Applications of microstructural characterization and computational modeling in damage analysis of a turbine blade exposed to service conditions in a power plant

Microstructural characterization and computational modeling were used to analyze the damage produced by overheating of a turbine blade exposed to service conditions in a power plant. Various electron-optical techniques were used to characterize the microstructure. Localized overheating was reflected by the microstructural features of the blade material particularly the extent of interdiffusion between the coating and alloy substrate, coarsening of the γ′-phase, and re-precipitation of M23C6 carbide by a discontinuous mechanism at grain boundaries. Damage associated with these effects included creep cavities at grain boundaries and intergranular oxidation leading to ductile intergranular cracking at the leading edge of the blade. Most evidence pointed out that improper internal cooling of the blade resulted in excessive overheating at leading edge. Qualitatively, the temperature profile across the blade as indicated by microstructural variations was consistent with the results derived from computational modeling.