Thermal Cyclic Life of Functionally-Graded Gadolinium Zirconate/Yitria Stabilized Zirconia Thermal Barrier Coating

In this study, two types of thermal barrier coatings (TBC); duplex and functionally-graded coatings were deposited on superalloy Nimonic 263 substrates using air plasma spray process. The duplex coating consists of YSZ top coat and NiCrAlY bond coat. The functionally-graded coating consists of five layers with variable ratios of GZ/YSZ and YSZ/NiCrAlY whereby the composition gradually changes along the coating thickness. The TBC samples were subjected to isothermal heat treatment at 1100 °C for 100 hours before undergoing thermal cyclic tests at 1200 °C up to 20% spallation to evaluate the oxidation and thermal fatigue resistance of the coatings. Results indicate that the functionally-graded GZ TBC has a better cyclic life than the duplex YSZ TBC after isothermal heat treatment. The isothermal heat treatment also improved the thermal cyclic lifetime of the functionally-graded GZ TBC by more than threefold in comparison to the as-sprayed GZ TBC.