Effect of processing and interface on the durability of single and bilayer 7YSZ / gadolinium zirconate EB-PVD thermal barrier coatings

Gadolinium Zirconate (GZO) is known for its low thermal conductivity, high thermal stability and a favorable fast reaction with CMAS deposits that makes such a thermal barrier coating (TBC) more stable and less infiltrated in dusty turbine environments. In the present study, Electron Beam Physical Vapor deposited (EB-PVD) GZO/7YSZ bilayers were coated on superalloy bars having a NiCoCrAlY bond coat. Two different coaters that were either pilot production/lab scale size suitable for coating development (coater ESPRI) or small scale production/development size (SMART Coater) suitable for both development and production were used. The bilayers were compared to single layers of 7YSZ or GZO, respectively. Beside lifetime investigations of the various TBC systems special emphasis was put on the interface architecture between 7YSZ and GZO. The coatings where the transition between the two layers was done rapidly achieved the longest lifetime of all bilayers, regardless of the EB-PVD coater used. Nearly all GZO top coats showed a longer lifetime than the standard 7YSZ systems in furnace cycling testing at 1100 degrees C.