Abstract
The high temperature oxidation behavior of Inc-738/NiCrAlY/LaMgAl11O19 (LaMA) thermal barrier coating system was studied and compared with Inc-738/NiCrAlY/8YSZ coating system. The morphology of coatings, formation of TGO layer and degradation of coatings during oxidation process were investigated. The results indicated that the thermal cycling lifetime of LaMA coating was more than 8YSZ coating. The morphological evaluation of LaMA coating revealed that the recrystallization of amorphous phase was occurred. The 8YSZ ceramic top coat was sintered and microstructure was generated from columnar to equiaxed structure during thermal cycling process. Following the formation of a continuous alumina layer, undesirable oxides created at the TGO/bond coat (BC) interface in the LaMA coating system, whereas, unwanted oxides created at the TGO/top coat (TC) interface in the 8YSZ coating system and also it is believed that the oxidation of coating systems in steady-state stage was occurred under the diffusion-chemical mechanism and chemical mechanism, respectively. Therefore, the different failure mechanisms were observed in both coating systems. In the 8YSZ coating, the cracks nucleated at the TGO/TC interface, while in the LaMA coating, the cracks nucleation were occurred in TGO layer.
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