Properties Of Diamond-like Carbon Coatings Research Articles

Study on properties of diamond-like carbon coatings based on COMSOL

Comsol software was used to design and simulate the preparation of DLC coating on 316 stainless steel substrate by vacuum evaporation plating method. The influence of evaporation temperature on coating quality was explored by controlling substrate temperature factors, and the corrosion resistance of DLC was simulated. The simulation coating preparation results showed the surface distribution of the DLC coating prepared by vacuum evaporation is uneven, and the thickest core becomes thinner layer by layer along the periphery. Under the same conditions, the higher the evaporation temperature is, the better the coating quality is. The corrosion behavior of DLC coating over time was studied by simulating the corrosion of DLC coating in the human body environment. The simulation corrosion results showed that the corrosion rate of DLC coating in the human body environment was slow, and the corrosion rate of the metal matrix was significantly higher than that of DLC coating.

Influence of 1-Ethyl-3-methylimidazolium Diethylphosphate Ionic Liquid on the Performance of Eu- and Gd-Doped Diamond-like Carbon Coatings

A composite lubricating system that combines solid and liquid lubrication can create a synergistic effect by leveraging the strengths of both types of lubricants. Solid lubrication coatings possess advantageous load-bearing abilities and exhibit low volatility. By adopting this approach, the system retains the merits of solid lubrication while simultaneously harnessing the advantages of liquid lubrication. The unique properties of diamond-like carbon coatings (DLCs) offer the potential to create binding locations for lubricant additives by introducing dopant elements that have a high affinity with additives. In the present work, the combined use of europium-doped diamond-like carbon (Eu-doped DLC) with varying atomic concentrations of the dopant element (1.7 at. % and 2.4 at. %) and gadolinium-doped diamond-like carbon (Gd-doped DLC) with different atomic concentrations of the dopant element (1.7 at. % and 2.3 at. %) was studied alongside a pure DLC coating and the incorporation of an ionic liquid (IL) additive in a tribological block-on-ring system. The focus was on the 1-Ethyl-3-methylimidazolium diethylphosphate ionic liquid with a concentration of 1 wt. % in polyalphaolefin (PAO) 8. Among the investigated pairs, the coefficient of friction (CoF) of 1.7 at. % Eu-doped DLC coupled with the IL was the smallest in boundary, mixed, and elastohydrodynamic lubrication regimes. Quantification of wear was challenging due to minimal and localized wear on the DLC coating surfaces. The decrease in friction within the boundary lubrication regime underscores the promise of mechanical systems that integrate 1.7 atomic percent Europium-doped diamond-like carbon coatings with ionic liquids (IL). This study presents a compelling avenue for future scholarly exploration and research efforts focused on reducing friction and improving the efficiency of moving components, particularly in situations where tribological properties exert a substantial influence

Comparison of mechanical and tribological properties of diamond-like carbon coatings doped with Europium and Gadolinium produced by HiPIMS

Hydrogen-free diamond-like carbon (DLC) thin films can be employed for numerous applications, including engine components, once they exhibit good properties for that. They have been used as coatings due to their attractive properties, including high hardness, high wear resistance, and low CoF even under high load/pressure. One of the major limitations of hard hydrogen-free ta-C coatings applications is related to the low reactivity with oil additives used nowadays. The Ionic liquids (ILs) emerged as a novel class of lubricants that can be used in future lubricated systems due to possessing unique physical properties, like high thermal stability and conductivity. To improve the lubrication performance of DLC with ILs, the films were doped with rare earth metals such as Gd and Eu. These non-carbide-forming elements can be introduced in the DLC matrix, incorporated as single atoms, and improve the surface adsorption and reactivity of phosphorus-based IL, and consequently, the lubricating properties of DLC/ILs sliding contacts. However, many demanding applications require good performance across the different regimes (from boundary to hydrodynamic regime). Across all regimes, the boundary is the most challenging, where metal-to-metal contact occurs. Therefore, it is essential to study the influence of the doping elements on the doped-DLCs performance under the boundary regime. For comparison, a pure-DLC was used. In this study, Eu and Gd-DLC tribological systems are characterized by pin-on-disk test in dry conditions and by scratch test. Also, mechanical properties are studied through nano-indentation. Results show that samples doped with a low atomic concentration of Eu or Gd (1%–3%), despite having a CoF higher than un-doped DLC films, show typical values for pure-DLC coatings, like low specific wear rate (<10−16 m3/Nm) and high hardness (23 GPa), permitting, in the future, the combination of novel nanostructured alloyed-DLCs and ILs needed to achieve the optimal lubrication performance.

