Properties Of Diamond-like Carbon Films Research Articles

Frictional properties of DLC films in low-pressure hydrogen conditions

The effects of hydrogen gas on the frictional behavior of diamond-like carbon (DLC) films were investigated by varying the hydrogen pressure during a friction test. Hydrogenated DLC (a-C:H) and non-hydrogenated DLC (ta-C) coatings have been tested. The ta-C/ta-C tribopair exhibited a linear relationship between the hydrogen pressure and the average friction coefficients. On the other hand, the a-C:H/a-C:H tribopair exhibited an extremely low friction coefficient of less than 0.01 when the hydrogen pressure reached 5000Pa. In addition, the friction coefficients from the tests at increased and decreased hydrogen pressures exhibited loop-like behavior. It is considered that the hydrogen pressure and the hydrogen content of the DLC film has an effect on the tribofilms and that the tribofilms played an important role in the loop-like frictional behavior. The evaluation of the hydrogen content of the DLC films was carried out by the G-peak method. The value of logarithm of (N/S) can be used as a measure of the hydrogen content, where the intensity of the fitted G-peak; S, the maximum intensity of the G-peak; and N, the intensity of the photoluminescence background. The behavior of logarithm of (N/S) from the Raman spectra for various hydrogen pressures indicated an interesting relationship between the average friction coefficient and the hydrogen content of tribofilm on a-C:H ball. The relationship showed that the average friction coefficient decreases as a linear relationship with the increase in hydrogen content. These results show that the hydrogen pressure and tribofilms also play an important role in the superlow friction of the DLC films.

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.

Development of in-situ observation system of dynamic contact interface between dies and materials during microforming operation

Application of diamond like carbon (DLC) films are reported in several microforming processes, in view of its great tribological performance owe to the low friction and the high chemical stability. However, due to its high internal residual stress, the film properties with the low adhesion strength and the high wear rate under severe tribological conditions are still remain as technical issues. However, since the dynamic variation of the contact state cannot be observed during the forming operation, it is difficult to recognize the origin and the influential tribological factors of tool life for DLC coated microforming die. Therefore, the appropriate DLC film properties for the contact state in microforming operation have not been clarified. To observe the dynamic variation of the contact state during the microforming operation, present study developed a novel microforming die assembly installed the in-situ observation system with silica glass die and high speed recording camera. By using this system, the dynamic delamination behaviour of DLC films during the progressive micro-bending process was successfully demonstrated. The influential factors for the durability of DLC coated microdies were discussed.

Mechanical Properties and Surface Morphology of Diamond-Like Carbon Films with SiN<i><sub>x</sub></i> Interlayer

Diamond-like carbon (DLC) film has remarkable physical, mechanical, biomedical and tribological properties that make it attractive material for numerous industrial applications needs of advanced mechanical systems. In this study, deposition process of DLC films on Si (100) are performed by direct-current (DC) magnetron sputtering method. The effects of interlayer on the compositions, structures and mechanical properties of DLC films are studied. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies reveal the creation of high uniform surface morphology and low roughness DLC films with SiNxinterlayer. For comparison, DLC films with different interlayers are also grown. The Raman spectra are analyzed in order to characterize the film compositions. Indentation test was performed to value the mechanical properties of DLC films. Raman, SEM, and AFM analyses are correlated with the mechanical properties of the DLC films.

Investigation of the characteristics of DLC films on oxynitriding-treated ASP23 high speed steel by DC-pulsed PECVD process

In this study, diamond-like carbon (DLC) films are coated onto oxynitriding-treated ASP23 high-speed steel by DC-pulsed PECVD. The main research parameters of the DC-pulsed PECVD process are the various duty cycles (5%, 10%, 15% and 20%) used to examine the coating characteristics. In order to investigate the DLC film properties, a Raman spectroscopy analysis, wear test, adhesion, and hardness tests are performed. The experimental results show that the duplex coating layers have optimal properties when DLC films are treated with a low-pulse voltage (−1.5kV), a coating time of 90min and duty cycles maintained at 10%. As a result, the DLC/oxynitriding duplex-treated specimens with the highest surface hardness (Hv0.01 1931) and the lowest wear volume loss (3×10−3mm3) can be acquired. In addition, compared with non-treated (polarization resistance Rp=5×103Ωcm2) and oxynitriding-treated (Rp=8×103Ωcm2) specimens, the optimal DLC/oxynitriding duplex-treated ASP23 high-speed steel possesses the lowest corrosion current (Icorr=8×10−6Acm−2) and highest polarization resistance (Rp=1×104Ωcm2) in 3.5wt.% NaCl solutions. This result confirms that the DLC/oxynitriding duplex treatment enhances optimal wear and corrosion resistance.

