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Coated bearings in high-performance turbine engines have the potential to provide considerable improvement in engine reliability and service-life extension. One coating performance indicator is the level of vibration generated by rolling elements and their cage separators at high-speed bearing operation. This article introduces a nonintrusive, cage-mounted sensor that detects cage vibration and transmits wirelessly to a nearby receiver. The sensitivity of the cage-mounted sensor was compared to a housing-mounted accelerometer in the detection of seeded faults in coated and uncoated bearings. The smallest spall on an uncoated bearing that the sensor could detect was 28 µmdeep × 3.2 mm wide, with a reliability of ~40%. In contrast, the accelerometer consistently detected all levels of flaws, the smallest being 0.4 µm deep × 3.2 mm wide on the coated bearing, with a reliability of 55%. Despite the sensor having a detection rate less than the accelerometer, this research successfully demonstrated that the sensor could detect inner-racebearing flaws and established its sensitivity level. [ABSTRACT FROM AUTHOR]

Pulsed laser deposition (PLD) was employed to grow MoS x –WSe y composite films, where x = 1.18, y = 0.78. Scanning electron micrographs show that the films have a dense granular morphology. Crystallization, d-spacing and hexagonal sheet curvature within the film were studied with X-ray diffraction, electron diffraction and transmission electron microscopy. A predominant hexagonal MoS x phase was formed but contained W and Se, which were most likely present as substituents for Mo and S. There was no evidence for two separate crystalline phases. MoS x –WSe y composite films exhibited a larger expansion along the c-axis ( d-spacing between basal planes) than PLD MoS2 and WSe2 films grown by laser ablation of pure targets. The lattice spacing along the a-axis was expanded in comparison to the MoS2 film, and compressed in comparison to the WSe2 film. X-ray photoelectron spectroscopy showed a significant sulfur deficiency, and verified both of S and Se bonding in the film. High-resolution electron microscope images exhibited significant curvatures of the (002) basal planes in the films. The bending behavior of basal planes was explained by S vacancies and Se substitution on the atomic site of S layers. The tribological properties of the composite films were measured in dry and wet conditions using a ball-on-disc tribometer. The reduced friction was correlated with the increased crystallinity and increased separation of basal planes in the composite films. [ABSTRACT FROM AUTHOR]

Tribological properties of three-phase composite coatings consisting of nanocrystalline WC, amorphous diamond-like carbon (DLC), and nanocrystalline WS2 are evaluated. The WC/DLC/WS2 coatings have 0.5 μm thickness, 7–8 GPa hardness, excellent wear resistance, and low friction coefficients: 0.03 in vacuum, and 0.15 in air; with unique friction recovery in cycling between dry and moist environments. The benefits of carbide/dichalcogenide/DLC nanocomposites for aerospace tribology are highlighted. [ABSTRACT FROM AUTHOR]

