The influence of γ′ sub/super solvus on the microstructural characteristics and deformation mechanisms during the high-temperature deformation process of Ni-Cr based superalloy

Abstract

The precipitate is a microscopic structure that cannot be ignored in Ni-based superalloys. During the thermal deformation process, due to the coupled effects of precipitates, high temperature, and applied stress, the presence of precipitates can influence the evolution of microstructure and the transition of deformation mechanisms. This study systematically investigates the thermal deformation behavior of Ni-Cr based superalloy in γ′ sub-solvus (containing precipitates) and γ′ super-solvus (without precipitates) states at different strain rates, further elucidating the impact of γ′ precipitates on the microstructural evolution of Ni-Cr based superalloy. The results indicate that deformation in the γ′ sub-solvus state activates high-density planar slip dislocations, resulting in higher energy storage. At high strain rates (>0.1 s⁻¹), the pinning effect of the precipitates slows down the migration of grain boundaries, thereby inhibiting the growth of recrystallization. Furthermore, at high strain rates, the uneven deformation of the matrix results in higher dislocation density and energy within the alloy, leading to a tailing effect of the γ′ precipitates. In γ′ sub-solvus state, its recrystallization mechanism is discontinuous dynamic recrystallization, which is related to the nucleation stimulated by precipitates. In γ′ super-solvus state, discontinuous dynamic recrystallization is the primary grain refinement mechanism, while continuous dynamic recrystallization serves as a secondary mechanism. This work may provide a theoretical basis for the microstructure design and mechanism exploration in the hot deformation process of γ′-strengthened alloys.