Influence of impurity content and porosity of plasma-sprayed yttria-stabilized zirconia layers on the sintering behaviour

Vaßen, Robert; Czech, N.; Malléner, W.; Werner, Stefan; Stöver, D.

doi:10.1016/s0257-8972(01)01269-5

Cited by 105 publications

(50 citation statements)

References 7 publications

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“…In-service degradation, accompanied by increased risk of spallation, is the major concern. There are strong indications [1][2][3][4][5][6][7][8] that spallation is commonly related to sintering and associated stiffening of the zirconia top coat, particularly [9][10][11][12][13][14] when this is accelerated by the presence of impurities, such as calcia-magnesia-alumina-silica (CMAS), either from the original powder or deposited during service. This concern is likely to become even more prominent as turbine entry temperatures continue to rise.…”

Section: Introductionmentioning

confidence: 99%

A sintering model for plasma-sprayed zirconia TBCs. Part I: Free-standing coatings

2009

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A sintering model is presented for prediction of changes in the microstructure and dimensions of free-standing, plasma-sprayed (PS) thermal barrier coatings (TBCs). It is based on the variational principle. It incorporates the main microstructural features of PS TBCs and simulates the effects of surface diffusion, grain boundary diffusion and grain growth. The model is validated by comparison with experimental data for shrinkage, surface area reduction and porosity reduction. Predicted microstructural changes are also used as input data for a previously developed thermal conductivity model. Good agreement is observed between prediction and measurement for all these characteristics. The model allows separation of the effects of coating microstructure and material properties, and captures the coupling between densifying and non-densifying mechanisms. A sensitivity analysis is presented, which highlights the importance of the initial pore architecture. Predictions indicate that the microstructural changes which give rise to (undesirable) increases in thermal conductivity and stiffness are very sensitive to surface diffusion.

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Section: Introductionmentioning

confidence: 99%

A sintering model for plasma-sprayed zirconia TBCs. Part I: Free-standing coatings

2009

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“…It's also clear that grain growth, and associated reduction in the scattering of radiation, can contribute to increased heat transfer. Increases in coating stiffness [19][20][21] also occur during sintering, as a consequence of intersplat locking and splat stiffening, leading to increased danger of spallation [18,20,[22][23][24][25][26]. This is particularly problematic [27][28][29][30][31] when it is accelerated by the presence of impurities, such as calciamagnesia-alumina-silica (CMAS), either from the original powder or deposited during service.…”

Section: Introductionmentioning

confidence: 99%

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work

2009

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A review is presented of how heat transfer takes place in plasma sprayed (zirconia-based) thermal barrier coatings (TBCs) during operation of gas turbines. These characteristics of TBCs are naturally of central importance to their function. Current state-of-the-art TBCs have relatively high levels of porosity (~15%) and the pore architecture (ie its morphology, connectivity and scale) has a strong influence on the heat flow. Contributions from convective, conductive and radiative heat transfer are considered, under a range of operating conditions, and the characteristics are illustrated with experimental data and modelling predictions. In fact, convective heat flow within TBCs usually makes a negligible contribution to the overall heat transfer through the coating, although what might be described as convection can be important if there are gross through-thickness defects such as segmentation cracks. Radiative heat transfer, on the other hand, can be significant within TBCs, depending on temperature and radiation scattering lengths, which in turn are sensitive to the grain structure and the pore architecture. Under most conditions of current interest, conductive heat transfer is largely predominant. However, it is not only conduction through solid ceramic that is important. Depending on the pore architecture, conduction through gas in the pores can play a significant role, particularly at the high gas pressures typically acting in gas turbines (although rarely applied in laboratory measurements of conductivity). The durability of the pore structure under service conditions is also of importance, and this review covers some recent work on how the pore architecture, and hence the conductivity, is affected by sintering phenomena. Some information is presented concerning the areas in which research and development work needs to be focussed if improvements in coating performance are to be achieved.

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“…Many researchers have studied the relationship between the thermal conductivity and the microstructure. Studies shows that cracks parallel to the direction of the matrix and pores can effectively reduce the thermal conductivity while cracks vertical to the direction of the matrix increases the heat transfer [9][10][11] . The amount of different phase contents of the TBCs will have varying impact on the thermal conductivity.…”

Section: Introductionmentioning

confidence: 99%

Effect of Microstructure on the Thermal Conductivity of Plasma Sprayed Y<sub>2</sub>O<sub>3</sub> Stabilized Zirconia (8 %YSZ)

Hu¹,

Khan²,

Wang³

et al. 2017

Preprint

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In this paper, the effect of microstructure on the thermal conductivity of plasma-sprayed Y2O3 stabilized ZrO2 (YSZ) thermal barrier coatings (TBCs) is investigated. Nine freestanding samples deposited on aluminum-base superalloy are studied. Cross-section morphology such as pores, cracks, m-phase content, grain boundary density of the coated samples are examined by scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). Multiple linear regressions are used to develop quantitative models which describe the relationship between the particle parameters, m-phase content and the microstructure such as porosity, crack-porosity, the length density of small-angle-crack and the length density of big-angle-crack. Moreover, the relationship between microstructure and thermal conductivity is investigated. Results reveal that the thermal conductivity of the coating is mainly determined by the microstructure and grain boundary density at room temperature (25 ℃) and by the length density of big-angle-crack, monoclinic phase content and grain boundary density at high temperature (1200 ) ℃ .

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Influence of impurity content and porosity of plasma-sprayed yttria-stabilized zirconia layers on the sintering behaviour

Cited by 105 publications

References 7 publications

A sintering model for plasma-sprayed zirconia TBCs. Part I: Free-standing coatings

A sintering model for plasma-sprayed zirconia TBCs. Part I: Free-standing coatings

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work

Effect of Microstructure on the Thermal Conductivity of Plasma Sprayed Y<sub>2</sub>O<sub>3</sub> Stabilized Zirconia (8 %YSZ)

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