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  • 1.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Chen, Zhe
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    BENDING FATIGUE OF THERMAL BARRIER COATINGS2017In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2017, VOL 6, AMER SOC MECHANICAL ENGINEERS , 2017, article id V006T24A004Conference paper (Refereed)
    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 the present 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 10000-50000 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 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.

  • 2.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Chen, Zhe
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Bending Fatigue of Thermal Barrier Coatings2017In: 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)
    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.

  • 3.
    Eriksson, Robert
    et al.
    Siemens Industrial Turbomachinery AB, Berlin, Germany.
    Gupta, Mohit
    University West, Trollhättan, Sweden.
    Broitman, Esteban
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Nylén, Per
    University West, Trollhättan, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Stresses and Cracking During Chromia-Spinel- NiO Cluster Formation in TBC Systems2015In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 24, no 6, p. 1002-1014Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBC) are used in gas turbines to reduce the temperatures in the underlying substrate. There are several mechanisms that may cause the TBC to fail; one of them is cracking in the coating interface due to extensive oxidation. In the present study, the role of so called chromia-spinel-NiO (CSN) clusters in TBC failure was studied. Such clusters have previously been found to be prone to cracking. Finite element modeling was performed on a CSN cluster to find out at which stage of its formation it cracks and what the driving mechanisms of cracking are. The geometry of a cluster was obtained from micrographs and modeled as close as possible. Nanoindentation was performed on the cluster to get the correct Young’s moduli. The volumetric expansion associated with the formation of NiO was also included. It was found that the cracking of the CSN clusters is likely to occur during its last stage of formation as the last Ni-rich core oxidizes. Furthermore, it was shown that the volumetric expansion associated with the oxidation only plays a minor role and that the main reason for cracking is the high coefficient of thermal expansion of NiO.

  • 4.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    A STUDY ON CRACK CONFIGURATIONS IN THERMAL BARRIER COATINGS2017In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2017, VOL 6, AMER SOC MECHANICAL ENGINEERS , 2017, article id V006T24A005Conference paper (Refereed)
    Abstract [en]

    Spallation of thermal barrier coatings subjected to thermal fatigue occurs through cracking in or close to the metal ceramic interface. To better match an experimentally observed damage progression curve with initially slow crack growth followed by rapid crack growth, a multitude of crack paths were modeled in a finite element analysis. Comparisons with experimental data enabled the most likely crack path to be identified. It was shown that the most likely failure type for the studied TBC system was crack initiation from pre-existing defects in the thermal barrier coating which propagated into the interface, leading to spallation. The results were used to fit a crack propagation model.

  • 5.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Failure mechanisms in APS and SPS thermal barrier coatings during cyclic oxidation and hot corrosion2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thermal Barrier Coatings (TBCs) are advanced material systems that are being used in the hot sections of gas turbines such as combustor, turbine blades, and vanes. The top ceramic coating in TBCs provides insulation against the hot gases and the intermediate metallic bond coat provides oxidation and corrosion resistance to the underlying turbine components.

    Durability of thermal barrier coatings is very important for the overall performance of the gas turbine. TBCs can fail in several different ways and there is a combination of more than one failure mechanism in most situations. One of the most widely used TBC is atmospheric plasma sprayed (APS) yttria stabilized zirconia (YSZ). Both the deposition technique and the TBC material have certain limitations. The main aim of this research is to study new TBC materials and/or new deposition techniques and compare with the conventional YSZ and understand their failure mechanisms during cyclic oxidation and hot corrosion.

    Thermal cyclic oxidation of a newly developed high purity nano YSZ thermal barrier coating has been studied. Cross sectional analysis of exposed as well as completely failed samples showed a mixed-type failure caused by crack propagation parallel to the bond coat/top coat interface. The majority of the damage occurred towards the end of the coating life. A finite element model has been developed to study the probability of crack growth along different paths that leads to the final failure.

    Hot corrosion mechanism in suspension plasma sprayed two-layer gadolinium zirconate/YSZ, three-layer dense gadolinium zirconate/gadolinium zirconate/YSZ, and a single-layer YSZ has been studied in the presence of sodium sulfate and vanadium pentoxide. The test results showed that gadolinium zirconate coatings were more susceptible to corrosion compared to YSZ coatings despite gadolinium zirconate coatings having lower reactivity with the corrosive salts.

