Local order and associated deformation mechanisms in the γ phase of nickel base superalloys

Abstract

Using X-ray diffraction, atom probe nanoanalysis, T.E.M. associated with in situ deformation, the presence of local order in the γ matrix of a monocrystalline MC2 superalloy is demonstrated. In Ni2CoCr the model alloy of this phase, as well as in the γ MC2 matrix, the existence at room temperature of a strong short range order of {1 1/2 0} special point type is emphasized. It induces high friction stresses opposing the movement of dislocations which have to propagate in planar arrays in the corresponding materials. In addition, long range ordered L12 hyperfine precipitates appear in the γ MC1 samples annealed at 750°C. They induce several pairs of dislocations at the head of the moving pile-ups in order to cut them.