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.     

Tribological performances of the boron carbide coatings sliding against silicon carbide and silicon nitride balls under various relative humidity conditions

Boron carbide (B₄C), silicon carbide (SiC) and silicon nitride (Si₃N₄) can achieve low coefficient of friction (Cof) under high relative humidity condition. Therefore, B₄C/SiC and B₄C/Si₃N₄ tribo-pairs may exhibit outstanding tribological behaviors, while the tribological investigation is poor. In present investigation, we performed the friction tests of the B₄C/SiC and B₄C/Si₃N₄ tribo-pairs under various relative humidity conditions, and revealed that the B₄C/SiC tribo-pair is a promising candidate for high relative humidity engineering applications. Surprisingly, the B₄C/SiC tribo-pair exhibited much better tribological behaviors than the B₄C/Si₃N₄ tribo-pair with the same test condition and tribochemical products. This is mainly attributed to less wear debris on the SiC ball and the formation of a stable tribochemical film containing boric acid and silica gel.     

Synergistic effect of surface textures and DLC coatings for enhancing friction and wear performances of Si3N4/TiC ceramic

To enhance the tribological properties of Si₃N₄ based ceramics, surface textures of dimples combined with DLC coatings are fabricated on Si₃N₄/TiC ceramic surface by nanosecond laser and plasma enhanced chemical vapor deposition (PECVD). The dry friction and wear performances are evaluated by unidirectional sliding friction tests using a rotary ball-on-disk tribometer. Results reveal that the friction and wear properties of Si₃N₄/TiC ceramics are significantly enhanced by DLC coatings or dimpled textures, and the DLC coatings combined with dimpled textures show the best efficiency in reducing friction, adhesion and wear. This improvement can be explained by the synergistic effect of DLC coatings and surface textures, and the synergistic mechanisms are attributed to the formation of lubrication film and secondary lubrication, debris capture of dimpled textures, increased surface hardness and mechanical interlocking effect, and reduced contact area.     

Friction-induced physical and chemical interactions among diamond-like carbon film,steel ball and water and/or oxygen molecules

Friction and wear behaviors of diamond-like carbon (DLC) film sliding against steel ball were investigated on a ball-on-disk test rig at different relative humidity (RH) in a nitrogen environment. The worn surface morphology of the steel ball was observed on a scanning electron microscope (SEM), while the chemical states of some typical elements on the worn surface of DLC film were investigated by means of X-ray photoelectron spectroscopy (XPS). The result showed that the DLC film recorded continuously increased friction coefficient and wear rate with increasing relative humidity from 5% to 100%. In dry nitrogen (RH < 5%), thick and compact transferred carbon-rich layer was observed covering on the worn surface of steel ball, while the chemical states of the original and worn film surface showed no obvious change. In humid nitrogen, distinct changes of the chemical states on the worn surface of DLC film took place, indicating that tribochemical reactions such as the oxidation of DLC film and the interactions between DLC film and steel ball were involved in the friction process. Therefore, it was proposed that the friction and wear behaviors of DLC film were dependent on the friction-induced physical and chemical interactions among DLC film, steel ball and water and/or oxygen molecules. The roles of environment in the friction and wear behaviors of DLC film were discussed in terms of the friction-induced physical and chemical interactions.     

Controllable wear behaviors of silicon nitride sliding against sintered polycrystalline diamond via altering humidity

The tribological behaviors of silicon nitride (Si₃N₄) sliding against sintered polycrystalline diamond (PCD) were investigated by varying the relative humidity (RH) in the testing atmosphere. The results indicated that higher RH corresponds to higher wear loss of Si₃N₄ and the wear loss of PCD almost fell close to zero. Especially in the case of 85% RH, both a maximum wear loss of Si₃N₄ and a maximum friction coefficient were achieved. In addition, this study revealed insights into the interface chemistry effects on the wear behavior of Si₃N₄ under humidity. When water molecules were introduced into the testing atmosphere, the hydrolysis reaction occurred on the Si₃N₄ surface with the formation of the Si‐O‐Si bond across the sliding interface. And then, the hydration reaction dominated the process, during which Si‐OH was formed through the bond fracture of the Si‐O‐Si. The X‐ray photoelectron spectroscopy results showed that the ratios of Si‐OH/Si‐O and Si‐N/Si‐OH+Si‐O bonds increased as the relative RH levels increased. As a consequence, the wear loss of Si₃N₄ significantly increased. Thus, due to the hydrolysis and hydration reactions, the tribological behaviors of Si₃N₄ against sintered polycrystalline diamond can be essentially controlled via varying RH levels.     

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.     

