Failure Mechanism of Thermal Barrier Coatings on Nozzle Guide Vanes Fabricated from Nickel-Based Single-Crystal Superalloy under Gas Thermal Shock Conditions

The objective of this study was to investigate the early failure behavior of thermal barrier coatings on single-crystal nozzle guide vanes under gas thermal shock conditions. The microstructure and mechanical properties of the thermal barrier coating before and after the gas thermal shock tests were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and microhardness testing. The results indicate the presence of a mixed layer containing Ni, Cr, Al, Zr, and O at the base of the ceramic layer, and reveal failure behavior in the thermal barrier coating. The analysis suggests that the incomplete formation of the thermal growth oxide layer between the ceramic layer and the bonding layer, before the deposition of the YSZ ceramic layer, led to the easy diffusion of elements from the bonding layer into the root of the ceramic layer during the gas thermal shock process, resulting in the formation of a mixed layer. In the test environment, significant thermal stress was generated in the mixed layer, leading to transverse cracks and ultimately causing early failure of the thermal barrier coating. Consequently, the "incomplete initial TGO layer" model is proposed.