Mathematical Analysis of Microstructural Characterizations for Thermally Grown Oxide Layers in Thermal Barrier Coatings

The thermomechanical properties of thermal barrier coatings (TBCs) such as elastic modulus, thermal conductivity, and coefficient of thermal expansions are determined by pores, cracks, and splat boundaries, which affect the thermoelastic properties of thermally grown oxide (TGO) layer and the fracture behavior in TBCs. The thermoelastic characteristics thus have been investigated through mathematical analysis, as functions of microstructure and TGO layer. TriplexProTM-200 system was applied to prepare TBC samples using different commercialized powders. The surface of each TBC was reheated by a plasma flame without powder feeding in a certain condition with same equipment, and then cooled rapidly to create vertical type cracks on the top coat. The microstructural characterizations for TGO layers in the relatively porous and dense TBCs with the vertical cracks were analyzed through mathematical approaches. According to the thermoelastic theory a couple of governing partial differential equations was derived, and a finite volume method was developed to evaluate the thermoelastic characteristics like temperature distribution profiles, displacement, and stresses, induced by a thermal fatigue for the governing equa4522 Jaegwi Go and Je-Hyun Lee tions. It demonstrates that the microstructure of the top coat and the thickness of the TGO layer were crucial factors to the thermoelastic behaviors.