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Jonnalagadda, Krishna Praveen
Alternative names
Publications (10 of 12) Show all publications
Jonnalagadda, K. P., Mahade, S., Kramer, S., Zhang, P., Curry, N., Li, X.-H. & Peng, R. L. (2019). Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 °C. Journal of thermal spray technology (Print), 28(1-2), 212-222
Open this publication in new window or tab >>Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 °C
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2019 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 1-2, p. 212-222Article in journal (Refereed) Published
Abstract [en]

The current investigation focuses on understanding the influence of a columnar microstructure and a sealing layer on the corrosion behavior of suspension plasma sprayed thermal barrier coatings (TBCs). Two different TBC systems were studied in this work. First is a double layer made of a composite of gadolinium zirconate + yttria stabilized zirconia (YSZ) deposited on top of YSZ. Second is a triple layer made of dense gadolinium zirconate deposited on top of gadolinium zirconate + YSZ over YSZ. Cyclic corrosion tests were conducted between 25 and 900 °C with an exposure time of 8 h at 900 °C. 75 wt.% Na2SO4 + 25 wt.% NaCl were used as the corrosive salts at a concentration of 6 mg/cm2. Scanning electron microscopy analysis of the samples’ cross sections showed that severe bond coat degradation had taken place for both the TBC systems, and the extent of bond coat degradation was relatively higher in the triple-layer system. It is believed that the sealing layer in the triple-layer system reduced the number of infiltration channels for the molten salts which resulted in overflowing of the salts to the sample edges and caused damage to develop relatively more from the edge.

Keywords
columnar microstructure, composite of gadolinium zirconate and YSZ, hot corrosion, suspension plasma spray
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:liu:diva-154778 (URN)10.1007/s11666-018-0780-5 (DOI)000456599500019 ()2-s2.0-85055998259 (Scopus ID)
Funder
VINNOVA
Note

This article is an invited paper selected from presentations at the 2018 International Thermal Spray Conference, held May 7-10, 2018, in Orlando, Florida, USA, and has been expanded from the original presentation.

Available from: 2018-11-06 Created: 2019-02-26 Last updated: 2019-02-26
Jonnalagadda, K. P., Eriksson, R., Li, X.-H. & Peng, R. L. (2019). Fatigue life prediction of thermal barrier coatings using a simplified crack growth model. Journal of the European Ceramic Society, 39(5), 1869-1876
Open this publication in new window or tab >>Fatigue life prediction of thermal barrier coatings using a simplified crack growth model
2019 (English)In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 39, no 5, p. 1869-1876Article in journal (Refereed) Published
Abstract [en]

Models that can predict the life of thermal barrier coatings (TBCs) during thermal cycling fatigue (TCF) tests are highly desirable. The present work focuses on developing and validating a simplified model based on the relation between the energy release rate and the TCF cycles to failure. The model accounts for stresses due to thermal mismatch, influence of sintering, and the growth of TGO (alumina and other non-protective oxides). The experimental investigation of TBCs included; 1) TCF tests at maximum temperatures of 1050 °C, 1100 °C, 1150 °C and a minimum temperature of 100 °C with 1 h and 5 h (1100 °C) hold times. 2) Isothermal oxidation tests at 900, 1000 and 1100 °C for times up to 8000 h. The model was calibrated and validated with the experimental results. It has been shown that the model is able to predict the TCF life and effect of hold time with good accuracy.

Keywords
Thermal barrier coatings, Thermal cycling fatigue, Life prediction model, Energy release rate
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:liu:diva-154780 (URN)10.1016/j.jeurceramsoc.2018.12.046 (DOI)000459950700016 ()
Note

Funding agencies: Vinnova in Sweden

Available from: 2019-02-26 Created: 2019-02-26 Last updated: 2019-03-20
Jonnalagadda, K. P., Zhang, P., Gupta, M., Li, X.-H. & Peng, R. L. (2019). Hot gas corrosion and its influence on the thermal cycling performance of suspension plasma spray TBCs. In: Proceedings of ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. Paper presented at ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, Phoenix, Arizona, USA, June 17-21, 2019. New York, NY: American Society of Mechanical Engineers
Open this publication in new window or tab >>Hot gas corrosion and its influence on the thermal cycling performance of suspension plasma spray TBCs
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2019 (English)In: Proceedings of ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, New York, NY: American Society of Mechanical Engineers , 2019Conference paper, Published paper (Refereed)
Abstract [en]

