ISOTHERMAL OXIDATION OF PHYSICAL VAPOR-DEPOSITED PARTIALLY-STABILIZED ZIRCONIA THERMAL BARRIER COATINGS

Thermal barrier coatings (TBCs), consisting of physical vapor deposited (PVD) partially stabilized zirconia (PSZ, 8 Wt.%Y2O3) and a diffusion aluminide bond coat, were characterized as a function of time after oxidative isothermal heat treatment at 1373 K in air. The experimental characterizations was conducted by X-ray diffraction analysis and scanning electron microscopy (SEM) with energy-dispersive spectroscopy. During cooling to room temperature, spallation of the PSZ ceramic coatings occurred after 200 and 350 h of isothermal heat treatment. This failure was always sudden and violent, with the TBC popping from the substrate. The monoclinic phase of zirconia was first observed on the bottom surface of the PVD PSZ after 200 h of isothermal heat treatment. The failure of TBCs occurred either in the bond coat oxidation products of alphaAl2O3 and rutile TiO2 Or at the interface between the oxidation products and the diffusion aluminide bond coat or the PSZ coating.