    Thermal cycling behavior of a high chromium bond coat has been studied. Cross-sectional analysis showed formation of sandwich type microstructure with chromium rich oxide and alumina as the top and the bottom layers.

    Inter-diffusion of minor elements between different MCrAlY coatings – substrate systems has been studied using, diffusion simulation software, DICTRA. The simulation results showed that the diffusion of minor elements in the coatings is dependent on the rate of β phase depletion in the beginning. After the depletion of β phase there was no clear dependence of the coating composition on the diffusion of minor elements.

  • 6.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Li, X. -H.
    Siemens Ind Turbomachinery AB, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Factors Affecting the Performance of Thermal Barrier Coatings in the Presence of V2O5 and Na2SO42016In: JOURNAL OF CERAMIC SCIENCE AND TECHNOLOGY, ISSN 2190-9385, Vol. 7, no 4, p. 409-415Article in journal (Refereed)
    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.

  • 7.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Beijing Gen Research Institute Min and Met, Peoples R China.
    Li, Xin-Hai
    Siemens Ind Turbomachineiy AB, Sweden.
    Ji, Xiaojuan
    Beijing Gen Research Institute Min and Met, Peoples R China.
    Yu, Yueguang
    Beijing Gen Research Institute Min and Met, Peoples R China.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    A study of damage evolution in high purity nano TBCs during thermal cycling: A fracture mechanics based modelling approach2017In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 37, no 8, p. 2889-2899Article in journal (Refereed)
    Abstract [en]

    This work concerns the study of damage evolution in a newly developed high purity nano 8YSZ thermal barrier coating during thermal cyclic fatigue tests (TCF). TCF tests were conducted between 100 degrees C-1100 degrees C with a hold time of 1 hat 1100 degrees C, first till failure and later for interrupted tests. Cross section analysis along the diameter of the interrupted test samples revealed a mixed-type failure and that the most of the damage occurred towards the end of the coatings life. To understand the most likely crack growth mechanism leading to failure, different crack growth paths have been modelled using finite element analysis. Crack growing from an existing defect in the top coat towards the top coat/TGO interface has been identified as the most likely mechanism. Estimated damage by the model could predict the rapid increase in the damage towards the end of the coatings life. (C) 2017 Elsevier Ltd. All rights reserved.

  • 8.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Li, Xin-Hai
    Ji, Xiaojuan
    Yu, Yueguang
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    A Study of Damage Evolution in High Purity Nano TBCs During Thermal Cycling: A Fracture Mechanics Based modeling approach.2017In: ASME Turbine Expo, Elsevier, 2017, Vol. 37, p. 2889-2899, article id 8Conference paper (Refereed)
    Abstract [en]

    This work concerns the study of damage evolution in a newly developed high purity nano 8YSZ thermal barrier coating during thermal cyclic fatigue tests (TCF). TCF tests were conducted between 100 °C–1100 °C with a hold time of 1 h at 1100 °C, first till failure and later for interrupted tests. Cross section analysis along the diameter of the interrupted test samples revealed a mixed-type failure and that the most of the damage occurred towards the end of the coating’s life. To understand the most likely crack growth mechanism leading to failure, different crack growth paths have been modelled using finite element analysis. Crack growing from an existing defect in the top coat towards the top coat/TGO interface has been identified as the most likely mechanism. Estimated damage by the model could predict the rapid increase in the damage towards the end of the coating’s life.

  • 9.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Beijing General Reseach Institute of Mining and Metallurgy, Beijing, China.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Ji, Xiaojuan
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Yu, Yueguang
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Comparison of Damage Evolution During Thermal Cycling in a High Purity Nano and Conventional Thermal Barrier Coating2017In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 332, p. 47-56Article in journal (Refereed)
    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.

  • 10.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Li, Xin-Hai
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Corrosion Mechanism in Thermal Barrier Coatings During Exposure to a Gas Mixture of N2-CO-CO2-SO22017Conference paper (Refereed)
  • 11.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Mahade, Satyapal
    Department of Engineering ScienceUniversity West, Trollhättan, Sweden.
    Curry, Nicholas
    Treibacher Industrie AG, Althofen, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Markocsan, Nicolaie
    Department of Engineering Science University West, Trollhättan, Sweden.
    Nylén, Per
    Department of Engineering Science University West, Trollhättan, Sweden.
    Björklund, Stefan
    Department of Engineering Science University West, Trollhättan, Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO42017In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, no 1, p. 140-149Article in journal (Refereed)
    Abstract [en]

