Abstract:By means of calculating the elements diffusion mobility and γ￠-phase directional coarsening rate of Ni-Cr-Co-W-Mo-Al-Ta single crystal superalloys with different compositions, the effect of element reaction on the rate of element diffusion and γ￠-phase directional coarsening was studied. Results show that during the γ￠-phase directional coarsening period, the rafted rate of γ￠-phase changes with composition and stress, and the rafted time is decreased with the stress increasing. The driving force of the elements diffusion and γ￠-phase directional coarsening during tensile creep are related to the applied stress and elastic modulus. Element reaction has effect on the diffusion rate of Al. As the total content of Ta+Mo and the ratio of Ta/W increased, the diffusion activation energy of Al is increased and diffusion rate decreased, and the rafted time of γ￠-phase is elongated. In the diffusion field of γ￠-phase directional coarsening, the formation of γ￠-order phase is attributed to the concentration of the atoms Al and Ta, which is a spontaneous process of the decreased free energy. The Al, Ta atoms with bigger radius are diffused to {100} planes to form the stable arranging order and the linking bond of the atoms with different kinds, which is a main reason of γ￠-order phase formation with Ll2 structure