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Relationships between Coating Microstructure and Thermal Conductivity in Thermal Barrier Coatings – A modelling Approach
University West, Department of Engineering Science, Division of Mechanical Engineering and Natural Sciences. (Termisk sprutning)ORCID iD: 0000-0002-2965-488X
University West, Department of Engineering Science. (PTW)ORCID iD: 0000-0001-7787-5444
University West, Department of Engineering Science, Division of Manufacturing Processes. (PTW)ORCID iD: 0000-0002-2857-0975
Show others and affiliations
2010 (English)In: International Thermal Spray Conference and Exposition, ITCS Singapore 2010: 3-5 May 2010,  Singapore, Düsseldorft: DVS Media , 2010, 66-72 p.Conference 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. 66-72 p.
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: urn:nbn:se:hv:diva-3076ISBN: 978-3-87155-590-9 (print)OAI: oai:DiVA.org:hv-3076DiVA: diva2:392133
Conference
Thermal Spray 2010: Global Solutions for Future Applications
Available from: 2011-01-26 Created: 2011-01-26 Last updated: 2016-08-16Bibliographically approved
In thesis
1. Contributions to multivariate process capability indices
Open this publication in new window or tab >>Contributions to multivariate process capability indices
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Luelå: , 2012. 36 p.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Mathematics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-4456 (URN)9789174393989 (ISBN)
Available from: 2012-06-28 Created: 2012-06-26 Last updated: 2012-06-28Bibliographically approved
2. Design of Microstructures in Thermal Barrier Coatings: A Modelling Approach
Open this publication in new window or tab >>Design of Microstructures in Thermal Barrier Coatings: A Modelling Approach
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. 40 p.
Series
Technical report / Department of Materials and Manufacturing Technology, Chalmers University of Technology, ISSN 1652-8891 ; 81
Keyword
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:nbn:se:hv:diva-5065 (URN)
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
3. Design of Thermal Barrier Coatings: A modelling approach
Open this publication in new window or tab >>Design of Thermal Barrier Coatings: A modelling approach
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. TBC is a duplex material system consisting of an insulating ceramic topcoat layer and an intermetallic bondcoat layer. TBC microstructures 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. Failure in APS TBCs is mainly associated with the thermo-mechanical stresses developing due to the thermally grown oxide (TGO) layer growth at the topcoat-bondcoat interface and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs.The objective of this thesis work was two-fold for one purpose: to design an optimised TBC to be used for next generation gas turbines. The first objective was to investigate the relationships between coating microstructure and thermal-mechanical properties of topcoats, and to utilise these relationships to design an optimised morphology of the topcoat microstructure. The second objective was to investigate the relationships between topcoat-bondcoat interface roughness, TGO growth and lifetime of TBCs, and to utilise these relationships to design an optimal interface. Simulation technique was used to achieve these objectives. Important microstructural parameters influencing the performance of topcoats were identified and coatings with the feasible identified microstructural parameters were designed, modelled and experimentally verified. It was shown that large globular pores with connected cracks inherited within the topcoat microstructure significantly enhanced TBC performance. Real topcoat-bondcoat interface topographies were used to calculate the induced stresses and a diffusion based TGO growth model was developed to assess the lifetime. The modelling results were compared with existing theories published in previous works and experiments. It was shown that the modelling approach developed in this work could be used as a powerful tool to design new coatings and interfaces as well as to achieve high performance optimised morphologies.

Place, publisher, year, edition, pages
Trollhättan: University West, 2014. xvi, 85 p.
Series
PhD Thesis: University West, 5
Keyword
Thermal barrier coatings, Microstructure, Thermal conductivity, Young’s modulus, Interface roughness, Thermally grown oxide, Lifetime, Finite element modelling, Design
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-7181 (URN)978-91-87531-06-4 (ISBN)
Public defence
2015-01-28, 09:00 (English)
Opponent
Supervisors
Available from: 2014-12-16 Created: 2014-12-16 Last updated: 2016-08-16Bibliographically approved

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