Properties of ZrO2-7wt%Y2O3 Thermal Barrier Coatings in Relation to Plasma Spraying Conditions

1997 ◽  
Author(s):  
C. Funke ◽  
B. Siebert ◽  
D. Stöver ◽  
R. Vaßen
Keyword(s):  
Elastic Modulus ◽  
Plasma Spraying ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Free Edge ◽  
Ceramic Coatings ◽  
Thermal Barrier ◽  
Normal Stresses ◽  
Barrier Coatings ◽  
Plasma Sprayed

Abstract Superalloy samples were coated with thermal barrier coatings (TBC). This TBC-system consisted of two layers. The first layer was a vacuum-plasma sprayed, corrosion resistant layer (MCrAlY) which also acted as a bond coat. The ceramic top layer was atmospheric-plasma sprayed Y2O3-stabilized ZrO2. In order to produce different microstructures, the plasma-spraying parameters for the production of the ceramic coatings were varied. The different ceramic coatings were characterized in terms of porosity and mean elastic modulus. The porosity distribution was also investigated due to its influence on the measured elastic modulus. To record the changes of the plasma sprayed Zirconia due to sintering, the mean elastic modulus of selected coatings was measured as a function of annealing time. One series of TBC-coated specimens was cyclically oxidized at a maximum temperature of 1100°C. After 500 h of thermal cycling, creep within the MCrAlY-bond coat led to a coating failure at both the internal beveled edge and free edge around the specimen. A finite element analysis study of the cyclic oxidation experiment was performed to gain insight into the stress redistributions within the bond coat as a function of time. During the initial temperature increase, critical tensile normal stresses developed above the MCrAlY-Zirconia interface at the free edge. However, these normal stresses became compressive for all following cooling cycles. On the other hand, large tensile normal stresses developed above the MCrAlY-Zirconia interface at the beveled edge during all the cooling cycles. Therefore, high normal stresses responsible for debonding were present within the ceramic coating during all cooling cycles with the most critical stresses occurring at the free edge during the first cooling cycle and near the beveled edge for all the following cooling cycles.

Microstructure of Thermal Barrier Coatings (TBC's) Obtained by Using Plasma Spraying and VPA Methods

2012 ◽  
Vol 706-709 ◽  
pp. 2412-2417 ◽  
Author(s):  
Marek Góral ◽  
Stanislaw Dudek ◽  
Ryszard Filip ◽  
Jan Sieniawski
Keyword(s):  
Plasma Spraying ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Nickel Superalloy ◽  
Atmospheric Plasma ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Bond Coats ◽  
Pack Aluminizing ◽  
Plasma Sprayed

Thermal Barrier Coatings are the main type of coatings used for protecting turbine blade surfaces and the surface of modern jet engines combustion chamber parts. Depending on the type of engine element, the coatings are produced as plasma-sprayed MeCrAlY bond-coats with a ceramic outer layer or as Pt-modified aluminide coatings with a ceramic EB-PVD-deposited layer. Currently, research is being conducted on the deposition of a new type of coatings consisting of bond-coats with mulitlayer structure. In the article, the results of the study on the obtainment of TBC's with multilayer structure are presented. To obtain the metallic bond-coat, the process of atmospheric plasma spraying and the out of pack aluminizing (VPA) method were combined. The coatings were deposited on the surface of Rene 80 nickel superalloy. The first layer of the coating was a plasma-sprayed MCrAlY bond-coat, on which a diffusion aluminide layer was deposited with out of pack method. On the bond-coat, a standard ceramic zirconium oxide (ZrO2*20Y2O3) layer was deposited. The microstructure analysis, was conducted, using light and SEM microscopy. The phase and chemical composition analyses were done using EDS and XRD methods.

NONDESTRUCTIVE IMPEDANCE SPECTROSCOPY EVALUATION OF THE BOND COAT OXIDATION IN THERMAL BARRIER COATINGS

2007 ◽  
Vol 14 (05) ◽  
pp. 935-943 ◽  
Author(s):  
L. YANG ◽  
Y. C. ZHOU ◽  
W. G. MAO ◽  
Q. X. LIU
Keyword(s):  
Impedance Spectroscopy ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Equivalent Circuit Model ◽  
Isothermal Oxidation ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Barrier Coatings ◽  
Plasma Sprayed

In this paper, the impedance spectroscopy technique was employed to examine nondestructively the isothermal oxidation of air plasma sprayed (APS) thermal barrier coatings (TBCs) in air at 800°C. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were also used to characterize the microstructure evolution of TBCs. After oxidation, the thermally grown oxide (TGO), which was mainly composed of alumina as confirmed by EDX, formed at the upper ceramic coat/bond coat interface, the lower bond coat/substrate interface, and the bond coat. Impedance diagrams obtained from impedance measurements at room temperature were analyzed according to the equivalent circuit model proposed for the TBCs. Various observed electrical responses relating to the growth of oxides and the sintering of YSZ were explained by simulating the impedance spectra of the TBCs.