Vertical few-layer thick graphene petals are grown on macro-porous carbon foam surfaces having an intrinsic open porosity of 75%. This provides a hierarchical porous structure with a potential for surface adsorption/desorption or wetting/dewetting based thermal energy storage applications. Carbon foams have a combined advantage of large surface area and high thermal conductivity critical for thermal energy storage, but they are prone to oxidation and exhibit low adsorption enthalpies for lightweight hydrocarbons. Here we report graphene petal decoration of carbon foam surfaces and subsequent chemical modification through boron nitride incorporation in hexagonal carbon planes of both carbon foams and graphene petals. This chemically reactive hierarchical structure is characterized with FESEM, Raman, XRD, and XPS measurements. Methanol wetting enthalpy of this three-dimensional hierarchical material was measured with a solution calorimeter, and had shown a six fold increase (from 78 to 522 J/g of foam) as compared to the carbon foam prior to the surface modification. Influences of petal decoration on the surface morphology of carbon foam, BN chemical modification, structure and stoichiometry of the hierarchical material surface, and methanol wetting enthalpy improvement are discussed in detail. The applicability of this hierarchical porous material for thermal energy applications is established. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ag-doped micropattern surfaces produced by photolithography method. • Formation of Ag particles on the tops of pillars due to temperature-activated diffusion. • Formation of small Ag nanoparticles in areas between pillars due to sputtering of Ag. • Rate of Ag+ ion release depended on the etching depth and Ag particle distribution. • Samples demonstrated a pronounce antibacterial effect toward Escherichia coli strains. Abstract Photolithography methods offer ample opportunities for creating biological surface patterns over large areas. Herein, samples with patterned surface having the same Ag total coverage area and content, but different surface topography made of periodically spaced Ag/Si pillars with a diameter of 10 and 50 μm and a height of 3, 1, and 0.2 μm were produced by photolithography technique and studied to uncover the dependences of bactericide ion release on surface topography and antibacterial effect on Ag+ ion concentration. Reactive ion etching of Si wafers in areas unprotected by Ag capping layer was accompanied by a number of competing processes: (i) formation of Ag particles on the tops of pillars due to temperature-activated diffusion and coalescence, (ii) sputtering of Ag from the pillar to surface and redeposition into the etching cavities, resulting in the formation of small Ag nanoparticles located in areas between pillars, (iii) precipitation of AgSi x phase as a result of chemical interaction of sputtered Si ions with Ag ions and atoms in surrounding plasma. Samples with the largest pillar heights which had also Ag particles formed between pillars demonstrated the fastest Ag+ ion release and, correspondingly, a noticeable antibacterial effect toward antibiotic-resistant hospital Escherichia coli K-261 strains already after 3 h. All samples showed 100% antibacterial effect after 24 h. Thus our results open up new possibilities for the production of scalable micropattern surfaces with controlled bactericide ion release and pronounced antibacterial characteristics for future applications in the orthopedic field. [ABSTRACT FROM AUTHOR]

The tribological properties of cold sprayed Ni-WC metal matrix composite (MMC) coatings were investigated under dry sliding conditions from room temperature (RT) up to 400 °C, and during thermal cycling to explore their temperature adaptive friction and wear behavior. Characterization of worn surfaces was conducted using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy to determine the chemical and microstructural evolution during friction testing. Data provided insights into tribo-oxide formation mechanisms controlling friction and wear. It was determined that the steady-state coefficient of friction (CoF) decreased from 0.41 at RT to 0.32 at 400 °C, while the wear rate increased from 0.5 × 10 −4 mm 3 /N·m at RT to 3.7 × 10 −4 mm 3 /N·m at 400 °C. The friction reduction is attributed primarily to the tribochemical formation of lubricious NiO on both the wear track and transfer film adhered to the counterface. The increase in wear is due to a combination of thermal softening of the coating and a change in the wear mechanism from adhesive to more abrasive. In addition, the coating exhibited low friction behavior during thermal cycling by restoring the lubricious NiO phase inside the wear track at high temperature intervals. Therefore, cold sprayed Ni-WC coatings are potential candidates for elevated temperature and thermally self-adaptive sliding wear applications. [ABSTRACT FROM AUTHOR]

The tribological behavior of MoS 2 and WS 2 transition metal dichalcogenide (TMD) spray coatings in low-viscosity hydrocarbon environments was investigated. Sliding tests were performed in two hydrocarbons – hydrophilic ethanol and hydrophobic dodecane and were compared to tests in humid air and dry nitrogen conditions. Coating steel surfaces decreased friction across all test conditions, with the largest and most sustainable decreases being in dry nitrogen and dodecane environments, where friction coefficients of less than 0.1 were sustained. Analysis was performed using scanning electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. Friction reductions in dodecane were explained by reduced oxidation of the coating, due to protection from the hydrophobic hydrocarbon film, allowing basal plane alignment and uninhibited sliding of TMD sheets. • Transition-metal dichalcogenide (TMD) solid lubricants can be used synergistically with low lubricity fuels and synthetic oils. • Pin-on-disk tests reported for MoS 2 adn WS 2 coatings on steel coupons in humid air, dry nitrogen, ethanol, and dodecane. • Synergistic low friction and wear behavior was shown for TMD coatings in dodecane, whereas ethanol promoted coating wear. [ABSTRACT FROM AUTHOR]