Structure and Properties of Diamond-like Carbon Films on Stainless Steel

Structure and Properties of Diamond-like Carbon Films on Stainless Steel

Influences of Pulse Frequency on Structure and Mechanical Properties of DLC Films Synthesized by Pulsed Cathodic Arc Evaporation

Diamond-like carbon (DLC) films were prepared on the Si (100) substrates by pulsed cathodic arc plasma. The influences of given pulse frequency on the microstructure, morphology, mechanical and optical properties of DLC films were investigated by Raman spectroscopy, atomic force microscopy, Knoop sclerometer, X-ray double-crystal surface profilometer. The results showed that the variation of pulse frequency could significantly change the microstructure of DLC films, including the size and ordering of sp2carbon clusters and movement or diffusion of carbon atoms. The increasing of pulse frequency led to the variation of the relative fraction of Csp3/Csp2. The hardness and internal stress of the DLC films were affected accordingly. The results might contribute to the synthesis of DLC films with excellent structure and properties by cathodic arc evaporation.

Effects of tribological behavior of DLC film on micro-deep drawing processes

To decrease the size effects of friction in microforming, three kinds of surface coatings, such as diamond-like carbon (DLC), TiN and MoS2, were deposited on surfaces of dies with plasma based ion implantation and deposition (PBII & D) method and magnetron sputtering technique, respectively. The tribological behavior of surface coatings was analyzed considering plastic deformation of specimen at contact interface. The analyses indicate that there is a lower coefficient of friction (COF) and a high wear resistance under the condition of large strain/stress when using the DLC film. The graphitization of DLC film occurs after 100 times of tests. The mechanism of graphitization was analyzed considering energy induced by friction work. The effects of DLC film properties on qualities of micro-deep drawn parts were investigated by analyzing the reduction of wall thickness, etc. The results indicate that DLC film is very helpful for improving the qualities of the micro-parts.

DLC coating on a trench-shaped target by bipolar PBII

Bipolar-type plasma based ion implantation (bipolar PBII) and deposition is a promising coating technique, especially for the complex-shaped target surface. In this study, diamond-like carbon (DLC) films were prepared by a bipolar PBII technique to a trench-shaped target (20mm pitch and 10mm depth), and the uniformity, structural and mechanical properties of DLC films coated on the top, inside wall and bottom surfaces of the trench were evaluated by surface profilometer, Raman spectroscopy and nanoindentation hardness tests. Moreover, plasma simulation was conducted to reveal the DLC coating mechanism for finding the optimum coating conditions. Particle-In-Cell with Monte Carlo Collision (PIC–MCC) method and Direct Simulation Monte Carlo (DSMC) method were used for computing the plasma behavior. As a result, thickness uniformity of DLC films was improved with decreasing negative pulse voltage. On the other hand, the thickness of DLC films on the inside wall of the trench was much smaller than those of the top and bottom surfaces of the trench. This is because the conformal ion sheath cannot be formed around the inside wall, which in turn leads to the decrease of incidence ion flux to the inside wall, and the idea has been verified through the simulation of plasma behavior. From the Raman measurements of DLC coatings on the inside wall, it is observed that the Raman G-peak position shifts to a higher wave number and the Full Width at Half Maximum of G-peak (FWHM(G)) decreases to a smaller value compared to those of the films on the top and bottom surfaces. These indicate that the structure of DLC coatings on the inside wall surface has changed compared to those on top and bottom surfaces, i.e., graphitized, which results in the reduction of hardness.

Diamond-Like Carbon Films Formed by Pulsed Supersonic Plasma Flow Deposition

A new technique for the formation of diamond-like carbon thin films with high growth rate on silicon wafers and glass surfaces was investigated. A pulsed plasma source based on disk magnetohydrodynamic accelerator was used; methane was a precursor. Scanning electron and atomic-force microscopy, X-ray photoemission spectroscopy techniques and Raman spectroscopy were used for film characterization. We varied the deposition conditions (pulse time, distance to the source, silicon substrate temperature) to optimize diamond-like carbon film properties. Nitrogen treatment allows us to make nitrogen-doped diamond-like carbon films. We used the oxydgen plasmachemical etching of diamond-like carbon films. Thick nanoporous diamond-like carbon films were formed.