    This study investigates the corrosion resistance of two-layer Gd2Zr2O7/YSZ, three-layer dense Gd2Zr2O7/ Gd2Zr2O7/YSZ, and a reference single-layer YSZ coating with a similar overall top coat thickness of 300-320 µm. All the coatings were manufactured by suspension plasma spraying resulting in a columnar structure except for the dense layer. Corrosion tests were conducted at 900 °C for 8 h using V2O5 and Na2SO4 as corrosive salts at a concentration of approximately 4 mg/cm2. SEM investigations after the corrosion tests show that Gd2Zr2O7-based coatings exhibited lower reactivity with the corrosive salts and the formation of gadolinium vanadate (GdVO4), accompanied by the phase transformation of zirconia was observed. It is believed that the GdVO4 formation between the columns reduced the strain tolerance of the coating and also due to the fact that Gd2Zr2O7 has a lower fracture toughness value made it more susceptible to corrosion-induced damage. Furthermore, the presence of a relatively dense layer of Gd2Zr2O7 on the top did not improve in reducing the corrosion-induced damage. For the reference YSZ coating, the observed corrosion-induced damage was lower probably due to combination of more limited salt penetration, the SPS microstructure and superior fracture toughness of YSZ.

  • 12.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Li, Xin-Hai
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yu, Yueguang
    Modeling the Diffusion of Minor Elements in Different MCrAlY-Superalloy Coating/Substrates at High Temperature2017In: The Minerals, Metals & Materials Series., 2017Conference paper (Refereed)
  • 13.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Beijing Gen Research Institute Min and Met, Peoples R China.
    Li, Xin-Hai
    Siemens Ind Turbomachinery AB, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yu, Yueguang
    Beijing Gen Research Institute Min and Met, Peoples R China.
    Modeling the Diffusion of Minor Elements in Different MCrAlY-Superalloy Coating/Substrates at High Temperature2017In: ENERGY MATERIALS 2017, SPRINGER INT PUBLISHING AG , 2017, p. 251-263Conference paper (Refereed)
    Abstract [en]

    As demands of energy supply have been increased continuously and at the same time the uses of fossil fuel are limited and the greenhouse effect should be minimized, the gas turbine industries have been making efforts to increase gas turbine efficiency and to reduce emissions for power generations. One of the efforts is a continuous development of high temperature capacity of ceramic thermal barrier coatings (TBCs) and metallic MCrAlY overlays. The MCrAlY overlays are used as both protective coatings and bond coats to TBCs on underlying superalloy components in the gas turbines. During high temperature exposure, elemental diffusion occurs between the bond coat and the substrate which can affect the overall coating performance. The present study investigates the diffusion of minor elements like Re, Ta, Si, Mo and Ti in various MCrAlY overlays and superalloy substrates. An oxidation-diffusion model has been used to study the elemental diffusion. The diffusion process contains two stages: beta depletion stage and the b depleted stage. In the stage when MCrAlY overlays exhibit gamma + beta microstructure, the diffusion of minor elements in the coatings was observed to be related to the b depletion rate. After that the diffusion of the minor elements did not show any clear dependence on the coating composition. The development principle of the elemental diffusion is discussed in detail.

  • 14.
    Jonnalagadda, Krishna Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Thermal Barrier Coatings: Failure Mechanisms and Life Prediction2019Doctoral 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.

  • 15.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Arts and Sciences.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, 61283, Finspång, Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Fatigue life prediction of thermal barrier coatings using a simplified crack growth model2019In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 39, no 5, p. 1869-1876Article in journal (Refereed)
    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.

  • 16.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Arts and Sciences.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, 61283 Finspång, Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Thermal barrier coatings: Life model development and validation2019In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 362, p. 293-301Article in journal (Refereed)
    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.

  • 17.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Mahade, Satyapal
    Department of Engineering Science, University West, Trollhättan, Sweden.
    Kramer, Stephanie
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhang, Pimin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Curry, Nicholas
    Treibacher Industrie AG, Althofen, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 degrees C2019In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 1-2, p. 212-222Article in journal (Refereed)
    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 degrees C with an exposure time of 8h at 900 degrees C. 75wt.% Na2SO4+25wt.% NaCl were used as the corrosive salts at a concentration of 6mg/cm(2). 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.

