Tribological Properties Of Diamond-like Carbon Films Research Articles

Effect of bias gradient delta on mechanical and tribological properties of DLC films sputtered on ACM

Diamond-like carbon (DLC) films were prepared on acrylate rubber (ACM) by varying the substrate bias voltage with bias gradient deltas of 25 V, 50 V, and 100 V during magnetron sputtering. The microstructure, mechanical and tribological properties of DLC films on ACM substrate were systematically investigated by SEM, AFM, Raman and XPS et.al in detail. The results show that the DLC film with a bias gradient delta of 25 V exhibited the most sp3 content and with the decrease of bias voltage gradient delta, the sp3 content in DLC films shows an increasing trend. The ratio of H/E increases as the bias gradient delta decreases. The results of friction tests indicated that the wear resistance of DLC films is influenced by their bias gradient deltas, surface roughness, residual stress, adhesive strength, and the ratio of H/E&H3/E2. Furthermore, decreasing the bias gradient delta resulted in a reduction in wear volume. Among the tested films, the DLC film with a bias gradient delta of 25 V exhibited the lowest CoF of 0.14 and the least wear volume of 0.98 mg, respectively. These findings suggest that the said film prepared on ACM displays excellent wear resistance.

Effects of sp3 bond ratio and modulation ratios on nanotribology behaviors of diamond-like carbon coatings investigated using atomistic nanoscratching simulations.

Diamond-like carbon (DLC) films are amorphous solids in which carbon atoms are linked by hybridized sp3, sp2, and sp bonds. The mechanical and tribological properties of DLC films can be adjusted by tuning the sp2/sp3 bond ratio. These films are typically used as protective coatings for components such as dies, automotive engines, mechanical seals, hard disk drives, biological engineering devices, and micro/nano-electromechanical systems. Further exploration of the mechanical and tribological behavior of DLC films is important for enhancing functional design for the above applications. The simulation results show that single-layer DLC with a higher sp3 ratio has better resistance to indentation. Single-layer DLC with a lower initial sp3 ratio has lower friction and a shorter repeated cycle in the friction force curve due to an increase in the graphitization of the friction interface. Single-layer DLC with a higher sp3 ratio has a higher coefficient of friction because compared with the normal force, the friction force is much more sensitive to an increase in the sp3 ratio. Molecular dynamics simulations based on the Tersoff potential were performed using the open-source code LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator).

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.

Improved mechanical and tribological properties of diamond-like carbon films by adjusting pulsed substrate bias

In order to obtain super-hard films with excellent mechanical and tribological properties, diamond-like carbon (DLC) films were prepared on ultra-fine grained cemented carbide substrates by linear magnetic filtered arc ion plating (AIP) under different negative pulsed bias voltages. The result indicated that the pulsed bias voltage had a strong effect on the structure and properties of DLC films. The as-deposited films showed very smooth surfaces because of the magnetic filtration system. Upon increasing the bias voltage from 0 to −1000 V, the fraction of sp3 bonds first increased and then decreased, while the ratio ID/IG exhibited the opposite tendency. The maximum sp3 bond fraction of 74.4 % was determined at −200 V, resulting in the highest hardness, elastic modulus, and elastic recovery of the films. Furthermore, the films exhibited excellent tribological properties with the lowest friction coefficient of 0.073 at −200 V, which was associated with the super-high hardness and low surface roughness. The improved mechanical and tribological properties of DLC films could be achieved by using the appropriate pulsed bias voltage.

Effects of the inclination angles of DLC end face micro-texture on the tribological properties of dry gas seal rings

To improve the tribological performance of the seal rings in the dry gas seal, the elliptical micro-textures with different inclination angles (0°, 45°, 90°, 135°) were processed on the end face of SiC static rings by nanosecond laser. Diamond-like carbon (DLC) films were then deposited on the micro-textured end face. Under dry friction condition, the end-face friction and wear test was conducted to simulate the actual working state of the dry gas seal at start-up phase. The effects of micro-texture inclination angles and DLC phase change on the tribological properties of seal rings were investigated. The possible friction reduction mechanism was analyzed. The results show that compared with the smooth surface, the elliptical micro-texture can effectively improve the tribological properties of DLC films. At the same time, the inclination angle of the elliptical micro-texture has a remarkable influence on the tribological properties. When the micro-texture inclination angle is 90°, the static ring sample has the best friction reduction and wear resistance performance. Compared with the untextured sample, the average friction coefficient is reduced by 46.15%. The wear reduction characteristics of the textured end face are mainly contributed to the capturing effect of the texture on wear particles.

