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A comparative study of the cyclic thermal oxidation of PVD nickel aluminide coatings

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SURF Static components used in the hot sections of gas turbines increasingly have a thermal barrier coating (TBC) of partially yttria-stabolized zirconia (PYSZ) routinely applied to improve their high temperature properties. Developments are also in progress to make TBCs better suited for use on rotating components such as blade. To help protect against high temperature oxidation of such components, an intermediate bond coat is applied, typically of an MCrAlY-type metal alloy. An alternative bond coat material is nickel-aluminium intermetallic alloy. Various processing routes have been studied for both bond coat and TBC deposition. A potentially attractive processing route is to deposit both bond coat and TBC by a physical vapor deposition (PVD) method; this would have the advantage of permitting sequential deposition in the same coating cycle. Whilst much research as been carried out on PVD MCrAlY and PYSZ coatings, relatively little work has been carried out on PVD NiAl, deposition by three ion-assisted PVD coating routes: arc, electron-beam, and sputter ion plating. Coatings were deposited on a nickel-based alloy (Inconel 600) and an AISI 304 stainless steel. The differences in microstructure and phase composition from each deposition method are reported, together with data on the cyclic oxidation performance. The influence of process parameters on coating characteristics and degradation mechanisms is discussed.

A comparative study of the effect of mechanical and ultrasound agitation on the properties of electrodeposited Ni/Al2O3 nanocomposite coatings.

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SURF In our study, Ni/Al2O3 nanocomposite coatings were obtained by electrochemical deposition of alumina nanoparticles from nickel Watts baths with different concentrations of Al2O3 particles in solution. A comparison of the effects of mechanical (300 rpm) and ultrasonic (24 kHz, 38 W cm- 2) stirring on the properties of electrodeposited Ni/Al2O3 composite coatings was performed, observing an enhancement of the Al2O3 incorporation in the composite coating and an improvement of the uniformity of particles distribution in the nickel metal matrix when ultrasonic energy was applied to the process. Moreover, the characterization of the coatings also showed that for both types of agitation, the incorporation of Al2O3 nanoparticles led to changes in the morphology and structure of the nickel matrix leading to an improvement of its tribological properties. These properties were further enhanced when ultrasonic stirring was used during the composite coating electrodeposition.

A comparative study of the effects of saccharin and beta-SiC nano-particles on the properties of Ni and Ni–Co alloy coatings.

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SURF The effects of saccharin and SiC nano-particles on the properties of Ni and Ni–Co based coatings electrodeposited in modified Watt's baths by sediment co-deposition (SCD) technique were studied. Surface morphologies of Ni and Ni–Co coatings were changed by using saccharin and SiC nano-particles. X-ray diffraction (XRD) results revealed that peak positions and the phase structure of the studied coatings did not change appreciably while the crystallite size and preferred orientation were significantly varied by using SiC nano-particles and particularly saccharin. Although the incorporation of SiC nano-particles had a slight influence on the microhardness of Ni based coatings, using saccharin enhanced their microhardness. However, there was no noticeable difference between the microhardness of Ni–45Co and Ni–45Co/saccharin coatings (containing 45 wt.% Co) while the microhardness of Ni–55Co/SiC nanocomposite coatings (containing 55 wt.% Co) was higher than Ni–45Co and Ni–45Co/saccharin coatings. The potentiodynamic polarization measurements indicated that the corrosion resistance of Ni/saccharin and Ni–45Co/saccharin coatings was better than pure Ni and Ni–45Co coatings. Additionally, the corrosion properties of Ni/SiC and Ni–55Co/SiC nanocomposite coatings were markedly higher than other coatings. Ni–55Co/SiC nanocomposite coatings showed the highest microhardness and corrosion resistance compared to all studied coatings. The unique properties of Ni–55Co/SiC nanocomposite coatings were linked to their alloy matrix and the amount of SiC nano-particles (8.1 vol.%).

A comparative study of the fretting wear of hard carbon coatings.

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Different types of hard C coatings were investigated with respect to fretting wear behaviour and compared to reference PVD titanium nitride coating. Hard C coatings investigated are CVD diamond and diamond-like C coatings produced by RF, arc and laser-assisted deposition. Coatings exhibit low coeff. of friction and are remarkably resistant against fretting wear damage when compared to PVD Ti nitride coating, although hardness of C coatings is not always superior. Performance of hard C coatings is discussed in terms of wear phenomena.

A comparative study of the influence of plasma treatments, PVD coatings and ion implantation on the tribological performance of Ti-6Al-4V

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SURF Mechanical and tribological properties of Ti-6Al-4V were characterized. Using commercial thermionic triode plasma-assisted PVD system, hot- filament-supported glow discharges were produced with different compositions of N, C and H. Plasma-diffusion treatments all increased load support provided by substrate but reduced bulk fatigue strength. PAPVD titanium nitride coating increased surface microhardness but provided limited load support. N-ion implantation increased low-load surface microhardnesses and improved fatigue resistance without improving overall load support by substrate. Elevated temps. and increased process times in plasma-diffusion treatments increased surface roughness, although this effect was reduced by depositing thin Ti layer by PAPVD, before plasma treatment.

