Effect of elastic constant misfit on the orientation of the γ′ disk in Ni–Al alloys: Theoretical study using density functional theory and micromechanics

The high creep resistance of Ni − Al alloys is attributed to the stability and morphology of the disk-shaped γ ′ phase under loading conditions, which is a rafted structure. However, the origin of the stability or morphology of the γ ′ disk in Ni − Al alloys remains unclear. In this study, the effects of the misfit strain and the elastic constant misfit between γ and γ ′ phases on the Ni 3 Al γ ′ -rafted structure in Ni − Al alloys were investigated. The morphology of the γ ′ phase in the γ matrix under tensile stress was energetically investigated using anisotropic Eshelby’s ellipsoidal inclusion analysis in the theory of elasticity (micromechanics). The elastic constants and misfit strains for micromechanics were calculated using density functional theory atomistic simulations. The disk-shaped γ ′ on the { 100 } plane was generally energetically favored, and the disk normal to the tensile direction was energetically favorable compared to other { 100 } disks under 〈 100 〉 tensile stress, indicating that rafting would occur in this case. However, when the elastic constant misfit was not considered, no orientation dependence was observed for the { 100 } disks even under tensile stress along certain 〈 100 〉 . Our results suggest that the elastic constant misfit between γ and γ ′ phases is one of the reasons for the rafted structure of the γ ′ phase in Ni − Al alloys. The effect of the misfit was larger with an increase in temperature, driving the formation of the rafted γ ′ phases.