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In the present investigation the effect of the substrate dilution on room and high temperature (550 and 700 °C) tribological behaviour of nickel based hardfaced coating deposited by plasma transferred arc onto a grey cast iron was investigated and compared to the uncoated grey cast iron. At room temperature, the wear loss of coatings was independent of the substrate dilution and similar to the grey cast iron. At high temperatures, coating produced with high dilution displayed the highest wear resistance between all the samples. This is attributed to the formation of a protective tribo-layer resulting from the agglomeration of a high amount of oxide debris due to its lower oxidation resistance when compared to the sample produced with low dilution. [ABSTRACT FROM AUTHOR]

In the last years, vanadium rich coatings have been introduced as possible candidates for self-lubrication due to their optimum tribological properties. In the present investigation, the influence of V incorporation on the wear performance of TiSiN films deposited onto WC substrates by d.c. reactive magnetron sputtering is reported. The results achieved for TiSiVN films were compared and discussed in relation to Ti 0.80 Si 0.15 N, TiN and Ti 0.82 V 0.15 N coatings prepared as references. The tribological properties of the coatings were evaluated at room temperature on a pin on disk tribometer equipment using two different counterparts: Al 2 O 3 and HSS balls. The wear tracks, ball-wear scars and wear debris were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDS). Tribological tests indicated that the wear rate and the friction coefficient of Ti 0.80 Si 0.15 N coating decreased with continuous increase of V content being the overall behavior strongly dependent on the counterpart ball material. For Al 2 O 3 balls the wear rate and friction coefficient of coatings were much lower compared to sliding against HSS steel balls. Ti 0.80 Si 0.15 N showed the lowest wear resistance among all tested coatings, independently of the counter-body. For V rich coatings tested with Al 2 O 3 balls the polishing wear mechanism was observed, whereas adhesion wear took place when tested against HSS balls. [ABSTRACT FROM AUTHOR]

Abstract: Pin-on-disc is widely used to evaluate tribological properties of thin films. However, the results are often present without standard uncertainties; moreover, in many cases the standard uncertainty is replaced by standard deviation, which is a strong underestimation of real uncertainty. In this study we have followed ISO and NIST guidelines to investigate the possible sources of uncertainties related to friction and wear rate measurement and to apply them on two selected coating systems – TiN and DLC. We show that influence of operator is a significant contribution to the uncertainty of the wear rate, particularly in the case of very low wear of DLC coatings. We discuss why variance should be used instead statistic deviation and suggest a method to calculate uncertainties in case of small number of measurements. The paper could be used as a guide to evaluate friction and wear data of thin films and coatings using the pin-on-disc technique. [Copyright &y& Elsevier]

Abstract: Amorphous carbon (a-C) based coatings are possible candidates as a surface treatment for various biocompatible materials used in medicine. In this study, the carbon coatings co-sputtered with Zr, deposited by dc unbalanced magnetron sputtering in Ar (non-hydrogenated, i.e. a-C/Zr) and Ar+CH4 (hydrogenated, i.e. a-C:H/Zr) discharges, were investigated and compared with pure carbon films. Polished pure commercial Ti grade 2 and Ti grade 5 ELI (Ti6Al4V) discs were used as substrates. To improve the coating/substrate adhesion, a gradient Ti-based interlayer was deposited (~450nm). The coating structure was characterized by X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy; the chemical composition was measured by electron probe microanalysis. The adhesion was evaluated by scratch-test and the hardness was measured by nanoindentation. Tribological testing of the coatings was carried out using unidirectional pin-on-disc experiments; pure titanium balls were used as counterparts. The wear rate of the coatings was negligible except for the films with the highest Zr content deposited on Ti grade 2 substrates. [Copyright &y& Elsevier]

Abstract: A W–S–C self-lubricating coating was deposited by d.c. magnetron sputtering from carbon and tungsten disulfide targets on steel substrates. The coating showed a carbon content of 42at% and a S/W ratio of 1.26. The film was characterized (structure, hardness, adhesion) and tribologically tested using a pin-on-disk device. The load and number of cycles were varied and the corresponding wear tracks were thoroughly investigated by several techniques. Moreover, the wear tracks were monitored with Raman spectroscopy including in-situ measurements. The W–S–C coating exhibited friction and wear decreasing with the applied load. It has been demonstrated that the running-in process is related with changes in the Raman spectra on the wear tracks. [Copyright &y& Elsevier]

