Revealing the creep-fatigue deformation mechanism for a directionally-solidified Ni-based superalloy DZ445 at 900 °C

The total strain-controlled creep-fatigue behavior of a first generation directionally-solidified Ni-based superalloy DZ445 at 900 degrees C in air was reported in the previous investigation. The deformation mechanisms with different dwell times for this superalloy were further expounded from the reduction in area, surface cracks, internal voids, stability of gamma' strengthening phase, and dislocation characteristics in this investigation. The results demonstrated the reduction in area increased, the number of the surface cracks on the vertical section decreased and the number and area fraction of internal voids increased with the increase of tensile dwell time. The non-directional coarsening trend of the secondary gamma' precipitate increases with increasing the dwell time. These microstructure changes affirmed that the deformation of DZ445 goes through transformations from the typical fatigue mode into the mixture of creep and fatigue, and further into the compound of creep and ductile when the dwell time is initially applied and continuously increased.