EB-PVD alumina (Al2O3) as a top coat on 7YSZ TBCs against CMAS/VA infiltration: Deposition and reaction mechanisms

Naraparaju, Ravisankar; Pubbysetty, Raghu Praveen; Mechnich, Peter; Schulz, Uwe

doi:10.1016/j.jeurceramsoc.2018.03.027

Cited by 58 publications

(31 citation statements)

References 30 publications

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“…In Figure 8 both the experimentally estimated, and GRD model based viscosity is plotted for different temperature ranges. One can find that the viscosity prediction of the GRD model for CMAS1 at 1260 • C is~0.5 Pa s, and the experimental value is close to 5.8 Pa s [26], which is almost 11 times higher.…”

Section: • Density and Viscosity Of Molten Cmasmentioning

confidence: 66%

“…On the other hand, viscosity for the investigated CMAS was estimated by two methods: Experimental and theoretical. For a particular CMAS chemical composition (here, CMAS1: 41.68(SiO 2 )-24.56(CaO)-12.43(MgO)-11.05(Al 2 O 3 )-8.71(FeO)-1.57(TiO 2 )-0(SO 3 ) at.%) in the temperature range of 1200-1400 • C, the obtained viscosity shows a rapid decrease with increased temperature [26]. Due to the complicated data measurement techniques at high temperature, only one data was taken at each temperature.…”

Section: • Density and Viscosity Of Molten Cmasmentioning

confidence: 99%

“…The latter approach was systematically analyzed in some previous experimental works [24][25][26], where the CMAS infiltration behavior was compared for different top coat microstructures. It was found out that by using the optimized columnar microstructure the CMAS infiltration kinetics could be changed, where infiltration mainly proceed due to the capillary forces.…”

Section: Introductionmentioning

confidence: 99%

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Flow Kinetics of Molten Silicates through Thermal Barrier Coating: A Numerical Study

et al. 2019

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Infiltration of molten calcium–magnesium–alumina–silicates (CMAS) through thermal barrier coatings (TBCs) causes structural degradation of TBC layers. The infiltration kinetics can be altered by careful tailoring of the electron beam physical vapor deposition (EB-PVD) microstructure such as feather arm lengths and inter-columnar gaps, etc. Morphology of the feathery columns and their inherent porosities directly influences the infiltration kinetics of molten CMAS. To understand the influence of columnar morphology on the kinetics of the CAMS flow, a finite element based parametric model was developed for describing a variety of EB-PVD top coat microstructures. A detailed numerical study was performed considering fluid-solid interactions (FSI) between the CMAS and TBC top coat (TC). The CMAS flow characteristics through these microstructures were assessed quantitatively and qualitatively. Finally, correlations between the morphological parameters and CMAS flow kinetics were established. It was shown that the rate of longitudinal and lateral infiltration could be minimized by reducing the gap between columns and increasing the length of the feather arms. The results also show that the microstructures with long feather arms having a lower lateral inclination decrease the CMAS infiltration rate, therefore, reduce the CMAS infiltration depth. The analyses allow the identification of key morphological features that are important for mitigating the CMAS infiltration.

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Section: • Density and Viscosity Of Molten Cmasmentioning

confidence: 66%

Section: • Density and Viscosity Of Molten Cmasmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Flow Kinetics of Molten Silicates through Thermal Barrier Coating: A Numerical Study

et al. 2019

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“…To date, two strategies to mitigate the destruction of TBCs from CMAS have been proposed . One is to deposit a dense out layer, either noble metals (eg, Pt/Pd) or ceramics (eg, Al 2 O 3 ), on the 7YSZ topcoat . However, application of an out layer not only increases the material and manufacturing costs, but also induces significant thermal expansion mismatch between the out layer and the 7YSZ topcoat.…”

Section: Introductionmentioning

confidence: 99%

“…16,17 One is to deposit a dense out layer, either noble metals (eg, Pt/Pd) or ceramics (eg, Al 2 O 3 ), on the 7YSZ topcoat. [18][19][20][21][22] However, application of an out layer not only increases the material and manufacturing costs, but also induces significant thermal expansion mismatch between the out layer and the 7YSZ topcoat. Furthermore, despite the poor reactivity of the out layer material (eg, Pt/Pd), it can gradually dissolve into the CMAS melt in the long-term exposure.…”

mentioning

confidence: 99%

A novel CMAS‐resistant material based on thermodynamic equilibrium design: Apatite‐type Gd₁₀(SiO₄)₆O₃

