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Thermal Barrier Coatings: Durability Assessment and Life Prediction
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
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: urn:nbn:se:liu:diva-96816ISBN: 978-91-7519-569-8 (print)OAI: oai:DiVA.org:liu-96816DiVA: diva2:643497
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
List of papers
1. Influence of isothermal and cyclic heat treatments on the adhesion of plasma sprayed thermal barrier coatings
Open this publication in new window or tab >>Influence of isothermal and cyclic heat treatments on the adhesion of plasma sprayed thermal barrier coatings
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2011 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no 23-24, 5422-5429 p.Article in journal (Refereed) Published
Abstract [en]

The adhesion of thermal barrier coatings (TBC) has been studied using the standard method described in ASTM C633, 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 substrate coupons of Ni-base alloy Hastelloy X. The bond coat (BC) is of a 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 at 1100 °C up to 290 h, 2) thermal cycling fatigue (TCF) at 1100 °C up to 300 cycles and 3) thermal shock at ~ 1140 °C BC/TC interface temperature up to 1150 cycles. The adhesion of the specimens is reported and accompanied by a microstructural study of the BC and the thermally grown oxides (TGO), as well as a discussion on the influence of BC/TC interfacial damage on adhesion properties of TBC. The adhesion was found to vary with heat treatment, as well as with heat treatment length.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Thermal barrier coating, TBC, adhesion, thermal cycling fatigue, thermal shock, burner rig test
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67882 (URN)10.1016/j.surfcoat.2011.06.007 (DOI)000294103700025 ()
Available from: 2011-05-02 Created: 2011-05-02 Last updated: 2017-12-11Bibliographically approved
2. Fractographic and microstructural study of isothermally and cyclically heat treated thermal barrier coatings
Open this publication in new window or tab >>Fractographic and microstructural study of isothermally and cyclically heat treated thermal barrier coatings
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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.

Keyword
Thermal barrier coating, TBC, fractography, adhesion, thermal cycling, burner rig
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67883 (URN)10.1016/j.surfcoat.2012.02.040 (DOI)000335542100014 ()
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
3. Influence of substrate material on the life of atmospheric plasmas prayed thermal barrier coatings
Open this publication in new window or tab >>Influence of substrate material on the life of atmospheric plasmas prayed thermal barrier coatings
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2013 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 232, no 15, 795-803 p.Article in journal (Refereed) Published
Abstract [en]

Thermal barrier coatings (TBCs) are used in gas turbines to prolong the life of the underlying substrates and to increase the efficiency of the turbines by enabling higher combustion temperatures. TBCs may fail during service due to thermal fatigue or through the formation of non-protective thermally grown oxides (TGOs). This study compares two atmospheric plasma sprayed (APS) TBC systems comprising of two identical TBCs deposited on two different substrates (Haynes 230 and Hastelloy X). The thermal fatigue life was found to differ between the two TBC systems. The interdiffusion of substrate elements into the coating was more pronounced in the TBC system with shorter life, however, very few of the substrate elements (only Mn and to some extent Fe) formed oxides in the bond coat/top coat interface. Fractography revealed no differences in the fracture behaviour of the TBCs; the fracture occurred, in both cases, to about 60% in the top coat close to the interface and the remainder in the interface. Nanoindentation revealed only small differences in mechanical properties between the TBC systems and a finite element crack growth analysis showed that such small differences did not cause any significant change in the crack driving force. The oxidation kinetics was found to be similar for both TBC systems for the formation of Al2O3 but differed for the kinetics of non-Al2O3 TGOs where the TBC system with shortest life had a faster formation of non-Al2O3 TGOs caused by a faster Al depletion. The difference in non-Al2O3 TGO growth kinetics was considered to be the main reason for the difference in life.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Thermal barrier coating; TBC; Substrate influence; Interdiffusion; Fatigue life; Oxidation kinetics
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-96810 (URN)10.1016/j.surfcoat.2013.06.101 (DOI)000327691300103 ()
Available from: 2013-08-27 Created: 2013-08-27 Last updated: 2017-12-06Bibliographically approved
4. TBC bond coat-top coat interface roughness: influence on fatigue life and modelling aspects
Open this publication in new window or tab >>TBC bond coat-top coat interface roughness: influence on fatigue life and modelling aspects
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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.

