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Structure adhesion and corrosion resistance study of tungsten bisulfide doped with titanium deposited by DC magnetron co-sputtering
Abstract
Titanium-doped tungsten bisulfide thin films (WS2-Ti) were grown using a DC magnetron co-sputtering technique on AISI 304 stainless steel and silicon substrates. The films were produced by varying the Ti cathode power from 0 to 25W. Using energy dispersive spectroscopy (EDS), the concentration of Ti in the WS2 was determined, and a maximum of 10% was obtained for the sample grown at 25W. Moreover, the S/W ratio was calculated and determined to increase as a function of the Ti cathode power. According to transmission electron microscopy (TEM) results, at high titanium concentrations (greater than 6%), nanocomposite formation was observed, with nanocrystals of Ti embedded in an amorphous matrix of WS2. Using the scratch test, the coatings’ adhesion was analyzed, and it was observed that as the Ti percentage was increased,the critical load (Lc) also increased. Furthermore,the failure type changed from plastic to elastic. Finally, the corrosion resistance was evaluated using the electrochemical impedance spectroscopy (EIS) technique, and it was observed that at high Ti concentrations, the corrosion resistance
was improved, as Ti facilitates coating densification and generates a protective layer
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Thin film of tungsten oxide (WO3) has been studied extensively as an electrochromic material and has numerous applications in electrochromic devices, smart windows, gas sensors and optical windows. In order to explore the possibility of using it in electrochromic devices, thorough study the optical properties of the WO3 is an important step. The WO3 layers have been grown by hotfilament metal oxide deposition technique under atmospheric pressure and an oxygen atmosphere. By FTIR and Raman scattering studies we found that the films contain hydrates. We have observed that the thin films of WO3 can be satisfactorily grown by this technique.
The method of preparation tungsten disulfide thin film with RF sputtering on 3Cr13 martensitic stain less steel was researched in this paper. Different power, pressure and deposition time had been taken to prepare samples. Then the samples were tested by XRD, SEM to analyzing phase, surface topography and chemical constitution. Binding force and frictional wear coefficient of tungsten disulfide thin film was also tested. The results showed that non-crystalline tungsten disulfide thin film could be prepared by RF sputter, films’ S/W ratio were usually less-than 2,and were impacted by sputter technological parameter obviously, when the deposition power strengthen S/W ratio was lower, when the deposition time lengthen S/W ratio was higher. The binding force of the film was impacted by sputter technological parameter obscurely. The coefficient of friction of the sample prepared by RF sputter had inverselyproportional relationship with S/W ratio in definitive range.
Thin films of tungsten disulfide (WS2) were deposited on 3Cr13 martensitic stain less steel substrate by RF sputtering. The as-deposited films were annealed at 200,400 and 600°C for 2h in vacuum. The vacuum degree was 510-4Pa. Composition, surface morphology, structure properties and tribological behavior were studied by EDS, SEM, X-ray diffraction techniques and tribometer, respectively. At 200°C, the films showed low crystallization structure and the tribological behavior was not improved obviously. But at 400°C, the films tribological behavior were improved obviously and non-crystalline to hexagonal structural transition appeared. When annealing temperature rose to 600°C, the films were desquamated from substrate. The results suggested that suitable vacuum annealing was able to promote crystallization and improve tribological performance of RF sputtering WS2 films.
Adaptive nanocomposite coating materials that automatically and reversibly adjust their surface composition and morphology via multiple mechanisms are a promising development for the reduction of friction and wear over broad ranges of ambient conditions encountered in aerospace applications, such as cycling of temperature and atmospheric composition. Materials selection for these composites is based on extensive study of interactions occurring between solid lubricants and their surroundings, especially with novel in situ surface characterization techniques used to identify adaptive behavior on size scales ranging from 10−10 to 10−4 m. Recent insights on operative solid-lubricant mechanisms and their dependency upon the ambient environment are reviewed as a basis for a discussion of the state of the art in solid-lubricant materials.
Phase separation may occur in a way that the growth is not in extent but in amplitude. Only in the unstable region such a procedure is thermodynamically feasible. In a phase diagram the unstable region is defined by the spinodal. When a system has crossed this locus, phase separation occurs spontaneously without the presence of a nucleation step. This process is known as spinodal decomposition and commonly results to a high interconnectivity of the two phases. The Cahn-Hilliard equation describes the kinetics of the process. In this note both processes (nucleation and spinodal) are depicted schematically.
