Properties Of Diamond-like Carbon Research Articles

The development of B/Cr co-doped DLC coating by FCVA deposition system and its tribological properties at 300 °C

The diamond-like carbon (DLC) coating prepared using filtered cathodic arc deposition (FCVA) lost its promising wear resistance under high temperatures. Element-doped DLC coatings have been investigated to suppress carbon oxidation reaction and subsequently enhance the wear resistance in high-temperature environments. Previous research clarified the excellent tribological properties of boron-doped DLC (B-DLC) but identified challenge such as arc discharge extinguishment and coating declamation (under high-temperature friction test). In this study, the introduction of Argon gas (10 sccm) during the deposition process stabilized stable arc discharge, resulting in high hardness and deposition rate. Moreover, a chromium interlayer and varying concentration of Cr dopant (0.5 %, 1.0 %, 3.0 % at.) were added to B-DLC to develop a stable, co-doped DLC with low friction and high wear resistance. Raman spectroscopy and nano-indentation revealed an increase in the disordered carbon structure and reduction in hardness and Young's Modulus with Cr doping. Macroscopic ball-on-disk friction test, showed 1 % Cr-doped B-DLC (a-C:B:Cr1) coating exhibited super low friction (avg. coefficient 0.02) and a low specific wear rate (<5.0 × 10−6 mm3/Nm). Raman spectroscopy indicated that the transferred graphite-like tribo-film onto the surface of Si3N4 counterparts contributed to stable low friction. Additionally, XPS analysis on the DLC coatings' wear track suggested the rich BB bond might contribute to its high wear resistance. This successful improvement on element-doped DLC prepared by FCVA provided valuable insights for further exploration of DLC coating applied to various working situations.

Chemical and mechanical analysis of hard coatings exposed under the supercritical CO2 Venus atmospheric surface conditions

The extremely hot and dense environment on Venusian surface will degrade almost any material via atmosphere-surface interactions, therefore the exploitation of its soil and atmosphere is very challenging. Exploring rovers are designed with mostly mechanical parts, and the knowledge of the effect of Venusian exposure on mechanical and tribological systems is very important for the longevity of the missions. Herein, we studied the effect of 3-day Venusian exposure on selected interfaces. It was found that diamond-like carbon (DLC) and Ti-doped molybdenum disulfide (TiMoS2) experienced negligible morphological changes, whereas polycrystalline diamond (PCD) and PS400 (plasma sprayed Ni-alloy) formed few-microns thick sulfur-containing reacted surface layers after exposure. Also, PCD retained its structural integrity, while the mechanical properties of DLC deteriorated the most, manifested as 49% decrease in hardness. The hardness of PS400 and TiMoS2 degraded to a lesser degree, with 8 and 26% decrease, respectively. The above coatings could be candidate materials to coat structural and bearing systems in the rovers, probes, and drills for future missions to Venus.

The synergistic mechanism of transition layer and transfer layer on dry sliding wear of multi-layered diamond-like carbon (DLC) coating at wide temperature

The wear resistance of 17-4PH stainless steel was improved at wide temperature (25–200 °C) by depositing multi-layered Cr/CrC/DLC coating. The results showed that the lubricating effect of the transfer layer led to a reduction of the friction coefficient to 0.03. DLC coating had a protective effect on the 17-4PH substrate, and the surface of the coating was basically not worn at 25–100 °C. This study focused on the wear mechanism and frictional chemical reaction mechanism of multi-layered coatings at wide temperatures. With the increase of temperature, the wear mechanism of DLC coating changed from abrasive wear to adhesive wear, and finally delamination. The complex tribochemical reaction in the wear process led to the dynamic change of its graphitization transformation, which affected the formation of the transition layer and the change in surface mechanical properties of the coating. This was mainly because the transition layer Cr/CrC and Si3N4 played a role in inhibiting the graphitization transformation of DLC layer during the wear process, thus affecting the friction properties of DLC.

