Thermal Stability of GH4065A Superalloy Based on Microstructural and Performance Evolution Following Long-Term Aging

This study investigates the thermal stability of a GH4065A superalloy at intermediate temperatures by conducting long-term aging treatments for 100–6000 h at 700–800 °C. Secondary γ′-phase coarsening and intergranular M₆C carbide precipitation occurred during aging. The activation energy for secondary γ′-phase coarsening was 259.89 ± 25.45 kJ mol⁻¹, suggesting that this process was predominantly controlled by elemental diffusion. The tensile strength at a testing temperature of 700 °C was stably above 1200 MPa for the alloys aged at 700 °C but continuously declined as the aging temperature increased, with a direct correlation identified between the secondary γ′-phase coarsening and strength reduction upon aging. Increasing the aging temperature transitioned the deformation mechanism from Orowan bowing around the γ′ phase to dislocation slip through the broadened matrix channels, leading to decreased strength. Long-term aging effectively eliminated intermediate-temperature intergranular brittle fracture. The elongation to failure at a testing temperature of 700 °C increased by approximately 35% after aging at 800 °C for 6000 h, attributed to grain-boundary diffusion of W and Mo and intragranular softening, which improved the deformation coordination ability at the grain boundaries. Finally, the precipitation of intergranular M₆C particles after prolonged aging promoted plastic deformation via micropore aggregation.

Graphical Abstract