High-temperature tribological properties of diamond-like carbon films: A review

Abstract The rapid development of aerospace industry has made more and more machinery parts of equipment working at high temperature. Due to the lubrication failure of lubricating oil and grease at high temperature, solid lubricant coatings are almost the only effective method to achieve super low friction at high temperature. In recent years, the tribological properties of diamond-like carbon (DLC) films have been extensively studied at high temperature. The present study reviews the microstructure of DLC films and the influence of doping different elements on the structure of DLC films. Second, the mechanical properties and thermal stability of pure DLC films and DLC doped with different elements are also described. DLC films have different microstructures and tribological properties by different preparation methods. Finally, the high-temperature lubrication failure mechanism of DLC films and the tribological properties of DLC films when doped with different elements are discussed from the macro and micro perspectives.

Nano-scratch and nano-indentation study of diamond-like carbon/NiP-SiC nanocomposite bilayer

To overcome the poor adhesion of diamond-like carbon (DLC) films to the steel substrate, an interlayer can be used. In this study, the effect of the addition of NiP-SiC nanocomposite coating as an interlayer in comparison to the NiP coating has been investigated on tribological properties of the DLC layer. Using nano-scratch and nano-indentation tests, the mechanical and nanotribological behaviour of the DLC layers, such as scratch resistance, coefficient of friction, interfacial adhesion between DLC layer and substrate, and hardness were characterised. DLC/NiP-SiC samples showed higher adhesion, hardness, elastic modulus, and lower friction coefficient. These results reveal the improved tribological properties of DLC film by applying the NiP-SiC nanocomposite interlayer in comparison to using the pure NiP interlayer.

High temperature solid/liquid lubrication behaviours of DLC films

AbstractThe high temperature solid/liquid lubrication performances of DLC (diamond like carbon) films were investigated by a ball‐on‐disc tribometer under perfluoropolyether (PFPE) oil. The friction and wear behaviours of DLC films sliding against a Si3N4 ball at different friction pairs, sliding speeds and temperatures were evaluated systematically under dry friction. Moreover, tribological properties of DLC films were investigated under PFPE oils lubrication at elevated temperature. The experimental results show that the solid–liquid synergy lubrication is beneficial to improve the tribological properties of the steel‐related friction system and the tribological properties of the friction pair are significantly influenced by lubrication modes under PFPE oil lubrication, especially at high temperature. Tribotests show that the friction system exhibited low friction behaviours under PFPE oil due to the excellent thermal stability of PFPE oil. Coefficient of friction (CoF) of the friction system is as super low as 0.029 under PFPE oil.

The unusual tribological behavior of diamond‐like carbon films under high vacuum

We fabricate F‐doped and F‐S‐codoped diamond‐like carbon (DLC) films using plasma‐enhanced chemical vapor deposition system. The hardness, Raman spectra, and high‐vacuum tribological behaviors indicate that the films are DLC films. The hardness is close related to the tribological properties of DLC films under high vacuum. The high hardness of DLC films would be helpful for obtaining the long lifetime under high vacuum. The lifetimes of F‐S‐codoped DLC films are about 120 and 140 seconds, which is attributed to the fast graphitization under high vacuum. The lifetime of F‐doped DLC films is prolonged to the value of around 300 and 440 seconds, X‐ray photoelectron spectroscopy analysis exhibits the existence of the “adsorption” F, and transmission electron microscopy analysis shows that the “adsorption” F could react with Fe to form layered FeF2 nanocrystal at the initial sliding, which could be helpful for prolonging the lifetime of F‐doped DLC films under high vacuum. This investigation opens a new window to overcome the disadvantage of F, S‐doped DLC films under high vacuum.

