Design for 1200 °C creep properties of Ni-based single crystal superalloys: Effect of γ′-forming elements and its microscopic mechanism

Enhancing ultra-high temperature mechanical properties of turbine blade-manufacturing Ni-based single-crystal superalloys is crucial to advanced aero-engines. However, the service temperature still does not rise to 1200 °C, at which severe microstructure degradation and accelerated plastic deformation due to thermal activation deteriorate creep resistance. This work investigates the effect of γ′-forming elements, including Al and Ta, on 1200 °C/80 MPa creep properties and its corresponding mechanism. The creep property is sensitive to Al and Ta addition, reaching its peak in our designed composition region. The microstructure evolution during creep is also sensitive to Al and Ta; particularly, adding γ′-forming elements facilitates abnormal rattan-shaped γ′ phase formation. Evidenced by typical three-stage creep behavior, “cubic-raft-collapse” microstructural evolution, and dislocation configuration analysis, 1200 °C creep resistance would originate primarily from classical 1100 °C creep strengthening mechanisms. Besides, the detrimental impact of the rattan-shaped γ′ phase is revealed, which should also be considered. Further research indicates that Al addition produces a lower degree of γ′-solubility, more negative lattice misfit, higher γ′-fraction, and more rattan-shaped γ′ phase, while Ta addition produces lower γ′-solubility, more positive misfit, higher γ′-fraction and more rattan-shaped γ′ phase. The alloying composition-phase/interface-properties relationship has been established for 1200 °C creep, which explains the peak performance of SCA4 alloy. These results provide new opportunities to design superalloys that resist ultra-high temperature service and elevate the service temperature limit.