Performance Of Diamond-like Carbon Coatings Research Articles

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.

Effect of cryogenic pretreatments on the microstructure and mechanical performance of diamond-like carbon coatings for high-speed alloys

Hydrogenated diamond-like carbon coatings (DLCs) with Cr/WC + C interlayers were deposited using a plasma-enhanced chemical vapor deposition (PECVD) method onto the surface of M35 high-speed alloys suffered by various pre-treatments including annealing and deep cryogenic cooling. Scanning electronic microscopy, transition electronic microscopy, X-ray diffractometry, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the microstructure, and hardness indentation, scratch testing, and friction testing were used to measure the mechanical performance of the DLCs. The results showed that different pretreatments led to variations in the microstructure of the M35 alloy, which influenced the coating growth process. Although all the pretreatments resulted in the same fraction of carbon-hybrid structures of the top DLC layer, the best combination of adhesion strength, hardness, friction, and wear resistance was found when the alloy was tempered at 525 °C for 1 h, followed by cryogenic treatment at −180 °C for 6 h. In contrast with the DLC deposited onto M35 alloy substrate pretreated by only 525 °C for 1 h tempering, the above pretreatment could improve adhesion force by 20 %, hardness by 15 %, and wear resistance by approximately 50 %.

Friction Response of Piston Rings for Application-like Starvation and Benefit of Amorphous Carbon Coatings

The oil supply at the interface between the top ring and the cylinder liner (TRCL) plays a major role in an internal combustion engines efficiency. In particular, the interface forms a trade-off between the serving of enough lubricant for sufficient lubrication conditions and emissions through subsequent combustion. This can lead to deficient top ring lubrication conditions. In this study, a new developed reciprocating long-stroke tribometer, enabling the variation of oil supply, is used to investigate such application-like starved lubrication conditions of the TRCL interface. With the simulative investigations, a comparison with the fired engine is possible. The performance of diamond-like carbon coatings is compared to standard nitrided piston rings. It was found that the tetrahedral amorphous carbon (ta-C) coatings exhibit up to 31% reduced friction as well as a lower wear under starved lubrication conditions. Simulative investigations show a good correlation between engine friction and tribometer measurements for selected oil supply conditions.

Performance of diamond-like carbon coatings (produced by the innovative Ne-HiPIMS technology) under different lubrication regimes

Piston rings (PR) are responsible for over 24% of the friction losses in internal combustion engines. To minimize the friction losses and improve the life span of PR it was tested a new developed variation of the diamond like carbon (DLC), in this case, deposited on a plasma atmosphere of Argon and Neon with high power impulse magnetron sputtering (HiPIMS) power supply at P = 0,8 Pa and with a bias of −80 V. These coatings were compared with the widely used Chromium nitride (CrN) and DLCs deposited in pure Argon atmosphere. The tribology tests were performed on a block-on-ring setup with counter-body, loads, velocities and lubrication that represented the real conditions of the PR. The analyses of the results were performed using the stribeck curves where it was observed an improvement of 15.7% in friction losses of the DLC deposited with 25% of Ne in the discharge gas when compared with CrNs at the mixed lubricated regime. As well as an improvement on wear resistance on boundary regime. The wear tests were analyzed with profilometry and wear track optical microscope images.

Research on the Performance of Diamond-Like Carbon Coatings on Cutting Aluminum Alloy: Cutting Experiments and First-Principles Calculations

The purpose of this study is to investigate the cutting performance of amorphous carbon (a-C) coatings and hydrogenated amorphous carbon (a-C:H) coatings on machining 2A50 aluminum alloy. First-principles molecular dynamics simulation was applied to investigate the effect of hydrogen on the interaction between coatings and workpiece. The cross-section topography and internal structure of a-C and a-C:H films were characterized by field emission scanning electron microscopy and Raman spectroscopy. The surface roughness of the deposited films and processed workpiece were measured using a white light interferometer. The results show that the a-C-coated tool had the highest service life of 121 m and the best workpiece surface quality (Sq parameter of 0.23 μm) while the workpiece surface roughness Sq parameter was 0.35 and 0.52 μm when machined by the a-C:H-coated and the uncoated tool, respectively. Meanwhile, the build-up edge was observed on the a-C:H-coated tool and a layer of aluminum alloy was observed to have adhered to the surface of the uncoated tool at its stable stage. An interface model that examined the interactions between H-terminated diamond (111)/Al(111) surfaces revealed that H atoms would move laterally with the action of cutting heat (549 K) and increase the interaction between a-C:H and Al surfaces; therefore, Al was prone to adhere to the a-C:H-coated tool surface. The a-C coating shows better performance on cutting aluminum alloy than the a-C:H coating.

