Properties Of Amorphous Carbon Coatings Research Articles

Effects of racetrack magnetic field strength on structure and properties of amorphous carbon coatings deposited by HiPIMS using deep oscillation pulses

In this study, non‑hydrogenated diamond like carbon (DLC) coatings were deposited by sputtering a graphite target in argon (Ar) by high power impulse magnetron sputtering (HiPIMS) using deep oscillation pulses. The effects of the magnetic field strength (B) tangential to surface of the target racetrack on the deposition parameters were studied. The structure, adhesion, and mechanical properties of DLC coatings deposited at different B were investigated by scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), scratch test, and nanoindentation. The tribological properties of the DLC coatings were evaluated using ball on disk wear test under dry and lubricated test conditions. It was found that the peak target current and substrate current density increased as B increased due to the enhanced electron confinement which results in an increased ionization efficiency. The enhanced ion bombardment was beneficial for improving the structure and properties of DLC coatings. As B increased, the DLC coatings exhibited more compact structure, smaller carbon mounds, and higher sp3 bond fractions. The improvement of the microstructure of the DLC coatings contributed to improved hardness and wear resistance of the coatings in both dry and lubricated test conditions. However, the deposition rate decreased at higher B owing to the high probability of back-attraction of carbon ions. The results suggested that controlling B in the range of 600 G to 700 G is important for achieving fully dense structure, high sp3 bond fractions, and high hardness for the DLC coatings deposited using HiPIMS. A further increase in B to 850 G showed no significant changes in the magnetic field induced effects on the structure and properties of the coatings.

Antimicrobial and Aging Properties of Ag-, Ag/Cu-, and Ag Cluster-Doped Amorphous Carbon Coatings Produced by Magnetron Sputtering for Space Applications.

Inside a spacecraft, the temperature and humidity, suitable for the human crew onboard, also creates an ideal breeding environment for the proliferation of bacteria and fungi; this can present a hazard to human health and create issues for the safe running of equipment. To address this issue, wear-resistant antimicrobial thin films prepared by magnetron sputtering were developed, with the aim to coat key internal components within spacecrafts. Silver and copper are among the most studied active bactericidal materials, thus this work investigated the antibacterial properties of amorphous carbon coatings, doped with either silver, silver and copper, or with silver clusters. The longevity of these antimicrobial coatings, which is heavily influenced by metal diffusion within the coating, was also investigated. With a conventional approach, amorphous carbon coatings were prepared by cosputtering, to generate coatings that contained a range of silver and copper concentrations. In addition, coatings containing silver clusters were prepared using a separate cluster source to better control the metal particle size distribution in the amorphous carbon matrix. The particle size distributions were characterized by grazing-incidence small-angle X-ray scattering (GISAXS). Antibacterial tests were performed under both terrestrial gravity and microgravity conditions, to simulate the condition in space. Results show that although silver-doped coatings possess extremely high levels of antimicrobial activity, silver cluster-doped coatings are equally effective, while being more long-lived, despite containing a lower absolute silver concentration.

Structure and mechanical properties of Ni and Cr binary doped amorphous carbon coatings deposited by magnetron sputtering and pulse cathodic arc

This paper studies the structure and mechanical properties of amorphous carbon coatings (a-C) modified by Ni and Cr binary doping. The a-C:(Nix+Cry) coatings were deposited using pulsed cathodic carbon arc technique with direct current magnetron sputtering.Microstructure, surface morphology and chemical composition of the a-C:(Nix+Cry) coatings were analyzed via Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy. Friction parameters of the coating were studied under the condition of dry sliding using a "sphere-plane" method. It has been established that the structure of binary doped coatings mainly consists of an amorphous carbon matrix, primarily with sp2 bonds, chromium carbide and nickel metal clusters. The dependence of the Сsp3/Сsp2 ratio and microhardness on the composition in the coating has been specified. The Ni/Cr ratio in the coating with the optimal content of Csp2 and C-Cr carbide phases resulting in a decrease in the wear rate of the counterbody has been determined. At the same time, binary doping of carbon coatings substantially changes in both the phase compositions and surface morphology, which leads to the stabilization of the friction coefficient and reduces the counterbody wear rate.

