Diamond-like Carbon Coatings Research Articles

PVD coatings on punches for low interfacial adhesion to pharmaceuticals

The modification of the surface chemistry of steels is a crucial way to optimize different industrial processes, whether low or high adhesion is needed. In the case of compression of pharmaceuticals for tablet production, punches must have non-sticking properties to inhibit pharmaceutical adhesion. For this kind of application, it is necessary to develop hard coatings with low surface energy and static friction. For this aim, we investigated the physical, chemical, structural, mechanical, and tribological properties of diamond-like carbon (DLC) and transition metal dichalcogenides (TMD - WSC and WS2) coatings. In addition, we analyzed the potential of these coatings for pharmaceutical tablet fabrication. The coatings' surface free energy (SFE) was lower than that of blank steel, indicating better anti-adherent properties. The friction and morphology analysis showed that the tablets have less adhesion when in contact with selected coatings contrasting with higher adhesion in the uncoated sample. WSC was the coating showing the lowest adhesion for the four formulations studied in detail (paracetamol, fluvoxamine maleate, ibuprofen, and fertilizer). The results show that WSC is a suitable coating for the punches to produce tablets.

Tribochemical investigation of Cr-doped diamond-like carbon with a MoDTC-containing engine oil under boundary lubricated condition

Cr-doped diamond-like carbon (Cr-DLC) coatings were deposited and investigated for their tribological properties. A hybridized deposition technique consisted of a bipolar plasma-based ion implantation and deposition (PBII&D) and magnetron sputtering was used for the deposition. Raman spectra revealed an increase of ID/IG upon the Cr introduction, indicating the embedded CrCx act as catalysts to produce sp2 sites. The coefficients of friction (COF) were effectively reduced once MoDTC was added to the base oil. X-ray photoelectron spectroscopy (XPS) confirmed the presence of MoO3, MoS2, and MoS2−xOx in the MoDTC-derived tribofilm. The contribution of MoS2−xOx decreased with the Cr content, suggesting that the wear particles of CrCx intervenes in the process of MoDTC decomposition by preventing the oxidation of MoS2 sheets.

Impact of Temperature Variation on Friction Behaviour of Rare Earth-Doped Diamond-like Carbon Coatings with Ionic Liquid Lubricants

This research paper investigates the tribological performance of diamond-like carbon (DLC) coatings doped with rare earth metals (europium and gadolinium) as well as pure DLC lubricated with ionic liquid additives (trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate {[P66614][DEHP]} and 1-ethyl-3-methylimidazolium diethyl phosphate {[EMIM][DEP]}) in Polyalphaolefin 8 (PAO8). The study aims to examine the effect of temperature on the interaction between the coatings and additives by conducting tribological experiments using a block-on-disk setup at temperatures of 60 °C, 80 °C, and 100 °C. The primary objective is to evaluate the performance of doped DLC coatings compared to pure DLC coatings with ionic liquid additives in the lubricant in boundary lubrication conditions at various high working temperature environments. The experiments reveal that doped DLC coatings with ionic liquid additives exhibit superior tribological performance compared to pure DLC coatings. The rare earth metal dopants play a positive role in the formation of a tribofilm on the surface of the coatings as it interacts with ionic liquids, resulting in a lower coefficient of friction (CoF). Temperature influences the performance of the coatings and additives. The CoF increases with temperature for pure DLC coatings, while for doped DLC coatings it was significantly less. These findings highlight the influence of temperature on the tribological behavior of DLC coatings. Overall, this study contributes valuable insights into the impact of rare earth metal dopants and ionic liquid additives on the tribological performance of DLC coatings under different temperature conditions. The results demonstrate the potential of utilizing doped DLC coatings with ionic liquid additives as an effective approach to enhance the performance of mechanical systems.

Study on properties of diamond-like carbon films deposited by RF ICP PECVD method for micro- and optoelectronic applications

