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Fractographic and microstructural study of isothermally and cyclically heat treated thermal barrier coatings
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.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Volvo Aero Corporation, Trollhättan, Sweden.
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2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 243, 82-90 p.Article in journal (Refereed) Published
Abstract [en]

The fracture surfaces from adhesion tested thermal barrier coatings (TBC) have been studied by scanning electron microscopy. The adhesion test have been made using the standard method described in ASTM 633, which makes use of a tensile test machine to measure the adhesion. The studied specimens consist of air plasma sprayed (APS) TBC deposited on disc-shaped substrates of Hastelloy X. The bond coat (BC) is of NiCoCrAlY type and the top coat (TC) consists of yttria–stabilised–zirconia. Before the adhesion test, the specimens were subjected to three different heat treatments: 1) isothermal oxidation 2) thermal cycling fatigue (TCF) and 3) burner rig test (BRT). The fracture surfaces of the adhesion tested specimens where characterised. A difference in fracture mechanism were found for the different heat treatments. Isothermal oxidation gave fracture mainly in the top coat while the two cyclic heat treatments gave increasing amount of BC/TC interface fracture with number of cycles. Some differences could also be seen between the specimens subjected to burner rig test and furnace cycling.

Place, publisher, year, edition, pages
2014. Vol. 243, 82-90 p.
Keyword [en]
Thermal barrier coating, TBC, fractography, adhesion, thermal cycling, burner rig
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-67883DOI: 10.1016/j.surfcoat.2012.02.040ISI: 000335542100014OAI: oai:DiVA.org:liu-67883DiVA: diva2:414006
Note

On the day of the defence date of the Thesis the status of this article was Manuscript.

Available from: 2011-05-02 Created: 2011-05-02 Last updated: 2017-12-11Bibliographically approved
In thesis
1. High-temperature degradation of plasma sprayed thermal barrier coating systems
Open this publication in new window or tab >>High-temperature degradation of plasma sprayed thermal barrier coating systems
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Thermal barrier coating systems (TBCs) are used in gas turbines to prevent high-temperature degradation of metallic materials in the combustor and turbine. One of the main concerns regarding TBCs is poor reliability, and accurate life prediction models are necessary in order to fully utilise the beneficial effects of TBCs. This research project aims at developing deeper understanding of the degradation and failure mechanisms acting on TBCs during high temperature exposure, and to use this knowledge to improve life assessments of TBCs. The present work includes a study on the influence of coating interface morphology on the fatigue life of TBCs and a study on the influence of some different heat treatments on the adhesive properties of TBCs.

The influence of coating interface morphology on fatigue life has been studied both experimentally and by modelling. Large interface roughness has been found experimentally to increase fatigue life of TBCs. The modelling work do, to some extent, capture this behaviour. It is evident, from the study, that interface morphology has a large impact on fatigue life of TBCs.

Three thermal testing methods, that degrade TBCs, have been investigated: isothermal oxidation, furnace cycling and burner rig test. The degraded TBCs have been evaluated by adhesion tests and microscopy. The adhesion of TBCs has been found to depend on heat treatment type and length. Cyclic heat treatments, (furnace cycling and burner rig test), lower the adhesion of TBCs while isothermal oxidation increases adhesion. The fracture surfaces from the adhesion tests reveal that failure strongly depends on the pre-existing defects in the TBC.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. 49 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1484
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67885 (URN)LIU–TEK–LIC–2011:23 (Local ID)978-91-7393-165-6 (ISBN)LIU–TEK–LIC–2011:23 (Archive number)LIU–TEK–LIC–2011:23 (OAI)
Presentation
2011-05-27, ACAS, Plan 2, A-huset, Campus Valla, Linköpings universitet, Linköping, 13:15 (Swedish)
Opponent
Supervisors
Available from: 2011-05-02 Created: 2011-05-02 Last updated: 2011-09-27Bibliographically approved
2. 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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Eriksson, RobertBrodin, HåkanJohansson, Sten

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