformation resistance of the material. The reciprocating test results showed that DLC films deposited on untreated and plasma nitrided samples reduced the coefficient of friction because of the formation of transfer film between sliding/mating surfaces. Also, wear rates improved significantly after duplex treatment in consequence of high plastic deformation resistance of duplex treated samples. The highest wear resistance was obtained in lubricated condition while the lowest wear resistance was for the samples tested in dry conditions.

Mechanical Properties and Surface Morphology of Diamond-Like Carbon Films with SiN<i><sub>x</sub></i> Interlayer

Diamond-like carbon (DLC) film has remarkable physical, mechanical, biomedical and tribological properties that make it attractive material for numerous industrial applications needs of advanced mechanical systems. In this study, deposition process of DLC films on Si (100) are performed by direct-current (DC) magnetron sputtering method. The effects of interlayer on the compositions, structures and mechanical properties of DLC films are studied. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies reveal the creation of high uniform surface morphology and low roughness DLC films with SiNxinterlayer. For comparison, DLC films with different interlayers are also grown. The Raman spectra are analyzed in order to characterize the film compositions. Indentation test was performed to value the mechanical properties of DLC films. Raman, SEM, and AFM analyses are correlated with the mechanical properties of the DLC films.

Influences of Pulse Frequency on Structure and Mechanical Properties of DLC Films Synthesized by Pulsed Cathodic Arc Evaporation

Diamond-like carbon (DLC) films were prepared on the Si (100) substrates by pulsed cathodic arc plasma. The influences of given pulse frequency on the microstructure, morphology, mechanical and optical properties of DLC films were investigated by Raman spectroscopy, atomic force microscopy, Knoop sclerometer, X-ray double-crystal surface profilometer. The results showed that the variation of pulse frequency could significantly change the microstructure of DLC films, including the size and ordering of sp2carbon clusters and movement or diffusion of carbon atoms. The increasing of pulse frequency led to the variation of the relative fraction of Csp3/Csp2. The hardness and internal stress of the DLC films were affected accordingly. The results might contribute to the synthesis of DLC films with excellent structure and properties by cathodic arc evaporation.

DLC coating on a trench-shaped target by bipolar PBII

Bipolar-type plasma based ion implantation (bipolar PBII) and deposition is a promising coating technique, especially for the complex-shaped target surface. In this study, diamond-like carbon (DLC) films were prepared by a bipolar PBII technique to a trench-shaped target (20mm pitch and 10mm depth), and the uniformity, structural and mechanical properties of DLC films coated on the top, inside wall and bottom surfaces of the trench were evaluated by surface profilometer, Raman spectroscopy and nanoindentation hardness tests. Moreover, plasma simulation was conducted to reveal the DLC coating mechanism for finding the optimum coating conditions. Particle-In-Cell with Monte Carlo Collision (PIC–MCC) method and Direct Simulation Monte Carlo (DSMC) method were used for computing the plasma behavior. As a result, thickness uniformity of DLC films was improved with decreasing negative pulse voltage. On the other hand, the thickness of DLC films on the inside wall of the trench was much smaller than those of the top and bottom surfaces of the trench. This is because the conformal ion sheath cannot be formed around the inside wall, which in turn leads to the decrease of incidence ion flux to the inside wall, and the idea has been verified through the simulation of plasma behavior. From the Raman measurements of DLC coatings on the inside wall, it is observed that the Raman G-peak position shifts to a higher wave number and the Full Width at Half Maximum of G-peak (FWHM(G)) decreases to a smaller value compared to those of the films on the top and bottom surfaces. These indicate that the structure of DLC coatings on the inside wall surface has changed compared to those on top and bottom surfaces, i.e., graphitized, which results in the reduction of hardness.

Chromium-doped diamond-like carbon films deposited by dual-pulsed laser deposition

Diamond-like carbon (DLC) and Cr-doped diamond-like carbon layers were studied. DLC and Cr-DLC were deposited on silicon and titanium substrates (Ti-6Al-4V) by dual-pulsed laser ablation using two KrF excimer lasers and two targets (graphite and chromium). The composition was analyzed using wavelength-dependent X-ray spectroscopy. The Cr content increased from 2.2 to 17.9 at%. The topology and surface properties as roughness of layers were studied using scanning electron microscopy and atomic force microscopy. With the chromium concentration increased the roughness and the number of droplets. Carbon and chromium bonds were determined by Raman spectroscopy. With an increase in chromium content the ID/IG ratio increased. Mechanical properties of DLC films with various chromium content were evaluated. Hardness (reduced Young’s modulus) was determined by nanoindentation and reached of 51 GPa (309 GPa). Films adhesion was studied using scratch test and with concentration of chromium increased up to 20 N.

Correlations between deposition parameters, mechanical properties, and microstructure for diamond-like carbon films synthesized by RF-PECVD

Diamond-like carbon (DLC) films were synthesized on silicon substrates by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). The reactant gas was pure acetylene and the working pressure, working power, and deposition time were, respectively, varied to comprehensively investigate their influence on the microstructure and mechanical properties of DLC films. A digital phase-shifting Twyman–Green interferometer was utilized to measure the residual stress resulting from the deposition process. Raman spectrometer and nanoindentation system were, respectively, utilized to clarify the constituent microstructure, hardness, and elastic modulus of DLC films. The results reveal that the hardness and elastic modulus are both closely correlated to the sp 3 content (I D/I G ratio), which is greatly dependent on working power but much less on working pressure and deposition time. Furthermore, the self-bias voltage is more dependent on working power than on working pressure and deposition time, a tendency contrary to that of the thickness investigation. Finally, it was found that the residual stress may be influenced by the ion energy and film temperature as well as the sp 3 content.