Diamond-like carbon (DLC) films as electrochemical electrodes

Amorphous carbon can be any mixture of carbon bonds of sp3, sp2, and even sp1, with the possible presence of hydrogen. The group of mixture, of which there is a high fraction of diamond-like (sp3) bonds, is named diamond-like carbon (DLC). Unlike the crystalline carbon materials: diamond, graphite, carbon nanotube, fullerene and graphene, DLC can be deposited at room temperature without catalyst or surface pretreatment. Furthermore, its properties can be tuned by changing the sp3 content, the organization of sp2 sites and hydrogen content, and also by doping. This paper firstly reviewed the electrochemical properties of DLC films and their applications.

J1110103 マイクロ金型への表面テクスチャリングとそのドライ摩擦・摩耗特性評価([J111]摩擦・摩耗制御のための材料及び表面改質)

As development of micro electro mechanical systems (MEMS) technology, microforming is gaining attention. And, lubricant-free microforming process is a strong demand. Due to the low effect of lubricant in microscale dimensions, the tribological issues in microforming confronts with further severe problems to enhance the performance of microdie surface. So an approach to enhance the tribological performance is applying the micro-textured structure to the surface of microdie with expecting the function of wear debris ejecting effect. Micro-texturing was realized by using stainless steel wire mesh as a masking during the ionized vapored deposition of diamond-like carbon (DLC) coating film. To characterize the basic tribological properties of micro-textured DLC films under dry condition, the ball-on-disk type tribology test was carried out. In view of the confirming wear debris ejecting effect, titanium oxide nanoparticles were intentionally added as artificial wear debris. As results, the micro-textured DLC film showed low coefficient of friction, while the conventional non-textured DLC films showed the significantly large value. Wear track observation after the friction tests revealed that the stable tribological properties of textured DLC films were attributed to the promotion of wear debris ejection, which can prevent the ploughing and adhesion inside the apparent area of contact.

Effect of ion bombardment on the phase composition and mechanical properties of diamond-like carbon films

It is established that the addition of hydrogen to methane in the reaction mixture upon the fabrication of diamond-like carbon films via the plasma-enhanced chemical vapor deposition method decreases residual stresses in the obtained films and significantly reduces their growth rate. The films were investigated via atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Irradiation of the prepared films with P+ and PF 4 + ions results in strong sample swelling with increasing dose, as well as in a decrease in the compressive stress up to transition to tensile one reaching saturation. Moreover, the fraction of sp 3 bonds increases with increasing ion dose while the fraction of sp 2 bonds decreases symmetrically with the processes proceeding faster upon irradiation with molecular ions. Qualitative mechanisms explaining the experimental results are proposed.

Effect of deposition temperature on growth, structure and mechanical properties of diamond-like carbon films co-doped by titanium and silicon

Titanium and silicon co-doped diamond-like carbon films are deposited on Si substrates by middle-frequency magnetron sputtering Ti80Si20 composite target. The influences of deposition temperature on the growth rate, chemical composition, structure, surface and mechanical properties of the film are investigated. The results show that the growth rate of the film decreases as substrate temperature increases. With the increasing of substrate temperature, Ti and Si atom content values in the film increase, while C atom content value decreases. At high temperatures, the film has low sp3C fraction, surface contact angle, compressive stress, and high hardness, and elastic modulus. The influences of deposition temperature on the growth and bonding structure of the film are analyzed in view of the subplantation growth model. The changes in surface and mechanical properties are correlated with the growth mechanism and microstructures of the film.

氩气对类金刚石薄膜性能的影响

氩气对类金刚石薄膜性能的影响

Micro-texturing of DLC Thin Film Coatings and its Tribological Performance Under Dry Sliding Friction for Microforming Operation

As an approach to enhance the tribological performance of diamond like carbon (DLC) coating films for dry microforming operations, the present study applied the micro-textured structures to the DLC films. Micro-texturing was realized by using stainless steel wire mesh as a masking during the ionized physical vapor deposition (I-PVD) of DLC films. Tribological performance of fabricated micro-textured structures with a width of 40 and 80μm and an interval of 30 and 40μm were evaluated by the ball-on-disk type friction tester. To simulate the severe contact state of dry microforming operation, normal pressure of 1.2GPa was applied for 100,000 times rotations under unlubricated condition. As results, the micro-textured DLC films with structure size of 40μm showed the excellent stable variation with relatively low coefficient of friction (COF) of μ = 0.01-0.06, while the conventional non-textured DLC films showed the significantly large deviation with high COF of μ > 0.25. In comparison between the different micro-texture sizes, the smaller structure size of 40μm showed the lower COF than that of 80μm, although the larger amount of wear debris from DLC films were generated. Additional wear track observation after the friction tests revealed that the stable tribological properties of textured DLC films were attributed to the promotion of wear debris ejection, which can prevent the plowing inside the apparent area of contact.

