Thickness-related failure behaviors of the thermal barrier coatings under thermal gradient cycling

Abstract

The ZrO2–7 wt% Y2O3 (7YSZ) is the most commonly used ceramic layer in the thermal barrier coating (TBC) system due to its low thermal conductivity. However, the thermal stress-induced coating failure would damage its performance and limit its application. In the present study, a burner rig is employed to attain the operating temperature field and conduct the thermal gradient cycling tests of the coating. Moreover, the failure modes of the YSZ coating with different thicknesses (100, 200, and 400 μm) are investigated. The results show that the coating with 200 μm thickness has the most extended cyclic lifetime (>340 cycles), while 100 μm and 400 μm thick coatings have cyclic lifetimes of 240 and 80 cycles, respectively. The coating microstructure evolution, thermal growth oxides (TGO) thickness, and coating sintering behaviors are considered to explain the phenomenon. Furthermore, a TGO growth/sintering competitive failure model is proposed to describe the failure behaviors and elucidate the failure mechanisms of the coating with different thicknesses. The coatings with different thicknesses have different temperature distributions in the same external conditions. It results in different TGO growth rates and different degrees of coating sintering. The balance of TGO growth and coating sintering makes the 200 μm thick coating the most extended cyclic lifetime.