Thermal barrier coatings (TBCs) manufactured with suspension plasma spray (SPS) are promising candidates for use in gas turbines due to their high strain tolerance during thermal cyclic fatigue (TCF). However, corrosion often occurs alongside thermal fatigue and coating durability under these conditions is highly desirable. The current study focuses on understanding the corrosion behavior and its influence on the thermal cyclic fatigue life of SPS TBCs. Corrosion tests were conducted at 780 OC using a mixed-gas (1SO2-0.1CO-20CO2-N2(bal.) in vol. %) for 168h. They were later thermally cycled between 100-1100 ⁰C with a 1h hold time at 1100 ⁰C. Corrosion test results indicated that the damage predominantly started from the edges and a milder damage was observed at the center. Nickel sulfide was observed on top of the top coat and also in the columnar gaps of the top coat. Chromium oxides were observed inside the top coat columnar gaps but close to the bond coat/top coat interface. They were believed to reduce the strain tolerance of SPS TBCs to an extent and also amplify the thermal mismatch stresses during TCF tests. This, together with a fast growth of alumina during the TCF, resulted in a significant drop in the TCF life compared to the standard TCF tests.

Place, publisher, year, edition, pages
New York, NY: American Society of Mechanical Engineers, 2019
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:liu:diva-161516 (URN)10.1115/GT2019-90104 (DOI)000502167600050 ()978-0-7918-5867-7 (ISBN)
Conference
ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, Phoenix, Arizona, USA, June 17-21, 2019
Note

Funding agencies: Vinnova in SwedenVinnova

Available from: 2019-11-04 Created: 2019-11-04 Last updated: 2020-01-09Bibliographically approved
Jonnalagadda, K. P. (2019). Thermal Barrier Coatings: Failure Mechanisms and Life Prediction. (Doctoral dissertation). Linköping: Linköping University Electronic Press
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)
Opponent
Supervisors
Available from: 2019-02-26 Created: 2019-02-26 Last updated: 2019-03-04Bibliographically approved
Jonnalagadda, K. P., Eriksson, R., Li, X.-H. & Peng, R. L. (2019). Thermal barrier coatings: Life model development and validation. Surface & Coatings Technology, 362, 293-301
Open this publication in new window or tab >>Thermal barrier coatings: Life model development and validation
2019 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 362, p. 293-301Article in journal (Refereed) Published
Abstract [en]

The failure of thermal barrier coatings (TBCs) during thermal cyclic fatigue (TCF) tests depends mainly on the thermal mismatch between the coating and the substrate, the thermally grown oxides (TGO) at the top coat-bond coat interface, and the sintering of the top coat. Understanding the interplay between these factors is essential for developing a life model. The present work focuses on further development of a previously established fracture mechanics based life model and its validation by comparing with the experimental results. The life model makes use of a Paris' law type equation to estimate the cycles to failure based on micro-crack growth. The fitting parameters for the Paris' law were obtained from the experimentally measured crack lengths after the interruption of TCF tests at different cycles. An alternative approach to obtain the fitting parameters through video monitoring was also discussed. It is shown that regardless of the approach to obtain the fitting parameters, the life model in its current form is able to predict the TCF life at different temperatures with reasonable accuracy. However, at very high temperatures (1150 °C) the predictive capabilities of the model appeared to be poor.

Keywords
Thermal barrier coatings, Thermal cyclic fatigue, Life modeling, Life prediction
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:liu:diva-154779 (URN)10.1016/j.surfcoat.2019.01.117 (DOI)000461526400035 ()
Note

Funding agencies: VINNOVA in Sweden

Available from: 2019-02-26 Created: 2019-02-26 Last updated: 2019-04-03
Jonnalagadda, K. P., Yuan, K., Li, X.-H., Ji, X., Yu, Y. & Peng, R. L. (2018). Influence of Top Coat and Bond Coat Pre-Oxidation on the Corrosion Resistance of Thermal Barrier Coatings in the Presence of SO2. In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBOMACHINERY TECHNICAL CONFERENCE AND EXPOSITION, 2018, VOL 6: . Paper presented at ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, Lillestrøm, Oslo, Norway, June 11-15, 2018. AMER SOC MECHANICAL ENGINEERS, Article ID V006T24A018.
Open this publication in new window or tab >>Influence of Top Coat and Bond Coat Pre-Oxidation on the Corrosion Resistance of Thermal Barrier Coatings in the Presence of SO2
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2018 (English)In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBOMACHINERY TECHNICAL CONFERENCE AND EXPOSITION, 2018, VOL 6, AMER SOC MECHANICAL ENGINEERS , 2018, article id V006T24A018Conference paper, Published paper (Refereed)
Abstract [en]

