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Articular cartilage is a water-lubricated naturally occurring biological interface imparting unique mechanical and ultralow frictional properties in bone joints. Although the material of cartilage, synovial fluid composition, and their lubricating modes and properties have been extensively investigated at various scales experimentally, there is still a lack of understanding of load bearing, adhesion, and friction mechanisms of the cartilage-cartilage interface from an atomistic perspective under heavy loads. In this study, the effect of loading on adhesion and frictional behavior in articular cartilage is investigated with a proposed atomistic model for top layer cartilage-cartilage contact in unhydrated conditions using molecular dynamics (MD) simulations. Pull-off tests reveal that cohesive interactions occur at the interface due to formation of heavily interpenetrated atomistic sites leading to stretching and localized pulling of fragments during sliding. Sliding tests show that friction is load- and direction-dependent with the coefficient of friction (COF) obtained in the range of 0.20-0.75 at the interface for sliding in parallel and perpendicular directions to the collagen axis. These values are in good agreement with earlier nanoscale experimental results reported for the top layer cartilage-cartilage interface. The COF reduces with an increase in load and tends to be higher for the parallel sliding case than for the perpendicular case owing to the presence of the constant number of H-bonds. Overall, this work contributes toward understanding sliding in unhydrated biointerfaces, which is the precursor of wear, and provides insights into implant research.

The effects of ultra-high-molecular-weight polyethylene (UHMWPE) as a filler on the tribological and mechanical properties of two biocompatible epoxies were studied. SU-8 and Structalit 8801 (a tra...

Liquid absorption and tribological studies of epoxy-based composite with ultra-high molecular weight polyethylene and MoS2, sliding against steel, were conducted. Composites, as coating and as a bulk, were soaked in water, base oil, ionic liquid, and lithium-based grease for different intervals of days or months. Liquid weight percent gain was more in polar liquids when compared to non-polar. Coated composite soaked in grease for 10 days showed coefficient of friction of 0.08 with wear life of more than 1 million cycles and wear-rate of 1.7 × 10−8 mm3/N m. Bulk polymer composite soaked in grease for 180 days provided the least coefficient of friction of 0.06 and specific wear-rate of 2.60 × 10−7 mm3/N m.

SU-8 polymer with talc particle (30 wt-%) and liquid perfluoropolyether (PFPE) (30 wt-%) fillers was used as a composite to fabricate conical tip-cantilever device. The composite tip demons...

In this study, an electric field was applied to align carbon nanofibers (CNF) in an epoxy matrix and the tribological performances were evaluated. The epoxy/aligned CNF composites were fabricated with different weight percentages of non-functionalized CNFs (0.2–2 wt%) with which friction and wear tests were carried out keeping sliding direction normal to fiber orientation. The wear resistance of 1 wt% random and aligned composites improved by 3.5 and 25 times, respectively, compared to pure epoxy (20 N load). Moreover, the friction coefficient reduced from 0.6 for pure epoxy to 0.44 and 0.24 for random and aligned CNF/epoxy composites, respectively. Improved thermal stability, normal load carrying capacity and lubricating effect of CNFs contributed to the superior wear resistance of aligned composites.

Copper is an outstanding ingredient of friction materials (FMs) due to its multi-functional performance. Despite all its various positive contributions in FMs, it has been recently reported as a hazard for an aquatic life and has become a focus of concern for the FM Industry. Hence in the current work, group of novel ingredients was explored for Cu-replacement. Some conducting ingredients were added to compensate the conductivity of Cu. One more novel ingredient Promaxon-D was used as a theme ingredient. The developed pads (metal-free) were characterized for tribological properties on the inertia dynamometer as per JASO-C-406 standards. It was concluded that Promaxon-D proved successful in Cu-replacement almost in all respects barring wear. With increase in an amount of Promaxon-D, most of the properties got improved.