Effects of Varying Power and Argon Gas Flux on Tribological Properties and High-Speed Drilling Performance of Diamond-Like Carbon Coatings Deposited using High-Power Impulse Magnetron Sputtering System

This study examines the effects of different pulse powers and gas fluxes on the mechanical and tribological properties and high-speed drilling performance of diamond-like carbon coatings deposited on tungsten carbide substrates by high-power impulse magnetron sputtering. It is shown that an appropriate pulse power is essential in improving the mechanical and tribological properties of the coatings. Specifically, coatings deposited with a pulse power of 5 kW possess a high hardness and good tribological properties, as evidenced by a high hardness-to-elastic modulus ratio. The optimal deposition parameters are determined to be a pulse power of 5 kW and an argon flux of 80 sccm. The resulting coating (designated as C80/5) has the highest hardness (24.95 GPa) of the various coatings and wear rates 11.1, 7.3 and 6.2 times better than those of the bare WC substrate under loads of 6 N, 10 N and 14 N, respectively. Moreover, the coating has low coefficient of friction values of 0.086, 0.098 and 0.062 under loads of 6 N, 10 N and 14 N, respectively. The micro-drilling tests show that the drill coated with C80/5 has a lifetime three times longer than that of an uncoated micro-drill.

Experimental investigation of tribological properties of laser textured tungsten doped diamond like carbon coating under dry sliding conditions at various loads

Laser micro texturing technique has shown its potential in reducing friction and wear at various mechanical interfaces such as automotive and cutting tools etc. Automotive parts are coated with Diamond-like Carbon (DLC) coatings to enhance their performance. Due to stringent condition at the automotive contacts and demand for performance enhancement, increase in performance of DLC coatings is required. In this study laser micro texturing is being combined with tungsten doped DLC coating. In order to analyze the benefits of laser micro texturing on tungsten doped DLC coating. Tribological testing was conducted on a reciprocating test rig at various loading conditions. The results indicated that laser textured tungsten doped DLC coating showed the lower coefficient of friction compared to un-textured tungsten doped DLC coating at a load of 15 N, 25 N and 35 N. Higher graphitization was observed in the case of un-textured coating at 35 N load.

Investigation of tribological behaviour of DLC coating on hyper-eutectic Al-Si alloys, a review

Abstract Diamond-like Carbon (DLC) coatings are used significantly in modern industries because of their outstanding tribological performance. The objective of this review is to explore the wide range of deposition methods and wear performance of DLC coatings. Earlier DLC coatings are broadly used in various industrial applications like electronics, shaving and optical. Whereas due to rapidly changing automobile performance such as standard production and racing engine vehicles the DLC coatings are used well as surface coatings for pistons, piston rings, ball bearings, and cylinder liners etc. Moreover, due to high wear resistance, adhesive protection and low coefficient of friction properties the coatings are used extensively in tribological applications.

An investigation on the micro cutting performance of diamond-like carbon coatings using finite element method

In an effort to prolong the tool life and improve the tooling performance in micro cutting, it is attractive and promising to apply diamond-like carbon (DLC) coatings on micro tools. Comprehensive understandings of micro cutting performance under various coating circumstances are essential for choosing optimum coating conditions so as for potentially improving cutting tool designs. In the study, the cutting characteristics of a DLC-coated tool has been extensively evaluated and compared with those of an uncoated tool under constant and various uncut chip thickness (UCT) using 2D plane-strain finite element method (FEM). The thermo-mechanical modelling approach has been validated at different UCT in micro milling. Besides, the influence of coating friction coefficient, coating thickness as well as UCT on the cutting forces and tool temperatures has been determined and analysed through design of experiment. It is found that appropriate UCT in micro cutting is of the greatest importance for achieving desirable coating performance of micro tools.

