DLC Coatings Research Articles

Effect of structure and deposition technology on tribological properties of DLC coatings alloyed with VIA group metals

The results of a comprehensive research on atomic structure, phase composition, micromechanical and tribological characteristics of alloyed DLC coatings have been presented. The coatings have been deposited by reactive magnetron sputtering in acetylene-nitrogen gas mixtures of different compositions (a-C:H:Cr), by plasma-assisted chemical vapor deposition in atmospheres of silicone-organic precursor gases (a-C:H:Mo:Si), and by nonreactive magnetron sputtering of a composite target (a-C:H:W).

Effect of ZDDP concentration on the thermal film formation on steel, hydrogenated non-doped and Si-doped DLC

This work focuses on the ZDDP concentration (1, 5 and 20wt%) to form a ZDDP film on surfaces during static thermal tests at 150°C. Silicon-doped and hydrogenated DLC coatings, as well as steel as reference, were studied using Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The results show that, on the three surfaces, the structure of the ZDDP thermal film consists of identical groups of pyrophosphate and zinc oxide, while the sulphuric groups are dissimilar. On the steel surface, the sulphuric part consists of a mixture of organic sulphide and sulphohydryl groups, but on H-DLC and Si-DLC only organic sulphide groups are found; there are no sulphohydryl groups. Moreover, both ATR-FTIR and XPS show that different concentrations of ZDDP do not affect the final chemical structure of the ZDDP thermal film on any of the studied surfaces. In addition, the XPS results show that the thickness of the thermal film is linear with the concentration for the whole range from 1 to 20wt%, supporting also its uniform chemical structure. These thicknesses further show that the reactivity of the ZDDP film is higher on the steel surface than on the DLC coatings.

Surface characterization and biological evaluation of silver-incorporated DLC coatings fabricated by hybrid RF PACVD/MS method

Since the biological response of the body towards an implanted material is mainly governed by its surface properties, biomaterials are improved by various kinds of coatings. Their role is to provide good mechanical and biological characteristics, and exclude some disadvantages like post-implantation infections. This phenomenon may be reduced by introduction of silver as an antibacterial agent. This study evaluates the Ag-DLC films synthesized by the hybrid RF PACVD/MS method according to the patent number PL401955-A1 worked out inter alia by the authors. Such tests as XPS, SEM, EDS, AFM, FTIR, Raman and ICP-TOF-MS were used to determine surface properties of the coatings. The obtained results were correlated with the biological response estimated on the basis of cells viability assay (osteoblast cells line Saos-2) and bacterial colonization test (Escherichia coli strain DH5α). Results showed that the hybrid RF PACVD/MS method allows one to get tight coating preventing the diffusion of harmful elements from the metallic substrate. Ag concentration increases with the growing power density, it occurs in metallic state, does not create chemical bonds and is evenly dispersed within the DLC matrix in the form of nanoscale silver clusters. Increasing silver content above 2at.% improves bactericidal properties, but decreases cell viability

The effect of alloying on the structure and peculiarities of tribological behavior of vacuum-deposited diamond-like coatings

In this work, we report the results of a study of the atomic and crystalline structures, phase and chemical compositions and tribological properties of DLC coatings deposited by plasma-assisted (PA) CVD (a-C:H:Si and a-C:H:Si:Mo) and magnetron reactive sputtering (a-C:H:Cr). The a-C:H:Si:Mo coatings revealed the formation of ultra-dispersed inclusions of either molybdenum carbides or silicides, whereas no such inclusions were found in the a-C:H:Si compound. The a-C:H:Cr coatings that were deposited in an acetylene–nitrogen gas mixture exhibited a nanocomposite structure composed of chromium, its carbide and nitride phases. The tribological tests showed that the DLC coatings with silicon and silicon–molybdenum have a high friction coefficient and a low working performance, while the chromium-containing coatings have high levels of their mechanical and tribological characteristics, making them promising materials for operation under high contact pressures.

Friction and wear behaviour of Mo–W doped carbon-based coating during boundary lubricated sliding

A molybdenum and tungsten doped carbon-based coating (Mo–W–C) was developed in order to provide low friction in boundary lubricated sliding condition at ambient and at high temperature. The Mo–W–C coating showed the lowest friction coefficient among a number of commercially available state-of-the-art DLC coatings at ambient temperature. At elevated temperature (200°C), Mo–W–C coating showed a significant reduction in friction coefficient with sliding distance in contrast to DLC coatings. Raman spectroscopy revealed the importance of combined Mo and W doping for achieving low friction at both ambient and high temperature. The significant decrease in friction and wear rate was attributed to the presence of graphitic carbon debris (from coating) and ‘in situ’ formed metal sulphides (WS2 and MoS2, where metals were supplied from coating and sulphur from engine oil) in the transfer layer.