Multi-functionality of copper (Cu) in friction materials renders its replacement extremely difficult. However, rising ecological concerns and the imminent ban on its usage make it mandatory to look for an efficient substitute. The present paper explores a possibility to replace particulate Cu filler by stainless steel swarf (SSS) in the brake-pads. A series of five realistic multi-ingredient brake-pads containing SSS as a focussed ingredient was developed by increasing its amount from 0 to 20 wt% in the step of 5%. In another set of pads 10% of SSS was replaced by 10 wt% Cu n particulate form keeping all ingredients same to compare the performance of two fillers. These pads were characterized for their physical, mechanical and tribological properties. Tribo-performance using realistic test parameters was evaluated on the brake inertia dynamometer as per JASO C 406 standard. It was observed that with an increase in the amount of SSS, almost all the properties of brakes pads, including wear resistance improved significantly. Nonetheless, Cu- containing pad proved slightly better in recovery ratio and wear performance by 10%, but inferior in the case of fade µ (µ-coefficient of friction) and recovery µ. Worn surface analysis with scanning electron microscope (SEM) confirmed that SSS had poor interfacial adhesion with the matrix which led to a higher wear of SSS filled pads as compared to the Cu filled pads.

We examine the role of important alloying elements (Al, Y), on friction and wear mechanisms of Mg as a function of temperature. Friction and wear tests of Mg–5%Al and Mg–5%Y alloys performed at room temperature, 100 °C and 150 °C reveal that addition of Al and Y significantly reduces the coefficient of friction. However, despite higher hardness of Mg–5%Y alloy, its wear rate was found to be higher than Mg–5%Al alloy at elevated temperatures. We show that this behaviour, observed for Mg–5%Y alloy at elevated temperature, can be attributed to its higher surface energy than Mg–5%Al and pure Mg, leading to enhanced adhesive wear, which is detrimental to tribological applications.

Epoxy with ultra-high molecular weight polyethylene (UHMWPE) and MoS2 fillers was coated on a bearing steel (SAE 52100). Frictional and wear properties of the coated samples in sliding contact were investigated on a pin-on-disc tribometer under a normal load of 10 N and a linear sliding speed of 1 m/s against a bearing steel ball. The optimized coating composition (72 wt% Epoxy + 7 wt% hardener + 18 wt% UHMWPE + 3 wt% MoS2) showed highly improved tribological properties compared to pure epoxy and other epoxy-based composites. There was 75% reduction in the coefficient of friction (COF) in the dry interfacial condition (COF reduced from 0.2 to 0.05) over pure epoxy and 80% reduction with grease as the lubricant. The specific wear-rate of the composite was lower by five orders of magnitude over that of pure epoxy. Other mechanical properties such as hardness, tensile strength, and Young's modulus of the composite showed increments of 86%, 121%, and 43%, respectively, with respect to those of pure epoxy. 2–3 wt% of MoS2 had drastic effects on improving strength and reducing friction and wear of the composites. For dry sliding, initial abrasive and adhesive wear mechanisms led to transfer film formation on the steel counterface, and the shearing was mainly within the transfer film. For the grease-lubricated case, a thin layer of grease helped in easy shearing, and the transfer film formation was avoided. This epoxy-based composite will have applications as tribological coatings for journal bearings.

The main objective of this investigation is to evaluate the tribological performance of dual-coatings of epoxy composites (epoxy with 10 wt% of graphene and 10 wt% of base oil) on different hard intermediate layers (diamond-like-carbon, tungsten carbide and titanium aluminium nitride) deposited on D2 steel. Friction and wear tests were conducted at 10 N and 15 N normal loads, and 0.63 m/s linear sliding speed and the counterface was a 4 mm steel ball. Among all dual-coatings, the combination of DLC intermediate layer and epoxy composite top layer furnished the least coefficient of friction of 0.09 and wear-life exceeded 2 × 105 cycles with no or negligible wear. In comparison, only hard or only soft coating had very limited wear-life.

In our earlier study, epoxy-based composites with graphene (10 wt-%) and in situ liquid fillers (base oil SN150 or perfluoropolyether at 10 wt-%) were found to provide low friction and highly wear ...

This work examines the micrometer-scale wear behavior of pure Mg and its composites at various loads (100–500 mN) under single and multiple scratch conditions. The Mg-0.4Ce alloy reinforced with na...

