Effects of Initial Grain Size and Strengthening Phase on Thermal Deformation and Recrystallization Behavior of GH4096 Superalloy

GH4096 alloy were used for disks and shafts of advanced gas turbine engines owing to its excellent properties such as resistance to creep, fatigue, and corrosion as well as microstructure stability up to about 700 degrees C. In this study, GH4096, a hard-to-deform disk superalloy, was processed through an advanced cast and wrought route to avoid the expensive power metallurgy (P/M) route. Many types of full-scale disk forgings possessing homogeneous fine-grained microstructures were successfully carried out, and the ultrasonic inspectability was comparative to that of the alloy produced by the P/M route. The effects of the initial grain size and strengthening phase on hot deformation behavior and dynamic recrystallization (DRX) were studied by OM, SEM, EBSD, and TEM under different deformation parameters. The results showed that as the initial grain size decreased within the temperature range of 1050-1120 degrees C, the flow peak stresses decreased and the fractions of DRX increased. With an increase in the initial grain size, the thermal deformation temperature required for complete dynamic recrystallization decreased, and also the critical strain of dynamic recrystallization decreased. The initial grain size and the strain did not affect the recrystallized grain size when deformed at a sub-solvus temperature. The thermal deformation constitutive equations related to the initial grain sizes were established and the activation energies of thermal deformation related to the original grain sizes were calculated. The effect of gamma' phase size on the thermal deformation behavior in as-cast microstructure was studied. In the sub-solvus temperature range, the thermal deformation resistance could be effectively reduced with the increase in the size of gamma' phase, the critical strain of DRX was decreased, and the DRX fraction was also increased. The dynamic recrystallization mechanisms related to the gamma' phase and initial grain size were also discussed. DRX nucleation takes place at the sub-grains near original grain boundaries for samples with larger initial grain size deformed at sub-solvus temperature. For samples with fine initial grain size, the interface slip of incoherent gamma' phase is the significant dynamic softening mechanism during the sub-solvus temperature deformation. For as-cast samples, the main dynamic softening mechanism is original grain boundary bowing out DRX nucleation and coarse second-phase-induced DRX nucleation.

Automated summary

GH4096 alloy is used in advanced gas turbine engines due to its excellent properties. In this study, GH4096 was processed through an advanced cast and wrought route to avoid expensive power metallurgy (P/M) route. The effects of initial grain size and strengthening phase on hot deformation behavior and dynamic recrystallization were studied.