Non-hydrogenated Diamond-like Carbon Films Research Articles

Nanoindentation of Amorphous Carbon: a combined experimental and simulation approach

Amorphous carbon (aC), in particular diamond-like carbon (DLC), is one of the most studied and promising coating materials, but many of the atomic-scale mechanisms involved in their plastic deformation process are not fully understood. The mechanical response of non-hydrogenated DLC films with different sp3 concentrations is investigated using nanoindentation experiments, ab-initio simulations, and classical molecular dynamics simulations. Experimental characterization is carried out with Raman spectroscopy and Electron Energy Loss Spectroscopy (EELS). Ab-initio and classical simulations show good agreement for sp1, sp2 and sp3 content of in-silico samples. Elastic modulus and hardness of DLC films increase with sp3 content, for sp3 between 10% and 55%, and excellent agreement is obtained between experiments and simulations. Simulated strain distributions are shown to be highly anisotropic, unlike continuum-scale predictions for the use of a perfectly spherical indenter in an amorphous solid. MD simulations also reveal two different plasticity modes depending on the sp3 level of the indented sample. For films with sp3 concentrations less than 40%, plasticity is mainly mediated by the sp2 to sp3 transition. For larger sp3 concentrations, DLC plastic deformation is attributed to densification due to bond rearrangement. All in all, our work offers a comprehensive study of DLC, revealing unexpected plastic deformation mechanisms that had not been considered before. Our study might help to the fundamental understanding of amorphous carbon coatings for both scientific and technological purposes.

Effect of sp3 Content on Adhesion and Tribological Properties of Non-Hydrogenated DLC Films.

Non-hydrogenated diamond-like carbon (DLC) films with various ratios of sp3/sp2 were prepared on cemented carbide YG8 with DC magnetron sputtering technology. A pure graphite target was selected as the carbon source. Before DLC deposition, a surface etching pretreatment was carried out by mid-frequency magnetron sputtering method, using Ti atoms to improve adhesion strength. The ratios of sp3/sp2 were adjusted by bias voltages. In order to investigate the effect of the ratio of sp3/sp2 on adhesion and tribological properties, Raman spectra, XPS spectra, adhesion scratch test and ball-on-disk dry friction tests were applied. The results indicated that the ratio of sp3/sp2 fluctuated with bias voltage, increasing in the range of 0.74 to 0.98. The adhesion strength decreased from 31.5 to 18.4 N with the increasing ratio of sp3/sp2, while the friction coefficient rose in DLC-Si3N4 and dropped in DLC-Ti6Al4V. For DLC-Ti6Al4V, the oxidation of Ti6Al4V had a greater influence than graphitization of DLC. The hard oxides of Ti6Al4V broke the graphite transfer layer leading to a high friction coefficient. The wear rate was approximately linearly related to bias voltage. The coefficients of the linear regression equation were influenced by different friction materials. The adhesion strength and the friction coefficient were fitted as a function of the ratio of sp3/sp2.

氧气氛环境对无氢类金刚石膜红外性能的影响

氧气氛环境对无氢类金刚石膜红外性能的影响

Infrared and mechanical properties of the oxygen-doped non-hydrogenated diamond-like carbon film prepared by pulsed laser deposition

The non-hydrogenated diamond-like carbon films were prepared by the femtosecond laser in the oxygen atmosphere, and the influence of the oxygen atmosphere on the microstructural, surface, infrared and mechanical properties of the oxygen-doped diamond-like carbon films were researched. The oxygen atmosphere was propitious to reduce the granules on the surfaces but increase the surface roughness of the diamond-like carbon DLC films. During the pulsed laser deposition, the carbon and oxygen atoms were inclined to form the CO bond, CO bond and CC hybridized bond, when the oxygen pressure was lower than 5 m Torr. Although the CO and CO bonds led one additional absorption band and two additional absorption peaks in the infrared spectra of the oxygen-doped diamond-like carbon films, their transmission in the medium infrared band increased. Nano-hardness of the DLC films was reduced when the oxygen pressure increased dominantly because the CC sp3 bonds with higher atomic binding energy were replaced the CO bonds with lower atomic binding energy.