In this paper, hybrid polymeric composites of epoxy with two solids (UHMWPE and MoS2) and one liquid (base oil SN150) fillers were prepared to improve the thermal, mechanical and tribological properties for load bearing applications. Due to relatively high friction of solid lubricants compared to liquid lubricants, base oil was incorporated into the epoxy composite as liquid filler to achieve enhanced tribological properties. All the experiments were conducted with two interfacial conditions: polymer composite against steel (EN31) and polymer composite against itself. The base oil-filled epoxy composite showed excellent tribological performance with specific wear rate in the range of 10−7 mm3/Nm and low coefficient of friction of 0.08–0.1 at a constant nominal contact pressure of 0.611 MPa and speed 1 m/s. Durable transfer film formation was identified as the main wear reduction mechanism. These fillers also made the surface of epoxy hydrophobic in nature which reduced adhesion and friction. By adding fillers, thermal degradation temperature of the composite was increased by 22.8%. The lubrication mechanism was identified as mixed lubrication with three different sub-regimes.

In this study, two different analytical models were developed to predict electrical conductivity of random and aligned nanofiber/polymer composites. Model-I calculated conductivity using micromechanics based analytical equation and model-II calculates effective conductivity by considering the composite as simplified fiber–fiber contact network based equivalent resistor model. The models incorporated the effect of filler geometry, concentration, orientation, interphase and percolation threshold. Electron tunneling along thin insulating layers between conductive fillers was considered as the major contributor of conductivity. The proposed models were validated with measured conductivity from random and electric field aligned CNF/epoxy composites of different concentrations. The models were further validated with literature data on the conductivity of random and aligned CNT and CNF/polymer composites. The proposed models can also be extended to predict electrical conductivity of nanocomposites with fillers with different geometry.

This study investigates nanoscale adhesion and frictional behavior of an idealized cartilage-cartilage top layer atomistic contact model with nanoconfined water at the interface under range of load using three dimensional molecular dynamics (MD) simulations. Analysis reveals that water significantly replaces the cohesive interactions with adhesive at regions of unhydrated cartilage-cartilage contact by engulfing water molecules. These water molecules improve the load-bearing capacity and reduces frictional forces at the interface. Interfacial water also inhibits debonding at the interface during pull-off test at higher loads. Sliding tests reveal that at higher load-induced confined geometries there is a significant reduction in the frictional forces up to five times in comparison to dry collagen-collagen contact. Interaction energy curves predict that water molecules completely wet the collagen and thus provide an in-situ interfacial lubrication. Finally, the intermolecular interactions unveil the presence of substantial amount of water molecules at the interfaces to reduce friction drastically at the interface employing water-water interactions. Overall, a hydrated atomistic model for top layer cartilage-cartilage lubricated contact is developed and studied for adhesion and friction behavior and underlying mechanisms which is useful for understanding in-vivo boundary lubricated interfaces and design enhanced implant solutions.

Good friction materials should satisfy diverse and contradictory performance requirements such as adequate friction ( µ ≈ 0.35–0.45), resistance to wear, fade, squeal, judder, etc. in consort with good recovery and less noise producing tendency. To achieve center point of all these conflicting criteria and selection of best overall performing friction material is multiple criteria decision making (MCDM) problem and very difficult task. Decision maker can easily make decision with single criteria without the help of any optimization tool by maximizing beneficial criteria and minimizing non-beneficial criteria. However, it is extremely challenging task if decision making involves several number of conflicting criteria. Few techniques are reported in the literature such as ‘multiple criteria decision model’, ‘Multi-attribute decision model’, ‘extension evaluation method’ (EEM), etc. for performance ranking of friction materials. However, the simplicity, reliability, applicability, time devoted for the analysis, etc. are always most important aspects of selecting a right tool for the analysis. In this paper application of a technique ‘multiple objective optimization on the basis of ratio analysis’ (MOORA) has been first time employed for performance ranking of friction materials. A comparative study of MOORA and currently used methods MCDM and EEM are also presented. MOORA proved to be the best tool based on the criteria such as simple to use, fast, flexible, and efficient one.