W/WC bilayers were grown using the DC magnetron sputtering technique and varying substrate temperature. The mechanical and tribological behaviors were characterized using the nanoindentation and pin-on-disk techniques. The hardness and Youngs modulus tended to increase, while the coef fi cient of friction tended to be stable with increasing substrate temperature. Moreover, better mechanical and tribological performances were observed for all of the coated systems compared with the uncoated steel. Furthermore, the inclusion of a W interlayer did not signi fi cantly in fl uence the hardness; nevertheless, this interlayer dramatically improved the coating tribological behavior, thus producing less coating damage and decreasing the wear rate.
TiSiN–WS2 hard-lubricant coatings were deposited on WC/TiC/Co cemented carbides by arc ion plating and middle-frequency magnetron sputtering. The microstructure, mechanical properties and tribological performance were examined. Results showed that WS2 layer had (0 0 2) and (1 0 1) multi-orientation structure and TiN grains of TiSiN layer became bigger due to the annealing effect in deposition of WS2 layer. As the thickness of WS2 layer increased, hardness of TiSiN–WS2 coatings decreased largely while the adhesive strength increased, which is mainly beneficial from the release of residual stress of TiSiN layer in deposition process of WS2 layer and the low tensile stress caused by the lubricant effect of WS2 in scratch test. The deposition of WS2 layer on top of TiSiN layer significantly improved coatings’ tribological performance with lower friction coefficient, less adhesive materials and smaller wear rate of steel ball. Even after WS2 layer was worn out, the friction coefficient was still lower than TiSiN coating, which is attributed to that WS2 remaining in wear track still worked.
Cobalt–chromium–molybdenum (CoCrMo) alloys are widely used in total hip and knee joint replacement, due to high mechanical properties and resistance to wear and corrosion. They are able to form efficient artificial joints by means of coupling metal-on-polymer or metal-on-metal contacts. However, a high concentration of stress and direct friction between surfaces leads to the formation of polyethylene wear debris and the release of toxic metal ions into the human body, limiting, as a consequence, the lifetime of implants.The aim of this research is a surface modification of CoCrMo alloys in order to improve their biocompatibility and to decrease the release of metal ions and polyethylene debris. Thermal treatment in molten salts was the process employed for the deposition of tantalum-enriched coating. Tantalum and its compounds are considered biocompatible materials with low ion release and high corrosion resistance.Three different CoCrMo alloys were processed as substrates. An adherent coating of about 1 μm of thickness, with a multilayer structure consisting of two tantalum carbides and metallic tantalum was deposited. The substrates and modified layers were characterized by means of structural, chemical and morphological analysis. Moreover nanoindentation, scratch and tribological tests were carried out in order to evaluate the mechanical behavior of the substrates and coating. The hardness of the coated samples increases more than double than the untreated alloys meanwhile the presence of the coating reduced the wear volume and rate of about one order of magnitude.
Thermomechanical processing (TMP) is associated with two major requirements: (i) to produce usable shapes through primary working (ingot breakdown) and secondary mill operations (hot rolling or forging) and (ii) to optimize mechanical properties through microstructure control during the different stages of the thermomechanical process. This paper reviews the thermomechanical processing of beta titanium alloys in general and high temperature deformation mechanisms, microstructure control during TMP, and final mechanical properties in particular.
Thin films of WO3 have been deposited from a gas mixture of WF6 and H2O in the temperature range 200–700°C. The microstructure of the films could be controlled by the total pressure and linear gas flow velocity. A homogeneous nucleation leading to a porous oxide film was observed at 50 Torr and low gas flow velocities. In contrast, depositions carried out at 10 Torr on sapphire (011̄2) substrates resulted in a wide deposition window for monoclinic WO3 films. These films exhibited a microstructure with columnar grains, with each grain exhibiting an epitaxial relation towards the substrate. The observed epitaxial orientations were determined to be (100)WO3//(011̄2)substrate, (010)WO3//(011̄2)substrate and (001)WO3//(011̄2)substrate with the corresponding in-plane relationships [110]WO3//[100]substrate, [101]WO3//[100]substrate and [011]WO3//[100]substrate. The deposition rate of the WO3 was higher than 1 μm/h also at 300°C. A kinetic investigation showed that the deposition process was controlled by mass transport.
