Diamond-like Carbon Research Articles

Diamond-like carbon coating reduces connection screw head stripping after multiple tightening.

The stability of implant-abutment joint is fundamental for the long-term success of implant rehabilitation. The screw loosening, fracture, and head deformation are among the most common mechanical complications. Several surface treatments of titanium screws have been proposed to improve their resistance and stability. Diamond-like carbon (DLC) coating of the materials is widely used to increase their wear resistance and durability. The present study aimed to evaluate the effect of carbon fiber coating on the screw head on screw removal torque and screw head stripping. One hundred titanium implant screws were used, 50 without coating (Group 1) and 50 with DLC coating of the screw head (Group 2). Each screw was tightened with a torque of 25Ncm and unscrewed ten times. The removal torque was measured with a digital cap torque tester for each loosening. Optical 3d measurement of the screw head surface was performed by a fully automatic machine before and after multiple tightening to investigate surface modifications. The reverse torque values decreased with repeated tightening and loosening cycles in both groups without significant differences (p>0.05). Optical measurements of surface dimensions revealed average changes of 0.0357mm in Group 1 and 0.02312mm in Group 2, which resulted to be statistically significant (p<0.001). The DLC coating of the retention screw head can prevent its distortion and wear, especially after multiple tightening.

First-principles molecular dynamics simulations for the properties of boron-doped tetrahedral amorphous carbon

Based on first-principles molecular dynamics (FPMD) simulations combined with a liquid quenching method, we study the effects of boron doping at 0 %, 2 %, 4 %, 6 % on the properties of tetrahedral amorphous carbon (ta-C) with an initial density of 3.0 g/cm3. The results of bond structures and internal stress show the promotion of graphitization with increase in the concentration of boron doping. In addition, simulation of electronic states reveals that the Fermi level shifts to valence band and the intensity of density of electronic states near Fermi level increases with the boron concentration increasing. A covalent bond formation between carbon and boron atoms is also shown by analyzing projected densities of electronic states (PDOS) and electron density distribution. The results of electronic state and bond formation strongly indicate that the boron-doped ta-C is like a p-type semiconductor. The present simulation results provide useful information for deeper understanding on the physical properties of boron-doped ta-C.

Formation and Prediction of the Properties of Ion-Plasma Diamond-Like Coatings under Nitrogen Stabilization

Formation and Prediction of the Properties of Ion-Plasma Diamond-Like Coatings under Nitrogen Stabilization

Tensile testing as alternative evaluation method for enhanced adhesion of diamond-like carbon coatings with different titanium buffer layers

A tetrahedral amorphous carbon (ta-C) is widely used in industrial environments. However, application in extreme environments requires improved interfacial adhesion strength. This study proposes a new method to determine the adhesion strength of ta-C coating using the microtensile test, which is applied to improve the adhesion strength of ta-C coating by varying the Ti buffer layer microstructure. The tensile properties recorded in the stress-strain curve can be used to determine the difference between the absorbed energy and resistance to plastic deformation, which is then used to calculate fracture toughness. Moreover, to determine the adhesion strength, the crack density and spallation size were evaluated by measuring the cracks on the slip surface. The results show that compared to the columnar Ti buffer layer microstructure, the ta-C coating with a dense and flat Ti buffer layer microstructure more effectively improved the composite mechanical properties (columnar Ti layer H = ∼39 GPa, E = ∼430 GPa; dense Ti layer H = ∼48 GPa, E = ∼468 GPa), crack resistance (crack density = 6.4 % on columnar Ti layer; 1.5 % on dense Ti layer) and increased the dissipation energy during plastic deformation. Additionally, the dense Ti buffer layer microstructure reduced the wear rate (3.1 × 10−7 mm3/N∙m) and inhibited crack generation under long-term continuous frictional contact due to stress release in the ta-C coating. This finding clarifies the importance of the buffer layer with the suggested microstructural modifications for the wear resistance of ta-C coating.

Study of the Industrial Application of Diamond-Like Carbon Coatings Deposited on Advanced Tool Steels

The utilization of diamond-like carbon (DLC) coatings has emerged as a promising strategy to enhance the performance, durability, and functionality of industrial tools and components. Recognized for their exceptional attributes such as hardness, wear resistance, low friction, and biocompatibility, DLC coatings have achieved widespread acclaim for their potential to improve the capabilities of tool steels for different applications. This present study shows a comprehensive investigation into the application of DLC coatings on a diverse range of tool steel substrates, encompassing 1.2379, 1.2358, Caldie, K340, HWS, and Vanadis 4. The main aim is to show the effects of DLC coatings on these substrates and to provide an in-depth analysis of their properties during forming processes. Furthermore, this study explores the practical utilization of DLC-coated tool steel components, with a particular focus on their role in cold forming dies. Additionally, the study reviews the application of duplex treatments involving plasma nitriding to enhance DLC coating performance. To sum up, this study pursues a threefold objective: to investigate DLC coatings’ performance on diverse tool steel substrates; to assess the potential for improvement through nitriding; and to evaluate the behavior of DLC coatings in the cold stamping of S235 steel, which is of great technological and industrial interest to the cold forging sector.

