Failure mechanism of one side coated thermal barrier coating

Two layered structure thermal barrier coatings were prepared by electron beam physical vapor deposition. The changes on microstructure and the failure mode of the specimen during thermal cyclic oxidation were analyzed by scanning electron microscopy (SEM) and impedance spectroscopy (IS). It is shown that the spallation of one side coated TBCs occurred mainly in YSZ top coat, instead of in thermally grown oxide (TGO) layer as often observed in double sides coated TBCs. Stress analysis indicates that during thermal cycling, double sides coated TBCs are mainly subjected to the thermal mismatched shear stress parallel to the sample surface, but one side coated TBCs are subjected not only to the shear stress, but also to the stress along the normal direction, and finally crack inside the YSZ. IS method can characterize the initiation and expansion of the transversal crack in the TBCs.