Thermophysical and microstructural characterisation of modified thick yttria stabilised zirconia thermal barrier coatings (original) (raw)
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Advances in Materials Science and Engineering : An International Journal (MSEJ), 2016
Thermal Barrier Coatings (TBCs), routinely prepared from Ceramic based compositions (typically 8%Y2O3-ZrO2or 8YSZ) are being engineered to protect the metallic components from degradation in applications like gas turbines, jet and automotive engines. With a goal of finding improved TBC materials a wide variety of ceramics are being researched worldwide. Before physically preparing the TBCs of uncommon compositions in the laboratory, their suitability to perform can be predicted. Limited accessibility to detailed and realistic information on the influence of newer compositions (other than 8YSZ) on TBCs warrants methods to obtain this information.
Modified thick thermal barrier coatings: Thermophysical characterization
Journal of the European Ceramic Society, 2004
Thermophysical properties of modified zirconia based thick thermal barrier coatings (8Y 2 O 3-ZrO 2 , 25CeO 2-2.5Y 2 O 3-ZrO 2 and 22MgO-ZrO 2) were characterized at temperature range of RT-1300 C. Coatings were studied in laser-glazed and phosphate sealed state, and their properties were compared to as-sprayed coatings. Laser glazing affected only slightly on thermal conductivity of the studied coatings. If the segmentation cracks, induced by laser glazing, were oriented vertically like in the case of laser-glazed 8Y 2 O 3-ZrO 2 coating, thermal conductivity was increased in some degree. But if the orientation of the segmentation cracks was deviated from the vertical direction or if the cracks were branched, thermal conductivity was decreased. This was the case with the laserglazed 25CeO 2-2.5Y 2 O 3-ZrO 2 and 22MgO-ZrO 2 coatings. Phosphate based sealing treatments were found to increase the thermal conductivity of all coatings. Aluminium phosphate sealing also lowered the high temperature stability of the 8Y 2 O 3-ZrO 2 coating down to 1000 C. In 8Y 2 O 3-ZrO 2 and 25CeO 2-2.5Y 2 O 3-ZrO 2 based coatings thermal conductivity was increased in consecutive measurement cycles, caused mainly by the sintering based phenomena in which the contact between overlapping lamellae was improved. Thermal conductivity of the 22MgO-ZrO 2 based coatings was increased significantly in the first measurement cycle because of the unstabilization of zirconia-caused by precipitation of MgO.
Characterization of thermal barrier coatings with a gradient in porosity
Surface & Coatings Technology, 2005
A major problem in thermal barrier coatings (TBC) applied to gas turbine components is the spallation of ceramic coating under thermal cycling processes. In order to prevent spallation and improve the thermomechanical behaviour of the TBC, graded ceramic coatings can be produced. For this purpose we are developing a new concept of Thermal Barrier Coating (TBC) that consist of a conventional NiCoCrAlY bond coat and an atmospheric plasma sprayed ZrO 2 -8 wt.%Y 2 O 3 top coat graded in porosity on an Inconel 738 LC substrates. The aim of this work is to produce coatings with low thermal conductivity and better thermomechanical behaviour due to the gradient in porosity which reflects a gradient in the elastic properties. Absolute porosity was measured with a mercury porosimetry and by image analysis. The second technique was also used to estimate the porosity variation along the cross-section. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to observe the morphology and coating microstructure. The microhardness was measured with a Vickers indenter and 0.981 N load. The microhardness has been evaluated for coatings in as-sprayed condition and after annealing at 1100 8C during 100 h. The results show a fast increase of the hardness after annealing. After thermal shock heating at 1000 8C, 1 h and quickly cooling in water no spallation was observed for 100 cycles. D 2004 Published by Elsevier B.V.
Stabilize Consequences of Y2O3 in Zirconia Thermal Barrier Coatings (TBC)
The accumulation of cubic stabilizing oxides is a pre-requisite for the use of Zirconia as a main voter in thermal barrier coating. These can be added in ample amounts to form a partially stabilized Zirconia or to form a fully stabilized Zirconia. Zirconia yttria (ZrO2.Y2O3) coating deposited by plasma spray method is widely used in industry as a thermal barrier coating (TBC). Development of narrative and innovative ceramic materials, which have brought about significant hi-tech change, predominately by Y 2 O 3 for the accumulation of varying amounts of cubic stabilizing oxide. This paper is a study on the effect of stabilizer on performance of ZrO 2 thermal barrier coatings. For experimentation, Y2O3 complete characterization was done with ZrO2.Y2O3 coated samples to optimize the micro structural, mechanical properties and characterization, using the latest techniques. It was observed that porosity content in all the coated samples was not very high. However the porosity content was uniformly distributed and pore size was small. It has been revealed that, in case of small porosity content, hardness values of thermal barrier coating with stabilizing effect of yttria were not very high.
