Mechanical and microstructural characteristics of detonation gun sprayed NiCrAlY + 0.4 wt% CeO2 coatings on superalloys

The microstructure and mechanical properties of detonation gun sprayed NiCrAlY + CeO₂ alloy coatings deposited on superalloys were investigated. The morphologies of the coatings were characterized by using the techniques such as optical microscopy, X-ray diffraction and field emission scanning electron microscopy/energy-dispersive analysis. The coating depicts the formation of dendritic structure and the microstructural refinement in the coating was due to ceria. Average porosity on three substrates was less than 0.58% and surface roughness of the coatings was in the range of 6.17–6.94 μm. Average bond strength and microhardness of the coatings were found to be 58 MPa and 697–920 H_V, respectively.     

An in-situ chemical reaction deposition of nanosized wurtzite CdS thin films

Nanocrystalline CdS thin films were deposited on glass substrates by an ammonia-free in-situ chemical reaction synthesis technique using cadmium cationic precursor solid films as reaction source and sodium sulfide based solutions as anionic reaction medium. Effects of ethanolamine addition to the cadmium cationic precursor solid films, deposition cycle numbers and annealing treatments in Ar atmosphere on structure, morphology, chemical composition and optical properties of the resultant films were investigated by X-ray diffraction, field emission scanning electron microscope, energy dispersive X-ray analysis and UV-Vis spectra measurements. The results show that CdS thin films deposited by the in-situ chemical reaction synthesis have wurtzite structure with (002) plane preferential orientation and crystallite size is in the range of 16 nm-19 nm. The growth of film thickness is almost constant with deposition cycle numbers and about 96 nm per cycle.     

Temperature dependent microstructure of MTES modified hydrophobic silica aerogels

Hydrophobic silica aerogels were prepared using a single step sol-gel process followed by ethanol supercritical drying. Using tetraethoxysilane (TEOS) as a precursor and ammonium hydroxide as a catalyst the aerogel surface was chemically modified with methyltriethoxysilane (MTES). A MTES/TEOS molar ratio of 0.5 (M5) was used. The microstructure of the surface modified aerogels was evaluated as a function of heat treatment temperature over a range of 200-500 °C. The thermal stability was analyzed by simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC) and the microstructure was evaluated by physisorption analysis (BET) and scanning electron microscopy (SEM). The chemical composition and hydrophobicity/hydrophilicity of the aerogels were investigated by Fourier Transform-Infrared (FT-IR) spectroscopy. The M5 aerogels, which were initially hydrophobic, exhibited partial hydrophilicity at treatments above 244.5 °C and complete hydrophilicity above 429.9 °C. The surface area of the aerogels ranged from 776.65-850.20 m²/g. Pore size increased after heat treatment, ranging from 16.25 to 18.52 nm vs. an initial pore size of 14.71 nm. The maximum pore size of 18.52 nm was found at the lowest heat treatment temperature (~ 200 °C). Heat treatment had a mixed effect on the pore volume, as pore volumes decreased at lower treatments (~ 200-400 °C) and increased at higher heat treatments (~ 450-500 °C) relative to the untreated aerogels. With initial heat treatment the Si-CH₃ group began to oxidize to Si-OH. Aerogels heated above 429.9 °C exhibited hydroxyl polymerization leading to aerogels with large particles and a dense microstructure.     

Correlation between thermal properties and aluminum fractions in CrAlN layers deposited by PVD technique

The CrAlN coatings are a good alternative to conventional CrN coatings especially for high temperature oxidation-resistance applications. Different CrAlN coatings were deposited on silicon (100) by PVD (Physical vapor deposition) technique from two targets (chromium and aluminum) in a reactive nitrogen atmosphere at aluminum applied negative voltage (−300, −500, −700 and −900 V). The composition, structural, mechanical and thermal properties of the as-deposited coatings were systematically characterized by energy dispersive analysis of X-rays, X-ray diffraction, nanoindentation, and the “Mirage effect” experiments.The X-ray diffraction (XRD) data show that in general CrAlN coatings were crystallized in the cubic NaCl B1 structure, with the (1 1 1) and (2 0 0) diffraction peaks observed. Two-dimensional surface morphologies of CrAlN coatings were investigated by atomic force microscope (AFM). The results show that with increasing aluminum proportion the coatings became more compact and denser and their increased correspondingly, showing a maximum hardness of about 36 GPa (30 at% of Al) which is higher than that of CrN. Moreover, the results in this work demonstrate that the variation of aluminum fraction alter the resulting columnar grain morphology and porosity of the coatings. However, the thermal properties are greatly affected by these morphological alterations. The correlation between aluminum fraction in CrAlN coatings and its thermal properties revealed that the conductivity and the diffusivity are influenced primarily by size and shape distribution of the pores and secondarily by a decrease of the stitch parameter dimension.     

