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Design of Thermal Barrier Coating Systems
University West, Department of Engineering Science, Research Enviroment Production Technology West. (Thermal Spray, PTW)ORCID iD: 0000-0003-0209-1332
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Thermal barrier coatings (TBC’s) are used to provide both thermal insulation and oxidation protection to high temperature components within gas turbines. The development of turbines for power generation and aviation has led to designs where the operation conditions exceed the upper limits of most conventional engineering materials. As a result there has been a drive to improve thermal barrier coatings to allow the turbine to operate hotter for longer.

The focus of this study has been the development of a new generation of TBC system for industrial implementation. The goal for these new coatings was to achieve lower conductivity and longer lifetime than those coatings used today. The route taken to achieve these goals has been twofold. Firstly an alternative stabiliser has been chosen for the zirconium oxide system in the form of dysprosia. Secondly, Control of the powder morphology and spray parameters has been used to generate coating microstructures with favourable levels of porosity.

Samples have been heavily characterised using the laser flash technique for evaluation of thermal properties. Measurements were performed at room temperature and at intervals up to 1200°C. Samples have also been tested in their as produced state and after heat treatments of up to 200 hours.

Lifetime evaluation has been performed using the thermo-cyclic fatigue test to expose coating systems to successive cycles of heating and cooling combined with oxidation of the underlying metallic coating.

Microstructures have been prepared and analysed using SEM. An image analysis routine has been used to attempt to quantify changes in microstructure features between coating types or coating exposure times and to relate those changes to changes in thermal properties

Results show that dysprosia as an alternative dopant gives a reduction in thermal conductivity. While small at room temperature and in the as produced state; the influence becomes more pronounced at high temperatures and with thermal exposure time. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levels of porosity.

In relation to lifetime, the target of double the thermo-cyclic fatigue life was achieved using a coating with engineered porosity. Introducing a polymer to the spray powder helps to generate large globular pores within the coating together with a large number of delaminations. Such a structure has shown to be highly resistant to TCF testing.

Place, publisher, year, edition, pages
Gothenburg: Chalmers University of Technolgy , 2012. , p. 75
Keywords [en]
Thermal Barrier Coating, Atmopsheric Plasma Spraying, Thermal Conductivity, Thermo-cyclic fatigue
National Category
Materials Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-4898OAI: oai:DiVA.org:hv-4898DiVA, id: diva2:578057
Presentation
2012-06-08, C118, University West, Gustava Melins Gata 2, Trollhättan, 14:27 (English)
Opponent
Supervisors
Available from: 2012-12-20 Created: 2012-12-17 Last updated: 2018-07-25Bibliographically approved
List of papers
1. Evolution of thermal conductivity of dysprosia stabilised thermal barrier coating systems during heat treatment
Open this publication in new window or tab >>Evolution of thermal conductivity of dysprosia stabilised thermal barrier coating systems during heat treatment
2012 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, ISSN 0257-8972, Vol. 209, p. 38-43Article in journal (Refereed) Published
Abstract [en]

Dysprosia stabilised zirconia coatings offer a potential reduction in thermal heat transfer for thermal barrier coating systems with the added benefit of being producible with existing equipment and spray knowledge. However, there is little information on the long term performance of such systems relative to the standard coatings. While a low thermal conductivity is important for a gas turbine; sintering resistance is important to maintain properties over the lifetime of a component.

In this study, four dysprosia stabilised zirconia coatings are compared with a standard yttria stabilised coating in present industrial use.

Samples were exposed to isothermal furnace conditions at 1150 °C from 5 to 200 hours to observe the sintering resistance of the coating systems. Tests carried out include microstructural analysis with SEM, thermal conductivity measurements using laser flash analysis and porosity changes monitored using image analysis.

