Hot deformation behavior and micro-structure evolution of superalloy GH742

Hot deformation behavior of superalloy GH742 was studied by isothermal compression test conducted on MTS machine. Flow stress data at various temperatures from 950℃ to 1150℃and strain rates from 0.001 s-1 to 1 s-1 were obtained, microstructure evolution during deformation under the above conditions was also investigated. The results show that when deformation was performed at single phase region above 1075℃, rather low flow stress is exhibited, the apparent activation energy approachs the activation energy of grain boundary diffusion, the deformation mechanism is controlled by grain growth rate and the fully recrystallized structures can be achieved. In two phase region, GH742 alloy presents considerably high activation energy, with decreasing temperature and increasing strain rate the flow stress increases swiftly, while the dynamic recrystallization was strongly prohibited. At transition temperature between single and two phase regions, a discontinuous change in flow stress was observed, and the apparent activation energy sharply increased, strain induced dynamically precipitated γ′ phase inhibits the migration of grain boundaries, the diameter of the recrystallized grain is drastically reduced with increase of plastic strain, and the microstructure was effectively refined.