Reasons for the stable existence of γ’ phase and strengthening mechanism of GH4720Li nickel-based superalloy

Abstract The characteristics of γ′ phase in forgings and heat treatment of GH4720Li superalloy were investigated under a transmission electron microscope by thermal deformation tests under gradient heating process. The experimental results show that there are Cr–Co rich region around the γ′ phase after forging and heat treatment, which guarantees the stable existence of the γ′ phase in the matrix and provides the first barrier to prevent dislocations from cutting the γ′ phase. Therefore, the stable existence of primary γ′ at relatively high temperature plays a key role in the retention of fine grains; The Cr–Co rich region around the secondary γ′ phase and the tertiary γ′ phase can effectively prevent the occurrence of Ostwald ripening, and maintain the uniform and diffuse two kinds of small size phases, so the precipitation strengthening effect is greatly affected.