Tribological properties of DLC films deposited on steel substrate with various surface roughness

Tribological properties of diamond-like carbon (DLC) films in water were investigated concerning with the influence of surface roughness and various mating materials. The DLC films were deposited by pulsed-bias CVD method on AISI630 stainless steel. The substrate roughness (R_a) is in the range of 1.4–740 nm. AISI 440C, AISI 304 stainless steel and brass balls were used as a mating ball. The friction coefficients of DLC films against with AISI 440C stainless steel ball indicated under 0.1 irrespective of the roughness. The film having smooth surface (R_a=1.4 nm) had severe damage at a load of 9.4 N. However, the film having rough surface (R_a=263 nm) had no damage at the same load. The specific wear rate of the steel ball increased with increase of roughness of the surface. In the case of AISI 304 stainless steel ball, the specific wear rate of the ball showed similar tendency. The friction with brass ball showed relatively high friction coefficient in the range of 0.12–0.25. However, the damage on the films could not be observed after friction test. It is considered that the roughness of the surface is important factor for the rupture of the film in water environment.     

Tribological properties of DLC films with different hydrogen contents in water environment

Diamond-like carbon (DLC) films were deposited on silicon wafers by thermal electron excited chemical vapor deposition (CVD). To change the hydrogen content in film, we used three types of carbon source gas (C₇H₈, CH₄, and a CH₄+H₂) and two substrate bias voltages. The hydrogen content in DLC films was analyzed using elastic recoil detection analysis (ERDA). Tribological tests were conducted using a ball-on-plate reciprocating friction tester. The friction surface morphology of DLC films and mating balls was observed using optical microscopy and laser Raman spectroscopy.Hydrogen content in DLC films ranged from 25 to 45 at.%. In a water environment, the friction coefficient and specific wear rate of DLC films were 0.07 and in the range of 10⁻⁸–10⁻⁹ mm³/Nm, respectively. The friction coefficient and specific wear rate of DLC film in water were hardly affected by hydrogen content. The specific wear rate of DLC film with higher hardness was lower than that of film with low hardness. Mating ball wear was negligible and the friction surface features on the mating ball differed clearly between water and air environments, i.e., the friction surface on mating balls in water was covered with more transferred material than that in air.     

Corrosion,wear and wear–corrosion behavior of graphite-like a-C:H films deposited on bare and nitrided titanium alloy

This work presents a comparative wear, corrosion and wear–corrosion (the last one in a simulated physiological solution) study of graphite-like a-C:H (GLCH) films deposited on bare and nitrided Ti6Al4V alloy. Films, deposited by r.f. PACVD, presented low porosity and promoted high corrosion resistance. The friction coefficient of the films was very low with appreciable wear resistance at room conditions. However, due to the simultaneous action of both load and the corrosive environment in wear–corrosion tests a marked reduction in the coating lifetime was observed. Unexpectedly, films deposited on the nitrided alloy presented a lifetime at least ten times shorter than that of films on bare alloy. We explain such a result in terms of film/substrate interaction. The weak GLCH/nitrided alloy interaction facilitates fluid penetration between the film and the substrate which leads to a fast film delamination. Such an interpretation is supported by force curve measurements, which show that the interaction between GLCH and nitrided alloy is four times weaker than that between GLCH and bare alloy.     

Nano-texture for a wear-resistant and near-frictionless diamond-like carbon

The effect of nano-scale surface texture on wear resistance of diamond-like carbon (DLC) films was studied using a reciprocating ball-on-flat tribometer in dry, humid, and liquid water environments. The nano-scale surface texture was produced by depositing ∼1 μm thick DLC films onto silicon substrates pre-textured with pyramidal wells and polystyrene spheres. The surface roughness of the textured DLC films was about 50 nm in both cases. The friction and wear behavior of the flat and nano-textured DLC films were tested with AISI 440C-grade stainless steel balls at a contact load creating about 360 nm deep Hertzian deformation which is significantly larger than the surface roughness. At this condition, nano-texturing did not affect the friction coefficient, but it significantly reduced the wear of DLC films in dry and humid nitrogen compared to flat DLC. In dry nitrogen, the nano-textured DLC films showed the ultra-low friction without substantial wear of DLC and deposition of thick transfer films onto the counter-surface. The wear reduction appeared to be related to the stress relief in the nano-textured DLC film. In liquid water, surface features on the nano-textured DLC films were diminished due to tribochemical oxidation and material removal at the sliding interface.     

