Ni‐based superalloys are extensively used in high‐temperature aerospace applications due to their excellent mechanical strength, oxidation resistance, and microstructural stability. The long‐term exposure of these alloys to elevated temperatures, however, leads to degradation of the ordered γ′ phase and instability of carbides, ultimately impairing mechanical performance. This study elucidates the role of ordered phase and carbide evolution in determining the mechanical response of a (DS) CM247 Ni‐based superalloy subjected to thermal cycling under representative service conditions. Comprehensive microstructural characterization using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed coarsening and morphological transformation of the γ′ precipitates, accompanied by degeneration and cracking of MC‐type carbides. The formation of precipitate‐free zones and surface oxidation in thermally exposed (TE500) specimens contributed to a reduction in yield and ultimate tensile strength at 750°C. Interestingly, an inverse trend was observed at 850°C, attributed to the coarsening of γ′ precipitates and a change in carbide morphology. The pronounced susceptibility of TE500 samples to carbide cracking and associated dislocation pile‐ups facilitated premature failure. These findings highlight the synergistic effect of ordered phase stability and carbide evolution on the mechanical performance of Ni‐based superalloys, offering valuable insights for enhancing the life and reliability of components operating in extreme environments.
Chandra et al. (Sat,) studied this question.