A Study of Failure Development in Thick Thermal Barrier Coatings Karin Carlsson LITH-IEI-TEK--07/00236--SE Examensarbete Institutionen för ekonomisk och industriell utveckling
Examensarbete LITH-IEI-TEK--07/00236--SE A Study of Failure Development in Thick Thermal Barrier Coatings Karin Carlsson Handledare: Examinator: Håkan Brodin SIEMENS Industrial Turbomachinery AB Sten Johansson IEI, Linköping University Linköping, 6 December, 2007
Avdelning, Institution Division, Department Division of Engineering Materials Department of Management and Engineering Linköpings universitet SE-581 83 Linköping, Sweden Datum Date 2007-12-06 Språk Language Svenska/Swedish Engelska/English Rapporttyp Report category Licentiatavhandling Examensarbete C-uppsats D-uppsats Övrig rapport ISBN ISRN LITH-IEI-TEK--07/00236--SE Serietitel och serienummer Title of series, numbering ISSN URL för elektronisk version http://www.ikp.liu.se/kmt/ http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-10397 Titel Title A Study of Failure Development in Thick Thermal Barrier Coatings Studie av skadeutvecklingen hos tjockt termiskt barriärskikt Författare Author Karin Carlsson Sammanfattning Abstract Thermal barrier coatings (TBC) are used for reduction of component temperatures in gas turbines. The service temperature for turbines can be as high as 1100 o C and the components are exposed to thermal cycling and gases that will cause the component to oxidize and corrode. The coatings are designed to protect the substrate material from this, but eventually it will lead to failure of the TBC. It is important to have knowledge about when this failure is expected, since it is detrimental for the gas turbine. The scope of this thesis has been to see if an existing life model for thin TBC also is valid for thick TBC. In order to do so, a thermal cycling fatigue test, a tensile test and finite element calculation have been performed. The thermal cycling fatigue test and finite element calculation were done to find correlations between the damage due to thermal cycling, the number of thermal cycles and the energy release rate. The tensile test was preformed to find the amount accumulated strain until damage. The thermal cycling lead to failure of the TBC at the bond coat/top coat interface. The measurment of damage, porosity and thickness of thermally grown oxide were unsatisfying due to problems with the specimen preparation. However, a tendency for the damage development were seen. The finite element calculations gave values for the energy release rate the stress intensity factors in mode I and mode II that can be used in the life model. The tensile test showed that the failure mechanism is dependent of the coating thickness and it gave a rough value of the maximum strain acceptable. Nyckelord Keywords Thick Thermal Barrier Coatings, Thermal Cycling Fatigue, Tenile Test with Acoustic Emission, Failure Development
Abstract Thermal barrier coatings (TBC) are used for reduction of component temperatures in gas turbines. The service temperature for turbines can be as high as 1100 o C and the components are exposed to thermal cycling and gases that will cause the component to oxidize and corrode. The coatings are designed to protect the substrate material from this, but eventually it will lead to failure of the TBC. It is important to have knowledge about when this failure is expected, since it is detrimental for the gas turbine. The scope of this thesis has been to see if an existing life model for thin TBC also is valid for thick TBC. In order to do so, a thermal cycling fatigue test, a tensile test and finite element calculation have been performed. The thermal cycling fatigue test and finite element calculation were done to find correlations between the damage due to thermal cycling, the number of thermal cycles and the energy release rate. The tensile test was preformed to find the amount accumulated strain until damage. The thermal cycling lead to failure of the TBC at the bond coat/top coat interface. The measurment of damage, porosity and thickness of thermally grown oxide were unsatisfying due to problems with the specimen preparation. However, a tendency for the damage development were seen. The finite element calculations gave values for the energy release rate the stress intensity factors in mode I and mode II that can be used in the life model. The tensile test showed that the failure mechanism is dependent of the coating thickness and it gave a rough value of the maximum strain acceptable. v
A.3 Tensile Test with Acoustic Emission 53 Figure A.15. 1500 µm test 1. Figure A.16. 1500 µm test 2.
54 A.4 Appendix Chemical Analyses Figure A.17, A.18, A.19, A.20, A.21 and A.22 are line scans. Figure A.23 and A.24 are mappings. Figure A.17. K0. Analysis started in the top coat. Figure A.18. The result from the line scan. Spectrum (x) represent the point where the measurement was done.
A.4 Chemical Analyses 55 Figure A.19. K300. Analysis started at the top of the bond coat. Figure A.20. The result from the line scan. Spectrum (x) represent the point where the measurement was done.
56 Appendix Figure A.21. K450. Analysis started at the top of the bond coat. Figure A.22. The result from the line scan. Spectrum (x) represent the point where the measurement was done.
A.4 Chemical Analyses 57 Figure A.23. A internal bond coat oxide from K450. Figure A.24. The results from the line scan. The different graphs represent different materials oxygen, silicon, chromium, cobalt, nickel, yttrium and aluminum.
58 Appendix
Upphovsrätt Detta dokument hålls tillgängligt på Internet eller dess framtida ersättare under 25 år från publiceringsdatum under förutsättning att inga extraordinära omständigheter uppstår. Tillgång till dokumentet innebär tillstånd för var och en att läsa, ladda ner, skriva ut enstaka kopior för enskilt bruk och att använda det oförändrat för ickekommersiell forskning och för undervisning. Överföring av upphovsrätten vid en senare tidpunkt kan inte upphäva detta tillstånd. All annan användning av dokumentet kräver upphovsmannens medgivande. För att garantera äktheten, säkerheten och tillgängligheten finns det lösningar av teknisk och administrativ art. Upphovsmannens ideella rätt innefattar rätt att bli nämnd som upphovsman i den omfattning som god sed kräver vid användning av dokumentet på ovan beskrivna sätt samt skydd mot att dokumentet ändras eller presenteras i sådan form eller i sådant sammanhang som är kränkande för upphovsmannens litterära eller konstnärliga anseende eller egenart. För ytterligare information om Linköping University Electronic Press se förlagets hemsida http://www.ep.liu.se/ Copyright The publishers will keep this document online on the Internet or its possible replacement for a period of 25 years from the date of publication barring exceptional circumstances. The online availability of the document implies a permanent permission for anyone to read, to download, to print out single copies for his/her own use and to use it unchanged for any non-commercial research and educational purpose. Subsequent transfers of copyright cannot revoke this permission. All other uses of the document are conditional on the consent of the copyright owner. The publisher has taken technical and administrative measures to assure authenticity, security and accessibility. According to intellectual property law the author has the right to be mentioned when his/her work is accessed as described above and to be protected against infringement. For additional information about the Linköping University Electronic Press and its procedures for publication and for assurance of document integrity, please refer to its www home page: http://www.ep.liu.se/ c Karin Carlsson