Abstract: In this paper, we review the results on the tribological behavior of nanocomposite coatings composed of nanoplatelets of transition metal dichalcogenides (TMD) immersed in a C-rich amorphous matrix. It is shown that such a microstructure produces low friction coefficients under different operating conditions such as air humidity, contact pressure or temperature. Special attention is paid to the analysis of the worn surfaces after the tests by Raman spectroscopy, Auger electron spectroscopy and transmission electron microscopy. Nanoscale analysis of the wear track has revealed the formation of a thin tribolayer exclusively consisting of TMD platelets oriented to exhibit the lowest friction. In some cases, the depth reorientation of the originally randomly oriented TMD platelets as a reaction to the sliding process has been observed. This self-adaptation explains the low friction coefficient together with a high load-bearing capacity and a limited sensitivity to air humidity. Finally, future perspectives for self-lubricant nanocomposite coatings based on the TMD-C concept are presented. [Copyright &y& Elsevier]

Abstract: We have developed hard self-lubricant coatings combining a hard matrix (TiN) and a self-lubricant phase in the form of inorganic-like WS2 fullerene. The nanoparticles were injected from the preparation chamber directly to the sample surface during reactive sputtering from a Ti target in Ar/N2 atmosphere. The injection of the particles led to the local oxidation of the matrix due to the flow of residual oxygen from the preparation chamber; therefore, the final composite was TiN/Ti–O–WS2. The observation of the composite film by scanning and transmission electron microscopies showed the incorporation of the WS2 nanoparticles; however, their bonding with the matrix was weak. The analysis of the wear tracks did not show any presence of WS2 in the contact. [Copyright &y& Elsevier]

Abstract: Mo–S–C self-lubricating coatings were deposited by d.c. magnetron sputtering from carbon and molybdenum disulphide targets. The power ratio of the targets was varied in order to prepare films with carbon content in the range 0–55at.%. Whatever the carbon content, the S/Mo ratio was higher than 1.25. The hardness of the films increased almost linearly with the carbon content. X-ray photoelectron spectroscopy showed evidence of Mo–C bonds; nevertheless, the size of molybdenum carbide grains was expected to be very small, since X-ray diffraction did not reveal any peaks related to any Mo–C phase. The coatings tested by pin-on-disc exhibited low friction, decreasing with increasing carbon content, when humid air was present. In nitrogen, the friction of all films was lower than 0.02 except for the reference MoS2 (0.04). Mo–S–C outperformed the wear resistance of MoS2; on the other hand, the results were in some cases hindered by the low adhesion of the coatings. The films were very sensitive to air exposure leading to surface oxidation. [ABSTRACT FROM AUTHOR]

Abstract: Chromium nitride-based coatings are often used in application at high temperature. They possess high wear and oxidation resistance; however, the friction coefficient is typically very high. Therefore, we doped CrN coatings by carbon with the aim to improve tribological properties at elevated temperature, particularly to lower the friction. CrCN coatings were prepared by cathode arc evaporation technology using constant N2 flow and variable C2H2 flow. The coatings with a thickness of 3–4μm were deposited on hardened steel substrates and high-temperature resistant alloy. The carbon content varied from 0at.% (i.e. CrN) up to 31at.%. The standard coating characterization included the nano-hardness, adhesion, chemical composition and structure (including hot X-ray diffraction). Wear testing was done using a high temperature tribometer (pin-on-disc); the maximum testing temperature was 700°C. The coatings with carbon content 12–31at.% showed almost identical tribological behaviour up to 700°C. [Copyright &y& Elsevier]

