DLC Coatings Research Articles

The high temperature tribological behavior of Si, O containing hydrogenated diamond-like carbon (a-C:H/a-Si:O) coating against an aluminum alloy

Si added DLC coatings may be of value for engineering applications where a low COF and high wear resistance are required for the extended service life, during which the operating temperatures may increase above 200 °C. Hot/warm forming dies, machining tools, or critical sliding components such as the upper compression rings in combustion engines are among the components that operate under demanding conditions. This study examines friction, wear and adhesion behavior of multilayered DLC coatings consisting of a top layer of H-DLC and an inner layer rich in Si and O (a-C:H/a-Si:O) tested against Al-6.5% Si (319 Al) at temperatures above 200°C where DLC coatings typically show high COF and wear. The a-C:H/a-Si:O coatings maintained the low room temperature (25°C) steady state COF (μS of 0.17) up to 400°C with a μS of 0.04 at 200°C and 0.11 at 400°C. Low wear rates (W) were observed in the same temperature range with W=2.86×10−5mm3/Nm at 25°C and 16.23×10−5mm3/Nm at 400°C. Micro-Raman spectroscopy studies of the coating surface revealed a constant ID/IG ratio of 0.4–0.6 between 25°C and 400°C. It was suggested that incorporation of Si hindered temperature induced bulk graphitization (due to suppression of sp2 bond formation) of the coating and thus accounted for the low coating wear. Scanning electron microscopy observations indicated formation of a transfer layer on 319 Al contact surface when tested against 319 Al. Cross-sectional transmission electron microscopy of the transfer layer formed on 319 Al at 400°C revealed that they consisted of amorphous C with traces of SiC, transferred from the a-C:H/a-Si:O and mechanically mixed with Al. X-ray photoelectron spectroscopy of the transfer layer revealed the formation of C–OH, C–H and Si–O bonds. Accordingly, the low steady state friction obtained up to 400°C could be attributed to H and OH passivation of the C and Si in the coating surface and in the transfer layers.

Friction and Wear Characteristics of Hydrogenated and Hydrogen-Free DLC Coatings when Lubricated with Biodegradable Vegetable Oil

Large amount of unsaturated and polar component of oils enhance the lubrication of ferrous materials. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, consequently improving the fuel efficiency and durability of these components. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetal oil must be investigated. A ball-on-plate tribotester was used to run the experiments using stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC sliding against 440C stainless steel ball. Raman analysis was performed to investigate the structural change of the coatings. At high temperatures, the CoF decreases in both coatings but the wear rate increases in the a-C:H and decreases in the ta-C DLC-coated plates. CoF and wear rate (coated layer and counter surface) are mostly influenced by coating graphitization. The degree of graphitization increases with increasing temperature. Graphitization occurs in the tribological contact because of friction-induced heating under contact and high contact stress conditions.

Torsional Fretting Wear Behavior of Duplex DLC Coatings Deposited on Ion Nitriding Treated LZ50 Steel

Duplex ion nitriding/DLC coatings were prepared on LZ50 steel. Characterizations were detected by scanning electron microscopy, atomic force microscope, Raman spectroscopy, dynamic ultra-micro hardness tester, and profilometer. The torsional fretting wear behaviors of DLC coatings and substrate LZ50 steel against GCr15 steel ball in dry conditions were studied under angular displacement amplitudes within a range of 0.1°–5°, constant normal load of 50 N, and rotational speed of 0.8° s−1. DLC coatings presented dense structure and high hardness. Compared with the substrate, DLC coatings removed the mix fretting regime and shifted the slip regime to low angular displacement amplitudes. The friction torques of DLC coatings were lower than that of the substrates. In the partial slip regime, the damage of DLC coatings was low. In the slip regime, the damage mechanism combined with delamination, abrasive wear, and graphitization. The DLC coatings exhibited good capability for anti-torsional fretting damage.

Surface hardening of optic materials by deposition of diamond like carbon coatings from separated plasma of arc discharge

This article considers the issue of strengthening of optic materials used in the IR spectrum by deposition of diamond like carbon coatings from separated plasma arc discharge. The report shows results of tests of bare and strengthened optical materials such as BaF2, MgF2, Si, Ge, including the testing of their strength and spectral characteristics. Results for the determination of optical constants for the DLC coatings deposited on substrates of Ge and Si, by using separated plasma, are also presented. Investigations showed that surface hardening of optical materials operable in the IR range, by the deposition of diamond like carbon coating onto their surface, according to this technology, considerably improves operational properties and preserves or improves their optic properties.