Improvement of EB-PVD thermal barrier coatings by treatments of a vacuum plasma-sprayed bond coat

2008 ◽  
Vol 203 (1-2) ◽  
pp. 160-170 ◽  
Author(s):  
U. Schulz ◽  
O. Bernardi ◽  
A. Ebach-Stahl ◽  
R. Vassen ◽  
D. Sebold
Keyword(s):  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Vacuum Plasma ◽  
Plasma Sprayed

scholarly journals Ceramic Thermal Barrier Coatings for Turbine Engine Components

1982 ◽  
Author(s):  
D. S. Duvall ◽  
D. L. Ruckle
Keyword(s):  
Thermal Barrier Coatings ◽  
Ceramic Coatings ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Turbine Engine ◽  
Thermal Environments ◽  
Strain Tolerance ◽  
Endurance Testing ◽  
Plasma Sprayed ◽  
Cooling Air

The durability of plasma sprayed ceramic thermal barrier coatings subjected to cyclic thermal environments has been improved substantially by improving the strain tolerance of the ceramic structure and also by controlling the substrate temperature during the application of the coating. Improved strain tolerance was achieved by using ceramic structures with increased porosity, microcracking or segmentation. Plasma spraying on a controlled-temperature substrate also has been shown to improve durability by reducing harmful residual stresses. The most promising of the strain tolerant ceramic coatings have survived up to 6000 cycles of engine endurance testing with no coating or vane platform damage. In side-by-side engine tests, thermal barrier coatings have shown that they greatly reduce platform distress compared to conventionally coated vanes in addition to permitting reductions in cooling air and attendant increases in engine efficiency.

Thermal Cycling Behavior of Lanthanum-Cerium Oxide Thermal Barrier Coatings Prepared by Air Plasma Spraying

2007 ◽  
Vol 336-338 ◽  
pp. 1759-1761 ◽  
Author(s):  
Wen Ma ◽  
Yue Ma ◽  
Sheng Kai Gong ◽  
Hui Bin Xu ◽  
Xue Qiang Cao
Keyword(s):  
Cerium Oxide ◽  
Plasma Spraying ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Room Temperature ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Air Plasma Spraying ◽  
Cyclic Testing ◽  
Barrier Coatings

Lanthanum-cerium oxide (La2Ce2O7, LC) is considered as a new candidate material for thermal barrier coatings (TBCs) because of its low thermal conductivity and high phase stability between room temperature and 1673K. The LC coatings with different La2O3 contents were prepared by air plasma spraying (APS) and their lifetime was evaluated by thermal cyclic testing from room temperature to 1373 K. The structures of the coatings were characterized by XRD and SEM and the deviation of the composition from the powder was determined by EDS analysis. Long time annealing for the freestanding coating at 1673K reveals that the near stoichiometric LC coating is stable up to 240h, and the stability decreases with increasing the deviation from stoichiometric LC composition. During thermal cyclic testing, spallation was observed within the top coat near the bond coat. It is considered that the effect of intrinsic stress caused by the coefficient of thermal expansion (CTE) mismatch between top coat and bond coat is larger than that of thermally grown oxide (TGO) and the bond adherence of top coat with TGO.

scholarly journals The Numerical Modeling of Thermal Stress Distribution in Thermal Barrier Coatings

2017 ◽  
Vol 62 (3) ◽  
pp. 1433-1437
Author(s):  
A. Jasik
Keyword(s):  
Thermal Stress ◽  
Stress Distribution ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Thermal Spraying ◽  
Ceramic Coatings ◽  
Thermal Barrier ◽  
Insulation Layer ◽  
Barrier Coatings ◽  
Thermal Stress Distribution

Abstract The paper presents the results of numerical calculations of temperature and thermal stress distribution in thermal barrier coatings deposited by thermal spraying process on the nickel based superalloy. An assumption was made to apply conventional zirconium oxide modified with yttrium oxide (8YSZ) and apply pyrochlore type material with formula La2Zr2O7. The bond coat was made of NiCoCrAlY. Analysis of the distribution of temperature and stresses in ceramic coatings of different thicknesses was performed in the function of bond-coat thickness and the type of ceramic insulation layer. It was revealed that the thickness of NiCrAlY bond-coat has not significant influence on the stress distribution, but there is relatively strong effect on temperature level. The most important factor influenced on stress distribution in TBC system is related with type and properties of ceramic insulation layer.

