Graphite-like Carbon Coatings Research Articles

Corrosion and tribocorrosion performance degradation mechanism of multilayered graphite-like carbon (GLC) coatings under deep-sea immersion in the western Pacific

Corrosion evolution of Cr/GLC multilayered coating exposed in the deep sea of the western Pacific after 342 days at various depths was investigated. Results showed that the atomic structure of the top-layer GLC layer remained almost unchanged after immersion, but severe corrosion across multi-scaled interfaces was significantly stimulated as the immersion depth increased. This further led to the weakening of coating density and adhesion strength, with the wear rate and corrosion rate being two orders of magnitude larger than those of the as-deposited coating. Therefore, reducing defect density and conductivity is the key to designing GLC coatings for deep-sea applications.

Enhanced corrosion resistance of graphite-like carbon coatings via dense ta-C interlayer encapsulating

Taking the combination of atomic bond density, in this work, the tetrahedral amorphous carbon (ta-C) layer with high sp3 bond were especially introduced into the sp2-riched graphite-like carbon (GLC) coatings, using a hybrid filtering cathodic arc and magnetron sputtering deposition technique. The focus was elaborated on the electrochemical behavior of coatings against the stimulated chloride solutions for marine applications. Results showed that inserting dense ta-C layer significantly encapsulated the intrinsic pore defects within GLC growth, thereafter enhancing the corrosion resistance remarkably. In particular, the coating porosity was reduced from 10.84 % for pristine GLC system to 3.19 % for GLC with ta-C sealing layer, accompanying with a reduction in corrosion current to 7.8 × 10−9 A/cm2 and an increment in protective efficiency to maximum value of 95.49 %. The small angle X-ray scattering (SAXS) analysis evidenced qualitatively that the coating porosity was suppressed greatly, which were well consisted with the enhanced corrosion resistance of GLC coating with ta-C sealing layer. Furthermore, the balance between pores sealing and interfacial matching could be tailored by controlling the thickness ratio of ta-C and GLC layers, enabling the achievement of both the compact structure and the superior corrosion resistance. These observations offer a new promising strategy to develop the protective coatings for harsh marine environment that required both excellent capability against corrosion and friction with long lifetime.

Investigation on the failure mechanism of graphite-like carbon coatings under cavitation erosion in distilled water

In this study, the use of graphite-like carbon (GLC) coatings deposited via magnetron sputtering to enhance the cavitation erosion (CE) resistance of 316L stainless steel is presented. The cross-sectional analysis and Rockwell testing show that the GLC coating exhibits the dense structure and good adhesion. The hardness and elastic modulus of the coating measured by nanoindentation reached 17.3 GPa and 197.3 GPa, respectively. Furthermore, the GLC coating exhibits excellent corrosion resistance upon electrochemical measurements. With the analysis of surface topography, chemical composition and carbon bonds, a model describing the CE failure mechanism of the GLC coatings is presented. The CE failure of the GLC can be divided into four primary stages: an initial generation of striated bulges with the release of internal stress accompanied with graphitization, followed by the generation of micro-cracks, the coating spallation with the interlinked micro-cracks and the final coating delamination.

The Spontaneous Escape Behavior of Silver from Graphite-like Carbon Coatings and Its Effect on Corrosion Resistance.

Silver-doped graphite-like carbon (Ag-GLC) coatings were prepared on the surface of aluminum alloy and single-crystal silicon by magnetron sputtering under different deposition parameters. The effects of silver target current and deposition temperature, as well as of the addition of CH4 gas flow, on the spontaneous escape behavior of silver from the GLC coatings were investigated. Furthermore, the corrosion resistance of the Ag-GLC coatings were evaluated. The results showed that the spontaneous escape phenomenon of silver could take place at the GLC coating, regardless of preparation condition. These three preparation factors all had an influence on the size, number and distribution of the escaped silver particles. However, in contrast with the silver target current and the addition of CH4 gas flow, only the change in deposition temperature had a significant positive effect on the corrosion resistance of the Ag-GLC coatings. The Ag-GLC coating showed the best corrosion resistance when the deposition temperature was 500 °C, which was due to the fact that increasing the deposition temperature effectively reduced the number of silver particles escaping from the Ag-GLC coating.

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.

Microstructure, mechanical and tribological properties of graphite-like carbon coatings doped with tantalum

The tantalum doped graphite-like carbon (Ta-GLC) coatings were obtained by magnetron sputtering. The variations of microstructure, mechanical and tribological properties by Ta content were systematically assessed. The results revealed that as the doping amount of Ta increased, the columnar structure of the coatings became coarser and the content of sp3C in the coatings decreased, and the hardness and elastic modulus of the Ta-GLC coatings were decreased correspondingly. However, the adhesion strength between the coatings and substrates was improved after Ta doping. Besides, the Ta-GLC coating with 4.79 at% Ta content exhibits the lowest wear rate of 2.55 × 10−8 mm3/Nm, which is approximately only one third of the value of non-doped GLC coating. This was mainly related to the synergistic effect of higher adhesion strength, graphitization structure and the formation of TaC and Ta nanoclusters in the Ta-GLC coating.

