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Influence of Isothermal Heat Treatment on Porosity and Crystallite Size in Axial Suspension Plasma Sprayed Thermal Barrier Coatings for Gas Turbine Applications
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0003-1897-0171
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.ORCID iD: 0000-0002-9578-4076
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.ORCID iD: 0000-0001-5521-6894
2017 (English)In: Coatings, ISSN 2079-6412, Vol. 7, no 1, p. 1-14, article id 4Article in journal (Refereed) Published
Abstract [en]

xial suspension plasma spraying (ASPS) is an advanced thermal spraying technique, which enables the creation of specific microstructures in thermal barrier coatings (TBCs) used for gas turbine applications. However, the widely varying dimensional scale of pores, ranging from a few nanometers to a few tenths of micrometers, makes it difficult to experimentally measure and analyze porosity in SPS coatings and correlate it with thermal conductivity or other functional characteristics of the TBCs. In this work, an image analysis technique carried out at two distinct magnifications, i.e., low (500×) and high (10,000×), was adopted to analyze the wide range of porosity. Isothermal heat treatment of five different coatings was performed at 1150 °C for 200 h under a controlled atmosphere. Significant microstructural changes, such as inter-columnar spacing widening or coalescence of pores (pore coarsening), closure or densification of pores (sintering) and crystallite size growth, were noticed in all the coatings. The noted changes in thermal conductivity of the coatings following isothermal heat treatment are attributable to sintering, crystallite size growth and pore coarsening

Place, publisher, year, edition, pages
2017. Vol. 7, no 1, p. 1-14, article id 4
Keywords [en]
axial suspension plasma spraying; thermal barrier coatings; sintering; pore coarsening; nano-sized pores; crystallite size growth; thermal conductivity
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-10505DOI: 10.3390/coatings7010004ISI: 000395504700004OAI: oai:DiVA.org:hv-10505DiVA, id: diva2:1063007
Available from: 2017-01-09 Created: 2017-01-09 Last updated: 2018-08-09Bibliographically approved
In thesis
1. Design of Suspension Plasma Sprayed Thermal Barrier Coatings
Open this publication in new window or tab >>Design of Suspension Plasma Sprayed Thermal Barrier Coatings
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thermal barrier coatings (TBCs) are widely used on gas turbine components to provide thermal insulation, which in combination with advanced cooling, can enable the gas turbine to operate at significantly higher temperatures even above the melting temperature of the metallic components. There is a permanent need,mainly due to environmental reasons, to increase the combustion temperature inturbines, hence new TBC solutions are needed. By using a liquid feedstock in thermal spraying, new types of TBCs can be produced. Suspension plasma/flame or solution precursor plasma spraying are examples of techniques that can be utilized for liquid feedstock thermal spraying. This approach of using suspension and solution feedstock, which is an alternative to the conventional solid powder feedstock spraying, is gaining increasing research interest since it has been shown to be capable of producing coatings withsuperior performance. The objective of this research work was to identify relationships between process parameters, coating microstructure, thermal conductivity and lifetime in suspension plasma sprayed TBCs. A further objective was to utilize these relationships to enable tailoring of the TBC microstructure for superior performance compared to state-of-the-art TBC used in industry today, i.e. solid feedstock plasma sprayed TBCs. Different spraying techniques, namely suspension high velocity oxy fuel, solution precursor plasma and suspension plasma spraying (with axial and radial feeding) were explored and compared to solid feedstock plasma spraying. A variety of microstructures, such as highly porous, vertically cracked and columnar, were produced and investigated. It was shown that there are strong relationships between microstructure, thermo-mechanical properties and performance of the coatings. Specifically, axial suspension plasma spraying wasshown as a very promising technique to produce various microstructures as wellas highly durable coatings. Based on the experimental results, a tailored columnar microstructure design for a superior TBC performance is also proposed.

Place, publisher, year, edition, pages
Trollhättan: University West, 2018. p. 96
Series
PhD Thesis: University West ; 20
Keywords
Microstructure; Thermal Barrier Coatings; Axial Injection; Suspension Plasma Spraying; Porosity; Thermal Conductivity; Fracture Toughness; Lifetime
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12336 (URN)978-91-87531-92-7 (ISBN)978-91-87531-91-0 (ISBN)
Public defence
2018-06-15, F104, University West, Trollhättan, 10:15 (English)
Opponent
Supervisors
Available from: 2018-05-25 Created: 2018-05-23 Last updated: 2018-05-25

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Ganvir, AshishMarkocsan, NicolaieJoshi, Shrikant

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