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

2015 ◽  
Vol 275 ◽  
pp. 276-282 ◽  
Author(s):  
Zhonghua Zou ◽  
Jack Donoghue ◽  
Nicholas Curry ◽  
Lixia Yang ◽  
Fangwei Guo ◽  
...  
Keyword(s):  
Comparative Study ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Plasma Sprayed

scholarly journals Thermal Shock and Oxidation Stability Tests to Grade Plasma Sprayed Functionally Gradient Thermal Barrier Coatings

2019 ◽  
Vol 1 (1) ◽  
pp. 1-11
Author(s):  
Pasupuleti Kirti Teja ◽  
Parvati Ramaswamy ◽  
Narayana Murthy S.V.S.
Keyword(s):  
Thermal Barrier Coatings ◽  
Inconel 718 ◽  
Oxidation Stability ◽  
Ceramic Coatings ◽  
Functionally Graded ◽  
Yttria Stabilized Zirconia ◽  
Thermal Barrier ◽  
Stabilized Zirconia ◽  
Barrier Coatings ◽  
Plasma Sprayed

Functionally graded layers in thermal barrier coatings reduce the stress gradient between the overlaid ceramic coatings and the underlying metallic component. Introduced to alleviate early onset of spallation of the coating due to thermal expansion mismatch, this facilitates improvement in the life of the component. Conventional thermal barrier coatings typically comprise of duplex layers of plasma sprayed 8% yttria stabilized zirconia (ceramic) coatings on bond coated (NiCrAlY) components/substrates (Inconel 718 for example). This work highlights the superiority of plasma sprayed coatings synthesized from blends of the intermetallic bond coat and ceramic plasma spray powders on Inconel 718 substrates in three-layer configuration over the duplex layered configuration. Assessed through (a) thermal shock cyclic tests (at 1200oC and 1400oC) in laboratory scale basic burner rig test facility and (b) oxidation stability test in high temperature furnace (at 800oC and 1000oC) the functionally graded coatings of certain configurations exhibited more than double the life of the conventional 8% yttria stabilized zirconia duplex (double layer) coatings. Micro- and crystal structure analysis support the findings and results are detailed and discussed.

scholarly journals Mechanisms Controlling the Performance and Durability of Thermal Barrier Coatings

2000 ◽  
Author(s):  
Daniel R. Mumm ◽  
Anthony G. Evans
Keyword(s):  
Thermal Cycling ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Large Scale ◽  
Mechanical Performance ◽  
Thermal Protection ◽  
Crack Nucleation ◽  
Ceramic Coatings ◽  
Thermal Barrier ◽  
Barrier Coatings

Abstract Thermal protection systems based on ceramic thermal barrier coatings (TBCs) are used extensively to protect hot-section components in gas turbine engines. They comprise thermally insulating ceramic coatings, deposited on an aluminum-containing intermetallic bond coat (BC) that provides oxidation protection. A thin thermally-grown oxide (TGO layer forms between the TBC and BC during cyclic thermal exposure. Each of the system constituents evolves in service and all interact during thermal cycling to control the thermo-mechanical performance of the system. Exposed to thermal cycling conditions, TBC systems are susceptible to loss of adhesion and spalling failures. Multiple failure mechanisms exist, dependent upon differing thermal histoiy and processing approach for various coating systems. Coating failure is ultimately controlled by the large residual compression in the TGO and its role in amplifying the effects of imperfections in the vicinity of the TGO. The failure occurs through a process involving crack nucleation, propagation and coalescence events. For a particular commercial system, it is found that the TGO ‘ratchets’ into the bond coat with each thermal cycle, at an array of interfacial sites. The displacements induce strains in the superposed TBC that cause it to crack. The cracks extend laterally as the TGO ratcheting process proceeds, until the cracks from neighboring sites coalesce. Once this happens, the system fails by large scale buckling. It is shown that the displacements are ‘vectored’ by a lateral component of the growth strain in the TGO. The relative roles of bond coat visco-plasticity, initial interface morphology, and phase evolution are discuss. The behavior observed for this system is compared with predictions of a ratcheting model, as well as with the behavior observed for other commercial coating systems.

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