Tribochemical induced wear and ultra-low friction of superhard ta-C coatings

Employing a broad parameter study, friction and wear properties of amorphous carbon coatings (a-C), tetrahedral amorphous carbon coatings (ta-C) and single crystalline diamond were investigated in boundary lubrication regime, using an oscillating ball-on-flat test setup with engine oil, glycerol, and glycerol monooleate (GMO) lubrication. Ultra-low friction (µ < 0.04) was confirmed with glycerol and GMO. At the same time, very high wear of the superhard ta-C coating was found for GMO solely.A systematic study of lubricant chemistry, surface impurities, testing temperature, counter body material, and the carbon coating regarding sp3-fraction and crystallinity was conducted, indicating a strong difference between low abrasion wear and high chemical wear.Based on the measured data, the chemical nature and wear promoting factors are considered, suggesting detrimental interaction of amorphous sp3-carbon in the coating and unsaturated carbon bonds in the lubricant.Furthermore, a relation for low friction of GMO and contact pressure was established, leading to lowest friction for contact pressure below 600MPa. High wear on either component of the ball-on-plate-geometry of the test setup led to a change of the contact area, thus strongly influencing frictional behavior of the tribometer model test.

Effects of atomic structure on the frictional properties of amorphous carbon coatings

Diamond-like carbon (DLC) films are widely used as protective coatings against wear and corrosion and have attracted a lot of attention in the last few decades. However, it is very difficult to determine the hybridization and structure of amorphous carbon experimentally during sliding. Therefore, in this work, molecular dynamics (MD) simulations are employed to investigate the nano-tribological properties of amorphous carbon with and without hydrogen atoms doped. The simulation models are built with DLC/DLC interface and diamond/DLC interface for different densities of carbon. As we found, both the carbon bonding network and the carbon hybridization have significant effect on the frictional properties of DLC films. The unsaturated carbon atoms, which are in sp2 or sp1 hybridization, can lead to the formation of covalent bonds between the two contacting surfaces resulting in stick-slip type of friction. With an increase of sp3 bonding content in tetrahedral carbon and doping of amorphous carbon with hydrogen atoms decrease the steady-state value of friction force and reduce the amount of the stick-slip motion.

Effect of Ag content on the microstructure, tribological and corrosion properties of amorphous carbon coatings on 316L SS

The mechanical durability and stability of a-C:Ag nanocomposite coatings deposited on 316L stainless steel substrates were investigated with respect to Ag content. The coatings were prepared using graphite and Ag targets. The coatings were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). XPS and Raman spectroscopy confirmed the formation of sp2 clusters in the a-C coating with 4.46at.% Ag content. Surface roughness was found to be reduced by increasing the Ag content in a-C coatings as confirmed by AFM analysis. TEM analysis also showed the presence of nanostructured Ag in the a-C matrix. The tribological and corrosion properties of these coatings were also investigated. Hardness and Young's modulus were found to decrease with increase in Ag content. The experimental results revealed that the friction coefficient could be significantly reduced due to inclusion of Ag in the composite coating. In particular, the coating with an Ag content of 4.46at.% showed the best tribological behavior. Inclusion of Ag also improved the corrosion resistance of the composite coating. It was concluded that Ag content in a-C:Ag nanocomposite coating has a significant effect on the tribological and corrosion properties of the coating. Experimental results revealed that optimum Ag content (4.46at.%) in a-C:Ag nanocomposite coatings may be effectively utilized to protect 316L stainless steel substrates.

Effect of titanium or chromium content on the electrochemical properties of amorphous carbon coatings in simulated body fluid

Amorphous carbon coatings (a-C) incorporated with various titanium and chromium content (Ti/a-C and Cr/a-C) were deposited on 316L substrates using unbalanced magnetron sputtering. The relevant electrochemical characteristics in simulated body fluid (SBF) indicated that Ti/a-C and Cr/a-C coatings could enhance the anticorrosion abilities of 316L substrates via increasing charge transfer resistant (Rct) due to formation of titanium and chromium oxides. However, the more Ti incorporation is likely to weaken the anticorrosion ability of Ti/a-C coatings due to more sp2 content. On the contrary, the more Cr incorporation can enhance the anticorrosion ability of Cr/a-C coatings owing to more sp3 content.