Effect of rubber substrates on the flexibility and tribological properties of diamond-like carbon coatings

In this study, closed-field unbalanced magnetron sputtering was employed to deposit a diamond-like carbon (DLC) film with Cr as the middle layer on three elastomeric substrates, namely nitrile rubber (NBR), fluorine rubber (FKM), and ethylene propylene diene monomer (EPDM) rubber, respectively. In addition, effects of these rubber substrates on the structure and properties of DLC films were investigated. Results revealed that after the bending test, several new cracks are produced on the DLC-coated EPDM rubber and NBR rubber, while debonding is not observed, indicative of the good flexibility and adhesion of DLC films on EPDM rubber and NBR rubber. Furthermore, tribological properties of NBR rubber and EPDM rubber were significantly improved by the DLC film, and almost no film damage was observed on the wear track, while the DLC coated-FKM exhibited severe wear due to the gradual peeling of the coating. Film shedding was caused by the extremely smooth FKM substrate, which led to low film adhesion. Different tribological properties of the coated rubbers were closely related to the difference in surface roughness and mechanical properties of the rubber substrates. • Using unbalanced magnetron sputtering technology to deposit DLC with Cr as a interlayer on NBR, EPDM, FKM • The substrate roughness shows considerable influence on the adhesion. • The friction properties of coated NBR, EPDM and FKM are compared systematically.

The properties of diamond-like carbon coatings used for artificial joints

The properties of diamond-like carbon coatings used for artificial joints

Effect of Molybdenum Content on Mechanical and Tribological Properties of Diamond-Like Carbon Coatings over Titanium β-21S Alloy

Molybdenum-doped diamond-like carbon (Mo-DLC) coatings have been deposited on titanium β-21S alloy (Ti–15Mo–3Nb–3Al–0.2Si) using plasma-enhanced chemical vapor deposition (PECVD) equipped with pulsed-DC magnetron sputtering. Mo contents in the deposited coatings have been controlled with an applied sputtering pulse duty cycle. Chemical composition, structure, morphology, and topography have been studied using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM), respectively. XRD pattern of the coating with highest Mo content shows the presence of carbide phase. Smooth features with low roughness values are observed in low Mo content coating, whereas high Mo content coating shows granular characteristics with a high roughness value. Raman spectra reveal the increased graphitic content for the highest metal concentration in the coatings, wherein the nanohardness is also determined to be highest, at about ~18–19 GPa. Furthermore, the ball-on-disk tribometry test on Mo-DLC coating with highest nanohardness shows a low coefficient of friction (COF) of 0.2 with low wear loss compared to that of the substrate (0.62).

CVD-diamond nanoparticle synthesis for DLC film application

Diamond-like carbon (DLC) films have been extensively applied as a solid lubricant and as a protective coating due to their attractive chemical, mechanical, and tribological properties. Furthermore, these properties of DLC coatings can be improved with the incorporation of nanoparticles of different materials, especially diamond nanoparticles (DNPs). Herein, the incorporation of chemical vapor deposition (CVD) DNPs was done from a deionized aqueous colloidal solution by using a controlled pulsed valve, which is an innovative aspect of this work. The CVD DNPs were pulverized into the plasma region and incorporated in the DLC films bulk with controllable size particle distribution and density. In addition, an enhanced process to obtain DNPs with suitable size distribution was established by using a high energy ball milling technique, centrifugation, and a special chemical cleaning process. The DLC films were deposited on a metallic substrate via a modified, pulsed DC plasma-enhanced chemical vapor deposition (PECVD) technique, with an additional cathode. X-ray diffractometry (XRD) and scanning electronic microscopy (SEM) techniques showed that an aqueous colloidal solution of high-purity DNPs with a mean diameter of 32 nm was obtained. Dynamic light scattering (DLS) results showed that it is possible to control particle size distribution by varying the milling and centrifugation time lengths. Therefore, a valuable result was that DLC films could be deposited with DNPs by using clean water without affecting deposition rate, the adhesion between the DLC films and substrates, the structural quality of the film, and keeping lower coefficient of friction.