In this paper, a comparison of Diamond-like Carbon (DLC) films with different sp3 fraction content prepared by Radio Frequency Inductively Coupled Plasma Enhanced Chemical Vapour Deposition (RF ICP PECVD) was presented. Structural, surface, optical, and mechanical properties of deposited DLC films were analyzed with the use of awide range of measurement techniques. The investigated films were deposited on silicon (Si), amorphous silica (SiO2), and metallic (Ti6Al4V) substrates at room temperature. The deposited DLC films have sp3 fraction content ranging from 35 % to 70 %, uniform, compact and dense microstructure. The investigation indicates that the properties of DLC films required for micro- and optoelectronic applications improve with the sp3 fraction content. The refractive index (n) increased from 1.976 to2.086, packaging density (PD) from 0.964 to 0.744, electrical resistivity (ρ) from 2.1 ∙ 1010 to 4.4 ∙ 1011 Ωcm, hardness (H) from 16.4 19.1 to GPa and elastic modulus (E) from 109 to 129 GPa. However, the 50 % sp3 DLC thin film exhibited the highest resistance to cracking (H3/E2 = 0.44). The decrease of Urbach energy (EU) from 0.75 to 0.46 eV was observed for the DLC film with the highest sp3 fraction content, while all investigated DLC samples had similar optical bandgap energy (Egopt ≈ 1.3 eV). The research has shown that it is possible to obtain DLC coatings using the RF ICP PECVD technique that has better properties than films deposited by the classic PECVD technique.

Effects of Diamond-like Carbon and Tungsten-Carbide Carbon Coatings on Tribological Performance of Cam–Tappet Conjunction

Cam–tappet contacts are responsible for ~7.5% of the internal combustion engine’s (ICE) total frictional losses. The application of coatings can improve the tribological performance of these contacts. In this paper, the application of a WC-C coating as a novel approach for cam–tappets in comparison with DLC coating is investigated. The tribological performance of the coated contacts are evaluated by a novel model comprising combined implicit analytical and explicit numerical methods. This model considers the coupled tribo-dynamic behaviour whilst obtaining detailed tribological performance. The combined approach provides a computationally efficient platform. The results show that application of DLC or WC-C can improve the film thickness value by up to 41%. They can improve boundary friction, whilst increasing the viscous friction.

Structural and Mechanical Properties of DLC/TiN Coatings on Carbide for Wood-Cutting Applications

In this work, the diamond-like carbon and titanium nitride (DLC/TiN) multilayer coatings were prepared on a cemented tungsten carbide substrate (WC—3 wt.% Co) using the cathodic vacuum arc physical vapor deposition (Arc-PVD) method and pulsed Arc-PVD method with a graphite cathode for the deposition of TiN and carbon layers, respectively. The structural and mechanical properties of the prepared coatings were studied, and different techniques, such as scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy, and microindentation techniques investigated their microstructure, composition, and phases. The prepared coatings had a multilayer structure with distinct phases of DLC, TiN, and carbide substrate. The potentiodynamic polarization method (PDP) was performed for the DLC/TiN multilayer coatings in 3% NaCl solution to evaluate the corrosion resistance of the prepared coatings. It has been shown that the DLC layer provided the coating with a polarization resistance of 564.46 kΩ. Moreover, it has been demonstrated that the DLC/TiN coatings had a high hardness of 38.7–40.4 GPa, which can help to extend the wood-cutting tools’ life.

Electrochemical characteristics and damage behaviour of DLC-coated 316L stainless steel for metallic bipolar plates of PEMFCs

ABSTRACT A diamond-like carbon (DLC) coating was deposited on the surface of 316L stainless steel using the arc ion plating (AIP) method to improve the life and efficiency of the metallic bipolar plate for polymer electrolyte membrane fuel cells (PEMFCs). The electrochemical characteristics and damage behaviour were investigated in an accelerating solution simulating the PEMFCs operation environment. A result of the experiment showed the corrosion current density of all specimens with DLC coatings was lower than that of the base metal. However, when the thickness of the DLC coating was 0.3 and 0.5 μm, the corrosion resistance was lower than that of the base metal. This is thought to be because defects on the coating surface result in crevice corrosion of the gap between the coating layer and the intermediate layer or between the coating layer and the base metal, further accelerating corrosion.

Adsorption elucidation of amino acids on diamond-like carbon coatings for biomedical applications using dispersion-corrected DFT

Understanding the interactions between biomolecules (proteins) and nanomaterials surface is of great importance for developing new biomedical devices. Diamond-like carbon (DLC) is considered an excellent candidate for coating materials for bone organ and tooth replacement. In this paper, Dispersion-corrected Density Functional Theory (DFTD) calculations were performed to elucidate the adsorption behavior of amino acid molecules over Diamond-Like Carbon (DLC) coatings surfaces.In order to examine the effect of carbon hybridization (sp3/sp2 ratio) on the adsorption process, three kinds of DLC surfaces are selected DLC1, DLC2, and DLC3 with sp3/sp2 ratios of 20/80, 52/48, and 76/24 respectively. Molecular optimization, electronic properties, molecular electrostatic potential (MEP), the density of states (DOS), and Infrared analysis for DLC surfaces and amino acids before and after adsorption are investigated. NBO and QTAIM results reveal that the adsorption is physical in nature owing to the presence of non-covalent bonds between the considered molecules. DLC1 with a low sp3/sp2 ratio has more affinity to amino acids than DLC2 and DLC3.