On the adhesion and wear resistance of DLC films deposited on nitrile butadiene rubber: A Ti-C interlayer

To promote the adhesion strength between diamond-like carbon (DLC) films and nitrile butadiene rubber (NBR) substrates, titanium-doped carbon (Ti-C) films prepared by dual-target magnetron sputtering under varied substrate bias voltages were used as an interlayer on the rough NBR. The surface topography and structure of Ti-C films were investigated by atomic force microscopy (AFM) and Raman spectra. Raman analysis indicates that the increase of substrate bias voltage leads to an increase of the number or the size of sp2 clusters in the Ti-C interlayer. The adhesion strength and tribological properties of DLC films coated on NBR substrate were scrutinized by a scratch tester and a ball-on-disk tribometer, respectively. It was found that DLC film with a Ti-C interlayer at a certain bias voltage exhibited superior wear resistance with a low coefficient of friction (CoF) during the sliding of 6000 laps. No clear damages in the coatings were observed from the wear tracks. Besides, the scratch test also revealed a reliable adhesion when the interlayer was prepared at −150 V, as confirmed by a scratch crack width of ~50 μm as compared to that of the pure DLC film increasing to ~ 120 μm. Therefore, a Ti-C interlayer could significantly enhance the adhesion and wear resistance of DLC thin films deposited on NBR.

A comparative study of surface morphology, mechanical and tribological properties of DLC films deposited on Cr and Ni nanolayers

Applying metallic interlayer between diamond-like carbon (DLC) and substrate is a promising method to improve the adhesion and efficiency of DLC films. Understanding how the interlayer parameters affect the properties of DLC coatings leads to production of long-time excellent performance of them. In this study, DLC films deposited by PECVD and 10, 20 and 40 nm layers of Ni and Cr were sputtered on silicon substrates to use as the adhesion layers. The role of chemical structure and physical parameters (surface roughness) of interlayers on the final properties of DLC films were investigated using atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoscratch and nanoindentation techniques. It was found that a lower surface roughness with a sharp and homogenous distribution of particles sizes (height) results in formation of a smooth DLC film with lower friction coefficient, more stress reduction and better adhesion strength. It was discussed that the chemical structure of the interlayer was important in the solubility and diffusion of carbon atoms and consequently in instability of sp3 and sp2 bonding. Results demonstrated that 40 nm Cr interlayer, not only improved the adhesion of the DLC films but also generated the lowest friction coefficient, better wear resistance and the highest hardness (27 GPa).

Enhancement in the tribological properties of Cr/DLC multilayers in methane: structural transformation induced by sliding

Diamond-like carbon (DLC) films respond as a lubricating material under some atmosphere conditions, such as N2, moisture. Nevertheless, incomplete knowledge about the key factors, which control the performances of film under distinct gases, limits the further use of them. Herein, the tribological properties of DLC film and Cr/DLC multilayers with different modulation periods were studied under methane. Frictional tests conducted under methane show that Cr/DLC film exhibits a great reduction in friction and wear compared to that of DLC film. An interpretation for tribological performances of films was proposed by considering repassivation and structural transformation taking place at the sliding interface. It is chemical passivation that plays a major role in the tribological properties of DLC film, while the Cr/DLC multilayers possess the lower friction coefficient because of the structural transformation induced by shearing. This study is important for broadening applications of DLC film in the industrial field and reducing energy waste.

Superlow friction and diffusion behaviors of a steel-related system in the presence of nano lubricant additive in PFPE oil

The lubrication performances of diamond like carbon (DLC) films were investigated by a ball-on-disc tribometer under perfluoropolyether (PFPE) oil lubrications. The influence of nano lubricant additives in PFPE oil on the tribological properties of DLC films was evaluated. The experimental results show that the solid-liquid synergy lubrication is beneficial to improve the tribological properties of the steel-related friction system and the tribological properties of the friction pair are significantly influenced by lubrication modes and the types and contents of nano lubricant additives under PFPE oil lubrication. The friction system exhibits super low friction behaviors under PFPE oil with nano MoS2 lubricant additive lubrication due to the excellent compatibility of nano MoS2 additives with PFPE oil. Coefficient of friction (CoF) of the friction system is as super low as 0.02 under PFPE oil with 0.2 wt.% nano MoS2 additive lubrication. Superlow friction mechanism is attributed to the pointlike contact of nano MoS2 additive as soft phase and the excellent diffusion behaviors of nano MoS2 additives in PFPE oil. The potential usefulness of nano MoS2 particles as the lubricant additives in PFPE oil for the steel/DLC films has been demonstrated.

