Microstructure Evolution and Interface Stability of Thermal Barrier Coatings with Vertical Type Cracks in Cyclic Thermal Exposure

In this study, the effects of intrinsic feature of microstructure in thermal barrier coatings (TBCs) with and without vertical cracks on the microstructure and mechanical properties were investigated in cyclic thermal exposure. The hardness values of TBCs with vertical cracks were higher than those without vertical cracks, showing a good agreement with microstructure. The TBC prepared without vertical cracks using the 204-NS was delaminated after 250 cycles in the cyclic thermal exposure test. The TBCs with and without vertical cracks prepared with 204 C-NS and the TBC with vertical cracks prepared with 204 NS showed a sound condition without any cracking at the interface or spalling of top coat. After the thermal exposure of 381 cycles, the hardness values were increased in the survived TBC specimens, and the thicknesses of TGO layer for the TBCs with 204 C-NS and 204 NS were measured as in the ranges of 5-9 and 3-7 mu m, respectively. In the thermal shock test, the advantage of vertical cracks for thermal durability of TBC could be well investigated, showing relatively longer sustained cycles in the TBCs with vertical cracks. The TBCs with vertical cracks are more efficient in improving thermal durability than those without vertical cracks in cyclic thermal exposure.