Abstract: The tribological properties of nitrides and oxides of transition metal thin films deposited by reactive magnetron sputtering have been thoroughly studied for three decades. Nevertheless, there are still several gaps in knowledge. The majority of studies are focused on a limited number of metals, namely Ti, Al and Cr, while other potentially attractive compounds are aside the main attention. Even in case of TiN, probably the most studied hard thin film, the frictional and wear behaviour brings many controversies. Despite significant progress of analytical and computational methods, the analysis of the wear behaviour is still a great challenge. We are presenting here a summary of our recent work on tungsten nitride (nitrogen content 0–58at.%) and tungsten oxide (oxygen content 0–75at.%) coatings deposited by reactive magnetron sputtering. Our aim has been the analysis of the connection of fundamental properties of these films, such as chemical composition, structure, hardness, Young’s modulus and residual stress, with their tribological properties – friction coefficient and wear rate. We have been focused mainly on the description of the dominant wear mechanisms influencing the tribological properties. The tribological tests have been carried out both at room and elevated temperature; the temperature was increased in steps until immediate coatings failure. The tungsten nitride coatings with the “worst” parameters generally considered as vital for high wear resistance, such as hardness, were considered to have the best tribological performance. [Copyright &y& Elsevier]

Abstract: Chromium nitride (CrN) and multilayers Cr/CrN coatings were deposited by low cathodic arc technology. The thickness of Cr and CrN layers was identical; two different multilayer coatings were deposited with layer thicknesses of 85 and 160 nm. The structural analysis showed that CrN coatings exhibited the cubic CrN phase, while a mixture of CrN, Cr2N and Cr phases was observed in the case of multilayers. The annealing of the samples at 800 and 900 °C in air led to: (1) the decomposition of the chromium nitride phases into chromium; (2) a moderate oxidation by forming a thin Cr2O3 layer on the coating surface and, (3) carbon diffusion from the steel substrate. The chemical composition depth analysis performed by glow discharge optical emission spectroscopy (GDOES) showed a nitrogen-rich layer below the surface oxide layer for Cr/CrN multilayers. The multilayer structure, clearly visible by GDOES at room temperature, disappeared at 800 °C. Friction and wear analysis carried out by pin-on-disc in the temperature range 600–800 °C followed by the wear track observation by scanning electron microscopy showed that the dominant feature influencing the tribological properties was the formation of a tribolayer. The tribolayer consisted of small wear debris particles of chromium oxide pressed together and well adhered in the wear track. The multilayer Cr/CrN coatings showed a slightly better wear resistance than CrN film. [Copyright &y& Elsevier]

Abstract: Transition metal dichalcogenides belong to the more developed class of materials for solid lubrication. However, the main limitation of these materials is the detrimental effect of air humidity causing an increase in the friction. In previous works, molybdenum diselenide has been shown to be a promising coating retaining low friction even in very humid environment. In this study, Mo–Se–C films were deposited by sputtering from a C target with pellets of MoSe2. Besides the evaluation of the chemical composition, the structure, the morphology, the hardness and the cohesion/adhesion, special attention was paid to the tribological characterization. The C content varied from 29 to 68at.% which led to a progressive increase of the Se/Mo ratio. As a typical trend, the hardness increases with increasing C content. The coatings were tested at room temperature with different air humidity levels and at temperatures up to 500°C on a pin-on-disc tribometer. The friction coefficient of Mo–Se–C coatings increased with air humidity from ∼0.04 to ∼0.12, while it was as low as 0.02 at temperature range 100–250°C. The coatings were very sensitive to the elevated temperature being worn out at 300°C due to adhesion problems at coating–titanium interface. [Copyright &y& Elsevier]