The present era is dominated by nano-materials. Researchers are keen to explore the potential of nano-particles (NPs) in composites because of their intensive interaction with the matrix and surfaces due to very large surface area. Potassium titanate (KT) is used as a filler in a good quality non-asbestos organic (NAO) friction materials (FMs). Based on a little information available in the literature, it is claimed to reduce friction-fluctuations, fade and wear. However, exact role of KT in FMs is not so clear due to contradictory findings. Interestingly, no paper is available on exploration of NPs of KT in FMs. Keeping this in view, two realistic multi-ingredient NAO FMs in the form of brake-pads with identical compositions but differing in size of a theme ingredient, KT were developed. One composite was without KT (K 0 ), while two composites containing 3% micro and 3% nano-KT particles were designated as K M and K N . These were characterized for physical, mechanical and tribological performance. Initial tribo-evaluation of composites was done on a reduced scale prototype (RSP) under various operating conditions. Final tribo-performance was evaluated on a full scale brake dynamometer following JASO C 406 Schedule using gray cast iron disc. Various performance parameters such as performance µ, fade µ, recovery µ; fade ratio, recovery ratio, wear resistance etc. were used to evaluate the performance of FMs. Both testing data (prototype and realistic machine) showed that almost all performance parameters were significantly and beneficially affected due to NPs of KT. Nano-KT particles proved to improve performance µ and wear resistance significantly compared to its micro-partner. Worn surface analysis of pads and discs was done to understand wear mechanism by SEM and EDAX technique. It was finally concluded that Nano-KT particles have a potential to enhance performance of FMs significantly.

Epoxy-based composites are promising tribological coatings. The tribological properties of epoxy composites with filler materials such as graphene, graphite, and liquid lubricants (base-oil SN150 and perfluoropolyether) are studied. The composite coatings were applied on cylindrical steel surface and a steel ball was used as the counterface. Tests were conducted at 10 N normal load and 0.63 m/s linear sliding speed. Among all coatings, epoxy filled with graphene and SN150 lubricant provided the lowest coefficient of friction of 0.09 with wear cycles exceeding 200,000 and specific wear rate of 5.4×10−7 mm3/N-m. Speed effects on friction were also evaluated.

SU-8, an epoxy-based polymer, is industrially very useful material for fabricating microsystems such as micro-electro-mechanical systems. However, for optimal performance, it is necessary to further improve the mechanical and tribological properties of SU-8. Different weight percentages (wt%) of graphite and talc particles are added to SU-8 for the enhancement of mechanical as well as tribological properties. The composite with the optimized composition of SU-8+15 wt% graphite+15 wt% talc has shown superior properties compared with pure SU-8 and other composites tested. This composite shows ~4 times lesser steady-state coefficient of friction (~ 0.2), ~3 times higher elastic modulus (~7.97 GPa) and ~2 times greater hardness (~0.52 GPa) over those of pure SU-8. Also, there is a decrease in the wear rate by ~10 3 times. This optimized composite, which showed nano to micron scale texturing on the surface, has performed better in comparison with single or mixed fillers with different wt% ratios. The wear mechanism for filler content up to 10 wt% was found to be fatigue and delamination, whereas for higher filler content the abrasive wear mechanism was dominant.

Poor tribological properties of SU-8, a promising MEMS structural material, have been recently addressed by developing a perflouropolyether (Z-dol) lubricant droplet-filled SU-8 composite. The composite shows wear durability four orders of magnitude greater than that of SU-8. The chemical reaction between the SU-8 and PFPE molecules and the physical self-lubrication mechanism were found responsible for this dramatic improvement. In this work, the self-lubrication mechanism at the ball–composite interface of SU-8+5 wt% Z-dol composite was further investigated by varying sliding speed. Effects of normal load on the tribological responses of SU-8+5 wt% Z-dol composite was also investigated independently and various possible wear mechanisms are proposed.

SU-8, an epoxy-based negative photoresist polymer, is highly suitable for making micro-electro-mechanical systems (MEMS) structures. Despite fabrication advantages, its bulk mechanical and tribological properties are the main limitations for application as MEMS material. Carbon filler materials such as graphene, graphite and multi-walled carbon nanotube (MWCNT) are added to SU-8 for tribological and mechanical property enhancements. SU-8/(5 wt%) graphite composite has performed better for the steady-state coefficient of friction at all loads including for the speed effect. SU-8/(5 wt%) MWCNT has shown excellent wear resistance. At 10 wt% graphite content, SU-8/graphite is superior in tribological performance to other composites tested.

