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A modelling approach to design of microstructures in thermal barrier coatings
University West, Department of Engineering Science, Division of Manufacturing Processes. (PTW)ORCID iD: 0000-0002-2857-0975
University West, Department of Engineering Science, Division of Production Engineering. (PTW)ORCID iD: 0000-0001-7787-5444
2013 (English)In: Journal of Ceramic Science and Technology, ISSN 2190-9385, Vol. 4, no 2, 85-92 p.Article 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.

Place, publisher, year, edition, pages
2013. Vol. 4, no 2, 85-92 p.
Keyword [en]
thermal barrier coatings; yttria stabilised zirconia; OOF; microstructure; thermo-mechanical properties, WIL, Work-integrated learning
Keyword [sv]
AIL
National Category
Production Engineering, Human Work Science and Ergonomics Materials Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering; Work Integrated Learning
Identifiers
URN: urn:nbn:se:hv:diva-5064DOI: 10.4416/JCST2012-00044Scopus ID: 2-s2.0-84881101933OAI: oai:DiVA.org:hv-5064DiVA: diva2:589663
Available from: 2013-01-18 Created: 2013-01-18 Last updated: 2016-08-16Bibliographically approved
In thesis
1. 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
2. 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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