Abstract: Transition metal dichalcogenides (TMD) have been one of the best alternatives as low friction coatings for tribological applications, particularly in dry and vacuum environments. However, besides their deficient behavior in humid containing atmospheres, their extensive application has also been restricted due to their low load-bearing capacity. In order to overcome these problems, recently the alloying with C has been tried with the expectation of simultaneously improving the coatings hardness and reaching sliding contacting phases more convenient for achieving low friction in humid environments. The practical application of this concept was extensively studied with the W–S–C system, with the C addition being achieved either by reactive or co-sputtering processes. The best tribological results were obtained by co-sputtering from a C target embedded with an increasing number of WS2 pellets. Excellent results were reached from the more than one order of magnitude increase in the coatings hardness up to friction coefficients which are close to those of the references of self-lubricating coatings: TMD for dry or vacuum atmospheres or C-based coatings for terrestrial sliding conditions. Following the good results achieved with W–S–C system, other TMDs systems have been envisaged to be studied. The main focus was placed on the Mo–Se–C system. In this paper, the general comparison between W–S–C and Mo–Se–C coatings is presented. The main effort is pointed on the tribological behavior of both systems when tested by pin-on-disk against steel counterpart balls under different testing conditions: applied normal loads, temperatures and relative humidity of the atmospheres. Both coatings were deposited by co-sputtering from a C target with a varying number of TMD pellets which could lead to C contents in the films in the range from 30 up to 70at.%. A Ti interlayer was interposed between the films and the substrates for improving the adhesion. Typically, W–S–C films are harder than Mo–Se–C films. From the tribological point of view, W–S–C films are more thermally stable than Mo–Se–C films although the friction coefficients of these last ones are lower when tested in humid containing atmospheres. [Copyright &y& Elsevier]

Abstract: W–S–C films were deposited by magnetron sputtering in an Ar atmosphere with a Ti interlayer. A carbon target with several pellets of WS2 incrusted in the zone of the preferential erosion was used. The number of pellets was changed to modify the carbon content in the films, which varied from 29 up to 70at%. Doping W–S films with carbon led to a substantial increase of the hardness in the range 4–10GPa; the maximum of hardness was obtained for coatings with the carbon content of 40at%. X-ray diffraction (XRD) patterns showed that there was a loss of crystallinity with the increase of the carbon content in the film. The coatings were tested by pin-on-disk from room temperature (RT) up to 400°C. At RT, the friction coefficient was in the range 0.2–0.30. At temperatures higher than 100°C, the friction is below 0.05 for all compositions. The tribological behavior of the coatings with increasing temperatures depended on the films carbon content. For low-carbon content up to 40%, the wear rate was almost independent of the temperature up to 300°C, while it increased dramatically in the case of the coatings with high-carbon content. In general, the limiting temperature for W–S–C coatings is 400°C. [Copyright &y& Elsevier]

Abstract: In this study, tungsten oxide coatings with 13 and 75at% of oxygen were prepared by DC reactive magnetron sputtering from a pure W target in an Ar+O2 atmosphere. The coating hardness (H) decreased with increasing oxygen content from 25 to 7.7GPa. The values of H/E ratio were 0.08 and 0.07 for W87O13 and W25O75, respectively. The tribological measurements were carried out on a pin-on-disc tribometer at room temperature, with a load of 5N and steel 100Cr6, ceramic Si3N4 and Al2O3 balls as sliding partners. The wear track and wear debris were visualised by scanning electron microscopy and the chemical composition of the later was estimated by energy-dispersive X-ray analysis. The friction coefficient was rather high in case of the W87O13 coating reaching values in the range from 0.7 to 0.75 for both counterpart materials, and slightly lower for W25O75 (∼0.50). The coating wear rate decreased with increasing oxygen content with the Al2O3 ball, while using Si3N4 ball as a counterpart showed an opposite trend. The coating with low oxygen content was more resistant to abrasive wear. [Copyright &y& Elsevier]