Assessment of Mechanical and Tribological Properties of Diamond-Like Carbon Coatings on the Ti13Nb13Zr Alloy

Abstract The paper presents the results of tests on the geometric structure of the surface, hardness and tribological tests of coatings produced by the method of physical vapor deposition (PVD) on the Ti13Nb13Zr alloy. Hardness was determined using MCT3 from Anton Paar, by instrumental indentation. A diamond indenter with Berkovich geometry was used for the measurement.Model tribological tests were carried out in reciprocating motion under conditions of technically dry friction, friction with lubrication of synovial fluid and Ringer’s solution. The counter-sample in the tested friction nodes was a ball of Al2O3 with a diameter of 6 mm. Nanometer hardness measurements showed that as a result of the diamond-like carbon coating (DLC), the hardness increased by an 7-fold. The lowest friction coefficients among all tested friction nodes were obtained for the material combination Ti13Nb13Zr a-C:H - Al2O3 regardless of the conditions of testing. In the case of technically dry friction, the coefficient of friction decreased by 80%, synovial fluid by 70%, and in the case of Ringer’s solution by 88% compared to the results obtained for Ti13Nb13Zr.

Green Tribology: Orientation Properties of Diamond-Like Carbon Coatings of Friction Units in Lubricating Media

Multidisciplinary conceptual approach to studying the friction in friction couples differing in the friction surfaces, their structure, structural organization in thin layers, lubricants, and loads in the contact zones using different methods for recording the sliding and rolling friction is presented. The possibility of controlling the boundary friction using deposited coatings and the orientation effect of these coatings on lubricating materials in friction couples was demonstrated. Application of diamond-like carbon coatings onto working surfaces of parts of heavy-duty friction units (engines, tooth gears, contacts between a metalworking tool and a part being machined, etc.) allows the content of additives in lubricating oils to be significantly reduced and thus the consumption of lubricating materials to be decreased, up to complete abandonment of the use of oils containing expensive or environmentally unfriendly additives.

Effects of pulse power and argon flux flow rate on mechanical and tribological properties of diamond-like carbon coatings prepared using high power impulse magnetron sputtering technology

Diamond-like carbon (DLC) coatings were deposited on SKH51 disks using a high power impulse magnetron sputtering (HiPIMS) system. Preliminary experiments were performed to determine the HiPIMS conditions which maximized the DLC coating hardness. The composition, structure, mechanical and tribological properties of the DLC coatings were then systematically explored for different values of the HiPIMS pulse power and argon flux flow rate. For given values of the HiPIMS deposition time, pulse current and deposition distance, a high DLC coating nanohardness (19.77 GPa) was obtained using a pulse power of 5 kW and an argon flux flow rate of 100 sccm. However, the coating exhibited the lowest adhesive strength (i.e., a critical load (Lc) of just 6 N). By contrast, the coating prepared with a pulse power of 5 kW and an argon flux flow rate of 80 sccm had the highest nanohardness (22.88 GPa) and a greatly improved adhesive performance (Lc = 73 N). However, it showed the lowest wear rate among all of the coatings when sliding against an Al2O3 ball under loads of 6–14 N. The coating deposited with a pulse power of 4 kW and an argon flux flow rate of 100 sccm possessed the highest critical load of all the coatings (Lc = 94 N), and thus exhibited the longest wear life when sliding against the Al2O3 ball (∼129,756 cycles). When sliding against an AISI 52100 ball, all of the coatings showed an excellent tribological performance, including a low wear rate and a long wear life (more than 150,000 cycles).

Relationship between hardness and optical properties of diamond-like carbon coatings

Correlation between hardness and optical properties of diamond-like carbon (DLC) coatings is considered. Various methods for the characterization of mechanical, chemical and optical properties of DLC coatings are used; however, some of these methods are destructive, and others are non-destructive. It was found that optical properties of DLC coatings are proportional to their hardness. The mathematical expression that allows to calculate the hardness of a DLC coating according to its refractive index is proposed. Therefore, it is possible to avoid the use of destructive methods (such as nano-indentation technique) to characterize DLC coatings.

Structure and optical properties of diamond-like carbon coatings

Using a hybrid method of cathodic arc (PVD) and chemical (CVD) deposition from the gas phase, a new type of coatings containing high amount of sp3 bonds of carbon, capable of absorbing effectively light has been developed.This thin film material is a promised one for optical devices operating in open space environment as antireflective coating for photoreceiver bodies. The hybrid method permits to obtain effective light absorbing coatings having excellent mechanical and tribological properties and is able to sustain temperature cycling in a range from plus 150 to minus 100 oC. The optical characteristics of DLC coatings were studied depending on the content of sp2bound content. The combined physical and chemical deposition of DLC coatings allows to achieve a sufficiently high light absorption (a~10 5 cm–1) and low reflection with a relatively small coating thickness about 1 mm. It has been established that the antireflective properties of such coatings depend on the conditions for their preparation, first of all on hydrocarbon gas pressure

Deposition behavior and tribological properties of diamond-like carbon coatings on stainless steels via chemical vapor deposition

A systematic investigation was carried out to observe the deposition rate of a diamond-like carbon (DLC) coating on two stainless steel substrates by chemical vapor deposition (CVD). The objective of this research is to study the deposition behavior of the DLC coating and its tribological properties in different combinations of methane (CH4) and nitrogen, which were used as precursor gases. The results reveal that the deposition rate increases with increasing CH4 content up to 50vol%. The hardness of the DLC-deposited layer also increases while the friction coefficient decreases with increasing CH4 gas content up to 50% in the precursor gas mixture.

