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Impact of Impurity Content on the Sintering Resistance and Phase Stability of Dysprosia- and Yttria-Stabilized Zirconia Thermal Barrier Coatings
University West, Department of Engineering Science, Division of Mechanical Engineering. (PTW)ORCID iD: 0000-0003-0209-1332
University of Manchester.
Academy of Sciences of the Czech Republic, Institute of Plasma Physics.
Academy of Sciences of the Czech Republic, Institute of Plasma Physics.
Show others and affiliations
2014 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 23, no 1-2, 160-169 p.Article in journal (Refereed) Published
Abstract [en]

Dysprosia-stabilized zirconia (DySZ) is a promising candidate to replace yttria-stabilized zirconia (YSZ) as a thermal barrier coating due to its lower inherent thermal conductivity. It is also suggested in studies that DySZ may show greater stability to high temperature phase changes compared to YSZ, possibly allowing for coatings with extended lifetimes. Separately, the impurity content of YSZ powders has been proven to influence high-temperature sintering behavior. By lowering the impurity oxides within the spray powder, a coating more resistant to sintering can be produced. This study presents both high purity and standard purity dysprosia and YSZ coatings and their performance after a long heat treatment. Coatings were produced using powder with the same morphology and grain size; only the dopant and impurity content were varied. Samples have been heat treated for exposure times up to 400 h at a temperature of 1150 °C. Samples were measured for thermal conductivity to plot the evolution of coating thermal properties with respect to exposure time. Thermal conductivity has been compared to microstructure analysis and porosity measurement to track structural changes. Phase analysis utilizing x-ray diffraction was used to determine differences in phase degradation of the coatings after heat treatment. © 2013 ASM International.

Place, publisher, year, edition, pages
Springer, 2014. Vol. 23, no 1-2, 160-169 p.
Keyword [en]
atmospheric plasma spray (APS), thermal and phase stability of coatings, thermal barrier coatings (TBCs), thermal conductivity, zirconia, WIL, Work-integrated Learning
Keyword [sv]
AIL
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Work Integrated Learning
Identifiers
URN: urn:nbn:se:hv:diva-5695DOI: 10.1007/s11666-013-0014-9ISI: 000329106200021Scopus ID: 2-s2.0-84891833854OAI: oai:DiVA.org:hv-5695DiVA: diva2:663402
Conference
2013 International Thermal Spray Conference, held May 13-15, 2013, in Busan, South Korea
Available from: 2013-11-11 Created: 2013-11-07 Last updated: 2016-02-11Bibliographically approved
In thesis
1. Design of Thermal Barrier Coating Systems
Open this publication in new window or tab >>Design of Thermal Barrier Coating Systems
2014 (English)Doctoral 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 at higher temperatures for longer.

The focus of this thesis has been to design thermal barrier coatings with lower conductivity and longer lifetime than those coatings used in industry today. The work has been divided between the development of new generation air plasma spray (APS) TBC coatings for industrial gas turbines and the development of suspension plasma spray (SPS) TBC systems.

The route taken to achieve these goals with APS TBC’s 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.

In terms of development of SPS TBC systems, these coatings are relatively new with many of the critical coating parameters not yet known. The focus of the work has therefore been to characterise their lifetime and thermal properties when produced in a complete TBC system.

Results demonstrate that dysprosia as an alternative stabiliser 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 longer thermal exposure time. The trade-off for this lowered thermal conductivity may be in the loss of high temperature stability. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levelsof porosity.

In relation to lifetime, double the thermo-cyclic fatigue (TCF) life relative to the industrial standard 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 was shown to be highly resistant to TCF testing.

SPS TBC’s were shown to have much greater performance relative to their APS counterparts in thermal shock life, TCF life and thermal conductivity. Columnar SPS coatings are a prospective alternative for strain tolerant coatings in gas turbine engines.

Place, publisher, year, edition, pages
Trollhättan: University West, 2014. 109 p.
Series
PhD Thesis: University West, 3
Keyword
Industrial Gas Turbine; Aero Turbine; Thermal Barrier Coating; Atmospheric Plasma Spraying; Suspension Plasma Spraying; Thermal Conductivity; Thermo-cyclic fatigue; Thermal Shock
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-5931 (URN)978-91-977943-9-8 (ISBN)978-91-977943-8-1 (ISBN)
Public defence
2014-02-28, F127, University West, Gustava Melins Gata 2, Trollhättan, 09:53 (English)
Opponent
Supervisors
Available from: 2014-02-19 Created: 2014-02-19 Last updated: 2015-06-24Bibliographically approved

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