A comparative study of the microstructure and oxidation behavior in supersonic and conventional air plasma sprayed thermal barrier coatings.

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A comparative study of the structure and chemical properties of nanocomposite TiCaPCON-Ag coatings.

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PROT To induce antibacterial activity in bioactive TiCaPCON coatings, materials have been doped with Ag in a quantity of 0.4–4.0 at %. Silver has been introduced into the coatings via two methods. Coatings with 0.4, 1.2, and 4.0 at % Ag content have been fabricated via simultaneous sputtering of a compositional TiC0.5-Ca3(PO4)2 target, which was obtained via self-propagating high temperature synthesis, and of a metallic Ag target. TiCaPCON-Ag (4.0 at %) coating was also fabricated via ion Ag implantation of preliminarily obtained TiCaPCON. The content and element distribution over the thickness of the coating were studied via glow discharge optical emission spectroscopy (GD-OES). The structure and morphology of the coatings have been probed via scanning electron microscopy. The results showed the formation of Ag particles in both the bulk and on the surface of the coatings, but their size and distribution over the coating thickness are found to depend on both the Ag concentration and method of sputtering of coatings. The effect of substrate temperature on Ag particle distribution in the coating is established. The study of kinetics of Ag dissolution via inductively coupled plasma mass-spectrometry and electrochemical methods has revealed that Ag dissolution rate is defined by the ratio of Ag nanoparticle size to the thickness of an oxide layer on the surface.

A comparative study of titanium nitrides, , TiNbN and TiCN, as coatings for biomedical applications

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A comparative study on the crystallization behavior of electroless nickel phosphorus and Ni-Cu-P deposits

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A comparative study on the direct and pulsed current electrodeposition of hydroxyapatite coatings on surgical grade stainless steel.

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SURF Hydroxyapatite [Ca10(PO4)6(OH)2, (HAP)] coatings were developed on 316L stainless steel substrate from the electrolyte containing hydrogen peroxide (H2O2) with the concentration ranging from 600 to 3000 ppm by both the direct and pulsed current electrodeposition methods. The effects of direct current density upon the addition of H2O2 into the electrolyte on the phase purity and morphology of the as-deposited coatings were reported. The influence of pulsed parameters such as peak current density and pulse on and off time on the deposit compositions was also examined and compared with direct continuous current deposition in relation to the crystallinity, microstructure and the corresponding phases. X-ray diffraction (XRD) and Fourier transform infrared spectroscopic (FT-IR) techniques were performed in order to assure the purity, phase compositions of the coating and the morphology of the coating were characterized by scanning electron microscopic (SEM) technique. The results showed that the coating consists of mixed phases of calcium phosphate (Ca-P) in the absence of H2O2 in the electrolytic bath. Whereas the addition of H2O2 lowers the deposition current with the formation of smooth and uniform layer comprised solely of HAP. It is highly beneficial to increase the peroxide concentration from 600 to 2000 ppm for the deposition of pure HAP. While increasing the peroxide concentration to 3000 ppm, the coating morphology is not uniform as evidenced from the SEM result. Moreover, the increased adhesion and crystallinity of the HAP coating were achieved by pulsed current electrodeposition method at lower current density with longer pulse off time. The results of pulsed electrodeposition show that the relaxation time of the pulse is beneficial for the growth of HAP because it allows the diffusion of ions from bulk solution to the surface of electrode and thus lowers the concentration polarization in the next pulse on time. The combination of pulsed electrodeposition and addition of H2O2 into the electrolyte promisingly improve the physico-chemical properties of HAP coating.

A comparative study on the electrochemical behaviour of amorphous and nanocrystalline cobalt–tungsten electrodeposited coatings.

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Title alloy was electrodeposited from a citrate bath and deposit morphology is reported with XRD patterns and SEM images with cyclic voltammograms to allow a Mott-Schottky analysis. Nyquist and Bode plots are shown with equivalent circuits for both amorphous and nano crystalline cases. Deposits were nodular but with micro cracking in some cases. OCP data suggests the deposits where in a passive state. n-type semiconductor behaviour was observed for passive films formed on the surface. 40 refs

A comparative study on the microstructure and surface property evaluation of coatings produced from nanostructured and conventional WC–Co powders HVOF-sprayed on aluminium 7075.

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A comparative study on the performance of suspension plasma sprayed thermal barrier coatings with different bond coat systems.

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A comparative study on the photocatalytic activities of microporous and nanoporous TiO2 layers prepared by electrochemical anodization.

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A comparative study on the photocatalytic efficiency of ZnO thin films prepared by spray pyrolysis and sol-gel method.

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