Ceramic coatings: Effect of deposition method on damping and modulus of elasticity for yttria-stabilized zirconia (original) (raw)
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Journal of Thermal Spray Technology, 2013
Plasma generated by the SG-100 torch was applied to spray suspension formulated with the use of ZrO 2 + 8 wt.% Y 2 O 3 (8YSZ) and ZrO 2 + 24 wt.% CeO 2 + 2.5 wt.% Y 2 O 3 (24CeYSZ) as solid phases. The suspensions were formulated with the use of 20 wt.% solid phase, 40 wt.% water, and 40 wt.% ethanol. The plasma spray parameters were optimized by keeping constant: (a) the electric power of 40 kW and (b) the working gas compositions of 45 slpm for Ar and 5 slpm for H 2 . On the other hand, the spray distance was varied from 40 to 60 mm and the torch linear speed was varied from 300 to 500 mm/s. The coatings were sprayed onto stainless steel substrates, and their thicknesses were in the range from 70 to 110 lm. The coating microstructures were analyzed with a scanning electron microscope. Mechanical properties were tested with the different methods including the indentation and scratch tests. The indentation test, carried out with various loads ranging from 100 to 10,000 mN, enabled to determine elastic modulus and Martens microhardness. YoungÕs modulus of the coatings was in the range of 71-107 GPa for 8YSZ and 68-130 GPa for 24CeYSZ coatings. The scratch test enabled the authors to find the scratch macrohardness.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000
Yttria (8 wt.%) stabilized zirconia (YSZ) with a NiCrAlY bond coat was atmospherically plasma sprayed on mild steel substrates using various processing parameters including YSZ coating thickness, bond coat thickness, stand off distance, and substrate temperature. The cracking behavior of these coatings under four point bending load was examined using an acoustic emission (AE) recorder. The numbers of AE events exhibited during the elastic and plastic deformation of coatings were analyzed. Using multi-linear regression analysis, the number of AE events was correlated to the spray parameters. This analysis revealed that coatings with thicker YSZ top coat and NiCrYAl bond coat sprayed on a heated substrate at shorter stand off distance exhibited more AE activity and released higher AE energy under the bending. The greater emission activity and higher AE energy were evidence of severe cracking. 0 2000 Elsevier Science S.A. All rights reserved.
The Stiffness of Plasma Sprayed Zirconia Top Coats in TBCs
1999
Yttria-stabilised zirconia coatings have been deposited onto nickel superalloy substrates by air plasma spraying (APS). Free standing layers were then obtained by chemical dissolution techniques. The in-plane Young's modulus values exhibited by these layers were measured using the techniques of cantilever bending and ultrasonic resonant frequency testing during flexural vibration. Young's modulus data were also obtained by nanoindentation of regions remote from microcracks. The values obtained by bending and frequency measurement were found to be considerably lower than that expected for bulk zirconia, whereas those obtained by the nanoindentation experiments were much closer to that of the bulk ceramic. Tests were also performed on samples which had been heat treated at 1100˚C and 1300˚C. It was found that the stiffness rose significantly after such treatments. This is attributed to sintering processes which generated extensive healing of microcracks.
Elastic behaviour of thin stabilized-zirconia coatings
Materials Science Forum, 2004
The residual stress in thin coatings of yttria stabilised-zirconia produced by Low Pressure Plasma Spraying were measured by X-ray Diffraction, using laboratory as well as synchrotron radiation sources. The specific microstructure, with absence of texture and fine distribution of nearly equiaxed grains, point out that despite the markedly anisotropic nature of cubic zirconia, coatings can be considered as macroscopically isotropic. This picture is also confirmed by the results of a parallel study, where the X-ray elastic constants were measured in-situ along two crystallographic directions ([440] and [620]): measured values agree fairly well with those calculated from single-crystal data under the Neerfeld-Hill assumptions. SR XRD provided a detailed information on the stress field across the thickness of the zirconia coatings. In particular the presence of a stress gradient was observed and modelled. The average stress is compressive, and increases with the coating thickness. Compression tend to increase from the surface toward the inside of the coating reaching a maximum of ~-1.0 GPa in a 24 µm coating.