High power impulse magnetron sputtering was used to deposit thin (~ 100 nm) zinc oxide (ZnO) films from a ceramic ZnO target onto substrates heated to 150 °C. The resulting films had strong crystallinity, highly aligned (002) texture and low surface roughness (root mean square roughness less than 10 nm), as determined by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and atomic force spectroscopy measurements. Deposition pressure and target–substrate distance had the greatest effect on film microstructure. The degree of alignment in the films was strongly dependent on the gas pressure. Deposition at pressures less than 0.93 Pa resulted in a bimodal distribution of grain sizes. An initial growth layer with preferred orientations (101) and (002) parallel to the interface was observed at the film–substrate interface under all conditions examined here; the extent of that competitive region was dependent on growth conditions. Time-resolved current measurements of the target and ion energy distributions, determined using energy resolved mass spectrometry, were correlated to film microstructure in order to investigate the effect of plasma conditions on film nucleation and growth. [ABSTRACT FROM AUTHOR]

Abstract: Accurate prediction of heat transfer from micro and nanoscale devices is very important for their operation and reliability. While the general consensus is that the heat transfer coefficient increases at the smaller scales, the literature also indicates contradiction in the scaling across length scales. In this paper, we present an experimental technique to accurately characterize heat transfer from micro to nano scales using infrared microscopy on nanofabricated specimens that are integrated with micro heaters. The heat transfer coefficient for quiescent air is found to be about two orders of magnitude higher than its bulk counterpart. It also showed pronounced inversely proportional relationship with temperature and suggested that solid to air conduction is the dominant mode of heat transfer. It was found that pressure only indirectly influences heat transfer. Based on the experimental data, we present an empirical relationship for the heat transfer coefficient that depends on the ratio of the surface area to cross-sectional area, temperature of the heated solid and its proximity to other solid bodies. [Copyright &y& Elsevier]

The effect of V additions on reactively magnetron sputtered ZrO2 coatings was investigated with respect to their structural and mechanical properties. Coatings with different V-contents were co-sputtered from Zr and V targets using an Ar+O2 discharge. The X-ray diffraction patterns show a change from monoclinic (0–2.2at.% V) to cubic/tetragonal ZrO2 based phase (5.8at.% V) and finally X-ray amorphous structure at even higher V-content (17.4at.% V). Hardness and Young's modulus decrease beyond 5.8at.% V from 17.4 to 7.5GPa and from 230 to 150GPa, respectively. At 25°C, the coefficient of friction (COF) is ~0.2 for low V-contents and above 0.5 for high V-contents, respectively. Differential scanning calorimetry of powder samples showed a characteristic exothermic peak at ~600°C, which is due to the formation of the ZrV2O7 phase. This phase decomposes above 740°C in ZrO2 and liquid V2O5. The latter phase provides a self-lubricious layer in the sliding contact, decreasing the COF below 0.2 at 800°C for V-contents of 17.4at.%. The endothermic nature of melting of the V2O5 phase is suggested as the basis for thermal management abilities of tribological coatings, where the frictional heat generated in severely loaded sliding contacts and thus local flash temperatures are efficiently reduced. [ABSTRACT FROM AUTHOR]

Molecular dynamics is used to study the interfacial thermal conductance between graphitic structures and metals. It is shown that with different metals, the conductance can vary by ∼4-fold, allowing the control of thermal transport in nanocomposites and nanoelectronic devices. The experimental values of conductance are higher by 10–20MWm−2 K−1 compared to simulations. We suggest that in addition to lattice vibrations, an electromagnetic coupling between Johnson–Nyquist electric currents in the metal and graphite may contribute to the interfacial thermal conductance. [ABSTRACT FROM AUTHOR]

