Microstructure Influence on the Functional Properties of Gd2Zr2O7/YSZ TBC Systems

Higher operating temperature in modern gas turbines is a permanent demand as it results in lower harmful emissions and increased fuel economy. New TBC materials, able to address these demands, have been extensively investigated in the past. Among them Gadolinium Zirconate (GZ) is evidenced due to its low thermal conductivity, excellent phase stability and good ability to resist CMAS attack. However, GZ has lower fracture toughness than YSZ which can limits seriously its thermal cyclic performance. In this study, different configurations of GZ/YSZ TBCs have been produced by Suspension Plasma Spraying (SPS) and investigated, with the aim to better understand the effect of the different microstructural features on the TBCs performances. Cross sections and top surface morphology of as sprayed TBCs were analyzed by scanning electron microscopy (SEM). Porosity measurements were made using water intrusion and image analysis methods. Thermal conductivity of the as sprayed TBCs was measured using laser flash technique. The samples underwent also to thermal cyclic testing. The results of the investigations showed that the microstructure of the GZ topcoat plays a crucial role on its functional performances. The influence of the different porosity features and porosity classes is analyzed and discussed in detail.