Journal of the European Ceramic Society, 2007
Widely used in turbines for propulsion and power generation, thermal barrier coatings (TBCs) increase the efficiency of turbine engines by allowing them to work at higher temperatures, due to their thermal insulating properties. Typically TBC systems consist of a metallic bondcoat (BC) and a ceramic topcoat (TC). Previous research has revealed that ceramic TCs possess an amplitude-dependent mechanical behaviour and that they can be used as damping treatments, due to their good damping properties. The microstructure and the properties of ceramic TCs vary significantly depending on the employed deposition technique. This work investigates the differences in the mechanical behaviour of yttria-stabilised zirconia (YSZ with 8 wt% yttria) TC deposited by atmospheric plasma spraying (APS) and electron beam-physical vapour deposition (EB-PVD), by means of tests run with the amplitude dependent damping (ADD) test rig and of scanning electron microscopy (SEM) analysis.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000
Yttria (8 wt.%) stabilized zirconia (YSZ) with a NiCrAlY bond coat was atmospherically plasma sprayed on mild steel substrates using various processing parameters including YSZ coating thickness, bond coat thickness, stand off distance, and substrate temperature. The cracking behavior of these coatings under four point bending load was examined using an acoustic emission (AE) recorder. The numbers of AE events exhibited during the elastic and plastic deformation of coatings were analyzed. Using multi-linear regression analysis, the number of AE events was correlated to the spray parameters. This analysis revealed that coatings with thicker YSZ top coat and NiCrYAl bond coat sprayed on a heated substrate at shorter stand off distance exhibited more AE activity and released higher AE energy under the bending. The greater emission activity and higher AE energy were evidence of severe cracking. 0 2000 Elsevier Science S.A. All rights reserved.
Elastic constants of LPPS stabilized-zirconia coatings
2002
The elastic constants of yttria stabilised-zirconia coatings produced by a recently developed Low Pressure Plasma Spraying system were measured by in-situ diffraction in a fourpoint bending device. The anisotropic nature of the cubic zirconia coatings was investigated by collecting diffraction data under increasing load along two crystallographic directions ([440] and [620]). The four point bending was such to add compression to the measured coating surface, in order to progressively increase the compressive (residual) stress already present in the material. Unlike conventional Plasma Spray ceramic coatings, the elastic constants and the anisotropy of the studied LPPS coatings are comparable with those of the corresponding bulk materials. Average compressive residual stress in excess of-500 MPa was found in ~24 µm thick coatings.
Ceramics International, 2011
Nanostructured yttria stabilized zirconia (YSZ) coatings were deposited by Atmospheric Plasma Spraying (APS). X-ray diffraction (XRD) was used to investigate their phase composition, while scanning electron microscopy (SEM) was employed to examine their microstructure. The coatings showed a unique and complex microstructure composed of well-melted splats with columnar crystal structure, partially melted areas, which resembled the morphology of the powder feedstock, and equiaxed grains. Vickers microhardness of nanostructured zirconia coatings was similar to that of the conventional ones and strongly depended on the indentation load. Otherwise, a higher thermal shock resistance was found. This effect was addressed to the retention of nanostructured areas in coating microstructure and to the corresponding high porosity. #
Acta Materialia, 2008
The effect of porosity on the thermal diffusivity and elastic modulus has been studied on artificially aged, free-standing thermal barrier coatings (TBCs) produced by air plasma spray (APS). The activation energy of the sintering phenomenon was estimated from the variation in diffusivity with time and temperature. X-ray diffraction was used to evaluate the phase stability of 7 wt.% yttria partially stabilized zirconia (YPSZ) coatings. The thermal diffusivity and elastic modulus as measured by photothermal techniques and three-point bending, respectively, are reported as a function of the ageing time. Correlations between the thermal and mechanical parameters are investigated by suitable models based on the microstructural features revealed by electron microscopy. The reliability of porosity information provided by image analysis and used as input for the modelling is critically discussed.
Strain, 2010
Thermal barrier coatings (TBCs) are widely adopted to protect mechanical components in gas turbine engines operating at high temperature. Basically, the surface temperature of these components must be low enough to retain material properties within acceptable bounds and to extend component life. From this standpoint, air plasma-sprayed (APS) ceria and yttria co-stabilized zirconia (CYSZ) is particularly promising because it provides enhanced thermal insulation capabilities and resistance to hot corrosion. However, essential mechanical properties, such as hardness and Young's modulus, have been less thoroughly investigated. Knowledge of Young's modulus is of concern because it has a significant effect on strain tolerance and stress level and, hence, on durability. The focus of the present study was to determine the mechanical properties of APS CYSZ coatings. In particular, X-ray diffraction (XRD) is adopted for phase analysis of powders and as-sprayed coatings. In addition, scanning electron microscopy (SEM) and image analysis (IA) are employed to explore coating microstructure and porosity. Finally, the Young's modulus of the coating is determined using nanoindentation and a resonant method. The results obtained are then discussed and a cross-check on their consistency is carried out by resorting to a micromechanical model.