Synergistic effect of γ' precipitate optimization on the high-temperature strength and ductility of FGH4113A superalloy

Turbine disks must possess both high strength and ductility simultaneously to ensure safe operation, but conventional superalloys typically exhibit a critical inverse relationship between these two properties. Heat treatment is key to enhancing strength-toughness in powder metallurgy superalloys, yet current research struggles to resolve this trade-off. To address this, the present study proposes a two-stage cooling strategy during solution heat treatment—initial slow cooling followed by accelerated cooling. This approach modulates the precipitation of distinct γ' populations, wherein coarse γ' precipitates promote Orowan bypass mechanisms to enhance dislocation storage efficiency, while fine γ' precipitates induce anti-phase boundary strengthening upon shearing, thereby contributing to the simultaneous improvement of high-temperature strength and ductility. For the sample subjected to solution treatment with continuous cooling at 150 °C/min, the volume fractions of coarse γ' (225.17 nm), medium γ' (138.30 nm), and fine γ' (32.82 nm) precipitates were 26.9%, 19.5%, and 1.1%, respectively. When the cooling rate was adjusted to 65 °C/min down to 1080 °C followed by forced accelerated cooling at 300 °C/min, the average diameter of coarse γ' precipitates increased to 250.76 nm, while that of medium γ' decreased to 82.61 nm and fine γ' slightly reduced to 27.97 nm. Notably, the volume fractions of these three precipitate populations remained largely unchanged, measured at 28.5%, 17.9%, and 1.8%, respectively. As a result, the yield strength at 800 °C exhibited a moderate increase from 920 MPa to 983.5 MPa, accompanied by an improvement in ultimate tensile strength from 1079 MPa to 1112 MPa. More significantly, the elongation after fracture was substantially enhanced from 13.4% to 23.5%. After implementing the two-step cooling strategy, the yield strength contribution from coarse γ' precipitates decreased from 195 MPa to 178 MPa, while that from medium γ' precipitates increased significantly from 230.3 MPa to 281.9 MPa. These changes are attributed to the refined medium γ' precipitates falling more optimally within the strong shearing regime, thereby enhancing their strengthening efficiency. This study develops a γ' precipitate optimization strategy through two-stage cooling to overcome the strength-ductility trade-off, significantly advancing the design of high-temperature superalloys for turbine disk applications.