Sub-solvus solution rejuvenation heat treatment enhances intermediate-temperature creep resistance of superalloys beyond original properties

Conventional rejuvenation heat treatment (RHT) for crept single-crystal (SX) superalloys generally employs full solution treatment above the γ′-solvus, promoting dynamic annihilation of crystal defects such as dislocations and re-establishment of γ/γ′ dual-phase microstructure. However, not all crystal defects introduced during plastic deformation are deleterious; certain dislocations can enhance the phase-interface stability. This work proposes a sub-solvus solution RHT with the maximum solution temperature slightly below γ′ solvus. For specimens subjected to creep interruption at 760 °C, following sub-solvus solution RHT, the rupture life rejuvenates to several times that of the original standard heat treatment (SHT) state. After the sub-solvus solution RHT, the γ′ precipitates become slightly coarser and show a noticeable deviation in size compared with the original SHT state, while most dislocations and stacking faults within γ′ precipitates are eliminated and the γ/γ′ interfaces contain reorganized interfacial dislocation networks that evolve into a equilibrium configuration. These equilibrium dislocation networks effectively drag mobile dislocations and inhibit shearing of stacking faults into γ′ precipitates, substantially decreasing steady-state creep rate by an order of magnitude. This work gives new insight of rejuvenating the repaired beyond the original and provides an approach of tailoring creep-induced crystal defects during rejuvenation.