ISOTHERMAL OXIDATION OF PHYSICAL VAPOR-DEPOSITED PARTIALLY-STABILIZEDZIRCONIA THERMAL BARRIER COATINGS

Thermal barrier coatings (TBCs), consisting of physical vapor deposite d (PVD) partially stabilized zirconia (PSZ, 8 Wt.%Y2O3) and a diffusio n 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 sca nning electron microscopy (SEM) with energy-dispersive spectroscopy. D uring cooling to room temperature, spallation of the PSZ ceramic coati ngs occurred after 200 and 350 h of isothermal heat treatment. This fa ilure was always sudden and violent, with the TBC popping from the sub strate. The monoclinic phase of zirconia was first observed on the bot tom surface of the PVD PSZ after 200 h of isothermal heat treatment. T he failure of TBCs occurred either in the bond coat oxidation products of alphaAl2O3 and rutile TiO2 Or at the interface between the oxidati on products and the diffusion aluminide bond coat or the PSZ coating.