Tribological behaviors of amorphous carbon under water lubrication through a bottom-up coarse-grained method

The tribological behaviors of diamond-like carbon (DLC) are investigated through a coarse-grained (CG) modeling method, in which DLC and its force field are coarse-grained and validated based on the mechanical properties of DLC. It is found that the wear of the slider causes the loose structure of interfacial carbon clusters, and the influence of water changes from static interfacial separation to hydrodynamic lubrication. The tribological behaviors are similar to those in all-atom systems, which indicates the unchanged underlying mechanisms after coarse-graining and proves the accuracy of CG methods. Since the CG methods can efficiently reduce the particle numbers, it has great potential to predict the mechanical properties of these films and other amorphous materials with an experimental thickness.

Combining multi-scale surface texturing and DLC coatings for improved tribological performance of 3D printed polymers

Polymer components fabricated by additive manufacturing typically show only moderate strength and low temperature stability, possibly leading to severe wear and short lifetimes especially under dry tribological sliding. To tackle these shortcomings, we investigated the combination of single- and multi-scale textures directly fabricated by digital light processing with amorphous diamond-like carbon (DLC) coatings. The topography of the samples and conformity of the coatings on the textures are assessed and their tribological behaviour under dry conditions is studied. We demonstrate that the surface textures have a detrimental tribological effect on the uncoated samples. This changes with the application of DLC coatings since friction substantially reduces and wear of the textures is not observed anymore. These trends are attributed to the protection of the underlying polymer substrate by the coatings and a reduced contact area. The best tribological performance is found for a coating with highest hardness and hardness-to-elasticity ratios. Moreover, multi-scale textures perform slightly better than single-scale textures due to a smaller real contact area. Summarizing, we verified that the high flexibility and low production costs of 3D printing combined with the excellent mechanical and tribological properties of DLC results in synergistic effects with an excellent performance under dry sliding conditions.

Systematically Study the Tensile and Compressive Behaviors of Diamond-like Carbon.

It is important to understand the mechanical properties of diamond-like carbon (DLC) for use not only in frictionand wear-resistant coatings, but also in vibration reduction and damping increase at the layer interfaces. However, the mechanical properties of DLC are influenced by the working temperature and its density, and the applications of DLC as coatings are limited. In this work, we systematically studied the deformation behaviors of DLC under different temperatures and densities using compression and tensile testing of DLC by molecular dynamics (MD) methods. In our simulation results, the values of tensile stress and compressive stress decreased and tensile strain and compressive strain increased as the temperature increased from 300 K to 900 K during both tensile and compressive processes, indicating that the tensile stress and tensile strain depend on the temperature. During the tensile simulation, Young's modulus of DLC models with different densities had a different sensitivity to the increase in temperature, and the DLC model with a high density was more sensitive than that with a low density, which was not seen in the compression process. We conclude that the Csp3-Csp2 transition leads to tensile deformation, while the Csp2-Csp3 transition and relative slip dominate compressive deformation.

Optimizing diamond-like carbon coatings - From experimental era to artificial intelligence

Diamond-like carbon (DLC) coatings are widely used for numerous engineering applications due to their superior multi-functional properties. Deposition of good quality DLC is governed by energy per unit carbon atom or ion and plasma kinetics, which are independent parameters. Translating independent parameters to dependent parameters to produce a best DLC is subjected to deposition method, technology, and system configurations which may involve above 50 combinations of bias voltage, chamber pressure, deposition temperature, gas flow rate, etc. Hence DLC coatings are optimized to identify the best parameters which yield superior properties. This article covers DLC introduction, the role of independent parameters, translation of independent parameters to dependent parameters, and discussion of four generations of DLC optimization. The first-generation of DLC optimization experimentally optimizes the parameter-to-property relationship, and the second-generation describes multi-parameter optimization with a hybrid of experimental and statistical-based analytical methods. The third generation covers the optimization of DLC deposition parameters with a hybrid of statistical methods and artificial intelligence (AI) tools. The ongoing fourth generation not only performs multi-parameter and multi-property optimization but also use AI tools to predict DLC properties and performance with higher accuracy. It is expected that AI-driven DLC optimizations and progress in virtual synthesis of DLC will not only assist in resolving DLC challenges specific to emerging markets and complex environments, but will also become a pathway for DLC to enter a digital-twin era. • DLC quality is a function of carbon ion energy, an independent parameter. • Translating independent to dependent parameters make above 50 experimental combinations. • New DLC markets need robust optimizations for fabrication and properties. • AI/ML optimizations have ability to provide optimal solutions for new DLC markets.