Abstract: CrN coatings prepared by low arc deposition technology on hardened steel substrates were studied in this paper. Wear testing was done using a high temperature tribometer (pin-on-disc); the maximum testing temperature was 500 °C in order to prevent significant softening of substrate. Evaluation of friction coefficient with the number of cycles was measured at different temperatures and the wear rates of coatings and balls were determined. Three different materials were used as counter-parts: 100Cr6 bearing steel, Si3N4 and Al2O3 balls with a diameter of 6 mm. The coating microstructure was studied by X-ray diffraction (XRD) measured in situ up to 600 °C; the chemical composition was obtained by energy dispersive X-ray analysis (EDX). Mechanical properties of these coatings were studied by scratch and microhardness testing. Morphology of coating surface, ball scars, wear tracks and wear debris were examined by scanning electron microscopy (SEM). The experiments have shown strong dependency of tribological parameters on temperature. Wear of CrN coating sliding against the 100Cr6 ball was not measurable. Generally, the wear rate of coating increases with temperature when sliding with ceramic balls. The wear debris analysis has shown that the tribochemical wear is dominant at high temperature (Si3N4 balls), while the sliding process with the Al2O3 balls can be described as a three-body wear with the wear particles consisting mainly of chromium oxides conglomerated into relatively homogenous layer protecting coating from rapid wear. The average dimension of wear particles decreases with temperature, while the protecting layer thickness increases. [Copyright &y& Elsevier]

Abstract: The tribological behaviour of TiCN coating prepared by unbalanced magnetron sputtering is studied in this work. The substrates made from austenitic steel were coated by TiCN coatings during one deposition. The measurements were provided by high temperature tribometer (pin-on-disc, CSM Instruments) allowing measuring the dependency of friction coefficient on cycles (sliding distance) up to 500°C. The evolution of the friction coefficient with the cycles was measured under different conditions, such as temperature or sliding speed and the wear rate of the ball and coating were evaluated. The 100Cr6 balls and the Si3N4 ceramic balls were used as counter-parts. The former were used at temperatures up to 200°C, the latter up to 500°C. The wear tracks were examined by optical methods and SEM. The surface oxidation at elevated temperatures and profile elements composition of the wear track were also measured. The experiments have shown considerable dependency of TiCN tribological parameters on temperature. Rise in temperature increased both friction coefficient and the wear rate of the coating in case of 100Cr6 balls. The main wear mechanism was a mild wear at temperatures up to 200°C; fracture and delamination were dominating wear mechanisms at temperatures from 300 to 500°C. [Copyright &y& Elsevier]

Abstract: PVD-coated instruments are often used at elevated temperatures. However, the friction and wear data of these coatings at temperatures exceeding room temperature are still lacking. In order to help remedy this lack, three coatings widely spread in industrial applications, TiN, TiCN and CrN, taken from standard production of customer''s coating centre were comparatively measured up to 500 °C. The coatings were deposited on hardened steel substrates either by unbalanced magnetron sputtering or arc evaporation deposition. The measurements were done using a high-temperature tribometer (pin-on-disc, CSM Instruments). The evolution of friction coefficient with sliding distance (number of cycles) was measured at different temperatures and the wear rate of the ball and coating were evaluated. 100Cr6 balls and the Si3N4 ceramic balls were used as counterparts. The wear tracks were examined optically and by SEM. The surface oxidation at elevated temperatures and chemical composition inside and outside the wear track was also measured by EDX analysis. [Copyright &y& Elsevier]

Providing lubrication at high temperature in the presence of oxygen is a significant technological challenge. We apply reactive molecular dynamics to study tribological properties of vanadium pentoxide, an active lubricious component of oxidation-resistant hard coatings. We explore sliding on V 2 O 5 in a wide range of conditions and note its tendency to melt in sliding conditions at elevated temperatures and/or pressures. We observe a stick-slip-like collective mechanism of sliding in crystalline V 2 O 5 at room temperature, that requires further exploration from theoretical prospective. We find that even a single layer of V 2 O 5 on the surface of the coating is an effective lubricant at high temperatures, which is a vital piece of information for coating design. • Crystalline V 2 O 5 at room temperature exhibits a stick-slip-like collective mechanism of sliding. • At elevated temperatures or high loads in sliding conditions V 2 O 5 melts, reducing friction. • Coefficient of friction of V 2 O 5 reduces with the increase of temperature. • Sliding force of amorphous/liquid V 2 O 5 depends on the network connectivity. • Even a single layer of V 2 O 5 is an effective lubricant. [ABSTRACT FROM AUTHOR]

