The synergistic effects of boron (B) and rare earth (RE) elements on the microstructure and stress rupture properties were investigated in a Ni-based superalloy. The stress rupture lifetime at 650 °C/873 MPa significantly increased with the addition of B as a single element. Furthermore, the stress rupture lifetime reached its peak (303 h), with a certain amount of B and RE added together in test alloys. Although the grain size and morphology of the γ′ phase varied a little with the change in B and RE addition, they were not considered to be the main reasons for stress rupture performance. The enhancement in stress rupture lifetime was mostly attributed to the segregation of the B and RE elements, which increased the binding force of the grain boundary and improved its strength and plasticity. In addition, the enrichment of B and RE inhabited the precipitation of carbides along grain boundaries. Furthermore, nano-scale RE precipitates containing sulfur (S) and phosphorus (P) were observed to be distributed along the grain boundaries. The purification of grain boundaries by B and RE elements was favorable to further improve the stress rupture properties.

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.