Nano-Characterization of Ceramic Top-Coat/Metallic Bond-Coat Interface for Thermal Barrier Coating Systems by Plasma Spraying

Abstract

Characterization at the ceramic top-coat/metallic bond-coat interfacial region was conducted for several kinds of the plasma sprayed thermal barrier coating (TBC) systems by means of a transmission electron microscope (TEM), an electron probe micro-analysis (EPMA) and so forth, in order to find out the optimum compositional and structural conditions of the coating components together with the optimum coating processing condition for designing the advanced TBC systems. Specimens with different coating features were prepared systematically by using different coating parameters such as the top-coat spraying conditions and reheat-treatment conditions. Especially, the reheat-treatment was applied to the TBC specimen with different temperature either in air or in inert argon (Ar) gas atmosphere. It was found that in the case of reheattreatment in air the thermally grown oxide (TGO) was developed at the interface as multiple oxide layers; one is Al 2 O 3 layer developed discontinuously at directly above the bond-coat and another is the mixed oxides layer consisting of the Al, Cr, Co, Ni oxide particles on the Al 2 O 3 layer. Such a TGO layer was heterogeneous and imperfect layer with containing many kinds of defects. On the contrary, the TGO layer formed by the reheat-treatment in Ar was composed dominantly of the continuous and fairly purified Al 2 O 3 layer with large grain size and homogeneous layer thickness. The growth mechanism and influencing factors for TGO were discussed in some detail on the basis of the nanocharacterization and quantitative evaluation of TGO.

In Situ Observation of Failure Behavior for Plasma Sprayed Thermal Barrier Coating Systems under Static Loadings

“…For the specimen oxidized at 1100ºC, for instance, the TGO layer developed at the TC / BC interface was composed of the multiple oxide layers; one is high-purity Al 2 O 3 layer directly above the BC and another is the mixed oxide layer consisting mainly of Al, Cr, Co and Ni over the Al 2 O 3 layer. In addition, the wart-like oxide was also developed [6]. For the specimen oxidized at 1000ºC, on the contrary, the thickness of TGO layer was much thinner than that of the specimen oxidized at 1100ºC and there were only a few wart-like oxides.…”

Mechanism of Vertical Microcracking in CaO&middot;SiO<SUB>2</SUB>-CaO&middot;ZrO<SUB>2</SUB> Sprayed Thermal Barrier Top Coating

“…1) ZrO 2 -base sprayed coatings can effectively protect the base metal of hot section component of gas turbines exposed to high temperatures though comparatively thin; consequently it is commonly used as the thermal barrier coating (TBC). 2,3) Conventional ZrO 2 -Y 2 O 3 coatings, however, do not have sufficient thermal shock resistance and it is still necessary to improve the quality of ZrO 2 -base ceramic coatings.…”

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

“…[3][4][5][6][7] Thus, suppressing masstransfer through the -Al 2 O 3 scale is anticipated to further improve the durability of TBCs.…”