Degradation of the TBC system during the static oxidation test

This study was done on the IN-738 type alloy with thermal barrier coatings. On the basic surface of the NiCoCrAlY superalloy, VPS-sprayed powder was applied as the bond-coat. In addition, ZrO2 x 8%Y2O3 powder was used for a deposition outside the top surface of a ceramic layer by the APS method. Appropriate control of the spraying process parameters permitted to obtain a gradient of porosity on the thickness of the ceramic coating. Then a static oxidation test at 1100 degrees C and for 1100 h was performed. The basic conclusions of that testing showed that main degradation modes of the gradient thermal barrier coating system were connected with formation of porous NiAl2O4 oxides in the thermally grown oxide area and, consequently, formation of micro-cracks, delamination of a ceramic layer and final spallation of a ceramic top-coat.