A Study of Failure Development in Thick Thermal Barrier Coatings
Independent thesis Advanced level (degree of Magister), 20 points / 30 hpStudent thesis
Thermal barrier coatings (TBC) are used for reduction of component temperatures in gas turbines. The service temperature for turbines can be as high as 1100ºC 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.
Place, publisher, year, edition, pages
Institutionen för ekonomisk och industriell utveckling , 2007. , 71 p.
Thick Thermal Barrier Coatings, Thermal Cycling Fatigue, Tensile Test with Acoustic Emission, Failure Development
Other Materials Engineering
IdentifiersURN: urn:nbn:se:liu:diva-10397ISRN: LITH-IEI-TEK-A--07/00236--SEOAI: oai:DiVA.org:liu-10397DiVA: diva2:17147
2007-11-23, IKP3, A-huset, Linköpings universitet, Linköping, 15:15