Novel thermal barrier coatings that are resistant to high-temperature attack by glassy deposits

Aygun, Aysegul; Vasiliev, Alexander L.; Padture, Nitin P.; Ma, Xinqing

doi:10.1016/j.actamat.2007.08.028

Cited by 264 publications

(148 citation statements)

References 31 publications

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“…The present study found a similar result when using volcanic ash subjected to a high temperature of 1250°C. 7YSZ was found to have little resistance to VA penetration, which is consistent with what others have observed in CMAS [9,22]. In the present experiments, a significant phase transformation to m-ZrO 2 phase was not detected in the rare earth-doped samples.…”

Section: Discussionsupporting

confidence: 81%

On the resistance of rare earth oxide-doped YSZ to high temperature volcanic ash attack

Xia

Yang

et al. 2016

Surface and Coatings Technology

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Thermal barrier coatings (TBCs), such as 7-8 wt.% yttria stabilized zirconia (YSZ), are widely used to reduce the temperature of coated materials. However, when a turbine operates in a harsh environment, for example a volcanic ash attack, sand and ash particles ingested by the engine could be deposited on the TBC surfaces as molten calcium-magnesium-alumino-silicate (CMAS). CMAS melts and penetrates into TBCs at high temperatures, which causes a loss of strain tolerance and results in the premature failure of the top coat. It is recognized that the formation of CMAS is inevitable due to exposing the turbine to sand and ash; therefore, CMAS mitigation solutions are among the top challenges for materials scientists. To some extent, CMAS is the biggest weakness of the traditional 7-8YSZ TBC material. The thermochemical interactions between YSZ and real volcanic ash are investigated in this paper as a means to alleviate the volcanic ash attack by understanding the underlying mechanisms. 7YSZ, 0.5Gd-8YSZ and 3Er-7YSZ powders and free-standing plates were prepared, respectively. The effect of the volcanic ash on the three different samples was investigated using an X-ray diffraction, scanning electron microscopy, a scanning transmission electron microscopy, and a differential scanning calorimetry. The phase transformations and reaction of TBCs materials subjected to a volcanic ash attack were examined and the volcanic ash degradation and mitigation mechanisms were discussed. It was found that rare earth-doped YSZ samples suffered less damage from the volcanic ash attack than the standard 7YSZ. The results demonstrate that rare earth-doped YSZ may be effectively utilized to mitigate a volcanic ash attack.

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Section: Discussionsupporting

confidence: 81%

On the resistance of rare earth oxide-doped YSZ to high temperature volcanic ash attack

Xia

Yang

et al. 2016

Surface and Coatings Technology

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“…This type of damage to 7YSZ TBCs, both APS and EB-PVD, is similar to what has been observed in aircraft gas-turbine engines but from deposits of molten calciummagnesium-alumino-silicate (CMAS) sand from the environment [15][16][17][18][19][20][21][22][23][24]. The molten CMAS glass penetrates the TBC microstructure and forms a relatively stiff glaze upon cooling [15][16][17][18][19]24].…”

Section: Introductionmentioning

confidence: 51%

“…For comparison, the chemical compositions of the CMAS sand [19] and the Eyjafjallajökull volcanic ash [36] from previous studies are also included in Table 1. Figures 2B, 2C, 2D, and 2E are corresponding EDS elemental maps of Si, Ca, Fe, and Zr, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…The molten CMAS glass penetrates the TBC microstructure and forms a relatively stiff glaze upon cooling [15][16][17][18][19]24]. This results in the reduction of TBC strain-tolerance during engine heating-cooling cycles, causing the TBC to detach from the substrate much more quickly than if the CMAS was not present [20,21].…”

Section: Introductionmentioning

confidence: 99%

“…One such TBC composition is ZrO 2 (71.4 mol% or 73.0 wt%) containing 3.6 mol% (6.8 wt%) Y 2 O 3 , 20.0 mol% (16.9 wt%) Al 2 O 3 , and 5.0 mol% (3.3 wt%) TiO 2 in solid solution (YSZ+Al+Ti) which has been designed to resist attack by molten CMAS and volcanic ash, and it has been shown to be effective [19,22,[24][25][26]. Another TBC composition is gadolinium zirconate Gd 2 Zr 2 O 7 , which was originally developed as an alternative to 7YSZ TBCs due to the much lower (about half) thermal conductivity of Gd 2 Zr 2 O 7 [27][28][29][30].…”

Section: Introductionmentioning

confidence: 99%

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Degradation of Thermal Barrier Coatings from Deposits and Its Mitigation

Padture¹

2011

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Ceramic thermal barrier coatings (TBCs) used in gas-turbine engines afford higher operating temperatures, resulting in enhanced efficiencies and performance. However, in the case of syngas-fired engines, fly ash particulate impurities that may be present in syngas can melt on the hotter TBC surfaces and form glassy deposits. These deposits can penetrate the TBCs leading to their failure. In experiments using lignite fly ash to simulate these conditions we show that conventional TBCs of composition 93wt% ZrO 2 + 7wt% Y 2 O 3 (7YSZ) fabricated using the air plasma spray (APS) process are completely destroyed by the molten fly ash. The molten fly ash is found to penetrate the full thickness of the TBC. The mechanisms by which this occurs appear to be similar to those observed in degradation of 7YSZ TBCs by molten calcium-magnesium-aluminosilicate (CMAS) sand and by molten volcanic ash in aircraft engines. In contrast, APS TBCs of Gd 2 Zr 2 O 7 composition are highly resistant to attack by molten lignite fly ash under identical conditions, where the molten ash penetrates ~25% of TBC thickness. This damage mitigation appears to be due to the formation of an impervious, stable crystalline layer at the fly ash/Gd 2 Zr 2 O 7 TBC interface arresting the penetrating moltenfly-ash front. Additionally, these TBCs were tested using a rig with thermal gradient and simultaneous accumulation of ash. Modeling using an established mechanics model has been performed to illustrate the modes of delamination, as well as further opportunities to optimize coating microstructure. Transfer of the technology was developed in this program to all interested parties.

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