This paper seeks to address the potential of using ionic liquids as nanolubricants on Polyether-ether-ketone (PEEK) surface. We characterize the tribological properties of two ionic liquids, namely1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetrafluoroborate. The tribological data are compared with those of perfluoropolyether (PFPE) and Multiply Alkylated Cyclopentanes (MAC) data obtained from previous study. Ionic liquids at lower concentration of 0.4wt% (in solution prior to deposition) showed lower wear lives as compared to those for PFPE and MAC. However, at higher concentration of 4wt%, these ionic liquids have the same wear lives as those of PFPE and MAC, but show considerably lower coefficients of friction. Mechanisms of nanolubrication for ionic lubricants vis-a-vis those of PFPE and MAC are explained.

Introduction Health insurance is emerging fast as an important mechanism to finance health care needs of the people. Complexity of the health insurance industry has been much talked about and less understood in the Indian scenario. Hence, it is imperative to assess the level of awareness that the population has with respect to health insurance policies. Materials and methods Cross-sectional prospective study conducted over a period of 6 months, at the third-party administrator (TPA) desk of the hospital. The data was collected using a preformed close-ended questionnaire after obtaining consent from all the participants. Only patients admitted in the hospital availing cashless hospitalization were included in the study. The study was undertaken with the objective to determine the level of awareness about insurance policies and procedures among those insured and identify the problems faced by those insured when availing cashless treatment. Responses to the variables in the questionnaire were compiled and tabulated using Excel 2010. Results Response rate of 76% was observed. 56% of the study population were planned admissions and 44% were admitted through emergency department. The study showed that about 56% of the principal policy holders were between 30 and 50 years of age. The awareness regarding the terms and conditions of the health care insurance policy and the servicing TPA was found to be 70%. However, on interacting with patients it came to light that despite being appraised by their insurance agent, they faced challenges while availing health care benefits under health care insurance and were ignorant about the procedure involved. For the current admission, in 78% of the cases, the TPA responded within 24 hours of intimation; however, in 22% cases there were delays in response from the TPA mostly attributed to communication gap between the Insurance Company and the TPA. Preexisting disease was not covered in 14% cases. 82% cases had to wait for more than 2 hours for the final clearance from the TPA. Over the years, as ascertained in 2016 also, the scenario of insurance has not undergone significant change. Conclusion Strategies to optimize claims by bringing about a uniformity in the rates being charged by the hospitals for different procedures are needed to increase coverage. How to cite this article Jain K, Sinha SK, Jain D, Kumar R. Does Health Insurance give Us an Assurance? A Study on the Extent of Coverage of Health Insurance at a Tertiary Care Hospital in North India. Int J Res Foundation Hospc Health Adm 2016;4(1):25-30.

The main objective of this investigation is the evaluation of the performance of hard diamond-like-carbon (DLC) or tungsten carbide (WC) and soft (epoxy composite) dual-coatings on the internal combustion (IC) engine piston rings as a protective coating to reduce their wear. The rings were coated with DLC or WC by physical vapor deposition (PVD) method and then soft polymeric composite coating (epoxy/graphene/base oil SN150) was applied on the hard coating. The tribological tests of the dual-coated piston rings were conducted for 3.6 × 105 cycles at 1500 rpm engine speed and 50% rated load of a diesel engine in order to evaluate the wear performance of the piston rings. Scuffing of cylinder liner and piston rings interface was prevented by the application of polymer composites over the hard-coated rings. DLC hard and soft polymer composite dual coating over the top piston ring was found to have the lowest wear rate 1.69 × 10−12 mm3/N·m compared with the wear rate of dual coatings on the middle and lower rings.

Industrial lubricants are invariably used with organo-metallic additives [such as complex sulphates and phosphates Zinc dialkyldithiophosphate (ZDDP)] for tribological performance enhancement of machines such as internal combustion (IC) engines. However, these additives are environmentally harmful and they also have damaging effects on the steel components of the engine. Hence, there is an urgent need to find alternative solutions for enhancing the tribological performance of lubricants and components without the application of such harmful additives. Epoxy-based composites are promising tribological coatings, which can provide low friction and high wear life under dry, as well as base-oil lubricated conditions. The present chapter focuses on reviewing the mechanisms of achieving improved mechanical properties with a low coefficient of friction (CoF) in typical demanding applications, such as IC engines. The applications of epoxy composite coatings can be in extreme contact conditions such as engine piston rings and bearings. The best suitable coatings, namely epoxy/graphene/SN150 with DLC and WC as the intermediate hard coatings, were applied on the piston rings of a diesel engine and experiments were performed in order to permit wear analysis of coated rings.