  • 18.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Mahade, Satyapal
    Högskolan Väst, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Kramer, Stephanie
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
    Zhang, Pimin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Curry, Nicholas
    Treibacher Industrie AG, Althofen, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB,Finspång,Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 °C2019In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 1-2, p. 212-222Article in journal (Refereed)
    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.

  • 19.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Beijing Gen Res Inst Min and Met, Peoples R China.
    Li, Xin-Hai
    Siemens Ind Turbomachinery AB, Sweden.
    Ji, Xiaojuan
    Beijing Gen Res Inst Min and Met, Peoples R China.
    Yu, Yueguang
    Beijing Gen Res Inst Min and Met, Peoples R China.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Influence of Top Coat and Bond Coat Pre-Oxidation on the Corrosion Resistance of Thermal Barrier Coatings in the Presence of SO22018In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBOMACHINERY TECHNICAL CONFERENCE AND EXPOSITION, 2018, VOL 6, AMER SOC MECHANICAL ENGINEERS , 2018, article id V006T24A018Conference 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.

  • 20.
    Mahade, Satyapal
    et al.
    Univ West, Sweden.
    Curry, Nicholas
    Treibacher Ind AG, Austria.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Markocsan, Nicolaie
    Univ West, Sweden.
    Nylen, Per
    Univ West, Sweden.
    Influence of YSZ layer thickness on the durability of gadolinium zirconate/YSZ double-layered thermal barrier coatings produced by suspension plasma spray2019In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 357, p. 456-465Article in journal (Refereed)
    Abstract [en]

    In this work, three double layered thermal barrier coating (TBC) variations with different gadolinium zirconate (GZ) and YSZ thickness (400GZ/100YSZ, 250GZ/250YSZ and 100GZ/400YSZ respectively, where the prefixed numbers before GZ and YSZ represent the layer thickness in mu m), were produced by suspension plasma spray (SPS) process. The objective was to investigate the influence of YSZ thickness on the thermal conductivity and thermal shock lifetime of the GZ/YSZ double layered TBCs. The as sprayed TBCs were characterized using SEM, XRD and porosity measurements. Thermal diffusivity measurements were made using laser flash analysis and the thermal conductivity of the TBCs was calculated. The double layered TBC with the lowest YSZ (400GZ/100YSZ) thickness showed lower thermal diffusivity and thermal conductivity. The double layered TBCs were subjected to thermal shock test at a TBC surface temperature of 1350 degrees C. Results indicate that the TBC with a higher YSZ thickness (100GZ/400YSZ) showed inferior thermal shock lifetime whereas the TBCs with low YSZ thickness showed comparatively higher thermal shock lifetimes. Failure of the TBCs after thermal shock test was analyzed using SEM and XRD to gain further insights.

  • 21.
    Mahade, Satyapal
    et al.
    University of West, Sweden.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Curry, Nicholas
    Treibacher Ind AG, Austria.
    Li, Xin-Hai
    Siemens Ind Turbomachinery AB, Sweden.
    Bjorklund, Stefan
    University of West, Sweden.
    Markocsan, Nicolaie
    University of West, Sweden.
    Nylen, Per
    University of West, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Engineered architectures of gadolinium zirconate based thermal barrier coatings subjected to hot corrosion test2017In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 328, p. 361-370Article in journal (Refereed)
    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.

  • 22.
    Yuan, Kang
    et al.
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yu, Yueguang
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Li, Xin-Hai
    Department of Management and Engineering, Linköping University, S.
    Ji, Xiaojuan
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Shen, Jie
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Thermal fatigue failure of thermal barrier coatings with a high-Cr MCrAIY bond coat2016In: Proceedings of the International Thermal Spray Conference (ITSC), 2016, Vol. 324, p. 273-278Conference paper (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) were air-plasma sprayed onto Hastelloy X substrates. The TBCs consisted of a high-Cr MCrAlY (M for Ni and Co) bond coat and a yttria-stabilized zirconia (YSZ) top coat. The TBC samples were thermally cycled between 100 ºC and 1100 ºC with 1 hour dwell time at 1100 ºC. The thermal fatigue failure of the TBCs was investigated via microstructure analyses. The final fatigue failure of the TBCs was caused by the formation of interface-parallel cracks in the YSZ top coat. The formation of the cracks was found to be strongly related to the oxidation behaviour of the MCrAlY bond coat. The development of the oxide layers was therefore studied in detail. A thermokinetic model was also used to deepen the understanding on the elemental diffusion behavior in the materials.

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