Microstructure and tribological property of nanocrystalline Co–W alloy coating produced by dual-pulse electrodeposition

The nanocrystalline Co–W alloy coatings were produced by dual-pulse electrodeposition from aqueous bath with cobalt sulfate and sodium tungstate (Na₂WO₄). Influence of the current density and Na₂WO₄ concentration in bath on the microstructure, morphology and hardness of the Co–W alloy coatings were investigated using an X-ray diffraction, a scanning electronic microscope and a Vickers hardness tester, respectively. In addition, the friction and wear properties of the Co–W alloy coating electrodeposited under different condition were evaluated with a ball-on-disk UMT-3MT tribometer. The correlation between the electrodeposition condition, the microstructure and alloy composition, and the hardness and tribological properties of the deposited Co–W alloy coatings were discussed in detail. The results showed that the microhardness of the deposited Co–W alloy coating was significantly affected by its average grain size, W content and crystal orientation. Smaller grain size, higher W content and strong hcp (1 0 0) orientation favor the improvement of the hardness for Co–W alloy coatings. The deposited Co–W alloy coating could obtain the maximum microhardness over 1000 kgf mm⁻² by careful control of the electrodeposition conditions. The tribological properties of the electrodeposited Co–W alloy coating were greatly affected by its grain size, microhardness, surface morphologies and composition, and could be significantly improved by optimizing the electrodeposition condition.     

Studies of nanocrystalline Pd alloy films coated by electroless deposition

The microstructures of thin coating films of pure palladium and palladium alloys deposited from organic electrolytes onto different metallic substrates by electroless plating method have been investigated. The coatings are dense, pore-free 0.005–1 μm thick films with high adhesive strength to the substrate surface. X-ray spectral analysis, X-ray phase analysis, transmission and scanning electron microscopy were used to determine the composition and structure of alloy coatings of binary systems: Pd–Au, Pd–Ag, Pd–Ni, Pd–Pb, and ternary system Pd–Au–Ni. The coatings of Pd–Au, Pd–Ag, and Pd–Ni have a solid solution structure, whereas Pd–Pb is intermetallic compound. It has been found that the deposited films consist of nanocrystalline grains with sizes in the range of 11–35 nm. Scanning and transmission electron microscopy investigations reveal the existence of clusters formed by nanocrystalline grains. The origin for the formation of nanocrystalline structures of coating films is discussed.     

Optimization of GaN nucleation layer deposition conditions on sapphire substrates in HVPE system

The influence of deposition conditions of nucleation GaN layer on the properties of high-temperature GaN layer, grown on sapphire substrates, was investigated. The hydride vapor phase epitaxy (HVPE) three-section horizontal hot-wall furnace technique was applied. Various temperatures, HCl flows and time intervals of nucleation layer growth were utilized. Based on previous studies the following experimental conditions were selected: temperature was kept at 450 or 570 °C, and HCl flows were 8 or 10 sccm/min. The duration of nucleation layer deposition was 5, 7 and 9 min. The scanning electron microscopy technique was applied for the investigation of nucleation layer morphology after migration. Thick GaN layers were deposited during the three-step growth process at 1060 °C. Samples with various surface morphologies were obtained. Photoluminescence spectra and X-ray measurements were performed, which permitted clarifications of the influence of growth conditions of the nucleation layer on the properties of high-temperature layers.     