Tribological behavior of uncoated and DLC-coated CoCr and Ti-alloys in contact with UHMWPE and PEEK counterbodies

There are very few studies of PEEK wearing against DLC. In this study, DLC and Zr-DLC coatings were deposited by magnetron sputtering onto Ti alloy substrates. Coated and un-coated Ti alloy samples were tribologically tested in multidirectional pin-on-disk equipment against UHMWPE and PEEK. CoCr alloy was also tested as control. Each of the materials was tested for 2 million cycles (Mc) in bovine serum lubricant (37°C). Gravimetrical weight loss and changes in surface profile were similar when tested against UHMWPE. However, Zr-DLC samples delaminated after 1.2 Mc. When tested against PEEK, both coated samples delaminated, despite that the coatings maintained their structural integrity. The synergetic effect of stress-induced corrosion through biological fluid and high cyclic shear stress may have caused interface fatigue and subsequent delamination of both coatings.

Evaluation of the surface properties of PEEK substrate after two-step plasma modification: Etching and deposition of DLC coatings

This paper presents results of research on the change of the surface properties of poly (ether–ether–ketone) PEEK substrates under the influence of two-stage processes of the coatings production. Those modification processes included the etching procedure in oxygen, nitrogen and methane atmosphere, as well as synthesis of carbon coatings in methane plasma. After both the etching process and the synthesis of diamond like carbon DLC coating, the modified samples were analysed in terms of the changes in surface geometry, its chemical composition, nano-scale mechanical properties, the contact angle and the surface free energy, as well. The work also includes a comparison of changes in the friction coefficient for each set of process parameters applied in the synthesis of carbon coatings.

Development of low-friction and wear-resistant surfaces for low-cost Al hot stamping tools

In this study, advanced surfaces and coatings have been developed using plasma thermochemical treatment, PVD coating, electroless Ni-BN plating and duplex surface engineering to produce low-friction and wear-resistant surfaces for cast iron stamping tools. Their microstructural and nano-mechanical properties were systematically analysed and the tribological behaviour of these new surfaces and coatings were evaluated. The experimental results have shown that under dry sliding condition, the tribological behaviour of aluminium differed great from that of steel regardless of the counterpart material. Highly reactive aluminium had a strong tendency to solder with tool surfaces during dry sliding. However, the lubricity of gray cast irons can be significantly improved by Ni-BN and DLC coatings. The coefficient of friction reduced from about 0.5 for untreated cast irons to about 0.2 sliding against aluminium. Duplex treatment combining plasma nitrocarburising with low- friction coatings showed superior durability than both DLC and Ni-BN coatings.

Influence of Wettability and Mechanical Properties on Tribological Performance of DLC Coatings under Water Lubrication

DLC coatings are currently used in a wide variety of industrial fields because of their outstanding properties such as high hardness, high wear resistance, low friction and so on under oil lubrication as well as no lubrication. In order to evaluate the tribological performance of DLC coatings under water lubrication, eight types of DLC coatings were evaluated by water-lubricated sliding tests at sliding velocities of 0.02 m/s and 0.1 m/s. The different DLC coating types comprised both hydrogenated and hydrogen-free DLC films that were deposited using different techniques: amorphous hydrogenated DLC (a-C:H), that doped with tungsten (a-C:H:W), that doped with silicon (a-C:H:Si) and hydrogen-free DLC (ta-C). DLC coatings showed low friction coefficient and excellent wear resistance. Friction coefficient and wear rate decreased with increasing sliding velocity. The effect of surface wettability and mechanical properties on tribological characteristics was investigated. Friction coefficient decreased as the contact angle increased. Hydrogen-free DLC coating with the highest hardness showed the highest friction and a larger wear rate. Furthermore, DLC coatings deposited with interlayer showed longer lifetimes.

Development, characterization and testing of tungsten doped DLC coatings for dry rotary swaging

The extensive use of lubricant during rotary swaging is particularly required for a good surface finish of the work piece and the reduction of tool wear. Abandonment of lubricant would improve the ecological process-balance and could also accelerate for further work piece refinements. Also cleaning of the manufactured components becomes obsolete. Thus, a dry machining is highly innovative, consequently new strategies to substitute the lubricant functions become necessary. To encounter the changed tribological conditions due to dry rotary swaging, low friction, tungsten doped, hard DLC coatings and structured surfaces are the most promising approaches. In this work the development of hard coating by means of reactive magnetron sputtering is presented, a promising layer variant is deposited on a set of tools and then tested and investigated in real use.

