Thermal cycling behavior of Srx(Zr0.9Y0.05Yb0.05)O1.95+x thermal barrier coatings by suspension plasma spraying

Abstract

The thermal barrier coatings (TBCs) consisting of Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x were prepared using the suspension plasma spraying (SPS) method. Precursor suspensions were prepared via co-precipitation for this purpose. Detailed microstructural, phase composition, and phase content analyses were conducted on these coatings, designated as SZYY-1 (x = 1.0), SZYY-2 (x = 0.9), and SZYY-3 (x = 0.8). Additionally, the coatings underwent a thermal cycling test at 1121°C for 1 h. To assess the morphology of thermally grown oxide (TGO) in a real coating, a finite element model was employed. SPS-SZYY-2 with columnar crystal structure was found to have the highest number of thermal cycling, up to 345 times. The thermophysical high-temperature properties of the coating can be effectively improved through suitable second-phase content. Microstructural and finite element analyses revealed that stress, primarily caused by the continuous growth of the Co₃O₄, NiO and Spinel (CNS) layer within TGO, was the predominant factor leading to coating failure. At elevated temperatures, transverse cracks formed at the interface between the bond coating and ceramic top coating due to mismatched thermal expansion and sintering effects, ultimately leading to coating degradation. Therefore, reducing the generation rate of large stresses in the coating, especially shear stresses, can effectively prevent the generation and propagation of transverse cracks and increase the thermal cycling life of TBCs.