This work aims to study the influence of the thickness on the wettability behaviour and on the tribological performance of thin WS 2 –C coatings doped with fluorine (F) deposited by magnetron sputtering. The morphology of the coatings did not change with the thickness decrease, revealing an increase on both the compactness and on the smoothening of the coating surface with F increase. Such an evolution led to more hydrophilic and less oleophilic surface behaviour. XRD results showed that the coatings start growing with an alignment of the (002) planes parallel to the substrate, which changed for randomly oriented crystals with the thickness increase. F insertion induced a decrease in the crystallinity, more evident in the case of thinner coatings. This result was corroborated by Raman analysis which showed a broadening of the main peaks assigned to WS 2. Tribological tests carried out at room temperature without lubrication showed lower friction coefficient for F-doped coatings, especially for the thinner one (in the overall test, average 0.03). Regarding the lubricated tests performed with pure PAO (polyalphaoleophin) oil, both thin coatings presented similar friction coefficients (∼0.07) in the steady-state regime. The tribolayer based on oriented W–S layers formed on the wear track for the F-doped coating can justify the very low friction achieved when testing in non-lubricated conditions. • F-containing W–S coatings contributes for the increased surface polarity and oleophobicity. • Thin coatings showed lower COF values than thick coatings when tested in RT condition. • In lubricated conditions, the oil repellence had a detrimental effect on the friction reduction. [ABSTRACT FROM AUTHOR]

Increasing requirements on high speed and dry cutting applications open up new demands on the quality of cutting tool materials. In this study, we evaluated the effect of Cr additions on the properties of Ti(Al)N/Cr(Al)N multilayered films deposited by magnetron sputtering. In particular, we studied the high temperature tribological properties and the cutting performance in real service drilling tests and compared the results with a monolayer Ti 0.47 Al 0.46 N reference film. Dry sliding experiments were performed using a pin-on-disc tribometer at room temperature and at 650 °C with Al 2 O 3 balls as counterparts. The drilling performance of the coatings was evaluated at cutting speeds in the range of 50–200 m/min. Wear of the drills in different zones (chisel edge and flank edge) was mapped after every 15 holes. [ABSTRACT FROM AUTHOR]

There are very few studies of PEEK wearing against DLC. In this study, DLC and Zr-DLC coatings were deposited by magnetron sputtering onto Ti alloy substrates. Coated and un-coated Ti alloy samples were tribologically tested in multidirectional pin-on-disk equipment against UHMWPE and PEEK. CoCr alloy was also tested as control. Each of the materials was tested for 2 million cycles (Mc) in bovine serum lubricant (37 °C). Gravimetrical weight loss and changes in surface profile were similar when tested against UHMWPE. However, Zr-DLC samples delaminated after 1.2 Mc. When tested against PEEK, both coated samples delaminated, despite that the coatings maintained their structural integrity. The synergetic effect of stress-induced corrosion through biological fluid and high cyclic shear stress may have caused interface fatigue and subsequent delamination of both coatings. [ABSTRACT FROM AUTHOR]

Amorphous carbon-based coatings (DLC) exhibit excellent mechanical and tribological properties such as high hardness, high elastic modulus, low friction and low wear. Reduced friction is often related to the formation of a low-friction tribolayer, which is formed during sliding and transferred to the counterpart. Here, we investigate the sliding of hydrogenated and non-hydrogenated DLC coatings alloyed with zirconium; pure DLC films are used as reference. The coatings were deposited by magnetron sputtering in Ar (non-hydrogenated) and Ar/methane atmosphere (hydrogenated) onto steel substrates and silicon wafers. The total thickness of the coatings was around 1.5 μm including a complex Ti/TiN/TiCN adhesion-improving interlayer with a thickness of 450 nm. All deposited coatings were amorphous, Zr/C ratio was approx. 0.05. The hardness was in the range of 9–13 GPa. Tribological tests were carried out in humid air at room temperature, at 100 °C and in nitrogen environment using pin-on-disk. Intermittent tribological test analysis has been performed to understand running-in behaviour. The worn surfaces and wear debris were analysed by Raman spectroscopy. Coatings alloyed with Zr showed lower friction and wear at room temperature compared to pure DLC. In general, Zr-doped hydrogenated coating outperformed the non-hydrogenated one when tested in an inert nitrogen atmosphere or at elevated temperature (100 °C), exhibiting almost super-low friction (μ = 0.03 in the steady-state regime) due to the formation of a homogenous, thick and stable tribolayer. [ABSTRACT FROM AUTHOR]

