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.