Interface Oxidation Process of ZrO2-8%Y2O3 / CoNiCrAlY Thermal Barrier Coating System

Thermal barrier coating (TBC) of a gas turbine blade suffers from high temperature oxidation. It is known that thermally growth oxidation (TGO) grows at the interface between ZrO2- 8%Y2O3 and CoNiCrAlY, and the TGO degrades the adhesive strength. The purpose of this study is to clarify the TGO growth process. Thermal aging tests of ZrO2-8%Y2O3 / CoNiCrAlY TBC systems under various temperature conditions were carried out. TGO growth process was observed by an electron probe micro analyzer (EPMA). Both TGO of Al and TGO of other elements were examined, and the thickness of the TGOs were examined. Results are summarized as follows. (1) The delamination occurred at a ZrO2-8%Y2O3 layer beside the interface. (2) The growth rate of complicated TGO which consisted of Co, Ni and Cr increased with an increase of temperature. However, the complicated TGO wasn’t related with the delamination life. (3) The delamination could occur if the thickness of Al TGO increased more than about 3 μm.

Characterization of Dielectric Properties of Alkoxy-Derived (Y,Yb)MnO3 Ferroelectrics/Insulator Stacking Layers

The (Y,Yb)MnO3 films were crystallized on Y2O3 layers using alkoxy-derived precursor solutions. As a result of investigation of the effect of the Y2O3 layer on the dielectric properties of the (Y,Yb)MnO3/Y2O3/Si, the crystallographic properties such as the orientation and surface morphology of the (Y,Yb)MnO3 thin films depended on the crystallographic appearance of the insulator layer. Following that, the dielectric properties of the MFIS structures varied. For the construction of excellent MFIS structure, the improvement of the orientation, crystallinity, and surface smoothness of the (Y,Yb)MnO3 film by the optimization of the microstructure and dielectric property of the insulator is necessary.

Solar Processing for the Glazing of ZrO2-Y2O3 Thermal Barrier Coatings: Reduction of Crack Initiation

The glazing of thermal barrier coatings using concentrated solar energy has already been demonstrated, but crack initiation appeared as a major drawback of this processing. In this paper, the thermo-mechanical effects resulting from the fast heating at high temperature were modeled. Crack initiation was found to result from high temperature gradients in the ceramic coating. Experiments performed on plasma-sprayed ZrO2-Y2O3 layer showed that a significant reduction of crack initiation was achieved when the specimen was preheated at temperatures in the range 500°C-800°C. The potential of the solar processing was improved and this technique becomes competitive with conventional laser processes.