Diamond-like Carbon Coatings Research Articles

Experimental study on the feasibility of alternative materials for tilting pad thrust bearings operating in transition to mixed friction

In hydrodynamic bearings traditional bearing alloys: Babbitts and bronzes are most frequently utilized. Polymer sliding layers are sometimes applied as a valuable alternative. Hard diamond-like carbon (DLC) coatings, which are also considered for certain applications may show some advantages, as well. Although material selection is of secondary importance in a full film lubrication regime it becomes important in mixed friction conditions, which is crucial for bearings with frequent starts and stops. Experimental research aimed at studying the performance of fluid film bearings in the specific operating regime, including the transition to mixed friction, is described in the paper. The tests were carried out on four tilting pad bearings of different material compositions: Steel/bronze, DLC/steel, steel/polyether ether ketone (PEEK), and steel/Babbitt. The tests comprised stopping under load and reproduction of the Stribeck curve by decreasing rotational speed to very low values, and observing the changes of friction force during the transition to mixed friction regime. Analysis of the transition conditions and other results showed clear differences between the tested bearings, illustrating the feasibility of less popular material compositions for bearings operating in specific conditions. More specifically, the DLC/steel bearing was demonstrating superior performance, i.e. lower friction, transition to mixed friction occurring at higher load, and more stable performance at start-stop regime over the other tested bearings.

Erosion mechanisms of DLC coatings deposited on polyimide and silica substrates when exposed to a pulsed gas discharge

The influence of spark discharges on the surface morphology and chemical composition of resistive diamond-like carbon (DLC) coatings designed to prevent breakdowns in gas electron multipliers (GEMs) has been studied. DLC coatings with thicknesses of approximately 200 nm and 66 nm were deposited in an inert argon atmosphere on polyimide substrates by high current pulsed magnetron sputtering and on silica (silicon oxide) substrates by vacuum arc method. Based on the analysis of images of optical and scanning electron microscopy, it was established that, the region of interaction between the gas discharge channel and the coating surface presents an accumulation of erosion craters with a characteristic linear size in the range of 20–40 μm. The value of current density passing in the region of interaction between the plasma in spark discharges and the sample is estimated to be of the order of 105 A/cm2, which is sufficient to ablate the coating and create thermal stresses of magnitude ∼4 GPa at the interface between the coating and the substrate. Thus, pulsed surface erosion, insufficient adhesive strength of the coating to the substrate, and poor thermal conductivity should be considered as the key reasons for destruction of the DLC coating.

Existence state of Ti in diamond-like carbon coatings and its effects on hybrid structure and residual stress: Molecular dynamics simulations

In this study, the modified embedded atom method potential function is selected via the LAMMPS platform and OVITO interface software to describe the interatomic interaction potential, which is used to simulate the existence states of doped Ti in Ti-doped diamond-like coatings as well as their effect on the hybrid structure, hardness, and residual stress of the coatings. The results indicate that Ti atoms preferentially combine with C atoms to form Ti–C bonds, thus rendering it difficult to form metallic Ti clusters. The formation of Ti-C bond clusters with high extent of ordering (nanoc-TiC) in the coating is related to the density (or sp3C fraction) of the coating; the higher the density, the higher is the critical content of Ti (CV-Ti) required to form nanoc-TiC. When the density of the coating ranges from 2.4 to 3.6 g/cm3, the CV-Ti is 2–6 at.%. When the Ti content in the coating is less than CV-Ti, Ti atoms existed only in amorphous Ti–C clusters, which is not conducive to the stability of the sp3C phase and significantly reduces the residual stress and hardness of the coating. When the CV-Ti is exceeded, nanoc-TiC formed and grew until the hybrid C–C bonds in the coating disappeared completely, thus increasing the residual stress of the coating.

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).