The effect of annealing on mechanical and tribological properties of diamond-like carbon multilayer films

The diamond-like carbon (DLC) multilayer films have been deposited by plasma CVD deposition onSi wafer substrate. The deposited films have then been post-annealed in vacuum at 250 °C for 2 h. Changes in internal stress, hardness, critical load, friction coefficient and wear have been investigated toassess the influence of annealing on mechanical and tribological properties of DLC multilayer films. At the same time, DLC single layerfilms are also deposited and annealed in the same method for a comparison.The results show that there is 28–33% decrease in internal stress and 10–13% decrease in hardness of theDLC single layer films after the anneal treatment. However, for the DLC multilayer films, there is 41–43% decreasein internal stress and less than 2% decrease in hardness. In addition, the annealed DLC multilayer filmhas the same friction and wear properties as that un-annealed film. This result indicates that the anneal treatment isan effective method for the DLC multilayer films to reduce the internal stress and to increase the critical load.The by-effect of the annealing, decrease of hardness and wear resistance of the multilayer film, can be restrictedby the multilayer structure.     

生物医用氮化碳薄膜的力学性能比较研究

使用磁控溅射法在生物医用NiTi合金基体表面制备了Ti／TiN、Ti／DLC以及Ti／CNx梯度薄膜,利用扫描电镜研究了薄膜的截面形貌,并使用划痕仪及摩擦磨损仪研究比较了薄膜的力学性能。结果表明：薄膜均表面平整,与基底结合紧密。Ti／CNx薄膜与NiTi合金基底的结合力大于Ti／DLC薄膜,略低于Ti／TiN薄膜。3种梯度薄膜均能有效改善NiTi合金的耐磨损性能,其中,Ti／CNx薄膜拥有最低的摩擦系数和最完整的磨损表面,耐磨性最好。     

A study of biotribological behavior of DLC coatings and its influence to human serum albumin

Diamond-like carbon (DLC) coatings has been synthesized on NiTi alloy substrates by arc enhanced magnetic sputtering (AEMS) system using graphite targets. The tribological behavior indicates that the friction coefficient and wear rate of DLC coatings deposited on NiTi alloy substrates is relatively higher in ambient air than that in simulated body fluid (SBF). In human serum albumin (HSA) solution, though the friction coefficient is higher than that in SBF, but it has quite low wear rate. The Raman spectrum shows that the low friction coefficient of DLC coatings is due to the graphitization during sliding, and the degree of graphitization is relatively lower in both SBF and HSA solution than them in ambient air. The friction mechanism of DLC coatings at different environments is then proposed. On the other hand, the kinematic viscosity and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) measurements show that the DLC coatings cannot induce the thermal and mechanical denaturation of HSA during sliding.     

Relationship between interlayer hardness and adhesion and pin-on-disc behaviour for fast atom beam source diamond-like-carbon films

The effect of interlayers of Ti, and Ti(C,N) on the adhesion, hardness and friction coefficient of DLC films deposited using a Fast Atom Beam (FAB) source has been studied. Values obtained for DLC films on top of interlayers were compared with those of DLC films directly deposited on Co-Cr substrates by both the FAB source and RF CVD techniques. The scratch test adhesion of such coatings can be classified in the following ascending order: DLC/Ti, DLC/no interlayer, DLC/Ti(C,N). The surface composite hardness is greatly improved by a Ti(C,N) interlayer. However, DLC films deposited on Ti(C,N) failed during the pin-of-disc test whilst those on Ti and without an interlayer exhibited low friction coefficients and excellent wear performance. An explanation is developed in order to explain the causes of film failure during the pin-on-disc test. For a given interlayer hardness, an adhesion threshold is required to survive the pin-on-disc test. The higher the hardness, the greater the required adhesion threshold, as interfacial shear stresses induced by the pin-on-disc are greater for hard surfaces, due to the smaller contact area.     

