Influence of YSZ layer thickness on the durability of gadolinium zirconate/YSZ double-layered thermal barrier coatings produced by suspension plasma spray

In this work, three double layered thermal barrier coating (TBC) variations with different gadolinium zirconate (GZ) and YSZ thickness (400GZ/100YSZ, 250GZ/250YSZ and 100GZ/400YSZ respectively, where the prefixed numbers before GZ and YSZ represent the layer thickness in mu m), were produced by suspension plasma spray (SPS) process. The objective was to investigate the influence of YSZ thickness on the thermal conductivity and thermal shock lifetime of the GZ/YSZ double layered TBCs. The as sprayed TBCs were characterized using SEM, XRD and porosity measurements. Thermal diffusivity measurements were made using laser flash analysis and the thermal conductivity of the TBCs was calculated. The double layered TBC with the lowest YSZ (400GZ/100YSZ) thickness showed lower thermal diffusivity and thermal conductivity. The double layered TBCs were subjected to thermal shock test at a TBC surface temperature of 1350 degrees C. Results indicate that the TBC with a higher YSZ thickness (100GZ/400YSZ) showed inferior thermal shock lifetime whereas the TBCs with low YSZ thickness showed comparatively higher thermal shock lifetimes. Failure of the TBCs after thermal shock test was analyzed using SEM and XRD to gain further insights.