Study on the Tensile and the Fatigue Behavior of Air Plasma Sprayed YSZ TBC Systems

Thermal barrier coating (TBC) system composing of bond coat, having two different metallic bond coating materials such as NiCoCrAlY and CoNiCrAlY, and top coat, 8YSZ (8 wt%Y2O3-ZrO2) ceramic coating was deposited on aluminum-based alloy by atmoshpheric plasma spray (APS). Fatigue test and tensile test both was performed for TBC sample. The tensile test and fatigue, both results showed that that fracture occurred in 8YSZ coating near the interface of ceramic-bond coating. These lead to the formation of weak inter-bonding strength and the failure of APS 8YSZ TBC. Moreover, in order to better understand the failure process, a deposition mechanism of coating was proposed. Experimental observations of the failed specimens subjected to tensile as well as fatigue loading showed that the coating cracking and spallation processes were different. Tensile results highlighted the different fracture mode and crack propagation up to macroscopic failure.