An Investigation of the Microstructural Evolution of a Service-Exposed Turbine Blade

A field-emission scanning electron microscope with an energy-dispersive X-ray spectroscopy system was used to study the microstructural evolution of nickel-based superalloy K465 during service, including γ′ degeneration, decomposition of MC carbides, and formation of creep cavities. Results show that the primary γ′ precipitates having regular and cubic morphologies are agglomerated together by elastic interaction energy and gradually evolve to more stable γ′ plates. The γ′ particles in the interdendritic region have higher coarsening rates than those in the dendrite core. The sizes of γ′ precipitates at various locations of the blade, characterized by quantitative metallography, are employed to estimate the temperature distribution of the airfoil. MC carbides react with the surrounding matrix, forming M₆C carbide and γ′ film. The interfaces between the carbides, both at grain boundaries and in grains, and the γ′ films are preferential sites for the nucleation and fast propagation of creep cavities.