Behavior Of Diamond-like Carbon Films Research Articles

Nanoindentation and scratching behaviors of diamond-like carbon films by coarse-grained molecular dynamics

High-performance coatings such as diamond-like carbon (DLC) films own thin thickness which is in the gap of experiment and molecular dynamics (MD), limiting the measurement of their intrinsic mechanical properties. To achieve the direct comparison between experiment and simulation, modified parameters of Tersoff potential describing the interaction among amorphous carbon accurately are proposed for coarse-grained MD simulations of DLC films. Such parameters are validated in compression and shear loadings compared with all-atom MD. A fitted mathematical contact model of the actual contact depth of indenter in nanoindentation is studied. By using this model, the elastic moduli of DLC films have been computed and the effect of relaxation is discussed. Besides magnified dimensions, the larger mass of coarse-grained beads enables the greater time interval, realizing the friction simulation of DLC films at experimental sliding velocities, and giving a methodological inspiration for the studies of mesoscopic simulations of amorphous materials.

Regulating the fretting behavior of diamond-like carbon films by changing the composition and structure

Reducing or eliminating the slip regime and mix regime is an effective way to reduce the fretting wear, while the diamond-like carbon (DLC) film, as a self-lubricating solid lubricant, can reduce friction coefficient while improving the surface strength. The most valuable thing is that DLC film can change the film's composition, structure, and physical and chemical properties by controlling its deposition process. This regularability can realize the reduction or elimination of slip regime and mix regime under different fretting conditions, so it is important to explore the changing regulation law of the fretting regime by changing the sp2/sp3 hybrid bond content ratio and microstructure of DLC film. Here, DLC films with different sp2/sp3 hybrid carbon content ratios were obtained by annealing; the fretting performance was studied under different normal loads and amplitudes. The following rules are obtained by drawing the running conditions fretting map and analyzing the tangential stiffness, friction coefficient and dissipation energy: with increasing the sp2/sp3 hybrid carbon content of DLC film, the fretting regime moves towards the slip regime, while the friction coefficient and dissipated energy will increase. In addition, the short-range ordered microstructure, such as onion-like carbon structure, will facilitate the fretting regime towards the partial slip regime. This work demonstrates the controllability and potential of DLC films in fretting.

Probing the tribological behaviors of diamond-like carbon film in water-based drilling fluid environment by varying normal loads

This paper investigates the friction behavior and mechanism of diamond-like carbon (DLC) film and 26CrMo alloy steel under different loads in water-based drilling fluid environment. The results show that the coefficient friction and wear degree of DLC film in water-based drilling fluid environment are significantly lower than that of 26CrMo alloy steel under both low and high load. Raman, SEM and other test results suggest that the graphitization degree of worn DLC surface and the transfer layer on the surface of friction pair will increase with the increase of load. DLC film shows superior lubrication and wear resistance in water-based drilling fluid environment. Meanwhile, further investigation suggests that the friction and wear behavior of DLC film in water-based drilling fluid environment is also affected by the synergy of rolling effect, filling effect and polishing effect. Moreover, the barite particles wrapped in graphene dust will produce a low-friction synergy at the friction interface even if the DLC film is worn through. The relevant research results not only help to enrich the basic theory of lubrication and wear resistance technology of DLC film, but also help to promote the practical engineering application of DLC film in oil and gas environment. • DLC film exhibits lower COF and wear in water-based drilling fluid environment. • Graphitization of DLC film and transfer layer increase with the increase of load. • Friction behaviors are affected by rolling effect, filling effect and polishing effect.

Roles of transfer layer and surface adhesion on superlubricity behaviors of diamond-like carbon film depending on rotating and reciprocating motion

The superlubrictiy behavior and mechanism of diamond-like carbon (DLC) film in vacuum were researched under rotating and reciprocating motion. Compared with the reciprocating motion, DLC film can reveal a more stable superlubricity state and lower wear under rotating motion. TEM, AFM, Raman and the first-principles calculation results show that the transfer layer would be quickly removed under reciprocating motion, but could be maintained stably under rotational motion, which may be one of the key factors for the stable superlubricity state of DLC films under rotating motion. The removal of tribofilm under reciprocating motion may be attributed not only to the stronger impact and instability in friction interface, but also to the strong adhesion effect of the friction interface.