Characterization and properties of amorphous carbon coatings prepared by middle frequency pulsed unbalanced magnetron sputtering at different substrate bias

The amorphous carbon (a-C) coatings were synthesized at different substrate bias using a middle frequency pulsed unbalanced magnetron sputtering technique. Some properties of the coatings were characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), nano-indentation tests, spectroscopic ellipsometry (SE). SEM measurement shows that the deposited a-C coatings are comparatively uniform. XPS and AES measurements show that sp3 content in a-C coatings changes with increasing substrate bias voltage. AES depth profile exhibits that the C element distributes uniformly across the coating thickness, and carbon atoms have penetrated into the Si substrate. Nano-indentation and spectroscopic ellipsometry tests indicate that the coating deposited at the substrate bias of 120V shows the optimized synthetic properties with higher nanohardness, higher elastic modus, higher refractive index and lower extinction coefficient. These results above are useful for the practical application of a-C as antireflection protection coatings. The influences of substrate bias on the sp3 fraction can be explanted by the sub-plantation model.

Combined influences of mechanical properties and surface roughness on the tribological properties of amorphous carbon coatings

Carbon films (∼2 μm thick) with a range of mechanical properties and underlying substrate roughnesses were evaluated for delamination and wear under conditions of combined impact and sliding contact. One-side-coated and both-sides-coated titanium alloy pin and disk wear couples were assessed using a custom-made impact/sliding pin-on-disk apparatus in a colloid-based blood volume expansion medium. The normal stress distribution along the film/substrate interface upon impact loading by a smooth titanium alloy pin was modelled analytically for each coated system. For disk surface roughness centre-line average ( R a) values below 0.05 μm, the area of disk film delamination was shown to correlate with the presence of tensile stress at the film/substrate interface. The interfacial tensile stress was shown to occur when there was a film/substrate elastic modulus mismatch, either within or outside the perimeter of contact, depending on the direction of the film modulus deviation. We propose that the tensile stress promotes delamination by lifting the film locally from the substrate. With increased disk R a, the area of disk coating loss tended to decrease, because the surface roughness improved the mechanical bonding of the composite system.

Effect of Spraying Regimes on Properties of Amorphous Carbon Coatings

Effect of Spraying Regimes on Properties of Amorphous Carbon Coatings

Mechanical properties of amorphous carbon coatings prepared using plasma assisted chemical vapor deposition

Amorphous carbon/metal carbide gradient coatings were prepared by a combination of plasma assisted chemical vapor deposition and rf sputtering techniques. The structure of the coatings was characterized by scanning electron microscopy and transmission electron diffraction. A scratch tester measured the adhesion of the coatings. The depth-sensing indentation technique was used to measure the hardness, elastic and plastic properties of the amorphous carbon coatings. The measured results revealed that the amorphous carbon coatings with metal carbide interlayer have a uniform structure and better mechanical properties than that of pure amorphous carbon coatings.

Micromechanical properties of amorphous carbon coatings deposited by different deposition techniques

Amorphous carbon coatings about 20 nm thick are commonly used as an overcoat on magnetic thin-film rigid disks and tape and disk head surfaces to improve their wear performance. In this study, we deposited amorphous carbon coatings with thicknesses ranging from 20 to 400 nm on single-crystal silicon substrates by four deposition processes: cathodic arc, ion beam deposition, r.f.-plasma-enhanced chemical vapor deposition, and r.f. sputtering. R.f.-sputtered SiC coatings were also deposited for comparison. The hardness, elastic modulus, and scratch resistance of these coatings were measured by nanoindentation and microscratching using a nanoindenter. The cathodic arc carbon coatings followed by sputtered SiC coatings exhibited the highest hardness, elastic modulus, scratch resistance/adhesion, and residual compressive stresses. The critical load, a measure of the scratch resistance/adhesion of the coating, increases with thickness. The cathodic arc coatings of lower thicknesses (~ 30 nm) exhibited instant damage when the normal load exceeded the critical load, whereas thick coatings (greater than or equal to 100 nm) exhibited gradual damage through the formation of tensile cracks. The sputtered carbon coatings exhibited damage to the coating at very low loads and ploughing of the tip into the coating occurred right from the beginning of the scratch.

The effect of additional treatment on tribological properties of amorphous carbon coatings on metals

Abstract We have developed the effect of additional treatment on improvement of tribological properties of diamond-like coatings (DLCs) on steels. It is shown that a maximum realization of the strengthening properties of DLCs is possible either through preliminary hardening of the substrate with ion implantation and additional thermal treatment or using etching of the coating surface with ions of active gas.