Multilayered WC–Ti1−xAlxN coatings were deposited on AISI D2 steel using cathodic arc deposition method. These coatings contain structural defects such as pores or pinholes. Thus, the substrate is not completely isolated from the corrosive environment. These growth defects in the coatings are detrimental to corrosion resistance of the coatings used in severe corrosion environments. The localized corrosion of the coatings was studied in deaerated 3.5 wt.% NaCl solution using classical electrochemical technique (potentiodynamic polarization test). Coating characteristics were examined by means of glow discharge optical emission spectroscopy, scanning electron microscopy, auger electron spectroscopy and transmission electron spectroscopy. The porosity was calculated from a result of potentiodynamic polarization test of the uncoated and coated specimens. The calculated porosity is higher in the WC–Ti0.6Al0.4N than others, which is closely related to the packing factor. The positive effects of greater packing factor act on inhibiting the passage of the corrosive electrolyte to the substrate and reducing the localized corrosion kinetics. From the electrochemical tests and surface analyses, the major corrosion reaction of coatings is caused by defects (pores, pinholes and crevices), coating delamination and galvanic effect between the droplet and the coating.
The atmospheric pressure chemical vapour deposition reaction Of W(CO)(6), WOCl(4) or WCl(6) with HS(CH(2))(2)SH or HSC(CH(3))(3) at 350-600degreesC leads to thin films Of WS(2) on glass substrates. The WS2 films were nanocrystalline, showed a W:S ratio of 1:2 by EDAX and gave Raman bands at 416 and 351 cm(-1). The films were silver or gold in colour, adhesive to the substrate and showed Volmer-Webber type growth by SEM. Optical band gaps were 1.4 eV. The films were reflective in the visible region and transparent in the near IR.
WS2–Ag composite films were deposited on medium carbon steel substrate by RF magnetron sputtering method. The morphology and microstructure of the composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The tribological behavior was investigated using a ball-on-disk tribometer in vacuum and in humid air. In the range of Ag content of the film from 4.2 at.% to 40.4 at.%, Ag phase dispersed in amorphous WS2 matrix, and it changed from amorphous to crystalline structure with the increase of Ag content. The friction coefficients of composite films in humid air were lower and more stable than those of pure WS2 film, and the environmental sensitivity of tribological behavior decreased obviously with the addition of Ag in the films. At the content of 16.2 at.% Ag, the composite film was dense and adherent, and exhibited excellent tribological performance both in vacuum and in humid air.
The formation of ⊥c texture of WS2 thin films by solid state reaction between the spray deposited WO3 and gaseous sulfur vapours with Ni interfacial layer has been reported. X-ray diffraction technique has been used to measure the degree of preferred orientation and texture of WS2 films. Scanning electron microscopy, transmission electron microscopy and atomic force microscopy have been used to characterize the microstructure and morphology. The electronic structure and chemical composition was studied using X-ray photoelectron spectroscopy. The WS2 films comprise single crystalline quality hexagonal crystallites of 15μm×15μm size with their basal planes parallel to the substrate. The film consists of turbostratic stacking sequence of 2H and 3R polytypes of WS2. The tungsten-to-sulfur ratio was estimated to be 1:1.8. The various qualitative models used to explain promotional effects are briefly outlined and the plausible underlying mechanism of formation of ⊥c texture with nickel, in this study, is given.
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.
Thin sputtered tungsten films on various substrates (molybdenum or tungsten foils, quartz and glass slides) were reacted with H2S at temperatures from 400 to 1000 °C. In general, it was found that the WS2 crystallites nucleate from an amorphous WS3 phase. It was established that the substrate has a critical role in determining both the reaction onset temperature and the texture. For glass substrates, the reaction to give WS2 begins at T ⩾ 400 °C, and the WS2 grains grow predominantly with the van der Waals (vdW) planes parallel to the substrates (in this orientation, the c axis is perpendicular to the substrate, and is designated ⊥c) at 500 °C. On quartz substrates, reaction begins only at 650 °C and the texture is predominantly vdW planes perpendicular to the substrate )this orientation is designated ‖c) below 950 °C, and exclusively ∋ texture at higher temperatures. These differences between glass and quartz are believed to be due to sites on the quartz, absent (or present to a smaller extent) on glass, which strongly bind the tungsten and WS2. Molybdenum substrates give only the ‖c orientation even at 1000 °C, while bulk tungsten (or tungsten sputtered on tungsten) gives randomly oriented WS2. For oxidized tungsten on quartz, reaction onset is lowered to 500 °C (compared with 650 °C for W/quartz), and predominantly ⊥c orientation is obtained at 800 °C. Exclusively ⊥c orientation was never achieved with this system, even at 1000 °C. It was found that the ‖c orientation changes to the ⊥c orientation when diffusion conditions (temperature and time) were sufficient, indicating that the latter orientation is energetically favourable.
