Thermal cycling behaviors of different plasma-sprayed zirconate thermal/environmental barrier coating systems in water vapor atmospheres

As the demand for higher operating temperatures in gas turbine engines, low thermal conductivity thermal/environmental barrier coatings (T/EBCs) systems are urgently needed to protect the structural components of silicon carbide ceramic matrix composites (SiC CMCs). In this paper, several T/EBCs systems with zirconate as the top layer were prepared by air plasma spraying (APS) on environmental barrier coatings (EBCs) systems, and thermal cycling tests were carried out at 1400 °C in a 90 % H₂O-balanced O₂ water vapor atmosphere. When there were no transition layers, the zirconate top layer produced many horizontal and vertical cracks under severe thermal mismatch stress. When the transition layers existed, the thermal mismatch stress was obviously relieved and the horizontal cracks basically disappeared. The morphology of the vertical cracks in the zirconate top layer varied with the different transition layers, and no obvious cracks were found in both the Yb₂Si₂O₇ or mullite transition layers, indicating that they are highly resistant to crack extension. For the bonding layer, the addition of HfO₂ particles into the Si layer significantly suppressed crack propagation. These findings may contribute to laying the foundation for the material and structural design of transition layers in long-life T/EBCs systems.