Thermal barrier coatings (TBCs) degradation due to corrosion is one of the commonly observed failure types in land-based gas turbines due to the usage of low grade fuels. Sulfur in its gaseous form, as SO2, can attack the TBC system and result in the degradation of both the coating and the turbine component. The present study aims to understand the difference in the corrosion induced damage caused by SO2 gas mixture in different coating architectures. Corrosion tests were conducted at 780 degrees C in a tube furnace for a period of 168h. The inlet test gas had a composition of 1SO(2)-0.1CO-20CO(2)-N-2 (bal.) in vol. %. The coating architectures consisted of 1) an overlay coating, 2) a single-side bond coat TBC, 3) an all-side bond coat TBC, 4) an all-side bond coat TBC subjected to pre-oxidation prior to the corrosion tests. The results from the corrosion tests showed that the damage was the most severe for the overlay followed by single-side bond coat TBC. Between the other two systems, the TBC subjected to pre-oxidation had relatively lower corrosion damage. The corrosion damage started from the edges for the overlay and single-side bond coat TBC and as well as through the penetration of the gas through the coating. For the coatings with bond coat on all sides, the edge damage appeared to be considerably reduced and the damage is predominantly through the gas infiltration.

Place, publisher, year, edition, pages
AMER SOC MECHANICAL ENGINEERS, 2018
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:liu:diva-154767 (URN)10.1115/GT2018-76412 (DOI)000456908700068 ()978-0-7918-5112-8 (ISBN)
Conference
ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, Lillestrøm, Oslo, Norway, June 11-15, 2018
Note

Funding Agencies|Vinnova in Sweden

Available from: 2019-02-26 Created: 2019-02-26 Last updated: 2019-03-07Bibliographically approved
Eriksson, R., Chen, Z. & Jonnalagadda, K. P. (2017). Bending Fatigue of Thermal Barrier Coatings. Journal of engineering for gas turbines and power, 139(12), 122101-1-122101-6
Open this publication in new window or tab >>Bending Fatigue of Thermal Barrier Coatings
2017 (English)In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 139, no 12, p. 122101-1-122101-6Article in journal (Refereed) Published
Abstract [en]

Thermal barrier coatings (TBCs) are ceramic coatings used in gas turbines to lower the base metal temperature. During operation, the TBC may fail through, for example, fatigue. In this study, a TBC system deposited on a Ni-base alloy was tested in tensile bending fatigue. The TBC system was tested as-sprayed and oxidized, and two load levels were used. After interrupting the tests, at 10,000–50,000 cycles, the TBC tested at the lower load had extensive delamination damage, whereas the TBC tested at the higher load was relatively undamaged. At the higher load, the TBC formed vertical cracks which relieved the stresses in the TBC and retarded delamination damage. A finite element (FE) analysis was used to establish a likely vertical crack configuration (spacing and depth), and it could be confirmed that the corresponding stress drop in the TBC should prohibit delamination damage at the higher load.

Place, publisher, year, edition, pages
ASME Press, 2017
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-142274 (URN)10.1115/1.4037587 (DOI)000415791400010 ()2-s2.0-85029559590 (Scopus ID)
Available from: 2017-10-24 Created: 2017-10-24 Last updated: 2017-12-12Bibliographically approved
Jonnalagadda, K. P., Eriksson, R., Yuan, K., Li, X.-H., Ji, X., Yu, Y. & Peng, R. L. (2017). Comparison of Damage Evolution During Thermal Cycling in a High Purity Nano and Conventional Thermal Barrier Coating. Surface & Coatings Technology, 332, 47-56
Open this publication in new window or tab >>Comparison of Damage Evolution During Thermal Cycling in a High Purity Nano and Conventional Thermal Barrier Coating
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2017 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 332, p. 47-56Article in journal (Refereed) Published
Abstract [en]

