Mechanism of vertical crack formation in Yb2SiO5 coatings deposited via plasma spray-physical vapor deposition

Plasma spray-physical vapor deposition (i.e., PS-PVD) is a promising method for obtaining advanced environmental barrier coatings (EBCs). The EBCs must meet some requirements in the application, in which the thermal cycle performance affects the service lifetime. The preparation of artificial vertical cracks in Yb2SiO5 coatings is an effective approach for meeting the requirements above because vertical cracks provide a strain tolerance. To clarify the formation mechanism of vertical cracks during the PS-PVD, the effects of coating thickness and substrate temperature on the formation of vertical cracks were investigated. In addition, the interactions of spray powder and plasma flame during coating deposition were also characterized by optical spectroscopy. It is indicated that vertical cracks are formed due to a thermal expansion mismatch between Yb2SiO5 and mullite coating, transient cooling after deposition and the nucleation of evaporated Yb2SiO5 as well. Keywords: Environmental barrier coatings, Yb2SiO5 coating, Vertical crack, PS-PVD