Failure of a Thermal Barrier System Due to a Cyclic Displacement Instability in the Thermally grown Oxide

2000 ◽  
Vol 645 ◽  
Author(s):  
Daniel R. Mumm ◽  
Anthony G. Evans
Keyword(s):  
Bond Coat ◽  
Large Scale ◽  
Thermal Exposure ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Oxide Interface ◽  
Barrier Coating ◽  
Out Of Plane ◽  
Plane Displacement ◽  
Thermally Grown

ABSTRACTThe mechanism controlling the cyclic failure of a commercial thermal barrier system has been investigated. The system comprises an electron-beam physical vapor deposited (EB-PVD) yttria-stabilized zirconia thermal barrier coating (TBC), deposited on a (Ni Pt) Al bond coating. The thermally grown oxide (TGO) layer that forms between the TBC and bond coat at high temperature is unstable with respect to out of plane displacement, provided initial perturbations are present. With cyclic thermal exposure, the TGO displaces into the bond coat at periodic interfacial sites. The out-of-plane displacements induce strains above the TGO, normal to the interface, that cause cracking. The cracks nucleate either within the TBC layer or at the TBC/TGO interface, and extend laterally until they coalesce with cracks from other sites and coating failure occurs by large scale buckling. The TGO displacements are accommodated by visco-plastic deformation of the underlying bond coat, and are driven by a lateral component of the growth strain in the TGO. The susceptibility of the TGO to out-of-plane displacement depends critically upon the initial morphology of the metal/oxide interface. The observed material responses are compared with predictions of a ‘ratcheting’ model.

Fracture Behavior of Plasma-Sprayed Thermal Barrier Coatings with Different Bond Coats upon Cyclic Thermal Exposure

2009 ◽  
Vol 620-622 ◽  
pp. 343-346
Author(s):  
Young Seok Sim ◽  
Sung Il Jung ◽  
Jae Young Kwon ◽  
Je Hyun Lee ◽  
Yeon Gil Jung ◽  
...  
Keyword(s):  
Bond Coat ◽  
Fracture Behavior ◽  
Thermal Exposure ◽  
Thermally Grown Oxide ◽  
Fatigue Tests ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Bond Coats ◽  
Barrier Coating ◽  
Tbc Systems

The effects of bond coat nature in thermal barrier coating (TBC) systems on the delamination or fracture behavior of the TBCs with different bond coats prepared using two different processes—air plasma spray (APS) and high velocity oxyfuel (HVOF)—were investigated by cyclic thermal fatigue tests. The TBCs with the HVOF bond coat were delaminated or fractured after 3–6 cycles, whereas those with the APS bond coat were delaminated after 10 cycles or show a sound condition. These results indicate that the TBC system with the APS bond coat has better thermal durability than the system with the HVOF bond coat under long-term cyclic thermal exposure. The hardness values of the TBCs (top coats) in both systems are dependent on applied loads, irrespective of the hardness of the bond coats and the substrate. The values are not responded to the bond coat nature or the exposure time. Thermally grown oxide (TGO) layers in both cases consist of two regions with the inner TGO layer containing only Al2O3 and the outer TGO layer of mixed-oxide zone containing Ni, Co, Cr, Al in Al2O3 matrix. The outer TGO layer has a more irregular shape than the inner TGO layer, and there are many pores within the outer layer. At failure, the TGO thickness of the TBC system with the HVOF bond coat is 9–13 m, depending on the total exposed time, and that of the TBC system with the APS bond coat is about 20 m. The both TBC systems show the diffusion layer on the side of substrate in the interface between the bond coat and the substrate. The relationship between the delamination or fracture behavior and the bond coat nature has been discussed, based on the elemental analysis and microstructural evaluation.