Effect of polytetrafluoroethylene content on electrochemical anticorrosion behaviors of electroless deposited Ni-P and Ni-P-polytetrafluoroethylene coatings in seawater

The Ni-P and Ni-P-polytetrafluoroethylene (PTFE) coatings with various PTFE contents were electroless deposited on carbon steel and characterized through X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The microstructural morphologies of the coatings significantly varied with the PTFE content. As a result, the electrochemical anticorrosion capabilities were seriously decreased with the increase of the PTFE content. The coating with a trace PTFE (PTFE emulsion concentration of 0.2 mL/L in the plating bath) possessed excellent anticorrosion both in sterilized and unsterilized seawater which has been attributed to the absence of nano pores blocked by the incorporated trace PTFE nano particles.     

Ellipsometry and transmission electron microscopy study of MoSi2 coatings after oxidation at high temperature in air

MoSi₂ coatings were deposited on Si (100) substrates by means of magnetron sputtering. The structural and optical properties of the coatings were then investigated through transmission electron microscopy (TEM) and UV-visible-near IR ellipsometry after heat treatments in air at two temperatures (1100 K and 1600 K). After annealing at 1100 K, no silica layer could be observed by TEM at the surface of the MoSi₂ coating, whereas annealing at 1600 K gave rise to a protective silica layer. As observed by TEM, this silica layer contained nanometric molybdenum silicide crystals. Increasing the annealing time at 1600 K from 20 min to 2 h resulted in both a higher concentration and growth of these molybdenum silicide crystals in the silica layer. An optical model, taking into account the observed microstructure and allowing a good fit of the ellipsometry data, was developed. It is also shown that the dielectric constants of the non-oxidized part of the MoSi₂ layer became modified when the annealing temperature (1100 K versus 1600 K) and the annealing time at 1600 K (20 min versus 2 h) were increased.     

Silver nanocluster–silica composite coatings with antibacterial properties

Silver nanocluster–silica composite coatings have been deposited by radio frequency (RF) co-sputtering on silica substrates. UV–visible absorption and X-ray diffraction spectra of the as deposited and heated samples revealed metal silver nanoclusters of different size, depending on the annealing treatment. The antibacterial activity of several as deposited and annealed samples has been verified in accordance to National Committee for Clinical Laboratory Standards (NCCLS). The antibacterial activity of these coatings was detected up to 450 °C.     

Deposition of diamond-like carbon films on the inner surface of narrow stainless steel tubes

Diamond-like carbon (DLC) films were deposited on the inner surface of 304-type stainless steel tube with an inner diameter of 10 mm by DC glow discharge plasma. The influence of the deposition time, pressure and the ratios of CH₄ in CH₄/Ar gas mixture on the DLC film deposition were investigated. The images of Scanning Electron Microscopy (SEM) show that the DLC films are featureless and free of porosity. Fibre-like structure was recognized on the film surface by Atomic Force Microscopy (AFM). The film deposition rate decreases with increasing the deposition time. Relative higher deposition rate (40 nm/min) can be obtained at 20-30 Pa, higher and lower pressure will significantly decrease the deposition rate. Raman spectrum analysis shows that the films deposited in 30 min at 20-30 Pa have more sp³ content. The corrosion resistance of the films was measured by potentiodynamic polarization test. The DLC films deposited on the inner surface of the 304-type stainless steel tube significantly improve its corrosion resistance.     

Influence of silicon content on the microstructure and hardness of CrN coatings deposited by reactive magnetron sputtering

CrN and CrSiN films were deposited on the stainless steel and silicon substrates by DC magnetron sputtering and their microstructural features were investigated by X-ray diffraction (XRD), scanning electron microscope (FE-SEM/EDS), and atomic force microscopy (AFM). The influence of Si content along with process parameters such as power on the microstructural characteristics of Cr–Si–N and CrN films were investigated and compared between each other. The power and increasing Si contents strongly influence the microstructural and hardness of the deposited films. XRD analysis of the coatings indicates a grain refinement with increase in Si content during deposition of coatings, which is tandem with AFM and SEM results. Also, the surface roughness and particle size are decreasing with addition of Si in the films. The hardness of CrN and CrSiN was measured by microhardness tester and found that introduction of Si content in the CrN system increases its hardness from 1839 Hv to 2570 Hv.     