Preparation and Characterization of Sulfurized Tungsten Doped Non-hydrogenated Diamond-Like Carbon Films

A tungsten doped non-hydrogenated diamond-like carbon (W-DLC) film was prepared by ion beam assisted deposition, and then W-DLC film was sulfurized by low temperature ion sulfurization. The structural analyses were performed on the scanning electron microscope, optical profilometer, Raman spectroscope and transmission electron microscope equipped with energy dispersive spectroscope. The results showed that the low temperature ion sulfurization treatment increase ID/IG ratio from 3.5 to 4.0 and 3.4 to 3.8 for sulfurized DLC and W-DLC films, respectively. The microstructures of sulfurized DLC film changed from amorphous to nanocrystalline/amorphous structure after low temperature ion sulfuration. The sulfurized W-DLC film was composed of nanocrystallites β-WC1−X, WS2 and FeS, which uniformly dispersed in the amorphous DLC matrix.

Impact wear testing of diamond-like carbon films for engine valve-tappet surfaces

There is a strong drive to reduce the energy losses from automotive engines in order to improve fuel economy and reduce emissions of pollutants. The demands of reducing engine losses are pushing engine manufacturers to consider using technologies such as diamond-like carbon (DLC) coatings to give enhanced wear protection of components and provide low friction operation. Valve-train component interactions are tribologically complex, with contacts commonly experiencing mixed boundary and elasto-hydrodynamic lubricated sliding wear, abrasive wear, impact and fatigue. Whilst there have been many studies of the mechanical properties and wear resistance of diamond-like carbon films, there have been fewer studies of the effect of impact at the contact loads and geometries relevant to the automotive valve-train. Thus, a series of inclined impact tests have been conducted at impact angles from 15° to 45° on hydrogenated and non-hydrogenated diamond-like carbon films with and without lubrication to understand how the films respond to impact under controlled conditions. The results have been compared to the coatings performance in a motored and instrumented cam–tappet testing rig. The results show that impact loading in the valve-train has a significant effect on coating durability. Coating durability is affected by impact angle and lubricant and counter-intuitively the introduction of lubrication decreases the coating durability. This is attributed to the lubricant preventing the formation of beneficial tribolayers and also forming an abrasive slurry where DLC wear particles are retained in the contact and create additional abrasive wear.

Extraordinary self-lubrication properties of non-hydrogenated diamond-like carbon films under humid atmosphere

Tribological properties of non-hydrogenated diamond-like carbon (DLC) films were investigated under humid (RH=80%) and dry (RH=5%) air. These films were deposited by pulsed laser deposition (PLD) at different substrate temperatures. Tribological properties of DLC fabricated by PLD is not sensitive to the relative humidity of testing environment. Because of the unique growth mechanism of DLC prepared by PLD, DLC is of “soft-hard” double layers, having a very low friction coefficient and wear rate under humid atmosphere. The minimum coefficient and wear rate of film under humid circumstance are 0.045 and 5.94×10−10 mm3N−1m−1, respectively, just a little bit more than those under dry condition. The root means square roughness of film is less than 1 nm. The sp3 content of film grown at room temperature (RT) is 72%, and the sp3 content decreases with temperature. Raman spectrum shows that the micro-structure is amorphous network. The largest hardness and elastic modulus of film are 51 GPa and 350 GPa, respectively and they reduce with increase of deposition temperature too. Water contact angles on surface are more than 90° which indicates that films fabricated by PLD are hydrophobic with low surface energy.