Fatigue behaviors of diamond-like carbon films

This work investigates the fatigue behaviors of diamond-like carbon (DLC) films by conducting cyclic tensile tests and interfacial fatigue tests via molecular dynamics. It is found that the strength of DLC films is reduced with the increasing cycle number due to the irreversible sp3-sp2 transition of carbon atoms induced by tensile deformation. Regions with high sp2C fraction are easy to deform owing to their weak strength, thus the atomic strains are almost localized in such regions. The weakest region is regarded as the defect of the films and suffers from the most severe strain localization. As a result, many sp3C atoms are transformed into sp2 hybridization in the defect, destroying the integrity of sp3C network. Hence, the film failure occurs in the defect because of its badly degraded strength. Furthermore, interfacial fatigue of DLC films is induced by the sp3-sp2 transition during the cyclic tensile tests.

Molecular dynamics study of the frictional behaviors of diamond-like carbon films

Molecular dynamics study of the frictional behaviors of diamond-like carbon films

Effect of the methane flow ratio on the structural and mechanical properties of high-entropy alloy co-doped DLC films

High-entropy alloy is co-doped in diamond-like carbon films by sputtering using a single (AlCrNbSiTiV) target. This study analyzed the effects of methane flow rates [Rm = CH4/(Ar + CH4) flow ratio], which varied in the range from 16 to 24%, on the morphological, phase structures, mechanical characteristics and tribological behavior of diamond-like carbon films. The diamond-like carbon film is characterized using Raman spectroscopy, nano-indentation, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and scratch testing. As a result, the element concentration in the diamond-like carbon films is quite near to the High-entropy alloy target composition, and the metal content of co-doped diamond-like carbon films decreases as the fraction of the methane reactive gas increases. For a monotonically increasing Rm flow ratio, the position of the G-peak is downshifted to a low wavenumber, a decrease in ID/IG ratio suggests a decrease in sp2/sp3 ratio, which is associated with the decrease in the fraction of graphite and the more disordered carbon structure. An increase in the Rm flow ratio results in increased hardness (H) and elastic modulus (E) and a decreased friction coefficient, wear rate, H3/E2 and H/E. Cutting tests using a tool coated in a diamond-like carbon film shows the cutter life was extended.

Frictional behaviors of diamond-like carbon films under water lubrication: A molecular dynamics study

This study investigates the influence of water lubrication on the friction of DLC films. It is found that water molecules at contact interfaces prevent the formation of interfacial C–C covalent bonds and show hydrodynamic lubrication effects, and thus effectively postpone the friction increase in initial friction stages. Moreover, for the small/medium amount of water molecules, they would diffuse into the DLC films during further sliding, hence highly decrease the interfacial density of carbon networks but inhibit their graphitization. This suggests that the degraded mechanical strengths of DLC films induced by the water diffusions at the interfaces contribute much to the friction reduction of these films, which improves the current understanding that such reduction is mainly caused by tribochemical reactions.

Influence of currents on tribological behavior of diamond-like carbon films

The diamond-like carbon (DLC) film is vastly applied for low-friction protective films at contact sliding surfaces. This work reported the characteristics and tribological properties of DLC, Cu-doped DLC (Cu-DLC) film and Ti-doped DLC (Ti-DLC) film formed by unbalanced magnetron sputtering system and analyzed the frictional tests and the morphology of wear scars. The current intensity at the sliding interface was set to a constant value in the whole current circuit for exploring the influence of current, including 0 A, 0.5 A, 1 A, 1.5 A and 2 A. The results showed the friction coefficient of DLC film decreased from 0.12 to 0.06–0.08 and then increases rapidly to 0.26 when the current increased to 2 A. The change in trend of friction coefficient of Cu-DLC film with the increase in current was the same with the DLC film. The minimum value was 0.12 at 1 A current. In the case of Ti-DLC film, when the current intensity enhanced from 0 to 2 A, the friction coefficient monotonically increased from 0.06 to 0.29. Furthermore, the wear rate of the films under higher current was larger than the wear rate of the films under lower current. This is due to the fact that frictional heat and Joule heat are generated at a relatively large current to make the surface of the film more susceptible to wear. The wear rate of Ti-DLC film is relatively larger as the arc ablation is the main wear mechanism of Ti-DLC film compared with pure DLC film and Cu-DLC film.

