Research on the Stability of Thermal Barrier Coatings under Thermal Cyclic Loading

2017 ◽  
Vol 730 ◽  
pp. 75-80 ◽  
Author(s):  
Jian Sun ◽  
Ying Qiang Xu ◽  
Wan Zhong Li ◽  
Kai Lv
Keyword(s):  
Cyclic Loading ◽  
Stress Field ◽  
Evaluation Method ◽  
Thermally Grown Oxide ◽  
Interfacial Stress ◽  
Thermal Barrier ◽  
Fea Model ◽  
Barrier Coating ◽  
The Stability ◽  
Evolution Behavior

Thermal barrier coating systems (TBCs) are widely used in turbines. However, premature failures have impaired the use of TBCs and cut down their lifetime. The thermally grown oxide layer (TGO) thickening and the material thermal expansion misfit under thermal cyclic loading significantly affect the interfacial stress field and stability of TBCs. In this study, the stability evaluation method of TBCs under thermal cyclic loading based on energy is established using the visco-elastoplastic and shakedown theorem. The semicircular shape interface is used to simplify the complicated interfacial undulations in FEA model. And actual TGO thickness obtained from experiment is used to simulate the bond coat oxidation. Then the effect of TGO thickening on the stability and stress field of TBCs under thermal cyclic loading is analyzed through the numerical simulation. It is concluded that estimating from the stress-strain evolution behavior, the local stability of the TBCs decreases with the TGO thickening, and assessing from energy, TBCs shows instable with TGO thickening.

Delamination toughness of electron beam physical vapor deposition (EB-PVD) Y2O3–ZrO2 thermal barrier coatings by the pushout method: Effect of thermal cycling temperature

2008 ◽  
Vol 23 (9) ◽  
pp. 2382-2392 ◽  
Author(s):  
M. Tanaka ◽  
Y.F. Liu ◽  
S.S. Kim ◽  
Y. Kagawa
Keyword(s):  
Electron Beam ◽  
Thermal Cycling ◽  
Bond Coat ◽  
Physical Vapor Deposition ◽  
Thermally Grown Oxide ◽  
Test Method ◽  
Thermal Barrier ◽  
Barrier Coating ◽  
Delamination Toughness ◽  
Cycling Temperature

A pushout test method was used to quantify effect of thermal cycling temperatures on the delamination toughness of an electron beam physical vapor deposited thermal barrier coating (EB-PVD TBC). The delamination toughness, Γi, was related to the maximum thermal cycling temperature, Th, equal to 1000, 1025, 1050, and 1100 °C. The measured delamination toughness varied from 9 to 95 J/m2. At Th = 1000 °C, Γi attained a maximum value, larger than that of the as-deposited sample and decreasing with increased Th. During the thermal cycling tests, the thermally grown oxide (TGO) was formed between the TBC and the bond coat deposited onto the superalloy substrate. Inside the TGO layer, mixture of Al2O3 and ZrO2 oxides was observed close to the TBC side with nearly pure Al2O3 phases close to the bond-coat side. During the pushout test, delamination occurred at the interface of the mixture and pure Al2O3 layer with an exception for Th = 1100 °C specimens where delamination also occurred at the interface between the TGO and bond-coat layers. The effect of thermal cycling temperatures on the delamination toughness is discussed in terms of the microstructural change and delamination behavior.

scholarly journals Development of Evaluation Method for Damage of Oxidation CoNiCrAlY Coating

2019 ◽  
Vol 804 ◽  
pp. 47-51
Author(s):  
Mo Chen ◽  
Kodai Yoshikawa ◽  
Zhen Qiang Song ◽  
Shijie Zhu
Keyword(s):  
Cross Sections ◽  
Gas Turbines ◽  
Evaluation Method ◽  
Thermal Spraying ◽  
Optical Microscope ◽  
Thermally Grown Oxide ◽  
Interfacial Damage ◽  
Barrier Coating ◽  
Plasma Sprayed ◽  
Conicraly Coating

The bond coat plays an important role in the failure of the thermal barrier coating (TBC) system used for gas turbines [1,2]. In this research, the CoNiCrAlY coated Ni-base superalloy specimens were used for developing evaluation method for interfacial damage in the coat. Samples were exposed at 1000°C and 1100°C for up to 1000 hours. The morphology and residual stress in the thermally grown oxide (TGO) layer on the CoNiCrAlY coating were characterized by microscopic observation and luminescence spectroscope, respectively. The microstructure and damage o\n both the coating surfaces and the cross sections were observed by optical microscope and scanning electron microscope. According to the results, the low pressure plasma sprayed CoNiCrAlY coating (LPPS) showed the thinnest TGO layer and lowest residual stress.Residual stress decreased with an increase in exposure time, depending on the morphology of TGO layer. The effects of thermal spraying methods on the oxidation of yttrium in TGO layer and BC layer and its influence on interfacial damage were discussed.