Mechanical Properties of Hydrogen Free Diamond-Like Carbon Thin Films Deposited by High Power Impulse Magnetron Sputtering with Ne

Hydrogen-free diamond-like carbon (DLC) thin films are attractive for a wide range of industrial applications. One of the challenges related to the use of hard DLC lies in the high intrinsic compressive stresses that limit the film adhesion. Here, we report on the mechanical and tribological properties of DLC films deposited by High Power Impulse Magnetron Sputtering (HiPIMS) with Ne as the process gas. In contrast to standard magnetron sputtering as well as standard Ar-based HiPIMS process, the Ne-HiPIMS lead to dense DLC films with increased mass density (up to 2.65 g/cm3) and a hardness of 23 GPa when deposited on steel with a Cr + CrN adhesion interlayer. Tribological testing by the pin-on-disk method revealed a friction coefficient of 0.22 against steel and a wear rate of 2 × 10−17 m3/Nm. The wear rate is about an order of magnitude lower than that of the films deposited using Ar. The differences in the film properties are attributed to an enhanced C ionization in the Ne-HiPIMS discharge.

Tribological properties of a tetrahedral amorphous carbon (ta-C) film under boundary lubrication in the presence of organic friction modifiers and zinc dialkyldithiophosphate (ZDDP)

Diamond-like carbon (DLC) films provide low friction and high wear resistance under lubricated conditions. In particular, tetrahedral amorphous carbon (ta-C) film has shown ultralow friction behavior under boundary lubrication with an organic friction modifier (FM), such as glycerol mono-oleate (GMO). On the other hand, there are many studies on the tribological properties of DLC films that are lubricated with oils with added zinc dialkyldithiophosphate (ZDDP). ZDDP, however, shows quite different tribological performance, which depends on the type of DLC film. The lubrication mechanism of ZDDP against DLC films has not yet been fully clarified. This research studied the effects of ZDDP additives on the tribological properties of a ta-C film under boundary lubrication with oils that contained organic friction modifiers. The tribological properties were evaluated using the reciprocating type cylinder-on-disk tribo-tester. ZDDP and three types of organic additives (GMO, glycerol mono-oleoyl ether (GME), and tallow diethanol amine (TDEA)) were added to poly-alpha olefin (PAO). Friction tests were carried out for the DLC/DLC tribo-pair under lubrication with PAO and PAO-based oils containing GMO, GME, TDEA, ZDDP, GMO+ZDDP, GME+ZDDP, and TDEA+ZDDP additives. Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM) were used for analyses of the ta-C surface after the friction tests. The ta-C film lubricated with PAO+FMs reached an ultralow friction coefficient of 0.02–0.03. On the other hand, the films with PAO+GMO+ZDDP and PAO+GME+ZDDP had increased friction coefficients and wear volumes compared to the PAO+FMs oils. The ta-C film lubricated with PAO+TDEA+ZDDP reached an ultralow friction coefficient of 0.028. The surface analyses demonstrated that the formation rate and chemical composition of the ZDDP-derived tribofilm depended on the combination of ZDDP and each FM. It was concluded that the formation rate and chemical composition of the ZDDP-derived tribofilm played an important role in the low friction behavior of the ta-C films that were lubricated with any of the oils with added ZDDP.

Improvement of the Tribological Properties of DLC/oxynitriding Duplex-treated AISI H13 Alloy Steel

In this study, diamond-like carbon (DLC) films were prepared by DC-pulsed plasma CVD after the oxynitride treatment of AISI H13 tool steel. In order to investigate the tribological properties of DLC films, a Raman spectroscopy analysis, wear test, adhesion and roughness tests were performed. The main parameters of the DC-pulsed plasma CVD process includes various pretreatment times of argon plasma (15, 30, 45 and 60 min). Experimental results showed that an oxynitride layer and the DLC films could be completely obtained after DLC/oxynitriding duplex treatment. The duplex coating layers had optimal adhesion (critical load reached to 10.65 N) and wear properties after DC-pulsed plasma was CVD treated via a low pulse voltage (–1.5 kV), pretreatment times of the argon plasma were 15 min and the substrate temperature was kept at 40°C. Meanwhile, the optimal DLC/oxynitriding duplex treated specimens possessed the lowest wear volume (2.25 × 10 –3 mm 3 ) and a lower friction coefficient (0.06).

Tribological Properties of DLC Films Deposited at Different Time under Low Temperature

The tribological properties of DLC(Diamond like carbon) films deposited for different time on mono-crystalline silicon were investigated by using the UMT-2 micro friction and wear tester. The surface topography, composition and hardness of the films were determined by three-dimensional topography instrument, Raman spectrum and nano mechanics tester. The worn surface topography of the films deposited for different time were observed by scanning electron microscopy. The results show that the thickness of the films deposited for different time is nonlinearly increased with the deposition time. The films are the standard nano-films. The surface hardness of the films is low because the films contain hydrogen composition and the deposition temperature is very low. The films deposited for different time have a good anti-friction property, which is improved when the deposition time is prolonged.