Effects of Interlayer on Mechanical Properties of Diamond-Like Carbon Coatings

This paper reports comparative studies on effects of interlayer on mechanical properties of diamond-like carbon (DLC) coatings. Two interlayers, TiC/Ti and CrC/Cr, were deposited and studied. The DLC coatings were prepared by using an unbalanced magnetron sputtering system. The chemical composition, micro-structure, constituted phases, and fundamental mechanical and tribological properties were evaluated. The results showed that the two amorphous (a-) DLC coatings were obtained. The a-DLC coating with the TiC/Ti interlayer showed higher adhesion, hardness and wear resistance than the one with the CrC/Cr interlayer.

Tribological Behavior of Carbon Based Coatings Adapted to Lubricant-Free Forming Conditions

In conventional deep drawing lubricants are applied to achieve low friction and wear. However, most lubricants contain environmental harmful ingredients. Global trends like sustainability and efficient resource usage motivate the development of lubricant-free deep drawing. However, dry contact conditions lead to intensive interaction between tool and workpiece especially for aluminum alloys with high adhesion tendency towards tool steel. First investigations revealed promising results for diamond like carbon (DLC) coated tools in lubricant-free tests. Therefore, in this study the lubricant-free friction and wear behavior of DLC coatings is investigated in strip drawing tests. To ensure industrial-like conditions commonly used deep drawing steel with zinc coating and an aluminum alloy were selected as sheet material. The properties of DLC coatings were modified at different scales to attain tailored tribological conditions. A laser based heat treatment achieved an increase of sp2 hybridization and thus leads to increased friction. Different mechanical pre- and post-treatment strategies like polishing and brushing proved that a smooth tool surface is beneficial for the tribological conditions in dry contacts. With laser generated structures a modification of friction was realized with varying degree of coverage for DC04. In contact with AA5182 the application of structures is limited due to adhesion.

Influence of frequency and C2H2 flow on growth properties of diamond-like carbon coatings with AlCrSi co-doping deposited using a reactive high power impulse magnetron sputtering

In this paper, diamond-like carbon (DLC) coatings with AlCrSi co-doping were deposited by a reactive high power impulse magnetron sputtering (HiPIMS) with utilizing a gas mixture of Ar and C2H2 as the precursor. The doping contents of Al, Cr and Si in the coatings were controlled by adjusting the C2H2 flow fraction in the gas mixture. The influences of the HiPIMS frequency and C2H2 flow on the microstructure, composition, mechanical properties and tribological behaviors of the AlCrSi-DLC coatings were researched carefully by using scanning electron microscope, X-ray photoelectron spectroscopy, nano-indentation and ball-on-plate tribometer, respectively. The results show that the doping AlCrSi contents increased as the C2H2 flow fraction decreased, along with the obvious structural transformation of the coatings from amorphous feature to carbide composites. The high C2H2 flow fraction tends to cause the target poisoning, resulting in the instability of the coating composition and the appearance of macro-droplets on the coating surface. The high pulse repeating frequency can effectively prevent the poisoning of the metal target and avoid the form of the arcing even at high C2H2 fraction, which is conducive to control the doping contents of the metal atoms and improve the surface quality of the AlCrSi-DLC coatings. In addition, the high frequency can facilitate the formation of the carbide, which has been expected to improve the hardness of the coatings. However, the existence of a mass of carbide phase causes serious abrasive wear of the coatings at low C2H2 fraction.

