On the Role of Microstructural Characterization in Damage Analysis of Turbine Blade Superalloys

We emphasize the importance of detailed microstructural characterization in damage analysis of turbine blade superalloys. Examples representing a variety of damage modes sustained during engine operation in the utility industry are presented. A one-to-one correspondence between microstructure and a given type of damage is developed using various electron-optical techniques to serve as a guide in interpreting the microstructures of damaged blades. Damage modes considered in the study include loss of mechanical strength due to coarsening of the strengthening γ′-phase in the γ matrix, creep and fatigue damage, detrimental grain boundary reactions involving the Cr-rich M₂₃C₆ carbide and γ′-phase, as well as precipitation of detrimental intermetallic compounds. Degradation of environmental resistance related to loss of mechanical strength is also elucidated.