Characterization of Thermally Grown Oxide on Cold Sprayed CoNiCrAlY Bond Coat in Thermal Barrier Coating

2011 ◽  
Vol 696 ◽  
pp. 324-329 ◽  
Author(s):  
Abreeza Manap ◽  
Dowon Seo ◽  
Kazuhiro Ogawa
Keyword(s):  
Electron Microscopy ◽  
Thermal Barrier Coating ◽  
Bond Coat ◽  
Oxidation Behavior ◽  
Mixed Oxides ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Bond Coats ◽  
Barrier Coating ◽  
Thermally Grown

This paper presents the results of a study of the microstructure and oxidation behavior of thermal barrier coating (TBC) with air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) top coat and CoNiCrAlY bond coat deposited using two different spraying techniques, low pressure plasma spray (LPPS) and cold spray (CS). The objective is to investigate the thermally grown oxide (TGO) thickness and oxide scale composition of TBC subjected to isothermal oxidation and creep tests at 900 °C by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDX) analyses in order to evaluate the reliability of the CS technique. It was found that the TGO thicknesses for TBC with CS bond coats were smaller and the TGO was composed of mainly alumina with little or no mixed oxides. TGO growth rate was also affected by the applied stress. Smaller TGO thicknesses were observed for the non-creep TBC for both CS and LPPS bond coats. Overall findings indicate that the oxidation behavior of the TBC with CS bond coat is superior compared to that of the TBC with LPPS bond coat.

Influence of Titanium in Nickel-Base Superalloys on the Performance of Thermal Barrier Coatings Utilizing γ−γ′ Platinum Bond Coats

2010 ◽  
Vol 133 (4) ◽  
Author(s):  
H. M. Tawancy ◽  
Luai M. Al-Hadhrami
Keyword(s):  
Thermal Barrier Coating ◽  
Bond Coat ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Ti Alloy ◽  
Coating System ◽  
Barrier Coating ◽  
Nickel Base Superalloys ◽  
Nickel Base ◽  
Thermally Grown

Titanium is a key element in nickel-base superalloys needed with aluminum to achieve the desired volume fraction of the strengthening γ′-phase. However, depending upon its concentration, titanium can degrade the adherence of aluminum oxide by forming TiO2 particles near the oxide-metal interface. This effect is extended to thermal barrier coating systems where in this case, the bond coat replaces the superalloy as the underlying substrate. Noting that the onset of failure of thermal barrier coating systems coincides with the first spall of the thermally grown oxide, titanium level in the superalloy can have an important effect on the useful life of the coating. Therefore, this study was undertaken to examine the effect of titanium on the performance of a thermal barrier coating system. Included in the study were two Ni-base superalloys with similar chemical composition except for the Ti content and a Pt-containing bond coat consisting of γ′+γ-phases all top coated with zirconia stabilized by 7 wt % yttria. Coating performance was evaluated from thermal exposure tests at 1150°C with a 24 h cycling period to room temperature. Various electron-optical techniques were used to characterize the microstructure. The coating system on the low-Ti alloy was found to outperform that on the high-Ti alloy. However, for both alloys, failure was observed to occur by loss of adhesion between the thermally grown oxide and underlying bond coat.

Influence of Titanium in Nickel-Base Superalloys on the Performance of Thermal Barrier Coatings Utilizing γ-γ′ Platinum Bond Coats

2010 ◽  
Author(s):  
H. M. Tawancy ◽  
Luai M. Al-Hadhrami
Keyword(s):  
Thermal Barrier Coating ◽  
Bond Coat ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Ti Alloy ◽  
Coating System ◽  
Barrier Coating ◽  
Nickel Base Superalloys ◽  
Nickel Base ◽  
Thermally Grown

Titanium is a key element in nickel-base superalloys needed with aluminum to achieve the desired volume fraction of the strengthening γ′-phase. However, depending upon its concentration, titanium can degrade the adherence of aluminum oxide by forming TiO2 particles near the oxidemetal interface. This effect is extended to thermal barrier coating systems where in this case, the bond coat replaces the superalloy as the underlying substrate. Noting that the onset of failure of thermal barrier coating systems coincides with the first spall of the thermally grown oxide, titanium level in the superalloy can have an important effect on the useful life of the coating. Therefore, this study was undertaken to examine the effect of titanium on the performance of a thermal barrier coating system. Included in the study were two Ni-base superalloys with similar chemical composition except for the Ti content, and a Pt-containing bond coat consisting of γ′+γ-phases all top coated with zirconia stabilized by 7 weight % yttria. Coating performance was evaluated from thermal exposure tests at 1150 °C with a 24-hour cycling period to room temperature. Various electron-optical techniques were used to characterize the microstructure. The coating system on the low-Ti alloy was found to outperform that on the high-Ti alloy. However, for both alloys, failure was observed to occur by loss of adhesion between the thermally-grown oxide and underlying bond coat.

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.

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.

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