Thermal barrier coatings (TBCs), consisting of a ceramic top coat and a metallic bond coat, offer resistance against high temperature degradation of turbine components. Cyclic oxidation of the bond coat, thermal stresses due to their thermal mismatches during cyclic operations, and sintering of the top coat are considered to be the common ways by which thermal barrier coatings fail. To reduce sintering, a nano structured high purity yttria stabilized zirconia (YSZ) was developed. The focus of this work is to compare the damage development of such high purity nano YSZ TBC during thermal cycling with a conventional YSZ TBC. Thermal cyclic fatigue (TCF) tests were conducted on both the TBC systems between 100 °C and 1100 °C with a 1 h hold time at 1100 °C. TCF test results showed that conventional YSZ TBC exhibited much higher life compared to the high purity nano YSZ TBC. The difference in the lifetime is explained by the use of microstructural investigations, crack length measurements along the cross-section and the difference in the elastic modulus. Furthermore, stress intensity factors were calculated in order to understand the difference(s) in the damage development between the two TBC systems.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
High purity nano, damage evolution, thermal cycling fatigue, crack length measurement, conventional TBC
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-142311 (URN)10.1016/j.surfcoat.2017.09.069 (DOI)000418968100007 ()2-s2.0-85030751243 (Scopus ID)
Note

Funding agencies: Vinnova in Sweden [2015-06870]

Available from: 2017-10-25 Created: 2017-10-25 Last updated: 2019-02-26Bibliographically approved
Jonnalagadda, K. P., Li, X.-H. & Peng, R. L. (2017). Corrosion Mechanism in Thermal Barrier Coatings During Exposure to a Gas Mixture of N2-CO-CO2-SO2. In: : . Paper presented at EUROMAT17, Thessaloniki 17-21 September 2017,Greece (pp. 1-1).
Open this publication in new window or tab >>Corrosion Mechanism in Thermal Barrier Coatings During Exposure to a Gas Mixture of N2-CO-CO2-SO2
2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
Keywords
high temperature corrosion, mixed gas corrosion, thermal barrier coatings, Amdry 964
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-143977 (URN)
Conference
EUROMAT17, Thessaloniki 17-21 September 2017,Greece
Available from: 2018-01-01 Created: 2018-01-01 Last updated: 2018-01-16Bibliographically approved
Mahade, S., Jonnalagadda, K. P., Curry, N., Li, X.-H., Bjorklund, S., Markocsan, N., . . . Peng, R. (2017). Engineered architectures of gadolinium zirconate based thermal barrier coatings subjected to hot corrosion test. Surface & Coatings Technology, 328, 361-370
Open this publication in new window or tab >>Engineered architectures of gadolinium zirconate based thermal barrier coatings subjected to hot corrosion test
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2017 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 328, p. 361-370Article in journal (Refereed) Published
Abstract [en]

Gadolinium zirconate (GZ) is considered as a promising top coat candidate for high temperature TBC applications. Suspension plasma spray has shown the capability to generate a wide range of microstructures including the desirable columnar microstructure. In this study, two different TBC architectures were deposited using the axial suspension plasma spray. The first variation was a triple layered TBC comprising of thin YSZ base layer beneath a relatively porous GZ intermediate layer and a dense GZ top layer. The second variation was a composite TBC architecture of GZ and YSZ comprising of thin YSZ base layer and GZ + YSZ top layer. Cross sectional SEM analysis of the layered and composite TBCs revealed a columnar microstructure. The porosity content of the deposited TBCs was measured using two methods (Image Analysis and Water Intrusion). The as-sprayed TBCs were exposed at 900 degrees C for 8 h to a corrosive salt environment consisting of a mixture of vanadium pentoxide and sodium sulfate. XRD analysis on the as-corroded TBCs top surface showed the presence of gadolinium vanadate in both the layered and the composite TBCs. SEM/EDS analysis of the top surface and the cross-section of the layered and composite TBCs after hot corrosion test revealed the infiltration of the molten salts through the columnar gaps. The composite TBC showed a lower hot corrosion induced damage compared to the layered TBC where a considerable spallation was observed. (C) 2017 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Gadolinium zirconate; Hot corrosion; Suspension plasma spray; Columnar microstructure
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:liu:diva-142965 (URN)10.1016/j.surfcoat.2017.09.005 (DOI)000413376900040 ()2-s2.0-85028920767 (Scopus ID)
Note

Funding Agencies|KK Foundation, Sweden [Dnr: 20140130]; AForsk foundation, Sweden [16-799]

Available from: 2017-11-13 Created: 2017-11-13 Last updated: 2017-11-29Bibliographically approved
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