Gradient microstructure evolution under thermo-mechanical coupling effects for a nickel-based powder metallurgy superalloy－Dynamic recrystallization coexist with static recrystallization

Abstract

In order to withstand special working conditions, it is of great significance to manufacture turbine disks with a gradient microstructure (disk core with fine and uniform grains and disk edge with coarse grains) along the radial direction. A new and effective forming way-gradient hot deformation is proposed, and a gradient structure from the edge to the center can be obtained. In the present work, the gradient deformation behavior, dynamic recrystallization kinetics, and microstructural evolution of a nickel-based powder metallurgy superalloy are studied by thermal gradient compression. Dynamic recrystallization kinetics of this superalloy is established. Recrystallization fraction increases from 72.6 %–93.6 % because of the gradient deformation degree. Microstructure changes significantly from the center to the edge along the radial direction, and average grain size ranges from 6.65 μm to 15.62 μm. There is a big difference between experimental value and calculated data of recrystallization fraction, which indicates that dynamic and static recrystallization take place in different areas simultaneously. Static recrystallization can coexist with dynamic recrystallization in the trapezoid sample by gradient hot deformation. The difference between experimental and calculated results is the static recrystallization, and the maximum values of static recrystallization fraction is around 30 %. A great number of dynamic recrystallization grains distribute along pre-existing grain boundary, second phases and twin crystal. The main means of static recrystallization nucleation is the bulge of original grain boundaries.