Spalling failure of a thermal barrier coating associated with aluminum depletion in the bond-coat

Shillington, E.A.G; Clarke, David R.

doi:10.1016/s1359-6454(98)00407-8

Cited by 282 publications

(96 citation statements)

References 16 publications

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“…5), due to disappearance of splat boundary and pores. The growth and coalescence of horizontal cracks were observed at the interface between the buffer layer and the top coat in the sample B, and between the buffer layers in the sample D. This microstructure of vertical cracked TBC system can enhance the thermal durability with improved strain compliance during operations [26]. As a result, the DLC TBCs with buffer layer will show superior thermal durability due to its vertical cracks.…”

Section: Jet Engine Thermal Shock Test and Comparisonmentioning

confidence: 88%

Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings

Song

Paik

Guo

et al. 2016

Surface and Coatings Technology

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The effects of microstructure design on the lifetime performance of lanthanum zirconate (La2Zr2O7; LZO) based thermal barrier coatings (TBCs) were investigated through various thermal exposure tests, such as furnace cyclic thermal fatigue, thermal shock, and jet engine thermal shock. To improve the thermal durability of LZO-based TBCs, composite top coats using two feedstock powders of LZO and 8 wt.% yttria doped stabilized zirconia (8YSZ) were prepared by mixing at different volume ratios (50:50 and 25:75, respectively). Also, buffer layers were introduced in layered LZO-based TBCs deposited by air plasma spray method. The TBCs with two buffer layers showed the best thermal shock resistance and thermal cyclic performance among all samples in all tests. For applications with mildly slow cooling rates, the thermal durability in single-layer TBCs is more effectively enhanced by controlling composite ratio in the blended powder, better than introducing a single buffer layer. For applications with fast cooling rates, the thermal durability can be effectively improved by introducing buffer layer than composite top coat, since buffer layer provides fast localized stress relief due to its high strain compliance. These research findings allow us to control the TBC structure and the buffer layer is efficient in improving thermal durability in the cyclic thermal exposure and thermal shock environments.

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Section: Jet Engine Thermal Shock Test and Comparisonmentioning

confidence: 88%

Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings

Song

Paik

Guo

et al. 2016

Surface and Coatings Technology

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“…This Al 2 O 3 scale, also referred to as the TGO, forms between the top coat and the MCrAlY bond coat [10,[17][18][19]. It is widely recognised that the growth of the TGO during service causes progressive build-up of stress in the system, leading to the spallation of the ceramic top coat and eventually causing detrimental effects to the turbine engine components [20][21][22]. The continuous growth of the TGO due to aluminium diffusion from the MCrAlY bond coat results in subsequent  phase depletion at the oxide/bond coat interface [23][24][25][26][27][28], causing mechanical and chemical degradation of the coating.…”

Section: Introductionmentioning

confidence: 99%

Modelling and experimental study on β-phase depletion behaviour of HVOF sprayed free-standing CoNiCrAlY coatings during oxidation

Chen

Jackson

Voisey

et al. 2016

Surface and Coatings Technology

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This paper investigates the β-phase depletion behaviour during oxidation of free-standing CoNiCrAlY (Co-31.7%Ni-20.8%Cr-8.1%Al-0.5%Y, all in wt%) bond coats prepared by high velocity oxy-fuel (HVOF) thermal spraying. The microstructure of the coatings was characterised using scanning electron microscopy with energy dispersive X-ray (EDX) analysis and electron backscatter diffraction (EBSD). It comprises a two phase structure of fcc-Ni and bcc -NiAl, with grain sizes varying largely from 0.5 to 2 µm for both phases.Isothermal oxidation tests of the free-standing coatings were carried out at 1100 C for times up to 250 h. The phase depletion behaviour at the surface was measured and was also simulated using Thermo-Calc and DICTRA software. An Al flux function derived from an oxide growth model was employed as the boundary condition in the diffusion model. The diffusion calculations were performed using the TTNi7 thermodynamic database together with the MOB2 mobility database. Reasonable agreement was achieved between the measured and the predicted element concentration and phase fraction profiles after various 2 time periods. Grain boundary diffusion is likely to be important to element diffusion in this HVOF sprayed CoNiCrAlY coating due to the sub-micron grains. Keywords IntroductionThermal barrier coatings (TBCs) are widely used to protect high temperature components in turbine engines from harsh operating environments [1,2]. TBC systems consist of a ceramic top coat, a metallic bond coat and a superalloy substrate [3][4][5]. Additionally, a thermally grown oxide (TGO) forms at the interface between the top coat and the bond coat during service at elevated temperature due to the fact that oxygen permeates through the ceramic top coat and oxidises the bond coat. The durability of the overall TBC system is largely determined by the microstructural, chemical and mechanical characteristics of the bond coat due to interdiffusion of element between the MCrAlY and the superalloy substrate. This is not considered in the present paper but has been studied by others, e.g. [29][30][31][32][33][34][35][36][37][38][39][40][41]. In these research works, the emphasis has been on substrate/bond coat interdiffusion and specific comparisons between measured and predicted β-phase depletion at the oxide/bond coat interface have not been considered. On the other hand, several analytical models concerned with the oxidation of 4 two phase systems in which the secondary phase dissolves during oxidation have been reported, e.g. [42][43][44][45][46][47][48]. In these models, the secondary phase depletion behaviour during oxidation can generally be represented by the parabolic diffusion law, Eq. (1), ~√( 1) where is the width of the second phase depletion zone and is the oxidation time.Considering the significance of β depletion on the degradation of TBCs, therefore, the aims of the work reported in this paper were to investigate specifically the kinetics of β depletion at the oxide surface in free-standing MCrAlY coatings ...

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“…[3][4][5][6][7] Thus, suppressing masstransfer through the -Al 2 O 3 scale is anticipated to further improve the durability of TBCs.…”

Section: Introductionmentioning

confidence: 99%

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

2009

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The oxygen permeability of an undoped polycrystalline -Al 2 O 3 wafer that was exposed to oxygen potential gradients was evaluated at temperatures up to 1973 K. Oxygen preferentially permeated through the grain boundaries of -Al 2 O 3 . The main diffusion species, which were attributed to oxygen permeation, depended on oxygen partial pressures (P O2 ), forming oxygen potential gradients. Under oxygen potential gradients generated by P O2 below about 1 Pa, oxygen permeation occurred by oxygen diffusing from regions of higher P O2 to regions of lower P O2 . By contrast, under oxygen potential gradients generated by P O2 above about 1 Pa, oxygen permeation proceeded by aluminum diffusing from regions of lower P O2 to regions of higher P O2 . In other words, O 2 molecules were adsorbed onto a surface at higher P O2 and subsequently dissociated into oxygen ions (forming Al 2 O 3 ), while oxygen ions on the opposite surface at lower P O2 were desorbed by association into O 2 molecules (decomposition of Al 2 O 3 ). The grain-boundary diffusion coefficients of oxygen and aluminum as a function of P O2 were determined from the oxygen permeation constants.

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Spalling failure of a thermal barrier coating associated with aluminum depletion in the bond-coat

Cited by 282 publications

References 16 publications

Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings

Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings

Modelling and experimental study on β-phase depletion behaviour of HVOF sprayed free-standing CoNiCrAlY coatings during oxidation

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

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