DLC 膜及び CNx 膜の低摩擦機構解明とタンタル含有 DLC 膜の摩擦特性

DLC 膜及び CNx 膜の低摩擦機構解明とタンタル含有 DLC 膜の摩擦特性

Investigations Regarding Process Stability Aspects in Thread Tapping Al-Si Alloys

The large number of drills and taps in automotive powertrain components make these processes to a considerable machining step. Due to the fact that hypereutectic Al-Si alloys tend to adhere on the tool surface, the machinability of these alloys is challenging. Especially the adhesion of Al has a negative influence on the chip transportation and leads to an increase of stochastic inclinations of clogging the chip flute. A variety of physical vapour deposition (PVD) coatings like TiCN, CrN, TiB2 on carbide metal taps have been tested in machining experiments. Also two types of DLC coatings have been compared in the tests. In order to improve the chip transportation, the tribological effects were determined by investigating the affinity of build-up edge and aluminium adhesion in the rake flank. Results are discussed in terms of materials, which are fit for purpose of automotive powertrain machining steps.

DLC コーティング技術と今後の動向

DLC コーティング技術と今後の動向

P056 切欠きを有するSUS316材の疲労強度に及ぼすDLC被覆処理の影響(メカボケーション学生研究発表セッション)

P056 切欠きを有するSUS316材の疲労強度に及ぼすDLC被覆処理の影響(メカボケーション学生研究発表セッション)

Analysis of Characteristics of DLC Coating Thin Film in Tungsten Carbide for Production of Medical Thermal-Infrared Lenses

This study was carried out on DLC thin film deposition technology used in infrared optical system production as a method of reducing the shape changes of the molding core and the consequent loss of life. Experiments on the deposition on silicon wafer and tungsten carbide used as a substrate for molding core were conducted at each processing condition using a filtered arc system, and it was found that the surface and mechanical properties were of the greatest quality when the substrate bias voltage of -150 V was used. In addition, it was confirmed that the PV and Ra characteristics were improved by the deposition of the DLC thin film.

Silver surface segregation in Ag-DLC nanocomposite coatings

AgDLC coatings were deposited by magnetron sputtering in order to evaluate: i) the Ag nanoparticle size distribution along the coatings thickness and ii) the silver stability in DLC coatings. Four different coatings were deposited, two AgDLC nanocomposite coatings containing 20at.% of Ag, with thicknesses of 250nm and 1000nm, a 250nm AgDLC nanocomposite coating with carbon barrier layer of 75nm and a multilayer coating, consisting of a pure Ag layer with a carbon barrier layer of 75nm. The coatings were characterized with respect to their structure (by means of X-ray diffraction (XRD)), morphology (by scanning electron microscopy (SEM)) and Ag distribution in depth (by glow discharge optical emission spectroscopy (GDOES)). The AgDLC nanocomposite coatings are composed of Ag nanograins (with a size of about 3nm) dispersed in an amorphous carbon matrix. The SEM results suggest a bimodal size distribution along the coatings thickness, it was found that Ag forms nanoparticles and aggregates with sizes ranging from 14nm up to 52nm on the coating's surface, whereas in bulk, no Ag nanoparticles were visible by SEM. The monitoring of the Ag stability at room temperature conditions during a period of 6months showed that Ag segregates to the coatings surface, in the AgDLC nanocomposite coating with 1000nm forming Ag nanofibers, while the thinner AgDLC (250nm) as well as the multilayer (Ag+DLC and AgDLC+DLC) coatings were stable over time.

Effect of plasma treatment on the surface properties of polydimethylsiloxane

ABSTRACTIn this work, the analysis of the plasma modification of polydimethylsiloxane (PDMS) substrates was conducted. The influence of the modification onto the changes occurred within the geometrical structure and chemical composition of the surface was analyzed. Due to the study of the atomic force microscopy, it was possible to determine the relationships between the surface development and applied process parameters, defining the conditions facilitating to obtain isotropic or anisotropic orientations of wrinkles. A precise analysis of the chemical composition of the surface, executed before and after the modification processes, enabled to define the changes in their elementary composition. Moreover, the modification influence onto the changes of the contact angle and the surface free energy were also analyzed. So, based on the research it was stated that the increase of value of the surface free energy is proportional to the sp3 phase contents in the DLC coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41635.

