Multilayered thermal barrier coating architectures for high temperature applications

Pyrochlore oxides of the rare earth zirconates are excellent candidates for use as thermal barrier coating (TBC) materials in highly efficient turbine engine operation at elevated temperatures (>1300°C). Pyrochlore oxides have most of the relevant attributes for use at elevated temperatures such as phase stability, low sintering kinetics and low thermal conductivity. One of the issues with the pyrochlore oxides is their lower toughness compared to the currently used TBC material viz. yttria (6-8 wt. %) stabilized zirconia (YSZ). In this work, arguments are advanced in favor of a multilayered coating approach to enhance erosion performance by improving toughness and lowering thermal conductivity of the TBCs. Unique multilayered coating design architectures were fabricated with alternating layers of pyrochlore oxide viz Gd₂Zr ₂O₇ and low k TBC (rare earth oxide doped t' YSZ) utilizing electron beam physical vapor deposition (EB-PVD) technique to reduce overall rare earth oxide content. Microstructure, phase, erosion resistance and thermal conductivity of the as-fabricated multilayered coatings were evaluated and compared with that of the single layered coatings.