Influence of diamond-like carbon coatings and micro-texturing on friction and wear of seal interfaces: Experiment and simulation study

For mechanical seal friction vice in dry friction conditions, due to friction wear serious failure, is the slurry pump and other instruments in the operation of the process of the urgent need to solve the problem. In this paper, in order to optimize and enhance the friction and wear problem of mechanical seal end face of slurry pump. Surface treatment of mechanical sealing rings with diamond-like carbon (DLC) coating and surface microtexturing, and at different rotational speeds and normal forces, the surface hardness, wear coefficient and dry friction coefficient of the sealing rings were analyzed by experimental comparison, and the wear morphology was collected by electron microscopy, having analyzed the results of the sets of, the end face structure of the mechanical seal was optimized. Based on Archard wear model simulation calculations, the seal ring wear depth and wear quality were obtained. The results show: under dry friction conditions, the synergistic effect of the DLC coating and the surface micro-texture (MT), the coefficient of friction is reduced by approx. 68% and the quality and depth of wear is minimized. Excessive speeds and normal forces are more prone to wear behavior caused by abrasive wear. Simulation results of surface treatment groups, DLC / MT group maximum wear depth is the smallest; wear quality test and simulation of the maximum error within 15.7%. The results of the study can provide a basis for a phosphoric acid plant slurry pump mechanical seal design.

Tetrahedral Amorphous Carbon Coatings with Al Incorporation Deposited by a Hybrid Technique of Sputtering and Arc Evaporation

In this paper, tetrahedral amorphous carbon (ta-C) coatings containing Al were deposited by a hybrid technique of sputtering and arc evaporation. The influence of Al incorporation in the structure and properties of the ta-C coatings were studied as a function of the Al concentration. It is found that Al tends to form a Al-O-C bond when the Al concentration is small. An Al-C bond was detected when the Al concentration is high. Al can facilitate the graphitization of the ta-C coatings and the graphite cluster size as well as the sp2/sp3 ratio of the coatings increase as the Al concentration increases. The decline of the sp3 fraction causes the drop in the hardness of the coatings. The incorporation of Al can effectively decrease the residual stress of the ta-C coatings. During friction tests, Al can facilitate the formation of the sp2-rich graphitic tribo-layer and decrease the friction coefficient. Nevertheless, the decline of the hardness due to the Al incorporation will result in the increase in the wear rate of the coating. It is believed that the ta-C coating with a proper concentration of Al appears to achieve a good comprehensive performance with high hardness, low residual stress, and a low friction coefficient and wear rate.

Improving the Quality of Tantalum Cylindrical Deep-Drawn Part Formation Using Different Lubricating Media-Coated Dies

Lubrication is one of the key factors to improve metal-forming quality. In the process of deep drawing, seizing tumors easily occur on the contact surfaces between the tantalum metal and the mold, which greatly affects the forming quality of the deep-drawn parts. Quality-forming quality problems that occur during the deep drawing of tantalum metal are studied from the perspective of lubrication in this paper. Three lubrication media, caster oil, PE (polyethylene) film, and DLC (Diamond Like Carbon) film, were adopted in the deep drawing of tantalum cylindrical cups. A universal testing machine and microscope were used to investigate the effect of lubrication media on the limit-drawing ratio, maximum forming force, and surface topography quality during the deep drawing process of the tantalum sheet. The results reveal that the lubrication of the PE film and DLC film can greatly improve the forming quality of the tantalum metal sheet, in which the DLC film has higher wear resistance and lower friction coefficient and can be used as the lubricating medium in the industrial forming process of tantalum deep-drawn parts.

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.