Improvement of the Tribological Properties of DLC/oxynitriding Duplex-treated AISI H13 Alloy Steel

In this study, diamond-like carbon (DLC) films were prepared by DC-pulsed plasma CVD after the oxynitride treatment of AISI H13 tool steel. In order to investigate the tribological properties of DLC films, a Raman spectroscopy analysis, wear test, adhesion and roughness tests were performed. The main parameters of the DC-pulsed plasma CVD process includes various pretreatment times of argon plasma (15, 30, 45 and 60 min). Experimental results showed that an oxynitride layer and the DLC films could be completely obtained after DLC/oxynitriding duplex treatment. The duplex coating layers had optimal adhesion (critical load reached to 10.65 N) and wear properties after DC-pulsed plasma was CVD treated via a low pulse voltage (–1.5 kV), pretreatment times of the argon plasma were 15 min and the substrate temperature was kept at 40°C. Meanwhile, the optimal DLC/oxynitriding duplex treated specimens possessed the lowest wear volume (2.25 × 10 –3 mm 3 ) and a lower friction coefficient (0.06).

Chromium-doped diamond-like carbon films deposited by dual-pulsed laser deposition

Diamond-like carbon (DLC) and Cr-doped diamond-like carbon layers were studied. DLC and Cr-DLC were deposited on silicon and titanium substrates (Ti-6Al-4V) by dual-pulsed laser ablation using two KrF excimer lasers and two targets (graphite and chromium). The composition was analyzed using wavelength-dependent X-ray spectroscopy. The Cr content increased from 2.2 to 17.9 at%. The topology and surface properties as roughness of layers were studied using scanning electron microscopy and atomic force microscopy. With the chromium concentration increased the roughness and the number of droplets. Carbon and chromium bonds were determined by Raman spectroscopy. With an increase in chromium content the ID/IG ratio increased. Mechanical properties of DLC films with various chromium content were evaluated. Hardness (reduced Young’s modulus) was determined by nanoindentation and reached of 51 GPa (309 GPa). Films adhesion was studied using scratch test and with concentration of chromium increased up to 20 N.

Molecular dynamics simulation for the influence of incident angles of energetic carbon atoms on the structure and properties of diamond-like carbon films

The influence of incident angles of energetic carbon atoms (0–60°) on the structure and properties of diamond-like carbon (DLC) films was investigated by the molecular dynamics simulation using a Tersoff interatomic potential. The present simulation revealed that as the incident angles increased from 0 to 60°, the surface roughness of DLC films increased and the more porous structure was generated. Along the growth direction of DLC films, the whole system could be divided into four regions including substrate region, transition region, stable region and surface region except the case at the incident angle of 60°. When the incident angle was 45°, the residual stress was significantly reduced by 12% with little deterioration of mechanical behavior. The further structure analysis using both the bond angles and bond length distributions indicated that the compressive stress reduction mainly resulted from the relaxation of highly distorted C–C bond length.

Tailoring the structure and property of silicon-doped diamond-like carbon films by controlling the silicon content

Diamond-like carbon (DLC) films have been extensively studied over the past decades due to their unique combination of properties; in particular, silicon-doped DLC (Si-DLC) films are of significant interest for tribological effects. But there are contradictory reports in the literature with regard to the effect of silicon content on the properties of DLC films. In this study, Si-DLC films were deposited by hollow cathode plasma immersion ion implantation (HCPIII) method, using mixtures of C2H2, Ar and diluted SiH4 (SiH4/Ar 10:90). The influences of Si addition on the surface morphology, structure, mechanical and tribological properties were investigated by a combination of surface analysis methods, nanomechanical and friction measurements. It was observed that addition of Si into DLC films lead to a decrease in the Raman band intensity ratio ID/IG. The root mean square values of Si-DLC films were increased along with the increase of Si concentration. Both the hardness and elastic modulus suffered degradation when the silicon concentration was low, but these properties recovered when Si concentration increased. The Si-DLC film with tensile stress and compressive stress can be obtained by choosing distinct contents of Si in the film. The coefficient of friction (COF) of Si-DLC films against GCr 15 steel ball under atmosphere firstly increased as the Si concentration increased up to 8.41at.%, then COF of Si-DLC films decreased with a further increase of Si concentration. The mismatch in the bond length, the difference of the mechanical property and the alteration of the colliding particles' energy were determined to be the basis for the changes in these properties.