Abstract: In this work, self-lubricant W–S–C films were alloyed with Cr by co-sputtering chromium and composite WS2–C targets. Besides the usual physical, chemical and mechanical characterization, including the evaluation of the chemical composition, the structure, the morphology, the hardness and the cohesion/adhesion, special attention was paid to the friction and wear analyses of the film deposited on intentionally roughened surfaces. The substrates were steel polished disks with different types of patterns produced by micromachining. To analyze the sliding process, in-situ techniques were applied, such as optical microscopy and Raman spectroscopy monitoring of the wear track. The surfaces in the contact were then analyzed by scanning electron microscopy (SEM) and 3D profilometry. The results showed that W–S–C–Cr coating exhibited remarkable ability to reduce the detrimental effect of deep grooves with irregular shape. For specific patterns on the substrate the friction and wear was even slightly lower compared to a polished sample. The grooves were filled with self-lubricant material and acted as reservoirs supporting formation of a low-friction tribolayer. [Copyright &y& Elsevier]

Ti 1 − x Al x N coatings with NaCl-type structure have been widely used in advanced machining and other high temperature applications due to their excellent mechanical, thermal and tribological properties. Here, we investigated the influence of Cr additions on the structure, mechanical properties and oxidation resistance, including the oxide scale characterization, of multilayered TiAlN/CrAlN coatings deposited by magnetron sputtering. The properties of Cr rich coatings were compared to a TiAlN film deposited as reference. XRD diffraction analysis revealed that all coatings showed an fcc NaCl-type structure. However, for the TiAlN monolayer Ti and Al are forming a solid solution whilst, for Cr rich coatings, a multilayer structure alternating TiAlN and CrAlN layers, also forming solid solutions, was grown as a result of the geometry of the targets distribution inside the deposition chamber in combination with a slow rotation of the sample holder and a sufficiently high deposition rate. TGA measurements showed that Cr additions increased the oxidation performance of the coatings. For Ti 0.47 Al 0.46 N, dual oxide layers occur when tested at 800 °C, being the porous inner one of TiO 2 and the outer a compact and continuous layer of Al-oxide which protects the coating from the oxidation. At 900 °C the oxidation resistance of this film degraded due to the fast Ti ions diffusion to the surface which impedes the formation of the continuous and protective Al oxide layer. Cr rich coatings showed different oxides scales depending on their chemical composition. For Ti 0.30 Al 0.46 Cr 0.26 N and Ti 0.28 Al 0.34 Cr 0.42 N, a Ti-O rich layer is formed on the top of a protective Al-Cr-O layer when the samples were tested at 900 °C and 1000 °C, being the oxide layers thicker for the higher temperature. Concerning the coating with the highest Cr content (Ti 0.28 Al 0.31 Cr 0.51 N), a compact and continuous Cr(Al) 2 O 3 oxide layer was formed at 900 and 1000 °C with residual TiO 2 islands on the top, contributing for a significant enhancement of the oxidation resistance. [ABSTRACT FROM AUTHOR]

The effects of Ni–Ti(–Cu) interlayers on the mechanical and tribological behaviour of W–S–C/Ni–Ti(–Cu) and W:DLC/Ni–Ti(–Cu) bilayer coatings have been investigated. The mechanical properties of the bilayers, measured at different depths by nanoindentation, exhibited a clear dependence on the combination between different Ni–Ti(–Cu) interlayers and top layers. The tribological performance of the bilayers was evaluated by pin-on-disk under different load conditions. The use of Ni–Ti(–Cu) interlayers improved the adhesion of the top layers and the resistance against surface damage such as delamination and cracking. Transmission electron microscopy analyses performed in the wear tracks of W–S–C/Ni–Ti and W:DLC/Ni–Ti bilayers tested with high load revealed that the formation of stabilised martensite was limited when a much harder top functional layer was employed. [ABSTRACT FROM AUTHOR]