Tribological properties of polyimide coatings filled with PTFE and surface‐modified nano‐Si3N4

Polyimide (PI) coatings filled with PTFE and nano‐Si₃N₄ were prepared by a spraying technique and successive curing. Nano‐Si₃N₄ particles were modified by grafting 3‐aminopropyltriethoxysilane to improve their dispersion in the as‐prepared coatings. Friction and wear performances and wear mechanisms of the coatings were evaluated. The results show that the incorporations of PTFE and modified nano‐Si₃N₄ particles greatly improve the friction reduction and wear resistance of PI coating. The friction and wear performance of the composite coating is significantly affected by the filler mass fraction and sliding conditions. PI coating incorporated with 20 wt % PTFE and 5 wt % modified nano‐Si₃N₄ displays the best tribological properties. Its wear rate is more than one order of magnitude lower and its friction coefficient is over two times smaller than that of the unfilled PI coating. Differences in the friction and wear behaviors of the hybrid coatings as a function of filler or sliding condition are attributed to the filler dispersion, the characteristic of transfer film formed on the counterpart ball and the wear mechanism of the coating under different sliding conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40410.     

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.     

Tribological behaviors of polycrystalline cubic boron nitride sliding against silicon nitride in air and vacuum conditions

In order to evaluate the friction and wear properties of polycrystalline cubic boron nitride (PCBN) based on the drilling tools cutting, the ball-on-disk tribological experiments of PCBN sliding against silicon nitride (Si₃N₄) were carried out in air and vacuum conditions. The tribological behaviors were investigated by Scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and Nanomap-D three-dimensional White Light Interferometer. The results demonstrate that the coefficient of friction (CoF) is closely interrelated with the changing tendency of loads, where the CoFs gradually decrease with the growth of the load whether in air or in vacuum on account of a transfer film in air and a change from sliding friction to rolling friction in vacuum. Moreover, the CoF in vacuum condition is invariably greater than that in air under the similar load owing to friction heat. Furthermore, no observable abrasion appears on Si₃N₄ in air while severe abrasive wear is dominant on Si₃N₄ in vacuum. In addition, there is more intense adhesion on PCBN in vacuum than that in air. The reason is that the friction heat is gathered in vacuum condition with a confined environment.     

Effect of load on the friction and wear characteristics of Si3N4-hBN ceramic composites sliding against steels

The tribological behaviors of Si₃N₄-hBN ceramic composites sliding against steels (austenitic stainless steel (ASS) and 45 steel) under dry friction conditions at different loads were investigated by using an MMW-1 type vertical universal friction and wear tester. The experimental results showed that the friction coefficients and wear rates first showed a decrease and then an increase with an increase in the load under dry friction conditions. The better tribological performance was exhibited by the SN10/ASS sliding pair under a load of 20 N (the friction coefficient was as low as 0.27 and the wear rates of both pin and disc had a magnitude of 10⁻⁶ mm³ N⁻¹ m⁻¹). This may be attributed to the formation of a black surface film (consisting of B₂O₃, SiO₂, and Fe₂O₃). For the same sliding pair, when the load was 10 N, the dominating wear mechanism was abrasive wear. Hence, the friction coefficient was higher (0.7). When the load increased to 30 and 50 N, the wear mechanism of the SN10/ASS sliding pair was a combination of abrasive and adhesive wears, and higher friction coefficients (0.48 and 0.72 under loads of 30 and 50 N, respectively) were obtained. On the other hand, the contents of hBN also showed a significant impact on the tribological behaviors of the Si₃N₄-hBN/ASS sliding pairs. When the hBN content was less than 10%, the friction coefficients of the Si₃N₄-hBN/ASS sliding pairs decreased with an increase in the hBN content. On the other hand, at hBN contents of 10% or more, the friction coefficients of the sliding pairs increased with an increase in the hBN content. Under the same experimental conditions, the Si₃N₄-hBN/45 steel pairs showed poor tribological properties as compared with the Si₃N₄-hBN/ASS pairs.     

Frictional behavior and wear resistance performance of gradient cermet composite tool materials sliding against hard materials

Gradient cermet composites possessing high surface hardness, flexural strength and interface bonding strength were fabricated using vacuum hot-pressing sintering. Ball-on-disk tests were performed to investigate the tribological properties of the gradient cermet composites against 440 C stainless steel, Al₂O₃ and Si₃N₄ balls at different sliding speed and load in comparison with traditional Ti(C,N) cermets. The tribological behavior was characterized in terms of friction coefficient and wear rate. The results showed that friction coefficient was significantly dependent on the sliding speed and load when sliding against Al₂O₃ and Si₃N₄. However, there was no obvious relation between them during sliding against 440 C stainless steel due to the formation of metal adhesive layer. Gradient cermet composites exhibited a higher friction coefficient but lower wear rate than traditional Ti(C,N) cermets. The main wear mechanism of gradient cermet composites was adhesion wear during sliding against 440 C stainless steel, while abrasion wear was the predominant mechanism during sliding against Al₂O₃ and Si₃N₄. It was expected that gradient cermet composites would be excellent candidates for cutting tool materials.     

