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TBC bond coat-top coat interface roughness: influence on fatigue life and modelling aspects
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
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2013 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 236, 230-238 p.Article in journal (Refereed) Published
Abstract [en]

Thermal barrier coatings (TBCs), when used in gas turbines, may fail through thermal fatigue, causing the ceramic top coat to spall off the metallic bond coat. The life prediction of TBCs often involves finite element modelling of the stress field close to the bond coat/top coat interface and thus relies on accurate modelling of the interface. The present research studies the influence of bond coat/top coat interface roughness on the thermal fatigue life of plasma sprayed TBCs. By using different spraying parameters, specimens with varying interface roughness were obtained. During thermal cycling it was found that higher interface roughness promoted longer thermal fatigue life. The interfaces were characterised by roughness parameters, such as Ra, Rq and Rq, as well as by autocorrelation, material ratio curves, probability plots and slope distribution. The variation of spray parameters was found to affect amplitude parameters, such as Ra, but not spacing parameters, such as RSm. Three different interface geometries were tried for finite element crack growth simulation: cosine, ellipse and triangular shape. The cosine model was found to be an appropriate interface model and a procedure for obtaining the necessary parameters, amplitude and wavelength, was suggested. The positive effect of high roughness on life was suggested to be due to a shift from predominantly interface failure, for low roughness, to predominantly top coat failure, for high roughness.

Place, publisher, year, edition, pages
2013. Vol. 236, 230-238 p.
Keyword [en]
thermal barrier coating, TBC, thermal cycling fatigue, interface, roughness, Ra
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-96811DOI: 10.1016/j.surfcoat.2013.09.051ISI: 000329884300032OAI: oai:DiVA.org:liu-96811DiVA: diva2:643479
Available from: 2013-08-27 Created: 2013-08-27 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Thermal Barrier Coatings: Durability Assessment and Life Prediction
Open this publication in new window or tab >>Thermal Barrier Coatings: Durability Assessment and Life Prediction
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thermal barrier coating (TBC) systems are coating systems containing a metallic bond coat and a ceramic top coat. TBCs are used in gas turbines for thermal insulation and oxidation resistance. Life prediction of TBCs is important as high-temperature exposure degrades the coatings through mechanisms such as thermal fatigue and the formation and growth of thermally grown oxides (TGOs). This thesis presents research on durability assessment and life prediction of air plasma sprayed TBCs.

The adhesion of thermal barrier coatings subjected to isothermal oxidation, thermal cycling fatigue and thermal shock was studied. The adhesion strength and fracture characteristics were found to vary with heat treatment type.

The influence of interdiffusion between bond coat and substrate was studied on TBCs deposited on two different substrates. The thermal fatigue life was found to differ between the two TBC systems. While fractography and nanoindentation revealed no differences between the TBC systems, the oxidation kinetics was found to differ for non-alumina oxides.

The influence of bond coat/top coat interface roughness on the thermal fatigue life was studied; higher interface roughness promoted longer thermal fatigue life. Different interface geometrieswere tried in finite element crack growth simulations, and procedures for creating accurate interface models were suggested.

The influence of water vapour and salt deposits on the oxidation/corrosion of a NiCoCrAlY coating and a TBC were studied. Salt deposits gave thicker TGOs and promoted an Y-rich phase. The effect of salt deposits was also evident for TBC coated specimens.

A microstructure-based life model was developed using the Thermo-Calc software. The model included coupled oxidation-diffusion, as well as diffusion blocking due to the formation of internal oxides and pores. The model predicted Al-depletion in acceptable agreement with experimental observations.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 65 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1527
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-96816 (URN)978-91-7519-569-8 (ISBN)
Public defence
2013-10-18, ACAS, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency
Available from: 2013-08-27 Created: 2013-08-27 Last updated: 2014-01-07Bibliographically approved

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