Effects of Negative Bias Voltage on Structure and Mechanical Properties of DLC Films Synthesized by FCVA Deposition

Diamond-like carbon (DLC) films have been given great attention in the last twenty years and applied in many fields due to its super mechanical property. In this paper, DLC films were prepared by filter cathodic vacuum arc (FCVA) deposition under different negative bias voltage. No spalling was found in all of as-prepared DLC films. X-ray photoelectron spectroscopy (XPS), Raman spectra were employed to analyze composition and structure, the results showed that as-prepared DLC films had tendency of graphite with increase of negative bias voltage. Mechanical properties were characterized by micro-hardness and pin-on disc tests, the results showed that the hardness of DLC films decreased with bias voltage, but still kept good wear resistant.

Structural and mechanical properties of DLC films prepared by bipolar PBII&D

In the present study, diamond-like carbon (DLC) films were prepared by bipolar plasma based ion implantation and deposition (PBII&D), and the structural and mechanical properties of the DLC films deposited on Si substrates were evaluated by Raman spectroscopy. In the PBII&D processing, the positive and negative pulse voltages were varied from 1 to 3 kV and from − 1 to − 15 kV, respectively. With an increase in the pulse voltages, the Raman G-peak position and I(D) / I(G) ratio increased, and the G-peak full width at half maximum (FWHM(G)) decreased, indicating graphitization of the DLC films. In the low wavenumber regime, the FWHM(G) increases when the G-peak shifts to higher wavenumbers, reaching a maximum value at around 1540 cm − 1 , and then decreases. This behavior was due to the structural changes occurring in the DLC films with an increase in the wavenumber. DLC to polymer-like carbon (PLC) transition occurred in the low wavenumber regime, and DLC to graphite-like carbon (GLC) transition occurred in the high wavenumber regime. Further, two different trends were observed in the relationship between the mechanical properties (hardness, elastic modulus, and internal stress) of the DLC films and the FWHM(G), originating from the structural change from DLC to GLC and PLC.

Surface characterization and nanomechanical properties of diamond-like carbon films synthesized by RF plasma enhanced chemical vapor deposition

Diamond-like carbon (DLC) films were synthesized by RF plasma enhanced chemical vapor deposition using acetylene as the carbon source and the effects of acetylene/nitrogen ratio in the reaction atmosphere, deposition pressure, and plasma post-treatment using different atmospheres on the surface roughness and mechanical properties of DLC films were investigated. Although the surface roughness, characterized by AFM, decreased as the acetylene/nitrogen ratio in the reaction atmosphere decreased, the hardness of DLC films measured by nanoindentation also decreased with the decrease of the acetylene/nitrogen ratio, which is consistent with the Raman results of the I D/I G ratio. Rougher films with higher residual stress were obtained when using a deposition pressure higher than 40.0 Pa (0.3 torr). For the effect of plasma post-treatment using different atmospheres, surface smoothing was found for the hydrogen plasma post-treatment, whereas nitrogen and argon plasma post-treatments resulted in surface roughening. Hydrogen plasma post-treatment was found to lower the surface roughness without significantly sacrificing the hardness.

Effects of working pressure on the deposition of diamond-like carbon films prepared by bipolar-type plasma based ion implantation

Diamond-like carbon (DLC) films are prepared by a bipolar-type plasma based ion implantation (PBII), and the deposition rate and the microstructure of the films are examined as a function of working pressure (P) in the range of 0.08–0.5Pa. The positive and negative pulse voltages are fixed at +2kV and −5kV, respectively. The optical emission spectra on the bipolar pulse plasma are also examined. It is found that the deposition rate is increased with increasing P. Raman analysis shows that the intensity ratio of D peak to G peak, ID/IG, suggesting the amount of graphite-like structure, is not significantly changed in this pressure range. However, ion beam analysis reveals that the density of the films is slightly decreased with increasing P, probably due to the increase of H concentration in the films. In addition, the hardness and elastic modulus of the films are also gradually decreased with increasing P. On the other hand, optical emission peaks from H, CH and C radicals are clearly observed. These peaks, especially CH radical, are increased in intensity with increasing P, indicating that the plasma density is increased. This result in the increase of the deposition rate and the results suggest that the rapid increase of CH radicals (and CH ion flux) at higher P presumably causes the slight reduction of the density and mechanical properties of DLC films due to the increase of H concentration.

Effect of Annealing on Implanted Ga of Diamond-Like Carbon Thin Films Fabricated by Focused-Ion-Beam Chemical Vapor Deposition

The effect of annealing on implanted Ga of diamond-like carbon (DLC) films on Si substrates fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD) was investigated. Thermal desorption spectroscopy showed two Ga+ peaks at 470 and 630 °C. These temperatures agree with the results of energy-dispersive X-ray diffraction analysis of Ga concentration in the film. Cross-sectional transmission microscopy revealed changes in the structure of the DLC film at each temperature. At approximately 400 °C, the Ga in the film migrated to the surface and desorbed. Above 600 °C, the Si in the DLC layer near the damaged Si substrate interface recrystallized. These results can be applied to enable deliberate control of the mechanical properties of DLC films fabricated by FIB-CVD.