Microstructure of a plasma-sprayed superalloy coating/substrate

Five different specimen preparation techniques were employed to characterize the microstructure of a cross-section of plasma-sprayed Rene 125 coating on a Rene 125 turbine blade substrate. These methods included optical microscopy, and transmission electron microscopy on three types of replicas and on thin foils. Interface and matrix precipitates were indentified using electron diffraction and energy dispersive spectrometry, with HfO₂ and (Hf, Zr)O₂ the predominant phases at the coating/blade interface, and both (Ti, Ta)C and HfO₂ present in the coating. Those blade precipitates examined contained Hf and Ta, with some Ti and a little Co. A unique dendritic structure of was also found intermittently along the interface. The combination of the five techniques provides a wide variety of information, and is a strong tool for characterizing complex microstructures.