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To meet the requirements of friction and corrosion resistance performance of helicopter transmission bearings under harsh environments, Ti/TiN/Ti-DLC multilayer composite films were prepared on a 40Cr15Mo2VN substrate by a non-equilibrium magnetron sputtering technique. The effects of different titanium currents on the structure, mechanical properties, and friction properties of the films were investigated by SEM, Raman spectroscopy, and nanoindentation. Moreover, the tribological and corrosion resistance of developed films under acidic conditions were investigated. The results show that the sp3-C/sp2-C ratio in the films gradually decreases with increasing Ti current from 0 A to 2 A, leading to decreased hardness and elastic modulus. The bonding force of the DLC films also gradually increases with increasing Ti current and reaches the maximum value of 41.69 N at 2 A; the friction coefficient of the films gradually decreases under a load of 20 N. In summary, the best performance of thin film at Ti-2 A was compared with the corrosion and wear performance of thin film and substrate in acetic acid solution and aqueous solution at Ti-2 A. The wear amount of thin film and substrate in aqueous solution is significantly lower than in acetic acid solution, and the corrosion potential of thin film is higher than that of substrate in both solutions, which can play a protective role against the substrate. [ABSTRACT FROM AUTHOR]

A series of Cr1-xAlxN (where x denotes the atom fraction of Al in Cr1-xAlxN film) films with different Al contents have been deposited by unbalanced reactive magnetron sputtering technique. The chemical composition, microstructure, surface morphology, cross-sectional structure, mechanical properties, thermal stability and tribological properties of the deposited films were studied by means of different techniques. It is found that with the increase of Al doping, the Al atoms either substitute the Cr atoms or occupy the interstitial sites in the CrN crystal lattice firstly, and when the Al doping content exceeds the solid solubility, superfluous Al atoms then exist in the form of amorphous or nanocrystal state in the films. Meanwhile, the grain size becomes smaller, and the microstructure gets denser because the Al doping leads to multiple crystal orientations and inhibits the grain growth. The Al doping induced solid solution hardening and grain boundary effects contribute to the high hardness of CrAlN films, and the dense structure as well as interstitial solid solution of Al, which can block the diffusion channel, endows the CrAlN films good oxidation resistance. Besides, a small amount of free Al existing in the films is favorable to improve the thermal stability without obvious loss of hardness. Finally, the relatively high hardness and good thermal stability make the Cr0.29Al0.71N film has relatively good tribological properties than CrN film under a wide temperature range, which extends the operating temperature of the CrN films in some fields. [ABSTRACT FROM AUTHOR]

Abstract: Amorphous hydrogenated carbon (a-C:H) films were deposited by medium frequency unbalanced magnetron sputtering with Ar/CH4 gases. The microstructure and vacuum tribological properties of the films in relation to internal stress and applied load (1, 2, 4 and 5N) were investigated. The results show that the bonded hydrogen in the film decreases and the graphitization of the film increases with increasing Ar ratio in the source gases. Meanwhile, all the films have ultra-low friction coefficients (about 0.005) but relatively short sliding lifetimes (shorter than 900s) in vacuum. Furthermore, the film can maintain a sliding lifetime longer than 3600s either by lower the internal stress (annealed at 200°C) or sliding at a small applied load (1N). It has been found that relaxation of the internal stress is the main case of the short sliding lifetime in vacuum, whereas it does not occur in air under the same tested conditions. [Copyright &y& Elsevier]

Abstract: Graphite-like amorphous carbon (GLC) films were fabricated by unbalanced magnetron sputtering on silicon and stainless steel substrates. The effects of deposition bias voltage on the microstructure, mechanical and tribological properties of the resultant films were investigated by means of X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), high resolution transmission electron microscopy (HRTEM), nano-indentation and tribological experiments, respectively. The results show that the present films are dominated by sp2 sites, and the microstructure and properties of the resultant films strongly depend upon the deposition bias voltage. Namely, the sp3 content, hardness, elastic modulus and critical load monotonically increase with increasing deposition bias voltage from 50 to 150V, and then they decrease with further increasing the bias voltage to 185V, while internal stress decreases at first and then increases with further increasing of deposition bias voltage. The films deposited at different bias voltages have high surface roughness. Tribological properties of the films are closely related with the deposition bias voltage, 150V is the optimum value for obtaining good wear resistance. [Copyright &y& Elsevier]

Abstract: Two types of diamond-like carbon (DLC) films with different bonding configurations were produced by pulse-assisted and DC-assisted plasma chemical vapor deposition. The chemical composition, surface morphology, microstructure, internal stress and tribological properties of the two films before and after the ultraviolet (UV) irradiation were investigated and compared. It was found that the UV irradiation had little effects on the chemical composition and surface morphology of both the films, but greatly influenced their tribological properties in the opposite trends. This result was attributed to the different changing outcomes of the bonding configuration induced by the UV actions of primary photo-dissociation and secondary recombination, wherein the inherent bonding configuration and internal stress played important roles. [Copyright &y& Elsevier]