Damage Accumulation Mechanisms in Thermal Barrier Coatings

1998 ◽  
Vol 120 (2) ◽  
pp. 149-153 ◽  
Author(s):  
G. M. Newaz ◽  
S. Q. Nusier ◽  
Z. A. Chaudhury
Keyword(s):  
Damage Evolution ◽  
Oxide Thickness ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Progressive Damage ◽  
Material System ◽  
Thermal Cycles ◽  
Delamination Crack ◽  
Barrier Coating ◽  
Electron Beam Plasma

Progressive damage evolution leading to spallation was investigated in Electron Beam—Plasma Vapor Deposition (EB-PVD) partially stabilized zirconia thermal barrier coating (TBC) applied to Nickel-based single crystal superalloy, Rene N5 with PtAl bondcoat. Thermal cycles were between 200-1177C. Progressive damage evolution was monitored using microscopy on samples subjected to a series of thermal cycles. Fick’s law can describe the thermally grown oxide (TGO) thickness for early cycles. However, at higher number of thermal cycles, damage in the form of microcracks and their link-up results in the development of a larger delamination crack through the TGO layer and monitoring oxide thickness becomes difficult. Thus, both oxidation kinetics and damage appears to play significant roles as they relate to spallation. As the early microcracks coalesce to form a major delamination crack, the susceptibility for TBC buckling is increased. The damage thickness continues to increase with number of thermal cycles indicating a progressive buckling condition. Estimation shows that a delamination crack length of about sixteen times the TBC thickness is needed for the current material system to cause buckling. Progressive microcrack linking to form a large delamination crack followed by progressive buckling of the TBC layer appear to promote spallation. Physical evidence of microcrack link-up and progressive buckling was found in specimens prior to complete spallation.

Modeling Thermally Grown Oxides in Thermal Barrier Coatings Using Koch Fractal

2019 ◽  
Author(s):  
Peter Warren ◽  
Sandip Haldar ◽  
Seetha Raghavan ◽  
Ranajay Ghosh
Keyword(s):  
Thermal Barrier Coating ◽  
Critical Role ◽  
Thermally Grown Oxide ◽  
Stress Generation ◽  
Interfacial Region ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Barrier Coating ◽  
Koch Fractal ◽  
Thermally Grown

Abstract Growth of the Thermally Grown Oxide (TGO) between the bond coat and thermal barrier coating (TBC) during service is one of the most common causes of failure within thermal barrier coating (TBC) systems. Initially this oxide will provide protection from oxidation for the substrate, but stress build up will contribute to delamination of the topcoat. Research has been carried out over the stresses caused by this TGO growth, and how to best mitigate these induced stresses. The interface topography plays a critical role for air plasma sprayed (APS) TBCs in development of stress profiles across the TGO/TBC interface [1, 2]. The APS TBCs fail by cracking in the TBC close to the TGO-TBC interface. Most models treat TGO as a sinusoidal wavelength interface. However, most TGO surfaces have been experimentally observed to have fractal like patterns at the interfacial region of the bondcoat and topcoat. Fractals provide us a better understanding of interactions at rough interfaces between two materials adhered to one another. In this work, we model the topography of the TGO using a Koch fractal. We find the geometry selected to model the TGO layer has a direct effect on the stress generation and creep strain during simulation.

TGO Formation with NiCoCrAlYTa Bond Coat Deposition Using APS and HVOF Method

2015 ◽  
Vol 1125 ◽  
pp. 18-22 ◽  
Author(s):  
S. Mohd Zulkifli ◽  
Muhammad Azizi Mat Yajid ◽  
Mohd Hasbullah Idris ◽  
M. Daroonparvar ◽  
Halimaton Hamdan
Keyword(s):  
Bond Coat ◽  
Oxidation Process ◽  
Thermally Grown Oxide ◽  
Inconel 625 ◽  
Thermal Barrier ◽  
Air Plasma Spray ◽  
Air Plasma ◽  
Continuous Layer ◽  
Barrier Coating ◽  
Coating Failure

Formation of thin and continuous layer of thermally grown oxide (TGO) in thermal barrier coating (TBC) are essential in order to avoid coating failure for high temperature applications. As-sprayed high velocity oxy-fuel (HVOF) bond coat can provide more uniform TGO layer in TBC system and much less oxide compare to air plasma spray (APS). In this paper, both APS and HVOF method are used to deposit NiCoCrAlYTa bond coat on Inconel 625 substrate followed by topcoat, YSZ deposition. Pre-oxidation process was done in normal oxygen furnace at 1000°C for 12 to 24 hours to study the characteristic of TGO formation via these two different methods. From the result obtained, it shows that HVOF method provide better TGO formation as compared to APS.

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