Behaviour Of Diamond-like Carbon Coatings Research Articles

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).

МЕТОДИКА НАНЕСЕНИЯ И ИСПЫТАНИЯ ИЗНОСОСТОЙКОСТИ АЛМАЗОПОДОБНЫХ КОМПОЗИТНЫХ ПОКРЫТИЙ

An important task in studying the properties of diamond-like coatings is the organization of the process to study its characteristics. The analysis of the available information on the structure and tribological behavior of diamond-like carbon coatings is considered. Laboratory studies on model samples are described.

The Effect of Bias Voltage and Acetylene Gas Flow Rate on the Wear Behavior of Diamond-like Carbon Coatings on M2 High-Speed Steel

This paper investigates the impact of bias voltage and acetylene flow rate on the mechanical, structural, and scratch performance of diamond-like carbon (DLC) coated high-speed steel (HSS) M2 commonly used in hydraulic vane pumps. The DLC coatings were produced through plasma-enhanced chemical vapour deposition, with micro-Raman spectroscopy used to analyze their structure via G-peak and D-peak measurements. Results showed that DLC deposited at 350 V and 100 sccm demonstrated high hardness (28.99 GPa) and modulus of elasticity (308.1 GPa), with the highest critical load of 167.246 mN indicating superior adhesion to the HSS M2 substrate at a higher bias voltage and lower flow rate. The minimum wear rate of 3.02 × 10−3 mm3/Nm was achieved with a thinner DLC coating deposited at 350V bias voltage and 100 sccm acetylene flow rate.

Friction behavior of diamond-like carbon coatings with different sp3 contents by atomistic-scale friction dynamics

The tribological performance of diamond-like carbon (DLC) coatings as a function of sp3 concentrations was investigated using molecular dynamics and experimental analysis. The results show that sp3 bonds proportion, hardness, and elastic modulus present an uptrend, whereas surface roughness displays a downtrend with the increase of SBV. Adhesive debris elements and no furrows features of the DLC coatings at low SBVs indicated the wear mechanism is dominated by adhesive wear. The DLC coatings at high SBVs were featured by obvious furrows and stacked abrasives, suggesting abrasive-wear-dominated. Atomistic-scale friction dynamics were used to reveal the friction mechanism. Interactions with the Si3N4 friction pair changed from carbon atoms chains or single atoms to atom groups with the increase of biases. The formation of the interfacial bonds changed from CN covalent bonds to CC covalent bonds. At high biases, there was a dissociation of many internal CC bonds that occurred in the DLC coatings. The bond evolution in friction simulation indicated the tribological mechanism transformed from adhesive wear to abrasive wear with an increase of the SBV. The DLC coating at the SBV of −30 V was located at the transformation point of two wear mechanisms, showing a well-established wear resistance.

Tribological Behavior of Diamond-like Carbon Coatings under Boundary Friction: Part II. Lubrication with Chemically Modified Layers

Tribological Behavior of Diamond-like Carbon Coatings under Boundary Friction: Part II. Lubrication with Chemically Modified Layers

Tribological Behavior of Diamond-like Carbon Coatings under Boundary Friction: Part I. Structure, Testing Methods, Lubrication by Adsorption Layers

Tribological Behavior of Diamond-like Carbon Coatings under Boundary Friction: Part I. Structure, Testing Methods, Lubrication by Adsorption Layers

Effect of diamond-like carbon coatings alloying with chromium and molybdenum on the lubricating properties of oils during friction in pair with steel

The results have been presented of an experimental study of the tribological behavior of diamond-like carbon coatings (DLC) doped with chromium and molybdenum obtained by reactive magnetron sputtering. The effect of alloying with these metals on the tribological characteristics of boundary lubrication of a DLC coating/steel contact has been studied for the case of three model lubricants (inactive, surfactant, and chemically active). It has been shown that doping with chromium and molybdenum improves both the tribological characteristics of coatings under dry friction and the lubricating properties of the model oils, while alloying with molybdenum provides lower coefficients of friction and less wear at dry and boundary friction than alloying with chromium.

Study of the methane flow influence in the micro-tribology behavior of DLC coatings deposited by PECVD: a Raman analysis

This paper presents a Raman spectroscopy study of the influence of methane flow on the micro-tribological behavior of diamond-like carbon coatings deposited with an industrial plasma-enhanced chemical vapor deposition system. Results have shown a direct relationship between the methane flow and thickness of the coatings. The analysis of the Raman spectra and deposition parameters allowed establishing the influence of H content with the methane flow, the disorder level and estimation of the sp3 fraction on the carbon coatings. The micro-tribology tests showed a strong dependence of the wear resistance and hardness with Raman parameters. The coating deposited at 72-sccm methane flow presented a thickness of 1.7 µm and a sp3 fraction of 0.33. This sp3 fraction gave rise to a hardness of 24 GPa and an excellent wear resistance of 3.3 × 10–6 mm3 N−1 mm−1 for this DLC coating. Wear tests showed a swelling in the wear profiles on this coating, which was associated with the occurrence of a re-hybridization process.

