Plasma-sprayed YSZ coatings: Microstructural features and resistance to molten metals (original) (raw)
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Archives of Civil and Mechanical Engineering
Yttrium-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are indispensable elements of present-day turbine propulsion systems. The ones deposited with atmospheric plasma spraying (APS) are characterized by required low thermal conductivity, but they are unable to survive frequent thermomechanical loading and therefore their application is limited to parts remaining stationary. Expanding capability of TBCs is sought in various areas, but the one realized through modification of most proliferated apparatus used for plasma spraying (PS) (from radial to axial injection) and substituting micrometric powders with the nano-structured suspension needs least changes in the industry established procedures and offers the highest property improvement. The present experiment covered the deposition of ZrO2-8Y2O3 YSZ TBC using both atmospheric and suspension PS processes. They were performed with commercial micrometric and nano-structured YSZ (8% Y2O3) powders. The coatings morphology and...
Ceramics International, 2012
In the present work, the hot corrosion behavior of two types of multilayer plasma sprayed TBC were investigated and compared with functionally graded and conventional TBCs. These kinds of multilayer coatings consisted of nano/μ alumina as a top coat on YSZ layer, a metallic bond coat and a functionally graded intermediate layer deposited between YSZ and bond coat layers. All the layers were sprayed on the Ni-base super alloy substrate. The hot corrosion resistance of the plasma sprayed coatings was examined at 1050°C for 40 h, using a fused mixture of 45 wt% Na 2 SO 4 + 55wt%V 2 O 5. Before and after hot corrosion, the microstructure and phase analysis of the coating were studied using scanning electron microscope and X-ray diffractometer. The results showed that, the Al 2 O 3 top layer acted as a barrier against the infiltration of the molten salt into the YSZ layer during exposure to the molten salt mixture at the high temperature and the multilayer coatings of zirconia/alumina with the nanostructured alumina as a top coat showed higher hot corrosion resistance. Also, the failure mechanisms of the functionally graded coating and duplex TBC were investigated. The spallation occurred between the graded layer and the bond coat/top coat in functionally graded TBC and duplex TBC, respectively.
Current Nanoscience, 2012
Yttria stabilized zirconia (YSZ) nanostructured and conventional coatings have been prepared by atmospheric plasma spraying (APS) on NiCoCrAlY-coated superalloy substrates. Bonding strength test was carried out based on the ASTM-C-633-01. To evaluate thermal insulation value of coatings, the thermal insulation capability test was designed and administered. Field emission scanning electron microscope (FESEM) and X-ray diffractometry (XRD) were employed to characterize the microstructures and the phase compositions of the powders and coatings. Nanostructured YSZ coating exhibited a bimodal microstructure consisting of nanosized particles retained from the powder and microcolumnar grains formed through the resolidification of the molten part of powder, whereas the microstructure of conventional YSZ coating consisted of columnar-grain splats. Both nanostructured and conventional YSZ coatings consisted of the non-transformable tetragonal phase. The results revealed that nanostructured coating, due to unique microstructure container of nanozones, presented improved bonding strength and thermal insulation capability as compared to the conventional coating.
Mechanical and microstructural charaterization of YSZ/Al2O3 /CeO2 plasma Sprayed coatings
Journal of Electrochemical Science and Engineering
In the present work, the surface characterization of YSZ/Al2O3 /CeO2 plasma sprayed coatings was performed to understand the surface characteristics. The content of the Yttria-stabilized zirconia (YSZ) was 60 wt.% , where alumina was varied from 30 to 38 wt.% and CeO2 from 2 to 10 wt.%, respectively. Ceramic coatings with a different percentage variation of composite materials were used to increase layer strength on a substrate of SS-304. The SEM micrographs were analysed to understand the features present on the surface of coatings, and XRD analysis was done to know the phases present in the coatings. Microhardness and porosity decrease with the addition of CeO2 in the YSZ-based coatings.
Surface & Coatings Technology, 2017
The paper describes the ceramic top coats of Thermal Barrier Coatings (TBC) obtained by Suspension Plasma Spraying (SPS). The spray process realized with different plasma torches allowed obtaining coatings having different morphology, namely, columnar-like and two-zones microstructure. The microstructures influenced the thermal transport properties of TBC's. The study analyses the thermophysical properties of yttria and yttria-with ceria-stabilized zirconia coatings, i.e. YSZ and YCeSZ, respectively. The spray processes were realized with the use of three different plasma spray torches: (i) SG-100; (ii) Axial III and (iii) hybrid WSP one. The deposition parameters were designed for each plasma torch separately. The microstructure of coatings was then analyzed using Optical and Scanning Electron Microscopy i.e. OM and SEM, respectively. The thermophysical properties of the coatings such as density, specific heat and thermal dilatation were measured using gas pycnometry, calorimetry and dilatometry methods respectively. The collected data were used, together with thermal diffusivity found with the use of laser flash method, to calculate the thermal conductivity of the deposits. The thermal conductivities of coatings were in a range from 0.63 to 0.99 [W/m•K] for YSZ samples and between 0.82 and 1.37 [W/m•K] in the case of YCeSZ coatings. Thermal transport properties were found to be influenced by the coatings' porosity and their microstructure. Finally, the thermal conductivity values were successfully validated using response function method, which can be an alternative to complex FEM methods.