Corrosion behavior of diamond-like carbon film induced by Al/Ti co-doping

Diamond-like carbon films with Al and Ti dopants (Al/Ti-DLC) were fabricated by a hybrid ion beam deposition system combined with a special design of splicing targets, in which the Al/Ti ratio was changed from 4.0 to 1.1 by tailoring the Al content. The structural evolution and corrosion behavior of Al/Ti-DLC films in 3.5 wt% NaCl solution were systematically investigated by comparing with the 316L SS and pure DLC film. Results revealed that compared with the pure DLC and 316L SS substrate, the Al/Ti-DLC film exhibited enhanced corrosion resistance by reducing the porosity and increasing the barrier for both the charge transfer and the diffusion of corrosive ions into the substrate. In particular, the anti-corrosion behavior of DLC film highly depended on the Al/Ti ratio, which decreased gradually with the Al/Ti ratio ranged from 4.0 to 1.1. Structural and EIS analysis indicated that this was ascribed to both the increased residual stress and sp2 hybridized fraction, which induced not only the formation and propagation of cracks during the corrosion process but also the high electric conductivity and low diffusion barrier of corrosive ions, accelerating the corrosion processes at the film/substrate interface.

Delamination of diamond-like carbon films on rough Si3N4 surfaces

ABSTRACTWe investigated the delamination behaviour of diamond-like carbon films on silicon nitride (Si3N4) substrates, considering the effect of the substrates surface roughness. The damage evolution at the film/substrate interface during indentation was simulated using a cohesive zone model, and the interfacial stress and energy release were determined. We discuss the influence of asperity size, thickness and Young's modulus of the films. The results show that the interfacial roughness hastens the onset of interfacial damage but delays the progression of film delamination owing to the effect of mechanical interlocking. The asperity size and film thickness also strong influence the delamination of diamond-like carbon films.

Fracture behavior of diamondlike carbon films deposited on polymer substrates

The authors investigated the fracture behavior of diamondlike carbon films deposited on polyethylene terephthalate substrates using two types of film synthesized under different sputtering-gas pressure conditions. Specifically, the influence of the hardness, indentation Young's modulus, and scratch toughness on the multiple cracking behavior of the films was explored. Based on microscratch and nanoindentation experiments, it was found that the sputtering-gas pressure conditions played an important role in the chemical composition and concomitant changes in the mechanical properties of the diamondlike carbon films. In particular, higher gas pressure conditions resulted in a lower hardness, indentation Young's modulus, and scratch toughness, which are presumably due to the presence of a large number of C–O bonds in the diamondlike carbon structure. In situ observations during tensile-loading experiments in conjunction with multiple crack analyses showed that the films synthesized under higher gas pressure conditions exhibited a high level of crack resistance to externally applied tensile strain. The estimated crack onset strain, i.e., the strain at which the first crack was generated, was approximately 2%, which is about 1.3 times higher than that for the diamondlike carbon films synthesized under lower gas pressure conditions.

Influence of Third Particle on the Tribological Behaviors of Diamond-like Carbon Films.

Tribological mechanisms of diamond-like carbon (DLC) films in a sand-dust environment are commonly unclear due to the complicated three-body abrasion caused by sand particles. This study investigates the three-body abrasion of the DLC film via molecular dynamics simulations. The influence factors such as the load, velocity, shape of the particle and its size are considered. It has been found that the friction and wear of the DLC film are determined by adhesion at a small load but dominated by both adhesion and plowing at a large load. A high velocity can increase the friction of the DLC film but decrease its wear, due to the response of its networks to a high strain rate indicated by such velocity. The shape of the particle highly affects its movement mode and thus changes the friction and wear of the DLC film. It is found that a small-sized particle can increase the friction and wear of the DLC film by enhancing plowing. These unique tribological mechanisms of the DLC film can help to promote its wide applications in a sand-dust environment.

Adhesion behavior of diamond-like carbon films with F and Si co-doping prepared by radio frequency reactive magnetron sputtering

Diamond-like carbon (DLC) films with F and Si co-doping (DLC:F:Si films) were deposited on medical 316L stainless steel substrates with radio frequency reactive magnetron sputtering by using trifluromethane (CHF3) and argon as source gases and SiC crystal target. The relations between the RF input powers and adhesion behavior of DLC:F:Si films were investigated. Surface morphology and roughness, hardness, sp2/sp3 hybridization ratio, and bonding configuration were characterized subsequently to demonstrate the adhesion evolution by Atomic force microscope (AFM), nanoindenter, Raman spectrometer, Fourier-transform infrared (FTIR) spectrometer and Friction and wear tester. The relative intensity of the CF symmetric stretch vibration (1160cm−1) to CF2 asymmetric stretch vibration (1220cm−1) and HFCC< stretch vibration (1620cm−1) to F2CC< stretch vibration (1710cm−1) as a function of RF input powers were especially demonstrated. The results show that choosing a appropriate RF input power can effectively modulate the structure and adhesion characteristics of DLC:F:Si films. The DLC:F:Si films prepared at about 200W RF input power have stable bond configuration and exhibit good adherence, hardness and wear resistance.