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

Recent Progress on the Tribology of Pure/Doped Diamond-like Carbon Coatings and Ionic Liquids

This review provides a comprehensive overview of recent advances in tribology concerning pure/doped diamond-like carbon coatings (DLCs) and ionic liquid (ILs) interaction. DLC coatings are often used in industrial machinery and processes where sliding occurs between surfaces, leading to wear and degradation of their surfaces. DLC coatings are optimized by adjusting operating and deposition parameters as well as doping them with other elements to improve performance, such as thermal stability and chemical resistance. ILs are a promising green lubricant option due to their low melting temperature, superior thermal stability, and high miscibility with organic substances. ILs have been studied as neat lubricants and additives, and their tribological properties have been investigated, including their use as extreme temperature lubricants. The tribological properties of pure/doped DLC coatings with ILs have also been explored, although limited research has been conducted in this area. The combined effect of DLCs and ILs shows great promise in reducing energy loss due to friction, promoting longevity, and conserving energy.

Investigation of water vapor barrier performances of diamond-like carbon coatings on flexible PET fabricated at room temperature

Polyethylene terephthalate (PET) emerges as the predominant packaging material for food and electronics. To prevent water vapor from penetrating the polymer, an effective method is to deposit a coating on it that does not damage it. Diamond-like carbon (DLC), which can be deposited at low temperatures, offers a promising protective coating. In this research, DLC coatings were chemical vapor deposited (CVD) on PET substrates using an anode layer linear ion source method. The findings indicate that the water vapor transmission rate (WVTR) of PET substrates coated with DLC coating was significantly reduced to as low as 0.12 g/(m2·24 h), which represents a 30 times reduction compared to the uncoated PET substrates. To further understand the mechanism of water vapor barrier capabilities, molecular dynamics (MD) simulation and first-principles density functional theory (DFT) calculation were carried out to verify the capability and active site of the adsorption and dispersion of water molecules on carbon coating and PET. In addition, the DLC coated PET exhibited exceptional flexibility, and even after subjecting it to 2160 bending cycles, it showed no signs of cracking, indicating its mechanical robustness and durability. This research serves as a strong reference for utilizing DLC to address water vapor permeation challenges.

Enhancing corrosion and tribology performance of stainless steel with DLC coatings: Effects of doping and multilayered structures

The increasing demand for energy production has expanded oil and gas extraction, particularly in harsh exploration sites with highly corrosive media. In the Brazil's pre-salt layer, rich in oil reserves, high NaCl content and CO2 presence may induce sweet corrosion. Corrosion resistant alloys are often used for better performance, and among them, austenitic stainless steels (SS) offer good balance of cost and properties. However, pre-salt acidic and salty environment may induce localized corrosion, making protective coatings a viable option to prolong the lifespan of components exposed to these environments. Diamond-like carbon (DLC) coatings are a great alternative, as besides being chemically stable, they improve mechanical properties of the coated material, such as higher hardness and wear resistance and lower friction coefficient. Therefore, the performance of different types of DLC on the anti-corrosion protection of SS was evaluated. Four DLC types were tested: a hydrogenated amorphous DLC; a multilayered film (DLC-M); and films with fluorine (DLC-F) and silicon (DLC-S). The films showed chemical and structural differences, evidenced by Raman, SEM/EDS and XPS analysis. Their tribological performances were evaluated through scuffing resistance tests; the base DLC showed the highest resistance, followed by DLC-F and DLC-M. DLC-S films didn't exhibit satisfactory tribological performance. For corrosion characterization, potentiodynamic polarization tests were conducted in NaCl and CO2-saturated NaCl solutions. In the NaCl tests, DLC films exhibited impressive anti-corrosion properties, with DLC-F delivering the highest performance, followed by DLC-M, DLC-S, and base DLC. 316 L SS showed high corrosion susceptibility in the CO2-saturated solution, but the coatings also improved corrosion resistance in this setting. The DLC, DLC-S and DLC-M showed similar Ecorr and jcorr values, while DLC-F demonstrated superior corrosion resistance with higher Ecorr and lower jcorr values.

Effect of arc-deposited diamond-like carbon (DLC) coating thickness on friction and size effects in high-speed micromilling of Ti6Al4V

Diamond-like carbon (DLC) can be considered one of the frontline coating materials for high-speed cutting tools owing to both abrasion resistance and solid lubricant properties. However, coating thickness increases the edge radius of the micro tools, which may result in adverse rubbing and plowing that need to be investigated. In this work, DLC coatings of 440, 640, and 1160 nm thicknesses with a ∼250 nm Cr interlayer are deposited on WC micro-end mills using a cathodic-arc system. DLC-coated surfaces exhibited enhanced tribological and mechanical properties compared to uncoated surfaces. Among the DLC-coated micro-end mills, the DLC-640 nm coated tool outperformed, manifesting the best machining performance by reducing friction and size effects together.