Abstract: Mo doped diamond-like carbon (Mo/DLC) films were deposited on Si substrates via unbalanced magnetron sputtering of molybdenum combined with plasma chemical vapor deposition of CH4/Ar. The microstructure of the films, characterized by transmission electron microscopy and selected area electron diffraction, was considered as a nanocomposite with nano-sized MoC particles uniformly embedded in the amorphous carbon matrix. The structure, morphology, surface composition and tribological properties of the Mo/DLC films before and after the atomic oxygen (AO) irradiation were investigated and a comparison made with the DLC films. The Mo/DLC films exhibited more excellent degradation resistant behaviors in AO environment than the DLC films, and the MoC nanoparticles were proved to play a critical role of preventing the incursion of AO and maintaining the intrinsic structure and excellent tribological properties of DLC films. [Copyright &y& Elsevier]

Abstract: Hydrogenated diamond-like carbon (DLC) films were deposited on Si (100) wafers by a plasma enhanced chemical vapor deposition technique using CH4 plus H2 as the feedstock. The effect of annealing temperature on the structure, mechanical and tribological properties of the resulting films were investigated by means of Raman spectroscopy, Fourier transformation infrared spectroscopy nanoindentation, stress analyzer and friction and wear testing on a ball-on-disk test rig. The results showed that the structure, hardness, Young''s modulus and the tribological properties of the films had no significant changes at lower annealing temperature up to 200 °C. At higher temperature above 200 °C, the annealing caused the effusion of hydrogen and the sp3 to sp2 transformation, which in turn, led to the more graphite-like structure with poorer mechanical and tribological properties. It was also found that the tribological properties were dependent not only on the annealing temperature, but also on the testing environment. The roles of annealing and environment in the tribological properties of DLC films are discussed in terms of the annealing-induced changes in the structure and mechanical properties of the films and the friction-induced physical and chemical interactions among the DLC films, steel ball and water and/or oxygen molecules. [Copyright &y& Elsevier]

Abstract: Friction behaviors of hydrogenated diamond-like carbon (DLC) film sliding against steel ball were investigated on a ball-on-disk test rig in different environment. The worn surface morphology of the steel ball was observed on a scanning electron microscope (SEM), and 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 friction behaviors of hydrogenated DLC film were very sensitive to the testing environment. In dry N2, the film provided a much low and stable friction coefficient of about 0.035. When the friction tests were performed in higher relative humidity and in dry O2, higher and unstable friction coefficient of more than 0.2 was obtained. It was found that in oxygen and/or water containing environments, the transferred carbon-rich layer on the counterpart steel ball was inhibited, and the friction-induced oxidation of the DLC film surface and the chemical reactions between the DLC film and steel ball were involved in the friction processes, which accounted for the higher friction coefficient of the DLC film. The roles of environment in the friction behaviors of DLC film were discussed in terms of the friction-induced physical and chemical interactions among the DLC film, steel ball and water and/or oxygen molecules. [Copyright &y& Elsevier]

Multi-Arc Ion Plating (MAIP) technology was used to deposit yttrium oxide (Y 2 O 3) ceramic thin films on Al 2 O 3 ceramics and silicon wafers. The effects of varying the O-to-Ar gas flow ratio (Rc: 0.5, 1.0, 1.5, 2.0) and the annealing conditions on the phase composition, microstructure, mechanical properties, and tribological performance of the Y 2 O 3 films were assessed. The films deposited at Rc values of 1.0 and 1.5 consisted of a single cubic phase structure. In contrast, films deposited at Rc values of 0.5 and 2.0 contained a small monoclinic phase and the cubic phase structure. The film deposited at an Rc value of 1.0 (oxygen flow rate of 200 sccm) exhibited a dense microstructure, the best mechanical properties (hardness of 14.2 ± 0.191 GPa), and the lowest friction coefficient (0.142 ± 0.003). Furthermore, the colour of the film changed from grey-black to white after annealing at 800 °C for 6 h. The oxygen vacancy of the thin film increased, with improving crystallinity, decreasing hardness and elastic modulus, and increasing grain size, friction coefficient and wear rate. The film exhibited the best tribological properties at 25 °C. [ABSTRACT FROM AUTHOR]