The role of abrasive particle size on the wear of diamond-like carbon coatings

Diamond-like carbon (DLC) coatings exhibit several attractive characteristics such as low coefficients of friction and low wear rates in certain environments. While the performance of DLC coatings under lubricated and dry contact has been a subject of extensive study, the study on the effect of abrasive media and three-body interactions on the wear of DLC coatings is not widespread in the literature. The present study focuses on the wear of DLC coatings in a highly abrasive environment with varying abrasive particle size under the mixed lubrication regime. Abrasive wear behavior of Diamond-like Carbon (DLC) coatings has been evaluated through tests conducted on a Block-on-Ring (BOR) tribometer where a DLC coated ring was rubbed against an uncoated steel block. An oil-water emulsion containing various sizes of sand particles was used as a lubricating fluid. Based upon results from surface analysis and cross-sectional microscopy studies, the lubricating fluid having no sand revealed no delamination or any major damage to the coating; rather two-body or asperity-asperity interactions removed some high spots from the coating surface. In contrast, when sand was introduced in the lubricating fluid as an abrasive medium, three-body abrasive wear was prevalent causing internal cracking within the coating followed by spallation and sequential removal of coating. The three-body wear mechanism is attributed to the entrainment of abrasive (sand) particles into the tribological contact. While the presence of sand particles dramatically influenced the DLC wear, the hardness of DLC coating seemed to surpass the effect of sand on the softer steel counterface wear, i.e. the material appeared to be primarily removed by the harder DLC asperities in the two-body cutting or ploughing wear mechanism.

Action of oil additives when used in DLC coated contacts

Under boundary lubrication conditions, different oil additives are used to prevent metal to metal contact by boundary film formation, thus reducing friction and wear of contact surfaces. With the introduction of diamond-like carbon (DLC) coatings, the major concern is the compatibility of coated surfaces with existing oils and additives, originally designed for uncoated metallic surfaces. The aim of the present work was to investigate the influence of extreme pressure, antiwear and friction modifier additives and their concentration on the tribological performance of DLC coatings in the boundary lubrication regime. Results show that antiwear and friction modifier additives have only minor effect on the frictional behaviour of DLC coatings. On the other hand, depending on the contact conditions, lubrication of steel/W doped DLC contacts with oils containing S based extreme pressure additives can result in greatly improved tribological performance caused by WS2 tribofilm formation.

Evaluation of DLC Coatings for High-Temperature Foil Bearing Applications

Diamondlike carbon (DLC) coatings, particularly in the hydrogenated form, provide extremely low coefficients of friction in concentrated contacts. The objective of this investigation was to evaluate the performance of DLC coatings for potential application in foil bearings. Since in some applications the bearings experience a wide range of temperatures, tribological tests were performed using a single foil thrust bearing in contact with a rotating flat disk up to 500°C. The coatings deposited on the disks consisted of a hydrogenated diamondlike carbon film (H-DLC), a nonhydrogenated DLC, and a thin dense chrome deposited by the Electrolyzing™ process. The top foil pads were coated with a tungsten disulfide based solid lubricant (Korolon™ 900). All three disk coatings provided excellent performance at room temperature. However, the H-DLC coating proved to be unacceptable at 300°C due to lack of hydrodynamic lift, albeit the very low coefficient of friction when the foil pad and the disk were in contact during stop-start cycles. This phenomenon is explained by considering the effect of atmospheric moisture on the tribological behavior of H-DLC and using the quasihydrodynamic theory of powder lubrication.

Improved adhesion of diamondlike coatings using shallow carbon implantation

A surface layer of metal carbides provides an excellent interface to achieve a highly adherent diamondlike carbon (DLC) coating. A plasma immersion ion implantation (PIII)-based procedure is described, which delivers a high retained dose of implanted carbon at the surface of aluminum alloys. A shallow implantation profile, followed by argon sputter cleaning and continued until a saturated carbon matrix is brought to the surface, provides an excellent interface for subsequent growth of DLC. At a carbon retained dose above 1018 atoms/cm2 the DLC adhesion exceeds the coating's cohesion strength. Regardless of the silicon content in the aluminum, the coating produced by this method required tensile strengths typically exceeding 140 MPa to separate an epoxy-coated stud from the coating in a standard pull test. Improved DLC adhesion was also observed on chromium and titanium. The reported tensile strength is believed to substantially exceed performance of DLC coatings produced by any other method.