Synthesis and characterization of diamond-like carbon coatings for drill bits using plasma-enhanced chemical vapor deposition

Synthesis and characterization of diamond-like carbon coatings for drill bits using plasma-enhanced chemical vapor deposition

Ultra-hydrophilic Diamond-like Carbon Coating on an Inner Surface of a Small-diameter Long Tube with an Amino Group by AC High-voltage Plasma Discharge

Ultra-hydrophilic Diamond-like Carbon Coating on an Inner Surface of a Small-diameter Long Tube with an Amino Group by AC High-voltage Plasma Discharge

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.

Effect of high-speed steel surface nitriding treatment on adhesion and wear resistance properties of nitrogen-doped diamond-like carbon coatings

Based on the principle of hollow cathode, diamond-like carbon (DLC) coatings were deposited on high-speed steel by plasma enhanced chemical vapor deposition (PECVD). The mechanism of the experimental parameters on the adhesion and wear behavior of the multilayer coatings, prepared by plasma nitriding substrate and DLC N-doping, were systematically investigated via Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), micro-Vickers tester, friction and wear tester analysis. It was found that the deposition speed and structure of DLC coatings can be efficiently improved by different contents of N doping. With the increase of nitrogen content, the content of sp3 bond in DLC coating first increased to 60.82 % and then decreased to 58.73 %. Meanwhile, the friction coefficient of DLC coating first decreased and then increased. Combined with plasma nitriding treatment for substrate, the wear resistance of DLC coating was effectively improved by optimizing the hardness gradient between the coating and the substrate. Under the same friction conditions, the wear rate was reduced by about 50 %, while the adhesion of DLC coating was improved from HF4 to HF1 in comparison with non-nitriding and non-N-doping DLC coatings. It was revealed by the mechanistic-based model that the resistance by nitriding layers played a more important role than an increase in coatings thickness due to the reasonable hardness gradient in resisting deformation. Based on the N-doped DLC + DLC structure, the surface hardness of the coating gradually increased to 1970.9 HV. The hard outer layer provided sufficient load-carrying capacity and wear resistance during the friction process, thus decreasing the generation of wear debris and the depletion of coating.

Effects of Different Silicon Substrates on the Structure and Properties of Deposited Diamond‐like Carbon Films

Diamond‐like carbon (DLC) has attracted much attention due to its unique properties such as excellent physicochemical and biological properties. Herein, DLC coatings are deposited on four different silicon substrates using a radio frequency plasma‐assisted chemical vapor deposition (RF‐PECVD) technique. The structure and mechanical properties of DLC coatings deposited on different types of silicon substrates under different powers are compared. The surface morphology of the samples is characterized by scanning electron microscopy. The surface roughness of DLC films deposited on different silicon substrates is measured by scanning probe microscopy (SPM). The structural changes of the coatings are investigated by visible Raman spectroscopy. The analysis of DLC films deposited on different silicon substrates reveals that the structure of DLC films deposited on silicon is affected by different crystal directions of silicon substrates (different atomic densities in different crystal directions) and different conduction modes (electronic conduction and hole conduction). Regarding the DLC films deposited on the same substrate, the overall performance of P‐type silicon is better at 150 W, and the overall performance of N‐type silicon is better when the deposition power is 100 W.

Study of the Influence of Silicon-Containing Diamond-like Carbon Coatings on the Wear Resistance of SiAlON Tool Ceramics