Investigation on tensile behaviors of diamond-like carbon films

The lubrication performance of diamond-like carbon films is significantly influenced by their deformations under loading. However, their deformation mechanisms are unclear so far due to their nanoscale thicknesses and complex microstructures. In this study, these mechanisms are explored by investigating the tensile response of the DLC films via molecular dynamics simulations. The atomic strain localizations are observed, and the regions where they occur are dominated by sp2 clusters. These clusters relax the film at small tensile-strains by releasing its residual energies. The sp3-sp2 transitions are present at large tensile-strains and prefer to occur in the strain-localized regions. This preference significantly improves the graphitization level in these regions and thus promotes the sp2 clusters to propagate. The propagation severely damages the sp3 networks and leads to the failure of the film. This research suggests that reductions of heterogeneities such as existences of large-sized sp2 clusters may be useful to delay the film failure by suppressing the initial strain localizations. It is demonstrated that the propagation of sp2 clusters for the DLC films can be induced by their deformation besides the high friction temperature in their wear tests. This demonstration can help to improve the understanding of their trigological mechanisms.

Effect of environmental hydrogen atoms on the tribological behaviors of diamond-like carbon films

Influence of environmental H atoms on the tribological behaviors of DLC films is investigated via molecular dynamics simulations. These H atoms significantly reduce the friction force, and the reduction mechanisms depend on friction temperatures. At low friction temperatures, the H atoms are concentrated near contact interfaces, and their passivations highly reduce the interfacial adhesion, resulting in the low friction force. However, high friction temperatures induce the significant diffusion of the H atoms into the DLC films and thermally expand such films and increase their graphitization, causing a wide region with easy-shear properties to reduce the friction force. It is believed that these mechanisms of friction reduction can improve the understanding of the superlow friction of DLC films in H2 environment.

Tribological behaviour of titanium alloy modified by carbon–DLC composite film

Diamond-like carbon (DLC) films were deposited on both the untreated and the prior carbon ion implanted Ti6Al4V alloys by plasma enhanced chemical vapour deposition (PECVD). The tribological behaviours were evaluated by conducting reciprocating wear tests against ZrO2 using a ball on disc tribotester. The effect of ion implantation dose and zone on mechanical and tribological behaviour of DLC films was studied by means of nanohardness and nanoscratch tester, SEM and three-dimensional surface profiler. The duplex treatment dramatically increased the surface hardness and bonding strength of film/substrate. Both carbon ion implantation and PECVD improved the wear resistance of titanium alloy, whereas the combined process of carbon ion implantation with the dose of 1016 ions cm−2 and PECVD offered the best wear resistance by a reduction of 94·3% in wear volume in comparison to untreated alloy. The cracks and deformations that induced local flaking failure under high contact stress played an important role in the wear and failure mechanisms.

Wear Behavior of Diamond-Like Carbon Film Coated by Filtered Cathodic Arc

Diamond-like carbon (DLC films were deposited on NiFe coupon by Filtered Cathodic Arc (FCA) technique. Two different DLC thicknesses were selected to compare thickness dependency on film properties change. The mechanical property as wear resistance under cyclic heating condition was investigated by nanoindenter (Hysitron). The detail of DLC film composition change was also studied using X-ray Photoelectron Spectroscopy (XPS). The roles of heating in material composition and wear behavior of DLC films are discussed. The effect of DLC film thickness is also considered. The results showed that thinner DLC (2 nm) has higher carbon oxidation resulting that deteriorate in wear resistance as compare to thicker one (5 nm). The heating accelerates these oxidation and wear in this study. .

S114026 DLC膜のなじみ挙動に及ぼす荷重負荷速度の影響

S114026 DLC膜のなじみ挙動に及ぼす荷重負荷速度の影響

Effects of environmental molecular characteristics and gas–surface interaction on friction behaviour of diamond-like carbon films

The superlow friction behaviours of diamond-like carbon (DLC) films in three different inert environments (dry N2, CO2 and Ar gas) were investigated and compared. The friction of the DLC films in dry N2 and CO2 was superior to that in dry Ar, and was dependent on the environmental exposure time. The possible reason is that N2 and CO2 have the same molecular characteristic of lone pair electrons at both sides of the molecules, while Ar has no lone pair electrons. And a special gas–surface interaction due to π orbital–lone pair electrons interactions is present at the sliding interfaces of DLC films in dry CO2 and N2. A friction model in relation to environmental molecular characteristics and gas–surface interactions was proposed to explain the friction behaviours of DLC films.