Effect of polar groups in lubricants on sliding speed dependent friction coefficients of DLC coatings

The speed dependent friction coefficients of two types of DLC coatings, a-C:H and ta-C, were evaluated when lubricated with 1-hexadecene, which did not contain any functional group, and with oleic acid and oleyl alcohol that did. The friction coefficient measured for ta-C at a low sliding speed of 0·01 mm s−1 with the 1-hexadecene lubricant that did not contain any functional group was 0·22, which was higher than the value of 0·11 seen for a-C:H. The friction coefficients measured for a-C:H and ta-C at a high sliding speed of 50 mm s−1 with 1-hexadecene were 0·10 and 0·06 respectively. The friction coefficients measured with oleic acid and oleyl alcohol were 0·02 for a-C:H and less than 0·001 for ta-C. The results showed that the friction coefficient of ta-C was more strongly influenced by the functional group in the lubricants than that of a-C:H. It is assumed that this difference between the two coatings can be attributed to a difference in the capability to form a tribochemical reacted film under boundary lubrication. Under mixed lubrication, differences in lubricity also affected this friction coefficient difference, in addition to the properties of the tribochemical reacted film.

Sliding properties of Zr-DLC coatings: The effect of tribolayer formation

Amorphous carbon-based coatings (DLC) exhibit excellent mechanical and tribological properties such as high hardness, high elastic modulus, low friction and low wear. Reduced friction is often related to the formation of a low-friction tribolayer, which is formed during sliding and transferred to the counterpart. Here, we investigate the sliding of hydrogenated and non-hydrogenated DLC coatings alloyed with zirconium; pure DLC films are used as reference. The coatings were deposited by magnetron sputtering in Ar (non-hydrogenated) and Ar/methane atmosphere (hydrogenated) onto steel substrates and silicon wafers. The total thickness of the coatings was around 1.5μm including a complex Ti/TiN/TiCN adhesion-improving interlayer with a thickness of 450nm. All deposited coatings were amorphous, Zr/C ratio was approx. 0.05. The hardness was in the range of 9–13GPa. Tribological tests were carried out in humid air at room temperature, at 100°C and in nitrogen environment using pin-on-disk. Intermittent tribological test analysis has been performed to understand running-in behaviour. The worn surfaces and wear debris were analysed by Raman spectroscopy. Coatings alloyed with Zr showed lower friction and wear at room temperature compared to pure DLC. In general, Zr-doped hydrogenated coating outperformed the non-hydrogenated one when tested in an inert nitrogen atmosphere or at elevated temperature (100°C), exhibiting almost super-low friction (μ=0.03 in the steady-state regime) due to the formation of a homogenous, thick and stable tribolayer.

Tribological behavior and machining performance of non-hydrogenated diamond-like carbon coating tested against Ti–6Al–4V: Effect of surface passivation by ethanol

The role of an ethanol environment on the tribological behavior of non-hydrogenated DLC (NH-DLC) coatings sliding against Ti–6Al–4V was investigated. Pin-on-disk tests were performed under different test atmospheres consisting of dry argon (0% RH) and ambient air (40% RH) and also while the samples were submerged in water (H2O) and ethanol (C2H5OH). The running-in friction of the NH-DLC coatings under each condition was studied and the results were used to rationalize the drilling behavior of Ti–6Al–4V by NH-DLC coated tools. The highest running-in coefficient of friction (μR=0.55) was observed under a dry argon atmosphere. In ambient air, the μR was 0.42, while a reduction in μR to 0.21 was recorded when the tests were carried out in H2O. The observed reductions in μR were attributed to OH passivation of the NH-DLC surfaces. Ethanol was effective in providing OH passivation, as evident from the lowest μR of 0.15. Consistent with the friction measurements, a 45% reduction in drilling torque was obtained when 10% ethanol was blended with the metal removal fluid (MRF) consisting of water–oil (1:3) mixture compared to an ethanol free MRF.

Tribological Properties and Characterization of Diamond Like Carbon Coatings Deposited by MW/RF and RF Plasma‐Enhanced CVD Method on Poly(ether‐ether‐ketone)

Diamond like carbon coatings were manufactured by dual frequency plasma enhanced chemical vapour deposition method on a poly(ether‐ether‐ketone) substrates. In the presented work, modified surfaces were characterized in terms of the tribological parameters, surface topography, mechanical properties and the chemical composition. Obtained results of the research indicate that the highest resistance against wear, which means the most probable application abilities, presented the carbon coatings created in RF plasma with the use of nitrogen for the preliminary stage of preparation. Due to that modification, it was possible to limit the coefficient of friction from the value of c.a. 0.4–0.26 and 35 times decrease the specific wear rate. The DLC coatings deposited in RF plasma exhibited hardness of about 2 GPa with a relatively low contribution of sp3 phase and surface roughness.