DLC coatings have low adhesive bond strength with the substrate and a high level of residual stresses. This paper is devoted to researching a complex of characteristics of a DLC-Si coating deposited on samples of SiAlON ceramics with intermediate coatings (CrAlSi)N pre-formed to improve the adhesive bond strength employing vacuum-plasma spraying. DLC-Si coatings were formed by chemical vapor deposition in a gas mixture of acetylene, argon, and tetramethylsilane supplied through a multichannel gas purge system controlling the tetramethylsilane volume by 1, 4, 7, and 10%. The SiAlON samples with deposited (CrAlSi)N/DLC-Si coatings with different silicon content in the DLC layer were subjected to XPS and EDX analyses. Tribological tests were carried out under conditions of high-temperature heating at 800C. The nanohardness and elasticity modulus of the rational (CrAlSi)N/DLC-Si coating with Si-content of 4.1% wt. were 26 ± 1.5 GPa and 238 ± 6 GPa, correspondingly. The rational composition of (CrAlSi)N/DLC-Si coating was deposited on cutters made of SiAlON ceramics and tested in high-speed machining of aircraft nickel-chromium alloy compared to uncoated and DLC-coated samples. The average operating time (wear resistance) of (CrAlSi)N/DLC-Si(4.1% wt.)-coated end mills before reaching the accepted failure criterion was 15.5 min when it was 10.5 min for the original cutters.

Tribological Behavior of Doped DLC Coatings in the Presence of Ionic Liquid Additive under Different Lubrication Regimes

Diamond-like carbon (DLC) coatings are widely used in industries that require high durability and wear resistance, and low friction. The unique characteristics of DLC coatings allow for the possibility of creating adsorption sites for lubricant additives through the doping process. In this study, the combined use of europium-doped diamond-like carbon (Eu-DLC), gadolinium-doped diamond-like carbon (Gd-DLC), and pure DLC coatings and an ionic liquid (IL) additive, namely, trihexyltetradecylphosphonium bis (2-ethylhexyl) phosphate [P66614] [DEHP], with a 1 wt.% concentration in polyalphaolefin (PAO) 8 as a base lubricant was investigated. Higher hardness, higher thin-film adhesion, a higher ratio of hardness to elastic modulus, and a higher plastic deformation resistance factor were achieved with the Gd-DLC coating. The CoF of the Gd-DLC coating paired with the IL was superior compared to the other pairs in all lubrication regimes, and the pure DLC coating had a better performance than the Eu-DLC coating. The wear could not be quantified due to the low wear on the surface of the DLC coatings. The friction reduction demonstrates that tribological systems combining Gd-DLC thin films with an IL can be a potential candidate for future research and development efforts to reduce friction and increase the efficiency of moving parts in internal combustion engines, for instance.

Biomechanical characteristics of silver enriched diamond-like carbon coatings for medical applications

Silver enriched diamond-like carbon (Ag/DLC) coatings are gaining a reputation for medical applications as Ag doping improves the intrinsic biocompatibility and antimicrobial features of DLC, and higher Ag amounts improve its hemocompatibility and growth inhabitation of tumours etc. However, higher Ag amounts in DLC coatings can also lead to increased cytotoxic effects. This work presents the co-sputter deposition of Ag-enriched DLC coatings with 17, 40, and 65 at% Ag in a DLC matrix. The structural and mechanical properties of the coatings are studied with field emission scanning electron microscopy, electron dispersive X-ray, X-ray diffraction, contact surface profiler, and nanoindentation. The biocompatibility of 72 h and 168 h leached extracts of Ag/DLC coatings are assessed through Ag ion release rates in Dulbecco’s modified eagle medium using inductively coupled plasma optical emission spectroscopy and their corresponding biocompatibility profiles are mapped against the L929 mouse fibroblast cell line. EDX mapping shows a throughout distribution of Ag in DLC matrix instead of localization distributions and clustering. The XRD diffraction peaks reflect the amorphous-like behaviour of 17 at% Ag/DLC and prominent Ag crystallinity for 40 and 65 at% Ag/DLC coatings. The leached Ag ions concentration of 8 ppm demonstrated by the 65 at% Ag/DLC coating completely diminishes its biocompatibility. The results suggest that 17 at% Ag enriched DLC coatings are a safe candidate for biomedical application and retain biocompatibility when treated with extracts prepared over prolonged ion leaching periods of 168 h, when compared to 40 and 65 at% Ag/DLC coatings. Similarly, the 17 at% Ag/DLC coatings show less compromise on mechanical properties, which decline by over 50% for 40 and 65 at% Ag/DLC coatings. This work has extended the typical range of Ag for depositing safe and biocompatible DLC coatings for medical applications.