Nanostructured and conventional YSZ coatings deposited using APS and TTPR techniques
Surface and Coatings Technology, 2006
Multilayer thermal barrier coatings are candidate materials for high temperature applications that are novel because they employ a strain accommodating interlayer. Plasma sprayed coatings of nanostructured feedstock have shown promise in this direction. Layers of nanostructured yttria stabilized zirconia (nano-YSZ) and conventional YSZ were deposited on mullite substrates using the triple torch plasma reactor (TTPR), and on NiCrAlY coated steel substrates using the Praxair SG-100 plasma torch. It has been observed that a wide range of microstructures and porosities can be produced by combining these deposition techniques and varying the feedstock materials. This control over the microstructure enables the achievement of coating properties that can be tailored according to the application and environment.
Ceramics International, 2010
Thick plasma sprayed thermal barrier coatings are suitable for thermal and hot corrosion protection of metal components in land-based turbine and diesel engines. In this work, ceria-yttria co-stabilized zirconia coatings were deposited by atmospheric plasma spraying in a mixture of nontransformable tetragonal t 0 and cubic c zirconia phases. Free-standing coatings were isothermally annealed at 1315 8C for different times and their crystal structure was studied by XRD. No phase decomposition occurred. Columnar grains grew in the molten splats with increasing annealing time according to a preferential direction and, after 50 h of heat treatment, they were partially replaced by equiaxed grains. Both in-plane and out-ofplane thermal expansion coefficients (CTEs) were measured from coating expansion during heating. The CTE was slightly sensitive to thermal exposure in out-of-plane direction, whereas it kept almost constant in plane direction. The specific heat capacity Cp of annealed coatings, measured by differential scanning calorimetry (DSC), decreased in comparison with as-sprayed coating, due to high-temperature sintering.
2020
In this study, conventional and nanostructured yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were deposited by atmospheric plasma spraying (APS) on Ni superalloy with NiCrAlY as bond coat. The TBCs were exposed to isothermal oxidation tests in an electric furnace under air at 1100 ̊C for 100, 200, 300, 400 and 600 hours and were investigated in terms of microstructure and microcomposition by using the scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The nanostructured YSZ coatings showed a better performance at isothermal oxidation tests, in particular in terms of thickness of thermally grown oxide (TGO) layer which had a parabolic growth behavior.
Hot corrosion behavior of Al2O3 laser clad plasma sprayed YSZ thermal barrier coatings
Ceramics International, 2016
In the present study, the laser cladding of Al 2 O 3 on the top surface of air plasma sprayed (APSed) yttria stabilized zirconia (YSZ) coatings was carried out to improve the hot corrosion resistance of the thermal barrier coatings (TBCs) in the presence of molten salts. The coatings with and without laser cladding were subjected to a hot corrosion test at 1000°C for 30 h in which a mixture of 55 wt% V 2 O 5 and 45 wt% Na 2 SO 4 was used as the corrosive salt. SEM micrographs and EDS analysis confirmed the formation of YVO 4 rod-shaped crystals dispersed on the surface of the APSed YSZ coatings after hot corrosion test, while these crystals were hardly detected in the laser clad coatings. The SEM micrograph of the cross section of the APSed YSZ coatings revealed cracks and a thermally grown oxide (TGO) layer in the bond coat/top coat interface, which led to the complete delamination of the coatings. Supporting the SEM micrographs, XRD patterns indicated the transformation of metastable tetragonal zirconia (t ′-ZrO 2) to monoclinic zirconia (m-ZrO 2) after hot corrosion test. This structural transformation was due to the reaction of the molten salts with Y 2 O 3 (zirconia stabilizer) which destabilized the t ′-ZrO 2. To compare the hot corrosion resistance of the APSed YSZ and the laser clad coating, the volume percentage of the undesirable m-ZrO 2 was then calculated after the hot corrosion test. This calculation revealed a higher amount of m-ZrO 2 in YSZ (about 70 vol%) compared to that of the laser clad coating (about 13 vol%).