Keywords
Thermal barrier coating; Atmospheric plasma spraying; Thermal conductivity; Sintering
National Category
Materials Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-4692 (URN)10.1016/j.surfcoat.2012.08.018 (DOI)000310656200006 ()2-s2.0-84866883350 (Scopus ID)
Available from: 2012-09-27 Created: 2012-09-27 Last updated: 2017-12-07Bibliographically approved
2. Influence of Sensor contact on the Thermal Conductivity Values of Thermal Barrier Coatings: Part 1 Experimental
Open this publication in new window or tab >>Influence of Sensor contact on the Thermal Conductivity Values of Thermal Barrier Coatings: Part 1 Experimental
2010 (English)In: Proceedings of the 24th International Conference on Surface Modification Technologies: 7-9 sept, Dresden, 2010, p. 317-327Conference paper, Published paper (Refereed)
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-3115 (URN)ISBN 978-81-910571-2-6 (ISBN)
Conference
The 24th International Conference on Surface Modification Technologies (SMT 24),Dresden, Germany, September 7 - 9, 2010
Available from: 2011-01-27 Created: 2011-01-27 Last updated: 2016-02-11Bibliographically approved
3. Next Generation Thermal Barrier Coatings for the Gas Turbine Industry
Open this publication in new window or tab >>Next Generation Thermal Barrier Coatings for the Gas Turbine Industry
Show others...
2010 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, ISSN 1059-9630, Vol. 20, no 1-2, p. 108-115Article in journal (Refereed) Published
Abstract [en]

The aim of this study is to develop the next generation of production ready air plasma sprayed thermalbarrier coating with a low conductivity and long lifetime. A number of coating architectures wereproduced using commercially available plasma spray guns. Modifications were made to powder chemistry,including high purity powders, dysprosia stabilized zirconia powders, and powders containingporosity formers. Agglomerated & sintered and homogenized oven spheroidized powder morphologieswere used to attain beneficial microstructures. Dual layer coatings were produced using the two powders.Laser flash technique was used to evaluate the thermal conductivity of the coating systems from roomtemperature to 1200 C. Tests were performed on as-sprayed samples and samples were heat treated for100 h at 1150 C. Thermal conductivity results were correlated to the coating microstructure using imageanalysis of porosity and cracks. The results show the influence of beneficial porosity on reducing thethermal conductivity of the produced coatings.

Keywords
APS coatings, coatings for gas turbine components, porosity of coatings, TBC topcoats
National Category
Ceramics Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-4688 (URN)10.1007/s11666-010-9593-x (DOI)
Projects
KK-TBC
Available from: 2012-09-26 Created: 2012-09-26 Last updated: 2017-12-07Bibliographically approved
4. Evaluation of the Lifetime and Thermal Conductivity of Dysprosia-Stabilized Thermal Barrier Coating Systems
Open this publication in new window or tab >>Evaluation of the Lifetime and Thermal Conductivity of Dysprosia-Stabilized Thermal Barrier Coating Systems
Show others...
2013 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 22, no 6, p. 864-872Article in journal (Refereed) Published
Abstract [en]

The aim of this study was the further development of dysprosia stabilised zirconia coatings for gas turbine applications. The target for these coatings was a longer lifetime and higher insulating performance compared to today's industrial stan dard thermal barrier coating. Two morphologies of ceramic top coat were studied; one using a dual layer systems and the second using a polymer to generate porosity. Evaluations were carried out using laser flash technique to measure thermal properties. Lifetime testing was conducted using thermal shock testing and thermo-cyclic fatigue testing. Microstructure was assessed with SEM and Image analysis used to characterise porosity content. The results show that coatings with an engineered microstructure give performance twice that of the present reference coating.

Place, publisher, year, edition, pages
Materials Park, OH: , 2013
Keywords
Thermal spray, coating, 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-4911 (URN)10.1007/s11666-013-9932-9 (DOI)000321869400002 ()2-s2.0-84880511926 (Scopus ID)
Available from: 2012-12-20 Created: 2012-12-20 Last updated: 2017-12-06Bibliographically approved

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