Friction behavior of diamond-like carbon coatings with different sp3 contents by atomistic-scale friction dynamics

The tribological performance of diamond-like carbon (DLC) coatings as a function of sp3 concentrations was investigated using molecular dynamics and experimental analysis. The results show that sp3 bonds proportion, hardness, and elastic modulus present an uptrend, whereas surface roughness displays a downtrend with the increase of SBV. Adhesive debris elements and no furrows features of the DLC coatings at low SBVs indicated the wear mechanism is dominated by adhesive wear. The DLC coatings at high SBVs were featured by obvious furrows and stacked abrasives, suggesting abrasive-wear-dominated. Atomistic-scale friction dynamics were used to reveal the friction mechanism. Interactions with the Si3N4 friction pair changed from carbon atoms chains or single atoms to atom groups with the increase of biases. The formation of the interfacial bonds changed from CN covalent bonds to CC covalent bonds. At high biases, there was a dissociation of many internal CC bonds that occurred in the DLC coatings. The bond evolution in friction simulation indicated the tribological mechanism transformed from adhesive wear to abrasive wear with an increase of the SBV. The DLC coating at the SBV of −30 V was located at the transformation point of two wear mechanisms, showing a well-established wear resistance.

Structure and Property of Diamond-like Carbon Coating with Si and O Co-Doping Deposited by Reactive Magnetron Sputtering

In this paper, diamond-like carbon (DLC) coatings with Si and O co-doping (Si/O-DLC) were deposited by reactive magnetron sputtering using a gas mixture of C2H2, O2 and Ar to sputter a silicon/graphite splicing target. The O content in the Si/O-DLC coatings was controlled by tuning the O2 flux in the gas mixture. The composition, chemical bond structure, mechanical properties and tribological behavior of the coatings were investigated by X-ray photoelectron spectroscopy, Fourier infrared spectrometer, Raman spectroscopy, nanoindentation, a scratch tester and a ball-on-disk tribometer. The electrical resistivity of the Si/O-DLC coatings was also studied using the four-point probe method. The results show that the doping O tends to bond with Si to form a silicon–oxygen compound, causing a decrease in the sp3 content as well as the hardness of the coatings. The tribological performance of the coatings can be improved due to the formation of the silicon–oxygen compound, which can effectively reduce the friction coefficient. In addition, the insulating silicon–oxygen compound is doped into the C-C network structure, significantly improving the surface resistivity of the DLC coating with a low sp3 content. The Si/O-DLC coatings with good mechanical properties, tribological performance and electrical insulation properties might be used as protection and insulation layers for microelectronics.

Tribological Performance of Gd-DLC and Eu-DLC Coatings in the Presence of Synthetic Oils Containing Ionic Liquid Additives

The lubrication of gadolinium-doped diamond-like carbon (Gd-DLC) and europium-doped diamond-like carbon (Eu-DLC) coatings with trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate ([P66614][DEHP]) ionic liquid (IL) as 1 wt% additive in polyalphaolefin (PAO) 8 was studied. The results of the friction tests under boundary lubrication conditions showed that Gd-DLC and Eu-DLC coatings in the presence of the IL exhibit a friction reduction, especially with the high atomic concentration of doped metal. Later, the surface observation after the long-term wear test indicated that Gd-DLC coatings have less abrasive wear and higher anti-wear properties compared to Eu-DLC coatings due to the enhanced formation of tribofilms derived from the phosphorus of the IL on the steel ball as the counter body. From these results, we have concluded that the friction reduction and the anti-wear property in the presence of the IL can be improved by changing the type and the concentration of the doped metals. This clearly shows that the novel lubrication system combining the Gd-DLC and Eu-DLC coatings with the IL allows for guiding future research and development.Graphical abstract

Surface Roughness Influence on Tribological Behavior of HiPIMS DLC Coatings

The application of diamond-like carbon (DLC) coatings in dry machining of difficult-to-machine materials has been gaining popularity due to high inertness, low coefficient of friction (COF), and high hardness of these coatings. Although the effect of surface roughness on the tribological properties of DLC coatings is of paramount importance, usually it is overlooked and coatings performance analysis was accomplished generally on highly polished substrates. The generation of polished surfaces is a time-consuming, labor-intensive process and, in most cases, not feasible for the industry due to its high cost. This article focuses on determining the effect of substrate (cemented carbide, WC-Co) surface roughness on the load-bearing capacity and tribological properties of DLC coatings deposited by High Power Impulse Magnetron Sputtering (HiPIMS) in Ne–Ar gas plasma. The DLC films were deposited onto WC-Co substrates with three different surface roughness profiles and their tribological performance were evaluated using a reciprocating tribotest. The high surface roughness resulted in increased wear rate due to high levels of asperities and increased potential for premature delamination of the coatings, while also causing severe damage to the counterbody due to inhibition of transfer film formation.