Mechanical analysis and high temperature wear behaviour of AlCrN/DLC coated titanium alloy

The present investigation focused on the mechanical and the tribological behaviour of PVD coated Ti-6Al-4V for elevated temperature applications. The effects of AlCrN and DLC coatings on the surface of the titanium alloys produced by arc evaporation method were studied. Nano indentation, tensile and high temperature wear tests were carried out to evaluate the hardness, strength and tribological properties of coated Ti-6Al-4V. The DLC coating on the titanium alloy exhibits a higher hardness value of 1,125 HV. The results of tensile test made clear that both AlCrN and DLC coatings can improve the plasticity of uncoated Ti-6Al-4V alloy. High temperature sliding wear characteristics of AlCrN and DLC coatings was studied under lubricated condition for elevated temperature applications. The wear tests showed that the wear rates and friction coefficients of AlCrN and DLC coatings, both increases with the increasing temperature. The wear results were compared with those of uncoated Ti-6Al-4V titanium alloys, which exhibited a lower coefficient of friction (COF) due to the change of wear mechanism to slight abrasion wear from severe delamination. The superiority of the DLC coated Ti-6Al-4V was confirmed by the final results.

生体適合DLCコーティングの医療機器への応用

生体適合DLCコーティングの医療機器への応用

Progress and Prospect of DLC Coating Applied Technologies to Automotive Engine Component

Progress and Prospect of DLC Coating Applied Technologies to Automotive Engine Component

Evolution of the nano-scale mechanical properties of tribofilms formed from low- and high-SAPS oils and ZDDP on DLC coatings and steel

The evolution of the nano-mechanical properties of tribofilms formed in steel/steel, steel/a-C:H and steel/Si-DLC contacts lubricated with two commercial oils containing different amounts of SAPS additives (E6 and E7 grade) and a mineral base oil containing ZDDP additive were examined in this investigation for two very different time periods. An atomic force microscope (AFM) was used in different modes to measure the topography, film thickness and stiffness, while the nano-hardness was measured with a nano-indenter. In addition, FTIR microscope was used on selected samples to explain some of the tribofilm׳s mechanical modifications with chemical changes. The results have shown that the tribofilm׳s evolution and growth are very much surface and additive dependent, and are different for steel and DLC coatings.

Adsorption of alcohols and fatty acids onto hydrogenated (a-C:H) DLC coatings

Information about the interactions between lubricants and DLC coatings is scarce, despite there having been many studies over the years. In this investigation we used ToF-SIMS, XPS and contact-angle analyses to examine the adsorption ability and mechanisms with respect to two oiliness additives, i.e., hexadecanol and hexadecanoic acid, on an a-C:H coating. In addition, we analyzed the resistance of the adsorbed films to external influences like solvent cleaning. The results show that both molecules adsorb onto surface oxides and hydroxides present on the initial DLC surface and shield these structures with their hydrocarbon tails. This makes the surfaces less polar, which is manifested in a smaller polar component of the surface energy. We also showed that ultrasonic cleaning in heptane has no significant effect on the quantity of adsorbed molecules or on their chemical state. This not only shows the relatively strong adsorption of these molecules, but also provides useful information for future experimental work. Of the two examined molecules, the acid showed a greater adsorption ability than the alcohol, which explains some of the previously reported better tribological properties in the case of the acid with respect to the alcohol.

마그네슘 합금에 대한 DLC 코팅의 온도에 따른 마찰기구 해석

마그네슘 합금에 대한 DLC 코팅의 온도에 따른 마찰기구 해석

Performance of CoCrMo Alloy with Me-Doped DLC Coatings Prepared by a Magnetron Sputtering Method

Abstract To enhance the wear resistance of CoCrMo alloy used as hip joints for longer service time, the W-DLC (W doped-diamond like carbon) films and Ti-DLC (Ti doped-diamond like carbon) films were prepared by a DC magnetron sputtering method combined with ion source technique. The thickness of the as-prepared films was 1.89 μm. Results show that the coated CoCrMo alloy exhibits higher wear resistance in comparison with uncoated CoCrMo one, and the friction properties of W-DLC coated CoCrMo alloy are better than those of Ti-DLC coated CoCrMo alloy. The wear rates of uncoated CoCrMo, Ti-DLC coated CoCrMo and W-DLC coated CoCrMo are 15.25×10 −6 , 0.76×10 −6 , and 0.19×10 −6 mm 3 m −1 N −1 , respectively. Raman spectrum analysis shows that the excellent wear resistance of coated CoCrMo alloys is attributed to the graphitization of the top layer of DLC films during rubbing.