Keyword
thermal barrier coating, TBC, thermal cycling fatigue, interface, roughness, Ra
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-96811 (URN)10.1016/j.surfcoat.2013.09.051 (DOI)000329884300032 ()
Available from: 2013-08-27 Created: 2013-08-27 Last updated: 2017-12-06Bibliographically approved
5. Cyclic Hot Corrosion of Thermal Barrier Coatings and Overlay Coatings
Open this publication in new window or tab >>Cyclic Hot Corrosion of Thermal Barrier Coatings and Overlay Coatings
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2013 (English)In: Proceedings of ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, GT2013, The American Society of Mechanical Engineers (ASME) , 2013, Vol. 4, 1-8 p.Conference paper, Published paper (Refereed)
Abstract [en]

The influence, and interdependence, of water vapor and Na2SO4–50 mol% NaCl on the oxidation of a NiCoCrAlY coating and a thermal barrier coating (TBC) were studied at 750 °C. Water vapor was found to have a negligible effect on oxide composition, but influenced the oxide morphology on the NiCoCrAlY coating. Na2SO4–50 mol% NaCl deposits on the coatings influencedoxide composition, most notably by the promotion of a Y rich phase. The effect of Na2SO4–50 mol% NaCl deposits was also evident for the TBC coated specimen, where the formed metal/ceramic interface oxide was affected by salt reaching the interface by penetration of the zirconia TBC.

Place, publisher, year, edition, pages
The American Society of Mechanical Engineers (ASME), 2013
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-95556 (URN)10.1115/GT2013-95526 (DOI)000361499900009 ()978-0-7918-5518-8 (ISBN)
Conference
ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, GT2013, San Antonio, Texas, USA, June 3-7, 2013
Note

Paper No. GT2013-95526

Available from: 2013-07-08 Created: 2013-07-08 Last updated: 2016-05-13Bibliographically approved
6. Modeling of the microstructural evolution and lifetime prediction of MCrAlX coatings on Nickel based superalloys in high temperature oxidation
Open this publication in new window or tab >>Modeling of the microstructural evolution and lifetime prediction of MCrAlX coatings on Nickel based superalloys in high temperature oxidation
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2013 (English)In: Surface and Coatings Technology, Vol. 232, no 15, 204-215 p.Article in journal (Refereed) Published
Abstract [en]

At high temperature, MCrAlX coatings are deposited onto the surface of superalloy to provide oxidation and corrosion protection by forming a thermalgrowing oxide scale. In this project, the oxidation behavior of an HVOF CoNiCrAlYSi coating on IN792 was studied in both isothermal oxidation (900, 1000 and 1100 °C) and thermal cycling (1100-100 °C). The microstructural evolution in the MCrAlX coatings after oxidation was investigated. It was found that Al-rich β phase is gradually consumed due to two effects: surface oxidation and coating-substrate interdiffusion. Some voids and oxides along the coating-substrate interface, or inside the coating, were considered to play a role in blocking the diffusion of alloying elements. Based on the microstructural observation, an oxidation-diffusion model was developed by using Matlab and DICTRA software to predict the lifetime of MCrAlX coatings. Several effects influencing the microstructural evolution were included: surface oxidation, coating-substrate interdiffusion and diffusion blocking. The results showed good agreement between the experimental composition profiles and modeling ones. Furthermore, by choosing suitable diffusion blocking factors, the accuracy of coating life prediction could be improved.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
MCrAlX coating; HVOF; Life prediction; Interdiffusion; Oxidation; Diffusion blocking
National Category
Engineering and Technology Materials Engineering
Identifiers
urn:nbn:se:liu:diva-90013 (URN)10.1016/j.surfcoat.2013.05.008 (DOI)000327691300027 ()
Available from: 2013-03-14 Created: 2013-03-14 Last updated: 2014-10-08Bibliographically approved
7. Microstructure-based Life Prediction of Thermal Barrier Coatings
Open this publication in new window or tab >>Microstructure-based Life Prediction of Thermal Barrier Coatings
2014 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The widespread use of thermal barrier coatings (TBC) in gas turbines stresses the importance of accurate life prediction models for TBCs. During service, the TBC may fail due to thermal fatigue or through the formation of thermally grown oxides (TGOs). The current paper presents a Thermo-Calc/Dictra-based approach to life prediction of isothermally oxidised atmospheric plasma sprayed (APS) TBCs. The β-phase depletion of the coating was predicted and compared to life prediction criteria based on TGO thickness and Al content in the coating. All tried life models underestimated the life of the coating where the β-depletion-based model was the most conservative.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2014
Keyword
Thermal barrier coating, TBC, life prediction, isothermal oxidation, interdiffusion
National Category
Engineering and Technology Materials Engineering
Identifiers
urn:nbn:se:liu:diva-95554 (URN)10.4028/www.scientific.net/KEM.592-593.413 (DOI)000336694400091 ()
Conference
THERMEC,2-6 December, 2013, Las Vegas, USA
Available from: 2013-07-08 Created: 2013-07-08 Last updated: 2014-12-10Bibliographically approved

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