Designing hydrogen-free diamond like multilayer carbon coatings for superior mechanical and tribological performance

Diamond like carbon (DLC) coatings are extensively employed for their outstanding mechanical and tribological properties. To overcome the inherent high residual stress, therefore brittleness, DLC coatings with multilayer architecture were developed in the form of stacking alternate hard and soft layers to avoid premature failure under severe loading conditions. The current study was designed to investigate the impact of bilayer thickness (hard & soft) on wear of multilayer DLC particularly at high contact stress (2.0 GPa, 2.7 GPa, 3.0 GPa, 3.4 GPa). Seven DLC multilayer (1:1 bilayer ratio) samples with 1, 2, 5, 10, 20, 40, 80 bilayers were deposited on 440C steel and the overall coating thickness was mainatined at ∼1 µm. Moreover, the bilayer thickness effect was determined on mechanical, scratch adhesion and structural properties. Transmission electron microscope (TEM) was used to visualize discrete hard and soft layers in 80 bilayers (∼6 nm thin layer). G peak suppression and ID/IG increment were observed with reduction in bilayer thickness. Hardness, modulus, elastic strain to failure (H/E), plastic deformation resistance (H3/E2) and residual stresses showed an inverse relation with bilayer thickness. Furthermore, micro scratch adhesion decreases with layer thickness reduction. Only 100 nm and above bilayer thickness samples (1, 2, 5, 10 bilayers) could survive under high contact stress while the other three (20, 40, 80 bilayers) showed brittle failure using pin-on-disc tribometer. Additionally, 10 bilayers (100 nm thickness) produced the minimum wear (∼7.9 ×10−8 mm3/Nm) at 80 N.

Tribological properties of DLC and GLC coating for automotive engine components application under lubrication

Modern automotive designs are needed to increase mechanical and thermal loads that have longer lifespans and are lighter. The power transmissions and motors often use low-friction hard coatings to prevent wear and reduce friction. The Cr-doped graphite-like carbon method is employed for evaluating coating friction and responses to chromium-doped graphite-like carbon (Cr-GLC) under lubrication. Cr-GLC coatings and chromium-doped diamond-like carbon (Cr-DLC) coatings are arranged using physical vapor deposition (PVD) and plasma-enhanced chemical vapor deposition (PECVD), respectively. The results have demonstrated in comparison to the dry friction coefficient, the friction coefficient under lubrication conditions has been reduced by 40%. Due to its excellent frictional physicochemical properties and compact microstructure, Cr-DLC has an optimum tribological resistance that is significantly higher than that of Cr-GLC. Viscosity, corrosivity, and coating microstructure are used to measure the impact of composite elements. The most ideal characteristics of the Cr-GLC coating are attributed to the non-reaction of additives in oil with friction surfaces.

Editorial—Special Issue on Functional Surfaces: Manufacturing, Measuring, and Performance