Friction and wear properties of GLC and DLC coatings under ionic liquid lubrication

Abstract Cr-doped graphite-like carbon (Cr-GLC) coatings and Cr-doped diamond-like carbon (Cr-DLC) coatings were prepared by PVD and PECVD, respectively. The lubrication behaviour of the solid-liquid composite lubrication systems was investigated using two ionic liquids (ILs) as lubricants. The results show that the friction coefficient was reduced by approximately 40% compared with that under the dry condition, and the composite system exhibited a good synergistic lubrication effect. The Cr-DLC coating showed better tribological behaviour than the Cr-GLC coating, which can be ascribed to a better physicochemical film formation under friction and the compact microstructure of the Cr-DLC coating. The synergistic effect of the composite systems was affected by the viscosity and corrosiveness of the ILs and the microstructure of the coatings.

Mechanism for vacuum thermal stabilization of silver in graphite-like carbon coating and performance of electrical conductivity and corrosion resistance

To inhibit the spontaneous escape of silver from graphite-like carbon coatings, a series of silver-containing graphite-like carbon coatings were prepared by heated vacuum deposition. The effect of the substrate temperature during deposition on the spontaneous escape behavior of silver was studied, and a mechanism for vacuum thermal stabilization of silver is proposed. The results show that when the substrate temperature was increased from 80 to 250 °C, the thickness of the surface silver layer was reduced from 150 to 60 nm. When the substrate temperature was increased to 300 °C, no silver particles were found on the surface of the sample even after placing the sample in an atmospheric environment for 2000 h. Thus, heating in a vacuum can effectively suppress the spontaneous escape of silver and hence achieve the permanent retention of silver in the graphite-like carbon coatings. The electrical conductivity of the coating was close to that of a graphite plate, but the corrosion current density of this coating (7.147 × 10−6 A•cm−2) was an order of magnitude higher than that of the graphite plate. An approximately 300-nm silver-free carbon layer surface cover could effectively improve the corrosion resistance of the coating, and the conductivity of the coating satisfies the performance requirements for fuel cell plates. The growth of silver clusters that segregate at the interface of the graphite-like carbon clusters is promoted during coating deposition by the thermal activation energy of substrate heating, thereby inhibiting the spontaneous escape of silver caused by internal and external pressure differences.

Effects of complex graphite-like carbon coating on gear vibration noise

Abstract In this paper, the effects of substrate surface roughness and the addition of yttrium, cerium and tantalum on thickness uniformity of graphite-like carbon (GLC) coatings on gears were studied by magnetron sputtering method using mosaic targets. And noise reduction effects of gear pump deposited with complex GLC coatings were evaluated at different rotate speeds. The results showed that target-substrate distance, sputtering angle and surface roughness had influences on thickness uniformity of GLC coatings on gear. The introduction of elements Y, Ce and Ta into GLC coatings could effectively improve their thickness uniformity. The complex GLC coating with optimal thickness uniformity on gear exhibited significantly reduction effect for gear noise and the reduction effect for axial vibration was better than that of radial vibrations. Compared with uncoated gears, the noise for the coated gears was decreased by 10 dB at 2000 rpm. Good high-frequency noise reduction was obtained, which could be decreased by 19 dB in the range of 4000–10,000 Hz.

Dual-doped(Si-Ag) graphite-like carbon coatings with ultra-low friction and high antibacterial activity prepared by magnetron sputtering deposition

Silicon(Si) and silver (Ag) co-doped amorphous carbon (a-C:H:Si:Ag) coatings were prepared by magnetron sputtering deposition. The results of Raman analyses revealed that the coating was dominated by sp2 carbon bonds and had graphite like structure. The a-C:H:Si:Ag coating exhibited a very high elastic recovery rate of 82%. Tribological tests in saline solution (NaCl, 0.9 wt%) showed that the average friction coefficient and the wear rate of the coating were as low as 0.016 and 1.2 × 10−8 mm3/(N·m), respectively. The dual doped coating exhibited a high antibacterial rate over 99% against Escherichia coli though containing a small content of Ag. It also was found that the silver ions release from the coating was extremely slow, and the newly developed (a-C:H:Si:Ag) coating would be a promising long term antibacterial materials.