Tribological behavior of diamond-like carbon coatings with patterned structure deposited by the filtered cathodic vacuum arc

Patterned diamond-like carbon (DLC) coatings were deposited on a Si (100) substrate using the filtered cathodic vacuum arc technique. The effects of the patterning and of the coating thickness on tribological behavior of DLC coating were investigated using a ball-on-disk tribometer under dry and oil-lubrication conditions. The results suggest that 1 mm2 patterned structures delimited by 100-μm grooves can enhance the tribological properties. The coefficients of friction of the tested patterned films were 0.123 and 0.067 under dry and oil lubrication conditions, respectively, 10% and 21% lower than the coefficients of friction of the continuous DLC films with the same thickness. Raman spectroscopy measurements showed graphitized wear particles for both the continuous and patterned DLC films, but the debris of patterned DLC films having a greater degree of graphitization under dry sliding. The grooves of the patterned coatings could serve as a lubricant reservoir and trap the wear debris, which was beneficial for the tribological properties. The effect of the thickness of the patterned DLC films on their tribology behavior was also investigated. The 0.4-μm-thick patterned samples exhibited the lowest coefficients of friction of 0.105 and 0.058 under dry and oil lubrication conditions, respectively, while the 0.8-μm-thick patterned samples showed the lowest specific wear rate. In addition, the coefficients of friction of the patterned samples increased with an increase in the film thickness under oil lubrication conditions.

MICROSTRUCTURES AND HIGH-TEMPERATURE TRIBOLOGICAL BEHAVIORS OF MAGNETRON SPUTTERED DLC COATINGS

A diamond-like carbon (DLC) coating was deposited on YT14 cemented carbide cutting tools using an MS (magnetron sputtering), and the surface–interface morphologies, phases, and bonding energy of the obtained coatings were investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), respectively. The wear behaviors of DLC coatings were measured using high temperature wear tests. The results show that the [Formula: see text] and [Formula: see text] appear at 284.4, and 285.3[Formula: see text]eV, respectively, the DLC coating is composed of the crystal planes (111) and (220). The average COF of DLC coatings at 750, 800, and 850[Formula: see text]C was 0.1956, 0.2082, and 0.4085, respectively, the wear depth increases with the wear temperatures increasing: At 750[Formula: see text]C, the diamond planes (111) and (222) remained, while at 800 and 850[Formula: see text]C, only the diamond plane (111) still remained, the diamond plane (220) was oxidized, resulting in wear capability decreasing. The wear mechanism was composed of abrasive wear, delamination, and oxidation wear.

Structure and tribological behavior of diamond-like carbon coatings deposited on the martensitic stainless steel: The influence of gas composition and temperature

The relationship between the tribological behavior and inherent features of the DLC coatings (i.e. structural and mechanical properties) as a consequence of deposition conditions was investigated. Hence, a plasma nitrocarburising process as pretreatment followed by Diamond-Like Carbon (DLC) deposition by pulsed DC Plasma Assisted Chemical Vapor Deposition (PACVD) method, was utilized. Although a remarkable reduction in the friction coefficient of coated samples was observed, almost the same friction coefficient was measured for the DLC coatings (i.e. 0.2), regardless of their diverse intrinsic properties. As the H/C ratio in feeding gas and temperature increased up to certain values, the hardness and elastic modulus increased while the wear rate decreased. Therefore, the DLC coating deposited with the highest Hydrogen fraction at 160°C, exhibited the highest hardness and elastic modulus (i.e. 25.4GPa and 177.4GPa, respectively), as well as the lowest wear rate of 5.9×10−06mm3/N·m.