Abstract Surface treatments are intimately linked to mitigating or avoiding failures due to fatigue, corrosion, and wear. In addition, the advent of new challenges in the industry—mainly associated with an enhanced sustainability of industrial processes—makes surface engineering a critical scientific field. Controlling the superficial and subsuperficial aspects of integrity is crucial in keeping mechanical components at the allowed level of energy consumption. Hence, designing functional surfaces means examining more than just the operating surface processes to get an overview of the whole chain of inputs/outputs. It has been an absolute pleasure to be guest editors for ASTM International’s Materials Performance and Characterization Special Issue on Functional Surfaces: Manufacturing, Measuring, and Performance. The call for papers was based on the investigations presented at Symposium T of XX B-MRS Meeting in Iguassu Falls, Brazil, from September 25–29, 2022. In the symposium, four invited lectures, 12 oral presentations, and 11 posters were presented to the conference attendees. From this total, seven manuscripts were revised for the Special Issue. The other two papers are from the same meeting after we called through other symposia on surface processing. The papers herein cover relevant topics on surface engineering. The first two focus on plasma technology applied to structural steel to increase its tribological and corrosion behaviors and to a polymer for a microfluidic application. Furthermore, we can find an investigation into diamond-like carbon coatings applied to the automotive industry. Additive manufacturing is another presented technology, and the effect of laser on additive manufacturing was investigated in a fourth manuscript. Another case is the plasma transferred arc, which investigated the incorporation of intermetallic for exposure at high temperatures. Next, we have a pair of two papers using double-pack cementation, incorporating the effect of metallic elements or boron into their performances. Following that is one paper about the high-velocity oxygen fuel process using metallic alloys, and the final paper is about developing the gas tungsten arc welding technique through flux-core-double-wire, enhancing the wear performance through hard carbides. We sincerely thank the authors and reviewers for their hard work and dedication. We wholeheartedly thank the ASTM staff for dealing with the issues of publishing an outstanding journal. We hope that all papers contribute to the state-of-art of the surface engineering field. Professor Giuseppe Pintaude Universidade Tecnológica Federal do Paraná, Curitiba, Brazil Professor Ana Sofia C. M. d’Oliveira Universidade Federal do Paraná, Curitiba, Brazil Professor André P. Tschiptschin Universidade de São Paulo, São Paulo, Brazil Dr. Filipe Fernandes Instituto Superior de Engenharia do Porto (ISEP), Porto, Portugal

Effect of methane and acetylene pre-gases on the corrosion resistance of DLC coatings

Diamond-like carbon (DLC) coatings were applied to 304 stainless steel specimens using two different pre-gases: methane and acetylene.Compared to DLC prepared with acetylene pre-gas(DLC-C2H2). DLC prepared with methane pre-gas(DLC-CH4) has a denser coating body and a smoother surface.The DLC-C2H2 film shows crack defects on the surface, and the DLC-CH4 film has a lower sp2/sp3 ratio than DLC-C2H2. DLC-CH4 has better electrochemical characteristics and salt spray corrosion testing results than DLC-C2H2 films in NaCl solution. DLC-CH4 has a high charge transfer resistance of 9.54 × 103 Ω/cm2. Compared to DLC-C2H2, DLC-CH4 coatings form a more complete, continuous, smooth surface and a minor porosity in the coating body, inhibiting localized corrosion processes. The DLC-CH4 coatings have less sp2 phase, which results in lower electrical conductivity and limited electron transport at the coating surface. DLC-CH4 shows more excellent corrosion resistance.

Scientometric Study of Diamond-Like Carbon Coatings as Wear-Resistant Coatings

Scientometric Study of Diamond-Like Carbon Coatings as Wear-Resistant Coatings

Targeting Biomechanical Endurance of Dental-Implant Abutments Using a Diamond-Like Carbon Coating.

Abutment components (i.e., fixtures associated with oral implants) are essentially made of titanium (Ti), which is continuously exposed to the hash oral environment, resulting in scratching. Thus, such components need to be protected, and surface treatments are viable methods for overcoming long-term damage. Diamond-like carbon (DLC), an excellent protective material, is an alternative surface-treatment material for Ti abutments. Here, we demonstrate that a silicon interlayer for DLC film growth and the pulsed-direct current plasma-enhanced chemical vapor deposition (DC-PECVD) method enables the deposition of an enhanced protective DLC film. As a result, the DLC film demonstrated a smooth topography with a compact surface. Furthermore, the DLC film enhanced the mechanical (load-displacement, hardness, and elastic modulus) and tribological properties of Ti as well as increased its corrosion resistance (16-fold), which surpassed that of a bare Ti substrate. The biofilm formed (Streptococcus sanguinis) after 24 h exhibited an equal bacterial load (∼7 Log colony-forming units) for both the groups (Ti and DLC). In addition, the DLC film exhibited good cytocompatibility, owing to its noncytotoxicity toward human gingival fibroblast cells. Therefore, DLC deposition via DC-PECVD can be considered to be a promising protective and cytocompatible alternative for developing implant abutments with enhanced mechanical, tribological, and electrochemical properties.

