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Stress and Cracking during Chromia-Spinel-NiO Cluster Formation in Thermal Barrier Coating Systems
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0002-2857-0975
Linköping University.
Linköping University.
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2015 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 24, no 6, 1002-1014 p.Article in journal (Refereed) Published
Abstract [en]

Thermal barrier coatings (TBC) are used in gas turbines to reduce the temperatures in the underlying substrate. There are several mechanisms that may cause the TBC to fail; one of them is cracking in the coating interface due to extensive oxidation. In the present study, the role of so called chromia-spinel-NiO (CSN) clusters in TBC failure was studied. Such clusters have previously been found to be prone to cracking. Finite element modeling was performed on a CSN cluster to find out at which stage of its formation it cracks and what the driving mechanisms of cracking are. The geometry of a cluster was obtained from micrographs and modeled as close as possible. Nanoindentation was performed on the cluster to get the correct Young's moduli. The volumetric expansion associated with the formation of NiO was also included. It was found that the cracking of the CSN clusters is likely to occur during its last stage of formation as the last Ni-rich core oxidizes. Furthermore, it was shown that the volumetric expansion associated with the oxidation only plays a minor role and that the main reason for cracking is the high coefficient of thermal expansion of NiO.

Place, publisher, year, edition, pages
2015. Vol. 24, no 6, 1002-1014 p.
Keyword [en]
Chromia-spinel-NiO, failure mechanism, finite element modeling, oxide cluster, thermal barrier coating
National Category
Materials Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-7180DOI: 10.1007/s11666-015-0270-yOAI: oai:DiVA.org:hv-7180DiVA: diva2:772185
Note

Ingår i dissertation

Available from: 2014-12-16 Created: 2014-12-16 Last updated: 2016-08-16Bibliographically approved
In thesis
1. 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
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Available from: 2014-12-16 Created: 2014-12-16 Last updated: 2016-08-16Bibliographically approved

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