In situ synthesis of α-alumina layer at top yttrium-stabilized zirconia thermal barrier coatings for oxygen barrier

The thermally grown oxide (TGO) at the interface of a ceramic-bond coating plays an important role in the failure of the thermal barrier coating (TBC). Therefore, it is important to control the growth of TGO to improve its service lifetime. In this paper an aluminum film was first deposited on the surface of atmospheric plasma sprayed TBC by direct current circular magnetron sputtering. Then the TBC samples with the aluminum film received a vacuum heat treatment. In situ synthesis of α-Al2O3 layer was observed at the top of the ceramic coating through the reaction of Al and ZrO2. The schematic diagram and thermodynamic mechanism of in situ synthesis of α-Al2O3 layer were presented. The cross sections of as-sprayed and treated TBCs were characterized by field emission-scanning electron microscopy (FE-SEM). Both phase structures were analyzed by X-ray diffraction (XRD) and transmission electron microscope (TEM) assisted with energy dispersive spectroscopy (EDS) and focused ion beam (FIB). Finally, oxidation resistance was compared between as-sprayed TBCs and vacuum treated TBCs and the average thickness of TGO was 4.89±0.53 and 2.52±0.47 μm correspondingly.