Plasma Nitriding and DLC Coatings for Corrosion Protection of Precipitation Hardening Stainless Steel

A duplex treatment, combining a nitriding diffusion process and the deposition of DLC coatings is investigated as an option for corrosion protection of precipitation hardening steels, in order to increase the service life of components used in plastic injection molds. Hardness and mechanical resistance are determined and the corrosion resistance in two different media is analyzed. Non‐coated nitrided and non‐nitrided samples are also tested for comparison. Corrosion resistance is investigated by means of immersion, salt spray, and polarization tests. No signs of atmospheric corrosion are observed after the salt spray test and in acid media, the nitrided samples, with and without DLC, present the lowest mass loss. The duplex sample shows the best corrosion behavior in the electrochemical tests.

Characterization of thick and soft DLC coatings deposited on plasma nitrided austenitic stainless steel

Thick and soft a-C:H:Si coatings containing more than 45% hydrogen (thickness: 25–27μm, hardness: 6GPa, Young's Modulus 38GPa and low ratio of sp3 bonds) were deposited by PACVD with a DC pulsed discharge on nitrided (duplex sample) and non-nitrided austenitic stainless steel (coated sample). After deposition, the chemical, microstructural and tribological properties were studied. Finally, the adhesion and the atmospheric corrosion resistance of a-C:H:Si coatings were also investigated.In pin-on-disk tests, the friction coefficient using an alumina pin of 6mm in diameter as counterpart, under 0.59GPa Hertzian pressure was 0.05 for the coated samples and 0.076 for the duplex samples. These values were more than one order of magnitude smaller than the friction coefficient of the nitrided sample without coating, which was around 0.65. In the coated samples, the wear loss could not be measured. In ball-on-disk tests under dry sliding conditions, the coatings were tested under different Hertzian pressures (1.29, 1.44 and 1.57GPa) using a steel ball with a diameter of 1.5mm as counterpart. Using a normal load of 9N, the a-C:H:Si coating of the coated samples was broken and detached thus leading to a coefficient of friction of around 0.429. However, in contrast to that, the friction coefficient of the duplex samples remained stable and reached as maximum a value of 0.208.In abrasive tests, mass loss was undetectable in both duplex and coated samples. Furthermore it could be seen that the a-C:H:Si film showed only some smaller grooves and no severe damage or deformation. On the contrary, severe damage was observed in the only nitrided sample. With respect to adhesion, the critical load to break the coating was higher in the duplex sample (27N) than in the only coated sample (16.3N). By chemical analysis using the salt spray fog test, the duplex sample remained clean, but the coated sample failed and presented film delamination as well as general corrosion.

Reduction in EHL Friction by a DLC Coating

This work evaluates the influence of DLC coatings on the frictional behaviour of lubricated line contacts in the fluid friction regime. Experiments on a twin-disc machine showed a significant reduction in friction using DLC coated discs instead of uncoated ones. The experimental results are compared by calculations using a three-dimensional thermal elastohydrodynamic simulation model. According to the calculations, the lower heat conductivity of DLC coatings is the main reason for the reduction in friction. This is because of the higher temperature level in the lubricating gap, which results in a reduction in the effective lubricant viscosity and consequently in reduced frictional shear stress. Lower bulk temperatures of the discs are a further consequence of the low heat conductivity of DLC coatings. The resulting lower temperature at the inlet zone of the contact in the steady-state conditions also leads to larger lubricating gaps and to a further reduction in friction.