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 characteristics of nanometer Si3N4 filled poly(ether ether ketone) under distilled water lubrication

Nanometer Si₃N₄ filled poly(ether ether ketone) (PEEK) composite blocks with different filler proportions were prepared by compression molding. Their friction and wear properties under distilled water lubrication, as well as under ambient dry conditions, were investigated on a block on ring machine by running a plain carbon steel (AISI 1045 steel) ring against the PEEK composite block. The worn surfaces of nanometer Si₃N₄ filled PEEK and the transfer film were observed by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The results showed that distilled water could reduce the friction coefficient of nanometer Si₃N₄ filled PEEK but with the sacrifice of a large reduction in wear resistance. The SEM and EPMA pictures of the worn surfaces indicated that the wear mechanisms of nanometer Si₃N₄ filled PEEK under distilled water lubrication and ambient dry rubbing conditions were different. Under water lubrication, the dominant wear mechanism of the filled PEEK was severe abrasive wear with surface fracture. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1394–1400, 2001     

Friction and wear properties of Si3N4-hBN ceramic composites using different synthetic lubricants

This paper presents a tribological investigation of Si₃N₄-hBN composite ceramics using synthetic lubricants. The friction and wear properties of Si₃N₄-hBN ceramic composites sliding against TC4 titanium alloy (Ti6Al4V) were investigated via pin-on-disc tests. An axial compressive load of 10?N was applied with a sliding speed of 0.73?m/s. Three different lubrication conditions including simulated body fluid (SBF), physiological saline (PS) and bovine serum (BS) were used. For SBF lubrication, the friction coefficients and wear rates of Si₃N₄-hBN/Ti6Al4V pairs were varying with the increase of hBN contents. When using 20?vol% hBN, the average friction coefficient and wear rate of Si₃N₄ (0.28 and 3.5?× 10^?4 mm³ N^?1 m^?1) were as good as that of the pure Si₃N₄ (0.34 and 3.69?× 10^?4 mm³ N^?1 m^?1). Meanwhile, the processability of the Si₃N₄ material would be improved by adding hBN. It was worth to mention that when using 30?vol% hBN, the tribological performance of bearing combination deteriorated with extensive wear from the ceramic pin. This may due to the reduction of mechanical property caused by adding hBN and the occurring of tribochemical reaction. According to the worn surface examination and characterization, the main wear mechanism was abrasive and adhesion wear. Scratch grooves were observed on the metal disc, and metallic transform layers were seen on the ceramic pin. Moreover, surface lubrication film consisting of TiO₂, SiO₂·nH₂O, Mg(OH)₂, and H₃BO₃ were formed on the metal disc when using SBF lubrication and 20?vol% hBN content. Among the three lubrication conditions, SBF generally led to the best tribological performance. No surface lubrication film was found during BS and PS lubrications. This may be resulted from the absence of essential ions to promote the formation of surface lubrication film (PS lubrication) and the formation of a protein barrier on the surface of the metal disc (BS lubrication).     

Comparative study on wear behavior of plasma sprayed Al2O3 coatings sliding against different counterparts

Although the friction and wear behavior of plasma sprayed aluminum matrix ceramic coatings have been extensively discussed in the last decades, only few researches have been carried out the wear mechanisms sliding against different pairs. The tribological behaviors of plasma sprayed Al₂O₃ coating sliding against ZrO₂, Si₃N₄, Al₂O₃ and stainless steel balls in air were comparatively investigated in this study. It was showed that Al₂O₃ coating sliding against different counterparts exhibited diverse tribological behaviors, which could be mainly ascribed to the different mechanical properties of counterparts. Meanwhile, the tribochemical reactions influenced the friction performances significantly. Moreover, the transform of γ-Al₂O₃ to α-Al₂O₃ occurred during the friction, which was closely related to the coefficient of friction and thermal conductivities of counterparts. The main wear of Al₂O₃ coating sliding against ceramic materials resulted from the brittle fracture and abrasive wear. While it was dominated by adhesive wear when sliding against stainless steel, and accompanied with abrasive wear.     

