Effect of Rejuvenation Treatment on SX Ni-Based Superalloys Subjected to Low Cycle Fatigue

RejuvenationRejuvenation treatments with integrated hot isostatic pressingHot isostatic pressing have been proven to re-establish the γ/γ′ microstructureMicrostructure of single crystalline nickel-based superalloysNickel-based superalloy after creepCreep deformation, close porosityPorosity, and recover creepCreep strength to a significant extent. Therefore, rejuvenationRejuvenation treatment is expected to be effective in extending the service life of components such as turbine bladesTurbine blades for gas turbines resulting in reduced costs and improved sustainability compared to replacing the component. Since such components are subjected to combined creepCreep-fatigueFatigue loading, this investigation is aiming to answer the question if a rejuvenationRejuvenation procedure, which has proved to recover single crystalline superalloysSuperalloys after creepCreep, is effective in rejuvenating these materials after low cycle fatigueLow cycle fatigue. For this purpose, test samples have been subjected after high temperatureHigh temperature low cycle fatigueLow cycle fatigue experiments to a rejuvenationRejuvenation procedure. The materials microstructureMicrostructure has been studied by non-destructive X-ray computer tomographyX-ray computer tomography before and after rejuvenationRejuvenation. Subsequently, metallographic sections were prepared from rejuvenated samples and investigated by scanning electron microscopyElectron microscopy. Pores and precipitatesPrecipitates detected in high resolution section images were identified in the reconstructed volume and used to fit the metallographic section images into this volume. Pores and cracks emanating at pores during fatigueFatigue testing were closed by rejuvenationRejuvenation as long as they were not connected to the surface. Electron backscatter diffraction performed on the sections revealed that, in contrast to creepCreep samples, the fatigueFatigue samples were recrystallized during rejuvenationRejuvenation. It is concluded that fatigueFatigue damage cannot be reversed by the same rejuvenationRejuvenation procedure that is effective for creep damageCreep damage.