Determining the Tribological Properties of Diamond-Like Carbon Coatings Lubricated with Biodegradable Cutting Fluids

Abstract The aim of the study was to determine the effectiveness of the biodegradable cutting fluid used instead of classical, usually toxic. This paper presents the results of tribological studies of a-C:H coatings formed on HS6-5-2C steel by plasma-assisted chemical vapour deposition. The coating structures were examined using a JSM-7100F SEM. The coating microhardness was measured with a Matsuzawa tester. The surface texture analysis was performed before and after the tribological tests with a Talysurf CCI Lite optical profiler. The tribological properties were investigated using a T-01 M tester and a T-17 tester. The tests were carried out under dry friction conditions and lubricated friction conditions using a lubricant with zinc aspartate. The test results show that the layer formed at the interface prevented the moving surfaces. The investigations discussed in this paper have contributed to the development of non-toxic and environmentally-friendly manufacturing because of the use of biodegradable cutting fluid and thin, hard coatings.

Wear properties of diamond-like carbon coatings with silicon and chromium as adhesion layer using a high frequency reciprocating rig

The application of diamond-like carbon coatings to bearing surfaces is widespread from machining to bio-implants and has resulted in significant study of coating properties. The aim of this investigation was to determine the performance of two diamond-like carbon coatings, using chromium and silicon as adhesion layers. Linear reciprocating wear tests were carried out at room temperature using an AISI 440C steel ball reciprocating against the diamond-like carbon-coated metal substrate. The performance of the coatings under different contact pressures (500–3000 MPa); peak sliding velocities (28–378 mm/s); and stroke length, (1.5–4 mm). An electric resistance measurement was used to monitor coating failure owing to the dielectric nature of the tested coatings. An increase in contact pressure resulted in a decrease in number of cycles to failure for both the coatings. However, the number of cycles to failure increased proportionally with sliding speed. In addition, artifacts on the coating and blister formation generated coating debris which acted as a third body during the wear process. The debris caused complete delamination of the coatings initially at the ends of the wear scar. The silicon adhesion layer-coating samples were found to provide a greater resistance to failure due to it being thicker, harder, and more elastic as compared to samples having a chromium adhesion layer.

Influence of plasma nitriding treatment on the adhesion of DLC films deposited on AISI 4140 steel by PVD magnetron sputtering

Duplex surface treatments composed of diamond like carbon (DLC) coating followed by plasma nitriding have drawn attention for a while. In this study, AISI 4140 steel substrates were plasma nitrided at different treatment temperatures and times. Then, DLC films were deposited on both untreated and plasma nitrided samples using PVD magnetron sputtering. The effect of different plasma nitriding temperatures and times on the structural, mechanical and adhesion properties of DLC coatings was investigated by XRD, SEM, microhardness tester and scratch tester, respectively. It was found that surface hardness, intrinsic stresses, layer thickness values and phase distribution in modified layers and DLC coating were the main factors on adhesion properties of duplex coating system. The surface hardness and residual stress values of AISI 4140 steel substrates significantly increased with both DLC coating and duplex surface treatment (plasma nitriding + DLC coating). Increasing plasma nitriding temperature and time also increased the diffusion depth and the thickness of modified layers. Hard surface layers led to a significant improvement on load bearing capacity of the substrate material. However, it was also determined that the process parameters, which provided lower intrinsic stresses, improved the adhesion properties of the duplex coating system.

Synthesis of a-C coatings by HPPMS using Ar, Ne and He as process gases

Diamond-like carbon (DLC) coatings are used in numerous tribological applications, for example components of the automotive powertrain. The universal hardness HU of these coatings correlates with the sp3/sp2 bond ratio between the carbon atoms. Research on the synthesis of these coatings is upon physical vapor deposition (PVD) processes, especially the high power pulsed/impulse magnetron sputtering (HPPMS/HiPIMS). Synthesizing DLC coatings with a high sp3/sp2 ratio requires high energetic carbon ions, whose generation strongly depends on the HPPMS process parameters. Plasma diagnostics have shown that the energy of the carbon ions in the plasma strongly depends on the process gas mixture, the process gas pressure and the bias voltage. An increased fraction of high energetic carbon ions in the HPPMS plasma has been reported for process gases with a higher ionization energy as well as for higher bias voltage and lower process gas pressure. Therefore, the aim of this work is to investigate the correlation of the plasma parameters with the properties of DLC coatings. Ar, Ne and He were used as process gases. Process gas pressure and bias voltage were varied between p=0.5–2.5Pa and UB=−300–0V, respectively. The coatings were deposited in a high volume semi-industrial coating unit. It was observed that the coating properties strongly correlate with the results from the plasma diagnostics. Dependencies of the sp3/sp2 ratios and hardness on the ionization energy of the process gas, the process gas pressure and bias voltages could be found. Hardness values up to HU=45GPa have been achieved. In conclusion it can be claimed that synthesis of DLC coatings with high hardness is possible by HPPMS processes using process gas mixtures of Ar, Ne and He.