| Summary: | In this study, interfacial crack propagation behavior of Thermal Barrier Coatings (TBC) and Porous-TBC, which is named as P-TBC, was examined under a high-temperature fatigue loading in order to establish the basis of the method predicting precisely TBC delamination life. Yttria-stabilized zirconia for TBC and the mixed powder of yttria-stabilized zirconia and polyester for P-TBC as the top-coats were deposited by atmospheric plasma spray. For introducing the initial micro crack in TBC and P-TBC specimen, a tensile loading was given in advance of fatigue test. In-situ high-temperature fatigue tests were conducted at room temperature and 1073K, and the crack length was measured during the fatigue loading. It was found that the crack propagated along the interface between bond coat and substrate in TBC and P-TBC samples tested under room temperature. On the other hand, the crack propagated along the top coat/bond coat and bond coat/substrate interfaces in TBC samples, and it propagated along the bond coat/substrate interface in P-TBC samples tested under the test temperature condition 1073K. Quantitative discussion revealed that the interfacial crack propagation rate increased and decreased with apparent fatigue J integral which was proposed in this study. It was considered that this propagation behavior was caused by the coalescence of main crack and secondary crack existing ahead of the main crack and subsequent steady growth along the interface. Finally, Paris's law including apparent fatigue J integral was applied to those fatigue data. As a result, it was found that the data of crack propagation rate could be divided into steady state and acceleration state.
|
|---|