Nanoindentation study of magnetron-sputtered CrN and CrSiN coatings

CrN and CrSiN coatings were deposited on stainless steel substrate by reactive magnetron sputtering. The coatings were characterized for phases, chemical composition, microstructure, and mechanical properties by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM)/energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), and nanoindentation technique, respectively. The cubic phase was the only phase observed in both the coatings as observed in XRD results. A dense morphology was observed in these coatings deposited with high nitrogen and Si contents, 50:50 and 18.65 at.%, respectively. Nanoindentation measurement of CrN coatings, with Ar + N₂ proportions of 60:40, showed maximum hardness (H) and modulus (E) of 21 ± 0.85 GPa and 276 ± 13 GPa, respectively. The CrN coatings deposited in pure N₂ atmosphere showed H and E values of 27 ± 1.62 and 241 ± 10 GPa, respectively. The measured H and E values of CrSiN coatings were found to be 28 ± 1.40 GPa and 246 ± 10 GPa, respectively. The improved hardness in both the coatings was attributed mainly to a reduction in crystallite size, decrease in surface roughness, and dense morphology. The incorporation of Si into the CrN coatings has improved both hardness and Young’s modulus.     

Comparison study of biomimetic strontium-doped calcium phosphate coatings by electrochemical deposition and air plasma spray: morphology, composition and bioactive performance

In this study, strontium-doped calcium phosphate coatings were deposited by electrochemical deposition and plasma spray under different process parameters to achieve various coating morphologies. The coating composition was investigated by energy dispersive X-ray spectroscopy and X-ray diffraction. The surface morphologies of the coatings were studied through scanning electron microscopy while the cytocompatibility and bioactivity of the strontium-doped calcium phosphate coatings were evaluated using bone cell culture using MC3T3-E1 osteoblast-like cells. The addition of strontium leads to enhanced proliferation suggesting the possible benefits of strontium incorporation in calcium phosphate coatings. The morphology and composition of deposited coatings showed a strong influence on the growth of cells.     

Multiple dip deposition of CdS films prepared by oscillating chemical bath

Highly oriented CdS thin films with thicknesses greater than 1 μm were deposited using the oscillating chemical bath deposition technique with multiple dips at 75 °C, and from 15 to 75 min as deposition times. Samples with different thicknesses were deposited by repeating the chemical deposition process one, two and three times. All CdS films present the α-greenockite hexagonal structure with (002) as the preferential orientation. Band-gap energy values ranged from 2.35 to 2.42 eV, being the smaller value for the two dip processes. Energy dispersion spectroscopy measurements show good stoichiometry of the CdS films with 4.3 at.% as the maximum Cd variation.     

Influence of deposition parameters and heat treatment on the NO2 sensing properties of nanostructured indium tin oxide thin film

Highly oriented and transparent indium tin oxide (ITO) films have been deposited onto glass substrates by radio frequency magnetron sputtering at 648 K, under an oxygen partial pressure of 1 Pa. The effect of the sputtering power and annealing was studied. Transmission was measured with a double beam spectrometer and electrical analysis using four probe and Hall effect setup. Structural characterization of the films was done by X-ray diffraction. Characterization of the coatings revealed an electrical resistivity below 6.5 × 10^− 3 Ω cm. The ITO films deposited at 648 K were amorphous, while the crystallinity improved after annealing at 700 K. The optical transmittance of the film was more than 80% in the visible region. The surface morphology examined by scanning electron microscopy appears to be uniform over the entire surface area, after annealing. The NO₂ sensing properties of the ITO films were investigated. At a working temperature of 600 K, the ITO sensor showed high sensitivity to NO₂ gas, at concentrations lower than 50 ppm.     

Synthesis and characterization of bulk and coatings of hydroxyapatite using methanol precursor

Hydroxyapatite, an important bioceramic was synthesized in the bulk form and developed as a coating by a sol-gel route using alcoholic precursor. The bioactive coating was developed on bio-inert α-alumina and yttria stabilized zirconia substrates. The apatite phase began to form after the heat treatment of the precursor at 500 °C for 10 min. The complete crystallization of the apatite was obtained at 800 °C heat treatment for 10 min. The phase composition of the bulk and the coatings was identified by FT-IR spectroscopic and powder X-ray diffraction (XRD) techniques. Surface morphology was determined by scanning electron microscopy. The study indicates different surface textures for the powder and for the coatings on α-alumina and yttria stabilized zirconia substrates.     