Effect of Bondcoat Thickness on High Temperature Hot Corrosion of ZrO2-8Y2O3Thermal Barrier Coating
Thermal barrier coatings (TBCs) are widely used for industrial and aero turbines. The use of residual fuel oil is well known due to economic reasons, which causes hot corrosion. Hot corrosion over extended exposures reduces durability. Therefore, there is a requirement to develop new design approaches for TBCs in order to operate under hot corrosion environment. In this paper, the effect of bond coat thickness on the hot corrosion resistance was studied. Hot corrosion test were carried out in 50 wt.% Na2So4 + 50 wt.% V2O5 molten salt at 950 • C for 50 hours. The characterizations of the coatings included X-ray diffraction analysis, scanning electron microscopy and optical microscope. Results indicated that TBCs with thick bond coat exhibited superior hot corrosion resistance to the TBCs with conventional bond coat.
Enhanced thick thermal barrier coatings that exhibit varying porosity
Materials Science and Engineering: A, 2008
Thick thermal barrier coatings (TBCs) are defined within the current work as coatings that range from 1.5 to 2 mm in thickness. The microstructure and the porosity of the yttria partially stabilized zirconia (YPSZ) coating are controlled with respect to its resistance to thermal cycling fatigue (TCF). TBCs have been produced by means of a MCrAlY bond coat and YPSZ top coat, both sprayed by air plasma spray. Plasma spray experiments have been performed to obtain an appropriate coating microstructure. Ceramic coatings have been prepared at four levels of plasma jet energy to obtain different levels of porosity, with the aim of keeping the general ceramic coating microstructure constant.
Morphology and thermal conductivity of yttria-stabilized zirconia coatings
Acta Materialia, 2006
An electron beam directed vapor deposition method was used to grow 7 wt.% Y 2 O 3-ZrO 2 (7YSZ) coatings and the effects of substrate rotation upon the coating porosity, morphology, texture, and thermal conductivity were explored. As the rotation rate was increased, the texture changed from AE1 1 1ae to AE1 0 0ae. Under stationary deposition, the coatings were composed of straight columns, while low-frequency rotation resulted in wavy columns. Increases in rotation rate resulted in a gradual straightening and narrowing of the growth columns. The pore fraction slowly decreased as the rotation rate increased. The thermal conductivity was found to be inversely related to the pore fraction. The structural and thermal conductivity alterations are a result of changes to flux shadowing associated with specimen rotation in a gas jet-entrained vapor plume. The minimum thermal conductivity at a low rotation rate is 0.8 W/(m K), well below that of conventionally deposited coatings.
Methods for Film Synthesis and Coating Procedures
The fast consumption of fossil fuel resources and economic competitiveness makes it necessary to increase the efficiency of turbine engines. For this purpose, thermal barrier coating (TBC) has been used on some critical parts of gas turbines. Yttria-stabilized zirconia (YSZ) is widely and commercially used as a ceramic top coat material for TBC in the gas turbine system. On the other hand, the efforts to identify new material having better properties than YSZ have been continued. Gadolinium zirconate (GZ) is a promising alternative TBC material with its lower thermal conductivity, better sintering ability, and higher melting point and phase stability than YSZ. However, recent research studies on the responses of GZ-based TBC materials to the complex demands of modern gas turbine applications should be gathered under a study by comparing them with the results of traditional TBC material. This chapter discusses the GZ based TBC system, specifically addressing issues related to the production process and designing of the coating architecture, in comparison with some of the significant properties with YSZ and the test methodology. Moreover, the chapter also contains information about laser surface modification of the GZ-based TBC.
Vacuum, 2020
Oxidation is an inevitable failure mechanism under the operating temperature in gas turbines. To avoid negative effects of oxidation, ceramic-based materials having low thermal conductivity and high stability should be used to hot section components. In accordance with this purpose, thermal barrier coatings (TBCs) are used in order to increase the lifetime of gas turbine engine components that have not reached to desired levels yet. Yttria stabilized zirconia (YSZ) has been used as a conventional top coat material in TBCs. Increased the turbine inlet temperatures (TIT) promote to researchers to try higher stable material such as rare earth zirconates. In this study, CoNiCrAlY metallic powders were sprayed using a new emerging technique as called cold gas dynamic spray (CGDS) on Inconel 718 substrates. Single layer YSZ, Gd 2 Zr 2 O 7 and double-layered YSZ/Gd 2 Zr 2 O 7 were deposited by electron beam physical vapor deposition (EB-PVD) technique as top coat materials. In high temperature furnace, both TBC samples were isothermally oxidized at 1000 � C under different time periods. TBCs were examined as microstructural before and after oxidation tests. Thermally grown oxide (TGO) layer forming at the interface during oxidation were investigated and compared for each TBC systems. Oxidation and TGO growth behaviors were discussed.