Analysis of the friction behavior of DLC in warm bulk forming by using the ring compression test

The reduction of die wear is an effective way to decrease costs within bulk forming processes. Therefore, specific tool materials and heat treatments as well as special coatings are used to prolong the lifetime of the tools. Diamond-like carbon (DLC) coatings show high hardness and superior frictional behavior. However, these coatings seem to be inappropriate for hot forming due to degradation processes at elevated temperatures. But for warm forming, due to the lower temperature input into the cavity, DLC might be an appropriate coating. Friction influences the shear stresses on the cavity surface and is therefore an important factor for reducing die wear. Hence, the analysis of the frictional behavior of DLC coatings within warm forming by using the ring compression test will be presented within this paper. An amorphous hydrogenated carbon coating and six metallic doped amorphous hydrogenated carbon coatings (Cr, V and W each in two variants) are compared to CrN and no coating. Firstly, nomograms are graphed by the use of finite-element-analysis. Thereafter two test series are carried out varying forming temperature and lubrication. The results show that DLC coatings with and without metallic doping are able to reduce friction in warm forming. Within the investigations, an amorphous hydrogenated carbon doped with 15 % chromium shows the lowest friction factor and is able to reduce the friction factor compared to no coating by up to 64 % within warm forming.

Effect of composition on mechanical behaviour of diamond-like carbon coatings modified with titanium

In this study, diamond-like carbon (DLC) films modified with titanium were deposited by plasma decomposition of metallorganic precursor, titanium isopropoxide in CH 4/H 2/Ar gas atmosphere. The obtained films were composed of amorphous titanium oxide and nanocrystalline titanium carbide, embedded in an amorphous hydrogenated (a-C:H) matrix. The TiC/TiO 2 ratio in the DLC matrix was found to be dependent on the deposition parameters. The dependence of the films chemical composition on gas mixture and substrate temperature was investigated by X-ray photoelectron spectroscopy, whereas the crystallinity of TiC nanoparticles and their dimension were evaluated by X-ray diffraction. The size of TiC crystallites varied from 10 to 35 nm, depending on the process parameters. The intrinsic hardness of 10–13 GPa, elastic modulus of 170–200 GPa and hardness-to-modulus ratio of obtained coatings were measured by the nanoindentation technique. Obtained results demonstrated a correlation of mechanical properties with the chemical composition and the ratio of amorphous/crystalline phases in the films. In particular, the formation of nanocrystalline TiC with atomic concentration not exceeding 10% and with grain size between 10 nm and 15 nm resulted in significantly enhanced mechanical properties of composite material in comparison with ordinary DLC films.

Action of oil additives when used in DLC coated contacts

Under boundary lubrication conditions, different oil additives are used to prevent metal to metal contact by boundary film formation, thus reducing friction and wear of contact surfaces. With the introduction of diamond-like carbon (DLC) coatings, the major concern is the compatibility of coated surfaces with existing oils and additives, originally designed for uncoated metallic surfaces. The aim of the present work was to investigate the influence of extreme pressure, antiwear and friction modifier additives and their concentration on the tribological performance of DLC coatings in the boundary lubrication regime. Results show that antiwear and friction modifier additives have only minor effect on the frictional behaviour of DLC coatings. On the other hand, depending on the contact conditions, lubrication of steel/W doped DLC contacts with oils containing S based extreme pressure additives can result in greatly improved tribological performance caused by WS2 tribofilm formation.

Tribological behaviors of diamond-like carbon coatings on plasma nitrided steel using three BN-containing lubricants

In this work, diamond-like carbon (DLC) coatings were deposited on plasma nitrided AISI 1045 steel by magnetron sputtering. Three BN-containing additives and molybdenum dithiocarbamate (MoDTC) were added to poly-alpha-olefin (PAO) as additives. The additive content (mass fraction) in PAO was fixed at 0.5 wt%. The friction and wear characters of DLC coatings on nitrided steel discs sliding against AISI 52100 steel balls were tested under the lubricated conditions. It was found that borate esters have a higher load carrying capacity and much better anti-wear and friction-reducing ability than that of MoDTC. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were employed to explore the properties of the worn surface and the mechanism of friction and wear. According to the XPS analysis, the adsorbed organic N-containing compounds and BN are, possibly, the primary reason for the novel borate esters to possess a relatively constant coefficient of friction and lower wear rate. On the other hand, possibly, the MoDTC molecules break down during sliding and produce many Mo-oxides, and then the Mo-oxides destroy the DLC coating because of its sharp edge crystalline solid structure. After destroying the DLC coating, the MoDTC react with metals and form MoS 2 tribofilm, and decrease coefficient of friction of rubbing pairs.

