A diffraction study of the γ" phase in INCONEL 718 superalloy

The crystal structure and morphology of the gamma " phase in INCONEL 718 (IN-718) superalloy was studied by using theoretical prediction, transmission electron microscopy, and computer simulation. The experimental results show that (1) The gamma " phase has an ordered body-centered-tetragonal structure with lattice parameters alpha (gamma ") = b(gamma ") congruent to alpha (gamma) and c(gamma ") congruent to 2 alpha (gamma) and is coherent with the matrix (gamma); (2) the gamma " phase in IN-718 alloy forms as thin ellipsoidal discs on the {100} matrix planes with the c-axis being perpendicular to the discs; and (3) the orientation relationship between the gamma " phase and the matrix is (100)(gamma ")// (100)(gamma); [010](gamma "),// [010](gamma).