GH4706 Ni-based superalloy is widely used for aero-engine turbine disks operating below 700 °C, where high-temperature ductility is critical to avoid cracking during die forging and service. However, the microscopic mechanisms by which stabilization treatment regulates its high-temperature ductility remain insufficiently clarified. This study systematically investigated the tensile deformation behavior at a high temperature of 650 °C of the GH4706 Ni-based superalloy after stabilization treatment. Transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) were employed to characterize microstructural evolution and elemental redistribution to clarify the microscopic mechanisms by which stabilization treatment enhanced the high-temperature ductility of the GH4706 alloy. The experimental results indicated that better high-temperature plasticity was obtained, although tensile strength decreased slightly after stabilization. This improvement was mainly attributed to the precipitation of the η phase (Ni₃Ti) and its synergistic interaction with the matrix, which effectively enhanced the plastic deformation capacity of the GH4706 alloy at elevated temperatures. Moreover, η phase precipitation and elemental segregation enhanced grain boundary stability, thus inhibiting crack initiation and delaying necking. SIMS analysis revealed that boron, phosphorus, and sulfur showed significant segregation along grain boundaries during 650 °C tensile testing following stabilization—an effect considered crucial to the observed ductility enhancement. TEM observations further indicated that the interaction between η phase precipitation and the nucleation and evolution of stacking faults during deformation together reduced local stress concentrations and promoted uniform plastic deformation.

GH4079 is a newly developed Ni-based superalloy with a high content of alloying elements and excellent high-temperature mechanical performance. Rare earth (RE) elements are always added to superalloys to improve their stress rupture properties. This study explored how varying additions (0–0.22 wt.%) of lanthanum (La) and cerium (Ce) affected the precipitation and stress rupture performance of the GH4079 superalloy and revealed the related strengthening mechanisms. The addition of RE elements restrained the excessive growth of the γ′ phase to keep its particles fine and uniform, while more RE led to a larger quantity and size of RE-rich precipitates and carbides. At 650 °C and 882 MPa, La and Ce notably boosted the alloy’s stress rupture life. The sample with 0.22 wt.% RE showed optimal overall performance, with a stress rupture life of 179.3 h, more than three times that of the RE-free alloy (55.2 h). The improvement in the stress rupture properties by La and Ce was attributed to beneficial intracrystalline and grain boundary effects. RE reinforced the γ′ phase to impede dislocations and purified the grain boundaries by decreasing the segregation of P and S elements. Additionally, small-sized RE-rich precipitates combined with the fine γ′ phase formed zigzag grain boundaries, alleviating stress concentration and retarding intergranular crack propagation.