Faculty Sponsor's Department:
Reliable detection of critical damage occurring in structural parts in aeronautics is of highest importance to ensure safe operation. Non-destructive testing by ultrasonic resonance spectroscopy has shown great potential to detect damage that occurs during service of Ni-based superalloy jet engine turbine blades. Despite the commercial use of this technique, its limits, capabilities and fundamental interactions between ultrasonic waves and material microstructures and coatings are not yet well understood. Specifically, this investigation will focus on damage within aluminide coatings as protective layers on conventionally cast superalloy MAR-M 247 and its influence on resonance. The approach is to replicate in-service damage at the lab scale in a controlled environment while measuring corresponding changes in resonance behavior. Simple geometry samples were aluminide coated in the two-step “pack cementation” to produce substrate-coating structures simulating in-service turbine blades. Initial measurements show significant resonance shifts induced by the coating procedure, indicating that the applied resonance spectroscopy set-up is sensitive to aluminide coatings. Furthermore samples will be exposed to cyclic temperature in order to create coating defects such as thermal stress induced cracks and spallations similar to those observed in in-service turbine blades. Simultaneously resonance measurements will be taken to investigate how evolving damage further influences the resonance behavior.