This paper investigates the effect of the thickness of the thermally grown oxide (TGO) layer on the isothermal cyclic lifetime of plasma-sprayed yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). The TBCs were prepared with different initial TGO thicknesses through pre-oxidation. The results showed that the lifetime of the TBCs decreased significantly as the TGO thickness increased. There was a critical TGO thickness of 5 μm, beyond which the TBCs failed rapidly. The failure mode of the TBCs also changed with the TGO thickness, with cracking primarily occurring along the YSZ lamellae interfaces for TGO thicknesses below the critical thickness, and through the TGO or the interface between the TGO and YSZ coating for TGO thicknesses above the critical thickness.

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