EFFECT OF ALLOYING ELEMENTS ON CREEP AND FATIGUE DAMAGE OF NI-BASE SUPERALLOY CAUSED BY STRAIN-INDUCED ANISOTROPIC DIFFUSION

摘要

In order to make clear the mechanism of the directional coarsening (rafting) of γ' phases in Ni-base superalloys under uni-axial tensile strain, molecular dynamics (MD) analysis was applied to investigate effects of alloying elements on diffusion characteristics around the interface between the γ phase and the γ' phase. In this study, a simple interface structure model corresponding to the γ/γ' interface, which consisted of Ni as γ and Ni_3Al as γ' structure, was used to analyze the diffusion properties of Ni and Al atoms under tensile strain. The strain-induced anisotropic diffusion of Al atoms perpendicular to the interface between the Ni(001) layer and the Ni_3Al(001) layer was observed in the MD simulation, suggesting that the strain-induced anisotropic diffusion of Al atoms in γ' phase is one of the dominant factors of the kinetics of the rafting during creep damage. The effect of alloying elements in the Ni-base superalloy on the strain-induced anisotropic diffusion of Al atoms was also analyzed. Both the atomic radius and the binding energy with Al and Ni of the alloying element are the dominant factors that change the strain-induced diffusion of Al atoms in the Ni-base super-alloy.