Ravisankar Naraparaju, Uwe Schulz, German Aerospace Center, Cologne, Germany
Thermal Barrier Coatings (TBCs) offer protection against excessive heat to the parts that are used in the hot-sections of aero-engines. In general, hot components of gas turbine engines operating at high temperatures for propulsion and power generation are mainly made up of nickel-based superalloys. Currently 7 wt. % Yttria Stabilized Zirconia (7YSZ) is the state-of-the art TBC material primarily because of its low thermal conductivity and high toughness. These TBCs are commonly deposited by electron beam physical vapor deposition (EB-PVD) and by air plasma spraying (APS) techniques. EB-PVD is a physical vapor deposition technique in which a high energy electron beam targeted towards the ceramic material (ingot) causes it to melt and vaporize in the form of a cloud within the vacuum chamber. Microstructure formed by EB-PVD TBC entirely depends on processing conditions, but is primarily a columnar microstructure with porosity within the coating (inter-columnar gaps, voids between feather arms and intra columnar pores) which contributes towards better strain tolerance and thermal shock resistance properties with respect to plasma sprayed TBCs. The influence of process parameters on the microstructures of various TBCs will be presented in this talk.