In-situ investigation on the deformation and damage behaviour of diamond-like carbon coated thin films under uniaxial loading

In the present work, the failure behaviour of diamond-like carbon (DLC) coatings on thin steel substrate under uniaxial tensile loading is analyzed in-situ in scanning electron microscopy as well as ex-situ using focused ion beam cross section and transmission electron microscopy. Aim of the work is to find correlations between the failure behaviour of the coating system, the adhesion and the stress–strain behaviour of a DLC coating system under tensile loadings conditions. Therefore thin amorphous DLC films were coated onto thin stainless steel foils using a plasma assisted chemical vapour deposition technique. It is found from the in-situ investigations that at increasing strains cracks were formed in the coating, with decreasing spacing at higher strains. By comparing uncoated steels foils with coated systems the stress–strain behaviour of a DLC coating was determined. The DLC coating, although already strongly cracked, bears loads up to a total strain of 15%. Cross section analyses with a focused ion beam and microscopy techniques supported these investigations. During straining the formation of two deformation bands adjacent to the Cr adhesion layer was observed. This deformation bands also indicate a high interfacial adhesion.

Nanoindentation-induced deformation behaviour of diamond-like carbon coatings on silicon substrates

The deformation behaviour of diamond-like carbon (DLC) coatings on silicon substrates induced by indentation has been investigated. DLC coatings, deposited by a plasma-assisted chemical vapour deposition technique, were subjected to nanoindentation over a range of maximum loads from 100 mN to 300 mN. The resulting load-displacement plots displayed pop-ins for maximum loads of 200 mN and above, with no distinct pop-out for any of the loads studied. Compressive deformation of the coating, up to a strain of ∼ 9%, was observed. The coating–substrate composite was devoid of cracks at lower loads, but at the maximum load of 300 mN, ring cracks in the coating and a median crack in the substrate were observed. Furthermore, cracking, {111} slip and localized phase transformations were observed in the silicon substrate. The onset of these structural changes was correlated to the mechanical behaviour during indentation.

Surface properties and cell behaviour of diamond-like carbon coatings produced by plasma immersion

The morphology, microstructure and roughness of the diamond-like carbon (DLC) films produced by plasma immersion were investigated. Vero cells (fibroblasts) were utilized for the in vitro biocompatibility studies of the DLC-coated Ti–13Nb–13Zr alloy. In the cytotoxicity assay, fibroblast cells were cultured for a period of 24 h, and in the adhesion assay, cells were cultured for a period of 2 and 24 h. The cell morphology was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). No evidence was found that the presence of the DLC coating had any adverse effect. Our results show that the adherence of fibroblasts was significantly enhanced when Ti alloy was coated with DLC from the uncoated.

Superlow friction behavior of diamond-like carbon coatings: Time and speed effects

The friction behavior of a diamond-like carbon coating was studied in reciprocating sliding contact at speeds from 0.01 to 5 mm/s, in dry nitrogen. “Superlow” friction coefficients of 0.003–0.008 were obtained in continuous sliding at the higher speeds (>1 mm/s). However, friction coefficients rose to values typical of diamond-like carbon in dry and ambient air (0.01–0.1) at lower speeds (<0.5 mm/s) as well as in time-delayed, higher speed tests. The rise of the friction coefficients in both speed and time-delay tests was in good quantitative agreement with gas adsorption kinetics predicted by the Elovich equation for adsorption onto carbon. More generally, superlow friction could be sustained, suppressed, and recovered as a function of exposure time, demonstrating that duty cycle cannot be ignored when predicting performance of superlow friction coatings in devices.

Study of mechanical behavior of diamond-like carbon coatings by several instrumented tribometers

Mechanical applications of coatings obtained by physical vapor deposition (PVD) and plasma-assisted chemical vapor deposition (PA-CVD) are numerous. In many cases, the thickness of material deposited does not exceed 5 μm. This means that when the coated element is submitted to a load, the film is not thick enough to avoid transmission of a significant part of the applied stress to the substrate. In addition, during the service life of a part used for mechanical applications, the superficial film generally encounters fatigue type solicitations. These solicitations differ radically from a regularly increasing load applied by a classical scratch test apparatus. To study the mechanical behavior of thin films, specific test rigs must be developed. This paper focuses on tests performed on diamond-like carbon (DLC) films. The first test apparatus is a scanning electron microscope (SEM) in situ tribometer that was used to test DLC produced for aerospace applications. The second apparatus is a pin-on-disc type which performs a repetitive scratch test with acoustic emission monitoring. This apparatus was designed to study the fatigue behavior of hard coatings at room atmosphere with a solicitation localized in the film and with immediate detection of damage. Using the same hardness diamond indenters as on scratch test devices, tests were performed on a pin-on-disc tribometer. During these tests, the diamond undergoes almost no damage, which means that the contact geometry remains constant (as does the contact pressure). Another advantage is that the highest shear stress is located in the layer.