Zhang

Shan

et al. 2020

J Am Ceram Soc

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Calcium‐magnesium‐alumino‐silicates (CMAS) melt attack has been a critical issue for the thermal barrier coatings (TBCs) with ever‐increasing engine operating temperature. In this study, a novel CMAS‐resistant material apatite‐type Gd10(SiO4)6O3 is developed for TBCs application based on thermodynamic equilibrium design. The chemical reaction of Gd10(SiO4)6O3 bulk and CMAS melt is investigated at 1300°C. The CMAS corrosion resistance of Gd10(SiO4)6O3 bulk is evaluated and compared with the well‐studied CMAS‐resistant material Gd2Zr2O7 (GZO). It is found that Gd10(SiO4)6O3 shows a significantly enhanced CMAS resistance, including lower intrinsic CMAS infiltration rate (~1.09 μm/h1/2) and smaller infiltration upper limit (50‐62 μm) for a 20 mg/cm2 CMAS deposition. More importantly, for Gd10(SiO4)6O3, the CMAS infiltration only alters the composition but does not change the crystal structure or destroy microstructural integrity. The reaction mechanism is elucidated as following two stages: (a) surface Gd10(SiO4)6O3 quickly transforms into Ca2Gd8(SiO4)6O2 in suit by interdiffusion with CMAS melt and then is thermodynamically stable with CMAS melt, thereby effectively inhibiting the further CMAS infiltration and (b) with the ongoing interdiffusion of Gd/Ca, the CMAS‐infiltrated layer slowly thickens and follows a parabolic law. Meanwhile, the CMAS melt gradually precipitates Ca2Gd8(SiO4)6O2 and CaAl2Si2O8 (anorthite) until the melt is exhausted.

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A New Al₂O₃‐Protected EB‐PVD TBC with Superior CMAS Resistance

Qin,

Cao,

Gao

et al. 2023

Advanced Science

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Calcium‐magnesium‐aluminium‐silicate (CMAS) attack is a longstanding challenge for yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) particularly at higher engine operating temperature. Here, a novel microstructural design is reported for YSZ TBCs to mitigate CMAS attack. The design is based on a drip coating method that creates a thin layer of nanoporous Al2O3 around YSZ columnar grains produced by electron beam physical vapor deposition (EB‐PVD). The nanoporous Al2O3 enables fast crystallization of CMAS melt close to the TBC surface, in the inter‐columnar gaps, and on the column walls, thereby suppressing CMAS infiltration and preventing further degradation of the TBCs due to CMAS attack. Indentation and three‐point beam bending tests indicate that the highly porous Al2O3 only slightly stiffens the TBC but offers superior resistance against sintering in long‐term thermal exposure by reducing the intercolumnar contact. This work offers a new pathway for designing novel TBC architecture with excellent CMAS resistance, strain tolerance, and sintering resistance, which also points out new insight for assembly nanoporous ceramic in traditional ceramic structure for integrated functions.

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EB-PVD alumina (Al2O3) as a top coat on 7YSZ TBCs against CMAS/VA infiltration: Deposition and reaction mechanisms

Cited by 58 publications

References 30 publications

Flow Kinetics of Molten Silicates through Thermal Barrier Coating: A Numerical Study

Flow Kinetics of Molten Silicates through Thermal Barrier Coating: A Numerical Study

A novel CMAS‐resistant material based on thermodynamic equilibrium design: Apatite‐type Gd₁₀(SiO₄)₆O₃

A New Al₂O₃‐Protected EB‐PVD TBC with Superior CMAS Resistance

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EB-PVD alumina (Al2O3) as a top coat on 7YSZ TBCs against CMAS/VA infiltration: Deposition and reaction mechanisms

Cited by 58 publications

References 30 publications

Flow Kinetics of Molten Silicates through Thermal Barrier Coating: A Numerical Study

Flow Kinetics of Molten Silicates through Thermal Barrier Coating: A Numerical Study

A novel CMAS‐resistant material based on thermodynamic equilibrium design: Apatite‐type Gd10(SiO4)6O3

A New Al2O3‐Protected EB‐PVD TBC with Superior CMAS Resistance

Contact Info

Product

Resources

About

A novel CMAS‐resistant material based on thermodynamic equilibrium design: Apatite‐type Gd₁₀(SiO₄)₆O₃

A New Al₂O₃‐Protected EB‐PVD TBC with Superior CMAS Resistance