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Factors Affecting the Performance of Thermal Barrier Coatings in the Presence of V2O5 and Na2SO4
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
Siemens Ind Turbomachinery AB, Sweden.
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2016 (English)In: JOURNAL OF CERAMIC SCIENCE AND TECHNOLOGY, ISSN 2190-9385, Vol. 7, no 4, p. 409-415Article in journal (Refereed) Published
Abstract [en]

This study investigates the influence of temperature, salt concentration and thickness on the corrosion resistance of seven YSZ thermal barrier coatings in the presence of V2O5 and Na2SO4. For this study, a thick, high-porosity APS coating (670 gm) using hollow spherical powder (HOSP) and a thin, low-porosity APS coating (300 pm) using agglomerated and sintered (Aamp;S) powder were fabricated. Corrosion tests were conducted at 750 degrees C and 900 degrees C with a mixture of Na2SO4 and V2O5 for four hours. At each temperature, salt concentrations of 4,10 and 20 mg/cm(2) were used. SEM and XRD investigations after the corrosion tests revealed that a combination of low temperature and high salt concentration resulted in higher corrosion-induced damage to the thin TBC coatings. With regard to the thick TBC coatings, all except one sample failed during the corrosion test. This suggests that thick TBC coatings with higher porosity may not be suitable in corrosive environments.

Place, publisher, year, edition, pages
GOLLER VERLAG GMBH , 2016. Vol. 7, no 4, p. 409-415
Keywords [en]
HOSP; agglomerated and sintered YSZ; hot corrosion; TBC
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-134310DOI: 10.4416/JCST2016-00058ISI: 000391246300013OAI: oai:DiVA.org:liu-134310DiVA, id: diva2:1071682
Note

Funding Agencies|Vinnova, Sweden

Available from: 2017-02-06 Created: 2017-02-03 Last updated: 2019-02-26Bibliographically approved
In thesis
1. Thermal Barrier Coatings: Failure Mechanisms and Life Prediction
Open this publication in new window or tab >>Thermal Barrier Coatings: Failure Mechanisms and Life Prediction
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thermal barrier coatings (TBCs) use in the hot sections of gas turbine engine enables them to run at higher temperatures, and as a consequence, achieve higher thermal efficiency. For full operational exploitation of TBCs, understanding their failure and knowing the service life is essential. The broad objective of the current research is to study the failure mechanisms of new TBC materials and deposition techniques during corrosion and thermal cycling and to develop life models capable of predicting the final failure during thermal cycling.

Yttria-stabilized zirconia (YSZ) has constraints such as limited operation temperature, despite being the current industry standard. Pyrochlores of A2B2O7 type have been suggested as a potential replacement for YSZ and were studied in this work. Additionally, improvements to the conventional YSZ in the form of nanostructured YSZ were also explored. The requirement for the new deposition process comes from the fact that the existing low-cost deposition processes, like atmospheric plasma spray (APS), generally exhibit lower strain tolerance. A relatively new technique, suspension plasma spray (SPS), known to be promising with better strain tolerance, has been studied in this work.

At the gas turbine operating conditions, TBCs degrade and eventually fail. Common failure observed in gas turbines can be due to corrosion, thermal mismatch between the ceramic and the metallic layers, and bond coat oxidation during thermal cycling. SPS and APS TBCs were subjected to different test conditions to understand their corrosion behavior. A study on the multi-layered SPS TBCs in the presence of V2O5+Na2SO4 showed that YSZ based SPS coatings were less susceptible to corrosion damage compared to Gd2Zr2O7 SPS TBCs. A study on the influence of a sealing layer in multi-layered SPS TBCs in the presence of Na2SO4+NaCl showed that the sealing layer is ineffective if the material used for sealing is inert to the molten salts. A new study on the influence of corrosion, caused by a mixed-gas atmosphere, on the thermal cycling fatigue life of SPS TBCs was conducted. Results showed that corrosive products grew inside the top coat close to the bond coat/top coat interface along with accelerated growth of alumina. These, together, reduced the TCF life of corrosion exposed samples significantly. Finally, a study on the influence of salt concentration and temperature on a thin (dense) and a thick (porous) coating showed that thick and porous coatings have lower corrosion resistance than the thin and dense coatings. Additionally, a combination of low temperature and high salt concentration was observed to cause more damage.

Thermal cycling studies were done with the objective of understanding the failure mechanisms and developing a life model. A life model based on fracture mechanics approach has been developed by taking into account different crack growth paths during thermal cycling, sintering of the top coat, oxidation of the bond coat and the thermal mismatch stresses. Validation of such a life model by comparing to the experimental results showed that the model could predict the TCF life reasonably well at temperatures of 1100 °C or below. At higher temperatures, the accuracy of the model became worse. As a further development, a simplified crack growth model was established. This simplified model was shown to be capable of predicting the TCF life as well as the effect of hold times with good accuracy.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. p. 57
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1975
National Category
Manufacturing, Surface and Joining Technology Corrosion Engineering Materials Chemistry Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:liu:diva-154777 (URN)10.3384/diss.diva-154777 (DOI)9789176851388 (ISBN)
Public defence
2019-03-13, C3, C-huset, Campus Valla, Linköping, 10:15 (English)
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Available from: 2019-02-26 Created: 2019-02-26 Last updated: 2019-03-04Bibliographically approved

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