Effect of Initial TGO Thickness on the Thermal Cycling Lifetime of YSZ Coatings Under Gradient Thermal Cycling

Gradient thermal cycling test of thermal barrier coatings (TBCs) of different thicknesses of the initial thermally grown oxide (TGO) was performed to examine the influence of TGO thickness on the thermal shock lifetime. The TBC system consisted of cold-sprayed NiCoCrAlTaY bond coat and atmospheric plasma-sprayed YSZ. By controlling high temperature isothermal oxidation conditions, the TBCs with TGOs of five different thicknesses from 0.7±0.1 to 5.1±0.5μm were prepared for the test. The thermal cycling test with temperature gradient was performed at a peak surface temperature of 1150^oC and 150^oC difference across 250μm thick YSZ. The scanning electron microscopy (SEM) and x-ray diffraction analysis (XRD) were used to examine the surface morphology, cross sectional microstructure and phase structure of TBCs after thermal cyclic test. The results indicated that the lifetime of APS TBCs was significantly influenced by TGO thickness. The lifetime decreased by a factor of about 3 with the increase of initial TGO thickness from 0.7 to 5.1μm. The failure mechanisms of the TBCs under gradient thermal cycling test were examined and discussed.