Influence of Si atoms on the structure and electronic properties of amorphous DLC films

The paper considers the effect of silicon on the formation of the structure and properties of amorphous diamond-like carbon (DLC) films. Thin films of silicon-modified amorphous diamond-like carbon (DLC:Si) were synthesized by magnetron ion-plasma co-sputtering of a combined target. Studies of the structure and properties of amorphous DLC:Si films were carried out in the range of silicon concentrations up to 6.75 at.%. A change in the formation of the film structure is shown using atomic force microscopy (AFM) and transmission electron microscopy (TEM). Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS) revealed a significant change in the local structure of amorphous DLC:Si films. Which, in turn, leads to a change in the density of states of π-electrons in the band and, as a rule, to a change in the electronic properties.

Temperature dependent erosion and Raman analyses of arc-deposited H free thick DLC coating on Cr/CrN coated plasma nitrided steel

Development of H and metal dopant-free single phase thick diamond like carbon (DLC) coating on metal nitride layer for automobile applications is still a challenging task due to internal stress developed during deposition of DLC films. A simple process was followed to deposit thick Cr/CrN/DLC (0.25/0.75/6 μm) coating on plasma nitrided steel using an un-filtered cathodic vacuum arc system without applying any high pulse bias voltage. In addition, the coating was deposited at room temperature and it showed very good adhesion on plasma nitrided steel surface and exhibited a very low coefficient of friction ~0.06 ± 0.005. Temperature dependent solid particle erosion tests were conducted according to ASTM-G-76-18 standards at an impinging angle of 45°. Erosion resistance of the coating is 33, 11, 7 and 6 times better than nitrided steel substrate at test temperatures of 25, 200, 300 and 400 °C, respectively. Better erosion resistance performance of a coating infers the long life of the coating on automobile components. A multi-wavelength Raman study gives a better understanding of the structural properties of DLC. So, the Raman spectra of the coating were recorded using three different laser wavelengths: 405 nm, 532 nm and 633 nm. The thermal stability of the coating was studied using temperature dependent Raman spectroscopy. The coating showed good thermal stability until a temperature of 425 °C.

Frictional Properties of Element- and Compound-Doped Diamond-Like Carbon Films under Boundary Lubrication with Synthetic Base Oil

The frictional properties of diamond-like carbon (DLC) films under boundary lubrication with a synthetic base oil were investigated. The specimens tested were a-C:H, Cr-a-C:H, Ti-a-C:H, W-a-C:H, WC-a-C:H, Mo-a-C:H, MoS2-a-C:H, and Sn-a-C:H films. The tribological properties of DLC/steel contacts were evaluated using a reciprocating-type cylinder-on-disk tribotester. The DLC films exhibited different frictional properties depending on the type of doping elements and compounds used. Notably, the Sn-a-C film gave the lowest friction. The friction tests and static contact angle analyses revealed that the average friction coefficient decreased with a decrease in the static contact angle of the worn DLC film surface, demonstrating that the DLC films with relatively high surface wettabilities exhibited relatively low friction properties. Therefore, surface wettability plays an important role in determining the frictional properties of DLC films under boundary lubrication with synthetic base oil..

Modification Methods of Diamond like Carbon Coating and the Performance in Machining Applications: A Review

The ideal cutting-tool coating material is characterized by unique chemical and physical properties to achieve excellent cutting performance, a good thermal barrier effect, and a high-quality machined surface. Diamond-like carbon (DLC) coating, as a kind of cutting-tool coating material, has been used in cutting various materials due to its low coefficients of friction and thermal expansion, high hardness, and good chemical inert and thermal conductivity. This article mainly focuses on the modification methods for the DLC coating and their application in machining different materials. Firstly, the methods employed to improve the mechanical properties of DLC coating are reviewed and analyzed, including the multilayer structure design, transition layer, and doping other elements. Secondly, the machining performances of DLC-coated tools in the application of different materials are summarized. This review provides knowledge of modification mechanisms regarding DLC coating and its effects on mechanical properties. For machining different materials, it provides a reference to make a suitable selection and design of DLC coating to obtain better machining performance.