Microstructures and tribological properties of GLC coated 100Cr6 bearing steels

Low friction and hard amorphous carbon films were fabricated on 100Cr6 bearing steels via the unbalanced magnetron sputtering method. This paper studied the effect of graphite-like carbon (GLC) coatings on the wear resistance of 100Cr6, which are widely used in textile rings. The microstructures of the GLC coatings were investigated using scanning electron microscope (SEM), atomic force microscope (AFM), energy dispersive Spectrometer (EDS) and Raman. A comparative analysis using a ball-on-disc tribometer was carried out on 100Cr6 bearing steels with GLC coatings and those that had chromium-electroplated coatings. It was demonstrated that the GLC films on 100Cr6 presented better tribological properties, and the corresponding wear mechanisms were investigated. The tribological properties of GLC films under cryogenic treatment (−196 °C), annealing at temperatures of 300 °C and 350 °C were characterized. It was revealed that the friction coefficients decreased after using three kinds of treatments above.

Spontaneous escape behavior of silver from graphite-like carbon coating and its inhibition mechanism

A series of silver-doped graphite-like carbon coatings was prepared on the surface of aluminum alloy using the magnetron sputtering method. The spontaneous escape behavior and inhibition mechanism of silver from graphite-like carbon coating were studied. The results showed that when the sample prepared with a 0.01-A current on the silver target was placed in an atmospheric environment for 0.5h, an apparent silver escape phenomenon could be observed. However, the silver escape phenomenon was not observed for samples prepared with a 0.05-A current on the silver target if the sample was retained in a 10−1Pa vacuum environment, even after 48h. Compared with the sample placed in the atmospheric environment immediately after an ion plating process, the silver escape time lagged for 6h. Nanometer-thick pure carbon coating coverage could effectively suppress silver escape. When the coating thickness reached 700nm, permanent retention of silver could be achieved in the silver-doped graphite-like carbon coating. As the silver residue content in the graphite-like carbon coating increased from 2.27 at.% to 5.35 at.%, the interfacial contact resistance of the coating decreased from 51mΩcm2 to 6mΩcm2.

In Vitro Biocompatibility of MC3T3-E1 Osteoblast-like Cells on Arg-Gly-Asp Acid Peptides Immobilized Graphite-like Carbon Coating on Carbon/Carbon Composites

Carbon/carbon (C/C) composites were deposited with graphite-like carbon (GLC) coating, and then, Arg-Gly-Asp acid (RGD) peptides were successfully immobilized onto the functionalized GLC coating. GLC coating was utilized to prevent carbon particles releasing and create a uniform surface condition for C/C composites. RGD peptides were utilized to improve biocompatibility of GLC coating. Surface chemical characterizations of functionalized GLC coating were detected by contact angle measurement, X-ray photoelectron spectroscopy and Raman spectra. Optical morphology of GLC coatings was observed by confocal laser scanning microscopy. In vitro biological performance was determined using samples seeded with MC3T3-E1 osteoblast-like cells and cultured for 1 week. Surface characterizations and morphological analysis indicated that C/C composites were covered by a dense and uniform GLC coating. Contact angle of GLC coating was reduced to 27.2° when it was functionalized by H2O2 oxidation at 40 °C for 1 h. In vitro cytological test showed that the RGD peptides immobilized GLC coating had a significant improvement in biocompatibility. It was suggested that RGD peptides provided GLC coating with a bioactive surface to improve cell adhesion and proliferation on C/C composites.

Lubricated sliding wear mechanism of chromium-doped graphite-like carbon coating

The current research aims to discuss the tribological behaviour of Chromium-doped graphite-like carbon coatings and suggest a wear mechanism under both dry (in air) and boundary lubricated sliding condition based on phase composition of the wear product generated in wear track during pin-on-disc experiments. As expected, the friction coefficient reduces from 0.22 to 0.12 due to addition of lubricant. Raman analysis indicates that wear mechanism is oxidative in dry sliding condition whereas it is chemically reactive in the presence of lubricant. It is speculated that the key-factor of reduced friction and wear coefficient in lubricated condition is the formation of CrCl3 due to tribochemical reaction between coating and oil. CrCl3 has graphite-like layered structure; therefore it acts like solid lubricant.

Influences of added sand-dust particles on the tribological performance of graphite-like coating under solid–liquid lubrication

Graphite-like carbon (GLC) coatings were fabricated by unbalanced magnetron sputtering technique. Raman spectroscopy and XPS analysis confirmed the nanostructured GLC coatings have high concentration of sp2-hybridized carbon. HRTEM analysis demonstrated that the microstructure of GLC coatings was composed of nanocrystalline graphite, fcc-center cubic (fcc) diamond and amorphous carbon. The tribological performance of GLC coatings combined with five types of liquid lubricants (PFPE, PAO, SO, IL and MAC) has been investigated under the conditions without and with sand-dust particles. Experimental results showed that the obtained excellent low friction and wear-resistance was attributed to the synergistic effect of liquid lubricants and GLC coatings.