Effect of self-developed graphene lubricant on tribological behaviour of silicon carbide/silicon nitride interface

The research presented in this paper aims to investigate the effectiveness of different surface roughness and lubrication conditions on the interfacial tribological properties between silicon carbide (SiC) and silicon nitride (Si₃N₄) ceramics, particularly for providing insight into the mechanisms of how graphene reduces the friction and wear rate. The worn groove topography and surface composition were characterised in detail with 3D laser measuring microscopy and X-ray photoelectron spectroscopy. The tribological test results on the UMT-TriboLab show that a smooth initial surface is more likely to obtain a low friction coefficient and wear rate under water lubrication. The proper initial surface roughness for SiC and Si₃N₄ ceramics is approximately Ra 10?nm, and it will be lower in an alcohol or graphene aqueous solution. A large load does not worsen the tribological behaviour of a Si₃N₄ ball sliding against a SiC disk, and it reduces the friction coefficient and wear rate. Among the five lubrication states of dry friction, dry graphene lubrication, water lubrication, graphene solution lubrication, and self-developed graphene lubrication, the self-developed graphene lubricant can exhibit an ultra-low friction coefficient of 0.009 and ultra-low wear rate of 1.69?×?10^?7?mm³/N·m. The excellent tribological property of the graphene-coated ceramic surface helps the prepared lubricant to decrease the friction coefficient effectively. Furthermore, the graphene film can protect the SiC from being oxidised by water under the tribo-activated action, and therefore, lead to ultra-low wear rate under low friction condition. Alcohol improves the tribological property of the self-developed graphene lubricant, mainly because of the good wettability between graphene and ethanol. The self-developed graphene lubricant can be applied in water-lubricated ceramic bearings and motorised precision spindles.     

Friction and wear characteristics of ceramic particle filled polytetrafluoroethylene composites under oil-lubricated conditions

Five kinds of polytetrafluoroethylene (PTFE)-based composites were prepared: PTFE, PTFE + 30 vol % SiC, PTFE + 30 vol % Si₃N₄, PTFE + 30 vol % BN, and PTFE + 30 vol % B₂O₃. The friction and wear properties of these ceramic particle filled PTFE composites sliding against GCr15 bearing steel under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester. The worn surfaces and the transfer films formed on the surface of the GCr15 bearing steel of these PTFE composites were investigated by using a scanning electron microscope (SEM)and an optical microscope, respectively. The experimental results show that the ceramic particles of SiC, Si₃N₄, BN, and B₂O₃ can greatly reduce the wear of the PTFE composites; the wear-reducing action of Si₃N₄ is the most effective, that of SiC is the next most effective, then the BN, and that of B₂O₃ is the worst. We found that B₂O₃ reduces the friction coefficient of the PTFE composite but SiC, Si₃N₄, and BN increase the friction coefficients of the PTFE composites. However, the friction and wear properties of the ceramic particle filled PTFE composites can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of the PTFE composites can be decreased by 1 order of magnitude. Under lubrication of liquid paraffin the friction coefficients of these ceramic particle filled PTFE composites decrease with an increase of load, but the wear of the PTFE composites increases with a load increase. The variations of the friction coefficients with load for these ceramic particle filled PTFE composites under lubrication of liquid paraffin can be properly described by the relationship between the friction coefficient (μ) and the simplified Sommerfeld variable N/P as given here. The investigations of the frictional surfaces show that the ceramic particles SiC, Si₃N₄, BN, and B₂O₃ enhance the adhesion of the transfer films of the PTFE composites to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of the GCr15 bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. Meanwhile, the interactions between the liquid paraffin and the PTFE composites, especially the absorption of liquid paraffin into the surface layers of the PTFE composites, create some cracks on the worn surfaces of the ceramic particle filled PTFE composites; the creation and development of these cracks reduces the load-supporting capacity of the PTFE composites. This leads to the deterioration of the friction and wear properties of the PTFE composites under higher loads in liquid paraffin lubrication. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2611–2619, 1999     

Tribological behavior of ceramic materials (Si3N4, SiC and Al2O3) in aqueous medium

The friction and wear behavior of self-mated Si₃N₄, SiC and Al₂O₃ in water were investigated by varying the test conditions of applied load and sliding speed. It was found that, for self-mated Si₃N₄ and SiC ceramics, the tribochemical reaction resulted in surface smoothening with low friction coefficient at high load and high speed condition. Al₂O₃ shows high friction coefficient, but better wear rate (10⁻¹¹ mm²/N) than other ceramic materials.     

Tribological performance of DLC-coated ceramics against cemented carbide under dry sliding conditions

In order to improve the tribological behavior of Si₃N₄/TiC ceramics, DLC coating was fabricated on the ceramic surface through magnetron sputtering technology. The surface and cross-section micrographs, the adhesion between coating and substrate, the surface roughness and microhardness of the DLC-coated ceramics were investigated. Reciprocating friction tests sliding against cemented carbide ball were conducted under dry sliding conditions. The test results indicated that the DLC coating possessed superior tribological performance, which was conductive to decreasing the friction coefficient and enhancing the wear resistance of ceramics. The primary mechanisms responsible for performance improvement of the DLC-coated ceramics were attributed to the combined effects of low shear stress, excellent adhesion with substrate, high microhardness and good surface roughness. It was believed that the DLC coating was efficient in improving the load-carrying capacity and expanding the application area of ceramic materials.     

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.