Morphological characterization and analytical application of poly(3,4-ethylenedioxythiophene)-Prussian blue composite films electrodeposited in situ on platinum electrode chips

Electrochemical in situ preparation and morphological characterization of inorganic redox material-organic conducting polymer coatings as thin films on platinum electrodes are presented. Composite inorganic-organic coatings consist of Prussian blue (PB) and [poly(3,4-ethylenedioxythiophene)] (PEDOT), and PEDOT organic polymers doped with ferricyanide (PEDOT-FeCN). The PEDOT coating deposited from an aqueous solution containing the 3,4-ethylenedioxythiophene monomer and LiClO₄ as supporting electrolyte was used as a “reference” material (PEDOT-ClO₄). The composite coatings were prepared by electrochemical methods on platinum electrode chips, which consist of a 150 nm Pt layer deposited on 100-oriented standard 3″ silicon wafers. Electrochemical behavior of the composite inorganic-organic coatings is based mainly on inorganic component redox reactions. Different surface properties of the composite materials were studied. Thus, the roughness of the deposited films was measured by both atomic force microscopy (AFM) and profilometry, leading to roughness values ranging from 3 nm to 217 nm for PEDOT-ClO₄, and PEDOT-FeCN and PEDOT-PB coatings, respectively. AFM and Scanning Electron Microscopy pictures were also produced to characterize the film morphologies, and revealed a granular pattern of the deposited inorganic component inside the organic polymer matrix. Moreover, the adhesion properties of the composites were studied by AFM and proved to be very different from one material to the other depending on the film structure. The electrochemical responses of these composite coatings to H₂O₂ reduction were also investigated using chronoamperometry. A linear response over a concentration range from 1 × 10^− 4 to 1 × 10^− 5 M and a detection limit of 10 μM were obtained.     

Preparation of CVD diamond coatings on gamma titanium aluminide using MPECVD with various interlayers

CVD diamond coatings were deposited on to γ-TiAl surfaces using a microwave plasma enhanced CVD to improve wear properties and the performance of γ-TiAl. Diamond coatings were directly deposited on to γ-TiAl substrates and deposited on to TiC, Ti₅Si₃, Al₂O₃ + TiO₂, and Si interlayers prepared on γ-TiAl substrates. The diamond coatings deposited directly on γ-TiAl suffered severe delamination and cracked. Those deposited on TiC and Ti₅Si₃ interlayers partially delaminated, whereas those deposited on Al₂O₃ + TiO₂ and Si interlayers adhered well to the underlying surfaces. The diamond films obtained were characterized using scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Raman spectra showed that polycrystalline and nanocrystalline diamond films grew on γ-TiAl. Residual internal stresses of the diamond coatings deposited on interlayered-γ-TiAl were estimated experimentally from Raman spectra. The coatings prepared on Al₂O₃ + TiO₂/γ-TiAl and Si/γ-TiAl showed lower residual stresses.     

Deposition of CdS thin films onto Si(111) substrate by PLD with femtosecond pulse

The effect of laser fluence (laser incident energy in the range of 0.5-1.5 mJ/pulse with the same laser spot size of 0.5 mm × 0.7 mm) on the structural quality and optical properties synthesized by femtosecond pulsed-laser deposition has been studied. The structural quality and optical properties of the deposited CdS thin films were investigated by X-ray diffraction, atomic force microscopy and photoluminescence measurement. The studies revealed an improvement in the structural quality and optical properties of the CdS thin films with increasing the laser fluence in some range. However, too high laser fluence could lead to the structural quality and optical properties of the CdS thin films to degrade. We defined the optimum laser incident energy was around 1.2 mJ/pulse. And the kinetic energy of the plasma produced by femtosecond laser strongly affects the structure and properties of the deposited CdS thin films.