Character of dislocations at the γ/γ′ interfaces and internal stresses in nickel-base superalloys Original Research Article

It is experimentally observed in Ni-based superalloys that the dislocation substructure after deformation at elevated temperatures is different on horizontal and vertical γ/γ′ interfaces. Edge dislocation networks are predominantly observed at horizontal interfaces while screw dislocation segments are seen mostly on the vertical interfaces. A crystallographic model of the critical shear stress for dipole expansion for screw and 60° dislocation segments in the γ/γ′ interfaces is used to explain the observations in high γ′ volume fraction (∼70%) alloys. However, the same model is found to be inadequate in explaining the substructure observations in those alloys with lower γ′ volume fraction (∼40%) which have wider matrix (γ) channels (≈180 nm). It is shown by superimposition of the dislocationʹs stress field, the internal coherency stresses and the externally applied stress that between 60° and screw dislocation segments the former increase the internal stresses in vertical interfaces more than the latter.