Preparation of boron-doped diamond-like carbon films via enhanced-PECVD using an additional cathode

Boron-doped Diamond-Like Carbon (B:DLC) films with different concentrations of boron were produced in an Enhanced-PECVD reactor using trimethylborate (TMB) vapor as the boron source. An additional cathode system was incorporated inside the reactor to confine the plasma to grow B:DLC film on polished Ti-6Al-4 V and Silicon samples. The boron-containing coatings were evaluated and compared to a boron-free coating through several characterization techniques. Raman spectroscopy, Nano-hardness, XPS, RBS, and SEM techniques were employed to study the microstructure, hardness, chemical composition and bonding state, and morphology of the samples. Ball-on-disc tests were also conducted, using a tribometer to measure the friction coefficient and wear resistance. Boron was confirmed in the DLC film structure by XPS and RBS analyses. The XPS measurements showed that the boron bonding was accompanied by a higher content oxygen than carbon content, which increased with the TMB concentration. The sp3 content was evaluated, and the result showed a decrease of about 30 % with the higher solution concentration. As a consequence, the friction coefficient, wear, and hardness were affected. However, the adherence of the films was not compromised. Finally, our study indicated that the PECVD deposition system employing an additional cathode was suitable for the incorporation of boron into DLC films.

Tool-integrated thin-film sensor systems for measurement of cutting forces and temperatures during machining

Effective in-process control mechanisms are vital for the future development of production processes and ask for reliable monitoring of process variables. For this, new tool-integrated sensor systems for measuring cutting forces and temperature for machining of hardened steel are proposed. Thin-film technology is used to apply a thermoresistive temperature sensor in the chip-workpiece contact area for the first time on industrial cutting inserts with chip breaker geometry. Complementary piezoresistive thin-film sensors based on diamond-like carbon (DLC) and manganin layers were developed and deposited on a washer. It was placed beneath the indexable insert to measure the cutting forces. Turning experiments were conducted to study sensor life and accuracy. All sensors showed an adequate lifetime for laboratory purposes. Temperature compensation methods were investigated for force measurement and results compared to forces recorded by a dynamometric platform. While temperature compensation for the DLC-based sensor needs further optimization, results of the manganin-based sensor compared well with the expected cutting forces. The manganin thin-film sensor exhibited rapid responsiveness and great reproducibility, underscoring its prospective utility for real-time monitoring of cutting forces in machining operations.

Effect of cuttings particle content on the tribological behavior of Fe/DLC at casing and drill pipe joints: A molecular dynamics study

The presence of cuttings in the drilling fluid can exacerbate the wear of drill pipe joints and casing. Diamond-like carbon (DLC) films have ultra-low friction coefficients and high wear resistance, which have excellent research prospects in reducing the wear between drill pipe joints and casing. To investigate the impact of varying particle counts at the interface between Fe bulk and DLC film, this work builds a pertinent molecular dynamics model. The results show that the interfacial friction increases with increasing particle content, which leads to more severe abrasive wear on the Fe bulk and prevents the amorphous structure atoms in the Fe bulk from recovering to a body-centered cubic crystal structure. On the contrary, the DLC film is difficult to be affected by the particle motion because of its good tribological properties. Simultaneously, more silica particles reduce the space for the movement of water molecules and ultimately weaken the lubrication ability of water molecules.

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.

Ratiometric fiber optic fluorescent pH sensor for hydroxide diffusion measurements in concrete

This article delineates the development of an advanced ratiometric pH optode designed for protracted monitoring of pH dynamics in cementitious materials—a crucial aspect of structural management. The optode features a dual-layer Hydromed™ D4 polymer pellet incorporating a pH-sensitive Naphth-AlkyneOMe fluorescent probe (pKa ≈ 12) and CdSe quantum dots as an internal reference. The polymer matrix, optimized with diamond powder and carbon black, enhances the signal while minimizing light artifacts. Demonstrating a robust response to pH fluctuations, the optode, utilizing ratiometric measurements, enables steadfast monitoring for up to 75 days.The experimental setup includes a Delrin® sample compartment housing a glass slide with the optode connected to an optical fiber via an SMA connector. HydroMed™ D4 films, forming the pH-sensitive layer, are deposited on the glass slide and secured. The optode configuration is fine-tuned to optimize signal intensity by reducing its length. For optode-detector coupling, a 1000 µm core diameter optical fiber links the optode, and a 405 nm LED illuminates the sensing film. The emission signal is collected through the optical fiber, and signals are processed using computer-controlled lock-in amplifiers.In the investigation of hydroxide ion diffusion through a concrete sample, the optode's efficacy was validated, aligning with pH electrode measurements. Addressing long-term stability, a degradation model uncovered leisurely kinetics with commendable stability. Slow degradation kinetics, with a reaction rate coefficient of 1.6 × 10⁻⁷ s⁻¹ and a half-life of 1180 h, exceeded expectations.This pH optode, showcasing an accurate and resilient response to pH variations within the 10 to 12.5 range, stands as a promising tool for monitoring pH dynamics in low-pH cementitious materials. The incorporation of a degradation model underscores fidelity over prolonged durations and offers a blueprint for enduring surveillance of concrete structures.

