Abstract
The integrity of thermal barrier coatings (TBCs) plays an important role in the performance of turbine blades, nevertheless the effect of cooling hole on fracture of TBCs have been less studied. The present work aimed to study the stress evolution and fracture behavior of TBCs with cooling hole under cyclic thermal loadings. Cyclic thermal tests were conducted and the cracking behavior of TBCs around cooling hole was examined using scanning electron microscope (SEM). TBCs exhibited two types of cracks near the hole edge, i.e. surface crack in the top coat and interfacial crack, which could lead to local TBC spallation and shorten the TBC lifetime. To disclose the fracture mechanism, finite element (FE) analysis was also performed. The computed residual stress values were consistent with those measured by Raman spectroscopy tests. FE simulations indicated that the free-edge effect facilitated interfacial peeling and shear stresses near the cooling hole, and hence promoted the initiation of interfacial crack in TBCs. With the increase of thermal loading cycles, the interfacial crack propagated and then coalesced with the surface cracks in the top coat, leading to the final spallation of TBCs at the cooling hole.
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