Investigation of changes in the properties of diamond-like films under friction by the XPS method

The combination of unique physicochemical, mechanical and tribological properties of diamond-like coatings determines the prospects for their use in critical friction units, including those operating in a rarefied atmosphere and vacuum. The properties of diamond-like carbon (DLC) coatings depend on the contribution of the sp2 and sp3 fractions of the carbon hybrid atomic electron orbitals. Modern methods of determining the graphite and diamond proportion in coatings are time-consuming and insufficiently accurate. In addition, the determination of the sp3/sp2 ratio is often difficult due to the displacement of the energy position of the C1s electron line. In this paper, the change in the chemical state of carbon over the thickness of a diamond-like coating is studied by X-ray photoelectron spectroscopy. Analysis of the carbon line fine structure of the differential graphite spectra (sp2 bonds) and diamond (sp3 bonds) allowed us to establish the parameter δ, which determines the ratio of the graphite and diamond components in the DLC coating. Profiling with Ar+ ions of the diamondlike coating surface showed that with an increase in the etching time, the proportion of amorphized carbon increases, which means that the antifriction properties increase with the abrasion of the coating. The obtained regularities allow us to predict changes in the tribological properties of DLC coatings during operation. Ion profiling also allows to determine the thickness of coatings with high accuracy.

Investigation of optoelectrical and Schottky behavior of diamond-like carbon coating deposited by hollow cathode PACVD method

In the present study, diamond-like carbon (DLC) was deposited on a silicon substrate by hollow cathode plasma-assisted chemical vapor deposition (PACVD) method. After deposition, structural, optical and, electrical properties of DLC were investigated. The Raman spectroscopy proved that DLC layer successfully formed on the substrate. Scanning electron microscopy images showed that the DLC had a smooth and uniform surface with a thickness of about 392 nm. Energy-dispersive X-ray analysis demonstrated the presence of carbon as the main constituent of DLC in the formed layer. The optical properties of DLC were investigated by UV–Vis and photoluminescence spectroscopy. The absorption peak for the DLC was at 370 nm. Based on the results of UV–Vis spectroscopy, a tauc plot was calculated, and it was found that the DLC has a band gap of 2.37 eV. The PL spectra also showed that the DLC layer would emit at 410 nm if adequately excited. Also, the current-voltage characteristic for the Au/DLC/p-Si was measured. Based on the current-voltage results, the sensitivity parameter was calculated, which was equal to 9.71. Finally, based on the measured values, the feasibility of using the DLC layer as a semiconductor for use in Schottky junctions was investigated. • A uniform layer of DLC was deposited on a silicon substrate by hollow cathode PACVD method. •It was found that the DLC layer has a bandgap of 2.37 eV and the absorption peak located at 370 nm, which makes this material suitable for use as a detector in this range. •The gold electrodes were placed on the DLC by a sputtering method to form an Au/DLC/p-Si arrangement as a Schottky junction. •The electrical characterization of the Au/DLC/p-Si device was measured, and its basic parameters calculated, and finally, the possibility of using DLC as a semiconductor in the Schottky junction was investigated.

Ultrahigh radiation resistance of nanocrystalline diamond films for solid lubrication in harsh radiative environments

In this study, different types of carbon films, including diamond-like carbon (DLC), fullerene-like carbon (FLC), and nanocrystalline diamond (NCD) films, were studied in detail. The film structural and property changes before and after heavy-ion irradiation with increased displacement damage were investigated. The results reveal that radiation-induced structural changes result in heavily degraded lubricant properties of DLC and FLC films but can help improve the lubricant properties of NCD films. The displacement damage of 2.0 dpa was a threshold parameter above which the nanocomposite NCD films stepped into a quasi-saturation state to create an amorphous structure with an ultralong lifetime (more than 6.0 × 105 cycles) and excellent antiwear properties (magnitude of 10−7 mm3/N‧m), which is of great importance for the application of NCD films in nuclear reactors. The radiated NCD films could produce tribofilms configured in an amorphous structure, which provided superior lubricant properties to the graphitic tribofilms of DLC and FLC films. The results also contribute to a novel principle for prolonging the lifetime of solid lubricant films in ion-radiation environments, based on the significant tribological properties of the radiation-produced amorphous layer in a quasi-saturation state.