A theory to predict the orientation of radio-frequency (rf) sputter-deposited MoS2 films with respect to the substrate surface is presented. Oxygen-containing species such as H2O and -OH are postulated to be active sites that force crystallites to form with their basal planes perpendicular to the surface. X-ray diffraction is used to determine the crystallite orientation in films deposited on smooth, rough, or oxidized Si surfaces, as well as on fused silica or gold surfaces. The results support the theory. To produce MoS2 films with their crystallite basal planes parallel to a substrate surface (which has been suggested to be the low friction orientation), the active sites must be removed from the substrate by, for instance, heating in vacuum.
This study describes the synthesis, structure and friction behavior of titanium doped tungsten disulphide (Ti-WS2) nanocomposite solid lubricant thin films grown by cosputtering at room and 300 °C in situ substrate temperatures. The films were studied by focused ion beam (FIB) prepared cross-sectional scanning and transmission electron microscopies and X-ray diffraction (XRD) to determine the thin film structure and crystallinity as a function of varying titanium atomic percent and sputtering power. XRD confirmed that the pure WS2 thin films grown at room temperature (RT) and 300 °C were crystalline with hexagonal texture. Basal planes with c-axis orientated parallel to the substrate surface [(100) and (101) texture] were predominantly observed in all thin films. Co-sputtering at RT with any amount of Ti induced a dramatic change in the microstructure, i.e., Ti prevented the formation of crystalline WS2, making it amorphous with well-dispersed nanocrystalline (1–3 nm) precipitates. For RT friction tests, longer thin film lifetimes were exhibited when the thin films were doped with low amounts of Ti (∼ 5–14 at.%) in comparison to pure WS2 but there was no change in friction coefficient (∼ 0.1). For high temperature (500 °C) friction tests, slightly higher friction coefficients (0.2) but longer lifetimes were observed for the low at.% Ti doped thin films. Mechanisms of solid lubrication were studied by FIB prepared cross-sectional specimens and Raman spectroscopy wear maps inside the wear tracks to determine the sub-surface deformation behavior and formation of tribochemical products, respectively. It was determined that WS2 oxidized to form relatively low shear strength WO3 during wear (tribo-oxidation) and heating at 500 °C (thermal oxidation) as determined by Raman spectroscopy in the wear track and transfer film (third body) on the counterface.
Tungsten and molybdenum disulfides were produced in direct self-sustained combustion in argon between elementary sulfur and metal (W, Mo) nanopowders prepared by electrical explosion of wires. The results of XRD analysis show that the main phases of the synthesized nanopowders are hexagonal WS2 and MoS2. According to SEM and TEM observations, they are agglomerated nanolamellar particles of thickness 40–150 nm and width 100–3000 nm.Research highlights► Nanolamellar WS2 and MoS2 powders were prepared via direct reactions in argon. ► Addition of NaCl to Me+S mixtures results in a change of the reaction temperature. ► The sizes of coherent scattering regions for WS2 and MoS2 particles are 59 and 78 nm.
In this research work, W–S films doped with increasing contents of nitrogen and carbon were studied. The films were deposited with a Ti interlayer to promote the adhesion to the substrate. For low N or C contents the film presents the WS2 phase, whereas for higher content they are amorphous. Doping W–S films with N or C leads to significant improvements in the hardness (from 0.6 to 6 GPa). C-containing W–S films had better tribological behaviour than N-doped ones. In relation to undoped W–S films, more than one order of magnitude reduction in the wear coefficients was reached for W–S–C films, particularly for higher applied loads in the sliding contact (10 N).
Atomic-scale control and manipulation of the microstructure of polycrystalline thin films during kinetically limited low-temperature deposition, crucial for a broad range of industrial applications, has been a leading goal of materials science during the past decades. Here, we review the present understanding of film growth processes—nucleation, coalescence, competitive grain growth, and recrystallization—and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth. © 2003 American Vacuum Society.