Nitrogen-containing diamond-like carbon deposited on glass substrate via filtered cathodic vacuum arc with high-frequency pulsed DC substrate bias

This research investigates the properties of nitrogen-containing diamond-like carbon (N-DLC) coatings deposited on glass substrate using a high-frequency pulsed-DC substrate bias. The study involved comprehensive investigations to understand how variations in carbon bonding affect the properties of N-DLC coatings. By adjusting the voltage, frequency and duty ratio of the pulsed bias, it was possible to deposit an optical coating with a transmittance of up to 52 % at range of 800–2500 nm while effectively preventing the peeling of the DLC coating on the glass. With increasing the clustered graphite structure in the DLC coating, the sheet resistance was lowered from 2370 kΩ/□ to 36 kΩ/□, and the electrical properties were also improved. The findings provide valuable insights for optimizing N-DLC coatings for non-conductors, e.g., glass, rubber, polymer, and engineering ceramic.

A comprehensive evaluation of DLC coating on gear bending fatigue, contact fatigue, and scuffing performance

Modern advanced equipment demands higher reliability and longer service life, imposing increasingly stringent requirements on loading capacity of gears. Diamond-like carbon (DLC) coating significantly improves the friction and wear performance, which has potential to be applied to gears to enhance their loading capacity. In this study, a comprehensive evaluation of the DLC coating treatment on the loading capacity of 18CrNiMo7-6 gears was conducted. The surface morphology, hardness gradient, residual stress, and material microstructure of the DLC coated gears have been characterized. Additionally, bending fatigue, contact fatigue, and scuffing tests on the gears were performed, which took more than 1000 h. The results demonstrate that DLC coating significantly enhances surface microhardness, reaching up to 2000 HV, and surface residual compressive stress shows an increase of approximately 200 MPa. The DLC treated gear contact fatigue limits from 1570 MPa to 1770 MPa, and the scuffing limit temperature rises from 224.6 °C to 348.6 °C compared with grinding state. Although DLC coatings do not exhibit an improvement in gear bending fatigue strength, the composite treatment of shot peening combined with DLC coating still enhances its bending fatigue performance.

Effects of sp3 bond and modulation ratios on ultra-thin diamond-like carbon coatings using molecular dynamics nanoindentation

Effects of sp3 bond and modulation ratios on ultra-thin diamond-like carbon coatings using molecular dynamics nanoindentation

Nanoscale friction of tetrahedral amorphous diamond-like carbon film after thermal annealing

Diamond-like carbon (DLC) coatings have demonstrated significant potential as solid lubricants for a wide range of applications. However, thermal-induced structural changes lead to alterations in its mechanical and frictional properties. In this study, we investigate the friction properties of DLC films after high-temperature annealing, by conducting reciprocating single asperity scanning experiments of self-mated hydrogen-free DLC tribopair under ultra-high vacuum (UHV) conditions. As the annealing temperature increases, the coefficients of friction (COFs) first increase owing to the desorption of water molecules; while, with the further increase of temperature, friction shows a decreasing trend because of the high-temperature-induced sp3-to-sp2 rehybridization which lowers the interfacial shear strength. The insights gained from this study provide a better understanding of the frictional properties of DLC films.

Doping effects on the tribological performance of diamond-like carbon coatings: A review

Diamond-like carbon (DLC) coatings have garnered considerable interest due to their unique features, which include wear resistance with a low friction coefficient, high hardness, biocompatibility, and chemical inertness. Their tribological performance is highly dependent on tribological environment, structure, and mechanical properties of the coating. A major problem that can adversely impact the tribological properties of the DLC coating is insufficient adhesion to the substrate. This issue caused by mismatch of the substrate and coating thermal expansion coefficient (TEC) and high amount of internal stress in DLC coating. The limitations of DLC coatings for tribological performance can be overcome by incorporating different types of metallic and non-metallic elements into the coating structure. Recently, various efforts have been made to address this issue by doping certain elements into the DLC coating, including fluorine, nitrogen, silicon, and metals. This review discusses new advancements in doped DLC coatings designed to improve their tribological behavior in different specific applications such as high relative humidity, elevated temperature, and bio-implant.