Coatability of diamond-like carbon on 316L stainless steel printed by binder jetting

Diamond-like carbon (DLC) coatings are efficient in improving surface properties of functional components and parts. For conventionally manufactured materials and products, the DLC coatings are on a high level of development and industrially well established. However, with the advent of additive manufacturing technologies and the unique microstructure of the produced parts, so far the properties of the DLC coatings on these surfaces have not been extensively investigated. Additively manufactured materials possess process-related structural characteristics, such as residual porosity or an anisotropic material behavior, thereby leading to distinguished properties of the substrate/coating system compared to conventionally fabricated substrate materials. Therefore, 316L substrates are produced with an intended residual porosity and different building directions by binder jetting and subsequently coated with DLC in a magnetron sputtering process. Conventionally manufactured 316L substrates were also coated to evaluate the manufacturing effects on the DLC properties. Based on the analysis of DLC coated open pores, a model is developed to describe the growth mechanisms of thin PVD coatings on open pores of different size. The thin DLC coating entirely covers residual porosity when the pore size (opening diameter) is smaller than or equal to the coating thickness of ~3 µm. Independently of the residual porosity or building orientation, the DLC coating provides a high hardness of 24 GPa and reveals a high adhesion strength to all binder jetted 316 L substrates. Compared to conventional manufacturing routes, the combination of additive manufacturing and DLC deposition is a competitive approach to fabricate complex-shaped components and parts with enhanced surface properties.

TCAD Investigation of Differently Doped DLC Passivation for Large-Area High-Power Diodes

An electroactive passivation for high-voltage diodes with bevel termination has been investigated based on diamondlike carbon (DLC) films. Variations of the DLC properties, i.e., conductivity and geometry, have been investigated by experiments and numerical simulations to the purpose of gaining an insight on their influence on the diode leakage current and breakdown voltage. The role played by the DLC/Si interface has been investigated by characterizing metal–DLC–Si devices. Both boron and nitrogen doping have been investigated, and a TCAD setup has been provided accounting for the main transport features of the DLC material with different doping configurations. A significant polarization effect has been observed in the DLC material, which improves the DLC performance as a passivation material. High-voltage diodes have been characterized and simulated with different DLC layers on top of the bevel termination in order to identify the role played by conductivity and polarization on the blocking state. The correlation of leakage current and voltage breakdown with the DLC doping and thickness is provided and explained by the TCAD simulation results.

Properties of TiN–Al2O3–TiCN–TiN, TiAlN, and DLC‐coated Ti(C,N)‐based cermets and their wear behaviors during dry cutting of 7075 aluminum alloys

AbstractIn the work, TiAlN for physical vapor deposition (PVD), multilayer TiN‐Al2O3‐TiCN‐TiN for chemical vapor deposition (CVD), and diamond‐like carbon (DLC) for plasma‐enhanced chemical vapor deposition (PECVD) were deposited on the cermet inserts. Characteristics and wear behaviors of the three coated cermets during dry cutting of 7075 aluminum alloys were observed. The results show that TiN‐Al2O3‐TiCN‐TiN coatings have highest adhesion strength and hardness. At the cutting speed of 1100 r/min, the depth of 0.2 mm, and the feed rate of 0.1 mm/r, the three coated inserts show the best wear‐resistant properties. In this case, TiN/Al2O3/TiCN/TiN shows the worst wear‐resistant properties (value of the flank wear [VBB] = 0.062 mm), while DLC coatings show the most excellent wear‐resistant properties (VBB = 0.046 mm). During the cutting of aluminum alloys, which have high plasticity and low melting point, adhesive wear dominate on the flank of the inserts. The thickest coating of TiN/Al2O3/TiCN/TiN results in the bluntest cutting edge, which form the most serious adhesive worn zone. For the TiAlN and DLC coatings, due to a smaller cutting force, the two coatings have much better wear resistance. Further, the self‐lubricating properties of DLC show excellent effect on protecting the inserts. Thus, the DLC‐coated cermets have the best wear‐resistant properties. Further, the TiAlN‐coated cermets have the widest wear‐affected zone while the DLC coating has the narrowest.