Effects of Pre-heat Treatment on Tribological Properties of DLC Film

A diamond-like carbon (DLC) film exhibits excellent tribological properties. This type of film has an amorphous structure that is generally composed of hydrogen and carbon atoms, and it is the structure of sp2- and sp3-hybridized orbital carbon which brings about the extraordinary tribological properties of the DLC film. It is known that heating causes structural changes in a DLC film, and pre-heat treatment greatly affects the various properties of a DLC film. In this study, we focus on the effects of pre-heat treatment on the friction and wear properties of a hydrogenated DLC film and discuss the structural changes in the film. After pre-heat treatment, the tribological properties were evaluated using a ball-on-disk sliding tester. Our findings indicated that the friction and wear properties of the DLC film were improved by pre-heating up to 500 °C. An as-deposited DLC film had a friction coefficient of approximately 0.15, whereas it was approximately 0.03 for a film pre-heated at 500 °C. The structure of the DLC film was analyzed using micro-laser Raman spectroscopy. The analytic results of the Raman spectroscopy of the film surface showed that the G peak position had shifted toward a higher wave number. This result suggested that hydrogen had evolved from the DLC film because of pre-heat treatment. The half bandwidth of the G peak shifted toward a lower wave number with increases in the pre-heating temperature. This indicated that graphitization of the DLC film had been induced by pre-heat treatment. From these findings, we consider that the hydrogen evolution induced structural changes. Line analysis using micro-laser Raman spectroscopy was performed on a cross section of the pre-heated DLC film. The line analysis showed structural changes which were induced by hydrogen evolution, on the top of the DLC film. On the other hand, hydrogen evolution and graphitization were prevented inside the film, indicating that a gradient structure had been generated by pre-heat treatment. The low friction coefficient of the pre-heated DLC film was caused by graphitization of the DLC film surface. The graphite layer on the top of the film would induce lower shearing resistance at the sliding interface. This gradient structure of the DLC film plays an important role in improving the tribological properties of the pre-heated DLC film.

Evolution of coefficient of friction with deposition temperature in diamond like carbon thin films

Diamond like carbon (DLC) thin films, used as excellent solid lubricant, are grown on Si substrates at temperatures in the range of 100–600 °C using pulsed direct current magnetron sputtering to understand the role of substrate temperature on the tribological properties. Friction tests have been carried out using a micro-tribometer at a load of 2 N. Phase evolution in the films with temperature is studied using micro-Raman spectroscopy. Lateral force microscopy is employed to study the evolution of surface and friction topography in the films. We have observed an increase in the coefficient of friction (μ) from 0.05 to 0.30 with increase in deposition temperature. The films deposited below 400 °C exhibited excellent tribological properties with film deposited at 100 °C depicting the lowest value of μ (approx. 0.05). The films deposited above 400 °C have been found to wear out at early stages. The degradation in tribological properties of DLC films deposited at high temperatures is explained on the basis of structural transformation taking place during the film deposition.

Analysis of plastic deformation in diamond like carbon films–steel substrate system with tribological tests

The influence of plastic deformation of the substrate on the tribological properties of diamond like carbon (DLC) films was investigated in DLC films–steel substrate system. The tribological properties of DLC films deposited on different hardness steel were evaluated by a ball on disk rotating-type friction tester at room temperature under different environments. In dry nitrogen, DLC films on soft steel exhibited excellent tribological properties, especially obvious under high load (such as 20 N and 50 N). However, DLC films on hard steel were worn out quickly at load of 20 N. Plastic deformation was observed on soft steel after tribological tests. The width and depth of plastic deformation track increased with increase of the experimental load. Super low friction and no measurable wear were kept in good condition even large plastic deformation under high load conditions in DLC films–soft steel system. In open air, DLC films on soft steel exhibited high coefficient of friction and DLC films on ball were worn out quickly. Plastic deformation was not observed on soft steel because the contact area increased and the thick hardened layer on contact surface were formed by DLC films and debris particles together on the steel substrate. The wear track on steel became deep and wide with increase of loads and DLC films were worn out. The experimental results showed that super low friction and high wear resistance of DLC films on soft steel can be attributed to the good adhesion and plastic deformation. Plastic deformation played an active role in the tribological properties of DLC films on soft steel in the present work.