Atomic-scale evolution of hydrogenated fullerene-like carbon in the presence of black phosphorus

Hydrogenated diamond-like carbon (H-DLC) is widely used by the industry, but over the past few decades, its mechanical properties have been hindered by oxidation stemming from frictional contact and heat generation. Herein, we propose a solution by establishing a tribosystem that incorporates two-dimensional black phosphorus (BP) nanosheets and H-DLC. Experiments and atomistic simulations reveal that integration of BP nanosheets to the sliding interface not only shields H-DLC from oxygen erosion, but also creates reactive sites for the formation of hydrogenated fullerene-like carbon (FLC:H) via covalent and hydrogen bonding interactions, resulting in significantly reduced friction. These findings provide a novel insight into the atomic-scale evolution of FLC:H and reveal promising prospects for expanding the industrial application of hydrogenated carbon films.

Coatings and Surface Modification of Alloys for Tribo-Corrosion Applications

This review of the tribocorrosion of coatings and surface modifications covers nearly 195 papers and reviews that have been published in the past 15 years, as compared to only 37 works published up to 2007, which were the subject of a previous review published in 2007. It shows that the research into the subject area is vibrant and growing, to cover emerging deposition, surface modification and testing techniques as well as environmental influences and modelling developments. This growth reflects the need for machines to operate in harsh environments coupled with requirements for increased service life, lower running costs and improved safety factors. Research has also reacted to the need for multifunctional coating surfaces as well as functionally graded systems with regard to depth. The review covers a range of coating types designed for a wide range of potential applications. The emerging technologies are seen to be molten-, solution-, PVD- and PEO-based coatings, with CVD coatings being a less popular solution. There is a growing research interest in duplex surface engineering and coating systems. Surface performance shows a strong playoff between wear, friction and corrosion rates, often with antagonistic relationships and complicated interactions between multiple mechanisms at different scale lengths within tribocorrosion contacts. The tribologically induced stresses are seen to drive damage propagation and accelerate corrosion either within the coating or at the coating coating–substrate interface. This places a focus on coating defect density. The environment (such as pH, DO2, CO2, salinity and temperature) is also shown to have a strong influence on tribocorrosion performance. Coating and surface modification solutions being developed for tribocorrosion applications include a whole range of electrodeposited coatings, hard and tough coatings and high-impedance coatings such as doped diamond-like carbon. Hybrid and multilayered coatings are also being used to control damage penetration into the coating (to increase toughness) and to manage stresses. A particular focus involves the combination of various treatment techniques. The review also shows the importance of the microstructure, the active phases that are dissolved and the critical role of surface films and their composition (oxide or passive) in tribocorrosion performance which, although discovered for bulk materials, is equally applicable to coating performance. New techniques show methods for revealing the response of surfaces to tribocorrosion (i.e., scanning electrochemical microscopy). Modelling tribocorrosion has yet to embrace the full range of coatings and the fact that some coatings/environments result in reduced wear and thus are antagonistic rather than synergistic. The actual synergistic/antagonistic mechanisms are not well understood, making them difficult to model.

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).

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.

Diamond deposition on AlN using Q-carbon interlayer through overcoming the substrate limitations

Q-carbon, a quenched form of carbon, is a recently discovered carbon structure that has tremendous properties, compatibility, and potential for use in device fabrication and other electronic and mechanical applications. However, the non-equilibrium nature of the synthesis process and a very small window of growth parameters have limited the formation of Q-carbon to only low thermal conductive substrates. This study aims to overcome these limitations through extensive tuning of the parameters of diamond-like-carbon (DLC), the base structure required for the formation of Q-carbon. The as-deposited DLC films demonstrate ID/IG ratios ranging from 0.12 to 1.67, which are obtained through the optimization of laser energy density, rep rate, and deposition temperature during pulsed laser deposition. Utilizing Simulation of Laser Interaction with Materials, pulsed laser annealing (PLA) was used to directly transform the DLC films into Q-carbon while varying the PLA energy density from 0.3 J/cm2 to 1.2 J/cm2. Findings of Q-carbon formation on sapphire using different DLC films assisted in the preparation of a roadmap for overcoming the substrate limitations for Q-carbon formation. Further, Q-carbon is formed on AlN substrates for the direct deposition of diamond films without the requirement of a non-carbon interfacial layer or nanodiamond seeding layer. The large-area and uniform diamond growth on Q-carbon shows well-faceted and five-fold twinned growth with a 70 % improvement in the residual compressive stress of diamond on AlN. Such a method of diamond deposition on AlN provides the opportunity to address the thermal management issues in wide- and ultra-wide bandgap high-power electronic devices.