Effect of temperature and mating pair on tribological properties of DLC and GLC coatings under high pressure lubricated by MoDTC and ZDDP

Diamond-like carbon (DLC) and graphite-like carbon (GLC) coatings have good prospects for improving the surface properties of engine parts. However, further understanding is needed on the effect of working conditions on tribological behaviors. In this study, GLC and two types of DLC coatings were deposited on GCr15 substrate for investigation. The friction and wear properties of self-mated and steel-mated pairs were evaluated. Two temperatures (25 and 90 °C), three lubrication conditions (base oil, molybdenum dithiocarbamate (MoDTC)-containing oil, MoDTC+zinc dialkyldithiophosphate (ZDDP)-containing oil), and high Hertz contact stress (2.41 GPa) were applied in the experiments. The results showed that high temperature promoted the effect of ZDDP on steel-mated pairs, but increased wear under base oil lubrication. The increased wear for steel-mated pairs lubricated by MoDTC-containing oil was due to abrasive wear probably caused by MoO3 and β-FeMoO4. It was also found that in most cases, the tribological properties of self-mated pairs were better than those of steel-mated pairs.

Effect of nitrogen in the properties of diamond-like carbon (DLC) coating on Ti6Al4V substrate

The great interest in the study of diamond-like carbon films (a-C:H) is justified by its mechanical and tribological properties. However, the high internal stress of the film results in its difficult adhesion to the metallic substrate, which can be solved by nitrogen incorporation in the a-C:H film, allowing a formed film of lower internal stress. The objective of this work is to evaluate the influence of flow (20, 30 and 40sccm), CH4/Ar ratio (90/10 and 70/30) and voltage (400, 500, 600 and 700 V) in the a-C:H formation. For the best condition of the film, we studied the effect of nitrogen incorporation in the hardness and wear resistance of the a-C:H(N), modifying the nitrogen percentage in the treatment at 10% to 60% N2. The treatments were carried out in the Ti6Al4V substrate by DC-PECVD for two hours. For good adhesion of the films on the substrate, a silicon interlayer must be produced. The increase in the voltage above 600 V increases the ID/IG and film thickness, causing its delamination, and the gas ratio did not influence the a-C:H characteristics. The a-C:H film deposited with 30 sccm, 90/10 and 500 V was characterized as a-C:H (hard), with properties such as the hardness of 17 GPa, 30% H, 39% sp3 and ID/IG ratio of 0.58. Since nitrogen reduced the deposition rate, the total gas flow for the production of a-C:H(N) was performed with 40 sccm. The Raman spectra of a-C:H(N) films showed changes in D band intensity and displacement in relation to the nitrogen-free film spectrum, evidencing the incorporation of nitrogen in the film. The XPS analysis showed the linear increase of the nitrogen incorporation in the a-C:H(N) film with the increase of the amount of the N2 gas in the treatment, which caused, in general, a decrease in the amount of C–C sp3 bonding, increasing the adhesion of the film in the substrate and not necessarily the low wear resistance of the formed film.

Influence of currents on tribological behavior of diamond-like carbon films

The diamond-like carbon (DLC) film is vastly applied for low-friction protective films at contact sliding surfaces. This work reported the characteristics and tribological properties of DLC, Cu-doped DLC (Cu-DLC) film and Ti-doped DLC (Ti-DLC) film formed by unbalanced magnetron sputtering system and analyzed the frictional tests and the morphology of wear scars. The current intensity at the sliding interface was set to a constant value in the whole current circuit for exploring the influence of current, including 0 A, 0.5 A, 1 A, 1.5 A and 2 A. The results showed the friction coefficient of DLC film decreased from 0.12 to 0.06–0.08 and then increases rapidly to 0.26 when the current increased to 2 A. The change in trend of friction coefficient of Cu-DLC film with the increase in current was the same with the DLC film. The minimum value was 0.12 at 1 A current. In the case of Ti-DLC film, when the current intensity enhanced from 0 to 2 A, the friction coefficient monotonically increased from 0.06 to 0.29. Furthermore, the wear rate of the films under higher current was larger than the wear rate of the films under lower current. This is due to the fact that frictional heat and Joule heat are generated at a relatively large current to make the surface of the film more susceptible to wear. The wear rate of Ti-DLC film is relatively larger as the arc ablation is the main wear mechanism of Ti-DLC film compared with pure DLC film and Cu-DLC film.