The effect of duty cycle on the microstructure and properties of graphite-like amorphous carbon films prepared by unbalanced magnetron sputtering was investigated. The structure of the resultant carbon film is amorphous, as shown by high-resolution transmission electron microscopy. Raman analysis shows that the studied films are dominated by sp2 sites, and the intensity ratio of the D and G peaks ranges from 4.0 at a duty cycle of 20% to 6.0 at 50%, which is one order of magnitude larger than that of diamond-like carbon films, indicating an obvious increase in sp2 sites with duty cycle. The surface morphology was investigated by atomic force microscopy. The images show that the as-deposited carbon films have a very rough surface, and the maximum granular structure size is up to 180 nm in diameter and 50 nm in height. The hardness and internal stress of the resultant carbon films increase with increasing duty cycle, accompanied by an increase in sp2 fraction in the films, which is different from the diamond-like carbon films. In addition, the resultant carbon films show superior tribological properties with high load-bearing capacity and excellent wear resistance. The influence of duty cycle on the microstructure and properties is discussed in detail. [ABSTRACT FROM AUTHOR]

Highlights: [•] The doping effects of Ag on DLC film were investigated thoroughly. [•] The Ag concentration in the film was controlled by changing Ar/CH4 ratios. [•] The vacuum tribological properties of Ag/DLC film were investigated firstly. [•] The mechanisms related to it were also discussed. [ABSTRACT FROM AUTHOR]

Abstract: A serial of crystalline titanium oxide ceramic films were deposited at low temperature using microwave electron cyclotron resonance (MW-ECR) magnetron sputtering with different O2/Ar ratios. The influences of O2/Ar ratio on the deposition rate, morphology, crystalline nature, optical adsorption property of the obtained titanium oxide thin films were investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and UV–Vis spectra. Therefore, the optimum O2/Ar ratio for deposition of anatase TiO2 thin films on unheated glass substrate was realized in a MW-ECR magnetron sputtering process. The as-deposited anatase TiO2 films were transparent and were antireflective in the visible region. [Copyright &y& Elsevier]

Abstract: In this study, CrN films were deposited on stainless steel and Si (111) substrates via medium frequency magnetron sputtering under a systematic variation of the substrate bias voltage. The influence of the substrate bias voltage on the structural and the mechanical properties of the films were investigated. It is observed that there are two clear regions: (1) below −300V, and (2) above −300V. For the former region, the (111) texture is dominated as the substrate bias voltage is increased to −200V. The lattice parameter is smaller than that of CrN reported in the ICSD standard (4.140Å) and the as-deposited films exhibit tensile stress. Meanwhile, the surface roughness decreases and the N concentration show a slow increase. For the latter region, the (200)-oriented structure is formed. However, the lattice parameter is larger as compared with the value reported in the ICSD standard, and the surface roughness increases and the N concentration decreases obviously. In this case, the compressive stress is obtained. [Copyright &y& Elsevier]

Abstract: Hydrogenated amorphous carbon (a-C:H) films were deposited on steel and silicon wafers by unbalanced magnetron sputtering under different CH4/Ar ratios. Microstructure and properties of the a-C:H films were investigated via Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Atomic force microscopy (AFM) and substrate curvature method. The results revealed that CH4/Ar ratio played an important role in the H content but acted a little function on the sp3/sp2 ratio of the films. Also, the internal stress of those films was relatively low (<1GPa), and the deposition rate decreased firstly and then increased with the decrease of the CH4 fraction. The film deposited under CH4/Ar=1/1 (55sccm/55sccm) with moderate sp3 C–H / sp3 C–C had the best tribological properties. The composition, microstructure and properties of the a-C:H films were strongly dependent on the deposition process and composition of reactant gases. [Copyright &y& Elsevier]

MoS 2 -based films are the most widely used solid lubrication materials in the space environment. However, the environmental sensitivity of MoS 2 determines its low lifetime in low-orbit space environments rich in atomic oxygen (AO). To solve this problem, we optimize the film structure by doping with LaF 3 , which has a hexagonal structure and grain refinement properties. The TEM-FIB cross-section visualization illustrates that the LaF 3 doping can further reduce the voids in the film and improve densification, which improves the AO-resistance of the film and maintains excellent tribological properties with a low friction coefficient of 0.017 and a friction life of more than 1.5 × 106 laps after high-flux AO irradiation. [ABSTRACT FROM AUTHOR]

Abstract: The CrAlN films were deposited on silicon and stainless steel substrates by unbalanced magnetron sputtering system. The influence of substrate bias on deposition rate, composition, structure, morphology and properties of the CrAlN films was investigated. The results showed that, with the increase of the substrate bias voltage, the deposition rate decreased accompanied by a change of the preferred orientation of the CrAlN film from (220) to (200). The grain size and the average surface roughness of the CrAlN films declined as the bias voltage increases above −100V. The morphology of the films changed from obviously columnar to dense glass-like structure with the increase of the bias voltage from −50 to −250V. Meanwhile, the films deposited at moderate bias voltage had better mechanical and tribological properties, while the films deposited at higher bias voltage showed better corrosion resistance. It was found that the corrosion resistance improvement was not only attributed to the low pinhole density of the film, but also to chemical composition of films. [Copyright &y& Elsevier]