Effect of Reduction in Lateral Friction Coefficient due to Stable DLC Coating on

Effect of Reduction in Lateral Friction Coefficient due to Stable DLC Coating on

Development of DLC coating architectures for demanding functional surface applications through nano- and micro-mechanical testing

DLC coatings can combine high hardness with low friction. However, they are often deposited with high levels of intrinsic stress and display low adhesion strength resulting in poor performance in demanding applications. A highly topical challenge is to develop advanced DLC coatings capable of withstanding more demanding applications in the automotive, cutting tool, MEMS and oil and gas sectors. The results from several nanomechanical and tribological test techniques – nanoindentation, nano-scratch and nano-fretting (nano-wear) – can be used together to aid the design of DLC coating architectures for enhanced durability in specific applications. In this study the behaviour of multilayered DLC coatings (Cr/W–C:H/a-C:H, Cr/W–C:H/Si–a-C:H) was compared to that of CrN/a-C:H:W (WC/C). We have previously reported that in nano-wear tests the coating with the highest hardness and H/E displayed greater wear resistance [T.W. Liskiewicz et al., Surf. Coat. Technol. 237 (2013) 212]. By employing nano- and micro-scale tribological testing with probes of differing sharpness it is possible to change the sensitivity of the test to probe the response of the coating top layer or the entire multilayer coating–substrate system. In the nano-scratch tests using a spherical indenter with a 5 μm end radius the maximum stresses are located well within the top layer of the multilayer coatings and consequently the mechanical properties of this top layer dominate the nano-tribological behaviour. In the micro-scratch using a 25 μm spherical probe the stress field extends further towards the sub-layers and steel substrate and consequently the behaviour is completely different. Under these conditions the coating with the lowest hardness and H/E showed improved performance with higher critical loads for cracking and total coating failure. High resolution SEM imaging has been used to investigate this further. A simple contact model strongly suggests that cracking and failure events occur on the harder coatings when the maximum von Mises stress was located close to the interfaces in the multilayer systems.

Relationship Between the Nanoscale Topographical and Mechanical Properties of Tribochemical Films on DLC Coatings and Their Macroscopic Friction Behavior

The properties of tribochemical films play an important, or even the key, role with respect to friction in boundary lubrication. While their chemical behavior has already been widely studied, their mechanical properties are much less well understood. However, their nanoscale mechanical properties and behavior may reveal important information about a correlation with the macroscopic friction behavior. In this investigation, we looked at steel, a-C:H and Si-DLC in contact with steel lubricated using two commercial oils containing different amount of SAPS additives (E6 and E7 grade) and a mineral base oil containing the ZDDP additive. The tribofilms were characterized using an atomic force microscope with seven different parameters, i.e., the topography (features morphology), tribofilm surface coverage, nano-roughness, adhesion, film thickness, lateral force, i.e., nanoscale friction, and the film stiffness through force modulation. The results confirmed the formation of tribofilms on all the selected coatings and showed that the film formation and its nanoscale properties are dependent on the coating and the additive. Two distinctive groups of parameters were identified: one closely related to the surface energy of the materials and the other clearly distinguishing the DLC coatings from the steel. The adhesion and tribofilm thickness were found to correlate directly with the macroscopic friction, while the other parameters have higher-order dependences.

Fatigue and adhesion characterization of DLC coatings on steel substrates by perpendicular and inclined impact tests

During the Future Advanced Rotorcraft Drive System (FARDS) program, the Aviation Development Directorate (ADD), Aviation Applied Technology Directorate (AATD), Bell Helicopter Textron Inc., University of Toledo and the Aristotle University of Thessaloniki worked together to perform bearing coating tests. The mechanical properties of the DLC coating and its steel substrate were determined via nano-indentations and a FEM supported evaluation of the obtained results. The coating fatigue and adhesion were quantified by perpendicular and inclined impact tests respectively, coupled with appropriate finite element method (FEM) calculations. The inclined impact tests were conducted under lubricated conditions for avoiding abrasion caused by sliding friction on the coated surfaces. In this way, the coating fatigue failure during this test was mainly affected by the impact load, the material's properties and the film adhesion. The effects of these factors on the coating fatigue failure were described via an iterative FEM supported method. Using this method, the coating adhesion was estimated taking into account the exercised impact loads and the determined material properties.

In situ synthesized TiC–DLC nanocomposite coatings on titanium surface in acetylene ambient

TiC–DLC coatings were in situ synthesized on Ti target surface in acetylene ambient by cathodic arc evaporation. In this process, TiC–DLC composite phases were formed by chemical reaction between Ti target surface and ionized C ions. Different acetylene (C2H2) flow rate and synthetic time were designed as two independent variables to synthesize two series of coatings to study the effects of different synthetic parameters on structure of the coatings. Surface morphology, composition and structure of the coatings were investigated by SEM, EDS, XRD and Raman spectroscopy, respectively. The result showed that the structure and composition of the coatings on the titanium metal target surface could be controlled by changing the C2H2 flow rate. The uniform TiC-DLC composite phases were observed in the coatings, while both C2H2 flow rate and synthetic time could significantly affect the thickness and bonding state of the coatings.