Friction and wear behaviors of carbon-based multilayer coatings sliding against different rubbers in water environment

We have addressed the friction and wear behaviors of multilayer Cr/CrN/GLC (graphite-like carbon) coatings sliding against different rubbers in water environment. Stribeck curves and start–stop tests were presented to analyze the water-lubrication mechanism and tribological properties of coating/rubber tribopairs. Results exhibited that applied loads had a minor influence on the tribological performances of coating/rubber tribopairs compared to sliding speeds. The friction coefficients fluctuated during the test process, including in the start–stop process, which related to the viscoelasticity of rubbers. Furthermore, the different tribological performances of tribopairs were attributed to the hardness, surface wettability and tensile strength as well as viscoelasticity.

Tribological properties of graphite-like carbon coatings coupling with different metals in ambient air and water

Tribological properties of graphite-like carbon (GLC) coatings coupling with different metals of brass, Al, GCr15 and Ti in ambient air and water were investigated. The order of friction coefficients (FCs) was GLC–brass>GLC–Al>GLC–GCr15>GLC–Ti in both of the two environments, but the FC in water was lower than that in ambient air for each tribo-pair. Wear rates (WRs) decreases of the GLC coating in water were observed when sliding against Al, GCr15 and Ti. Though the WR of GLC coating sliding against brass increased in water, it was still comparatively low.

Irradiation of the graphite-like carbon films by ns-laser pulse

The effect of a nanosecond laser irradiation of graphite-like carbon (GLC) films deposited on Si substrate by the plasma jet technique was analyzed in this work. The GLC coatings were irradiated by the nanosecond Nd:YAG lasers operating at 1064nm (infrared (IR) radiation) and 532nm (visible (VIS) radiation), using a multi-shot regime. The laser irradiations lead to the surface ablation and partial disarrangement of the GLC coatings. The IR laser irradiation stimulates an increase in the fraction of the sp2 carbon bonds and formation of the nano-graphite cluster. The formation of SiC and graphite nanocrystallites was observed after VIS laser radiation by 24MW/cm2 energy density. FTIR results demonstrated that the reflectance of the laser irradiated carbon films decreases.

The Tribological Performances of Multilayer Graphite-Like Carbon (GLC) Coatings Sliding Against Polymers for Mechanical Seals in Water Environments

Graphite-like carbon (GLC) coatings are being increasingly used in mechanical seals, especially under the water-lubricated condition, to improve component durability by providing a low friction coefficient and high wear resistance. We have addressed the friction and wear performances of multilayer Cr/CrN/GLC coatings sliding against polyether–ether–ketone (PEEK), polyimide (PI), and polytetrafluoroethylene (PTFE) in distilled water under various applied loads and sliding speeds using a ring-on-block test rig. Stribeck curves were developed to analyze the water lubrication mechanisms. Start–stop tests were also carried out to evaluate the tribological performances of the coatings. Our results showed that the friction coefficients and wear rates of the polymers decreased with increasing sliding speeds. Compared to the applied load, the sliding speed had a major effect on the friction and wear performance of the polymer. Three coating/polymer tribopairs demonstrated different tribological behaviors, which were attributed to their different molecular structures, the different mechanical properties of the polymers, and the different lubrication mechanisms. The transfer film determined the lubrication mechanism of the three tribopairs and also resulted in the low friction coefficient and wear rate. The initial and steady-state friction coefficient also decreased with increases in the repeated start–stop times. Based on our results, we concluded that the coating/PEEK tribopair presented an excellent tribological performance that we ascribed to the chemical properties of PEEK and the hydrodynamic lubrication regime of the coating/PEEK tribopair at high sliding speeds.

Effect of ion cleaning pretreatment on interface microstructure, adhesive strength and tribological properties of GLC coatings on Al substrates

In this work, a series of ion cleaning procedures (bias and time) were performed on aluminum substrate surface prior to the deposition of graphite-like carbon (GLC) coatings. Special attention has been paid on the interface microstructure, coating/substrate bonding strength and tribological properties. It was found that ion cleaning critically influenced the adhesion and the wear resistance of GLC coatings. The optimization of ion cleaning pretreatment revealed that 400 V/30 min is the best ion cleaning conditions. HRTEM observations on the interfacial region showed that the oxide layer has been removed completely, a strong bonding diffusion interface formed. However, for the low energy ion cleaning (300 V/10 min), TEM observations on the interfacial region between the coating and the Al substrate showed that the oxide contamination still existed. The optimization of GLC layer thickness revealed that the GLC coating with 1 μm GLC layer exhibited the highest critical load and the lowest friction coefficient of 14.7 N and 0.065, respectively.