Influence of vertical cracks on failure mechanism of EB-PVD thermal barrier coatings during thermal cycling

The influence of surface vertical cracks in YSZ coating on the failure mechanism of thermal barrier coatings prepared by electron beam physical vapor deposition (EB-PVD) during thermal cycling was studied. The vertical cracks occurred at the initial stage of thermal cycling testing but did not directly cause the spallation of TBC. The mesh density of vertical cracks increased following thermal cycles. Calculation by finite elements analysis showed that a larger shear stress was generated by the formation of the vertical cracks just like what in the edge of the specimen. After thermal cycling testing, when the strength of equiaxial grain regions or thermally grown oxidation layer became lower than the shear stress, the spallation occurred along the vertical crack network.