Effect of grit blasting on the thermal cycling behavior of diffusion aluminide/YSZ TBCs

• TBCs including of CVD NiAl bond coat and EB-PVD YSZ ceramic coating with and without grit blasting process.
• Grain boundary ridges are the sites for spallation damage initiation in aluminide/YSZ TBCs.
• Ridges are removed, and no cavity formation and this damage initiation mode are suppressed.
• Damage initiation and progression occurs at the bond coat to TGO interface leading to a buckling failure behavior.

Thermal barrier coating system (TBCs) including of chemical vapor deposited NiAl bond coat and electron beam physical vapor deposited Y2O3–stabilized-ZrO2 (YSZ) ceramic coating with and without grit blasting process were investigated. The phase structures, surface and cross-sectional morphologies, cyclic oxidation behaviors of these coatings were studied in detail. Grain boundary ridges form on the surface of aluminide bond coat prior to the deposition of the ceramic coating by EB-PVD, which are shown to be the sites for spallation damage initiation in aluminide/YSZ TBCs. When these ridges are removed, there is no cavity formation and this damage initiation mode is suppressed. Damage initiation and progression occurs at the bond coat to TGO interface leading to a buckling failure behavior. A buckle failure once started may be arrested when it runs into a region of high bond coat to TGO interface toughness. Thus, complete failure requires further loss in toughness of the bond coat to TGO interface with additional cycling. From the result of thermal cycling, an averaged four folds lifetime improvement can be achieved with samples after grit blasting of bond coat surface as compared with those samples existence in ridges on the bond coats’ surface.