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Design of Microstructures in Thermal Barrier Coatings: A Modelling Approach
University West, Department of Engineering Science, Division of Mechanical Engineering. (PTW)ORCID iD: 0000-0002-2857-0975
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Plasma sprayed Thermal Barrier Coating systems (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. The material that is most commonly used in these applications is Yttria Stabilized Zirconia (YSZ) because of this ceramic’s favourable properties, such as low thermal conductivity, phase stability to high temperature, and good erosion resistance. The coating microstructures in YSZ coatings are highly heterogeneous, consisting of defects such as pores and cracks of different sizes which determine the coating’s final thermal and mechanical properties, and the service lives of the coatings. Determination of quantitative microstructure–property correlations is of great interest as experimental procedures are time consuming and expensive.

This objective of this thesis work was to investigate the relationships between coating microstructure and thermal-mechanical properties of TBCs, and to utilise these relationships to design an optimised microstructure to be used for next generation TBCs. Simulation technique was used to achieve this goal. Important microstructural parameters influencing the performance of TBCs were identified and coatings with the identified microstructural parameters were designed, modelled and experimentally verified. TBCs comprising of large globular pores with connected cracks inherited within the coating microstructure were shown to have significantly enhanced performance. Low thermal conductivity, low Young‘s modulus and high lifetime were exhibited by these coatings. The modelling approach described in this work can be used as a powerful tool to design new coatings as well as to achieve optimised microstructures.

Place, publisher, year, edition, pages
Göteborg: Chalmers University of Technology , 2013. , p. 40
Series
Technical report / Department of Materials and Manufacturing Technology, Chalmers University of Technology, ISSN 1652-8891 ; 81
Keywords [en]
thermal barrier coatings, microstructure, thermal conductivity, Young‘s modulus, lifetime, finite element modelling, design
National Category
Mechanical Engineering Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-5065OAI: oai:DiVA.org:hv-5065DiVA, id: diva2:589686
Presentation
2013-03-01, F127, University West, Trollhättan, 10:00 (English)
Opponent
Supervisors
Available from: 2013-03-11 Created: 2013-01-18 Last updated: 2016-08-16Bibliographically approved
List of papers
1. Design of Next Generation Thermal Barrier Coatings- Experiments and Modelling
Open this publication in new window or tab >>Design of Next Generation Thermal Barrier Coatings- Experiments and Modelling
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2013 (English)In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 220, p. 20-26Article in journal (Refereed) Published
Abstract [en]

Thermal barrier coating (TBC) systems have been used in the gas turbine industry since the 1980's. The future needs of both the air and land based turbine industry involve higher operating temperatures with longer lifetime on the component so as to increase power and efficiency of gas turbines. The aim of this study was to meet these future needs by further development of zirconia coatings. The intention was to design a coating system which could be implemented in industry within the next three years. Different morphologies of ceramic topcoat were evaluated; using dual layer systems and polymers to generate porosity. Dysprosia stabilised zirconia was also included in this study as a topcoat material along with the state-of-the-art yttria stabilised zirconia (YSZ). High purity powders were selected in this work. Microstructure was assessed with scanning electron microscope and an in-house developed image analysis routine was used to characterise porosity content. Evaluations were carried out using the laser flash technique to measure thermal conductivity. Lifetime was assessed using thermo-cyclic fatigue testing. Finite element analysis was utilised to evaluate thermal-mechanical material behaviour and to design the morphology of the coating with the help of an artificial coating morphology generator through establishment of relationships between microstructure, thermal conductivity and stiffness. It was shown that the combined empirical and numerical approach is an effective tool for developing high performance coatings. The results show that large globular pores and connected cracks inherited within the coating microstructure result in a coating with best performance. A low thermal conductivity coating with twice the lifetime compared to the industrial standard today was fabricated in this work.

Keywords
Thermal barrier coatings, Microstructure, Thermal conductivity, Lifetime, Finite element modelling, Young's modulus, WIL, Work-integrated learning, AIL
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Work Integrated Learning
Identifiers
urn:nbn:se:hv:diva-4687 (URN)10.1016/j.surfcoat.2012.09.015 (DOI)000317875800004 ()2-s2.0-84875498863 (Scopus ID)
Available from: 2012-09-26 Created: 2012-09-26 Last updated: 2018-07-03Bibliographically approved
2. Design of Low Thermal Conductivity Thermal Barrier Coatings by Finite Element Modelling
Open this publication in new window or tab >>Design of Low Thermal Conductivity Thermal Barrier Coatings by Finite Element Modelling
2011 (English)In: Surface Modification Technologies XXIV: SMT24, Dresden, September 7-9, 2010 / [ed] T. S. Sudarshan, Eckhard Beyer, and Lutz-Michael Berger, 2011, p. 353-365Conference paper, Published paper (Refereed)
Abstract [en]