Industrial lubricants are invariably used with additives (with high sulfur and phosphorous contents) for tribological performance enhancement. However, these additives are environmentally very harmful. Hence, there is an urgent need to find alternate solutions for enhancing the tribological performance of lubricants and components without the use of harmful additives. The objective of this work is to investigate the feasibility of using polymer composite coatings in enhancing the tribological properties of steel surfaces in dry and base oil lubricated conditions. Pure epoxy and its composite (with 10 wt-% of graphene or graphite powder) films were coated onto steel substrates and tested under dry and base oil lubricated conditions. Friction and wear experiments were conducted on a ball on cylinder tribometer between polymer/composite coated cylindrical steel surface (shaft) and an uncoated steel ball as the counterface. Tests were conducted at various normal loads and speeds. In dry condition at 3 N load ...

SU-8, a very promising structural polymer for the next-generation 3D fabrication of micro-electromechanical systems (MEMS), has extremely poor tribological properties. The improvement in tribological properties has been recently addressed by developing SU-8/talc (30 wt%) /perfluoropolyether (PFPE) (30 wt%) composite. This composite showed wear durability approximately five orders of magnitude greater in comparison with that of pure SU-8. This drastic increment was found to be because of the in situ lubrication mechanism provided by the PFPE liquid droplets present in the composite. In this present investigation, the lubrication mechanism for SU-8/talc (30 wt%)/PFPE (10, 20 and 30 wt%) composites was further investigated by varying sliding speed (0.1–1.0 m/s) and normal load (2 N and 4 N) using silicon nitride ball of 4 mm diameter as the counterface. The data show that the coefficient of friction and interfacial shear strength follows linear relations with the logarithm of the sliding velocity. Normal load has effect on marginally reducing the coefficient of friction.

In an earlier work, we demonstrated the development of SU-8 composites using perfluoropolyether (PFPE) as lubricant filler which reduced friction coefficient by ~7 times and enhanced wear life of SU-8 by more than four orders of magnitude. In this work, we have investigated the role of chemical bonding between SU-8 and PFPE molecules using two types of PFPE lubricants (i.e., Fomblin® Z-dol and Z-03) in improving the tribological properties of the composite. Z-dol has polar (–OH) end groups whereas Z-03 has non-polar (CF3) end groups. SU-8 with Z-dol (SU-8 + Z-dol) films yielded ~8 times greater wear life than SU-8 with Z-03 (SU-8 + Z-03) films and more by four orders of magnitude than pure SU-8. The nature of the films was analyzed in detail by chemical and physical characterization techniques like X-ray photoelectron spectroscopy, water contact angle and thermo-gravimetric analysis. The results validated the role of polar end functional group of Z-dol in covalent binding with SU-8 upon UV plasma treatment that resulted in improved tribological properties.

Purpose – The purpose of this study is to investigate the effects of zinc dialkyl dithiophophates (ZDDP) and ash-less triphenyl phosphorothionate (TPPT) on hydrogen-free diamond-like carbon (DLC) coatings. For many years, ZDDP have traditionally been used in engine oils as antiwear (AW) and extreme pressure (EP) additives. However, additives containing sulfated ash, phosphorus and sulfur (SAPS) have a detrimental effect on the exhaust after-treatment device found on modern vehicles. Besides the automotive industry, DLC is also used in hydraulic applications where zinc-free and ash-less hydraulic fluids have gradually gained popularity in recent years. Design/methodology/approach – The tribological tests were performed using a disk-on-cylinder tribometer, where the stationary hydrogen-free DLC-coated steel disk formed a line contact with an uncoated rotating steel shaft under lubricated conditions. Findings – It was found that TPPT and ZDDP separately at a concentration of 1.0 wt% increased the amount of friction of the base oil by approximately four times. TPPT appeared more effective than ZDDP in minimizing wear on the DLC-coated surface. Also, primary ZDDP seemed to have a more detrimental effect on the DLC-coated surface compared to a mixture of primary and secondary ZDDP. With regard to surface roughness of the hydrogen-free DLC-coated surface, the values corresponding to a lubricant containing TPPT were lower than those obtained for a lubricant with ZDDP and a lubricant without any additive. Originality/value – This is the first report on the effects of ZDDP and ash-less TPPT on the tribology of hydrogen-free DLC coatings.