Characterization of Thick Amorphous Carbon Films Formed by Pulse Bias Filtered Cathodic Vacuum Arc

To form several-micrometer-thick diamond-like carbon (DLC) films, pulse bias filtered cathodic vacuum arc deposition was performed. In this study, nonhydrogenated DLC films were evaluated using visible and ultraviolet Raman spectroscopy, an electron energy loss spectroscopy (EELS) and a nano indenter. All observations indicated that the sp3 ratio of the DLC films decreases with increasing applied pulse bias. However, a moderately high sp3 ratio of 42.3% was obtained for 500-nm-thick DLC films with a compressive stress of 3.5 GPa formed at a pulse bias of 500 V, a pulse width of 25 µs, and a frequency of 1500 Hz.

Mechanical and tribological properties of non-hydrogenated DLC films synthesized by IBAD

Diamond-like carbon (DLC) films have been deposited on Si(100) substrates by an ion beam assisted deposition (IBAD) system. The effect of ion bombardment energy on surface roughness, mechanical and tribological properties of the DLC films has been studied over the ion bombardment energy range of 100–800 eV. The measured results of atomic force microscopy (AFM) showed that the DLC films are very smooth and the surface roughness is lower than that of the Si substrate at certain ion bombardment energy. Elasticity and nanohardness of the DLC films were studied by a nanoindentation technique. From nanoindentation load-displacement curves, it was concluded that most of the DLC films have high elasticity. Comparing the nanohardness with the conventional knoop microhardness of the same series of samples, we saw that the values of knoop microhardness are much higher than those of nanohardness. The correlation of the sp 3 bond fraction in the films estimated from Raman spectroscopy with surface roughness, elasticity and hardness has been established. Tribological behavior of the DLC films sliding against the ZrO 2 ball was evaluated using a pin-on-disk tribometer. It was found that the surface roughness and the hardness have an effect on the friction coefficients.

Diamond-Like Coatings : Microstructural Evolution under Ion Beam Assistance

Non-hydrogenated diamond-like carbon films have been prepared by Dual Ion Beam Sputtering and Ion Beam Assisted Magnetron. The assistance parameters -ion energy, ion mass, ion flux/atom flux-have been systematically varied and their effect on the microsaucture of the films studied. The films have been characterised by Rutherford Backscattering Spectroscopy (RBS), High Resolution Transmission Electron Microscopy (HRTEM), Electron Energy Loss Spectroscopy (EELS), Positron Annihilation Spectroscopy (PAS), and Raman Spectroscopy (RS). RBS and PAS results showed that the density and the degree of disorder of the films go through a maximum with ion energy, and that the void concentration goes through a minimum. EELS and RS show that the films are mostly sp 2 bonded, with a maximum concentration of sp 3 bonding of about 16% for the largest values of density. The evolution of density with ion flux and energy is consistent with a combined effect of atomic displacements in the film leading to densification, and with damage buildup leading to progressive graphitisation as the energy is increased

Diamond-like carbon films synthesized by cathodic arc evaporation

Abstract Diamond-like carbon (DLC) films can be prepared by various techniques. Among these processes, the cathodic arc evaporation of a pure carbon source has the advantage that variables such as evaporation rate, substrate temperature and substrate bias voltage can be independently managed. Furthermore, it allows us to synthesize hydrogenated or hydrogen-free carbon films. Because of its negative temperature coefficient of electrical resistivity, carbon is a diffucult material to evaporate and the plasma stream generated from arc spots contains a large quantity of macroparticles. The present study of DLC films synthesized by arc evaporation introduces the solution employed to produce a pure carbon plasma stream for the formation of hard carbon films. The enhanced arc process based on a modified rectilinear plasma optic system is described and the influence of the process and deposition conditions in steering the arc spot motion and refining the plasma stream of macroparticles for carrying out high rate carbon film deposition are studied. The carbon films' features as analyzed by Raman spectroscopy, Fourier transform IR spectroscopy and scanning electron microscopy show that the films are dense non-hydrogenated DLC films under certain process conditions. These DLC films exhibit promising mechanical results such as a good hardness and an excellent adhesion level on high speed steel substrates.