Fundamental understanding of relationships between coating microstructure and thermal conductivity is important to be able to understand the influence of coating defects, such as delaminations and pores, on heat insulation in thermal barrier coatings (TBC). Object Oriented Finite element analysis (OOF) has recently been shown as an effective tool for evaluating thermo-mechanical material behaviour as this method is capable of incorporating the inherent material microstructure as an input to the model. The objective of this work was to evaluate a procedure where this technique is combined with Tbctool, a plasma-sprayed TBC like morphology generator, thus enabling development of low thermal conductivity coatings by simulation. Input parameters for Tbctool were computed from SEM images of sprayed microstructures using the image analysis software, Aphelion. Microstructures for as-sprayed as well as heat treated samples were evaluated. The thermal conductivities of the artificially generated microstructures were determined using OOF. Verification of the modelling procedure was performed by comparing predicted values by OOF with corresponding measured values using the laser flash technique. The results, although tentative in nature, indicate that the proposed simulation approach can be a powerful tool in the development of new low conductivity coatings.

National Category
Aerospace Engineering Energy Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-3818 (URN)
Conference
SMT24, Dresden, September 7-9, 2010
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2016-08-16Bibliographically approved
3. A modelling approach to design of microstructures in thermal barrier coatings
Open this publication in new window or tab >>A modelling approach to design of microstructures in thermal barrier coatings
2013 (English)In: Journal of Ceramic Science and Technology, ISSN 2190-9385, Vol. 4, no 2, p. 85-92Article in journal (Refereed) Published
Abstract [en]

Thermo-mechanical properties of TBCs are strongly influenced by coating defects, such as delaminations and pores, thus making it essential to have a fundamental understanding of microstructure-property relationships in TBCs to produce a desired coating. Object-Oriented Finite element analysis (OOF) has been shown previously as an effective tool for evaluating thermal and mechanical material behaviour, as this method is capable of incorporating the inherent material microstructure as an input to the model. In this work, OOF was used to predict the thermal conductivity and effective Young's modulus of TBC topcoats. A Design of Experiments (DoE) was conducted by varying selected spray parameters for spraying Yttria Stabilized Zirconia (YSZ) topcoat. Microstructure was assessed with SEM and image analysis was used to characterize porosity content. The relationships between microstructural features and properties predicted by modelling are discussed. The microstructural features having the most beneficial effect on properties were sprayed with another spray gun so as to verify the results obtained from modelling. Characterisation of the coatings included microstructure evaluation, thermal conductivity and lifetime measurements. The modelling approach in combination with experiments undertaken in this study was shown to be an effective way in achieving coatings with optimised thermo-mechanical properties.

Keywords
thermal barrier coatings; yttria stabilised zirconia; OOF; microstructure; thermo-mechanical properties, WIL, Work-integrated learning, AIL
National Category
Production Engineering, Human Work Science and Ergonomics Materials Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering; Work Integrated Learning
Identifiers
urn:nbn:se:hv:diva-5064 (URN)10.4416/JCST2012-00044 (DOI)2-s2.0-84881101933 (Scopus ID)
Available from: 2013-01-18 Created: 2013-01-18 Last updated: 2017-12-06Bibliographically approved
4. Relationships between Coating Microstructure and Thermal Conductivity in Thermal Barrier Coatings – A modelling Approach
Open this publication in new window or tab >>Relationships between Coating Microstructure and Thermal Conductivity in Thermal Barrier Coatings – A modelling Approach
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2010 (English)In: International Thermal Spray Conference and Exposition, ITCS Singapore 2010: 3-5 May 2010,  Singapore, Düsseldorft: DVS Media , 2010, p. 66-72Conference paper, Published paper (Refereed)
Abstract [en]

Fundamental understanding of relationships between coating microstructure and thermal conductivity is important to be able to understand the influence of coating defects, such as delaminations and pores, on heat insulation in thermal barrier coatings. Object-Oriented Finite element analysis (OOF) has recently been shown as an effective tool for evaluating thermo-mechanical material behaviour, because of this method's capability to incorporate the inherent material microstructure as an input to the model. In this work, this method was combined with multi-variate statistical modelling. The statistical model was used for screening and tentative relationship building and the finite element model was thereafter used for verification of the statistical modelling results. Characterisation of the coatings included microstructure, porosity and crack content and thermal conductivity measurements. A range of coating architectures was investigated including High purity Yttria stabilised Zirconia, Dysprosia stabilised Zirconia and Dysprosia stabilised Zirconia with porosity former. Evaluation of the thermal conductivity was conducted using the Laser Flash Technique. The microstructures were examined both on as-sprayed samples as well as on heat treated samples. The feasibility of the combined two modelling approaches, including their capability to establish relationships between coating microstructure and thermal conductivity, is discussed.

Place, publisher, year, edition, pages
Düsseldorft: DVS Media, 2010
Series
DVS-Reports ; Volume 264
National Category
Other Engineering and Technologies not elsewhere specified Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-3076 (URN)978-3-87155-590-9 (ISBN)
Conference
Thermal Spray 2010: Global Solutions for Future Applications
Available from: 2011-01-26 Created: 2011-01-26 Last updated: 2016-08-16Bibliographically approved

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