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 degrees C, at which severe microstructure degradation and accelerated plastic deformation due to thermal activation deteriorate creep resistance. This work investigates the effect of gamma '-forming elements, including Al and Ta, on 1200 degrees 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 gamma '-forming elements facilitates abnormal rattan-shaped gamma ' phase formation. Evidenced by typical three-stage creep behavior, cubic-raft-collapse microstructural evolution, and dislocation configuration analysis, 1200 degrees C creep resistance would originate primarily from classical 1100 degrees C creep strengthening mechanisms. Besides, the detrimental impact of the rattan-shaped gamma ' phase is revealed, which should also be considered. Further research indicates that Al addition produces a lower degree of gamma '-solubility, more negative lattice misfit, higher gamma '-fraction, and more rattan-shaped gamma ' phase, while Ta addition produces lower gamma '-solubility, more positive misfit, higher gamma '-fraction and more rattan-shaped gamma ' phase. The alloying composition-phase/interface-properties relationship has been established for 1200 degrees C creep, which explains the peak performance of SCA4 alloy. These results provide new opportunities to design superalloys that resist ultrahigh temperature service and elevate the service temperature limit.

Automated summary

This study investigates the effect of gamma'-forming elements, including Al and Ta, on the creep properties of turbine blade-manufacturing Ni-based single-crystal superalloys at 1200 degrees C. The study found that the creep properties are sensitive to the addition of Al and Ta, reaching their peak in a specific composition range. Additionally, adding gamma'-forming elements facilitates the formation of an abnormal rattan-shaped gamma' phase. The research also reveals that the addition of Al and Ta affects the microstructure evolution of the alloy.