The measurements of the Raman intensity are used mainly to determine quantitatively the amount, distribution and degree of crystallisation of different phases in a material, i.e. the Raman mapping. Our studies reveal that the analysis of relative and absolute Raman intensity is a very powerful tool, which allows to investigate and characterize the modifications of the structure in covalent bonded compounds, e.g. due to: (i) changes of BO6 octahedra by the substitution of the B site by lanthanides or rare earth elements and the incorporation of protons in the case of high temperature protonic conductors, (ii) changes of the long range order correlations as the function of the nanoregion organization: continuous evolution of the local symmetry towards the long range cubic one in the case of PbMg1/3Nb2/3O3–xPbTiO3 (PMN–PT) relaxor ferroelectrics, (iii) changes of the Si–O network caused by the depolymerisation resulting from the substitution of the Si4+ ions (covalent bonds) by the M+ cations (ionic bonds) or by the incorporation of the metallic nanoprecipitates and (iv) changes caused by the lixiviation/protonation of the surface layers of the Cultural Heritage stained glasses as a function of their corrosion degree and age.
The use of solid (dry) lubricants, particularly solid lubricant thin films, in space systems, including satellites and launch vehicles, is reviewed. Various types of satellites and their generic mechanical requirements are outlined. Mechanisms that use solid lubricant films are described. The types of solid lubricant films available, including burnished, bonded, and sputter-deposited, are reviewed and their properties assessed relative to application requirements. Future opportunities for insertion of solid lubricants as replacements for liquid or grease lubricants are identified.
Magnetron sputtering has become the process of choice for the deposition of a wide range of industrially important coatings. Examples include hard, wear-resistant coatings, low friction coatings, corrosion resistant coatings, decorative coatings and coatings with specific optical, or electrical properties. Although the basic sputtering process has been known and used for many years, it is the development of the unbalanced magnetron and its incorporation into multi-source `closed-field’ systems that have been responsible for the rise in importance of this technique. Closed-field unbalanced magnetron sputtering (CFUBMS) is an exceptionally versatile technique for the deposition of high-quality, well-adhered films. The development, fundamental principles and applications of the CFUBMS process are, therefore, discussed in some detail in this review. Also discussed are other important recent developments in this area, including the pulsed magnetron sputtering process, variable field magnetrons, and the combining of sputtering techniques with other surface coating, or surface modification techniques in duplex production processes.
This paper describes the synthesis, structure, and tribological behavior of nanocomposite tungsten disulphide (WS2) solid lubricant films grown by atomic layer deposition. A new catalytic route, incorporating a diethyl zinc catalyst, was established to promote the adsorption and growth of WS2. The films were grown down to 8 nm in thickness by sequential exposures of WF6 and H2S gases in a viscous flow reactor on Si, SiO2, stainless steel, and polycrystalline Si and electroplated Ni microelectromechanical systems structures. Films were studied by cross-sectional transmission electron microscopy (XTEM) with Automated eXpert Spectral Image Analysis (AXSIA) software for X-ray spectral images and X-ray diffraction to determine the coating conformality and crystallinity. The coatings exhibited a hexagonal layered structure with predominant preferentially orientated (0 0 2) basal planes. Regardless of orientation to the substrate surface, these basal planes when sheared imparted low friction with a steady-state friction coefficient as low as 0.008 to 50,000 cycles in a dry nitrogen environment. The formation of smooth transfer films during wear provided low interfacial shear stresses during sliding thus achieving low friction and wear. The XTEM combined with AXSIA of the wear tracks identified this mechanism and the effects of vapor phase reaction by-product etching on insulating and native polycrystalline Si and Ni surfaces.
Tungsten oxide (WO3) thin films have been produced by KrF excimer laser (lambda = 248 nm) ablation of bulk ceramic WO3 targets. The crystal structure, surface morphology, chemical composition, and structural stability of the WO3 thin films have been studied in detail. Characterization of freshly grown WO3 thin films has been performed using X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) measurements. The results indicate that the freshly grown WO3 thin films are nearly stoichiometric and well crystallized as monoclinic WO3. The surface morphology of the resulting WO3 thin film has grains of approximately 60 nm in size with a root-mean-square (rms) surface roughness of 10 nm. The phase transformations in the WO3 thin films were investigated by annealing in the TEM column at 30-500 degrees C. The phase transitions in the WO3 thin films occur in sequence as the temperature is increased: monoclinic --> orthorhombic --> hexagonal. Distortion and tilting of the WO6 octahedra occurs with the phase transitions and significantly affects the electronic properties and, hence, the electrochemical device applications of WO3.