Electro-deposition of adherent films of H2-free quality diamond-like carbon materials on SS-304 substrates using nanocrystalline SnO2 interlayer

H₂-free diamond-like carbon (DLC) films are deposited on bare as well as nanocrystalline SnO₂-coated stainless steel (SS) 304 substrates. SnO₂ films are deposited by electrolysis of 10 mM SnCl₂ solution in nitric acid medium and then subsequently heating the sample in oxygen-ambient condition. The carbon films, on the other hand, are prepared by dissociative cleavage of methanol under high DC potential of 1 kV. Deposition conditions are optimised to get the best quality films, which are characterized by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). It has been observed that films grown on SnO₂ interlayer are much more adherent when compared to those deposited on bare SS. Moreover, the quality of films on coated substrates is found to be much superior to those grown on bare SS. It is believed that the SnO₂ layer acts both as protective barrier against carbon diffusion into the SS substrate and also promotes nucleation due to anchorage of CH₃ and H⁺ radicals (necessary for growth of DLC film) onto its oxygen deficient sites.     

Humidity dependence on the friction and wear behavior of diamond-like carbon film in air and nitrogen environments

Diamond-like carbon (DLC) films were deposited on Si (100) wafers by a plasma enhanced chemical vapor deposition (PECVD) technique using CH₄ plus Ar as the feedstock. The friction and wear behaviors of the resulting film sliding against Si₃N₄ balls were investigated on a ball-on-disk test rig in air and nitrogen environments at a relative humidity from 5% to 100%. The worn surface morphologies of the DLC film and the Si₃N₄ counterpart were observed on a scanning electron microscope (SEM), while the chemical states of some typical elements thereon were investigated by means of X-ray photoelectron spectroscopy (XPS). It was found that the DLC film recorded continuously increased friction coefficient and wear rate with increasing relative humidity in air. It showed linearly increased friction coefficient with increasing relative humidity in nitrogen, in this case the wear rate sharply decreased and reached the minimum at a relative humidity of 40%, which was followed by an increase with further increase of the relative humidity. The interruption of the transferred carbon-rich layers on the Si₃N₄ balls, and the friction-induced oxidation of the films in higher relative humidity were proposed to be the main reasons for the increases of the friction coefficient and wear rate. Moreover, the oxidation and hydrolysis of the Si₃N₄ ball in higher relative humidity, leading to the formation of a tribochemical film that mainly consists of silica gel on the wearing surface, were also thought to have effects on the friction and wear behaviors of the DLC films.     

Microstructure and adhesion characteristics of diamond-like carbon films deposited on steel substrates

For tribological applications, the low friction coefficient and high microhardness of diamond-like carbon (DLC) films give significant advantages in cutting and forming non-ferrous materials. The inherently large residual stress of DLC films, however, prevents the depositing of thicker films. This study designed and implemented a compound interface, comprising a series of metal, metal nitride, and metal carbonitride interlayers deposited in a graded structure, between the DLC (a metal-doped a-C:H) film and M2 steel substrates. The tribological performance of the interface was evaluated using a scratch tester and ball-on-disk tribometer. Meanwhile, the failure mechanism of DLC deposited on M2 steel substrates was examined using SEM/EDS and TEM microscopy. Experimental results demonstrate an improved DLC hard coating with superior adhesion strength on the steel substrates.     

Study on the diamond-like carbon multilayer films for tribological application

In this paper, DLC multilayer films consisting of alternating layers of soft and hard carbon films were deposited on Si wafer by a plasma CVD deposition system. Different DLC multilayer films were prepared by varying the sub-layer thickness (from 1000 to 25 nm) and the ratio of hard to soft sub-layer (H/S) thickness (from 1:1 to 4:1). By using a ball-on-disk tribo-tester, the friction and wear properties of the DLC multilayer films were measured in vacuum, O₂ and dry-air environments respectively. By comparing with single-layer DLC film, the change of the multilayer structure has little influence on friction coefficient of the multilayer films. However, the wear rate of the DLC multilayer films is restricted effectively by constructed the multilayer structure in the film. The wear rate of the multilayer films is lower than that of the single film in reactive (O₂ and dry-air) environments. An DLC multilayer film with excellent wear resistance, approximately in the level of 10⁻⁸ mm³/Nm in different environments (dry-air, O₂ and vacuum), is obtained as the DLC multilayer film at a certain sub-layer thickness and ratio.     

