Evolution of the Thermal Conductivity of Dysprosia Stabilised Zirconia Thermal Barrier Coatings with Heat Treatment

Dysprosia stabilised zirconia coatings offer a potential reduction in thermal heat transfer for thermal barrier coating systems with the added benifit of being producible with existing equipment and spray knowledge. However, there is little information on the long term performance of such systems relative to the standard coatings. While a low thermal conductivity is important for a gas turbine; sintering resistance is important to maintain properties over the lifetime of a component.

In this study, four dysprosia stabilised zirconia are compared with a standard yttria stabilised coating in present industrial use. The coatings are a combination of high velocity oxy-fuel and air plasma sprayed bondcoats. Top-coats were produced in either dual layer morphology or using ceramic powder blended with a polymer porosity former.

Samples were exposed to isothermal furnace onditions at 1150°C from 5 to 200 hours to see the sintering resistnace of the coating systems. Samples were prepared for microstructural analysis with SEM. Thermal conductivity of the systems was measured using laser flash analysis after heat treatement and again at high temperature to assess thermal property evolution. Porosity changes were also monitored using image anaysis.