Failure Mechanism of 7YSZ Splat as Thermal Barrier Coating

An investigation of spallation behaviors of plasma-sprayed ZrO2-7wt.%Y2O3 (7YSZ) splat at high temperature was carried out to understand the failure mechanism of thermal barrier coating (TBC). In present work, 7YSZ splats prepared by atmospheric plasma spray (APS) were collected on mirror polished NiCoCrAlYTa bond coating holding at 250 °C, where the nickel base superalloy K4169 was used as substrate. Then the samples with splats were taken into air furnace for isothermal oxidation test at 900 °C for different time. The surface of splat and cross section of splat-bond coating interface during isothermal test were characterized using a focused ion beam (FIB) assisted field emission scanning electron microscope (FE-SEM). Besides, the compositions of thermally grown oxide (TGO) layer at splat-bond coating interface were analyzed after oxidation test. In addition, the schematic diagram of spallation process and oxidation model of splat has been presented at relatively high temperature.