Fabrication of DLC thin films with improved diamond-like carbon character by the application of external magnetic field

Diamond-like carbon (DLC) thin films were grown on Si-(100) substrates by a magnetically-assisted pulsed laser deposition (PLD) technique. The role of magnetic field on the structural, morphological, mechanical properties and deposition rate of DLC thin films has been studied. The obtained films were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and nanoindentation techniques. It was found that the diamond-like character, thickness and deposition rate of the DLC films increase in the presence of magnetic field. The films deposited under magnetic field exhibit a denser microstructure and smoother surface with lower surface roughness. Meanwhile, the mechanical properties of the magnetically processed DLC thin films experience an improvement, relative to the conventionally processed ones. It seems that the DLC films deposited under magnetic field can be better candidate for hard and wear resistance coating applications.     

Wear behaviors of TiN/TiCN/DLC composite coatings in different environments

Diamond like carbon (DLC) coatings have high wear resistance and low coefficient of friction and its features are being tried to be further developed. We deposited TiN/TiCN/DLC composite coatings on inconel substrates with closed field unbalanced magnetron sputtering system to improve the features of the conventional DLC coatings. Structural, chemical and bond types of the coating were obtained with the XRD, SEM, EDS and XPS analyses. Wear behaviors of the coatings were determined in atmosphere, distillated water and commercial oil conditions under low (2 N) and high (10 N) constant load values with using pin-on-disc tribo-test system. The wear results demonstrated that using the TiN/TiCN layers with the DLC coatings increased the load carrying capacity, decreased the CoF, and wear rates at the high load values.     

硬质合金刀具类金刚石涂层的摩擦磨损性能

以等离子体化学气相沉积技术在硬质合金刀具表面制备了类金刚石(DLC)涂层.研究了DLC涂层刀具和无涂层刀具的硬度,不同载荷、不同转速下两种刀具的摩擦磨损性能,以及在水润滑和油润滑条件下DLC涂层刀具的滑动摩擦行为.结果表明,DLC涂层刀具的平均硬度为2 099.9 HV,比无涂层刀具提高了48.3%;DLC涂层刀具的摩擦因数明显低于无涂层刀具,其磨损率随着载荷的增加而增大,随转速的增大而减小;油润滑比水润滑能更有效减缓摩擦作用.     

Low friction and protective diamond-like carbon coatings deposited by asymmetric bipolar pulsed plasma

Diamond-like carbon (DLC) thin films have been prepared at room temperature by plasma-enhanced chemical vapour deposition (PECVD) using pulsed-DC power and CH₄ as precursor. Tribological tests of these DLC films have been carried out with a nanotribometer and a calotest instrument adapted for wear measurements. Friction coefficients ranged from 0.15 to 0.20, which differ from values obtained by other techniques. In this study we have systematically measured the abrasive wear rate and friction coefficient of DLC films deposited at different conditions (pulse frequency and peak voltage), and we have discussed the results in terms of DLC structure and surface morphology. These films could find application as ultrathin anti-friction and anti-wear protective coatings, hydrophobic coatings, gas diffusion barriers and dielectric layers in electronic devices.     

Investigation of the tribological and biomechanical properties of CrAlTiN and CrN/NbN coatings on SST 304

