Failure mechanisms of thermal barrier coatings for high temperature gas turbine components under cyclic thermal loading

The mechanical behavior of PYSZ TBCs, deposited by EB-PVD and APS techniques, has been studied under thermal cyclic and isothermal loading. Two types of bond coats were chosen for the different multilayer systems: a single phase (Ni,Pt)-aluminide and a NiCoCrAlY overlay layer in the case of the EB-PVD and APS TBC respectively. The degradation of APS TBCs, i.e. crack evolution and oxidation kinetics during isothermal and thermal cyclic loading were systematically monitored and analyzed by means of scanning electron microscopy. Finally the life time results were summarized and compared with similar experiments previously described in literature. It was found out that isothermal and cyclic oxidation result similar damage mechanisms and oxide growth kinetics. In addition, isothermal oxidation of APS TBCs resulted in significant Al-depletion of the two-phase (gamma+betta) NiCoCrAlY bond coat, which finally led to a completely betta-depleted microstructure. The influence of maximum temperature and specimen geometry, i.e. substrate curvature radius on the life time of EB-PVD TBCs has been investigated. As expected, higher maximum temperatures resulted in shorter life times of the multilayer system. Additionally, cylindrical specimens with smaller outer diameter revealed the fastest failure. The experimental results were described using an analytical approach, based on the principles of linear elastic fracture mechanics. In contrast to conventional microscopic damage analysis of APS TBCs, two non-destructive methods were applied for investigation of EB-PVD TBCs: - Grey scale analysis for the evaluation of thermal strains at the surface of EB-PVD TBC during cooling phase of the cyclic oxidation. - Infrared thermography for quantitative description of the delamination crack kinetics, especially environmentally assisted subcritical crack growth phenomena at RT in dry air and H2O. Curvature measurements at initially flat test pieces have been carried out for the evaluation of residual stresses. The curvature change as a function of temperature was measured by means of a high temperature telescope system and an optical fleximeter respectively. From these results, the thermoelastic behavior of the EB-PVD TBC system as well as the residual stress distribution were calculated, basing on the main principles of elastic bending theory. Experimental results show a fairly good agreement with modeled curvature in the elastic regime.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2008

Author dc:creator

• Postolenko, Vitalii

Contributors dc:contributor

• Schneider, Jochen M.

• info:eu-repo/classification/ddc/620
• Lebensdauer
• Versagen
• Rissausbreitung
• Elastische Spannung
• Ingenieurwissenschaften
• Wärmedämmschichten
• Versagensmechanismen
• Eigenspannung
• Spannung
• Thermal Barrier Coatings
• failure mechanisms
• residual stress

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113165%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A50629