Effect of TGO thickness on isothermal cyclic lifetime of plasma-sprayed YSZ thermal barrier coatings

Isothermal thermal cycling test was performed on APS YSZ TBCs to examine the influence of TGO thickness on the thermal cyclic lifetime. The TBC system consisted of Inconel 738 substrate, cold-sprayed NiCoCrAlTaY bond coat (BC) and 8YSZ top coat. The TBCs with different thicknesses of TGOs were prepared through pre-oxidation. Results indicated that the lifetime of APS TBCs was significantly influenced by initial TGO thickness. As the TGO thickness increased from 1.3μm to 6.5μm, the lifetime of TBCs dropped from 124 cycles to 11 cycles. The TGO in all samples grew to a thickness of approximately 4.8 μm, for TBCs with the initial TGO less than 3.9μm. The crack propagation path leading to the spalling of YSZ transferred from YSZ lamellar interface within YSZ to a location passing through YSZ /bond coat interface with the increase of TGO thickness.