This study examines the influence of thin layer coatings of CrAlTiN and CrN/NbN, deposited via physical vapor, on the biocompatibility, mechanical, tribological, and corrosion properties of stainless steel 304. The microstructure and morphology of the thin CrAlTiN and CrN/NbN layers were characterized by scanning electron microscopy (SEM), EDX, and X-ray diffraction. The pin on disc wear test was performed on bare and metal-nitride coated SST 304 under a 15 N load at 60 rpm and showed that the wear rates of the thin CrAlTiN and CrN/NbN film coatings were lower than the bare substrate wear ratio. The coefficients of friction (COFs) attained were 0.64, 0.5, and 0.55 for the bare substrate, CrN/NbN coating, and CrAlTiN coating, respectively. Nano indentation tests were also performed on CrAlTiN-coated and CrN/NbN-coated SST 304. The nanohardnesses and Young's moduli of the coated substrates were 28 GPa and 390 GPa (CrN/NbN-coated) and 33 GPa and 450 GPa (CrA1TiN-coated), respectively. For comparison, the nanohardness and Young's modulus of the uncoated substrate were 4.8 GPa and 185 GPa, respectively. Corrosion tests were conducted, and the behaviors of the bare and metal nitride-deposited substrates were studied in CaCl₂ for seven days. The corrosion Tafel test results showed that the metal-nitride coatings offer proper corrosion resistance and can protect the substrate against penetration of CaCl₂ electrolyte. The CrN/NbN-coated substrates showed better corrosion resistance compared to the CrAlTiN-coated ones. In evaluating the biocompatibility of the CrAlTiN and CrN/NbN coatings, the human cell line MDA-MB-231 was found to attach and proliferate well on the surfaces of the two coatings.     

Mechanical and tribological properties of diamond-like carbon films prepared on steel by ECR-CVD process

Diamond-like carbon (DLC) films were prepared on AISI 440C steel substrates at room temperature by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) process in C₂H₂/Ar plasma under different conditions. In order to prevent the inter-diffusion of carbon and improve the adhesion strength of DLC films, functionally gradient Ti/TiN/TiCN/TiC supporting underlayers were deposited on the steel substrates in advance. Using the designed interfacial transition layers, relatively thick DLC films (1–2 μm) were successfully prepared on the steel substrates without delamination. By optimizing the deposition parameters, DLC films with hardness up to 28 GPa and friction coefficients lower than 0.15 against the 100Cr6 steel ball were obtained. In addition, the specific wear rates of the films were found to be extremely low (∼10⁻¹⁷ m³/Nm). The friction-induced graphitization mechanism of DLC was confirmed by micro-Raman analysis.     

A superhard diamond-like carbon film

A superhard hydrogen-free amorphous diamond-like carbon (DLC) film was deposited by pulsed arc discharge using a carbon source accelerator in a vacuum of 2×10⁻⁴ Pa. The growth rate was about 15 nm/min and the optimum ion-plasma energy was about 70 eV. The impact of doping elements (Cu, Zr, Ti, Al, F(Cl), N) on the characteristics of DLC films deposited on metal and silicon substrates was studied aiming at the choice of the optimum coating for low friction couples. The microhardness of thick (≥20 μm) DLC films was studied by Knoop and Vickers indentations, medium thick DLC films (1–3 μm) were investigated using a ‘Fischerscope’, and Young's module of thin films (20–70 nm) was studied by laser induced surface acoustic waves. The bonds in DLC films were investigated by electron energy loss spectroscopy (EELS), X-ray excited Auger electron spectroscopy (XAES), and X-ray photoelectron spectroscopy (XPS). The adhesion of DLC films was defined by the scratch test and Rockwell indentation. The coefficient of friction of the Patinor DLC film was measured by a rubbing cylinders test and by a pin-on-disk test in laboratory air at about 20% humidity and room temperature. The microhardness of the Patinor DLC film was up to 100 GPa and the density of the film was 3.43–3.65 g/cm³. The specific wear rate of the Patinor DLC film is comparable to that of other carbon films.     

A study of hard diamond-like carbon films in mid-frequency dual-magnetron sputtering

A series of hydrogen-free diamond-like carbon (DLC) films were deposited by a mid-frequency dual-magnetron sputtering under basic conditions of Cr and C target power density between 6 and 18 W/cm², bias voltage in a range of − 100 V to − 200 V, and a pure argon atmosphere. Microstructure, microhardness, adhesion, friction and wear properties were investigated for the DLC films to be used as protective films on cutting tools and forming dies, etc. The DLC films exhibited some combined superior properties: high hardness of 30–46 GPa, good adhesion of critical load of 50–65 N, and friction coefficient about 0.1 in air condition. Properties of the magnetron-sputtered carbon films showed a strong dependence on flux and energy of ion bombardment during growth of the films.