Environmental stability of the YSZ layer and the YSZ/TGO interface of an in-service EB-PVD coated high-pressure turbine blade

Kurzfassung

Hot corrosion of an in-service EB-PVD coated 1st stage high-pressure turbine (HPT) blade following an interactive CaSO4 infiltration/CMAS deposition process has produced reactive interfaces with the YSZ top coat and the TGO layer which were investigated by analytical scanning and transmission electron microscopy. Despite complete CaSO4 infiltration of the coating prior to CMAS deposition, spallation and macroscopic hardware damage were confined to the pressure surface close to the trailing edge. Due to the high lime-to-silica-ratio imposed by the CMAS deposits reaction zones along CaSO4/CMAS/YSZ interfaces typically consisted of a CaZrO3 layer and fine-grained Ca-FSZ particles enveloping rounded YSZ column tips. No interfacial reaction was observed between the YSZ column walls and the CaSO4 pore filling Possible terms for the formation of the unique CaSO4/CMAS microstructure are evaluated. Zirconia destabilization upon hot corrosion is discussed in the light of phase compatibilities in the systems CaO-Y2O3-ZrO2 and CaO-ZrO2-SiO2 and put into perspective with previous work on both, natural and synthetic hot corrosion deposits.