Abstract: Tungsten is an important material for energy harvesting applications due to its high chemical and thermal stability; however, the difficulty in obtaining single-crystal films leads to a large variation in the optical properties. The present work focuses on the radiative and optical properties of thin tungsten films at wavelengths from 1 to 20μm (wavenumbers from 10,000 to 500cm−1), considering microstructural variations. Four films of a nominal thickness of 70nm were deposited on silicon substrates using DC magnetron sputtering, and the effect of pre- and post-deposition treatments was investigated. Several analytical instruments were used to characterize the crystalline phases and microstructures, including X-ray diffraction, Rutherford backscattering, X-ray photoelectron spectroscopy, and scanning electron microscopy. The transmittance and reflectance of the film–substrate composites were measured at room temperature using a Fourier-transform infrared spectrometer. The dielectric function of each sample was obtained by fitting the measured radiative properties using the Drude–Lorentz dispersion model. The difference in the radiative properties between samples was analyzed and related to the crystalline phases and density. [Copyright &y& Elsevier]

Abstract: Vapor phase growth of gold, nickel and titanium metal nanoparticles on multiwall carbon nanotube (MWCNT) buckypaper by sputtering was investigated. The size and distribution of nanoparticles was dependent on the intrinsic binding energy of the metal elements, but could be altered to mimic that of metals with different binding energies by in situ modification of the MWCNT surfaces by energetic metal ions or annealing of the buckypaper. A range of average gold particle diameters from approximately 5–30nm could be produced depending on the intrinsic sputter process parameters (especially metal ion flux and kinetic energy) and defect density of the MWCNT surfaces, which could also be controlled by annealing prior to sputtering. The diameter of the MWCNTs had a significant influence on the geometry of the nanoparticles. Particles were elongated along the nanotube axis for tube diameters <30nm. Remarkably strong alignment of the particles along the nanotube axis was observed, especially for MWCNTs with higher defect densities. [Copyright &y& Elsevier]

Abstract: Silver tantalate was investigated as a potential lubricious material for moving assemblies in high temperature tribological applications. Three different approaches were explored for the creation of such materials on Inconel substrates: (1) powders produced using a solid state which were burnished on the surface; (2) monolithic silver tantalate thin films deposited by magnetron sputtering; and, (3) an adaptive tantalum nitride/silver nanocomposite sputter-deposited coating that forms a lubricious silver tantalate oxide on its surface when operated at elevated temperatures. Dry sliding wear tests of the coatings against Si3N4 counterfaces revealed friction coefficients in the 0.06–0.15 range at T ~750°C. Reduced friction coefficients were found in nanocomposite materials that contained primarily a AgTaO3 phase with a small amount of segregated Ag phase, as suggested by structural characterization using X-ray diffraction. Furthermore, cross-sectional transmission electron microscopy techniques determined that the reduced coefficient of friction at T ~750°C was primarily the result of the formation of a lubricious AgTaO3 phase that reconstructs during the wear process into a mechanically mixed layer of AgTaO3, Ta2O5, and Ag nanoparticles. [Copyright &y& Elsevier]

Abstract: Hafnium oxide (HfO2 or hafnia) holds promise as a high-index dielectric in optical devices and thermal barrier coatings, because of its transparency over a broad spectrum (from the ultraviolet to the mid-infrared) and chemical and thermal stability at high temperatures. In the present work, thin hafnia films of thicknesses from about 180 to 500nm are deposited on Si substrates using reactive magnetron sputtering. The crystalline structure and surface topography are characterized by X-ray diffraction and atomic force microscopy, respectively. The optical and radiative properties of the film–substrate composites are measured at room temperature using spectroellipsometry and Fourier-transform infrared spectrometry. The optical constants are obtained from about 0.37 to 500μm by fitting suitable models to the experimental results. Optical properties and dielectric function modeling are discussed with correlation to both film thickness and surface roughness. It is found that a single-oscillator dielectric-function model can describe radiative properties from about 1 to 20μm. By combining Cauchy''s formula (for the visible and near-infrared regions) with a multiple-oscillator Lorentz model (for the far-infrared region), a dielectric function is obtained for the HfO2 films that is applicable from the visible to the far-infrared. [Copyright &y& Elsevier]