Hydrogenated diamond-like carbon coatings doped with tungsten were deposited by reactive magnetron sputtering from graphite and composite graphite/tungsten target in an Ar/methane atmosphere. Polished steel samples for laboratory testing and commercial valve tappets were used as substrates. The microstructure of the coating was studied by transmission electron microscopy (TEM), Raman spectroscopy, and electron energy loss spectroscopy, adhesion by scratchtest method and mechanical properties by depth sensing nanoindentation. Coatings were tribologically tested in lubricated contact in laboratory (pin-on-disc) and field (engine) conditions. The worn surfaces were analysed by Raman and time-of-flight secondary ion mass spectroscopies and observed by TEM. The coatings showed excellent wear resistance with negligible wear; the worn surface was covered by a very thin solid tribolayer formed from oil additives. [ABSTRACT FROM AUTHOR]

Abstract: Ag–DLC coatings with Ag contents ranging from 1.3at.% to 13.1at.% were deposited by DC magnetron sputtering. The coatings were characterized with respect to their structure (by means of XRD and Raman spectroscopy), mechanical and tribological properties (by scratch test, nanoindentation, residual stress measurements and pin-on-disk test). The incorporation of 13.1at.% Ag resulted in the formation of Ag grains of 2–3nm which promoted the increase of graphite like bonds organized in rings. Regarding the mechanical properties, no variations were found for films with Ag contents lower than 13at.%; a reduction of both hardness and compressive residual stress was then observed for higher values. Pin-on-disk tests were performed at two different contact pressures (690MPa and 1180MPa) in dry sliding conditions against a zirconia counterpart. For the lower contact pressure the variations in the wear rate are well correlated with the coating structure and mechanical properties, while for the higher contact pressure the presence of Ag is relevant and Ag–DLC coatings are showing higher wear rate than DLC one. SEM analysis revealed the formation of Ag aggregates on the wear track and adhesion of silver to the counterpart. [Copyright &y& Elsevier]

Transition metal dichalcogenides such as MoS 2 are widely used as solid lubricants for vacuum applications. On the other hand, diamond-like carbon coatings exhibit excellent sliding properties in the ambient environment. Our Mo-S-C coatings deposited by pulsed d.c. sputtering combine both structures to obtain stable properties regardless of the testing conditions. The coatings were studied using HR-TEM and Raman spectroscopy, revealing amorphous nature of the coating. The tribological properties were evaluated by pin-on-disc method. The results showed high lubrication ability in all the testing conditions. HR-TEM and Raman spectroscopy were employed to show the structural characteristics of the wear traces. Our results indicate that the low-friction effect should be attributed to carbon structure re-arrangement since expected wear-induced MoS 2 formation was not observed. • Mo-S-C coatings were deposited by pulsed d.c. sputtering from C and MoS 2 targets. • The Mo-S-C coatings were studied using HR-TEM and Raman spectroscopy. • The tribological properties were evaluated from the room temperature up to 200 °C. • Friction coefficients lower than 0.03 for all the testing conditions were observed. • Low-friction effect was predominantly attributed to carbon bonds re-arrangement. [ABSTRACT FROM AUTHOR]

Abstract: We deposited C-based films doped with Cu and tested their sliding properties in olive oil as environment-friendly lubricant, which can be used in many mechanical systems, particularly in agriculture engineering. The coatings were deposited in a four unbalanced magnetron sputtering device combining C and C/Cu targets; argon (hydrogen-free films) and Ar/CH4 (hydrogenated films) atmospheres were used. Cu content of the films was in the range 5–14at.%. The hardness of the films was almost constant whatever the Cu content was. On the other hand, hydrogen-free coatings were much harder (about 15GPa) than hydrogenated ones (about 4GPa). The coatings were oleophilic and their sliding properties were evaluated using ball-on-plate tests with 200,000 cycles. The non-hydrogenated coating with 6at.% of copper showed the best tribological performance with negligible wear for all olive oil testing temperatures (i.e. up to 120°C). [Copyright &y& Elsevier]